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Filed Pursuant to Rule 424(b)(5)
Registration No. 333-202960

 

The information in this preliminary prospectus supplement is not complete and may be changed. This preliminary prospectus supplement and the accompanying prospectus are part of an effective registration statement filed with the Securities and Exchange Commission. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell these securities and are not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

 

Subject to completion, dated February 9, 2016

PROSPECTUS SUPPLEMENT

(To Prospectus dated August 19, 2015)

 

             Units

Each Consisting of One Share of Common Stock and

One Warrant to Purchase One Share of Common Stock

We are offering              units, with each unit consisting of one share of our common stock and one warrant to purchase one share of our common stock (and the              shares of our common stock issuable from time to time upon exercise of the offered warrants). The purchase price for each unit is $            . Each warrant will have an exercise price of $             per share, will be exercisable six months and one day after the date of issuance and will expire five years from the date of issuance. The units will not be issued or certificated. The shares of common stock and the warrants are immediately separable and will be issued separately, but will be purchased together in this offering. The shares of common stock, warrants and shares of common stock underlying the warrants are sometimes collectively referred to herein as the “securities.”

Our common stock is listed on NYSE MKT under the symbol “MSTX.” The last reported sale price of our common stock on February 8, 2016 was $0.43 per share. There is no established public trading market for the warrants and a public market may never develop. In addition, we do not intend to apply for listing of the warrants on the NYSE MKT, any other national securities exchange or any other nationally recognized trading system.

Investing in our securities involves a high degree of risk. See “Risk Factors,” beginning on page S-6 of this prospectus supplement, as well as the documents incorporated by reference in this prospectus supplement, for a discussion of the factors you should carefully consider before deciding to purchase our securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

 

		Per Unit		Total
Public offering price		$		$
Underwriting discounts and commissions(1)		$		$
Proceeds, before expenses, to us		$		$

 

(1)	We have also agreed to reimburse the representative of the underwriters for fees and expenses incurred by it in connection with this offering, up to a maximum of $75,000. See “Underwriting” beginning on page S-14 for more information.

The above summary of offering proceeds to us does not give effect to any exercise of the warrants being offered and issued in this offering.

The underwriters expect to deliver the securities offered hereby against payment on or about February , 2016.

Sole Book-Running Manager

Roth Capital Partners

The date of this prospectus supplement is February     , 2016.

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TABLE OF CONTENTS

Prospectus Supplement

 

ABOUT THIS PROSPECTUS SUPPLEMENT			S-1
PROSPECTUS SUPPLEMENT SUMMARY			S-2
THE OFFERING			S-4
RISK FACTORS			S-6
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS			S-8
USE OF PROCEEDS			S-9
DILUTION			S-10
DESCRIPTION OF THE SECURITIES WE ARE OFFERING			S-11
UNDERWRITING			S-14
LEGAL MATTERS			S-17
EXPERTS			S-17
WHERE YOU CAN FIND ADDITIONAL INFORMATION			S-17
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE			S-17

Prospectus

 

ABOUT THIS PROSPECTUS			ii
SUMMARY			1
RISK FACTORS			5
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS			5
USE OF PROCEEDS			6
SECURITIES WE MAY OFFER			6
DESCRIPTION OF COMMON STOCK AND PREFERRED STOCK			6
DESCRIPTION OF DEBT SECURITIES			10
DESCRIPTION OF WARRANTS			18
DESCRIPTION OF UNITS			20
LEGAL OWNERSHIP OF SECURITIES			21
PLAN OF DISTRIBUTION			24
LEGAL MATTERS			26
EXPERTS			26
INFORMATION INCORPORATED BY REFERENCE			26
WHERE YOU CAN FIND MORE INFORMATION			27

 

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ABOUT THIS PROSPECTUS SUPPLEMENT

This document is in two parts. The first part is the prospectus supplement, including the documents incorporated by reference, which describes the specific terms of this offering. The second part, the accompanying prospectus, including the documents incorporated by reference, provides more general information. Before you invest, you should carefully read this prospectus supplement, the accompanying prospectus, all information incorporated by reference herein and therein, as well as the additional information described under “Where You Can Find Additional Information” on page S-17 of this prospectus supplement. These documents contain information you should consider when making your investment decision. This prospectus supplement may add, update or change information contained in the accompanying prospectus. To the extent there is a conflict between the information contained in this prospectus supplement, on the one hand, and the information contained in the accompanying prospectus or any document incorporated by reference therein filed prior to the date of this prospectus supplement, on the other hand, you should rely on the information in this prospectus supplement. If any statement in one of these documents is inconsistent with a statement in another document having a later date—for example, a document filed after the date of this prospectus supplement and incorporated by reference in this prospectus supplement and the accompanying prospectus—the statement in the document having the later date modifies or supersedes the earlier statement.

You should rely only on the information contained or incorporated by reference in this prospectus supplement, the accompanying prospectus and in any free writing prospectuses we may provide to you in connection with this offering. We have not, and Roth has not, authorized any other person to provide you with any information that is different. If anyone provides you with different or inconsistent information, you should not rely on it. We are offering to sell, and seeking offers to buy, our securities only in jurisdictions where offers and sales are permitted. The distribution of this prospectus supplement and the offering of the common stock in certain jurisdictions may be restricted by law. Persons outside the United States who come into possession of this prospectus supplement must inform themselves about, and observe any restrictions relating to, the offering of the common stock and the distribution of this prospectus supplement outside the United States. This prospectus supplement does not constitute, and may not be used in connection with, an offer to sell, or a solicitation of an offer to buy, any securities offered by this prospectus supplement by any person in any jurisdiction in which it is unlawful for such person to make such an offer or solicitation.

We further note that the representations, warranties and covenants made by us in any agreement that is filed as an exhibit to any document that is incorporated by reference in the accompanying prospectus were made solely for the benefit of the parties to such agreement, including, in some cases, for the purpose of allocating risk among the parties to such agreements, and should not be deemed to be a representation, warranty or covenant to you. Moreover, such representations, warranties or covenants were accurate only as of the date when made. Accordingly, such representations, warranties and covenants should not be relied on as accurately representing the current state of our affairs.

 

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PROSPECTUS SUPPLEMENT SUMMARY

This summary highlights selected information about us, this offering and information appearing elsewhere in this prospectus supplement, in the accompanying prospectus and in the documents we incorporate by reference. This summary is not complete and does not contain all the information you should consider before investing in our securities pursuant to this prospectus supplement and the accompanying prospectus. Before making an investment decision, to fully understand this offering and its consequences to you, you should carefully read this entire prospectus supplement and the accompanying prospectus, including “Risk Factors” beginning on page S-6 of this prospectus supplement and the financial statements and related notes and the other information that we incorporated by reference herein, including our Annual Reports on Form 10-K and Quarterly Reports on Form 10-Q that we file from time to time.

Unless the context otherwise requires, all references in this prospectus to “Mast,” “we,” “us,” “our,” “the Company” or similar words refer to Mast Therapeutics, Inc., together with our consolidated subsidiaries.

Overview

We are a clinical-stage, biopharmaceutical company developing novel therapies for serious or life-threatening diseases with significant unmet needs. We are leveraging our Molecular Adhesion & Sealant Technology, or MAST, platform, derived from over two decades of clinical, nonclinical, and manufacturing experience with purified and non-purified poloxamers, to develop vepoloxamer (also known as MST-188), our lead drug candidate. Vepoloxamer has demonstrated multiple pharmacologic effects that may provide clinical benefit in a wide range of diseases and conditions typically characterized by impaired microvascular blood flow and/or damaged cell membranes. We currently are developing vepoloxamer for the treatment of sickle cell disease, heart failure, and stroke. We also are developing AIR001, a sodium nitrite solution for intermittent inhalation via nebulization. AIR001 has demonstrated positive hemodynamic effects in patients with pulmonary hypertension and we are developing it for the treatment of heart failure with preserved ejection fraction, or HFpEF.

We have devoted substantially all of our resources to research and development, or R&D, and to acquisition of our product candidates. We have not yet marketed or sold any products or generated any significant revenue and we have incurred significant annual operating losses since inception. We incurred a loss from operations of $29.7 million for the nine months ended September 30, 2015. As of September 30, 2015, we had an accumulated deficit of $264.8 million. Our cash, cash equivalents, and investment securities were $49.9 million as of September 30, 2015.

We continue to focus our resources primarily on the development of vepoloxamer. Enrolling subjects in EPIC, our pivotal Phase 3 study of vepoloxamer in patients with sickle cell disease, is one of our top priorities. We also are enrolling patients in a Phase 2 study of vepoloxamer for the treatment of chronic heart failure. In addition, we continue to pursue the opportunity for clinical development of vepoloxamer in ischemic stroke. Our vepoloxamer pipeline also includes a preclinical development program in resuscitation following major trauma (i.e., restoration of circulating blood volume and pressure).

Our second product candidate, AIR001, is in Phase 2 clinical development for the treatment of HFpEF. In February 2016, we announced positive top-line results from a randomized, double-blind, placebo-controlled Phase 2a study of AIR001 in 30 patients with HFpEF. In the Phase 2a study, AIR001 showed statistically significant improvement for the pre-specified primary endpoint and was generally well-tolerated. A second investigator-sponsored Phase 2a study of AIR001 is ongoing. We anticipate reporting interim data from a cohort of patients in that study around the middle of 2016. We obtained the AIR001 program through our acquisition of Aires Pharmaceuticals, Inc. in February 2014.

 

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Recent Developments

On February 1, 2016, we announced positive top-line results from a Phase 2a clinical study of AIR001 in patients with HFpEF, as discussed above. We also announced the selection of AIR001 by the Heart Failure Clinical Research Network, or HFN, for evaluation in a multicenter, randomized, double-blind, placebo-controlled Phase 2 clinical study of AIR001 in approximately 100 patients with HFpEF. The HFN will provide the platform to conduct the study and the HFN’s Coordinating Center will be the sponsor of the study. We plan to provide the test materials, nebulizers, regulatory and technical support, as well as financial support at milestones over the course of the study of approximately $3 million. We expect to enter into a contract with the HFN’s Coordinating Center in the coming weeks and that the Coordinating Center will submit an Investigational New Drug application to the U.S. Food and Drug Administration for clearance to conduct the study in the first quarter of 2016.

Corporate Information

In March 2013, we changed our name from “ADVENTRX Pharmaceuticals, Inc.” to “Mast Therapeutics, Inc.”

Our principal executive offices are located at 3611 Valley Centre Drive, Suite 500, San Diego, CA 92130 and our telephone number is (858) 552-0866.

 

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THE OFFERING

 

Public offering price		$             per unit
Common stock we are offering		shares, plus             shares of our common stock underlying the warrants offered in this offering.
Warrants we are offering		Each warrant will have an initial exercise price of $             per share of common stock, will be exercisable six months and one day after the date of issuance and will expire five years from the date of issuance. This prospectus supplement also relates to the offering of shares of our common stock issuable upon exercise of the warrants.
Common stock to be outstanding immediately after this offering		shares (assuming none of the warrants issued in this offering are exercised).
Limitation on exercise of the warrants		Any exercise notice with respect to the warrants delivered by a holder will be deemed automatically not to have been so delivered by such holder to the extent, but only to the extent, that delivery of shares of our common stock or any other security otherwise deliverable upon such exercise would result in such holder (together with such holder’s affiliates (as defined in Rule 13e-3 of the rules promulgated under the Securities Exchange Act of 1934, as amended, or the Exchange Act), and any other persons acting as a group together with such holder or any of such holder’s affiliates) having a “beneficial ownership,” as determined in accordance with Section 13(d) of the Exchange Act, and the rules thereunder, or “Beneficial Ownership,” of our common stock or any other class of any equity security (other than an exempted security) that is registered pursuant to Section 12 of the Exchange Act (a “Class”) in excess of 9.99% of the number of outstanding shares of our common stock or such Class (the “9.99% Ownership Limitation”).   Notwithstanding the foregoing, during any period of time in which a holder’s Beneficial Ownership of our common stock or any other Class is less than 5%, any exercise notice with respect to the warrants delivered by a holder will be deemed automatically not to have been so delivered by such holder to the extent, but only to the extent, that delivery of shares of our common stock or any other security otherwise deliverable upon such exercise would result in such holder (together with such holder’s affiliates and any other persons acting as a group together with such holder or any of such holder’s affiliates) having a Beneficial Ownership of our common stock or any other Class in excess of 4.99% of the number of outstanding shares of our common stock or such Class (the “4.99% Ownership Limitation”).   By written notice to us, any holder may from time to time increase or decrease the 4.99% Ownership Limitation to any other percentage not in excess of the 9.99% Ownership Limitation; provided that any such increase will not be effective until the 61st day after such notice is delivered to us.
Use of proceeds		We currently intend to use the net proceeds from this offering primarily to fund our clinical development programs of vepoloxamer in sickle cell disease and vepoloxamer and AIR001 heart failure, for regulatory, manufacturing and other commercial-readiness activities for vepoloxamer in

 

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		sickle cell disease, and for working capital and general corporate purposes. Please see “Use of Proceeds” on page S-9.
Risk factors		See “Risk Factors” beginning on page S-6 of this prospectus supplement, as well as the other information included in or incorporated by reference in this prospectus supplement and the accompanying prospectus, for a discussion of risks you should carefully consider before investing in our securities.
NYSE MKT symbol		Our common stock is listed on the NYSE MKT under the symbol “MSTX”. There is no established public trading market for the warrants, and a market may never develop. The warrants are not and will not be listed for trading on the NYSE MKT, any other national securities exchange or other nationally recognized trading system.
Transfer agent, warrant agent and registrar		American Stock Transfer & Trust Company, LLC

The number of shares of our common stock to be outstanding immediately after this offering as shown above assumes that all of the units being offered are sold, and is based on 163,614,297 shares of our common stock outstanding as of December 31, 2015 and excludes:

 

•

77,385,622 shares of our common stock issuable upon exercise of warrants outstanding as of December 31, 2015, with a weighted-average exercise price of $0.68 per share;

 

•

22,902,727 shares of our common stock issuable upon exercise of options outstanding as of December 31, 2015, with a weighted-average exercise price of $0.80 per share;

 

•

21,583,541 shares of our common stock available for future grants under our 2015 Omnibus Incentive Plan as of December 31, 2015.

 

•

12,478,050 shares of common stock that may be issued to the former stockholders of SynthRx, Inc., subject to the achievement of performance milestones, pursuant to the terms of the merger agreement with SynthRx; and

 

•

131,160 shares of our common stock sold after December 31, 2015 pursuant to our “at the market” equity offering program.

Unless otherwise indicated, all information in this prospectus supplement assumes that no exercise of the outstanding options and warrants described above or the warrants offered hereby.

 

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RISK FACTORS

Investing in our securities involves a high degree of risk and uncertainty. In addition to the other information included or incorporated by reference in this prospectus supplement and the accompanying prospectus, you should carefully consider the risks described in the “Risk Factors” section of our Quarterly Reports on Form 10-Q for the periods ended June 30, 2015 and September 30, 2015, which are incorporated by reference herein, before making an investment decision with respect to the securities. We expect to update these Risk Factors from time to time in the periodic and current reports that we file with the SEC after the date of this prospectus supplement. These updated Risk Factors will be incorporated by reference in this prospectus supplement and the accompanying prospectus. Please refer to these subsequent reports for additional information relating to the risks associated with investing in our common stock. If any of such risks and uncertainties actually occurs, our business, financial condition, and results of operations could be severely harmed. This could cause the trading price of our common stock to decline, and you could lose all or part of your investment.

RISKS RELATED TO THIS OFFERING

Our independent registered public accounting firm may conclude that there is substantial doubt regarding our ability to continue as a going concern.

Regardless of the amount of the net proceeds that we receive from this offering, if any, our independent registered public accounting firm may conclude, in connection with the audit of our consolidated financial statements for the year ended December 31, 2015, or any other subsequent period, that there is substantial doubt regarding our ability to continue as a going concern. If our independent registered public accounting firm issues a “going concern” opinion, it could impair our ability to finance our operations through the sale of equity, incurring debt, or other financing alternatives. If we fail to raise sufficient additional capital, we will not be able to completely execute our business plan. As a result our business would be jeopardized and the Company may not be able to continue. If we ceased operations, it is likely that purchasers of our common stock would lose their entire investment.

Our management will have broad discretion over the use of the net proceeds from this offering, you may not agree with how we use the proceeds and the proceeds may not be invested successfully.

Our management will have broad discretion as to the use of the net proceeds from this offering and could use them for purposes other than those contemplated currently and described under “Use of Proceeds” on page S-9. Accordingly, you will be relying on the judgment of our management with regard to the use of these net proceeds, and you will not have the opportunity, as part of your investment decision, to assess whether the proceeds are being used appropriately. It is possible that, pending their use, we may invest the net proceeds in a way that does not yield a favorable, or any, return for our company.

There may be future sales or other dilution of our equity, which may adversely affect the market price of our common stock.

We are generally not restricted from issuing additional common stock, including any securities that are convertible into or exchangeable for, or that represent the right to receive, common stock. The market price of our common stock could decline as a result of sales of common stock or securities that are convertible into or exchangeable for, or that represent the right to receive, common stock after this offering or the perception that such sales could occur.

You will experience immediate and substantial dilution in the net tangible book value per share of our common stock.

Because the price per unit being offered is substantially higher than the net tangible book value per share of our common stock, investors in this offering will suffer immediate and substantial dilution in the net tangible

 

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book value per share of common stock. Based on the public offering price of $             per unit, if you purchase securities in this offering, you will suffer immediate and substantial dilution of approximately $             per unit in net tangible book value of our common stock. See “Dilution” for a more detailed discussion of the dilution you may incur in connection with this offering.

There is no public market for the warrants to purchase shares of our common stock being offered by us in this offering.

There is no established public trading market for the warrants being offered in this offering, and a public market may never develop. In addition, we do not intend to apply to list the warrants on any national securities exchange or other nationally recognized trading system, including the NYSE MKT. Without an active market, the liquidity of the warrants will be limited.

Holders of our warrants will have no rights as a common stockholder until such holders exercise their warrants and acquire our common stock.

Until holders of warrants acquire shares of our common stock upon exercise of the warrants, holders of warrants will have no rights with respect to the shares of our common stock underlying such warrants. Upon exercise of the warrants, the holders thereof will be entitled to exercise the rights of a common stockholder only as to matters for which the record date occurs after the exercise date.

The warrants included in this offering may not have any value.

Each warrant has an initial exercise price of $             per share of common stock, will be exercisable six months and one day after the date of issuance and will expire five years from the date of issuance. In the event our common stock price does not exceed the exercise price of the warrants during the period when the warrants are exercisable, the warrants may not have any value.

Significant holders or beneficial holders of our common stock may not be permitted to exercise warrants that they hold.

The warrant agreement governing the warrants being offered hereby will prohibit a holder from exercising its warrants if doing so would result in such holder (together with such holder’s affiliates and any other persons acting as a group together with such holder or any of such holder’s affiliates) beneficially owning more than 9.99% of our common stock or any other class of any equity security (other than an exempted security) that is registered pursuant to Section 12 of the Exchange Act, or a Class. Furthermore, during any period in which a holder beneficially owns less than 5% of our common stock or any other Class, the warrant agreement will limit the ability of such holder to exercise its warrants if doing so would result in such holder (together with such holder’s affiliates and any other persons acting as a group together with such holder or any of such holder’s affiliates) beneficially owning more than 4.99% of our common stock or any other Class. As a result, you may not be able to exercise your warrants for shares of our common stock at a time when it would be financially beneficial for you to do so. In such circumstance you could seek to sell your warrants to realize value, but you may be unable to do so.

We may not have the ability to repurchase the warrants.

Under certain circumstances, if an extraordinary transaction (as defined in the warrants) occurs, holders of the warrants may require us to repurchase the remaining unexercised portion of such warrants for an amount of cash equal to the value of the warrant as determined in accordance with the Black Scholes option pricing model and the terms of the warrants. Our ability to repurchase the warrants depends on our ability to generate cash flow in the future. To some extent, this is subject to general economic, financial, competitive, legislative and regulatory factors and other factors that are beyond our control. We cannot assure you that we will maintain sufficient cash reserves or that our business will generate cash flow from operations at levels sufficient to permit us to repurchase the warrants.

 

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus and the SEC filings that are incorporated by reference into this prospectus supplement and the accompanying prospectus contain or incorporate by reference forward-looking statements within the meaning of Section 27A of the Securities Act and Section 21E of the Securities Exchange Act of 1934, as amended. All statements, other than statements of historical fact, included or incorporated by reference in this prospectus supplement or the accompanying prospectus regarding our strategy, plans, objectives, expectations, prospects, future operations, capital resources, financial position, projected costs of and progress with development of our product candidates, regulatory requirements, collaborations, competition, market exclusivity, intellectual property, and compliance with NYSE MKT listing standards are forward-looking statements. The words “believe,” “anticipate,” “estimate,” “plan,” “expect,” “intend,” “may,” “could,” “should,” “potential,” “likely,” “projects,” “continue,” “will,” and “would” and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. We cannot guarantee that we actually will achieve the plans, intentions or expectations expressed in our forward-looking statements and you should not place undue reliance on our forward-looking statements. There are a number of important factors that could cause our actual results to differ materially from those indicated or implied by forward-looking statements. These important factors include those set forth above under “Risk Factors.” These factors and the other cautionary statements made in this prospectus supplement and the accompanying prospectus should be read as being applicable to all related forward-looking statements whenever they appear in this prospectus supplement and the accompanying prospectus. Except as required by law, we do not assume any obligation to update any forward-looking statement. We disclaim any intention or obligation to update or revise any forward-looking statement, whether as a result of new information, future events or otherwise.

 

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USE OF PROCEEDS

We expect the net proceeds from this offering to be approximately $             million, after deducting the underwriting discounts and commissions and estimated offering expenses. The above does not give effect to any exercise of the warrants being offered and issued in this offering.

We currently intend to use the net proceeds from this offering primarily to fund our clinical development programs of vepoloxamer in sickle cell disease and vepoloxamer and AIR001 in heart failure, for regulatory, manufacturing and other commercial-readiness activities for vepoloxamer in sickle cell disease, and for working capital and general corporate purposes.

Pending the application of the net proceeds as described above, we expect to invest the net proceeds from this offering in short-term, interest-bearing, marketable securities.

 

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DILUTION

Purchasers of the units offered by this prospectus supplement and the accompanying prospectus will suffer immediate and substantial dilution in the net tangible book value per share of our common stock. Dilution in net tangible book value per share represents the difference between the amount per share paid by purchasers in this offering and the net tangible book value per share of our common stock immediately after this offering.

The net tangible book value of our common stock as of September 30, 2015, was approximately $22.0 million, or approximately $0.13 per share. Net tangible book value per share represents the amount of our total tangible assets, less the amount of our total tangible liabilities, divided by the total number of shares of our common stock outstanding. Dilution per share to new investors represents the difference between the amount per share paid by purchasers for each share of common stock in this offering and the net tangible book value per share of our common stock immediately following the completion of this offering.

After giving effect to the sale of              units at the public offering price of $             per unit, and after deducting underwriting discounts and commissions and estimated offering expenses payable by us, the net tangible book value of our common stock as of September 30, 2015 would have been approximately $             million, or approximately $             per share. This represents an immediate increase in net tangible book value of approximately $             per share to our existing stockholders and an immediate dilution in as-adjusted net tangible book value of approximately $             per share to purchasers of our securities in this offering, as illustrated by the following table:

 

Public offering price per unit				$
Net tangible book value per share as of September 30, 2015		$0.13
Increase per share attributable to this offering		$
As-adjusted net tangible book value per share as of September 30, 2015, after giving effect to this offering				$
Dilution per share to new investors participating in this offering				$

The foregoing table is based on 163,614,297 shares of our common stock outstanding as of September 30, 2015, and excludes:

 

•

77,385,622 shares of our common stock issuable upon exercise of warrants outstanding as of September 30, 2015, with a weighted-average exercise price of $0.68 per share;

 

•

22,455,807 shares of our common stock issuable upon exercise of options outstanding as of September 30, 2015, with a weighted-average exercise price of $0.81 per share;

 

•

22,030,461 shares of our common stock available for future grants under our 2015 Omnibus Incentive Plan as of September 30, 2015.

 

•

12,478,050 shares of common stock that may be issued to the former stockholders of SynthRx, Inc., subject to the achievement of performance milestones, pursuant to the terms of the merger agreement with SynthRx; and

 

•

131,160 shares of our common stock sold after September 30, 2015 pursuant to our “at the market” equity offering program.

To the extent that any outstanding options or warrants are exercised, new options are issued under our equity incentive plan, additional shares of common shares are sold under our “at the market” offering program, shares of common stock are sold under our employee stock purchase plan or we otherwise issue additional shares of common stock in the future at prices per share below the price per unit for any units sold in this offering, there will be further dilution to new investors.

The information above does not give effect to the potential exercises of the warrants offered by this prospectus supplement.

 

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DESCRIPTION OF THE SECURITIES WE ARE OFFERING

In this offering, we are offering for sale              units, with each unit consisting of one share of our common stock and one warrant to purchase one share of our common stock. The purchase price for each unit is $            . The units will not be issued or certificated. The shares of common stock and the warrants included in the units will be issued separately but can only be purchased together in the units in this offering.

Each warrant will have an initial exercise price of $            , will be exercisable six months and one day after the date of issuance, and will expire five years from the date of issuance.

Common Stock

The material terms and provisions of our common stock are described in the section titled “Description of Common Stock and Preferred Stock—Common Stock” in the accompanying prospectus.

Securities Exchange Listing

Our common stock is listed on the NYSE MKT under the symbol “MSTX.”

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is American Stock Transfer & Trust Company, LLC.

Warrants

The material terms and provisions of the warrants being offered pursuant to this prospectus supplement and the accompanying prospectus are summarized below. This summary is subject to and qualified in its entirety by the form of warrant, which will be filed with a Current Report on Form 8-K to be filed by us with the SEC in connection with this offering. You should review a copy of the form of warrant for a complete description of the terms and conditions applicable to the warrants included in the units.

Book-Entry Form. The warrants will be issued pursuant to the terms of the warrant agreement between us and American Stock Transfer & Trust Company, LLC, as warrant agent. The warrants will be initially issued in the form of global securities held in book-entry form. Upon issuance, each of the global warrants will be deposited with The Depository Trust Company (“DTC”) and registered in the name of Cede & Co., as nominee of DTC. Ownership of beneficial interests in a global warrant will be limited to persons who have accounts with DTC (‘‘DTC participants’’) or persons who hold interests through DTC participants. Beneficial interests in global warrants may not be exchanged for warrants in physical, certificated form except in limited circumstances. Owners of beneficial interests in a global warrant will not receive or be entitled to receive physical, certificated warrants. The global warrants and beneficial interests in the global warrants will be subject to the applicable procedures of DTC, including procedures for exercising a beneficial interest in a warrant and restrictions on transfer.

Exercise Price and Exercisability. Each warrant entitles the holder thereof to purchase one share of our common stock at an exercise price equal to $             per share. The warrants will be exercisable during the period commencing from six months and one day after the date of original issuance and ending on the date that is five years after their original issuance. If an effective registration statement is available for the issuance of the shares underlying the warrants, a holder may only exercise the warrants through a cash exercise. If, and only if, a registration statement relating to the issuance of the shares underlying the warrants is not then effective or available, a holder of warrants may exercise the warrants on a cashless basis, where the holder receives the net value of the warrant in shares of common stock. Shares issued pursuant to a cashless exercise would be freely

 

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tradable without restriction or further registration under the Securities Act by persons other than our affiliates (within the meaning of Rule 144 under the Securities Act).

The exercise price and the number and type of securities purchasable upon exercise of warrants are subject to adjustment upon certain corporate events, including certain mergers, consolidations, tender offer or exchange offer, reclassifications, stock dividends and stock splits, cash dividends, a sale of all or substantially all of our assets and certain other events.

Exercise Limitations. Notwithstanding any other provision of this description of our warrants and the warrant agreement, any exercise notice with respect to the warrants delivered by a holder will be deemed automatically not to have been so delivered by such holder to the extent, but only to the extent, that delivery of shares of our common stock or any other security otherwise deliverable upon such exercise would result in such holder (together with such holder’s affiliates (as defined in Rule 13e-3 of the rules promulgated under the Exchange Act) and any other persons acting as a group together with such holder or any of such holder’s affiliates) having Beneficial Ownership of our common stock or any other Class in excess of the 9.99% Ownership Limitation. Any purported delivery to any holder shall be void and have no effect to the extent, but only to the extent, that after such delivery, such holder would have Beneficial Ownership of our common stock or any such Class in excess of the 9.99% Ownership Limitation.

Notwithstanding the foregoing, during any period of time in which a holder’s Beneficial Ownership of our common stock or any other Class is less than 5%, any exercise notice with respect to the warrants delivered by a holder will be deemed automatically not to have been so delivered by such holder to the extent, but only to the extent, that delivery of shares of our common stock or any other security otherwise deliverable upon such exercise would result in such holder (together with such holder’s affiliates and any other persons acting as a group together with such holder or any of such holder’s affiliates) having a Beneficial Ownership of our common stock or any Class in excess of the 4.99% Ownership Limitation. Any purported delivery to any holder whose Beneficial Ownership of our common stock or any other Class is less than 5% shall be void and have no effect to the extent, but only to the extent, that after such delivery, such holder would have Beneficial Ownership of our common stock or any such Class in excess of the 4.99% Ownership Limitation.

For purposes of calculating Beneficial Ownership for each of the immediately two preceding paragraphs, the aggregate number of shares of our common stock beneficially owned by a holder will include the number of shares of our common stock issuable upon exercise of the warrants with respect to which the determination of such sentence is being made, but shall exclude the number of shares of our common stock which are issuable upon (i) exercise of the remaining, unexercised warrants beneficially owned by such holder, and (ii) exercise or conversion of the unexercised or unconverted portion of any of our other securities beneficially owned by such holder (including, without limitation, any convertible notes, convertible stock or warrants) that are subject to a limitation on conversion or exercise analogous to the limitation contained herein.

By written notice to us, a holder may from time to time increase or decrease the 4.99% Ownership Limitation to any other percentage not in excess of the 9.99% Ownership Limitation; provided that any such increase will not be effective until the 61st day after such notice is delivered to us.

Transferability. Subject to applicable laws, the warrants may be offered for sale, sold, transferred or assigned without our consent.

Exchange Listing. We do not plan on applying to list the warrants on the NYSE MKT, any other national securities exchange or any other nationally recognized trading system.

 

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Extraordinary Transactions. In the event of an extraordinary transaction, as described in the warrants and generally including any merger with or into another entity, sale of all or substantially all of our assets, tender offer or exchange offer, or reclassification of our common stock, we or any successor entity will pay at the holder’s option, exercisable at any time concurrently with or within 10 days after the consummation of the extraordinary transaction, an amount of cash equal to the value of the warrant as determined in accordance with the Black Scholes option pricing model and the terms of the warrants.

Rights as a Stockholder. Except by virtue of such holder’s ownership of shares of our common stock, the holder of a warrant does not have the rights or privileges of a holder of our common stock, including any voting rights, until the holder exercises the warrant.

 

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UNDERWRITING

We have entered into an underwriting agreement with Roth Capital Partners, LLC, acting as representative of the several underwriters, with respect to the securities in this offering. Subject to the terms and conditions of the underwriting agreement, we have agreed to issue and sell to the underwriters named below, and each underwriter severally has agreed to purchase, the respective number of units set forth opposite its name below:

 

Underwriter		Number of Units
Roth Capital Partners, LLC
Total

The underwriters are offering the units subject to their acceptance of the units from us and subject to prior sale. The underwriting agreement provides that the obligation of the underwriters to purchase the units offered hereby is subject to certain conditions and that the underwriters are obligated to purchase all of the units offered hereby if any are purchased.

The underwriters initially propose to offer the units directly to the public at the public offering price set forth on the cover page of this prospectus supplement. Any units sold by the underwriters to securities dealers will be sold at the applicable public offering price less a selling concession not in excess of $             per unit. If all of the units are not sold at the public offering price, the offering price and other selling terms may be changed by the underwriters. The units are offered subject to receipt and acceptance by the underwriters and to the other conditions of the offering, including the right to reject orders in whole or in part.

The following table shows the underwriting discount payable to the underwriters by us, and the proceeds, before expenses, payable to us both on a per unit basis and in total, in connection with this offering.

 

		Per Unit
Public offering price		$
Underwriting discounts and commissions		$
Proceeds, before expenses, to us		$

The expenses of this offering, not including underwriting discounts and commissions, are estimated to be approximately $            , which includes $75,000 that we have agreed to reimburse the representative for fees and costs incurred by it in connection with this offering.

In connection with the offering the underwriters may engage in stabilizing transactions and penalty bids in accordance with Regulation M under the Exchange Act:

 

•

Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum, and are engaged in for the purpose of preventing or retarding a decline in the market price of the common stock while the offering is in progress.

 

•

Penalty bids permit the representative to reclaim a selling concession from a syndicate member when the common stock originally sold by the syndicate member is purchased in a stabilizing transaction.

 

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These stabilizing transactions and penalty bids may have the effect of raising or maintaining the market price of our common stock or preventing or retarding a decline in the market price of the common stock. As a result, the price of our common stock may be higher than the price that might otherwise exist in the open market. Neither we nor the underwriters make any representation or prediction as to the direction or magnitude of any effect that the transactions described above may have on the price of the common stock. In addition, neither we nor the underwriters make any representations that the underwriters will engage in these stabilizing transactions or that any transaction, once commenced, will not be discontinued without notice.

The public offering price of the units and the exercise price and other terms of the warrants were negotiated between us and the underwriters, based on the trading price of our common stock prior to the offering, among other things. Other factors considered in determining the public offering price of the units and the exercise price and other terms of the warrants include the history and prospects of the Company, the stage of development of our business, our business plans for the future and the extent to which they have been implemented, an assessment of our management, general conditions of the securities markets at the time of the offering and such other factors as were deemed relevant.

Pursuant to the underwriting agreement, we have agreed to indemnify the underwriters against certain liabilities, including liabilities under the Securities Act, or to contribute to payments that the underwriters or such indemnified parties may be required to make in respect of any such liabilities.

We and all of our directors and executive officers have agreed that, subject to certain exceptions, without the prior written consent of Roth Capital Partners, LLC, we and they will not, (i) during the period ending 90 days, subject to an 18-day extension under certain circumstances (subject to clause (ii) below), following the date of the underwriting agreement, offer, pledge, transfer, assign, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant for the sale of, lend or otherwise dispose of any shares of our common stock or any securities convertible into or exchangeable or exercisable for our common stock or file, or cause to be filed, any registration statement under the Securities Act with respect to any of the foregoing, or (ii) during the period ending 60 days following the date of the underwriting agreement, directly or indirectly offer, sell, assign, transfer, pledge, contract to sell, or otherwise dispose of, any shares of Common Stock pursuant to that certain Sales Agreement dated as of August 21, 2015 between us and Cowen and Company, LLC as sales agent (the “ATM Agreement”). At any time and without public notice, Roth Capital Partners, LLC may, in its sole discretion, release some or all of the securities from these lock-up agreements.

The restrictions described above do not apply to certain transactions, including:

with respect to us:

 

•

the securities to be sold in this offering

with respect to our directors and executive officers:

 

•

the transfer of shares of common stock or any securities convertible into shares of common stock to us upon a vesting event of our securities or upon the exercise of options to purchase our securities, in each case on a “cashless” or “net exercise” basis or to cover tax withholding obligations and sales of shares of common stock to cover the exercise price of options and to fund tax obligations arising upon the exercise of options on the vesting of restricted stock.

Our common stock is listed on the NYSE MKT LLC under the symbol “MSTX.” There is no established public trading market for the warrants, and we do not intend to apply to list the warrants on any national securities exchange. The warrants included in the units are immediately separable from the shares of our common stock being offered as part of the units.

 

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The underwriters and certain of their affiliates may in the future provide various investment banking and other financial services for us and our affiliates.

A prospectus in electronic format may be made available on the websites maintained by the underwriters, if any, participating in this offering and the underwriters may distribute prospectuses electronically. Other than the prospectus in electronic format, the information on these websites is not part of this prospectus supplement, the accompanying prospectus or the registration statement of which this prospectus supplement and the accompanying prospectus form a part, has not been approved or endorsed by us or the underwriters, and should not be relied upon by investors.

 

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LEGAL MATTERS

The validity of the securities offered hereby will be passed upon for us by DLA Piper LLP (US), San Diego, California. Roth Capital Partners, LLC is being represented in connection with this offering by Ellenoff Grossman  & Schole LLP, New York, New York.

EXPERTS

The consolidated financial statements incorporated in this prospectus supplement by reference to the Annual Report on Form 10-K for the year ended December 31, 2014 have been so incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

WHERE YOU CAN FIND ADDITIONAL INFORMATION

We file annual, quarterly and current reports, proxy statements and other information with the SEC. You may read and copy any reports, statements and other information filed by us at the SEC’s Public Reference Room at 100 F Street, N.E., Washington, D.C. 20549. Please call (800) SEC-0330 for further information on the Public Reference Room. The SEC maintains an Internet website that contains reports, proxy and information statements and other information regarding issuers, including us, that file electronically with the SEC. The address for the SEC’s website is http://www.sec.gov.

We make available, free of charge, through our investor relations website, our Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q, Current Reports on Form 8-K, statements of changes in beneficial ownership of securities and amendments to those reports and statements as soon as reasonably practicable after they are filed with the SEC. The address for our website is http://www.masttherapeutics.com. The contents on our website are not part of this prospectus, and the reference to our website does not constitute incorporation by reference into this prospectus of the information contained at that site.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to incorporate by reference the information we file with it, which means that we can disclose important information to you by referring you to another document that we have filed separately with the SEC. You should read the information incorporated by reference because it is an important part of this prospectus supplement. We incorporate by reference the following information or documents that we have filed with the SEC (excluding those portions of any Form 8-K that are not deemed “filed” pursuant to the General Instructions of Form 8-K):

 

•

Our Annual Report on Form 10-K for the fiscal year ended December 31, 2014, filed with the SEC on March 24, 2015;

 

•

The portions of our definitive proxy statement filed with the SEC on April 29, 2015 in connection with our 2015 annual meeting of stockholders that are incorporated by reference into Part III of our Annual Report on Form 10-K for the fiscal year ended December 31, 2014;

 

•

Our Quarterly Report on Form 10-Q for the quarter ended March 31, 2015, filed with the SEC on May 11, 2015, our Quarterly Report on Form 10-Q for the quarter ended June 30, 2015, filed with the SEC on August 12, 2015, and our Quarterly Report on Form 10-Q for the quarter ended September 30, 2015, filed with the SEC on November 12, 2015;

 

•

Our Current Reports on Form 8-K filed with the SEC on January 6, 2015, January 7, 2015, January 12, 2015, January 27, 2015, February 3, 2015, February 9, 2015, March 2, 2015, April 23, 2015, May 19, 2015, May 28, 2015, June 16, 2015, June 25, 2015, August 21, 2015, September 15, 2015, September 30, 2015, October 7, 2015, November 2, 2015, November 9, 2015, January 7, 2016, January 11, 2016, and February 1, 2016; and

 

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•

The description of our common stock contained in our registration statement on Form 8-A filed with the SEC on April 27, 2004 (File No. 001-32157-04755401).

All reports and other documents we subsequently file pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act prior to the termination of this offering, including all such documents we may file with the SEC after the date of the initial registration statement and prior to the effectiveness of the registration statement, but excluding any information furnished to, rather than filed with, the SEC, will also be incorporated by reference into this prospectus supplement and deemed to be part of this prospectus supplement from the date of the filing of such reports and documents.

Any statement contained in any document incorporated by reference herein shall be deemed to be modified or superseded for purposes of this prospectus supplement to the extent that a statement contained in this prospectus supplement or any additional prospectus supplements modifies or supersedes such statement. Any statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus supplement.

We will provide without charge to each person, including any beneficial owner, to whom this prospectus supplement is delivered, upon written or oral request, a copy of any or all documents that are incorporated by reference into this prospectus supplement, but not delivered with the prospectus supplement, other than exhibits to such documents unless such exhibits are specifically incorporated by reference into the documents that this prospectus supplement incorporates. You should direct written requests to: Mast Therapeutics, Inc., 3611 Valley Centre Drive, Suite 500, San Diego, California 92130, Attn: Investor Relations, or you may call us at (858) 552-0866.

 

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PROSPECTUS

 

$150,000,000

Common Stock

Preferred Stock

Debt Securities

Warrants

Units

We may, from time to time in one or more offerings, offer and sell up to $150,000,000 in the aggregate of common stock, preferred stock, debt securities, warrants to purchase common stock, preferred stock or debt securities, or any combination of the foregoing, either individually or as units comprised of one or more of the other securities.

This prospectus provides a general description of the securities we may offer. We will provide the specific terms of the securities offered in one or more supplements to this prospectus. We may also authorize one or more free writing prospectuses to be provided to you in connection with these offerings. The prospectus supplement and any related free writing prospectus may add, update or change information contained in this prospectus. You should read carefully this prospectus, the applicable prospectus supplement and any related free writing prospectus, as well as the documents incorporated by reference before you invest in any of our securities. This prospectus may not be used to offer or sell any securities unless accompanied by the applicable prospectus supplement.

Our common stock is listed on the NYSE MKT under the symbol “MSTX.” On March 23, 2015, the last reported sale price for our common stock was $0.52 per share.

Investing in our securities involves a high degree of risk. See “Risk Factors ” on page 5 of this prospectus and in the documents incorporated by reference in this prospectus, as updated in the applicable prospectus supplement, any related free writing prospectus and other future filings we make with the Securities and Exchange Commission that are incorporated by reference into this prospectus, for a discussion of the factors you should consider carefully before deciding to purchase our securities.

We will sell these securities directly to investors, through agents designated from time to time or to or through underwriters or dealers. For additional information on the methods of sale, you should refer to the section entitled “Plan of Distribution” in this prospectus. If any underwriters are involved in the sale of any securities with respect to which this prospectus is being delivered, the names of such underwriters and any applicable commissions or discounts will be set forth in a prospectus supplement. The price to the public of such securities and the net proceeds we expect to receive from such sale will also be set forth in a prospectus supplement.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is August 19, 2015.

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ABOUT THIS PROSPECTUS			ii
SUMMARY			1
RISK FACTORS			5
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS			5
USE OF PROCEEDS			6
SECURITIES WE MAY OFFER			6
DESCRIPTION OF COMMON STOCK AND PREFERRED STOCK			6
DESCRIPTION OF DEBT SECURITIES			10
DESCRIPTION OF WARRANTS			18
DESCRIPTION OF UNITS			20
LEGAL OWNERSHIP OF SECURITIES			21
PLAN OF DISTRIBUTION			24
LEGAL MATTERS			26
EXPERTS			26
INFORMATION INCORPORATED BY REFERENCE			26
WHERE YOU CAN FIND MORE INFORMATION			27

 

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ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission, or the SEC, under the Securities Act of 1933, as amended, or the Securities Act, using a “shelf” registration process. Under this shelf registration process, we may from time to time sell common stock, preferred stock, debt securities or warrants to purchase common stock, preferred stock or debt securities, or any combination of the foregoing, either individually or as units comprised of one or more of the other securities, in one or more offerings up to a total dollar amount of $150,000,000. We have provided to you in this prospectus a general description of the securities we may offer. Each time we sell securities under this shelf registration, we will, to the extent required by law, provide a prospectus supplement that will contain specific information about the terms of that offering. We may also authorize one or more free writing prospectuses to be provided to you that may contain material information relating to these offerings. The prospectus supplement and any related free writing prospectus that we may authorize to be provided to you may also add, update or change information contained in this prospectus or in any documents that we have incorporated by reference into this prospectus. To the extent there is a conflict between the information contained in this prospectus and the prospectus supplement or any related free writing prospectus, you should rely on the information in the prospectus supplement or the related free writing prospectus; provided that if any statement in one of these documents is inconsistent with a statement in another document having a later date — for example, a document filed after the date of this prospectus and incorporated by reference into this prospectus or any prospectus supplement or any related free writing perspective — the statement in the document having the later date modifies or supersedes the earlier statement

We have not authorized any dealer, agent or other person to give any information or to make any representation other than those contained or incorporated by reference in this prospectus and any accompanying prospectus supplement, or any related free writing prospectus that we may authorize to be provided to you. You must not rely upon any information or representation not contained or incorporated by reference in this prospectus or an accompanying prospectus supplement, or any related free writing prospectus that we may authorize to be provided to you. This prospectus and the accompanying prospectus supplement, if any, do not constitute an offer to sell or the solicitation of an offer to buy any securities other than the registered securities to which they relate, nor do this prospectus and the accompanying prospectus supplement constitute an offer to sell or the solicitation of an offer to buy securities in any jurisdiction to any person to whom it is unlawful to make such offer or solicitation in such jurisdiction. You should not assume that the information contained in this prospectus, any applicable prospectus supplement or any related free writing prospectus is accurate on any date subsequent to the date set forth on the front of the document or that any information we have incorporated by reference is correct on any date subsequent to the date of the document incorporated by reference (as our business, financial condition, results of operations and prospects may have changed since that date), even though this prospectus, any applicable prospectus supplement or any related free writing prospectus is delivered or securities are sold on a later date.

As permitted by SEC rules and regulations, the registration statement of which this prospectus forms a part includes additional information not contained in this prospectus. You may read the registration statement and the other reports we file with the SEC at its web site or at its offices described below under “Where You Can Find More Information.”

 

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RISK FACTORS

Investing in our securities involves a high degree of risk. You should carefully consider the risk factors set forth under “Risk Factors” in Item 1A of our annual report on Form 10-K for the year ended December 31, 2014, which is incorporated by reference in this prospectus, together with all other information contained or incorporated by reference in this prospectus, as may be updated by our subsequent filings under the Exchange Act, and the risk factors and other information contained in any applicable prospectus supplement and in any related free writing prospectus in connection with a specific offering, before deciding whether to purchase any of the securities being registered pursuant to the registration statement of which this prospectus is a part. Each of the risk factors could adversely affect our business, operating results and financial condition, as well as adversely affect the value of an investment in our securities, and the occurrence of any of these risks might cause you to lose all or part of your investment. Additional risks and uncertainties that we do not presently know about or that we currently believe are not material may also adversely affect our business.

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus and our SEC filings that are incorporated by reference into this prospectus contain or incorporate by reference forward-looking statements within the meaning of Section 27A of the Securities Act and Section 21E of the Exchange Act. All statements, other than statements of historical fact, included or incorporated by reference in this prospectus regarding our development of our products, financial position, strategy, regulatory status, clinical and nonclinical studies, collaborations, commercial prospects, internal growth, competition, intellectual property, regulatory reforms, products, objectives of management, and compliance with NYSE MKT listing standards are forward-looking statements. Forward-looking statements may include, but are not limited to, statements about:

 

•

the initiation, scope, rate of progress, results and timing of our clinical and nonclinical studies of

 

•

our product candidates, including vepoloxamer;

 

•

the successful completion of our development programs and our ability to manage costs associated with clinical and nonclinical development of our product candidates, including vepoloxamer;

 

•

our ability to obtain and maintain regulatory approvals of our product candidates, including vepoloxamer;

 

•

our ability to commercialize and achieve market acceptance of our product candidates, including vepoloxamer;

 

•

our ability to protect our intellectual property and operate our business without infringing upon the intellectual property rights of others;

 

•

our estimates regarding the sufficiency of our cash resources and our need for additional funding; and

 

•

our intended use of the net proceeds from offerings of our securities under this prospectus.

The words “believe,” “anticipate,” “estimate,” “plan,” “expect,” “intend,” “may,” “could,” “should,” “potential,” “likely,” “projects,” “continue,” “will,” and “would” and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. Forward-looking statements reflect our current views with respect to future events, are based on assumptions and are subject to risks and uncertainties. We cannot guarantee that we actually will achieve the plans, intentions or expectations expressed in our forward-looking statements and you should not place undue reliance on these statements. There are a number of important factors that could cause our actual results to differ materially from those indicated or implied by forward-looking statements. These important factors include those discussed under the heading “Risk Factors” contained or incorporated in this prospectus and in the applicable prospectus supplement and any free writing prospectus we may authorize for use in connection with a specific offering.

 

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These factors and the other cautionary statements made in this prospectus should be read as being applicable to all related forward-looking statements whenever they appear in this prospectus. Except as required by law, we do not assume any obligation to update any forward-looking statement. We disclaim any intention or obligation to update or revise any forward-looking statement, whether as a result of new information, future events or otherwise.

USE OF PROCEEDS

Except as described in any prospectus supplement and any free writing prospectus in connection with a specific offering, we currently intend to use the net proceeds from the sale of the securities offered under this prospectus to fund continued development of our product candidates, including clinical studies, nonclinical testing and research-related manufacturing activities, to pursue regulatory approval for our product candidates and, potentially, to commercialize product candidates that receive regulatory approval, and for general corporate purposes, including working capital. We may also use a portion of the net proceeds to acquire or invest in technologies, product candidates, products and/or businesses that we believe will enhance the value of our company, although we have no current commitments or agreements with respect to any such transactions as of the date of this prospectus. We have not determined the amount of net proceeds to be used specifically for the foregoing purposes. As a result, our management will have broad discretion in the allocation of the net proceeds and investors will be relying on the judgment of our management regarding the application of the proceeds of any sale of the securities. If a material part of the net proceeds is to be used to repay indebtedness, we will set forth the interest rate and maturity of such indebtedness in a prospectus supplement. Pending use of the net proceeds, we intend to invest the proceeds in interest-bearing, marketable securities.

SECURITIES WE MAY OFFER

We may offer shares of common stock, shares of preferred stock, debt securities or warrants to purchase common stock, preferred stock or debt securities, or any combination of the foregoing, either individually or as units comprised of one or more of the other securities. We may offer up to $150,000,000 of securities under this prospectus. If securities are offered as units, we will describe the terms of the units in a prospectus supplement.

DESCRIPTION OF COMMON STOCK AND PREFERRED STOCK

The following description of our common stock and preferred stock, together with any additional information we include in any applicable prospectus supplement or any related free writing prospectus, summarizes the material terms and provisions of our common stock and the preferred stock that we may offer under this prospectus. While the terms we have summarized below will apply generally to any future common stock or preferred stock that we may offer, we will describe the particular terms of any class or series of these securities in more detail in the applicable prospectus supplement. For the complete terms of our common stock and preferred stock, please refer to our certificate of incorporation and our bylaws, each as amended to date, that are incorporated by reference into the registration statement of which this prospectus is a part or may be incorporated by reference in this prospectus or any applicable prospectus supplement. The terms of these securities may also be affected by the Delaware General Corporation Law, or the DGCL. The summary below and that contained in any applicable prospectus supplement or any related free writing prospectus are qualified in their entirety by reference to our certificate of incorporation and bylaws, as in effect at the time of any offering of securities under this prospectus.

 

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Common Stock

As of the date of this prospectus, our certificate of incorporation authorizes us to issue 500,000,000 shares of common stock, par value $0.001 per share, of which 159,458,376 shares were issued and outstanding as of March 20, 2015. Additional shares of authorized common stock may be issued, as authorized by our board of directors from time to time, without stockholder approval, except as may be required by applicable securities exchange requirements. The holders of common stock possess exclusive voting rights in us, except to the extent our board of directors specifies voting power with respect to any other class of securities issued in the future. Each holder of our common stock is entitled to one vote for each share held of record on each matter submitted to a vote of stockholders, including the election of directors. Stockholders do not have any right to cumulate votes in the election of directors.

Subject to preferences that may be granted to the holders of preferred stock, each holder of our common stock is entitled to share ratably in distributions to stockholders and to receive ratably such dividends as may be declared by our board of directors out of funds legally available therefor. In the event of our liquidation, dissolution or winding up, the holders of our common stock will be entitled to receive, after payment of all of our debts and liabilities and of all sums to which holders of any preferred stock may be entitled, the distribution of any of our remaining assets. Holders of our common stock have no conversion, exchange, sinking fund or redemption rights and have no preemptive rights to subscribe for any of our securities.

All of the outstanding shares of our common stock are fully paid and non-assessable. The shares of common stock offered by this prospectus or upon the conversion of any preferred stock or debt securities or exercise of any warrants offered pursuant to this prospectus, when issued and paid for, will also be, fully paid and non-assessable.

Securities Exchange Listing

Our common stock is listed on the NYSE MKT under the symbol “MSTX.”

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is American Stock Transfer & Trust Company.

Preferred Stock

As of the date of this prospectus, our certificate of incorporation authorizes us to issue 1,000,000 shares of preferred stock, par value $0.001 per share, none of which are outstanding. Pursuant to our certificate of incorporation, our board of directors has the authority to provide for the issuance, in one or more series, of our authorized preferred stock and to fix or alter the rights, preferences, privileges and restrictions granted to or imposed upon any series of our preferred stock. The rights, privileges, preferences and restrictions of any such series of our preferred stock may be subordinated to, pari passu with (including, without limitation, inclusion in provisions with respect to liquidation and acquisition preferences, redemption or approval of matters by vote or written consent), or senior to any of those of any present or future class or series of preferred stock or common stock. Our board of directors is also expressly authorized to increase or decrease the number of shares of any series prior or subsequent to the issue of that series, but not below the number of shares of such series then outstanding. The issuance of preferred stock may have the effect of decreasing the market price of our common stock and may adversely affect the voting power of holders of our common stock and reduce the likelihood that holders of our common stock will receive dividend payments and payments upon liquidation.

The particular terms of each class or series of preferred stock that we may offer under this prospectus, including redemption privileges, liquidation preferences, voting rights, dividend rights and/or conversion rights, will be more fully described in the applicable prospectus supplement relating to the preferred stock offered

 

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thereby. The rights, preferences, privileges and restrictions of any series of preferred stock that we may offer under this prospectus will be set forth in the certificate of designation relating to that series. We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from another report we file with the SEC, the form of any certificate of designation that describes the terms of the series of preferred stock we may offer before the issuance of the related series of preferred stock. The applicable prospectus supplement will specify the terms of the series of preferred stock we may offer, including, but not limited to:

 

•

the distinctive designation and the maximum number of shares in the series;

 

•

the number of shares we are offering and purchase price per share;

 

•

the liquidation preference, if any;

 

•

the terms on which dividends, if any, will be paid;

 

•

the voting rights, if any, of the shares of the series;

 

•

the terms and conditions, if any, on which the shares of the series shall be convertible into, or exchangeable for, shares of any other class or classes of capital stock;

 

•

the terms on which the shares may be redeemed, if at all;

 

•

any listing of the preferred stock on any securities exchange or market;

 

•

a discussion of any material or special United States federal income tax considerations applicable to the preferred stock; and

 

•

any or all other preferences, rights, restrictions, including restrictions on transferability, and qualifications of shares of the series.

The description of preferred stock above and the description of the terms of a particular series of preferred stock in any applicable prospectus supplement are not complete. You should refer to the applicable certificate of designation for complete information.

The DGCL provides that the holders of preferred stock will have the right to vote separately as a class on any proposal involving fundamental changes in the rights of holders of that preferred stock. This right is in addition to any voting rights that may be provided for in the applicable certificate of designation.

Anti-Takeover Effects of Provisions of our Charter Documents and Delaware Law

Provisions of the DGCL, our certificate of incorporation and our bylaws could make it more difficult to acquire us by means of a tender offer, a proxy contest or otherwise, or to remove incumbent officers and directors. These provisions, summarized below, are expected to discourage certain types of coercive takeover practices and takeover bids that our board of directors may consider inadequate and to encourage persons seeking to acquire control of us to first negotiate with our board of directors. We believe that the benefits of increased protection of our ability to negotiate with the proponent of an unfriendly or unsolicited proposal to acquire or restructure us outweigh the disadvantages of discouraging takeover or acquisition proposals because, among other things, negotiation of these proposals could result in an improvement of their terms. This summary does not purport to be complete and is qualified in its entirety by reference to the DGCL and our certificate of incorporation and bylaws.

Certificate of Incorporation and Bylaws

Preferred Stock. Under our certificate of incorporation, our board of directors has the power to authorize the issuance of up to 1,000,000 shares of preferred stock, all of which are currently undesignated, and to determine

 

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the price, rights, preferences, privileges and restrictions, including voting rights, of those shares without further vote or action by our stockholders. The issuance of preferred stock may:

 

•

delay, defer or prevent a change in control;

 

•

discourage bids for our common stock at a premium over the market price of our common stock;

 

•

adversely affect the voting and other rights of the holders of our common stock; and

 

•

discourage acquisition proposals or tender offers for our shares and, as a consequence, inhibit fluctuations in the market price of our shares that could result from actual or rumored takeover attempts.

Advance Notice Requirement. Stockholder nominations of individuals for election to our board of directors and stockholder proposals of other matters to be brought before an annual meeting of our stockholders must comply with the advance notice procedures set forth in our bylaws. Generally, to be timely, such notice must be received at our principal executive offices no later than the date specified in our proxy statement released to stockholders in connection with the preceding year’s annual meeting of stockholders, which date shall be not earlier than the 120th day, nor later than the close of business on the 90th day, prior to the first anniversary of the date of the preceding year’s annual meeting of stockholders.

Special Meeting Requirements. Our bylaws provide that special meetings of our stockholders may be called only at the request of our board of directors, president (unless there is a chief executive officer who is not the president, in which case a special meeting may be called at any time by the chief executive officer and not the president) or chair of the board of directors. Only such business shall be considered at a special meeting as shall have been stated in the notice for such meeting.

No Cumulative Voting. Our certificate of incorporation does not include a provision for cumulative voting for directors.

Indemnification. Our certificate of incorporation and bylaws provide that we will indemnify our officers and directors against losses as they incur in investigations and legal proceedings resulting from their services to us, which may include service in connection with takeover defense measures.

Removal of Directors. Our bylaws provide that the affirmative vote of the holders of at least 75% of our voting stock then outstanding is required to remove our directors, either with or without cause.

Authorized but Unissued Shares. Our authorized but unissued shares of common stock and preferred stock will be available for future issuance without stockholder approval. We may use additional shares for a variety of purposes, including future public offerings to raise additional capital, to fund acquisitions and as employee compensation. The existence of authorized but unissued shares of common stock and preferred stock could render more difficult or discourage an attempt to obtain control of us by means of a proxy contest, tender offer, merger or otherwise.

Delaware Anti-Takeover Statute

We are subject to Section 203 of the DGCL, an anti-takeover law. In general, Section 203 prohibits, with some exceptions, a publicly held Delaware corporation from engaging in a “business combination” with any “interested stockholder” for a period of three years following the date that stockholder became an interested stockholder, unless:

 

•

prior to that date, the board of directors of the corporation approved either the business combination or the transaction that resulted in the stockholder becoming an interested stockholder;

 

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•

upon consummation of the transaction that resulted in the stockholder becoming an interested stockholder, the interested stockholder owned at least 85% of the voting stock of the corporation outstanding at the time the transaction commenced, excluding for purposes of determining the number of shares of voting stock outstanding (but not the voting stock owned by the interested stockholder) those shares owned by persons who are directors and officers and by excluding employee stock plans in which employee participants do not have the right to determine whether shares held subject to the plan will be tendered in a tender or exchange offer; or

 

•

on or subsequent to that date, the business combination is approved by the board of directors of the corporation and authorized at an annual or special meeting of stockholders, and not by written consent, by the affirmative vote of at least 66-2/3% of the outstanding voting stock that is not owned by the interested stockholder.

Section 203 defines “business combination” to include any of the following:

 

•

any merger or consolidation involving the corporation and the interested stockholder;

 

•

any sale, transfer, pledge or other disposition of 10% or more of the assets of the corporation involving the interested stockholder;

 

•

subject to certain exceptions, any transaction that results in the issuance or transfer by the corporation of any stock of the corporation to the interested stockholder;

 

•

any transaction involving the corporation that has the effect of increasing the proportionate share of the stock of any class or series of the corporation beneficially owned by the interested stockholder; or

 

•

the receipt by the interested stockholder of the benefit of any loans, advances, guarantees, pledges or other financial benefits provided by or through the corporation.

In general, Section 203 defines an “interested stockholder” as any person who, together with the person’s affiliates and associates, beneficially owns, or within three years prior to the determination of interested stockholder status did beneficially own, 15% or more of the outstanding voting stock of the corporation.

The above provisions may deter a hostile takeover or delay a change in control of management or us.

DESCRIPTION OF DEBT SECURITIES

We may issue debt securities, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. The following description, together with the additional information we include in any applicable prospectus supplements or free writing prospectuses, summarizes the material terms and provisions of the debt securities that we may offer under this prospectus. While the terms we have summarized below will apply generally to any future debt securities we may offer under this prospectus, we will describe the particular terms of any debt securities that we may offer in more detail in the applicable prospectus supplement or free writing prospectus. The terms of any debt securities we offer under a prospectus supplement may differ from the terms we describe below. However, no prospectus supplement shall fundamentally change the terms that are set forth in this prospectus or offer a security that is not registered and described in this prospectus at the time of its effectiveness. As of March 24, 2015, we have no outstanding registered debt securities. Unless the context requires otherwise, whenever we refer to the “indentures,” we also are referring to any supplemental indentures that specify the terms of a particular series of debt securities.

We will issue any senior debt securities under the senior indenture that we will enter into with the trustee named in the senior indenture. We will issue any subordinated debt securities under the subordinated indenture and any supplemental indentures that we will enter into with the trustee named in the subordinated indenture. We have filed forms of these documents as exhibits to the registration statement, of which this prospectus is a part,

 

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and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC.

The indentures will be qualified under the Trust Indenture Act of 1939, as amended (the “Trust Indenture Act”). We use the term “trustee” to refer to either the trustee under the senior indenture or the trustee under the subordinated indenture, as applicable.

The following summaries of material provisions of the senior debt securities, the subordinated debt securities and the indentures are subject to, and qualified in their entirety by reference to, all of the provisions of the indenture and any supplemental indentures applicable to a particular series of debt securities. We urge you to read the applicable prospectus supplements and any related free writing prospectuses related to the debt securities that we may offer under this prospectus, as well as the complete indentures that contains the terms of the debt securities. Except as we may otherwise indicate, the terms of the senior indenture and the subordinated indenture are identical.

General

The terms of each series of debt securities will be established by or pursuant to a resolution of our board of directors and set forth or determined in the manner provided in an officers’ certificate or by a supplemental indenture. Debt securities may be issued in separate series without limitation as to aggregate principal amount. We may specify a maximum aggregate principal amount for the debt securities of any series. We will describe in the applicable prospectus supplement the terms of the series of debt securities being offered, including:

 

•

the title;

 

•

the principal amount being offered, and if a series, the total amount authorized and the total amount outstanding;

 

•

any limit on the amount that may be issued;

 

•

whether or not we will issue the series of debt securities in global form, and, if so, the terms and who the depositary will be;

 

•

the maturity date;

 

•

whether and under what circumstances, if any, we will pay additional amounts on any debt securities held by a person who is not a United States person for tax purposes, and whether we can redeem the debt securities if we have to pay such additional amounts;

 

•

the annual interest rate, which may be fixed or variable, or the method for determining the rate and the date interest will begin to accrue, the dates interest will be payable and the regular record dates for interest payment dates or the method for determining such dates;

 

•

whether or not the debt securities will be secured or unsecured, and the terms of any secured debt;

 

•

the terms of the subordination of any series of subordinated debt;

 

•

the place where payments will be made;

 

•

restrictions on transfer, sale or other assignment, if any;

 

•

our right, if any, to defer payment of interest and the maximum length of any such deferral period;

 

•

the date, if any, after which, and the price at which, we may, at our option, redeem the series of debt securities pursuant to any optional or provisional redemption provisions and the terms of those redemption provisions;

 

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•

provisions for a sinking fund purchase or other analogous fund, if any, including the date, if any, on which, and the price at which we are obligated, pursuant thereto or otherwise, to redeem, or at the holder’s option, to purchase, the series of debt securities and the currency or currency unit in which the debt securities are payable;

 

•

whether the indenture will restrict our ability or the ability of our subsidiaries to:

 

•

incur additional indebtedness;

 

•

issue additional securities;

 

•

create liens;

 

•

pay dividends or make distributions in respect of our capital stock or the capital stock of our subsidiaries;

 

•

redeem capital stock;

 

•

place restrictions on our subsidiaries’ ability to pay dividends, make distributions or transfer assets;

 

•

make investments or other restricted payments;

 

•

sell or otherwise dispose of assets;

 

•

enter into sale-leaseback transactions;

 

•

engage in transactions with stockholders or affiliates;

 

•

issue or sell stock of our subsidiaries; or

 

•

effect a consolidation or merger;

 

•

whether the indenture will require us to maintain any interest coverage, fixed charge, cash flow-based, asset-based or other financial ratios;

 

•

a discussion of certain material or special United States federal income tax considerations applicable to the debt securities;

 

•

information describing any book-entry features;

 

•

the applicability of the provisions in the indenture on discharge;

 

•

whether the debt securities are to be offered at a price such that they will be deemed to be offered at an “original issue discount” as defined in paragraph (a) of Section 1273 of the Internal Revenue Code of 1986, as amended;

 

•

the denominations in which we will issue the series of debt securities, if other than denominations of $1,000 and any integral multiple thereof;

 

•

the currency of payment of debt securities if other than U.S. dollars and the manner of determining the equivalent amount in U.S. dollars; and

 

•

any other specific terms, preferences, rights or limitations of, or restrictions on, the debt securities, including any additional events of default or covenants provided with respect to the debt securities, and any terms that may be required by us or advisable under applicable laws or regulations.

Conversion or Exchange Rights

We will set forth in the applicable prospectus supplement the terms under which a series of debt securities may be convertible into or exchangeable for our common stock, our preferred stock or other securities (including securities of a third party). We will include provisions as to whether conversion or exchange is mandatory, at the

 

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option of the holder or at our option. We may include provisions pursuant to which the number of shares of our common stock, our preferred stock or other securities (including securities of a third party) that the holders of the series of debt securities receive would be subject to adjustment.

Consolidation, Merger or Sale

Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the indentures will not contain any covenant that restricts our ability to merge or consolidate, or sell, convey, transfer or otherwise dispose of all or substantially all of our assets. However, any successor to or acquirer of such assets must assume all of our obligations under the indentures or the debt securities, as appropriate. If the debt securities are convertible into or exchangeable for our other securities or securities of other entities, the person with whom we consolidate or merge or to whom we sell all of our property must make provisions for the conversion of the debt securities into securities that the holders of the debt securities would have received if they had converted the debt securities before the consolidation, merger or sale.

Events of Default under the Indenture

Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the following are events of default under the indentures with respect to any series of debt securities that we may issue:

 

•

if we fail to pay interest when due and payable and our failure continues for 90 days and the time for payment has not been extended;

 

•

if we fail to pay the principal, premium or sinking fund payment, if any, when due and payable at maturity, upon redemption or repurchase or otherwise, and the time for payment has not been extended;

 

•

if we fail to observe or perform any other covenant contained in the debt securities or the indentures, other than a covenant specifically relating to another series of debt securities, and our failure continues for 90 days after we receive notice from the trustee or we and the trustee receive notice from the holders of at least 25% in aggregate principal amount of the outstanding debt securities of the applicable series; and

 

•

if specified events of bankruptcy, insolvency or reorganization occur.

We will describe in each applicable prospectus supplement any additional events of default relating to the relevant series of debt securities.

If an event of default with respect to debt securities of any series occurs and is continuing, other than an event of default specified in the last bullet point above, the trustee or the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series, by notice to us in writing, and to the trustee if notice is given by such holders, may declare the unpaid principal, premium, if any, and accrued interest, if any, due and payable immediately. If an event of default arises due to the occurrence of certain specified bankruptcy, insolvency or reorganization events, the unpaid principal, premium, if any, and accrued interest, if any, of each issue of debt securities then outstanding shall be due and payable without any notice or other action on the part of the trustee or any holder.

The holders of a majority in principal amount of the outstanding debt securities of an affected series may waive any default or event of default with respect to the series and its consequences, except defaults or events of default regarding payment of principal, premium, if any, or interest, unless we have cured the default or event of default in accordance with the indenture. Any waiver shall cure the default or event of default.

Subject to the terms of the indentures, if an event of default under an indenture shall occur and be continuing, the trustee will be under no obligation to exercise any of its rights or powers under such indenture at

 

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the request or direction of any of the holders of the applicable series of debt securities, unless such holders have offered the trustee reasonable indemnity or security satisfactory to it against any loss, liability or expense. The holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee, or exercising any trust or power conferred on the trustee, with respect to the debt securities of that series, provided that:

 

•

the direction so given by the holder is not in conflict with any law or the applicable indenture; and

 

•

subject to its duties under the Trust Indenture Act, the trustee need not take any action that might involve it in personal liability or might be unduly prejudicial to the holders not involved in the proceeding.

The indentures provide that if an event of default has occurred and is continuing, the trustee will be required in the exercise of its powers to use the degree of care that a prudent person would use in the conduct of its own affairs. The trustee, however, may refuse to follow any direction that conflicts with law or the indenture, or that the trustee determines is unduly prejudicial to the rights of any other holder of the relevant series of debt securities, or that would involve the trustee in personal liability. Prior to taking any action under the indentures, the trustee will be entitled to indemnification against all costs, expenses and liabilities that would be incurred by taking or not taking such action.

A holder of the debt securities of any series will have the right to institute a proceeding under the indentures or to appoint a receiver or trustee, or to seek other remedies only if:

 

•

the holder has given written notice to the trustee of a continuing event of default with respect to that series;

 

•

the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series have made a written request and such holders have offered reasonable indemnity to the trustee or security satisfactory to it against any loss, liability or expense or to be incurred in compliance with instituting the proceeding as trustee; and

 

•

the trustee does not institute the proceeding, and does not receive from the holders of a majority in aggregate principal amount of the outstanding debt securities of that series other conflicting directions within 90 days after the notice, request and offer.

These limitations do not apply to a suit instituted by a holder of debt securities if we default in the payment of the principal, premium, if any, or interest on, the debt securities, or other defaults that may be specified in the applicable prospectus supplement.

We will periodically file statements with the trustee regarding our compliance with specified covenants in the indentures.

The indentures provide that if a default occurs and is continuing and is actually known to a responsible officer of the trustee, the trustee must mail to each holder notice of the default within the earlier of 90 days after it occurs and 30 days after it is known by a responsible officer of the trustee or written notice of it is received by the trustee, unless such default has been cured or waived. Except in the case of a default in the payment of principal or premium of, or interest on, any debt security or certain other defaults specified in an indenture, the trustee shall be protected in withholding such notice if and so long as the board of directors, the executive committee or a trust committee of directors, or responsible officers of the trustee, in good faith determine that withholding notice is in the best interests of holders of the relevant series of debt securities.

 

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Modification of Indenture; Waiver

Subject to the terms of the indenture for any series of debt securities that we may issue, we and the trustee may change an indenture without the consent of any holders with respect to the following specific matters:

 

•

to fix any ambiguity, defect or inconsistency in the indenture;

 

•

to comply with the provisions described above under “Description of Debt Securities — Consolidation, Merger or Sale;”

 

•

to comply with any requirements of the SEC in connection with the qualification of any indenture under the Trust Indenture Act;

 

•

to add to, delete from or revise the conditions, limitations and restrictions on the authorized amount, terms or purposes of issue, authentication and delivery of debt securities, as set forth in the indenture;

 

•

to provide for the issuance of, and establish the form and terms and conditions of, the debt securities of any series as provided under “Description of Debt Securities — General,” to establish the form of any certifications required to be furnished pursuant to the terms of the indenture or any series of debt securities, or to add to the rights of the holders of any series of debt securities;

 

•

to evidence and provide for the acceptance of appointment hereunder by a successor trustee;

 

•

to provide for uncertificated debt securities and to make all appropriate changes for such purpose;

 

•

to add such new covenants, restrictions, conditions or provisions for the benefit of the holders, to make the occurrence, or the occurrence and the continuance, of a default in any such additional covenants, restrictions, conditions or provisions an event of default or to surrender any right or power conferred to us in the indenture; or

 

•

to change anything that does not adversely affect the interests of any holder of debt securities of any series in any material respect.

In addition, under the indentures, the rights of holders of a series of debt securities may be changed by us and the trustee with the written consent of the holders of at least a majority in aggregate principal amount of the outstanding debt securities of each series that is affected. However, subject to the terms of the indenture for any series of debt securities that we may issue or otherwise provided in the prospectus supplement applicable to a particular series of debt securities, we and the trustee may only make the following changes with the consent of each holder of any outstanding debt securities affected:

 

•

extending the stated maturity of the series of debt securities;

 

•

reducing the principal amount, reducing the rate of or extending the time of payment of interest, or reducing any premium payable upon the redemption or repurchase of any debt securities; or

 

•

reducing the percentage of debt securities, the holders of which are required to consent to any amendment, supplement, modification or waiver.

Discharge

Each indenture provides that, subject to the terms of the indenture and any limitation otherwise provided in the prospectus supplement applicable to a particular series of debt securities, we may elect to be discharged from our obligations with respect to one or more series of debt securities, except for specified obligations, including obligations to:

 

•

register the transfer or exchange of debt securities of the series;

 

•

replace stolen, lost or mutilated debt securities of the series;

 

•

maintain paying agencies;

 

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•

hold monies for payment in trust;

 

•

recover excess money held by the trustee;

 

•

compensate and indemnify the trustee; and

 

•

appoint any successor trustee.

In order to exercise our rights to be discharged, we must deposit with the trustee money or government obligations sufficient to pay all the principal of, and any premium and interest on, the debt securities of the series on the dates payments are due.

Form, Exchange and Transfer

We will issue the debt securities of each series only in fully registered form without coupons and, unless we otherwise specify in the applicable prospectus supplement, in denominations of $1,000 and any integral multiple thereof. The indentures provide that we may issue debt securities of a series in temporary or permanent global form and as book-entry securities that will be deposited with, or on behalf of, The Depository Trust Company or another depositary named by us and identified in a prospectus supplement with respect to that series. See “Legal Ownership of Securities” below for a further description of the terms relating to any book-entry securities.

At the option of the holder, subject to the terms of the indentures and the limitations applicable to global securities described in the applicable prospectus supplement, the holder of the debt securities of any series can exchange the debt securities for other debt securities of the same series, in any authorized denomination and of like tenor and aggregate principal amount.

Subject to the terms of the indentures and the limitations applicable to global securities set forth in the applicable prospectus supplement, holders of the debt securities may present the debt securities for exchange or for registration of transfer, duly endorsed or with the form of transfer endorsed thereon duly executed if so required by us or the security registrar, at the office of the security registrar or at the office of any transfer agent designated by us for this purpose. Unless otherwise provided in the debt securities that the holder presents for transfer or exchange, we will make no service charge for any registration of transfer or exchange, but we may require payment of any taxes or other governmental charges.

We will name in the applicable prospectus supplement the security registrar, and any transfer agent in addition to the security registrar, that we initially designate for any debt securities. We may at any time designate additional transfer agents or rescind the designation of any transfer agent or approve a change in the office through which any transfer agent acts, except that we will be required to maintain a transfer agent in each place of payment for the debt securities of each series.

If we elect to redeem the debt securities of any series, we will not be required to:

 

•

issue, register the transfer of, or exchange any debt securities of that series during a period beginning at the opening of business 15 days before the day of mailing of a notice of redemption of any debt securities that may be selected for redemption and ending at the close of business on the day of the mailing; or

 

•

register the transfer of or exchange any debt securities so selected for redemption, in whole or in part, except the unredeemed portion of any debt securities we are redeeming in part.

Information Concerning the Trustee

The trustee, other than during the occurrence and continuance of an event of default under an indenture, undertakes to perform only those duties as are specifically set forth in the applicable indenture and is under no

 

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obligation to exercise any of the powers given it by the indentures at the request of any holder of debt securities unless it is offered reasonable security and indemnity against the costs, expenses and liabilities that it might incur. However, upon an event of default under an indenture, the trustee must use the same degree of care as a prudent person would exercise or use in the conduct of his or her own affairs.

Payment and Paying Agents

Unless we otherwise indicate in the applicable prospectus supplement, we will make payment of the interest on any debt securities on any interest payment date to the person in whose name the debt securities, or one or more predecessor securities, are registered at the close of business on the regular record date for the interest payment.

We will pay principal of and any premium and interest on the debt securities of a particular series at the office of the paying agents designated by us, except that unless we otherwise indicate in the applicable prospectus supplement, we will make interest payments by check that we will mail to the holder or by wire transfer to certain holders. Unless we otherwise indicate in the applicable prospectus supplement, we will designate the corporate trust office of the trustee as our sole paying agent for payments with respect to debt securities of each series. We will name in the applicable prospectus supplement any other paying agents that we initially designate for the debt securities of a particular series. We will maintain a paying agent in each place of payment for the debt securities of a particular series.

All money we pay to a paying agent or the trustee for the payment of the principal of or any premium or interest on any debt securities that remains unclaimed at the end of two years after such principal, premium or interest has become due and payable will be repaid to us, and the holder of the debt security thereafter may look only to us for payment thereof.

Governing Law

The indentures and the debt securities will be governed by and construed in accordance with the laws of the State of New York, except to the extent that the Trust Indenture Act is applicable.

Ranking Debt Securities

The subordinated debt securities will be unsecured and will be subordinate and junior in priority of payment to certain other indebtedness to the extent described in a prospectus supplement. The subordinated indenture does not limit the amount of subordinated debt securities that we may issue. It also does not limit us from issuing any other secured or unsecured debt.

The senior debt securities will be unsecured and will rank equally in right of payment to all our other senior unsecured debt. The senior indenture does not limit the amount of senior debt securities that we may issue. It also does not limit us from issuing any other secured or unsecured debt.

Existing Subordinated Debt

As of December 31, 2014, we had no existing subordinated debt.

 

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DESCRIPTION OF WARRANTS

General

We may issue warrants for the purchase of common stock, preferred stock or debt securities. Warrants may be offered independently or together with common stock, preferred stock or debt securities offered by any prospectus supplement and may be attached to or separate from those securities. While the terms we have summarized below will apply generally to any warrants that we may offer under this prospectus, we will describe in particular the terms of any series of warrants that we may offer in more detail in the applicable prospectus supplement and any applicable free writing prospectus. The terms of any warrants offered under a prospectus supplement may differ from the terms described below.

We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from another report that we file with the SEC, the form of warrant and/or warrant agreement, which may include a form of warrant certificate, as applicable, that describes the terms of the particular series of warrants we may offer before the issuance of the related series of warrants. We may issue the warrants under a warrant agreement that we will enter into with a warrant agent to be selected by us. The warrant agent will act solely as our agent in connection with the warrants and will not assume any obligation or relationship of agency or trust for or with any registered holders of warrants or beneficial owners of warrants. The following summary of material provisions of the warrants and warrant agreements are subject to, and qualified in their entirety by reference to, all the provisions of the form of warrant and/or warrant agreement and warrant certificate applicable to a particular series of warrants. We urge you to read the applicable prospectus supplement and any related free writing prospectus, as well as the complete form of warrant and/or the warrant agreement and warrant certificate, as applicable, that contain the terms of the warrants.

The particular terms of any issue of warrants will be described in the prospectus supplement relating to the issue. Those terms may include:

 

•

the title of such warrants;

 

•

the aggregate number of such warrants;

 

•

the price or prices at which such warrants will be issued;

 

•

the currency or currencies (including composite currencies) in which the price of such warrants may be payable;

 

•

the terms of the securities purchasable upon exercise of such warrants and the procedures and conditions relating to the exercise of such warrants;

 

•

the price at which the securities purchasable upon exercise of such warrants may be purchased;

 

•

the date on which the right to exercise such warrants will commence and the date on which such right shall expire;

 

•

any provisions for adjustment of the number or amount of securities receivable upon exercise of the warrants or the exercise price of the warrants;

 

•

if applicable, the minimum or maximum amount of such warrants that may be exercised at any one time;

 

•

if applicable, the designation and terms of the securities with which such warrants are issued and the number of such warrants issued with each such security;

 

•

if applicable, the date on and after which such warrants and the related securities will be separately transferable;

 

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•

information with respect to book-entry procedures, if any;

 

•

the terms of any rights to redeem or call the warrants;

 

•

United States federal income tax consequences of holding or exercising the warrants, if material; and

 

•

any other terms of such warrants, including terms, procedures and limitations relating to the exchange or exercise of such warrants.

Each warrant will entitle its holder to purchase the principal amount of debt securities or the number of shares of preferred stock or common stock at the exercise price set forth in, or calculable as set forth in, the applicable prospectus supplement. The warrants may be exercised as set forth in the prospectus supplement relating to the warrants offered. Unless we otherwise specify in the applicable prospectus supplement, warrants may be exercised at any time up to the close of business on the expiration date set forth in the prospectus supplement relating to the warrants offered thereby. After the close of business on the expiration date, unexercised warrants will become void.

We will specify the place or places where, and the manner in which, warrants may be exercised in the form of warrant, warrant agreement or warrant certificate and applicable prospectus supplement. Upon receipt of payment and the warrant or warrant certificate, as applicable, properly completed and duly executed at the corporate trust office of the warrant agent, if any, or any other office, including ours, indicated in the prospectus supplement, we will, as soon as practicable, issue and deliver the securities purchasable upon such exercise. If less than all of the warrants (or the warrants represented by such warrant certificate) are exercised, a new warrant or a new warrant certificate, as applicable, will be issued for the remaining amount of warrants. If we so indicate in the applicable prospectus supplement, holders of the warrants may surrender securities as all or part of the exercise price for warrants.

Prior to the exercise of any warrants to purchase common stock, preferred stock or debt securities, holders of the warrants will not have any of the rights of holders of the common stock, preferred stock or debt securities purchasable upon exercise, including (i) in the case of warrants for the purchase of common stock or preferred stock, the right to vote or to receive any payments of dividends or payments upon our liquidation, dissolution or winding up on the common stock or preferred stock purchasable upon exercise, if any; or (ii) in the case of warrants for the purchase of debt securities, the right to receive payments of principal of, any premium or interest on the debt securities purchasable upon exercise or to enforce covenants in the applicable indenture.

Outstanding Warrants

As of March 20, 2015, there were outstanding warrants to purchase 79,149,568 shares of our common stock, of which warrants to purchase 409,228 shares were outstanding with an exercise price of $3.44 per share, warrants to purchase 1,062,500 shares were outstanding with an exercise price of $1.00 per share, warrants to purchase 1,816,608 shares were outstanding with an exercise price of $3.65 per share, warrants to purchase 2,046,139 shares were outstanding with an exercise price of $2.75 per share, warrants to purchase 10,625,000 shares were outstanding with an exercise price of $1.10 per share, warrants to purchase 28,097,400 shares were outstanding with an exercise price of $0.65 per share, warrants to purchase 13,081,428 shares were outstanding with an exercise price of $0.01 per share, and warrants to purchase 22,011,265 shares were outstanding with an exercise price of $0.75 per share. The warrants may be exercised for cash or, under certain circumstances, on a cashless basis, in which case we will deliver, upon exercise, the number of shares with respect to which the warrant is being exercised reduced by a number of shares having a value (as determined in accordance with the terms of the applicable warrant) equal to the aggregate exercise price of the shares with respect to which the warrant is being exercised.

 

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DESCRIPTION OF UNITS

The following description, together with the additional information we may include in any applicable prospectus supplement, summarizes the material terms and provisions of the units that we may offer under this prospectus. While the terms we have summarized below will apply generally to any units that we may offer under this prospectus, we will describe the particular terms of any series of units in more detail in the applicable prospectus supplement and any related free writing prospectus. The terms of any units offered under a prospectus supplement may differ from the terms described below. However, no prospectus supplement will fundamentally change the terms that are set forth in this prospectus or offer a security that is not registered and described in this prospectus at the time of its effectiveness.

We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from another report we file with the SEC, the form of unit agreement that describes the terms of the series of units we may offer under this prospectus, and any supplemental agreements, before the issuance of the related series of units. The following summaries of material terms and provisions of the units are subject to, and qualified in their entirety by reference to, all the provisions of the unit agreement and any supplemental agreements applicable to a particular series of units. We urge you to read the applicable prospectus supplement and any related free writing prospectus, as well as the complete unit agreement and any supplemental agreements that contain the terms of the units.

General

We may issue units comprised of one or more debt securities, shares of common stock, shares of preferred stock and warrants in any combination. Each unit will be issued so that the holder of the unit is also the holder of each security included in the unit. Thus, the holder of a unit will have the rights and obligations of a holder of each included security. The unit agreement under which a unit is issued may provide that the securities included in the unit may not be held or transferred separately, at any time or at any time before a specified date.

We will describe in the applicable prospectus supplement the terms of the series of units, including, but not limited to:

 

•

the designation and terms of the units and of the securities comprising the units, including whether and under what circumstances those securities may be held or transferred separately;

 

•

any provisions of the governing unit agreement that differ from those described below; and

 

•

any provisions for the issuance, payment, settlement, transfer or exchange of the units or of the securities comprising the units.

The provisions described in this section, as well as those described under “Description of Common Stock and Preferred Stock,” “Description of Debt Securities” and “Description of Warrants” will apply to each unit and to any common stock, preferred stock, debt security or warrant included in each unit, respectively.

Issuance in Series

We may issue units in such amounts and in numerous distinct series as we determine.

Enforceability of Rights by Holders of Units

Each unit agent will act solely as our agent under the applicable unit agreement and will not assume any obligation or relationship of agency or trust with any holder of any unit. A single bank or trust company may act as unit agent for more than one series of units. A unit agent will have no duty or responsibility in case of any default by us under the applicable unit agreement or unit, including any duty or responsibility to initiate any

 

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proceedings at law or otherwise, or to make any demand upon us. Any holder of a unit may, without the consent of the related unit agent or the holder of any other unit, enforce by appropriate legal action its rights as holder under any security included in the unit.

We, the unit agents and any of their agents may treat the registered holder of any unit certificate as an absolute owner of the units evidenced by that certificate for any purpose and as the person entitled to exercise the rights attaching to the units so requested, despite any notice to the contrary.

LEGAL OWNERSHIP OF SECURITIES

We can issue securities in registered form or in the form of one or more global securities. We describe global securities in greater detail below. We refer to those persons who have securities registered in their own names on the books that we or any applicable trustee or depositary or warrant agent maintain for this purpose as the “holders” of those securities. These persons are the legal holders of the securities. We refer to those persons who, indirectly through others, own beneficial interests in securities that are not registered in their own names, as “indirect holders” of those securities. As we discuss below, indirect holders are not legal holders, and investors in securities issued in book-entry form or in “street name” will be indirect holders.

Book-Entry Holders

We may issue securities in book-entry form only, as we will specify in the applicable prospectus supplement. This means securities may be represented by one or more global securities registered in the name of a financial institution that holds them as depositary on behalf of other financial institutions that participate in the depositary’s book-entry system. These participating institutions, which are referred to as participants, in turn, hold beneficial interests in the securities on behalf of themselves or their customers.

Only the person in whose name a security is registered is recognized as the holder of that security. Global securities will be registered in the name of the depositary. Consequently, for global securities, we will recognize only the depositary as the holder of the securities, and we will make all payments on the securities to the depositary. The depositary passes along the payments it receives to its participants, which in turn pass the payments along to their customers who are the beneficial owners. The depositary and its participants do so under agreements they have made with one another or with their customers; they are not obligated to do so under the terms of the securities.

As a result, investors in a global security will not own securities directly. Instead, they will own beneficial interests in a global security, through a bank, broker or other financial institution that participates in the depositary’s book-entry system or holds an interest through a participant. As long as the securities are issued in global form, investors will be indirect holders, and not legal holders, of the securities.

Street Name Holders

We may terminate a global security or issue securities that are not issued in global form. In these cases, investors may choose to hold their securities in their own names or in “street name.” Securities held by an investor in street name would be registered in the name of a bank, broker or other financial institution that the investor chooses, and the investor would hold only a beneficial interest in those securities through an account he or she maintains at that institution.

For securities held in street name, we or any applicable trustee or depositary will recognize only the intermediary banks, brokers and other financial institutions in whose names the securities are registered as the holders of those securities, and we or any such trustee or depositary will make all payments on those securities to them. These institutions pass along the payments they receive to their customers who are the beneficial owners,

 

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but only because they agree to do so in their customer agreements or because they are legally required to do so. Investors who hold securities in street name will be indirect holders, not legal holders, of those securities.

Legal Holders

Our obligations, as well as the obligations of any applicable trustee or third party employed by us or a trustee, run only to the legal holders of the securities. We do not have obligations to investors who hold beneficial interests in global securities, in street name or by any other indirect means. This will be the case whether an investor chooses to be an indirect holder of a security or has no choice because we are issuing the securities only in global form.

For example, once we make a payment or give a notice to the legal holder, we have no further responsibility for the payment or notice even if that holder is required, under agreements with its participants or customers or by law, to pass it along to the indirect holders but does not do so. Similarly, we may want to obtain the approval of the legal holders to amend an indenture, to relieve us of the consequences of a default or of our obligation to comply with a particular provision of an indenture, or for other purposes. In such an event, we would seek approval only from the legal holders, and not the indirect holders, of the securities. Whether and how the legal holders contact the indirect holders is up to the legal holders.

Special Considerations for Indirect Holders

If you hold securities through a bank, broker or other financial institution, either in book-entry form because the securities are represented by one or more global securities or in street name, you should check with your own institution to find out:

 

•

how it handles securities payments and notices;

 

•

whether it imposes fees or charges;

 

•

how it would handle a request for the legal holders’ consent, if ever required;

 

•

whether and how you can instruct it to send you securities registered in your own name so you can be a legal holder, if that is permitted in the future;

 

•

how it would exercise rights under the securities if there were a default or other event triggering the need for legal holders to act to protect their interests; and

 

•

if the securities are in book-entry form, how the depositary’s rules and procedures will affect these matters.

Global Securities

A global security is a security that represents one or any other number of individual securities held by a depositary. Generally, all securities represented by the same global securities will have the same terms.

Each security issued in book-entry form will be represented by a global security that we issue to, deposit with and register in the name of a financial institution or its nominee that we select. The financial institution that we select for this purpose is called the depositary. Unless we specify otherwise in the applicable prospectus supplement, The Depository Trust Company, New York, New York, known as DTC, will be the depositary for all securities issued in book-entry form.

A global security may not be transferred to or registered in the name of anyone other than the depositary, its nominee or a successor depositary, unless special termination situations arise. We describe those situations below under “—Special Situations When A Global Security Will Be Terminated.” As a result of these arrangements, the depositary, or its nominee, will be the sole registered owner and legal holder of all securities represented by a

 

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global security, and investors will be permitted to own only beneficial interests in a global security. Beneficial interests must be held by means of an account with a broker, bank or other financial institution that in turn has an account with the depositary or with another institution that does. Thus, an investor whose security is represented by a global security will not be a legal holder of the security, but only an indirect holder of a beneficial interest in the global security.

If the prospectus supplement for a particular security indicates that the security will be issued as a global security, then the security will be represented by a global security at all times unless and until the global security is terminated. If termination occurs, we may issue the securities through another book-entry clearing system or decide that the securities may no longer be held through any book-entry clearing system.

Special Considerations For Global Securities

As an indirect holder, an investor’s rights relating to a global security will be governed by the account rules of the investor’s financial institution and of the depositary, as well as general laws relating to securities transfers. We do not recognize an indirect holder as a holder of securities and instead deal only with the depositary that holds the global security.

If securities are issued only as global securities, an investor should be aware of the following:

 

•

an investor cannot cause the securities to be registered in his or her name, and cannot obtain non-global certificates for his or her interest in the securities, except in the special situations we describe below;

 

•

an investor will be an indirect holder and must look to his or her own bank or broker for payments on the securities and protection of his or her legal rights relating to the securities, as we describe above;

 

•

an investor may not be able to sell interests in the securities to some insurance companies and to other institutions that are required by law to own their securities in non-book-entry form;

 

•

an investor may not be able to pledge his or her interest in the global security in circumstances where certificates representing the securities must be delivered to the lender or other beneficiary of the pledge in order for the pledge to be effective;

 

•

the depositary’s policies, which may change from time to time, will govern payments, transfers, exchanges and other matters relating to an investor’s interest in the global security. We and any applicable trustee have no responsibility for any aspect of the depositary’s actions or for its records of ownership interests in the global security. We and the trustee also do not supervise the depositary in any way;

 

•

the depositary may, and we understand that DTC will, require that those who purchase and sell interests in the global security within its book-entry system use immediately available funds, and your broker or bank may require you to do so as well; and

 

•

financial institutions that participate in the depositary’s book-entry system, and through which an investor holds its interest in the global security, may also have their own policies affecting payments, notices and other matters relating to the securities. There may be more than one financial intermediary in the chain of ownership for an investor. We do not monitor and are not responsible for the actions of any of those intermediaries.

Special Situations When a Global Security Will Be Terminated

In a few special situations described below, a global security will terminate and interests in it will be exchanged for physical certificates representing those interests. After that exchange, the choice of whether to hold securities directly or in street name will be up to the investor. Investors must consult their own banks or brokers to find out how to have their interests in securities transferred to their own names, so that they will be direct holders. We have described the rights of holders and street name investors above.

 

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A global security will terminate when the following special situations occur:

 

•

if the depositary notifies us that it is unwilling, unable or no longer qualified to continue as depositary for that global security and we do not appoint another institution to act as depositary within 90 days;

 

•

if we notify any applicable trustee that we wish to terminate that global security; or

 

•

if an event of default has occurred with regard to securities represented by that global security and has not been cured or waived.

The applicable prospectus supplement may also list additional situations for terminating a global security that would apply only to the particular series of securities covered by the prospectus supplement. When a global security terminates, the depositary, and neither we nor any applicable trustee, is responsible for deciding the names of the institutions that will be the initial direct holders.

PLAN OF DISTRIBUTION

We may sell the securities to or through underwriters or dealers, through agents, or directly to one or more purchasers. A prospectus supplement or supplements (and any related free writing prospectus that we may authorize to be provided to you) will describe the terms of the offering of the securities, including, to the extent applicable:

 

•

the name or names of any agents or underwriters;

 

•

the purchase price of the securities being offered and the proceeds we will receive from the sale;

 

•

any over-allotment options under which underwriters may purchase additional securities from us;

 

•

any agency fees or underwriting discounts and other items constituting agents’ or underwriters’ compensation;

 

•

any public offering price;

 

•

any discounts or concessions allowed or reallowed or paid to dealers; and

 

•

any securities exchanges or markets on which such securities may be listed.

We may distribute the securities from time to time in one or more transactions at:

 

•

fixed price or prices, which may be changed from time to time;

 

•

market prices prevailing at the time of sale;

 

•

prices related to such prevailing market prices; or

 

•

negotiated prices.

Agents

We may designate agents who agree to use their reasonable efforts to solicit purchases of our securities for the period of their appointment or to sell our securities on a continuing basis. We will name any agent involved in the offering and sale of securities and we will describe any fees or commissions we will pay the agent in the applicable prospectus supplement.

Underwriters

If we use underwriters for a sale of securities, the underwriters will acquire the securities for their own account. The underwriters may resell the securities in one or more transactions, including negotiated transactions,

 

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at a fixed public offering price or at varying prices determined at the time of sale. The obligations of the underwriters to purchase the securities will be subject to the conditions set forth in the applicable underwriting agreement. Subject to certain conditions, the underwriters will be obligated to purchase all the securities of the series offered if they purchase any of the securities of that series. We may change from time to time any public offering price and any discounts or concessions the underwriters allow or reallow or pay to dealers. We may use underwriters with whom we have a material relationship. We will describe the nature of any such relationship in any applicable prospectus supplement naming any such underwriter. Only underwriters we name in the prospectus supplement are underwriters of the securities offered by the prospectus supplement.

We may provide agents and underwriters with indemnification against civil liabilities related to offerings under this prospectus, including liabilities under the Securities Act, or contribution with respect to payments that the agents or underwriters may make with respect to these liabilities.

Direct Sales

We may also sell securities directly to one or more purchasers without using underwriters or agents. Underwriters, dealers and agents that participate in the distribution of the securities may be underwriters as defined in the Securities Act, and any discounts or commissions they receive from us and any profit on their resale of the securities may be treated as underwriting discounts and commissions under the Securities Act. We will identify in the applicable prospectus supplement any underwriters, dealers or agents and will describe their compensation. We may have agreements with the underwriters, dealers and agents to indemnify them against specified civil liabilities, including liabilities under the Securities Act. Underwriters, dealers and agents may engage in transactions with or perform services for us in the ordinary course of their businesses.

Trading Markets and Listing of Securities

Unless otherwise specified in the applicable prospectus supplement, each class or series of securities will be a new issue with no established trading market, other than our common stock, which is currently listed on the NYSE MKT. We may elect to list any other class or series of securities on any exchange or market, but we are not obligated to do so. It is possible that one or more underwriters may make a market in a class or series of securities, but the underwriters will not be obligated to do so and may discontinue any market making at any time without notice. We cannot give any assurance as to the liquidity of the trading market for any of the securities.

Stabilization Activities

Any underwriter may engage in overallotment, stabilizing transactions, short covering transactions and penalty bids in accordance with Regulation M under the Exchange Act. Overallotment involves sales in excess of the offering size, which create a short position. Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum. Short covering transactions involve purchases of the securities in the open market after the distribution is completed to cover short positions. Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the securities originally sold by the dealer are purchased in a covering transaction to cover short positions. Those activities may cause the price of the securities to be higher than it would otherwise be. If commenced, the underwriters may discontinue any of these activities at any time.

Passive Market Making

Any underwriters who are qualified market makers on the NYSE MKT may engage in passive market making transactions in the securities on the NYSE MKT in accordance with Rule 103 of Regulation M, during the business day prior to the pricing of the offering, before the commencement of offers or sales of the securities. Passive market makers must comply with applicable volume and price limitations and must be identified as passive market makers. In general, a passive market maker must display its bid at a price not in excess of the

 

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highest independent bid for such security. If all independent bids are lowered below the passive market maker’s bid, however, the passive market maker’s bid must then be lowered when certain purchase limits are exceeded.

LEGAL MATTERS

The validity of the securities being offered by this prospectus will be passed upon for us by DLA Piper LLP (US), San Diego, California. If the validity of any securities is also passed upon by counsel any underwriters, dealers or agents, that counsel will be named in the prospectus supplement relating to that specific offering.

EXPERTS

The consolidated financial statements incorporated in this prospectus by reference to the Annual Report on Form 10-K for the year ended December 31, 2014 have been so incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of such firm as experts in auditing and accounting.

INFORMATION INCORPORATED BY REFERENCE

The SEC allows us to “incorporate by reference” into this prospectus the information we file with the SEC. This means that we can disclose important information to you by referring you to those documents. Any statement contained in a document incorporated by reference in this prospectus shall be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained herein, or in any subsequently filed document, which also is incorporated by reference herein, modifies or supersedes such earlier statement. Any such statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus.

We hereby incorporate by reference into this prospectus the following documents that we have filed with the SEC under the Exchange Act File No. 001-32157 (other than current reports on Form 8-K, or portions thereof, furnished under Items 2.02 or 7.01 of Form 8-K):

 

•

our Annual Report on Form 10-K for the fiscal year ended December 31, 2014, filed with the SEC on March 24, 2015;

 

•

our Current Reports on Form 8-K filed with the SEC on January 6, 2015, January 7, 2015, January 12, 2015, January 27, 2015, February 3, 2015, February 9, 2015, and March 2, 2015; and

 

•

the description of our common stock contained in our registration statement on Form 8-A filed with the SEC on April 27, 2004 (File No. 001-32157-041020580).

All documents that we file with the SEC pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act (other than current reports on Form 8-K, or portions thereof, furnished under Items 2.02 or 7.01 of Form 8-K) (i) after the initial filing date of the registration statement of which this prospectus forms a part and prior to the effectiveness of such registration statement and (ii) after the date of this prospectus and prior to the termination of the offering shall be deemed to be incorporated by reference in this prospectus from the date of filing of the documents, unless we specifically provide otherwise. Information that we file with the SEC will automatically update and may replace information previously filed with the SEC. To the extent that any information contained in any current report on Form 8-K or any exhibit thereto, was or is furnished to, rather than filed with the SEC, such information or exhibit is specifically not incorporated by reference.

 

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Upon written or oral request made to us at the address or telephone number below, we will, at no cost to the requester, provide to each person, including any beneficial owner, to whom this prospectus is delivered, a copy of any or all of the information that has been incorporated by reference in this prospectus (other than an exhibit to a filing, unless that exhibit is specifically incorporated by reference into that filing), but not delivered with this prospectus. You may also access this information on our website at www.masttherapeutics.com by viewing the “SEC Filings” subsection of the “Investors” menu. No additional information on our website is deemed to be part of or incorporated by reference into this prospectus. We have included our website address in this prospectus solely as an inactive textual reference.

Mast Therapeutics, Inc.

3611 Valley Centre Drive, Suite 500

San Diego, CA 92130 Attn: Investor Relations

(858) 552-0866

WHERE YOU CAN FIND MORE INFORMATION

As permitted by SEC rules, this prospectus omits certain information that is included in the registration statement of which this prospectus forms a part and its exhibits. Since this prospectus may not contain all of the information that you may find important, you should review the full text of these documents. If we have filed a contract, agreement or other document as an exhibit to the registration statement of which this prospectus forms a part, you should read the exhibit for a more complete understanding of the document or matter involved. Each statement in this prospectus, including statements incorporated by reference as discussed above, regarding a contract, agreement or other document is qualified in its entirety by reference to the actual document.

We are subject to the information reporting requirements of the Exchange Act, and, in accordance with these requirements, we file annual, quarterly and current reports, proxy statements, and other information with the SEC. You may inspect, read and copy the reports and other information we file with the SEC at the SEC’s Public Reference Room located at 100 F Street, N.E., Washington, D.C. You may obtain information on the operation of the Public Reference Room by calling the SEC at 1-800-SEC-0330. The SEC also maintains an internet website at http://www.sec.gov that contains our filed reports, proxy and information statements, and other information that we file electronically with the SEC. Additionally, we make these filings available, free of charge, on our website at www.masttherapeutics.com in the “SEC Filings” subsection of the “Investors” menu as soon as reasonably practicable after we electronically file such materials with, or furnish them to, the SEC. The information on our website, other than these filings, is not, and should not be, considered part of this prospectus, is not incorporated by reference into this prospectus, and should not be relied upon in connection with making any investment decision with respect to our securities.

 

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             Units

Each Consisting of One Share of Common Stock and

One Warrant to Purchase One Share of Common Stock

Prospectus Supplement

Sole Book-Running Manager

Roth Capital Partners

                    , 2016