Mast Therapeutics Prices Public Offering Of Units

SAN DIEGO, June 14, 2013 /PRNewswire/ -- Mast Therapeutics, Inc. (NYSE MKT: MSTX) today announced the pricing of an underwritten public offering of 50,000,000 units, each unit consisting of a fixed combination of one share of common stock and one warrant to purchase 0.5 of a share of common stock, at a public offering price of $0.50 per unit.  The units will not be issued or certificated and the shares of common stock and the warrants are immediately separable and will be issued separately, but purchased together.  Each warrant will have an exercise price of $0.65 per share and will expire five years from the date of issuance.  The Company has granted the underwriters a 30-day option to purchase up to an additional 7,500,000 units to cover over-allotments, if any.  The offering is expected to close on June 19, 2013, subject to customary closing conditions.  All of the shares in the offering are being sold by the Company. 

The Company expects to receive net proceeds from the offering of approximately $22.9 million, after deducting underwriting discounts and commissions and estimated offering expenses.  The Company intends to use the net proceeds primarily to fund EPIC, the Company's phase 3 clinical study of MST-188 in sickle cell disease, and for working capital and general corporate purposes. 

Piper Jaffray & Co. is acting as the sole book-running manager of the offering and Canaccord Genuity Inc. is acting as lead manager of the offering.  JMP Securities LLC and Brinson Patrick Securities Corporation are acting as financial advisors in connection with the offering.

A registration statement relating to the public offering of the securities described above has been filed with the Securities and Exchange Commission and was declared effective June 14, 2013.  The offering may be made only by means of a prospectus.  A copy of the final prospectus may be obtained by contacting: Piper Jaffray & Co., 800 Nicollet Mall, J12S03, Minneapolis, Minnesota 55402, or by telephone at (800) 747-3924, or by e-mail at prospectus@pjc.com.

This press release shall not constitute an offer to sell or the solicitation of an offer to buy these securities, nor shall there be any sale of these securities in any state or other jurisdiction in which such offer, solicitation, or sale would be unlawful prior to the registration or qualification under the securities laws of any such state or other jurisdiction.

About Mast Therapeutics
Mast Therapeutics, Inc. is a publicly traded biopharmaceutical company headquartered in San Diego, California.  The Company is leveraging the MAST (Molecular Adhesion and Sealant Technology) platform, derived from over two decades of clinical, nonclinical and manufacturing experience with purified and non-purified poloxamers, to develop MST-188, its lead product candidate, for serious or life-threatening diseases with significant unmet needs.  MST-188 is a cytoprotective, hemorheologic, anti-inflammatory and anti-thrombotic agent that has potential utility in diseases or conditions characterized by microcirculatory insufficiency (endothelial dysfunction and/or impaired blood flow). 

The Company is enrolling subjects in EPIC, a pivotal phase 3 study of MST-188 in sickle cell disease.  The Company plans to initiate a phase 2 clinical study of MST-188 in acute limb ischemia, a complication of peripheral arterial disease, in late 2013 or early 2014.  More information can be found on the Company's web site at www.masttherapeutics.com.

Mast Therapeutics™ and the corporate logo are trademarks of Mast Therapeutics, Inc.

Forward Looking Statements
Mast Therapeutics cautions you that statements included in this press release that are not a description of historical facts are forward-looking statements that are based on the Company's current expectations and assumptions. Such forward-looking statements include, but are not limited to, statements regarding the timing and closing of the offering, the net proceeds from the offering and their intended use and the Company's development plans for MST-188 in complications of peripheral arterial disease, including the timing of the initiation of the planned phase 2 study in acute limb ischemia.  Among the factors that could cause or contribute to material differences between the Company's actual results and the expectations indicated by the forward-looking statements are risks and uncertainties that include, but are not limited to: whether or when the offering will be completed; a shift in the allocation of the Company's resources from sickle cell disease to other indications, including acute limb ischemia, acute decompensated heart failure, blood transfusion and/or resuscitation of shock following major trauma; delays in the commencement of clinical studies, including as a result of difficulties in obtaining regulatory agency agreement on clinical development plans or clinical study design, opening trial sites, enrolling study subjects and manufacturing sufficient quantities of clinical trial material; the potential for institutional review boards or the FDA or other regulatory agencies to require additional nonclinical or clinical studies prior to initiation of the planned phase 2 clinical study of MST-188 in acute limb ischemia; and other risks and uncertainties more fully described in the Company's press releases and periodic filings with the Securities and Exchange Commission, including the Form S-1/A registration statement filed on June 14, 2013. The Company's public filings with the Securities and Exchange Commission are available at www.sec.gov.

You are cautioned not to place undue reliance on forward-looking statements, which speak only as of the date when made. Mast Therapeutics does not intend to revise or update any forward-looking statement set forth in this press release to reflect events or circumstances arising after the date hereof, except as may be required by law.

SOURCE Mast Therapeutics, Inc.

Ioana C. Hone (ir@mastthera.com), 858-552-0866 Ext. 303