UPDATE: Mast Therapeutics Initiates Phase 2 Study Of MST-188 In Patients With Acute Limb Ischemia

Mast Therapeutics, Inc. MSTX announced today that it has initiated a phase 2, clinical proof-of-concept study of MST-188 in combination with recombinant tissue plasminogen activator (rt-PA) in patients with acute lower limb ischemia. Acute limb ischemia (ALI), an acute complication of peripheral arterial disease, describes a sudden decrease in perfusion of a limb, typically in the legs, that often threatens viability of the limb. Patients presenting with ALI have a poor short-term outlook, with 30-day amputation rates as high as 30% and a mortality rate around 15%. MST-188 for the treatment of ALI has been granted orphan drug designation by the U.S. Food and Drug Administration. Martin Emanuele, PhD, Senior Vice President, Development, said: "Numerous experimental models, as well as clinical studies, demonstrate that MST-188 facilitates thrombolysis, repairs damaged cell membranes, and improves microvascular blood flow. When combined with rt-PA, we believe these activities will translate into faster thrombolysis in patients with ALI and in other acute thrombotic events such as stroke, while at the same time reducing vessel re-occlusion, reperfusion injury, and tissue necrosis." Brian M. Culley, Chief Executive Officer, said: "Initiating the ALI study represents further execution of our long-term strategy to maximize the value of MST-188 through its development in multiple areas of significant unmet medical need. I congratulate our clinical operations team for initiating this study consistent with our guidance, while at the same time opening 40 clinical sites in the U.S., as well as clinical sites in multiple countries outside the U.S., in our pivotal phase 3 EPIC study in sickle cell disease." About the Phase 2 Study The study will enroll approximately 60 patients from approximately 15 sites within and outside the U.S. with Rutherford Category IIa and IIb acute lower limb ischemia receiving catheter-directed rt-PA and compare a high and low dose of MST-188 against rt-PA alone. The primary objectives are to evaluate the safety and efficacy of MST-188 in combination with rt-PA and whether MST-188 results in more rapid thrombolysis and tissue perfusion. Secondary objectives are to assess the clinically-meaningful benefit of MST-188 in combination with rt-PA by measures such as duration of thrombolytic therapy, amputation-free survival, target limb re-interventions, and the need for endovascular or open surgical re-interventions. These objectives will be measured through up to 90 days of follow-up. The study is expected to take approximately 18 months to enroll. 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, and has initiated a phase 2, clinical proof of concept study to evaluate whether MST-188 improves the effectiveness of rt-PA in patients with acute limb ischemia. The Company also is developing MST-188 in heart failure and plans to announce its clinical development plans in this indication in the second half of 2014. More information can be found on the Company's web site at www.masttherapeutics.com. (Twitter: @MastThera) 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 relating to the potential of MST-188 to demonstrate safety and efficacy in combination with rt-PA in patients with acute limb ischemia and other acute complications of arterial disease, such as stroke, and the Company's clinical development plans for MST-188 in heart failure and the timing of any announcement of such plans. 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: the uncertainty of outcomes in ongoing and future studies of the Company's product candidates and the risk that its product candidates, including MST-188, may not demonstrate adequate safety, efficacy or tolerability in one or more such studies, including the phase 2 study in ALI; delays in the commencement or completion 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, manufacturing sufficient quantities of clinical trial material, being subject to a "clinical hold," and/or suspension or termination of a clinical study, including due to patient safety concerns or lack of funding; the potential for institutional review boards or the FDA or other regulatory agencies to require additional nonclinical or clinical studies prior to initiation of a phase 2 clinical study of MST-188 in heart failure or other indications; the potential that, even if clinical studies of a product candidate in one indication are successful, clinical studies in another indication may not be successful; the risk that, even if clinical studies are successful, the FDA or other regulatory agencies may determine they are not sufficient to support a new drug application; the Company's reliance on contract research organizations (CROs), contract manufacturing organizations (CMOs), and other third parties to assist in the conduct of important aspects of development of its product candidates, including clinical studies, and regulatory activities for its product candidates, and that such third parties may fail to perform as expected; the Company's ability to obtain additional funding on a timely basis or on acceptable terms, or at all; the potential for the Company to delay, reduce or discontinue current and/or planned development activities, including clinical studies, partner its product candidates at inopportune times or pursue less expensive but higher-risk and/or lower-return development paths if it is unable to raise sufficient additional capital as needed; the risk that, even if the Company successfully develops a product candidate in one or more indications, it may not realize commercial success with its products and may never generate revenue sufficient to achieve profitability; the risk that the Company is not able to adequately protect its intellectual property rights relating to the MAST platform and MST-188 or AIR001 and prevent competitors from duplicating or developing equivalent versions of its product candidates; and other risks and uncertainties more fully described in the Company's press releases and periodic filings with the Securities and Exchange Commission. 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.