Mast Therapeutics Initiates Sub-Study Within Phase 3 EPIC Trial

SAN DIEGO, June 16, 2014 /PRNewswire/ -- Mast Therapeutics, Inc. (NYSE MKT: MSTX) today announced that, in line with prior guidance, it has initiated patient enrollment in a sub-study within EPIC, its pivotal phase 3 study of MST-188 in sickle cell disease, to investigate and quantify the effect of MST-188 on tissue oxygenation, which will be measured utilizing a non-invasive, FDA-approved device.

MST-188 has been shown to reduce viscosity and adhesive frictional forces in blood and improve microvascular blood flow. Improvements in the flow of oxygen-carrying blood to tissues and organs can be expected to improve tissue oxygenation, shorten the duration of vaso-occlusive crisis, and limit tissue damage and end-organ dysfunction and failure.

Brian M. Culley, Chief Executive Officer, said: "Organ failure, which is the leading cause of premature death in adults with sickle cell disease, is thought to be the consequence of a lifetime of repeated vaso-occlusive events and the resulting ischemia. We believe that measuring effects on microvascular blood flow and tissue oxygenation during vaso-occlusive crisis will be useful to understanding MST-188's potential to improve long-term outcomes for sickle cell patients where multi-decade, survival trials are impractical. MST-188 has already demonstrated an ability to improve microvascular blood flow. Now, this sub-study will demonstrate whether MST-188 also improves tissue oxygenation. Together, these data will provide insight into the potential for MST-188 to reduce end-organ failure and associated premature death in individuals with sickle cell disease."

About the EPIC Sub-Study
The sub-study will enroll patients who are concurrently randomized in the EPIC clinical trial and will be conducted at selected EPIC sites in the U.S. The primary objective is to evaluate the effects of MST-188 on tissue oxygenation in subjects with sickle cell disease who are experiencing a vaso-occlusive crisis. Tissue oxygenation will be determined using a non-invasive, U.S. Food and Drug Administration (FDA)-approved device.

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 and conditions typically characterized by impaired microvascular blood flow and damaged cell membranes.

The Company is enrolling subjects in EPIC, a pivotal phase 3 study of MST-188 in sickle cell disease, and in a phase 2, clinical study to evaluate whether MST-188 improves the effectiveness of recombinant tissue plasminogen activator therapy in patients with acute limb ischemia. The Company also is developing MST-188 in heart failure and expects 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 usefulness of data from the EPIC sub-study, potential clinical benefits of MST-188 in sickle cell disease, and the Company's development of MST-188 in other indications, including heart failure. 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 MST-188 and the risk that MST-188 may not demonstrate adequate safety, efficacy or tolerability in one or more such studies, including EPIC; 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 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 potential that, even if clinical studies of MST-188 in one indication are successful, clinical studies in another indication may not be successful; 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 MST-188, including clinical studies, manufacturing, and regulatory activities, 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.