Mast Therapeutics Announces Positive Top Line Results From Phase 2 Study Of AIR001 For Pulmonary Arterial Hypertension And AIR001 Clinical Development Plan

- Data show improvements in hemodynamic parameters and exercise capacity
- AIR001 well-tolerated, with no treatment-related serious adverse events
- Data support further clinical development in pulmonary hypertension (PH)

SAN DIEGO, Sept. 8, 2014 /PRNewswire/ -- Mast Therapeutics, Inc. (NYSE MKT: MSTX) today reported top-line results from a Phase 2 study of AIR001 (sodium nitrite) inhalation solution for the treatment of pulmonary arterial hypertension (PAH).  Mast obtained the rights to the AIR001 program through its acquisition of privately-held Aires Pharmaceuticals, Inc. earlier this year. In the primary efficacy analysis of the Phase 2 study, all doses showed improvement in median pulmonary vascular resistance (PVR). In the secondary efficacy analysis, all doses showed improvements in the median distances obtained in the 6-minute walk test, including clinically-meaningful improvements at the highest dose level.  Additionally, AIR001 was well-tolerated, with no treatment related serious adverse events. In particular, methemoglobin levels remained normal (< 1.5%), which distinguishes AIR001 from safety concerns associated with intravenously-administered nitrite. 

Edwin L. Parsley, D.O., interim Chief Medical Officer, stated: "These results are promising and consistent with earlier findings of AIR001 as an agent that can have a positive effect on hemodynamic parameters in a PH population. To date, more than 120 individuals have received AIR001, including patients who have received repeat administration for as long as 12 months, patients who were treatment naive, and patients on PAH disease-specific background therapy.  Given the hemodynamic improvements observed, we feel AIR001 may be uniquely suited to address the serious unmet need facing the large number of patients with pulmonary hypertension associated with left heart disease. Consequently, we will be pursuing clinical development of AIR001 in that indication and plan to support multiple, institution-sponsored Phase 2a studies that will evaluate 1) acute hemodynamic effects, 2) acute effects versus placebo on maximum oxygen consumption and exercise hemodynamics, and 3) inhaled versus intravenous administration of nitrite, as well as the safety of multiple doses of AIR001, in patients with PH associated with left heart disease."

Brian M. Culley, Chief Executive Officer, stated: "We are encouraged by the results seen in the Phase 2 study of AIR001 and believe they further validate our acquisition of Aires. The data from the study show benefits consistent with prior studies and support further development of AIR001. We look forward to proceeding with the Phase 2a studies in PH associated with left heart disease and anticipate reporting preliminary study results as early as the second half of 2015."

About the Phase 2 Study (AIR001-CS05)
The Phase 2 study was a multi-center, open-label, randomized, parallel-dose study to determine the safety and efficacy of AIR001 in subjects with PAH.  Subjects were randomized into one of three treatment arms and treated with AIR001 for 16 weeks: 80 mg once daily after a 2-week "run-in" period of 46 mg once daily; 46 mg four times daily after a 2-week run-in period of 46 mg four times daily; or 80 mg four times daily after a 2-week run-in period of 46 mg four times daily.  The primary objective of the study was to evaluate the efficacy of inhaled nebulized AIR001 as determined by change in pulmonary vascular resistance (PVR) from baseline to week 16, measured immediately post-completion of AIR001 nebulization.  Secondary endpoints included change from baseline to week 16 in: 6‑Minute Walk Distance (6MWD) assessed immediately post-completion of AIR001 nebulization (peak), but no more than 40 minutes after completion of AIR001 nebulization; hemodynamic measurements of cardiac output, mean right atrial pressure and pulmonary capillary wedge pressure at peak; N-Terminal Pro-Brain Natriuretic Peptide (NT-proBNP); hemodynamics and 6MWD at trough; and quality of life measures.

The study was powered to enroll 90 patients, however, prior to its acquisition by Mast, Aires discontinued the study due to capital constraints.  Data is available from 29 patients who enrolled in the study.

About AIR001
AIR001 (sodium nitrite) inhalation solution, also known as Aironite®, is an intermittently nebulized formulation of nitrite. Under hypoxic conditions, AIR001 is converted to nitric oxide. Nitrite mediated nitric oxide formation has several beneficial effects, including dilation of blood vessels and reduction of inflammation and undesirable cell growth.

AIR001 has been granted orphan drug status by the U.S. Food and Drug Administration and the European Medicines Agency for the treatment of pulmonary arterial hypertension.

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 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 planning to initiate a Phase 2 clinical study of MST-188 in patients with acute decompensated heart failure in the first half of 2015 and to announce details of the study's design later this year.  In addition, the Company is developing AIR001, which it acquired in February 2014, in patients with pulmonary hypertension associated with left heart disease.  More information can be found on the Company's web site at (Twitter: @MastThera

Mast Therapeutics™ and the corporate logo are trademarks of Mast Therapeutics, Inc. Aironite® is a trademark of Aires Pharmaceuticals, Inc., a wholly-owned subsidiary of Mast Therapeutics.

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 clinical development plans and anticipated timing of achievement of development milestones for the Company's product candidates, including AIR001, such as commencement and completion of clinical studies and announcement of study results.  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 AIR001, may not demonstrate adequate safety, efficacy or tolerability in one or more such studies; 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 planned clinical study of a product candidate; 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 a product candidate 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 its product candidates, including clinical studies, manufacturing, 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

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.

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