Mast Therapeutics, Inc. is a biopharmaceutical company. The Company develops clinical-stage therapies for serious or life-threatening diseases with unmet needs. The Company focuses on developing new therapies for sickle cell disease, a chronic and genetic disorder classified as a rare, or orphan, disease in the United States of America and European Union, and for heart failure, a condition with an unmet need for treatment options. The Company's segment is engaged in the business of developing therapies for serious or life-threatening diseases. The Company focuses on its Molecular Adhesion and Sealant Technology (MAST) platform, to develop MST-188 (vepoloxamer) Injection, its lead product candidate. The Company also develops AIR001, a sodium nitrite solution for intermittent inhalation through nebulizer. The Company's AIR001 is in Phase II clinical development for the treatment of patients with HFpEF.