Mast Therapeutics, Inc., formerly ADVENTRX Pharmaceuticals, Inc., is a development-stage company biopharmaceutical company focused on developing product candidates. The Company's product candidate is ANX-188, a rheologic, antithrombotic and cytoprotective agent that improves microvascular blood flow and has application in treating a range of diseases and conditions, such as complications arising from sickle cell disease. As of December 31, 2011, the Company also is developing ANX-514, a detergent-free formulation of the chemotherapy drug docetaxel. The Company offers ANX-188 (purified poloxamer 188), ANX-514 (docetaxel for injectable emulsion) and Exelbine (vinorelbine injectable emulsion). In April 2011, the Company acquired SynthRx, Inc. In August 2011, the Company received a complete response letter from the Food and Drug Administration (FDA) stating that it could not approve the Exelbine Non Disclosure Agreement (NDA) in its present form.