Oxi0-4503 (now known as combretastatin A1 phosphate), a diphosphate prodrug of combretastatin A1, was developed by Mateon therapeutics as a second-generation, dual-mechanism vascular disrupting agent from the combretastatin family. On November 21, 2012, Oxi-4503 has been granted orphan designation by the US Food and Drug Administration for the treatment of acute myelogenous leukemia. It is known that the orphan drug designation qualifies a company for several benefits, including the potential for market exclusivity, development grants, and tax credits. Oxi0-4503 is currently participating in phase I/II clinical trial the treatment of patients with acute myelogenous leukemia or myelodysplastic syndrome. In addition, phase I clinical trial was successfully completed where was studied the safety of Oxi0-4503 in patients with advanced solid tumors.