Mast Therapeutics Inc. has initiated a new open-label extension study to evaluate repeat dosing of its experimental sickle cell disease (SCD) therapy, vepoloxamer (MST-188), in patients who have completed the company's phase III trial, EPIC, and are hospitalized for a subsequent vaso-occlusive crisis, a painful event in which sickled red blood cells "stick" to the endothelium and to each other and leads to blocking circulation and causing tissue damage.