A potent, reversible, ATP-competitive, thiazolidinedione inhibitor of PI3Kα (IC50 = 2 nM) and the common activating mutants of p100α (E542K, E545K, and H1047R) found in cancer; prevents proliferation in BT474 tumor xenografts and reduces MAPK signaling with twice daily dosing at 25 mg/kg.