WYE-354 is a potent cell-permeable inhibitor of mTOR (IC50 = 4.3 nM) which blocks signaling through both mTOR complex 1 (mTORC1) and mTORC2. It is a much weaker inhibitor of phosphatidylinositol 3-kinase α (IC50 = 1026 nM) and other kinases. WYE-354 induces G1 cell cycle arrest in both rapamycin-sensitive and rapamycin-resistant cancer cell lines, inhibits mTORC1 and mTORC2 in tumor-bearing mice, and reduces tumor growth in nude mice with PTEN-null tumors.