PKI-179 is an orally bioavailable dual inhibitor of PI3K and mammalian target of rapamycin (mTOR). In an in vitro enzymatic assay, it potently inhibits PI3K (IC50s = 8, 24, 17, and 74 nM for isoforms α, β, δ, and γ, respectively), two common PI3Kα mutants, E545K and H1047R (IC50s = 14 and 11 nM, respectively), and mTOR (IC50 = 0.42 nM). PKI-179 is selective for PI3K and mTOR over a panel of 361 other kinases at IC50 values up to 50 μM, hERG (IC50 > 30 μM), and cytochrome P450 (CYP) isoforms (IC50s > 30 μM), but does have activity for CYP2C8 (IC50 = 3 μM). It inhibits proliferation through the Akt/mTOR signaling pathway in MDA-361 breast and PC3MM2 prostate cancer cell lines in vitro (IC50s = 22 and 29 nM, respectively) and inhibits tumor growth in an MDA-361 mouse xenograft model when used at a dose of 50 mg/kg.