PF-04979064 is a highly potent and orally bioavailable PI3K/mTOR dual inhibitor developed through structure-based drug design. It inhibited mTOR, PI3Kα, β, δ and γ isoforms and AKT phosphorylation with IC50 as 2.64 nM, 0.395 nM, 0.111 nM, 0.122 nM and 28.3 nM, respectively. PF-04979064 exhibited cellular potency with an IC50 of 9.1 nM in a BT20 cell assay. PF-04979064 exhibited excellent in vitro potency, very good solubility, high LipE, excellent kinome selectivity, robust PK/PD correlation and tumor growth inhibition (TGI) in a U87MG mouse xenograft model, and acceptable predicted human clearance after incorporating both CYP- and AO-mediated metabolism. PF-04979064 is the back-up candidate to PF-04691502 which is in Phase I/II clinical trials for treating solid tumors.