PF-06843195 is a potent and PI3K-alpha subtype-selective phosphoinositide 3-kinase (PI3K) inhibitor (r at PI3K Ki = 2 nM/β, <18 nM/α, <280 nM/δ) th at inhibits cellular PI3Kα activity at a higher potency over th at of PI3Kδ/β and mTOR (AKT pT308 IC50 = 18/160/360 nM in r at PI3Kα/δ/β Rat1 lines; p70S6K pT389 IC50 = 1.5 μM in Rat1 myristoylated PI3K line). PF-06843195 is more potent against cellular AKT pT308 (MCF7/T47D IC50 = 7.8/8.7 nM) and proliferation (MCF7/T47D = 62/32 nM) than alpelisib (BYL719) in cultures.