CP-466722 is a rapidly reversible inhibitor of ATM, with an IC₅₀ of 4.1 μM, and has no effects on PI3K or closely related PI3K-like protein kinase (PIKK) family members. IC50 & Target: IC50: 4.1 μM (ATM)^[2] In Vitro: CP-466722 (CP466722, 6-10 μM) inhibits IR-induced ATM kinase activity, and the inhibition can be rapidly and completely reversed. CP466722 (6, 10 μM) inhibits p53 induction and ATM-dependent phosphorylation in mouse cells, but CP466722 fails to inhibit ATR activity and ATR-dependent phosphorylation of Chk1. CP466722 (6 μM) disrupts ATM-dependent cell cycle checkpoints in cells^[1]. CP466722 (1 µM) completely inhibits ATM-dependent phosphorylation in MCF7 cells. CP466722 (10 µM) reduces pKAP1 phosphorylation in MCF7 cells, with an IC₅₀ of 0.41 µM. CP466722 (10 µM) inhibits both pATM and pKAP1 signals^[2]. CP-466722 (CP466722, 5-50 μM) inhibits proliferation of SKBr-3 cancer cells more strongly than MCF-7 cancer cells. CP466722 (10 µM) also slightly increases proportions of MCF-7 and SKBr-3 cells in the G1 phase after treatment for 48 hours^[3].