Potent and selective ATM kinase inhibitor (IC50 = 0.6 nM in an enzyme inhibition assay). Exhibits > 600-fold selectivity for ATM over other kinases. Inhibits ATM kinase in an in vitro cellular assay (IC50 = 0.33 μM). Potentiates the antitumor effects of the topoisomerase 1 inhibitor irinotecan (CPT 11, Cat. No. 2688) in tumor bearing, immunocompromised mice. Orally bioavailable. Purity 98%. MW (observed): 434.47