A potent ATP-competitive inhibitor of ATM kinase (IC50 = 13 nM; Ki = 2.2 nM); sensitizes cells to both ionizing radiation and chemotherapeutic agents; induces senescent breast, lung, and colon carcinoma cells to undergo cell death; inhibits HIV-1 replication in C8166 human T-lymophocyte cells (IC50 = 2.4 μM)