The cytotoxic response to olaparib is ATM-specific. Effect of increasing doses of olaparib after 7 days exposure on survival of control LCL cells treated with 5μM of the ATM inhibitor, KU-55 933 (A) and PGA cells without (GFPsh) and (B) with (ATMsh) ATM knockdown. (C) Immunoblotting shows olaparib-induced dose-dependent phosphorylation of ATM-dependent targets in normal cells. IR provides a positive control.