THP1-A3A cells were treated with dox (1 μg/mL) to induce A3A expression and a small molecule inhibitor of ATM kinase (ATMi, KU55933). (a) Viability was determined by colorimetric change after incubation with a water-soluble tetrazolium salt. Statistical analysis was performed using a sum-of-squares F-test. Error bars indicate SEM. (b) Inhibition of ATM activity was analyzed by immunoblot of THP1-A3A cell lysates treated with dox (1 μg/mL), ATMi (10 μM), and combination. Antibodies to HA, Chk2, and phosphorylated Chk2 (T68) were used. GAPDH was used as a loading control.