Fig. 6
APE1 deficiency sensitizes ATM inhibitor in vitro and suppresses xenograft tumor growth in vivo. a HeLa NC and shAPE1 cells were treated with TBHP for 1 h and allowed to recover for 0 h to 24 h. The γH2AX, DNA-PKcs pS2056 and ATM pS1981 level were assayed by immunoblotting and actin was used as a loading control. b–d APE1 deficiency significantly increased apoptosis when combined with ATM inhibitor (Ku55933). HeLa NC and shAPE1 cells were pre-incubated 6 h with Ku55933 (10 μM) prior to TBHP treatment 1 h b–c, or HeLa cells were pre-incubated 6 h with E3330, Inhibitor III alone or with Ku55933 prior to TBHP treatment 1 h d, allowed to recover for 24 h post TBHP treatment, then the cleaved-PARP was analyzed by immunoblotting b; allowed to recover 48 h, apoptosis in each treatment group was analyzed by flow cytometry c–d. e–f ATM inhibition sensitized shAPE1 cells to irradiation in vivo. e The weights of the resected tumors were quantified. f Tumor volume was measured at indicated days and tumor growth curve was plotted. g–h ATM inhibition sensitized APE1 endonuclease activity inhibitor treated tumor cells to irradiation in vivo. g The weights of the resected tumors were quantified. h Tumor volume was measured at indicated days and tumor growth curve was plotted. The data are presented as the mean ± SEM from three independent experiments. The P-values were determined using an unpaired Student’s t-test (****P < 0.0001, ***P < 0.001, **P < 0.01, *P < 0.05)