ZR-ATMi cells are more sensitive than ZR-ctr cells to olaparib but not to iniparib. (A) ZR-75-1 cells were transfected with shATM-carrying vector (ZR-ATMi) and its siR5 negative control (ZR-ctr). ATM protein levels in ZR-ATMi and ZR-ctr cells were analyzed by Western blot. α-tubulin was used as an internal control. B-C ZR-ATMi and ZR-ctr cells were exposed to increased concentrations of olaparib (B) or iniparib for 72 hrs (C). Data are represented as mean ± SD. (D) Flow cytometry analysis of cell-cycle distribution of ZR-ATMi and ZR-ctr cells treated with the indicated concentrations with olaparib or iniparib for 72 hrs. E-F Quantitative analyses of colony formation. The numbers of DMSO-resistant colonies in ZR-ATMi and ZR-ctr cells were set to 100, while olaparib (E) or iniparib (F) treated cel1s were presented as mean ± SD. Asterisks indicate statistical significant difference (*P < 0.1; **P < 0.05).