MCF7-ATMi cells are more sensitive than MCF7-ctr cells to olaparib. A-B MCF7-ATMi and MCF7-ctr cells were exposed to increased concentrations of olaparib for 72 hrs (A) or were treated with olaparib (5 μM) for up to 96 hrs (B). Data are represented as mean ± SD. (C) Flow cytometry analysis of cell-cycle distribution of MCF7-ATMi and MCF7-ctr cells treated with the indicated concentrations with olaparib for 48 hrs. (D) DNA synthesis was measured by BrdU incorporation assay 48 hrs after olaparib treatment. (E) Quantitative analyses of colony formation. The numbers of DMSO-resistant colonies in MCF7-ATMi and MCF7-ctr cells were set to 100, while olaparib treated cel1s were presented as mean ± SD. Asterisks indicate statistical significant difference (*P < 0.1).