MCF-7 transduction with shATM-carrying vectors elicits a phenotype compatible with ATM defective cells. (A) MCF-7 cells were transfected with shATM-carrying vector (MCF7-ATMi) and its siR5 negative control (MCF7-ctr). ATM protein levels in MCF-7-ATMi and MCF-7-ctr cells were analyzed by Western blot. α-tubulin was used as an internal control. B-D Cell viability of MCF7-ATMi and MCF7-ctr cells upon treatment with IR (B) and doxorubicin (C). (D) MCF7-ctr cells were pre-treated with ATM inhibitor KU 55933 or its solvent before addition of doxorubicin as in (C). Data are represented as mean ± standard deviation (SD). (E) Flow cytometry analysis of cell-cycle distribution of MCF7-ATMi and MCF7-ctr cells upon treatment with IR and doxorubicin at indicated times. Asterisks indicate statistical significant difference (*P < 0.1; **P < 0.05).