ATR and carcinoma: ↓ Clonogenic ability of carcinoma. ↑ Apoptosis associated with the activation of caspase-3 and PARP cleavage in 4T1 cells. ↑ Depletion of Bcl-xL protein in 4T1 cells. Longer survival time, reduced tumor size, and higher numbers of apoptotic 4T1 cells. Normal NMuMG cells are less sensitive to ATR.