CHEK1 and breast cancer: Last, Cdk inhibition by Ro3306 prevented accumulation of γ-H2AX and RPA2-P in response to CHK1 inhibitor AZD7762 in RBCC (Figure 4G), suggesting that the increased initiation of DNA replication likely contributes to DSBs generation seen after CHK1 inhibition in radioresistant breast cancer cells.