ATR and cancer: Cisplatin exerts its cytotoxic effects via DNA cross-links which ultimately inhibit DNA synthesis and cause cell cycle arrest at the G2/M checkpoint.23 In turn, cancer cells appear to upregulate ATR transiently, a potential means of developing resistance to chemotherapy.24 Therefore, combining cisplatin with ATR inhibition could represent a way to subvert this resistance mechanism and enhance cytotoxicity.