Here, we show that cefepime phenocopies genetic PDL1 depletion in robustly increasing DNA damage and increasing sensitivity to distinct cytotoxic drugs and small molecule DNA-damage-inducing Chk1 inhibitors in various aggressive cancer cell lines, including glioblastoma multiforme, melanoma, bladder cancer, and ovarian cancer. Here, CHEK1 is linked to urinary bladder cancer.