CBP-93872 suppresses maintenance of DNA double-stranded break-induced G2 checkpoint, by inhibiting the pathway between ataxia-telangiectasia mutated (ATM) and ATM- and Rad3-related (ATR) activation. To examine the potential use of CBP-93872 for clinical applications, we analyzed the synergistic effects of platinum-containing drugs, oxaliplatin and cisplatin, pyrimidine antimetabolites, gemcitabine and 5-fluorouracil (5-FU), in combination with CBP-93872, on cell lethality in colorectal and pancreatic cancer cell lines. Treatment with CBP-93872 significantly increased cancer cell sensitivities to various chemotherapeutic agents tested through suppression of checkpoint activation. Our results thus reveal that combination treatment of CBP-93872 with known chemotherapeutic agents inhibits phosphorylation of ATR and Chk1, and induces cell death.