In this study, we evaluated the ability of the novel Chk1 inhibitor V158411 to potentiate the in vitro cytotoxicity of seven clinically used cytotoxic chemotherapy drugs with different mechanisms-of-action in two p53 mutant and one p53 wild-type colorectal carcinoma cell lines growing either anchorage dependently, anchorage independently or as multi-cellular tumor spheroids. The gene discussed is CHEK1; the disease is colorectal carcinoma.