CHEK2 and malignant colon neoplasm: In HT29 colon cancer cells, V158411 blocked etoposide induced autophosphorylation of Chk1 with an IC50 of 48 nM and Chk2 with an IC50 of 904 nM suggesting that the apparent selectivity of V158411 for Chk1 over Chk2 is closer to 19-fold in cells.