Notably, although CHK1 gene knock-out is lethal in embryos [31] and induces apoptosis in embryonic stem cells [32], the depletion of CHK1 by siRNA in somatic cells on its own has been reported to cause little cytotoxicity and enhance the efficacy of DNA-damaging drugs in p53-deficient cancer cell lines [33]. Here, CHEK1 is linked to cancer.