Chk1 inhibitors including UCN-01 are being introduced into clinical trials [24] in combination with genotoxic agents such as cytarabine (for the treatment of acute myeloid leukemia) [46] or cisplatin (for the treatment of advanced solid tumors) [47], and proof has been obtained that UCN-01 can actually inhibit Chk1 in vivo, in tumor cells [46], although the inhibitor may act on other kinases including Chk2 and PDK1 as well, at least in vitro. This evidence concerns the gene CHEK1 and acute myeloid leukemia.