Surprisingly, we found that when KU-55933 was used at a dose that blocks radiation-induced phosphorylation of p53 (S15), H2AX (S139), and CHK2 (T68) in an ATM-dependent manner in human tumor cell lines [24], it did in fact inhibit CHK2 phosphorylation >85% in irradiated hESCs (Figure 4). Here, CHEK2 is linked to neoplasm.