CHEK1 and acute myeloid leukemia: Flow cytometry analysis revealed that both BRCA1 and CHK1 are critical determinants of both cytarabine- and DNR-induced apoptosis in AML cells as indicated by the enhanced apoptosis seen in the knockdown cells after single drug treatment, while the effects of RAD51 knockdown seem DNR-specific since it only enhanced DNR-induced apoptosis (Figure 3).