Effect of combination of VX-680 and VP16 on apoptosis of AML blasts. (A) Cells from AML blasts were incubated with indicated doses of VX-680, VP16, or a combination of both for 72 hours before staining with annexin V-FITC and PI. The apoptosis was assessed by flow cytometry; Columns, mean; bars, SD. **P < .01; ***P < .001. (B) Cells from patient 12 (71% blasts) were incubated for 72 hours with indicated doses of VX-680 and VP16 before staining with annexin V-FITC. The percentages of apoptotic cells are displayed. (C) Sub-G₁ analysis of apoptotic blasts. Blasts from patient 12 were stained with PI. The percentage of apoptotic blasts in sub-G₁ (gate M1) is displayed.