Leukemic cell lines vary in their sensitivity to C9i. The leukemic cell lines shown were cultured for 18 hours in DMSO, 50 μM C9i, or 50 μM PCi (A); or DMSO, staurosporine, or staurosporine + 50 μM C9i (B). Staurosporine was used at 0.2 μM in responsive cells and 2.0 μM in nonresponsive cells. The cells were harvested, stained with annexin V, and analyzed by flow cytometry. Data (y-axis) are plotted as fold increase in annexin V⁺ cells. In panel A, ▦ represents the fold increase in cells incubated with PCi (P) compared with DMSO, and ▪ represents the fold increase in cells incubated with C9i (9) compared with DMSO. In panel B, ▦ represents the fold increase in cells incubated with staurosporine (ST) compared with DMSO, and ▪ represents the fold increase in cells incubated in staurosporine + C9i (9) compared with DMSO.