Annexin V/PI flow cytometric analysis of apoptotic population of HL-60 cells treated with PSP, CPT and PSP+CPT treatments. HL-60 cells were incubated with or without PSP (25 μg/ml) for 72 hours. The cells were subsequently exposed to CPT at concentrations of 0, 10, 100 and 1000 nM for five hours. Apoptotic cells were identified and quantified with flow cytometry with annexin V/PI staining. Results are expressed as means (SD) of four individual experiments analyzed with Winlist software.