Effect of PSP, CPT and PSP+CPT on cyclin E expression in HL-60 cells. (a) HL-60 cells were treated or pre-treated with PSP (25 μg/ml) for 72 hour before CPT (1 μM) was added. CPT was added at 72 hours and samples were collected after five hours of incubation. (b) Cyclin E was expressed in non-PSP-treated cells (control) and PSP-treated HL-60 cells. Results are expressed as means (SD) of four individual experiments analyzed with Winlist and Modfit software. * P < 0.001, vs. non-PSP treated. (c) Western blot analysis of whole cell lysate of cyclin E expression in HL-60 cells with and without PSP treatment.