The dose and time effect of PSP on human leukemia HL-60 cell proliferation. HL-60 cells were treated with various PSP concentrations (0-400 μg/ml) for 24, 48 and 72 hours. Cells proliferation was determined with cell densities analysis on the Multisizer. Values are expressed as mean (SD) (n = 4). * P < 0.001, vs. control.