CASP9 and cancer: The maximum activity of caspase 9 was observed in both PCC-treated cancer cell lines after 18 h (4.8 fold for SNU-423 and 5.0 fold for SNU-475), whereas after 24 h of PCC exposure, the caspase 3/7 and 8 activities were increased to a peak in both cancer cells and then gradually decreased at the later time points.