GL induced apoptosis in MCF-7 and MDA-MB-231 cells, but not in HMEC, determined by (A and D) quantitation of cytoplasmic histone associated DNA fragmentation, and (B) flow cytomitry analysis of Caspase 3 activity. Cells were treated with the indicated concentrations of GL or z-Gug (C) or DMSO (control) for 24 hours. Results are expressed as enrichment factor relative to cells treated with DMSO (control). Results are mean±SE (n=3). *Significantly different (P<0.05) between the indicated groups by one-way ANOVA followed by by Dunnett’s test. Similar results were observed in at least two independent experiments. Representative data from a single experiment are shown. Effect of pretreatment with general caspase inhibitor Z-VAD on GL-induced cytoplasmic histone-associated DNA fragmentation (E) and caspase 3 activity (F) in MCF-7 and MDA-MB-231 cells. Columns, mean (n=3); bars, SE. a, p<0.05, significantly different compared with control; b, p<0.05, significantly different compared with GL alone treatment group (one-way ANOVA followed by Bonferroni’s test for multiple comparisons).