Induction of caspase activities by ABL-N. MDA-MB-231 cells were treated with 20 μM ABL-N for indicated times. (a) Whole cell protein lysates were prepared and subjected to Western blot analysis for detection of cleavage of caspase-3 and caspase-9. (b) Induction of caspase activities by ABL-N in MDA-MB-231 cells. (c) Cleavage of PARP was induced by ABL-N. (d) Cells were pretreated with 50 μM of either z-VAD-fmk or z-DEVD-fmk for one hour, followed by 20 μM ABL-N for 24 hours, and caspase-3 activity, DNA fragmentation and sub-G1 DNA contents were determined. The data are expressed as means ± SE of three separate experiments. (e) Abrogation of PARP cleavage by caspase inhibitors.