ABT-737 induces apoptosis through the mitochondrial pathway in ALL cells. Cells were treated for 24 hours with 100 nM ABT-737 or DMSO, or pretreated for 1 hour with 200 μM ZVAD.fmk prior to addition of ABT-737. (A) PARP cleavage correlates with cell death, as analyzed by annexin-V staining and reported as percent alive. (B) Caspase-9 activation was measurable by a fluorometric assay. The amount of annexin-V–negative cells was recorded just prior to harvesting cells (percent alive). Note that in both panels A and B the amount of ABT-737 used was not sufficient to cause significant apoptosis in CEM-c1 cells, which is consistent with the results reported in Figure 2.