U937 cells were pretreated with the caspase inhibitor Z-VAD-FMK (20 µM) for 1 h, followed by treatment with 80 µM DIM for 12 h and 24 h. (a) Cells were stained with Annexin V/PI, and apoptosis was determined using flow cytometry. **Values for cells treated with DIM and Z-VAD-FMK were significantly reduced compared to values obtained for DIM alone by Student's t-test, p<0.01. (b–d) Total protein extracts were prepared and subjected to Western blot assay using antibodies as indicated.