Determination of (A) caspase 8 or (C) caspase 3 activation by a fluorimetric assay designed to detect cleavage of tetrapeptide substrates. HL60 cells (1 × 10⁶) were treated with 50 to 150 μg/mL of C1, C2, or C5 for 12 hours and lysates were analyzed for IETDase (caspase 8) or DEVDase (caspase 3) activities as described in Materials and Methods. Data shown are the mean ± SD of four independent experiments and are expressed as X increase in activity over the untreated HL60 cells. Kinetics of (B) caspase 8 or (D) caspase 3 activation in HL60 cells exposed to 100 μg/mL of C1 or C2 or 150 μg/mL of C5 for 4 to 18 hours. Data shown are representative of three independent observations.