Figure 2.

DOX- and Fas-mediated DNA fragmentation and membrane lysis is caspase dependent and reduced by P-gp function. CEM cell lines, CCRF (P-gp^low) or A7⁺ (P-gp^high) were labeled with ⁵¹Cr (lysis; a and c) and ¹²⁵IUdR (DNA fragmentation; b, d, and e) for 1 h, washed in growth media, and incubated for 16–48 h in 96-well plates (2 × 10⁴ cells/well) with cell death stimuli at final concentrations as follows: (a and b) DOX (0.1 μg/ml, 48 h); (c and d) anti-human Fas IgM mAb, CH-11 (0.01 μg/ml, 16 h). (a–d) Some A7⁺ cells were preincubated for 30 min with anti-P-gp mAb (MRK-16) (50 μg/ml, final concentration) and/or followed by 20 μM (final concentration) ZVAD-fmk or control ZFA-fmk inhibitor for 30 min. Cell death stimuli then were added as indicated. (e) A7⁺ cells were preincubated with increasing concentrations of MRK-16 mAb (1–100 μg/ml, M1 to M100), UIC2 mAb (0.1–5 μg/ml, U0.1 to U5) or verapamil (0.5–10 μM, V0.5 to V10), then treated with 1 or 10 ng/ml anti-Fas mAb for 16 h. These data are calculated as the mean ± SE of duplicate samples and are representative of at least two different experiments.