zVAD fails to prevent imatinib-induced cell death. BV173 cells (A) and K562 cells (B) were preincubated with 0.1% DMSO or 40 μM zVAD and subsequently treated with or without 1 μM imatinib for the indicated times. The PI-positive dead cells were determined by flow cytometry. Data represent means ± SEM of 4 individual experiments.