GSH depletion potentiates adaphostin toxicity. (A) K562 cells were incubated with diluent (3 hours) or 10 μM adaphostin for the indicated length of time. Cells were then stained with 100 μM mBCl for 15 minutes and assayed for fluorescence. K562 cells incubated with 1 mM BSO for 24 hours were used as a positive control for GSH depletion. Cells incubated without mBCl provided a negative control. Error bars are mean ± SD of 3 independent experiments. ^*P < .02 compared to control. ^**P < .05 compared to control. (B) K562 cells were treated for 24 hours with diluent, 2.5 μM adaphostin, or 5 μM imatinib mesylate in the presence of 0, 100 μM, 500 μM, 1 mM, or 2 mM BSO (added 10 minutes prior to adaphostin or imatinib mesylate). At the completion of the incubation, samples were stained with PI and analyzed for flow microfluorimetry for cells containing less than 2N DNA content. Error bars are mean ± SD of 3 independent experiments. (C) K562 cells were treated for 4 hours with 1 mM BSO (•) or diluent (○). After addition of the indicated concentration of adaphostin, incubation in the presence or absence of BSO was continued for an additional 24 hours. At the completion of the incubation, cells were resuspended in drug-free medium and assayed for clonogenic survival. Error bars, ± 1 SD from quadruplicate samples.