Effects of adaphostin on STI571-resistant cells.

(A) Induction of apoptosis. Parental or STI571-resistant K562 cells were incubated for 24 hours with diluent or the indicated concentration of adaphostin or STI571. Cells were then fixed, stained with Hoechst 33258, and examined for apoptotic nuclear changes. Results shown are the mean ± 1 SD from 3 independent experiments. Brackets indicate samples compared by t tests. NS indicates differences were not statistically significant. (B, C) Effects of STI571 and adaphostin on colony formation. Parental cells (open triangles) or STI571-selected cells maintained in the absence (open circles) or presence (closed circles) of 0.5 μM STI571 were incubated with the indicated concentration of STI571 for 48 hours (B) or adaphostin for 24 hours (C), washed, and plated in 0.3% agar in the absence of drug. Error bars, mean ± 1 SD for quadruplicate plates treated with the indicated drug concentration. Results from this experiment are representative of 3 independent experiments.