Effect of STI571 and doxorubicin on K562 and K562-R cell growth and survival.

Sensitivity of K562 and K562-R cells to STI571 (A) was quantitated by MTT assay as described in “Materials and methods.” Cells (in 96-well plates) were incubated with the indicated concentration of STI571 for 24 hours before analysis by MTT assay. Longer incubation intervals increased STI571 cytotoxicity in K562 cells but did not affect K562-R responsiveness (data not shown). The results represent the average ± SEM of 4 determinations and are compared to control untreated cells (set at 100% survival). (B) Doxorubicin sensitivity was analyzed after 24 hours' incubation with the indicated concentration of drug. Cell survival was estimated by MTT assays as described above.