Growth of cell lines in MTS assays following treatment with daunorubicin or imatinib. (A) Cell growth (survival and proliferation) after 2 days of culture in the presence of the indicated concentrations of daunorubicin was measured by colorimetric MTS assay in the presence or absence of 10 μg/mL verapamil. The absorbance is shown as a percentage of the absorbance for same cells cultured in the absence of daunorubicin. (B) Cell growth (survival and proliferation) after 3 days of culture in the presence of the indicated concentrations of imatinib was measured by the MTS assay. HEL erythroleukemia cells, which do not express BCR/ABL, were used as a control for parental and transduced K562 cells. The absorbance is shown as a percentage of the absorbance for same cells cultured in the absence of imatinib. The error bars show the SEM for triplicate samples at each dose of drug.