Cytotoxicity of mitoxantrone and imatinib assessed by FDA/PI and XTT methods. (A-B) FDA/PI assay. The cytotoxicity of mitoxantrone (A) or imatinib (B) was examined in K562/wild-type (○), K562/BCRP (▴), and K562/BCRP-MX10 cells (•). Cells were exposed to either drug at 37°C for 3 days and then stained with FDA and PI. Cellular fluorescence was measured by FACScan. Each point represents the mean value of 4 individual assays with SEM. (C-D) XTT assay and effects of FTC on resistance to mitoxantrone or imatinib. The cytotoxicity of mitoxantrone (C) or imatinib (D) was examined in K562/wild-type (triangles) and K562/BCRP-MX10 cells (circles) in the presence (open symbols) or absence (closed symbols) of 5 μM FTC, using the XTT assay. Cells were exposed to mitoxantrone for 5 days or to imatinib for 3 days at 37°C. Each point represents the mean value of 8 individual assays with SEM. (E-F) Effects of imatinib ± FTC on cell growth. Wild-type (Wt) K562 (E) or K562/BCRP-MX10 cells (F) were cultivated without any drugs (○) or with 5 μM FTC (□), 100 nM imatinib (•), or both drugs (▪). Cell proliferation was determined by counting cell number by Coulter Counter for up to 5 days. Cell numbers relative to day 0 are plotted. Each point represents the mean value of 4 to 5 individual assays with SEM. *P < .05, Student t test. NS indicates no significant difference.