Differential susceptibility of Ba/F3p210^Bcr-Abl, Ba/F3p210^E255K, and Ba/F3p210^T315I cells to imatinib mesylate. (A) Dose-response curves obtained by MTS assays after 48-hour exposure of Ba/F3p210^Bcr-Abl (wild-type [WT]; •), Ba/F3p210^E255K (E225K; ♦), and Ba/F3p210^T315I (T315I; ▴) cells versus the control 32D (▪) and untransfected Ba/F3 cells (×) to imatinib mesylate. Each data point represents means ± SD (n = 6). (B) Dose-dependent effect of imatinib mesylate on cytochrome c (Cyt. c) release. The immunoblots are representative of 3 independent experiments. (C) Flow cytometric analysis of apoptotic death in the 3 cell lines overexpressing wild-type or mutant Bcr-Abl after treatment with DMSO vehicle or 1 or 10 μM imatinib mesylate for 48 hours. Results are representative of at least 3 independent experiments. B1, B2, B3, and B4 represent annexin V^-/PI⁺, annexin V⁺/PI^+Z (late apoptosis), annexin V^-/PI^-, and annexin V⁺/PI^- (early apoptosis), respectively; FL1-H indicates annexin V-FITC; FL3-H, propidium iodide. The percentages in the graphs represent the percent of cell numbers in the respective quadrants.