Effect of PD184352/dasatinib in imatinib-resistant Bcr/abl⁺ leukemia cells. (A) K562 and K562/R cells, which display increased expression of Bcr/Abl (inset), were cultured in the presence of varying concentrations of imatinib or dasatinib for 48 hours. (B) K562/R cells were treated with 2 nM dasatinib with or without 5 μM PD for 48 hours, after which apoptosis was determined by annexin-V/PI analysis. (C) K562 and K562/Lyn cells, which display increased expression of p-Lyn and diminished expression of Bcr/Abl (inset), were cultured in the presence of the indicated concentrations of dasatinib for 48 hours, after which apoptosis was determined. (D) K562/Lyn cells were exposed to 5 μM PD184352 with or without 10 nM dasatinib for 48 hours, after which apoptosis was monitored by annexin-V/PI analysis (* denotes significant increase compared with drug treated alone; P < .05.) (E) Wild-type and mutant Brc-Abl/BaF3 cells were exposed to 3 μM PD184352 with or without 1.5 nM to 100 nM dasatinib alone or in combination for 24 hours, after which the percentage of apoptotic cells was determined by annexin-V/PI analysis. All values represent the means ± SD for duplicate determinations performed on 3 separate experiments.