Effect of combined treatment with imatinib and MPA on the induction of apoptosis. (A) 32D-p185 and (B) K562 cells were treated with MPA and/or imatinib at the doses indicated for 24 and 72 hours, respectively. Apoptosis was measured by annexin-V and PI staining. The percentage of annexin V-negative and -positive cells is indicated on each histogram. The annexin V-positive peak shown in the histogram includes both the annexin V-positive/PI-negative, and the annexin V-positive/PI-positive populations. At least 3 experiments with multiple drug combinations were performed on each cell line. One representative experiment at a selected combination of doses is shown.