AS602868 potentiates the cytotoxic effect of doxorubicin and AraC on leukemic blasts but not on normal CD34⁺ hematopoietic precursor cells. Cells from patients 4 (A) and 9 (B) were incubated with indicated doses of AS602868, doxorubicin, or a combination of both for 72 hours. Apoptosis was measured with annexin V/propidium iodide staining and quantified as described in “Materials and methods.” Histograms represent the percentages of apoptotic blasts measured in duplicate samples. (C) Leukemic cells from patient 4 were treated with AS602868, cytarabine, or a combination of both for 72 hours. Apoptosis was measured as in panel A. (D; top row) Cells from patient 10 were treated with the indicated doses of AS602868 and VP16 for 72 hours before analysis of apoptosis as described (panel D, bottom). CD34⁺ blasts from patient 10 were purified with magnetic CD34 microbeads and incubated with indicated doses of AS602868 for 72 hours. Cells were stained with anti-CD34-FITC and annexin V-PE antibody. (E) CD34⁺ cells were isolated from normal cord blood as described in “Materials and methods” and incubated with indicated doses of AS602868 alone or in combination with doxorubicin and cytarabine. Flow cytometry analysis was performed after double staining with anti-CD34-FITC antibody and annexin V-PE. Results represent percentages of apoptosis quantified as described in “Materials and methods.”