Effects of SU11248 and/or cytarabine on the proliferation of primary AML cells. Low-density peripheral blood mononuclear cells from patients with refractory and/or relapsed AML were incubated with cytarabine (0-8000 nM) and/or SU11248 (50 nM) for 48 hours and cellular proliferation was assessed with an XTT-based assay (error bars indicate standard error of the mean values). The results for cells treated with SU11248 are shown with the solid-line plots, and the results for cells treated with cytarabine alone are shown with the dashed-line plots. Single-agent SU11248 (50 nM) significantly inhibited the proliferation of FLT3 ITD AML cells (top) but not FLT3 WT AML cells (bottom). The addition of SU11248 to 250 or 500 nM cytarabine significantly inhibited proliferation of FLT3 ITD AML cells compared with cytarabine alone. In contrast, the effect of the combination of SU11248 and cytarabine on proliferation of FLT3 WT AML cells was not significantly different than that of single-agent cytarabine. ^**P < .01 compared with single-agent cytarabine (0 nM or 250 nM); ^*P < .05 compared with single-agent cytarabine (500 nM cytarabine).