Isobolograms for the effects of SU11248 and cytarabine on cellular proliferation. Cells were incubated with cytarabine, SU11248, or both for 72 hours and proliferation was assessed using an XTT-based assay. Results were analyzed using Calcusyn software for (A) MV4-11, (B) MOLM14, (C) BAF3 ITD FLT3, (D) FL-stimulated BAF3 WT FLT3, and (E) BAF3 D835V FLT3 cell lines (concentrations of agents are expressed in nM). For 90% inhibition (ED₉₀), the points fall to the left of the predicted line of additive effect, suggesting a synergistic interaction of cytarabine and SU11248. The drugs appear to have an additive effect for doses necessary to inhibit proliferation at 50% of untreated control. • indicates ED₅₀; ▪, ED₇₅; and ▾, ED₉₀. See Table 1 for CI values.