Isobolograms for the apoptotic effects of daunorubicin and SU11248 on FLT3 ITD–positive cell lines. Cells were incubated with daunorubicin, SU11248, or both for 48 hours and apoptosis was assessed with a flow cytometric assay. Results were used to construct isobolograms for (A) MV4-11, (B) MOLM14, and (C) BAF3 ITD FLT3 cells, with concentrations for each agent expressed in nM. Again, the doses necessary to produce a given effect fall far to the left of the lines of equivalence, suggesting a potent synergy between daunorubicin and SU11248. The experimental CI values are tabulated in Table 4. • indicates ED₅₀; ▪, ED₇₅; and ▾, ED₉₀.