Fig. 7

Targeting Flt3 can inhibit leukemia progression driven by tnFGFR1. When the primary cells from mice xenografted with BCR-FGFR1m or tnFGFR1 were treated with increasing concentrations of BGJ398 (N = 3), the BCR-FGFR1m cells show a dose dependent suppression of growth whereas the tnFGFR1 transformed cells only show a mild suppression of growth at the highest concentrations (A). Flow cytometric analysis of Annexin V staining (B) shows significant apoptosis only in the BCR-FGFR1m expressing cells. BGJ398 treatment specifically blocks phosphorylation of the full length fusion kinase, but has no effect on the tnFGFR1 and FLT3 signaling (C). When the same cells were treated with the AC220 FLT3 inhibitor (D), the tnFGFR1 transduced cells show a dose dependent suppression of growth, with the BCR-FGFR1m cells only showing slight growth suppression at the highest concentrations. Increased Annexin V staining in this case was only seen in the tnFGFR1 cells treated with AC220 (E). AC220 treatment specifically targets the Flt3 signaling (F). Survival analysis of mice (N = 5) xenografted with tnFGFR1 expressing cells shows a dose-dependent improvement in mouse survival following treatment with AC220, which is reflected in spleen weight and WBC count as well as the percentage of GFP+ leukemia cells in the peripheral blood (G-J). When mice (n = 5) inoculated with primary BCR-FGFR1 expressing leukemia cells and then treated after 7 days with either BGJ398 (30 mg/Kg) or AC220 (10 mg/Kg) alone, ANOVA statistical analysis with Bonferroni correction revealed that there was a significant increase in survival when each cohort was compared individually with the vehicle treated control group (K). A combination of BGJ398 and AC220 shows a further significant improvement in survival compared with single treatment of the two drugs. In pairwise comparisons the changes in survival were reflected in the spleen weight and the WBC between various treatments (L). ns = not significant. *p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001, ****p ≤ 0.0001. Bonferroni-Adjusted Alpha is 0.0125 for the combinational drug treatment