Inhibition of the activity of Kit mutants associated with secondary imatinib resistance by motesanib. Autophosphorylation (expressed as a percentage of vehicle control) of wild-type Kit (panel A) and Kit mutants associated with secondary imatinib resistance (panel B) was assessed in stably transfected Chinese hamster ovary cells treated for 2 hours with single 10-fold serial dilutions of motesanib. Representative data from 1 of 2 experiments are shown. Viability (expressed as the percentage of vehicle control) of Ba/F3 cells expressing the same Kit mutants treated for 24 hours with single 10-fold serial dilutions of motesanib was also assessed (panel C; not shown: D816V, which had a motesanib IC50 > 3 μM). Viability experiments were performed once and representative curves are shown (D816V was not evaluated because Ba/F3 cells expressing this mutant could not be established).