EXEL-0862 inhibits proliferation of human mast cells bearing D816V mutation and KIT phosphorylation. (A) Dose-response curves of HMC-1.1 and HMC-1.2 cells treated with EXEL-0862. Cells were exposed in vitro for 72 hours to increasing concentrations of EXEL-0862, and the MTS assay was used to evaluate growth inhibition. Graphs show data from a representative experiment performed in triplicate; error bars represent standard deviation. (B) KIT phosphorylation was inhibited by EXEL-0862 in a dose-dependent manner in HMC-1.1 and HMC-1.2 cells when exposed at the indicated concentrations for 3 hours. EXEL-0862 ICs were based on the MTS assay, as shown in panel A. Cell lysates were immunoprecipitated with antibody against KIT. Western blot analysis was performed with antiphosphotyrosine antibody.