EXEL-0862 induces apoptosis in human mast cells expressing D816V KIT. (A) EXEL-0862 induced PARP cleavage in a dose-dependent manner. HMC-1.1 and HMC-1.2 cells were exposed to EXEL-0862 at the indicated concentrations for 24 hours. Cell lysates were analyzed by Western blot with antibody against PARP. (B) EXEL-0862 induced PARP cleavage in a time-dependent manner. Cells were treated with 0.35 μM for 4, 24, and 48 hours, respectively. PARP was analyzed by Western blot. (C-D) Apoptosis analysis by flow cytometry of HMC-1.1 and HMC-1.2 cells exposed to escalating concentrations of EXEL-0862 for 24 hours and subjected to annexin V-PI double staining. Cells stained with annexin V were defined as apoptotic. Ratios between apoptotic cells and total cells are plotted and represent the mean ± SEM of experiments performed in duplicate.