In vivo inhibition of Kit phosphorylation and tumor growth by AP23848. (A) Murine tumors were induced by subcutaneous injection of the activation-loop mutant cell line P815. Following tumor establishment, mice were treated 3 times daily with 100 mg/kg AP23848. Tumor tissue was obtained from treated mice, 3 at 1 hour and 3 at 8 hours after dose, and from 2 untreated mice, and (top) lysates were immunoblotted with a phospho-specific antibody for Kit Y568/Y570. (Bottom) Phosphotyrosine levels were averaged for each cohort to generate the graph shown. (B) Tumor weight was calculated from the measured dimensions of the tumors before treatment and after treatment at the time that the mice were killed. Average tumor weight for the treated and untreated groups was calculated to generate the graph shown. P values (Student t test) show a statistically significant difference in tumor size between the control and treatment groups following therapy. Error bars depict standard deviation of the mean.