CHIR-258 inhibits FGFR3 phosphorylation and demonstrates antitumor effects in vivo. (A) When tumor size reached 200 mm³, mice were randomly assigned (8-10/group) to receive vehicle alone () or varying doses of CHIR-258 (○, 10 mg/kg; ▴, 30 mg/kg; ⋄, 60 mg/kg) daily by oral gavage for 21 days. Results are tumor volume, mean ± SD mm³, plotted against time. (B) At the completion of treatment, mice from each treatment group were humanely killed, and the tumors were removed for assay. Tumors were immediately homogenized in ice-cold lysis buffer and FGFR3 was immunoprecipitated from 1 mg protein with antihuman FGFR3 and immunoblotting with antiphosphotyrosine antibody (4G10) was performed (top row). Then blot was stripped and probed with an anti-FGFR3 antibody (αFGFR3) as a loading control (bottom row). (C) KMS11-derived tumors were analyzed by hematoxylin and eosin (H & E) staining (10 × magnification) and immunostaining for Ki-67 and cleaved caspase 3 (40 × magnification). Shown are representative data from vehicle- and 60 mg/kg-treated mice.