PRO-001 inhibits FGF-induced phosphorylation of WT-FGFR3 and proliferation of FGFR3-expressing FDCP cells. (A) RCJ cells overexpressing FGFR3 (RCJ-FGFR3) were serum starved, and then stimulated (+) with 20 ng/mL FGF9 for 5 minutes alone or following preincubation with a control (C) or a neutralizing anti-FGFR3 Fab (001). Total cell lysates were probed by Western blot with anti–P-JNK. In parallel, lysates were immunoprecipitated with anti-FGFR3 antibody and immunocomplexes were analyzed by Western with antiphosphotyrosine (4G10) and anti-FGFR3. (B) FDCP cells that stably express FGFR1, FGFR2, or FGFR3 were cultured in the presence of increasing amounts of PRO-001. Two days later, cell proliferation was determined by XTT analysis. Data are the average of duplicate cultures.