PD173074 inhibits FGFR3 autophosphorylation in MM cell lines and inhibits FGF-stimulated growth. (A) Immunoblot analyses of FGFR3-expressing cell lines after incubation with 5 or 25 nM PD173074, with (+) or without (-) FGF stimulation. Anti-FGFR3 immunoprecipitates probed with anti-phosphotyrosine (4G10; top) and anti-FGFR3 (bottom). (B) Human myeloma cell lines (HMCLs) expressing FGFR3 (+ve) (KMS11-LP1) or not (-ve) (8226-MM1), grown in serum-free conditions, were stimulated with aFGF/heparin and incubated with increasing concentrations of PD173074. Growth at 48 hours was assessed by MTT assay. Proliferation index (PI) = (HMCL+FGF)±drug/(HMCL-FGF).