Purpose: Previous gene expression studies have shown that fibroblast growth factor receptor 3 (FGFR3) is overexpressed in early stages of bladder cancer. To study the potential use of therapeutic antibodies against FGFR3, we have produced a collection of human single-chain Fv (scFv) antibody fragments by using phage display libraries.Experimental Design:Two ''naï l « ve''semi-synthetic human scFv libraries were used to select antibodies against the extracellular domain of FGFR3a(IIIc).The reactivity of the selected scFvs with a recombinant FGFR3 was characterized by an enzyme immunoassay and surface plasmon resonance analysis and with RT112 bladder carcinoma cells by a fluorescence-activated cell sorter. The capacity of the selected scFvs to block RT112 cell proliferation was determined. Results: We have isolated six human scFv antibody fragments directed against FGFR3. These human scFvs specifically bound FGFR3, but not the homologous molecule FGFR1. Biacore analysis was used to determine the affinity constants, which ranged from 12 to 40 nmol/L. Competition analysis showed that the FGF9 ligand was able to block the binding of two scFvs, 3C and 7D, to FGFR3, whereas FGF1 only blocked 7D. Immunoprecipitation and flow cytometric analysis confirmed the specificity of the antibodies to native membrane FGFR3. Two scFvs, 3C and 7D, gave an strong immunofluorescence staining of RT112 cells. Moreover, they recognized equally well wild-type and mutant FGFR3 containing the activating mutation S249C. Furthermore, they blocked proliferation of RT112 cells in a dose-and FGF-dependent manner. Conclusion: Our results suggest that these human anti-FGFR3 scFv antibodies may have potential applications as antitumoral agents in bladder cancer.The fibroblast growth factors (FGF) represent one of the largest families of polypeptide growth and differentiation factors for mesodermal and epithelial cells (1). FGFs have been implicated in multiple biological processes during embryo development, wound healing, hematopoiesis, and angiogenesis. In addition, FGFs have been shown to increase the invasiveness of a variety of tumors from prostate, bladder, kidney, breast, and pancreas (2-5).Although more than 20 FGFs with different effects on various cells have been reported, only five FGF receptors (FGFR) have been described (6, 7). These receptors share 55% to 72% homology at the protein level. The FGFR structure consists of an extracellular ligand-binding domain, a transmembrane domain, and an intracellular kinase domain. The ligand-binding domain contains three different immunoglobulin-like domains (called immunoglobulin I, immunoglobulin II, and immunoglobulin III). The ligand domain is followed by a single transmembrane domain and a cytoplasmic split tyrosine kinase domain in the intracellular domain. Alternative splicing of the mRNAs corresponding to FGFR1-3 gives place to two isoforms, a and h. Only isoform a, which contains the three immunoglobulin domains, has been found for FGFR3. Alternative splicing of FGFR3 transcripts ...
