FGFR3 - a possible therapeutic target for liver cancer

Hepatocellular carcinoma (HCC) is among the most frequent causes of death by cancer worldwide. The prognosis is poor and the currently available therapies are mostly insufficient. Much hope therefore focuses on the better understanding of the pathogenesis of this disease in order to develop new therapeutic options. Fibroblast growth factors (FGFs) and their receptors (FGFRs) are involved in many physiological and pathological processes, including carcinogenesis. Overexpression, mutations, and/or the generation of (splice)variants of FGF receptor 3 (FGFR3) have been implicated in the development of several cancer entities. Possible deregulations of FGFR3 in hepatocarcinogenesis have not been investigated so far. In precedent experiments we have gained evidence that the expression of FGFR3 and FGFR3-ligands is significantly elevated in a subset of HCC and that the FGFR3-system may be involved in the deregulated growth of premalignant and malignant liver lesions. The principle aim of this project is to study the functional importance of FGFR3 in the development and progression of HCC and its potential as a therapeutic target for HCC. The project will analyze systematically the alterations in the expression patterns of FGFR3 and the FGFR3-ligands and their functional significance for the development and further progression of liver tumors. The studies will comprise (i) the detailed characterization of the occurrence of FGFR3-variants (splice variants, soluble forms) and of FGFR3-ligands separately for the hepatic parenchyme and mesenchyme in non-malignant and malignant liver tissues. (ii) Different expression states of FGFR3-variants and FGFR3-ligands will be compared to growth and aggressive behaviour of hepatocarcinoma cells to specify the role of this receptor for growth and differentiation control. (iii) To understand the impact of the FGFR3-system in epithelial-mesenchymal interactions, we will study whether FGFR3-ligands affect growth of tumor stroma cells and neoangiogenesis, and whether stroma-derived FGFR3-ligands influence the behaviour of malignant hepatocytes. (iv) It will be attempted to antagonize tumor growth by targeting the FGFR3. For that purpose we will develop dominant-negative FGFR3 constructs, such as kinase-dead or soluble forms of the receptor, which will be put under the control of a doxycycline-inducible transactivator system. We will test the ability of these constructs to interfere with the growth and aggressive behaviour of liver tumor cells in vitro and in SCID-mice. It is expected that the kinase dead FGFR3 antagonizes the (autocrine) effects of the native receptor and that the soluble FGFR3 is released to the surrounding to bind and neutralize the FGFR3-ligands and to interfere with tumor-stroma interactions. (v) Finally, we will combine the blockade of FGFR3-mediated signaling with targeted therapies currently used for HCC treatment. The combinations will be tested in-vitro and in SCID-mice. The high incidence of HCC and poor prognosis of this disease underline the importance of successful research in this field. It is expected that these studies will uncover key alterations being crucial for the formation and progression of liver tumors. The knowledge gained will enable to develop innovative therapeutic strategies targeting HCC.

Hepatocellular carcinoma (HCC) is among the 5 most frequent causes of death by cancer worldwide. The prognosis is poor and the currently available therapies are mostly insufficient. Much hope therefore focuses on the better understanding of the pathogenesis of this disease in order to develop new therapeutic options. Fibroblast growth factors (FGFs) and their receptors (FGFRs) are involved in many physiological and pathological processes, including carcinogenesis. Overexpression, mutations, and/or the generation of (splice)variants of FGFRs have been implicated in the development of several cancer entities. Possible deregulations of FGFRs in hepatocarcinogenesis have not been investigated in detail so far. In the present project we have gained evidence that the expression of FGFR3, FGFR4 and respective ligands is elevated in >90% of HCC cases studied. Furthermore, over-expression of FGFR3 isoforms could be associated with larger size of primary tumors and tumor recurrence/infiltration. FGFR3, occurring in the two isoforms FGFR3-IIIb and FGFR3-IIIc, and FGFR4 were observed to show highly redundant effects in-vitro as well as in-vivo. Independent of whether FGFR3-IIIb, FGFR3IIIc or FGFR4 were over-expressed in hepatoma/hepatocarcinoma cell lines, receptor upregulation resulted in enhanced growth and invasive phenotype in in-vitro assays and an increased tumorigenicity of the cell lines in a SCID mouse model. On the other hand, knockdown of either FGFR3 or FGFR4 resulted in the opposite effects, i.e. decreased growth and aggressive behavior of the cells in-vitro and inhibition of tumor growth in-vivo. FGF9 was found to enhance proliferation and the invasive phenotype of hepatoma/hepatocarcinoma cells, which was blocked by knockdown of FGFR3 or the selective FGFR1-3 tyrosine kinase inhibitor NVP-BGJ398. Thus, the FGF9-mediated effects appear to be due to FGFR3 activation. To conclude, the present project provides profound knowledge on the functional role of the FGF9-FGFR3 axis and of FGFR4 for the malignant phenotype of HCC cells. Accordingly, blockade of FGFR3 and/or FGFR4 may be a promising therapeutic tool for the treatment of HCC patients in the near future.