Resistance of glioblastoma to radiotherapy is mainly due to tumour cell radioresistance, which is partially controlled by growth factors such as fibroblast growth factor (FGF). Because we have previously demonstrated the role of FGF-2 in tumour cell radioresistance, we investigate here whether inhibiting FGF-2 pathways by targeting fibroblast growth factor receptor (FGFR) may represent a new strategy to optimise the efficiency of radiotherapy in glioblastoma. Treating radioresistant U87 and SF763 glioblastoma cells with the FGFR inhibitor, SSR12819E, radiosensitises these cells while the survival after irradiation of the more radiosensitive U251 and SF767 cells was not affected. SSR128129E administration to U87 cells increases the radiation-induced mitotic cell death. It also decreased cell membrane availability of the FGFR-1 mainly expressed in these cells, increased this receptor's ubiquitylation, inhibited radiation-induced RhoB activation and modulated the level of hypoxia inducible factor, HIF-1α, a master regulator of hypoxia, thus suggesting a role of FGFR in the regulation of hypoxia pathways. Moreover, treating orthotopically U87 xenografted mice with SSR128129E before two subsequent local 2.5Gy irradiations significantly increased the animals neurological sign free survival (NSFS) compared to the other groups of treatment. These results strongly suggest that targeting FGFR with the FGFR blocker SSR128129E might represent an interesting strategy to improve the efficiency of radiotherapy in glioblastoma.
