FGFR1 Inhibition by Pemigatinib Enhances Radiosensitivity in Glioblastoma Stem Cells Through S100A4 Downregulation

Glioblastoma (GBM) is an aggressive and highly heterogeneous tumor that frequently recurs despite surgery followed by radio-chemotherapy and, more recently, TTFields. This recurrence is largely driven by glioblastoma stem cells (GSCs), which are intrinsically resistant to standard therapies. Identifying molecular targets that underlie this resistance is therefore critical. Here, we investigated whether the inhibition of FGFR1, previously identified as a key mediator of GBM radioresistance, using pemigatinib, a selective FGFR1-3 inhibitor, could enhance GSC radiosensitivity in vitro and in vivo. Pemigatinib treatment inhibited FGFR1 signaling, promoted proteasome-dependent FGFR1 degradation, and reduced the viability, neurosphere formation, and sphere size in GSCs with unmethylated MGMT, a subgroup known for poor response to standard treatments. In MGMT-unmethylated differentiated GBM cell lines, pemigatinib combined with temozolomide further enhanced radiosensitivity. Transcriptomic analysis revealed that pemigatinib treatment led to the downregulation of S100A4, a biomarker associated with mesenchymal transition, angiogenesis, and immune modulation in GBM. Functional studies confirmed that silencing S100A4 significantly improved GSCs' response to irradiation. In vivo, pemigatinib combined with localized irradiation produced the longest median survival compared to either treatment alone in mice bearing orthotopic GSC-derived tumors, although the difference was not statistically significant. These findings support further clinical investigation to validate these preclinical findings and determine the potential role of FGFR inhibition as part of multimodal GBM therapy.