P18.24.B SHORT EXPOSURE TO TTFIELDS INDUCES DNA REPAIR PATHWAY DOWNREGULATION AND RADIOSENSITIZATION IN GLIOBLASTOMA CELLS

Abstract BACKGROUND Glioblastoma (GBM) remains an aggressive brain tumor with limited therapeutic options. Tumor Treating Fields (TTFields) therapy, a non-invasive treatment utilizing alternating electric fields, is FDA-approved for newly diagnosed and recurrent GBM patients. TTFields disrupt mitosis and potentially impair DNA damage repair pathways. Here, we investigated whether a brief TTFields exposure sensitizes GBM cells to radiation by downregulating key DNA repair pathways. MATERIAL AND METHODS Glioblastoma cell lines (U87-MG, LN-229) were exposed to TTFields (200 kHz) for 2 hours. Western blot analyses assessed changes in protein levels of DNA repair genes FANCD2, FANCJ, FANCA, FANCB, BRCA1, and BRCA2. Clonogenic assays evaluated the radiosensitizing effects specifically in U87-MG cells by exposing them to 2 Gy radiation alone, TTFields alone (2h), or sequential TTFields followed by radiation. Colony counts were compared across treatment groups and controls. RESULTS Two-hour TTFields treatment significantly reduced protein expression levels of FANCD2, FANCJ, FANCA, FANCB, BRCA1, and BRCA2 across tested cell lines. In clonogenic assays with U87-MG cells, TTFields alone (2h) did not result in reduction in colony formation. Radiation alone markedly reduced colony formation. However, the sequential treatment (TTFields followed by radiation) significantly decreased clonogenic potential compared to controls, demonstrating a potent sensitization effect. CONCLUSION Our findings show that even a short (2-hour) TTFields exposure effectively downregulates critical DNA repair pathways, significantly enhancing radiosensitivity in GBM cells. These preclinical results highlight the importance of treatment timing and sequencing, aligning with the therapeutic rationale under investigation in the ongoing Phase 3 TRIDENT clinical trial (NCT04471844).