RADIATION-INDUCED LIPID METABOLISM IMPAIRS INNATE IMMUNITY TO PROMOTE GLIOBLASTOMA IMMUNE EVASION

Abstract AIMS Radiation therapy (RT) can trigger type I interferon (IFN-I) responses and anti-tumor immunity in various can- cers. However, glioblastoma inevitably recurs, suggesting RT does not generate a long-lasting immune response. This may be due to a highly immunosuppressive tumor microenvironment and/or RT-induced immune evasion. Our findings show that RT promotes fatty acid synthase (FASN)-mediated lipid synthesis, a metabolic program that reportedly suppresses IFN-I in viral immunity. We hypothesized that FASN induction similarly inhibits IFN-I in irradiated glioblastoma, limiting antitumor immunity. We aim to determine whether FASN blockade restores IFN-I signaling, enhances immune infiltration, and improves RT and immunotherapy efficacy. METHODS Murine glioblastoma cells were subjected to CRISPR/Cas9-mediated FASN knockout or treated with FASN in- hibitors (FASNi), then irradiated (6Gy) and analyzed 24h post-RT using RNA sequencing, LEGENDplex, and ELISA. In vivo, glioblastoma-bearing mice received FASNi (days 9-30), anti-PD-1 (twice weekly, days 15-24), and fractionated RT (5×6Gy, days 10-14). Survival was monitored (n=7/group), and tumor immune infiltration was assessed at day 20 using flow cytometry and multiplex imaging. Long-term survivors (>100 days) were rechal- lenged in the contralateral hemisphere. In some experiments, mice received anti-CD8 or anti-IFNAR antibodies. RESULTS Transcriptome analysis identified IFN-I signaling as the most enriched pathway in irradiated FASN-knockout cells, confirmed by increased IFN-I protein levels. In vivo, RT+FASNi inflamed glioblastoma tumors, enhancing CD11c and CD8 T-cell infiltration. Remarkably, adding anti-PD-1 to RT+FASNi further improved survival, with 86% of mice tumor-free at 100 days vs. 43% in other RT-treated groups. Rechallenged RT+FASNi+anti-PD-1 survivors did not develop a tumor when compared to naïve animals, demonstrating immunological memory. CD8 depletion or IFNAR blockade abrogated this effect, highlighting the critical role of IFN-I and CD8 CONCLUSION FASN inhibition restores IFN-I responses in irradiated glioblastoma, enhancing immune infiltration and im- munotherapy efficacy. These findings highlight FASN as a key target to shift glioblastoma from immunosup- pressive to immunoresponsive.