Abstract PR-007: Targeting FASN improves type I interferon responses in irradiated glioblastoma

Glioblastoma (GBM) is a devastating primary brain cancer with a median survival of 11-15 months. Radiotherapy (RT), the standard of care for GBM, increases adjuvanticity of cancer cells, by at least generating cancer cell intrinsic type I interferon (IFN-I) responses to jumpstart antitumor immunity. However, RT can also exacerbate potent immune inhibitory mechanisms to facilitate immune evasion. Among which, metabolic reprogramming of irradiated GBM represents an emerging mechanism of immune resistance. Notably, increased de novo lipid synthesis by the fatty acid synthase (FASN) is a hallmark of GBM that is emerging as a mechanisms of therapy resistance and immune escape. Because FASN was found to impair IFN-I in antiviral immunity, we hypothesize that FASN is preventing RT-induced IFN-I responses to promote GBM survival and evade immune recognition. To test this hypothesis, we first defined RT-induced metabolic changes by seahorse assay and metabolomics in the GL261 murine GBM model. We observed an increase in mitochondrial respiration, glycolysis and in lipid metabolism-related pathways in 10 gray (Gy) irradiated GL261 cells. Consistent with this last observation, we found upregulation of FASN expression by western blot and intracellular neutral lipid accumulation by BODIPY staining and transmission electron microscopy (TEM) in irradiated GL261 cells (10 Gy). Confirming the role of FASN, RT-induced accumulation of neutral lipids was reverted when GL261 cells were incubated with a pharmacologic FASN inhibitor. Next, to ask whether FASN was impairing IFN-I in irradiated GBM, GL261 cells were engineered to express an inducible shRNA silencing FASN (GL261shFASN) or its non-silencing control (GL261shNS). As expected, irradiation of GL261shNS cells enhanced the secretion of IFN-I cytokines. Strikingly, we found that FASN knockdown spontaneously induced IFN-beta and CXCL10 secretion, and this effect was even more pronounced when cells were irradiated. Finally, GL261shNS and GL261shFASN cells were orthotopically implanted in mice and IFN-I signaling was blocked using an antibody against the interferon alpha/beta receptor (IFNAR). FASN knockdown alone was sufficient to increase the median survival of mice bearing GL261shFASN tumors by 51 days vs. 35 days for GL261shNS tumors. Moreover, 33% of mice bearing GL261 tumors unable to express FASN remained tumor free for up to 100 days, while none of the GL261shNS-tumor bearing animal survived. This significant survival prolongation of mice bearing GL261shFASN tumor was completely abrogated when IFNAR was blocked. Overall, our findings suggest that FASN-mediated lipogenesis prevents RT-induced cancer cell intrinsic IFN-I to promote GBM survival. Consequently, it is possible that FASN acts as an immuno-metabolic checkpoint capable to regulate the immune system upon metabolic cues generated by RT. Citation Format: Mara De Martino, Camille Daviaud, Claire Vanpouille-Box. Targeting FASN improves type I interferon responses in irradiated glioblastoma [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PR-007.