IMMU-04. G-AMINOBUTYRIC ACID DRIVES GLIOBLASTOMA IN FEMALES IN AN IMMUNE-DEPENDENT MANNER

Abstract Communication with a neuronal network and accumulation of myeloid-derived suppressive cells (MDSCs) support GBM growth and therapeutic resistance. GBM incidence and outcomes differ between males and females. We previously demonstrated that granulocytic (gMDSCs) drive GBM in females. However, a lack of understanding of the host factors regulating distinct MDSC subset function remains to be a major obstacle for therapeutically targeting these cells in GBM. In this study, we identified γ-aminobutyric acid (GABA) pathway as a modulator of gMDSC activity. gMDSCs from both healthy adults and glioma patients, expressed significantly higher levels of GABA receptor B1 (GABBR1) and GABA receptor B2 (GABBR2) compared to monocytic MDSCs (mMDSCs). On contrary, GABA receptor A (GABAAR) subunits were not expressed in either MDSC subtype. Given these differences, we investigated the effect of GABA on MDSC metabolism and found an increase in L-arginine metabolism specifically in female gMDSCs following GABA treatment while no significant metabolic changes were observed in any other groups. In MDSCs, L-arginine can be metabolized via nitric oxide synthase (NOS2) or Arginase-1 (Arg-1). While treatment with GABA or the GABBR agonist baclofen increased NOS2 production in specifically in female gMDSCs, Arg-1 was not affected. Mechanistically, baclofen enhanced gMDSC-mediated T cell suppression in females. In preclinical models of GBM, baclofen treatment resulted in a truncated survival only in immunocompetent female mice, which was reversed by pharmaceutical inhibition of NOS2. Clinically, female patients on GABA analogs (pregabalin, gabapentin) had significantly lower 12-month survival probabilities compared to control population. This effect was not observed in male patients. Conversely, inhibition of GABBR with CGP35348 prolonged survival in female GBM models and reprogramed the immunosuppressive tumor microenvironment. Collectively, these results highlight that GABA alters anti-tumor immune response in a sex-specific manner. These results support the future assessment of GABA pathway inhibitors as potential immunotherapy agents in GBM.