TMIC-67. GLIOBLASTOMA AUGMENTS SYSTEMIC IMMUNUNOSUPPRESSION UPON LOSS OF TESTOSTERONE VIA ALTERATION OF GLUCOCORTICOIDS PRODUCTION

Abstract

Abstract While sex differences in incidence, genetics, and immune changes are established in glioblastoma (GBM), the specific contribution of sex hormones to these differences has not been fully explored. Testosterone has been shown to have a pro-tumorigenic effect on human and mouse GBM tumor cells. However, the systemic effect of testosterone in an immune competent model has not been tested. To test this, we performed castration or sham surgery on C57BL/6 male mice, followed by intracranial implantation of syngeneic glioma cells. Surprisingly, castrated mice exhibited more aggressive tumor growth compared to sham surgery controls, and this castration-induced aggressiveness could be reversed by administering exogenous testosterone. This finding was further confirmed by chemically blocking androgen receptor signaling using enzalutamide. We observed a significant increase in adrenocorticotropic hormone (ACTH) levels in the serum from castrated mice compared to the sham group after tumor implantation. Additionally, mass spectrometry analysis detected elevated levels of circulating glucocorticoids in castrated mice, and pharmacological blockade of glucocorticoid receptor using mifepristone reversed the shorted survival in castrated mice, but not in sham control. Flow analysis revealed decreased production of anti-tumor cytokines such as IFN-γ and TNF-α in CD4+ and CD8+ T cells from tumors and lymph nodes in castrated mice, suggesting systemic immunosuppression in these animals. Indeed, castration of immune-compromised mice, specifically NSG and RAG1KO strains, did not result in reduced survival. Moreover, when GBM cells were subcutaneously implanted into the flank, tumor growth in castrated mice was decelerated compared to sham controls. We also observed significantly lower ACTH levels in the flank tumor model compared to the brain tumor model, indicating a brain-specific effect of steroid hormones on tumor control. Taken together, these findings demonstrate that testosterone regulates T cell function through glucocorticoids, ultimately affecting GBM growth in a site-specific manner.