RADT-29. TARGETING ANDROGEN RECEPTOR FOR GLIOBLASTOMA: A NOVEL RADIOSENSITIZING THERAPY THROUGH TGF-Β/LIF/STAT3 PATHWAY AND IMMUNOMODULATION

Abstract

Abstract In the search for more effective treatments for glioblastoma (GBM), a primary brain malignancy, we explored the synergistic effects of androgen receptor antagonists (ARAs) and radiotherapy (RT). Prior research indicated that ARA treatment alone improved survival in GBM mouse models, primarily through the suppression of glioma cancer stem cells. Our recent investigations aimed to ascertain the radiosensitizing effects of ARAs when combined with RT. Initial in vitro experiments, using proliferation assays on cultured GBM cells, showed only mild radiosensitizing effects. ARAs, however, induced apoptosis, enriched the G2/M phase in cell cycling, and decreased expression in numerous DNA repair genes, which were confirmed through RNA sequencing and TCGA database analyses. Additionally, Western blotting revealed that ARAs modulated SMAD2/3 phosphorylations differentially in c-terminal and linker domains in the TGF-β pathway and suppressed LIF-STAT3 signaling. This intricate mechanism involving the alteration of key cellular signaling pathways led us to hypothesize that ARAs may potentiate RT in vivo. To validate this hypothesis, we conducted in vivo studies using an orthotopic GBM mouse model. Substantial synergy was observed between ARAs and brain RT, with combined ARA and RT treatment achieving 100% long-term survival and establishing immune memory, a significant increase compared to <50% survival for the ARA only group and 0% for the RT only group. Notably, we identified significant immunostimulating effects within the tumor microenvironment and systemically, as determined by immunohistochemistry and flow cytometry on peripheral blood and spleen, respectively. Our findings demonstrate that although ARAs show mild radiosensitizing effects on GBM cells in vitro, they significantly synergize with RT in vivo, via alterations in TGF-β/LIF/STAT3 signaling pathways which have been known to influence immunomodulation. The local and systemic immunomodulatory effects demonstrated in our studies by ARA treatment warrant further study combining ARA with immunotherapeutics.