OR30-04 Investigating the role of mitochondrial metabolic enzymes regulating immunosuppressive tumor microenvironment of castration-resistant prostate cancer

Abstract Disclosure: A. Dimeck: None. X. Yu: None. M. Long: None. K. Nastiuk: None. S. Dasgupta: None. Immunotherapy often fails to provide substantial clinical benefits to castration-resistant prostate cancer (CRPC) patients due to the challenges posed by the tumor microenvironment (TME). The prostate TME is highly heterogeneous and several factors within the TME such as metabolic and hypoxic stress create a hostile environment that drive immune suppression due to the presence of M2-like tumor-associated macrophages (TAMs) and poor infiltration of cytotoxic immune cells. However, the underlying mechanisms by which metabolic stress responses control immune suppression in the prostate TME remains relatively unexplored. Recent studies from our lab identified that dependency of CRPC on de-novo lipogenesis is primarily supported by glutamine metabolism regulated by the enzymatic activity of mitochondrial TCA cycle enzyme aconitase 2 (ACO2). This is achieved by androgen receptor (AR) and steroid receptor coregulator SRC-2 dependent transcriptional repression of SIRT3, a mitochondrial deacetylase that functions as a negative regulator of ACO2. Increased ACO2 promotes the biosynthesis of citrate, a precursor metabolite required for de novo fatty acid synthesis by reductive carboxylation of α-ketoglutarate to accentuate CRPC progression. Implantation of ACO2-depleted or constitutively active SIRT3 murine prostate cancer cells in syngeneic mouse significantly reduced progression of tumors and were eventually cleared compared to the WT-controls, which developed aggressive tumors. Single-cell RNA sequencing revealed significant alterations in immune cell populations among which macrophage population were differentially polarized. Isolated bone marrow-derived macrophages (BMDM) from non-tumor-bearing mice when incubated with tumor-conditioned media collected from ACO2-depleted PCa cells showed enrichment of pro-inflammatory M1-like macrophages (iNOS+, CD80+) compared to WT, which displayed increased pro-tumorigenic M2-like macrophages (Arg1+, CD206+). To identify the mechanisms, we performed metabolic and cytokine profiling of prostate tumors and isolated tumor interstitial fluid (TIF), and our data revealed ACO2/SIRT3 axis significantly altered several mitochondrial metabolites including amino acid aspartate that was enriched in the TIF. Moreover, CIBERSORTX analysis of immune cell population in CRPC samples demonstrated that pro-inflammatory macrophages were significantly enriched in SIRT3high tumors compared to SIRT3low, suggesting aspartate mediated metabolic alterations in the TME may support proliferation of tumor associated macrophages (TAMs) that enhance anti-tumor immune responses favoring CRPC regression. Presentation: Monday, July 14, 2025