IMMU-33. REPROGRAMMING OF MYELOID CELL METABOLISM VIA HEME OXYGENASE-1 INHIBITION POTENTIATES ANTI-TUMOR IMMUNITY IN A MURINE GLIOMA MODEL

Abstract Cancer cells exhibit a preference for aerobic glycolysis, a phenomenon known as the Warburg effect. Emerging evidence suggests that immune cells within the tumor microenvironment (TME) may employ a similar metabolic adaptation. Heme oxygenase-1 (HMOX-1), a metabolic regulatory gene, is elevated in myeloid cells of glioblastoma (GBM), yet its precise role in modulating immune suppression and energy utilization remains unclear. Our objective was to explore how targeting HMOX-1 activity in the GBM TME affects immune response and energy metabolism. We utilized syngeneic glioma models with C57BL/6J mice implanted with CT-2A cells, which were randomized into four treatment arms: intracranial (IC) injection of the HMOX-1 inhibitor zinc protoporphyrin (ZnPP), intraperitoneal (IP) injection of anti-PD-1, IC ZnPP + IP anti-PD-1, or IC saline (sham). For mechanistic studies, we developed a myeloid-specific knockdown model via adoptive cell transfer of myeloid-derived suppressor cells (MDSCs) transfected with Hmox-1 siRNA into CSF-1R myeloid-depleted mice. Immunophenotyping was conducted with flow cytometry. The Seahorse mitochondrial stress test was used for evaluation of energy dynamics. Downregulation of myeloid Hmox-1 expression and inhibition of HMOX-1 via ZnPP both led to heightened T cell activation, with increased IFN-γ expression in brain compared to untreated mice (P=0.039, 0.02, respectively). Notably, ZnPP treatment induced a compensatory elevation of PD-L1 in myeloid cells (P<0.0001). Both ZnPP monotherapy and anti-PD-1 + ZnPP combination therapy demonstrated enhanced median overall survival rates in comparison to sham and anti-PD-1 monotherapy groups, with the combined approach yielding the most significant survival advantage (P<0.0001). Metabolic analyses following Hmox-1 knockdown and ZnPP treatment revealed a shift away from cancer-like glycolytic shunting in MDSCs. Inhibiting the HMOX-1 pathway facilitated T cell activation and reversal of glycolysis-predominant metabolism in MDSCs, resulting in improved survival outcomes in a murine glioma model. Modulation of metabolic reprogramming in myeloid cells may potentiate anti-tumor immunity, especially in conjunction with checkpoint blockade.