1056 Modulation of Glycolytic Shunting in Myeloid Cells Via Heme Oxygenase-1 Pathway Results in Enhanced T Cell Activation and Improved Survival in a Murine Glioma Model

INTRODUCTION: Cancer cells preferentially utilize aerobic glycolysis (Warburg effect). Recent studies show similar metabolic reprogramming in immune cells of the tumor microenvironment (TME). Heme oxygenase-1 (HMOX-1), a metabolic regulatory gene, is known to be upregulated in glioblastoma (GBM) myeloid cells, but how HMOX-1 specifically modulates immunosuppression and energy utilization remains poorly understood. METHODS: Syngeneic glioma models with C57BL/6J mice implanted with CT-2A cells were treated with 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). Adoptive cell transfer of myeloid-derived suppressor cells (MDSCs) with siRNA knockdown of Hmox-1 into CSF-1R myeloid-depleted mice were used for mechanistic studies. Changes in glycolytic energy dynamics were assessed with the Seahorse mitochondrial stress test. Immunophenotyping was performed with flow cytometry. RESULTS: Myeloid Hmox-1 knockdown as well as HMOX-1 inhibition with ZnPP resulted in increased T cell activation with a significantly higher IFN-G expression in brain compared to non-treated mice (P = 0.039, 0.02, respectively). However, there was also a compensatory upregulation of PD-L1 in myeloid cells with ZnPP treatment (P < 0.0001). ZnPP monotherapy and combination therapy with anti-PD-1 + ZnPP led to improved median overall survival compared to sham and anti-PD-1 monotherapy arms, with combination therapy demonstrating the greatest survival benefit (P < 0.0001). Metabolic assays for both ZnPP treatment and Hmox-1 knockdown demonstrated a shift away from glycolysis-predominant metabolism in MDSCs, indicating a change in energy dynamics from the usual TME. CONCLUSIONS: HMOX-1 inhibition enhanced T cell activation, shifted MDSCs away from cancer cell-like glycolytic shunting, and improved survival in a murine glioma model. Modulation of metabolic reprogramming can have an anti-tumor, immune-activating effect that synergizes with checkpoint inhibition.