TMET-37. Targeting CD47 in the glioblastoma tumor microenvironment rewires metabolism to limit immunosuppression

Abstract Glioblastoma (GBM) is the most malignant brain tumor, and treatment with immunotherapy and current standard treatment has shown little efficacy, likely due to the significant immunosuppressive microenvironment. The transmembrane protein CD47 restricts innate immunosurveillance by binding to SIRPα on myeloid cells. Our patient biopsy data revealed strong immunoreactivity to CD47 in GBM compared to normal adjacent tissue (p < 0.05). We also showed that Temozolomide, the standard treatment of GBM, can upregulate CD47. Furthermore, high CD47 expression in GBM resulted in poor survival, suggesting it may be a target for GBM treatment. RNA-Seq data of established murine GBM CD47-overexpressed and knockout cell lines suggested that CD47 highly regulates mitochondrial-related metabolism, including Oxidative phosphorylation (OxPhos) and fatty acid (FA) metabolism. This data suggests a novel role of CD47 beyond the well-known ‘Don’t eat me” paradigm. Gene Ontology analysis showed that CD47-upregulated genes exhibit a strong enrichment in phospholipid synthesis. On the other hand CD47 knockdown in GBM cells decreases the key FA metabolism mediators and reduces mitochondrial maximal respiration by over 30-50% (p*<0.05), which is linked to the decrease of FA oxidation. Interestingly, lipidomics showed a 50% increase of cardiolipin (p < 0.05), a crucial phospholipid in the inner mitochondrial membranes that stabilizes mitochondrial function and resists apoptosis, which may contribute to CD47-regulated mitochondrial function. In addition, cardiolipin is believed to be released extracellularly and modulate microglial function, which may be associated with GBM immunosuppression. Moreover, blocking CD47 on microglia showed an opposite result from cancer cells, with increased mitochondrial respiration and fatty acid oxidation (FAO). This resulted in enhanced cell-mediated killing in cell mediated cytotoxicity models including patient derived GBM organoid models. (*p<0.005). Taken together, our data suggest that targeting CD47 may be a promising approach to reduce GBM metabolic plasticity and enhance microglia-mediated cytotoxicity.