Targeting epigenetic machinery to overcome myeloid cell-mediated resistance to anti-PD-1 therapy in GBM - PROJECT SUMMARY/ABSTRACT Myeloid cell-mediated immune suppression is one of the major factors responsible for resistance to anti- programmed cell death protein 1 (PD-1) therapy. Glioblastoma (GBM), a brain tumor with a dismal prognosis with current standard-of-care therapy, is enriched with immune-suppressive myeloid cell subsets in its tumor microenvironment and shows resistance to anti-PD-1 therapy. Therefore, there is an unmet need to develop strategies to overcome myeloid-derived immune suppression in order to provide durable clinical benefits of anti- PD-1 therapy in patients with GBM. Epigenetic machinery plays a key role in myeloid cell differentiation and establishing specific functional profiles. However, the impact of epigenetic regulation of intra-tumoral myeloid cells on resistance to immunotherapy has remained unexplored. The overall objective of the current proposal is to identify key epigenetic factors regulating immune-suppressive pathways and develop a novel strategy targeting the epigenetic regulator(s) to reverse myeloid-derived immune suppression in GBM. In our preliminary studies, we noted that immune-suppressive myeloid cell subsets in human GBM tumors have high expression of an epigenetic enzyme - histone 3 lysine 27 demethylase (KDM6B). GBM tumor-bearing mice carrying myeloid-cell specific Kdm6b deletion demonstrated improved survival. Additionally, the absence of Kdm6b increased chromatin accessibility and expression of genes associated with proinflammatory pathways including interferon response, phagocytic ability, and antigen-presentation in intratumoral macrophages and dendritic cells. Importantly, pharmacological inhibition of KDM6B with GSK-J4, a small molecule inhibitor, enhanced the efficacy of anti-PD-1 therapy in GL261 tumor-bearing mice with increased infiltration of effector T cells. Based on the preliminary findings, we hypothesize that KDM6B inhibition reprograms immune- suppressive myeloid cells into a proinflammatory phenotype, thereby enhancing T cell-mediated anti-tumor immunity to overcome resistance to anti-PD-1 therapy in GBM. In the current proposal, we will test our hypothesis using three specific aims: 1) To determine the mechanism of KDM6B-mediated functional and epigenetic regulation of phagocytosis and antigen presentation; 2) To identify the role of KDM6B in myeloid cell-mediated regulation of T cell function and localization; and 3) To evaluate the therapeutic potential of KDM6B inhibition in reversing the resistance to anti-PD-1 therapy. The research is innovative in the applicant’s opinion because this proposal will be one of the first to provide systems-level understanding of the role of epigenetic regulation of myeloid cell biology at a single-cell resolution in GBM. The proposed research is significant since it will investigate a novel strategy of targeting the epigenetic machinery to overcome myeloid cell-derived immune resistance to anti-PD-1 therapy in GBM. The long-term goal of this research endeavor is to develop personalized immunotherapies with epigenetic modulators in a tumor-specific manner.
