Targeting oncogenic epigenetic mechanisms in IDHmut/ATRXloss Astrocytoma - ABSTRACT Astrocytomas (WHO grade II and III) primarily occur in early-middle adult life. Most lower grade astrocytoma progress to higher grade including GBM (i.e., secondary GBM) despite the best standard-of-care therapy. Developing more effective therapeutic strategies requires a more complete understanding of the mechanisms employed by astrocytoma cells to escape anti-tumor immunity. The majority (~80%) of grade II & grade III astrocytoma carry mutations in isocitrate dehydrogenase (e.g., IDH1R132H), which typically occurs with p53 mutation and ATRX inactivation (i.e., IDH1R132H/p53mut/ATRXloss, triple-mut for simplicity), indicating that this triple mutation background has an important role in tumor growth potentially including immune evasion mechanisms. However, our current understanding of how triple-mut astrocytoma cells modulate the tumor microenvironment (TME) to suppress anti-tumor immunity is limited and inadequate. The goal of this project is to elucidate the cellular and molecular mechanisms by which triple-mut astrocytoma cells modulate TME immune cells and use these discoveries to develop novel strategies to sensitize triple-mut astrocytoma cells to emerging immunotherapeutics. Our recent published findings and preliminary data show that triple-mut induces multiple pathways critical to anti-tumor immunity including checkpoint ligands, IFN-γ signaling insensitivity, down- regulation of MHC-I and -II antigen presentation pathways (MHC APP), and dysregulated cytokine/chemokine profiles that modulate the astrocytoma immune microenvironment. Furthermore, we found that the components of the immune-modulating astrocytoma transcriptome are augmented by standard-of-care radiation (IR) and temozolomide (TMZ). Our findings implicate BET and EHMT as epigenetic determinants of astrocytoma immune- modulating transcriptome. Building on these interesting findings, we will pursue the following specific aims: (i) Determine the role of BETs in the immune-suppressive transcriptome in triple-mut astrocytoma cells at baseline and in response to standard-of-care radiation; (ii) Identify EHMT-dependent methylation events that drive IFN signaling insensitivity and MHC APP down-regulation in triple-mut astrocytoma cells; (iii) Determine if BET and EHMT inhibition in combination reprogram astrocytoma microenvironment and sensitize astrocytoma to anti- CTLA-4 therapy. These experiments will fill critical knowledge gaps in our understanding of BET-dependent and EHMT-dependent immunomodulatory pathways underlying astrocytoma cell: immune cell immunosuppressive interactions and their augmentation by IR and establish the potential for combinational strategies to sensitize triple-mut astrocytoma to emerging immunotherapeutics.
