Abstract 1248: The BRD8/p53 epigenetic switch re-establishes tumor suppression in glioblastoma

Abstract Glioblastoma (GBM) is the most common and deadly adult primary brain malignancy. Median survival is just 12-14 months, with only about 5% of GBM patients surviving 5 years after diagnosis. This picture has not substantially improved over decades and there is an urgent need to discover more specific and effective treatments for this deadly malignancy. We discovered the bromodomain-containing chromatin regulator BRD8 as essential to GBM lacking p53 mutations (TP53WT), which make up ~71% of cases (1). BRD8 maintains malignancy by crippling p53-mediated tumor suppression in a way distinct from previously described mechanisms: it reprograms the p53 network through the EP400 histone acetyltransferase complex and by bromodomain-directed occupancy of the histone variant H2AZ at p53-induced targets, enforcing a repressive chromatin state that prevents p53-mediated transactivation. Importantly, targeting BRD8 in TP53WT GBM remodels chromatin by evicting H2AZ and enhancing chromatin accessibility, enabling p53 to bind and transactivate its targets. This chromatin remodeling cascade (referred to as the “BRD8/p53 epigenetic switch”) re-establishes p53 activity in TP53WT GBM, normalizing gene expression, evoking cell cycle arrest, inhibiting gliomagenesis, and prolonging survival in xenograft models of TP53WT GBM. Our recent work: (i) reveals that BRD8 opposes p53 function in non-malignant brain cells; (ii) shows that the bromodomain of BRD8 is unique amongst the bromodomain-containing protein family, as it is the only one that selectively reprograms the p53 network; and (iii) demonstrates that targeting BRD8 works synergistically with MDM2 inhibition. Our findings present a previously unappreciated mechanism by which cancer cells side-step p53, indicate that targeting BRD8 re-establishes p53-mediated tumor suppression in TP53WT GBM, highlight unique features of the bromodomain of BRD8, and propose therapies using co-inhibition of BRD8 and MDM2 as a dual-level tactic for boosting up p53. Thus, our work sheds light on new principles of chromatin biology and offers new promise for treating patients with this devastating malignancy. (1) Sun et al. , 2023 Nature 613 (7942): 195-202. Citation Format: Xueqin Sherine Sun, Alea A. Mills. The BRD8/p53 epigenetic switch re-establishes tumor suppression in glioblastoma abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1248.