Abstract 3965: Histone H3 K27M mediated regulation of cancer cell stemness and differentiation in diffuse intrinsic pontine glioma (DIPG)

Abstract

Abstract Diffuse Intrinsic Pontine Glioma (DIPG) is a rare pediatric brain tumor with a median survival of 10-15 months. Histone H3 is mutated in 80% of DIPGs, dictating tumor location, onset, and outcome of this devastating disease. Therapeutic resistance remains a major obstacle to preventing tumor recurrence and is in part driven by cancer stem cells (CSCs), which exhibit self-renewal properties and tumorigenic potential. In previous studies, we have identified these proliferative and tumorigenic features in aldehyde dehydrogenase positive (ALDH+) CSCs in H3K27M mutant DIPG. Among the 19 ALDH isoforms known in humans, aldehyde dehydrogenase family 1 member A3 (ALDH1A3) is most highly expressed in malignant cells when compared to immune cells or oligodendrocytes in H3K27M DIPG biopsies, indicating an important mechanistic role in regulating stemness in DIPG. We hypothesize that ALDH-mediated cancer stemness and resistance may in part be driven by H3K27M. Indeed, ALDH1A3 expression was dramatically reduced in CRISPR-edited DIPG cells where the H3K27M mutation had been removed (H3K27M-KO). Furthermore, these cells lost their neurosphere forming potential, began to express glial fibrillary acidic protein (GFAP) and attached to the plastic, changes indicative of differentiation. Transcriptomic and GSEA pathway analyses suggested Wnt-dependent regulation of ALDH1A3, with Wnt 7b and Wnt 11 demonstrating the largest difference in the isogenic DIPGs. In addition, DNA repair, along with PI3K/AKT and Wnt signaling, were found to be upregulated upon radiation of DIPG cells, indicating future therapeutic opportunities to prevent radio resistance. We have co-targeted these cell-intrinsic vulnerabilities to eradicate CSCs in DIPG and prevent tumor recurrence, using a combination of radiotherapy, the PI3K/mTOR inhibitor GDC-0084 and the ALDH inhibitor Disulfiram. This combination has produced an exquisite synergy in cells, which we will test in clinically-relevant DIPG models. Taken together, through these studies we have gained mechanistic insight into H3K27M mediated regulation of cancer cell stemness and differentiation in DIPG, which appears to be mediated by Wnt-dependent signaling of ALDH1A3 and provides rationale for exploring new therapeutic targets. Citation Format: Monika Sharma, Brian Magnuson, Jeanette Cruz, McKenzie Kauss, Alexander Buschhaus, Mats Ljungman, Stefanie Galban. Histone H3 K27M mediated regulation of cancer cell stemness and differentiation in diffuse intrinsic pontine glioma (DIPG) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3965.