Zoë Cook

Background:  Diffuse Intrinsic Pontine Glioma (DIPG) is a universally lethal and highly aggressive pediatric brainstem tumor located in the pons.¹ DIPG is a rare condition, with only 200-300 cases per year in the United States, with average time of survival after diagnosis being ~9 months.⁸ Due to its location behind the blood brain barrier, and involvement of critical arteries and cranial nerves, DIPG is untreatable using traditional chemotherapeutics or surgical resection.¹ 85% of DIPG cells express H3K27M mutation, shown previously to block the activity of EZH2 (Enhancer of Zeste Homolog 2) methyl transferase, resulting in genome wide loss of DNA methylation.

Objective: Utilizing literature review, we explored how the H3K27M mutation drives the characteristic aggressive, infiltrative behavior of DIPG. Additionally, we aimed to further understand current challenges in treating DIPG and new methods being developed.

Methods: Utilizing the PubMed database, a search was conducted using the following keyterms: “DIPG”, “Diffuse Intrinsic Pontine Glioma”, “H3K27M”, “pHGG”, and “GD2 CAR T”. Results were limited to articles published between 2018 and 2023.

Conclusion: To confirm the loss of methylation effect induced by the H3K27M mutation, demethylase inhibitor GSK-J4 was studied. H3K27M DIPG cells treated with GSK-J4 had decreased tumor growth, increased inhibitory effects of radiation, and potentiated apoptic cell death.² H3K27M mutation leads to not only hypomethylation, but also hyperacetylation. Acetylation of lysine 27 on histone 3 (H3K27Ac) is mediated by the KAT3 family of acetyltransferases, including CREB-Binding Protein (CBP).⁴  Next, research was done to understand how this loss of methylation creates aggressive tumorigenic behavior. When compared to control groups, DIPG H3K27M cells showed altered differentiation potential, gene expression, and genome structure. H3K27M cell lines had elevated levels markers of ectoderm (OTX2), mesoderm (GSC), and trophectoderm (HCG).¹ These differences suggest that the H3K27M mutation may cause loss of hESC ability to downregulate stem cells & epithelial markers, leading to aberrant directed differentiation.¹ When allowed to differentiate entirely, the H3K27M cells showed increased expression of gene networks related to cell proliferation, tumor angiogenesis & progression, cell invasion, and neural stem cells.¹ Patient-derived DIPG cells showed 838 up-regulated genes and 949 down-regulated genes when compared to normal cell lines. Three significantly up-regulated genes were markers of glial progenitors, CCND2, SOX2, and OLIG2.³ Regarding changes in 3D genome structure, changes in Topologically Associated Domain (TAD) boundaries and DNA looping altered gene expression, enhancer landscape, and enhancer-promoter interactions to further drive tumorigenic behavior.³  Due to its unique location, DIPG is historically not treatable using traditional chemotherapy or surgical resection. Previous studies showed that H3K27M-mutated glioma cells highly express disialoganglioside (GD2). This provides a tumor target for GD2-directed chimeric antigen receptor (CAR) T cells.⁵ In a landmark study, two of three patients had significant radiographic improvements after IV administration of GD2-CAR T cells. Additionally, these patients showed improved neurological functioning, neural circuits, and quality of life.⁵

Work Cited:

1. Kfoury-Beaumont N, Prakasam R, Pondugula S, et al. The H3K27M mutation alters stem cell growth, epigenetic regulation, and differentiation potential. BMC Biol. 2022;20(1):124. Published 2022 May 30. doi:10.1186/s12915-022-01324-0
2. Nikolaev A, Fiveash JB, Yang ES. Combined Targeting of Mutant p53 and Jumonji Family Histone Demethylase Augments Therapeutic Efficacy of Radiation in H3K27M DIPG. Int J Mol Sci. 2020;21(2):490. Published 2020 Jan 13. doi:10.3390/ijms21020490
3. Wang J, Huang TY, Hou Y, et al. Epigenomic landscape and 3D genome structure in pediatric high-grade glioma. Sci Adv. 2021;7(23):eabg4126. Published 2021 Jun 2. doi:10.1126/sciadv.abg4126
4. Wiese M, Hamdan FH, Kubiak K, et al. Combined treatment with CBP and BET inhibitors reverses inadvertent activation of detrimental super enhancer programs in DIPG cells. Cell Death Dis. 2020;11(8):673. Published 2020 Aug 21. doi:10.1038/s41419-020-02800-7
5. Majzner RG, Ramakrishna S, Yeom KW, et al. GD2-CAR T cell therapy for H3K27M-mutated diffuse midline gliomas. Nature. 2022;603(7903):934-941. doi:10.1038/s41586-022-04489-4
6. McClymont K. What is a DIPG? The inoperable and incurable childhood brain tumour. The Sydney Morning Herald. Published October 23, 2022. https://www.smh.com.au/healthcare/what-is-a-dipg-the-inoperable-and-incurable-childhood-brain-tumour-20221021-p5brxa.html
7. Bender S, Tang Y, Lindroth Anders M, et al. Reduced H3K27me3 and DNA Hypomethylation Are Major Drivers of Gene Expression in K27M Mutant Pediatric High-Grade Gliomas. Cancer Cell. 2013;24(5):660-672. doi:https://doi.org/10.1016/j.ccr.2013.10.006