Abstract 2124: Vitamin C enhances H3K36me3 via NSD1 promoter demethylation and sensitizes GBM stem cells to DNA damaging agents
Authors: Khela Harmon , Sudhir Sweta , Fagundo-Lugo Maria , Lal Bachchu , Laterra John , Lopez-Bertoni Hernando 
Published: July 2021

Abstract
Primary brain tumors are among the most devastating forms of cancer. Due to profound genetic, epigenetic, and morphologic heterogeneity, GBM represents the most aggressive and lethal form of the disease. GBM exhibits aberrant patterns of DNA methylation, resulting in a highly distorted epigenome, yet the molecular circuits responsible for this epigenetic dysregulation remain unknown. Glioma stem cells (GSCs) are critical modulators of tumor propagation and therapeutic resistance in GBM, and epigenetic deregulation within this cell subpopulation is thought to play fundamental roles in GSC and GBM biology. Understanding and overcoming these tumorigenic epigenetic mechanisms in GSCs is crucial to developing more effective treatment protocols and improving clinical survival. DNA methylation is a reversible process involving the addition of methyl groups, typically, at cytosine residues and demethylation is catalyzed, in part, by the ten-eleven translocation (TET) family of enzymes. These enzymes function as deoxygenases that convert 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC). Multiple studies show negative correlations between 5hmC levels and glioma grade, and loss of 5hmC correlates with poor prognosis of GBM patients. These observations suggest that understanding the mechanisms of 5hmC deregulation in GBM and developing innovative ways to re-establish 5hmC levels in tumors can impact patient outcome. Ascorbate (Vitamin C) is a TET enzyme cofactor that has gained pre-clinical interest as an attractive antitumor agent for GBM due to its ability to regulate redox status, function as potent demethylating agent, and efficiently penetrate the blood-brain barrier. We show through various molecular and biochemical endpoints, that low-dose Vitamin C significantly replenishes 5hmC and decreases stemness in GSCs. We found that, in addition to increasing global levels of 5hmC, low-dose Vitamin C acts synergistically with temozolomide (TMZ) and irradiation to induce cell death in GSCs. We also present a novel mechanism whereby Vitamin C regulates promoter demethylation of the histone methyltransferase NSD1 resulting in an increase in H3K36me3 in GSCs. We propose the increase in H3K36me3 results in euchromatin states that are more susceptible to DNA damage therapies. Our findings strongly indicate that Vitamin C can undo tumor-promoting DNA hypermethylation and sensitize GSCs to conventional radio- and chemotherapeutics and suggest it might serve as an adjunct to standard-of-care GBM treatment.
Citation Format: Harmon Khela, Sweta Sudhir, Maria Fagundo-Lugo, Bachchu Lal, John Laterra, Hernando Lopez-Bertoni. Vitamin C enhances H3K36me3 via NSD1 promoter demethylation and sensitizes GBM stem cells to DNA damaging agents [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2124.