MGMT Expression Contributes to Temozolomide Resistance in H3K27M-Mutant Diffuse Midline Gliomas

Abstract

Diffuse midline gliomas (DMGs) show resistance to many chemotherapeutic agents including temozolomide (TMZ). Histone gene mutations in DMGs trigger epigenetic changes including DNA hypomethylation, one of which is a frequent lack of O6-methyl-guanine-DNA methyltransferase (<i>MGMT</i>) promoter methylation, resulting in increased MGMT expression. We established the NGT16 cell line with <i>HIST1H3B</i> K27M and <i>ACVR1</i> G328E gene mutations from a DMG patient and used this cell line and other DMG cell lines with <i>H3F3A</i> gene mutation (SF7761, SF8628, JHH-DIPG1) to analyze <i>MGMT</i> promoter methylation, MGMT protein expression, and response to TMZ. Three out of 4 DMG cell lines (NGT16, SF8628, and JHH-DIPG1) had unmethylated <i>MGMT</i> promoter, increased MGMT expression, and showed resistance to TMZ treatment. SF7761 cells with <i>H3F3A</i> gene mutation showed <i>MGMT</i> promoter methylation, lacked MGMT expression, and sensitivity to TMZ treatment. NGT16 line showed response to ALK2 inhibitor K02288 treatment <i>in vitro</i>. We confirmed <i>in vitro</i> that MGMT expression contributes to TMZ resistance in DMG cell lines. There is an urgent need to develop new strategies to treat TMZ-resistant DMGs.