The Identification by Shotgun Proteomics with High-Resolution Tandem Mass-Spectrometry of Histone Isoforms' Hypermethylation Phenotype as a Hallmark Characteristic of Human-IDH-Mutant High-Grade Gliomas: Epigenetic Applications for Genotoxicity-Based Biomarkers and Cancer Therapy Targets.

Histone post-translational modifications (PTMs) have been linked to various pathological processes, especially in cancer onset, where they are envisaged as obvious diagnostic biomarkers and pivotal predictors for pathological prognosis. Consequently, their mapping and characterization constitute a critical field of study facilitated by recent advances in the high-throughput mass spectrometry technique. The current study aimed to clarify the neurotoxicity mechanisms at the epigenetic level induced by environmental stressors by examining their potential to induce aberrant histone methylation as it is the most involved modification in carcinogenesis. Our protocol first consisted of a 3D neurospheroid model derived from human high-grade gliomas, followed by treatment with a pesticide mixture. Furthermore, we analyzed histone isoform-digested peptides by shotgun proteomics with high-resolution tandem mass spectrometry, complemented by Western blotting to validate epigenetic changes. Our results revealed two major findings: First, histone demethylation in nontreated samples emphasizes the aggressiveness and poor prognosis of high-grade gliomas. Second, histone hypermethylation phenotype in treated samples underlies the adaptive strategy employed by cancer cells to overcome stress and promote progression, which is a hallmark characteristic of isocitrate dehydrogenase (IDH)-mutated gliomas. Hence, our findings not only help bridge the gap in knowledge about chromatin regulation but also pave the way for the development of targeted therapeutic approaches modulating histone hypermethylation in gliomas.