THE EPIGENETIC REGULATORY PROTEIN CBX2 AS A NOVEL THERAPEUTIC TARGET FOR GLIOBLASTOMA

Abstract AIMS Glioblastoma (GBM) is the deadliest and most common form of brain tumour. The average length of survival for GBM patients remains low, in part, due to a lack of targeted therapeutics. Identification and validation of novel therapeutic targets is therefore crucial. Chomobox 2 (CBX2; a component of polycomb repressive complex 1 (PRC1)), represses gene expression and has a pro-oncogenic role in several aggressive cancer subtypes. CBX2 expression is elevated in GBM, however, very little is known about its role in this deadly disease. We aim to assess the phenotypic and gene expression effects of preventing CBX2-chromatin interaction in patient-derived GBM cell models, and to determine the functional mechanisms by which CBX2 promotes GBM progression; thereby determining its potential as a novel therapeutic target. METHOD Crucial to impactful target validation is the use of translationally relevant models, this study utilises a 3D spheroid model, using patient-derived cells, which more closely recapitulates the in vivo tumour microenvironment. GBM cell monolayers and spheroids were treated with SW2_152F, a selective CBX2 inhibitor. The phenotypic effects of CBX2 inhibition were assessed by cell count, CellTiter-Glo viability assays, fluorescence microscopy, and flow cytometry. Genes and biological pathways differentially regulated following CBX2 inhibition were assessed by RNA-sequencing and Gene Set Enrichment Analysis (GSEA). RESULTS Inhibition of CBX2 induced cell death and reduced cell viability in both 2D and 3D GBM cultures. RNA-seq and GSEA of SW2_152F-treated cells identified dysregulation of gene signatures involved in pro-oncogenic MYC and E2F signalling pathways, and dysregulation of genes associated with G2/M cell cycle progression. CONCLUSION Preventing CBX2-chromatin interaction induces GBM cell death. Further research will identify CBX2- chromatin binding sites to characterise the activity and direct regulatory role of CBX2 in GBM. Furthermore, we will assess the phenotypic and gene expression effects of CBX2 inhibition and depletion on ex vivo maintained GBM tissue biopsies.