OGC P21 EZH2: A novel therapeutic target in oesophageal adenocarcinoma

Abstract Background Enhancer of zeste homologue 2 (EZH2), the catalytic subunit of the histone lysine methyltransferase Polycomb Repressor Complex 2 (PRC2), mediates gene silencing of target genes epigenetically. It is over-expressed and associated with poor outcomes in numerous malignancies. EZH2 inhibitors are currently used in the treatment of follicular lymphomas and epithelioid sarcomas. Oesophageal adenocarcinoma (OAC) has predicted sensitivity to EZH2 inhibition due to the high prevalence of potentially sensitizing mutations. This in vitro study aimed to assess the efficacy of EZH2 inhibitors in the treatment of OAC. Methods Bioinformatical analysis of publicly available bulk RNA transcriptomic data from OAC samples included in the Cancer Genome Atlas (TCGA) database was carried out. OAC cell lines OE33, FLO1 and MFD1 cultured in 2D were treated with a panel of EZH2 inhibitors at a range of clinically relevant concentrations either as monotherapies or in combination with OAC standard of care (SOC) chemotherapies. Cell viability was assessed via colorimetric MTS assay at 72hrs and 6 days post-treatment. Results Median EZH2 mRNA expression levels calculated from OAC TCGA data were significantly greater than EZH2 mRNA expression in normal oesophageal tissue (p<0.01). OAC patients with high EZH2 expression had reduced median overall survival compared to patients with low EZH2 expression (13.1 months vs 32 months, p= 0.03). EZH2 inhibitors demonstrated efficacy as monotherapies in all 3 cell lines. EZH2 inhibitors in combination with 5-fluorouracil (5-FU) showed greater efficacy than 5-FU alone, demonstrated by reductions in 5-FU half-maximal inhibitory concentration (IC50) values. Conclusions These early in vitro results demonstrate the potential of EZH2 inhibition as a novel therapy in OAC, particularly in combination with current chemotherapy agents. Further in vitro work is focused on their efficacy in patient derived tumour organoid models.