Abstract 7552: Inhibition of histone methyltransferase EZH2 for immune-interception of colorectal cancer in Lynch syndrome

Abstract Introduction: Colorectal pre-cancers in Lynch Syndrome (LS) display a distinct immune profile thus presenting a unique opportunity to develop novel immune-interception approaches to halt carcinogenesis. Epigenetic modulation by EZH2 of immune-related genes has been implicated in many cancers including colorectal but it has yet to be explored in LS carcinogenesis. The main objective of this study is to test the effect of EZH2 inhibition on immune cell profiling, colorectal carcinogenesis, gene expression, and histone methylation, using ex vivo organoids and a LS mouse model. Methods: A mouse model of LS colorectal carcinogenesis (Villin-Cre;Msh2fl/fl;TgfβRII-KI; herein referred to as VCMsh2THu) and ex vivo colonic organoids were utilized to assess the effects of the EZH2 inhibitor GSK503. Mice were treated for 9-weeks with GSK503 with downstream studies exploring polyp multiplicity, changes to the immune landscape, and epigenetic analyses to derive mechanistic insights into EZH2 regulation in LS. Results: GSK503 significantly altered transcriptomic changes in VCMsh2THu organoids with tissue-specific tropism for dysplastic organoids as compared to organoids prepared from adjacent normal mucosa. GSK503 significantly increased CD4+and CD8+ T cells in splenocytes and colonic mucosa of treated mice compared to controls in vitro and in vivo. A preventive-dose (200μg/kg) of GSK503 for 9 weeks significantly reduced adenoma multiplicity in the large intestine of VCMsh2THu mice with significant changes in the immune landscape of treated mice compared to controls. The data suggests GSK503 significantly enriched both total and activated cytotoxic T-lymphocytes CD8+/CD137+), stromal macrophages (CD68+), and activated helper T-lymphocytes (CD4+/CD134+) in the large intestine of VCMsh2THu mice. Transcriptome and molecular analyses using IHC, Western blots, and computational tools showed activation of immune and apoptotic markers with concomitant reduction of H3K27 methylation levels in colonic crypts. ChIPseq analyses revealed decreased levels of H3K27me3 and H3K4me1 (enhancer), a slight increased levels of H3K27ac (enhancer) marks with no changes in levels of H3K4me3 in treated mice, indicating that EZH2 inhibition yields global reprograming of poised promoters and active enhancers in the LS mouse genome. Conclusions: Collectively, our findings reveal that GSK503 has a promising potential as an immuno-interception modality establishing the framework for launching phase I clinical trials with EZH2 inhibitors for LS carriers. Citation Format: Fahriye Duzagac, Charles M. Bowen, Laura Reyes-Uribe, Mahira Zaheer, Jacklyn Thompson, Nan Deng, Melissa Taggart, Abhinav Jain, Winfried Edelmann, Krishna M. Sinha, Eduardo Vilar. Inhibition of histone methyltransferase EZH2 for immune-interception of colorectal cancer in Lynch syndrome [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7552.