Abstract 2965: Epigenetic mechanisms involved in acquired resistance to combined chemotherapies in digestive cancer cells
Authors: Bachir Elsa Hadj , Poiraud Charles , Claux Hugo , Moghrabi Soumaya El , Paget Sonia , Duchêne Belinda , Jonckheere Nicolas , Neve Bernadette , Leteurtre Emmanuelle , Van Seuningen Isabelle , Vincent Audrey 
Published: June 2022

Abstract
Introduction. One of the challenges in the management of patients with cancer of the digestive tract is to prevent relapse. Epigenetic modifications (i.e. DNA methylation and histone marks) have been proven to be involved in the generation and maintenance of a subset of cells with stemness properties, that resist to conventional therapies. Our aim is to identify complexes of chromatin modifier enzymes (epienzymes) that are involved in acquired chemoresistance/aggressiveness of colon and pancreatic cancer cells.
Experimental procedures/Methods. A meta-analysis performed on public transcriptomics data from colorectal cancer (CRC) patients cross-referenced with our own data including basal-like pancreatic cancer samples identified a limited number of epienzymes associated with aggressive subtypes of digestive cancers. Among them, the demethylase KDM4B, specific of the lysine 9 of Histone 3, and the transcriptional repressor PRDM1 where found correlated to the expression of several typical markers of cancer stemness. To confirm the role of these epienzymes in colon and pancreatic cancer cell chemoresistance, we have developed several in vivo and in vitro 2D and 3D models of acquired resistance to oxaliplatin-based combined chemotherapies, including FOLFIRINOX and FOLFOX. In this work, these models as well as patient samples have been used to study (i) the dynamic expression profile of these epienzymes (RT-qPCR, immunofluorescent multiplex staining, single-cell analysis and spatial transcriptomics), (ii) the gene regulons that are bound by these epienzymes (CUT&RUN-seq) and (iii) the functional role of these epienzymes in cancer stemness (organoid and sphere-forming assays).
Results. We have shown that PRDM1 and KDM4B are expressed heterogeneously in cancer cell populations and overexpressed during specific time frames along the acquisition of resistance to oxaliplatin-based combined therapies both in colon and pancreatic cancer cells. Furthermore, we have obtained promising results regarding the binding of PRDM1 and KDM4B to key players of pluripotency/differentiation in chemoresistant colon cancer cells.
Conclusions. Altogether, our data indicate that specific expression of chromatin modifier enzymes, most likely acting as epigenetic complexes, are key milestones of acquired resistance to conventional therapies. This work will pave the way for considering epienzyme-epienzyme interactions as potent drug targets that could circumvent cancer cell aggressiveness.
Citation Format: Elsa Hadj Bachir, Charles Poiraud, Hugo Claux, Soumaya El Moghrabi, Sonia Paget, Belinda Duchêne, Nicolas Jonckheere, Bernadette Neve, Emmanuelle Leteurtre, Isabelle Van Seuningen, Audrey Vincent. Epigenetic mechanisms involved in acquired resistance to combined chemotherapies in digestive cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2965.