Organoid models for deciphering roles of the evolving landscape of epigenetic heterogeneity during aging in cancer development.

Background: Tumor initiation and development occur not necessarily by genetic changes alone, but in the context of the epigenome and cell microenvironment. Growing evidence indicate that cancer risk factors, such as aging and inflammation, may primarily modulate the epigenome, causing predisposition to cancer development by driver mutations. Thus, there is a need to study and model epigenetic changes preceding and associating with cancer development. We have developed ex vivo models for investigating the evolution and roles of DNA methylation changes during normal cell divisions and how these epigenetic changes play critical roles in early stages of tumor development. Results: We showed that spontaneous epigenetic changes, specifically promoter-DNA hypermethylation, have a very important role in tumor initiation by oncogenic driver mutations. We addressed the precursor role of aging-like spontaneous promoter-DNA hypermethylation in initiating tumorigenesis. Using mouse colon-derived organoids, we show promoter hypermethylation spontaneously arises in cells mimicking the human “aging-like” phenotype. The silenced genes activate the Wnt pathway, causing a stemlike state and differentiation defects. These changes render aged organoids profoundly more sensitive than young ones to transformation by BrafV600E producing the typical human proximal BRAFV600E-driven colon adenocarcinomas characterized by extensive, abnormal gene promoter CGI methylation or the methylator phenotype (CIMP). Conversely, CRISPR-mediated simultaneous inactivation of a panel of the silenced genes markedly sensitized to BrafV600E-induced transformation. We showed that “spontaneous” promoter hypermethylation, arising in an “aging-like” scenario, sufficiently affects genes with roles in negative regulation of Wnt pathway. Inactivation of these genes leads to increased stem cell state and defects in differentiation. Conclusion: Our studies tightly link aging-like epigenetic abnormalities to intestinal cell fate changes and predisposition to oncogene-driven colon tumorigenesis. The organoid-based model opens up an opportunity to study mechanisms underlying epigenetic heterogeneity arising during normal cellular processes and their role in cancer predisposition. Citation Format: Yong Tao, Byunghak Kang, Daniel Petkovich, Steve Baylin, Hariharan Easwaran. Organoid models for deciphering roles of the evolving landscape of epigenetic heterogeneity during aging in cancer development [abstract]. In: Proceedings of the AACR Special Conference on the Evolving Landscape of Cancer Modeling; 2020 Mar 2-5; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2020;80(11 Suppl):Abstract nr A36.