Abstract 258: An organoid model for investigating Lynch syndrome tumorigenesis

Abstract

Abstract Lynch syndrome (LS) is the most common inherited predisposition for developing colon cancer and is caused by germline variants in mismatch repair (MMR) genes. Still, the mechanism of tumorigenesis in these patients is unknown. An LS patient inherits one defective copy of an MMR gene. At some point in their lifetime, the remaining wild-type allele is lost in a cell rendering it entirely MMR deficient. MMR deficiency increases mutational rate and the chance of acquiring mutations in an oncogene or tumor suppressor that drive tumor initiation. However, loss of MMR in cells also leads to increased resistance to certain forms of DNA damage. Thus, our question is whether this phenotype imparts a selective advantage in colonic cells that may lead to clonal expansion of MMR-deficient cells as a first step towards tumorigenesis in LS patients. To test this, we are using stem cell-derived human colonic organoids and CRISPR gene editing to examine competition between MMR-deficient (MMRd) and MMR-proficient (MMRp) colonic cells over time. We have initially observed that MMRd stem cells are much more efficient at generating colonic organoids that grow larger and survive longer, consistent with our hypothesis of a selective advantage. To mimic the spontaneous loss of heterozygosity that occurs in LS patients’ colonic crypts, we are forming organoids from differentially labeled MMRd and MMRp stem cells. Live fluorescent imaging of individual organoids is used to quantify changes in cell population over time. Preliminary data indicate that MMRd cells can outgrow MMRp cells resulting in a shift in the ratio of green to red cells over a two-week time period while challenged with a DNA-damaging agent. These results suggest that loss of MMR function imparts an immediate selective advantage in colonic cells in response to DNA damage. Citation Format: Caroline Guild, Christopher Heinen, Samantha Nadeau. An organoid model for investigating Lynch syndrome tumorigenesis [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 258.