Abstract PR03: An integrative mouse model of gastric premalignancy that combines early genomic alterations with disease-relevant carcinogenic exposure
Authors: Sethi Nilay , Kikuchi Osamu , Duronio Gina , Stachler Matthew , McFarland James , Bass Adam J. 
Published: June 2022

Abstract
Carcinogenesis from dietary byproducts and inflammation is the strongest risk factor for gastric cancer, which carries a poor prognosis owing to its advanced stage at the time of diagnosis. We therefore have a critical need to characterize key molecular mechanisms of carcinogenesis at the earliest conception of this ominous disease. To this end, we designed an integrative mouse model that combines two essential contributors to the premalignant state: (1) disease-relevant carcinogenic exposure and (2) an early genomic alteration. We recently discovered that, contrary to the previously accepted paradigm, TP53 is mutated early in malignant progression, often occurring before dysplasia. Based on these findings, we adapted a transgenic mouse to conditionally delete Trp53 in the Lgr5+ stem cell compartment of the stomach, and then exposed these mice to drinking water containing the bile acid deoxycholate (DCA), a principal component of gastroduodenal reflux, and nitroso-compound MNU, a disease-relevant carcinogen. Deletion of Trp53 in gastric stem cells of untreated mice did not lead to detectable premalignant lesions. By contrast, inactivation of Trp53in Lgr5+ stem cells of DCA/MNU-treated mice led to a 3.5-fold increase in premalignant lesions compared to wild-type control mice after one year. Whole-exome sequencing of gastric lesions showed a mutational signature associated with MNU exposure, validating that carcinogenesis contributed to the emergence of premalignant gastric lesions. Three-dimensional organoid culture recapitulates epithelial cell orientation, differentiation, and behavior in vitro. To characterize and functionally study the epithelial compartment of premalignant lesions, gastric organoids were generated from the integrative mouse model, capturing critical intermediate states in the evolution of gastric premalignancy such as genome doubling. Unbiased gene expression analyses revealed that inactivation of Trp53 in gastric premalignancy leads to activation of interferon, WNT/stemness, and cell cycle checkpoint pathways. CDKN2A was the most notable cell cycle regulator induced by Trp53 loss, which prevented progression of disease and ultimately endowed a selective pressure for inactivation in route to cancer. Indeed, genomic analysis of patient data revealed that CDKN2A and TP53 are significantly coaltered in human gastric cancer. These data demonstrate that integrating early genomic events with disease-relevant carcinogenic exposure can generate a more faithful mouse model of the premalignant state than could be achieved by either method alone. By defining the precise molecular mediators that collaborate with carcinogenesis to endorse premalignant gastric lesions, we hope to inform the design of effective prevention strategies tailored to definitively treat patients before a window of opportunity has closed.
This abstract is also being presented as Poster A37.
Citation Format: Nilay Sethi, Osamu Kikuchi, Gina Duronio, Matthew Stachler, James McFarland, Adam J. Bass. An integrative mouse model of gastric premalignancy that combines early genomic alterations with disease-relevant carcinogenic exposure [abstract]. In: Proceedings of the AACR Special Conference on Environmental Carcinogenesis: Potential Pathway to Cancer Prevention; 2019 Jun 22-24; Charlotte, NC. Philadelphia (PA): AACR; Can Prev Res 2020;13(7 Suppl): Abstract nr PR03.