Abstract 24: Oncogenic KrasG12D and Cdkn2a/p16 knockout in LGR5 expressing progenitor cells synergize to advance adenoma and adenocarcinoma phenotypes in murine small intestine
Authors: Seckar Tyler , Sun Jing , Komissarova Elena V. , Sepulveda Jorge L. , Wang Timothy L. , Sepulveda Antonia R. 
Published: April 2023

Abstract
Background: KRAS activating mutations are reported in 42-54% and inactivation of CDKN2A/p16 in 14-30% of human small intestinal adenocarcinomas, suggesting a role in small intestine adenocarcinogenesis. The phenotypic effects of oncogenic KRAS and p16 loss have not been well characterized in small intestine (SI) adenocarcinogenesis. We targeted LGR5-expressing progenitor cells residing in intestinal crypts for conditional activation of Kras and/or Cdkn2a/p16 deletion to generate a murine model to study the single and combined effects of KRAS and p16 alterations driving gastrointestinal tumorigenesis. We hypothesized that oncogenic Kras and loss of Cdkn2a/p16 drives adenoma-adenocarcinoma sequence in murine SI.
Methods: We generated mice with conditional knockout of Cdkn2a/p16 (p16del: IL1bwt/tg;Lgr5-Cre+/−;p16fl/fl;Kraswt/wt), conditional expression of oncogenic KrasG12D (IL1bwt/tg;Lgr5-Cre+/−;KrasG12D/wt), or both alterations (p16del+KrasG12D: IL1bwt/tg;Lgr5-Cre+/−;p16fl/fl;KrasG12D/wt), in mice carrying the human interleukin 1 beta (IL1B) and expressing modified Cre under the Lgr5 promoter. Our control murine model expresses wild type p16 and KRAS (p16wt+Kraswt: IL1bwt/tg;Lgr5-Cre+/−;p16wt/wt;Kraswt/wt). These mice were initially generated to study esophageal adenocarcinogenesis and express the IL1b transgene in esophagus but not in SI. All mice were given bile acid in drinking water daily and were treated with tamoxifen to activate Cre in Lgr5-positive gastrointestinal epithelial progenitor cells. Mice were euthanized and gross and histologic alterations in the SI were examined from 4 to 21 months of age. 3D organoids were isolated from the SI of each mouse model.
Results: We examined 89 mice from 4 to 12 months of age. Mice with KRAS activation (KrasG12D) alone infrequently developed SI duodenal adenomas (6.25%: 1/16) compared to 50% (9/18) of mice carrying the combined P16del+KrasG12D genotypes (P=0.005). No adenomas were seen in 27 control and 28 p16del mice. Adenomas with high-grade dysplasia, intramucosal adenocarcinoma, and invasive adenocarcinoma were seen only in older p16del+KrasG12D mice (13-21 months). Single or multiple adenomas and adenocarcinomas were observed only in the duodenal segment of SI and not in the colon. 3D organoids isolated from each mouse model reproduce the intestinal histologic phenotype.
Conclusions: Loss of Cdkn2a/p16 and KRASG12D expression synergistically advances adenoma-adenocarcinoma tumorigenesis in the SI duodenum, providing a murine model that recapitulates SI adenocarcinogenesis in vivo. 3D SI organoids provide useful in vitro models for mechanistic studies of SI adenocarcinogenesis. These in vivo and in vitro models will enable identification of key molecular pathways that may be targeted with novel therapies for this rare cancer.
Citation Format: Tyler Seckar, Jing Sun, Elena V. Komissarova, Jorge L. Sepulveda, Timothy L. Wang, Antonia R. Sepulveda. Oncogenic KrasG12D and Cdkn2a/p16 knockout in LGR5 expressing progenitor cells synergize to advance adenoma and adenocarcinoma phenotypes in murine small intestine [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 24.