Abstract 58: Highly tractable stem cell-driven mouse model of colonic neoplasia with features of familial adenomatous polyposis
Authors: Powell Anne E. , Vlacich Gregory , Zhao Zhen-Yang , McKinley Eliot , Karns Rebekah , Washington Mary Kay , Manning Henry Charles , Aronow Bruce , Coffey Robert 
Published: May 2015

Abstract
The ApcMin mouse, which harbors a germline mutation in Apc, is the most widely utilized mouse model of colorectal neoplasia; a major drawback to this model is that the tumors arise mainly in the small intestine. In addition, tumorigenesis occurs randomly within the epithelium, complicating examination of the precise tumor cell-of-origin and local environmental cues that promote tumorigenesis. Given the growing importance of stem cells in tumor initiation, it is desirable to build models that target this population. To this end, it is surprising that elimination of one Apc allele in Lgr5+ stem cells does not result in subsequent loss of heterozygosity (LOH) and tumor formation.
We recently reported that Lrig1, a pan-ErbB inhibitor, marks a population of stem cells at the base of colonic crypts. To examine the dynamics of colonic tumor initiation and progression, and to compare our disease model with human patients, we examined tamoxifen-induced Lrig1-CreERT2/+;Apcfl/+ mice where Apc LOH occurs in the Lrig1+ stem cells yielding high-grade lesions, faithfully recapitulating this key genetic event in human colon cancer (CRC) initiation. Colonic lesions grow into the luminal space over the span of 50-100 days and can be visualized by both colonoscopic and FDG-PET non-invasive imaging. This inducible mouse model also harbors extra-colonic features of human Familial Adenomatous Polyposis (FAP), an autosomal dominant variant of CRC caused by germline mutations in APC. With stochastic LOH, affected individuals develop colonic adenomas that invariably progress to CRC and many patients develop peri-ampullary tumors, gastric abnormalities, desmoid and soft tissue tumors, along with characteristic eye findings. To further examine the molecular parallels between the mouse and human colonic tumors, we performed RNA-Seq analysis and validated selected targets with immunofluorescence. Interestingly, a number of genes were found to be differentially regulated in the Lrig1-CreERT2/+;Apcfl/+ colonic tumors compared to ApcMin colonic tumors, despite both models being driven by the Wnt/β-catenin pathway.
This model is the closest mimic of FAP to-date and represents a tractable system to test the efficacy of innovative therapeutic interventions whose efficacy can be monitored over time by colonoscopy and non-invasive imaging modalities. Our inducible system also allows a detailed dissection of the pre-neoplastic spatiotemporal events that occur following removal of one Apc allele in the mouse colon. To complement these studies, we are currently examining both Lgr5+ and Lrig1+ stem cell participation in colonic tumor initiation both in vivo and ex vivo at super resolution, using our newly developed Lrig1-Apple and Lrig1-Apple/+;Lgr5-EGFP fluorescent reporter mice.
Citation Format: Anne E. Powell, Gregory Vlacich, Zhen-Yang Zhao, Eliot McKinley, Rebekah Karns, Mary Kay Washington, Henry Charles Manning, Bruce Aronow, Robert Coffey. Highly tractable stem cell-driven mouse model of colonic neoplasia with features of familial adenomatous polyposis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 58. doi:10.1158/1538-7445.AM2014-58