Mouse models of colorectal cancer as preclinical models

Abstract

In this review, we discuss the application of mouse models to the identification and pre-clinical validation of novel therapeutic targets in colorectal cancer, and to the search for early disease biomarkers. Large-scale genomic, transcriptomic and epigenomic profiling of colorectal carcinomas has led to the identification of many candidate genes whose direct contribution to tumourigenesis is yet to be defined; we discuss the utility of cross-species comparative 'omics-based approaches to this problem. We highlight recent progress in modelling late-stage disease using mice, and discuss ways in which mouse models could better recapitulate the complexity of human cancers to tackle the problem of therapeutic resistance and recurrence after surgical resection.

Keywords: colorectal cancer; disease biomarker; mouse model; ome and omics; target identification; target validation.

Figure 1

Mouse models of advanced colorectal cancer (CRC) as research and preclinical tools. The development of genetically engineered mouse models (GEMMs) carrying gene mutations that closely match those found by deep‐sequencing of human colorectal carcinomas provide information on the homeostatic and tumourigenic role of a gene in the intestine. Orthotopic transplantation of select colorectal carcinoma cell lines to the caecum of immune‐deficient mice results in primary tumour growth and metastases to lymph nodes or liver. Prior to transplantation, colorectal carcinoma cell lines can be genetically manipulated to overexpress (cDNA vector) or inhibit (shRNA or CRISPR‐Cas9 vector) a gene of interest to rapidly assess its biological role or to validate potential therapeutic targets. Introducing a reporter gene, such as green fluorescent protein (GFP), to cells prior to transplantation allows in vivo monitoring of primary tumour or metastases growth, which is extremely useful when assessing responses to pharmacological agents or inducible genetic manipulation. Single‐cell suspensions from carcinomas can be flow‐sorted using cell‐specific markers to identify cells of interest, for example stem‐like cells for growth of organoids, or to gain further insight into the tumour cells of origin and their interactions with the microenvironment. Cultured cells can be utilised for drug sensitivity screens. Mouse models of advanced CRC can be used to screen for cancer driver genes and disease biomarkers.

Figure 2

Cross‐species comparative ‘omics’ approaches for colorectal cancer (CRC) gene, therapeutic target and early disease biomarker discovery. Despite their evolutionary distance, the gene content of the mouse and human genomes has been largely conserved through evolution and most cancer pathways are operative in both species. Sporadic, low‐level mutagenesis of Apc and Kras in the mouse colon results in a high frequency of invasive adenocarcinomas and liver metastases. Furthermore, serial biopsies of patient tumours is not realistic, but with the development of mouse colonoscopes to guide biopsy collection, this is now a possibility in mouse models. Cancer gene, therapeutic target and biomarker discovery in patient specimens is challenging because of genetic, epigenetic and environmental heterogeneity between patients. Since many of these variables can be controlled for in the inbred laboratory mouse, the comparison of human and mouse primary and metastatic colorectal cancer genomes, transcriptomes, epigenomes, and proteomes including ubiquitinomes, will provide a powerful reductionist tool for identification of the molecular alterations that drive CRC invasion and metastasis. CNV, copy number variation; TF, transcription factor.