Molecular Profiling of Prevention Strategies Using Rodent Models of Colorectal Cancer

Colorectal cancer (CRC) is the third most lethal cancer worldwide, caused by both genetic and environmental exposures, with underlying mechanisms that dovetail genetic, epigenetic, metabolomic, and gut microbiome influences. Adenomatous polyposis coli (Apc) is a tumor suppressor and a negative regulator of Wnt/b-catenin signaling, found mutated in over 70% of CRC cases. The current dissertation used two rodent models, one genetic and one environmental, in the context of cancer prevention to study the etiology of CRC and provide preclinical mechanistic insights. The environmental model incorporated a cooked meat derived mutagen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), to mediate multi-organ carcinogenesis in the rat. The study focused on microRNA (miRNA) profiling in the PhIP model. miRNAs are stable negative regulators of gene targets, and play important roles in cancer and pluripotency. Rat tumor profiles and human pan-cancer datasets defined a miRNA signature of PhIP-induced multi-organ tumorigenesis. The miR-21^high/miR-126^low/miR-29c^low/miR-215^low/miR-145^low signature was associated with poor survival and reduced Klf4 levels, being predictive of possible environmental exposure and paradigm-shifting from ‘genotoxic’ to epigenetic regulation of dietary heterocyclic amines. A genetic angle was provided by the Apc-mutant polyposis in rat colon (Pirc) model, which harbors a large number of polyps in the colon, and recapitulates human familial adenomatous polyposis (FAP). The second study employed sequencing technology for mRNA, miRNA and 16S rRNA to assess the crosstalk between host, gut microbiota, and a cancer preventive diet in the Pirc model. Dietary spinach reduced tumor outcomes significantly in the Pirc model, and reversed host genetic effects on microbiota. mRNA and miRNA analyses revealed the importance of an inflammatory response in Pirc tumorigenesis, and implicated specific miRNA-mRNA associations, such as miR-145/Serpine1 and miR-34a/Klf4. The third study utilized untargeted metabolomics to investigate metabolic changes in the Pirc model along with the prevention effects of dietary spinach. The preliminary results indicated purine and lipid metabolism are important for tumorigenesis and prevention of colorectal cancer. Current technologies are providing new insights at the molecular level, incorporating ‘big data’ with genetic and phenotypic read-outs, to identify underlying leads associated with a designed dietary prevention strategy, which might help to mitigate the worldwide burden of CRC