Cancer Prevention Program
Aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) are effective chemopreventive agents against colorectal adenomas, precursors of colorectal cancer. NSAIDs exert their chemopreventive effects through the inhibition of the cyclooxygenases (COX)1 and 2, key enzymes in the prostaglandin synthesis pathway. Initial studies suggest that genetic variation in prostaglandin synthesis can affect colorectal carcinogenesis. One of the main downstream products of the COX enzymes is prostaglandin E2 (PGE2). PGE2 is the most upregulated prostaglandin in colorectal cancer, and experimental studies directly implicate PGE2 in the development of colorectal neoplasia. Recent studies have shown that PGE2 signaling can activate epidermal growth factor receptor (EGFR) signaling, a second pathway of key importance in colorectal carcinogenesis. This study will evaluate the association between colorectal adenomas and genetic variability in enzymes, receptors, and signaling molecules in the prostaglandin/EGFR pathways. We will focus on proteins that: a) regulate PGE2 levels (prostaglandin E synthase (PGES) and 15- hydroxyprostaglandin dehydrogenase (PGDN); b) bind to PGE2 at the cell surface (receptors EP1, EP2, and EP4); or c) are involved in PGE2 cross-talk with EGFR signaling (Src and EGFR).
We will genotype individuals in an existing case-control study of 540 adenoma cases and 640 polyp-free controls. Participants were recruited through gastroenterology practices in Minnesota and information on health status, family history, dietary intake, physical activity, and NSAID use has been obtained. All patients underwent a full colonoscopy and completed questionnaires prior to diagnosis. Several of the target genes have been resequenced for polymorphism discovery (PGES, EP1, 2, and 4, EGFR) and resequencing of the other target genes (PGDN, Src) is underway. this study design maximizes available information regarding genetic variability in the prostaglandin/EGFR pathways by examining common haplotypes with tag SNPs, as well as specific candidate polymorphisms. As a secondary aim, interactions with NSAID use will be investigated to determine responses of genetically-defined subgroups. Gene-gene interactions will also be evaluated, providing a comprehensive analysis of the role of genetic variation in this pathway. This study of genetic variation in the prostaglandin/EGFR pathway will provide insights into the complex process of colorectal carcinogenesis, and increase understanding of the pharmacogenetics of NSAID chemoprevention.