Cyclooxygenase-2 and its role in colorectal cancer development

Cyclooxygenase 2 (COX-2), also called prostaglandin endoperoxide synthase 2, is involved in colorectal tumor development. This review deals with particular questions raised in this field such as the mechanisms of COX-2 related tumor promotion, the role of the different types of cells (epithelial and interstitial) expressing COX-2, the factors that trigger COX-2 induction, and the clinical potential of selective COX-2 inhibitors to treat or prevent colorectal tumors. Several mechanisms of COX-2 related tumor promotion have been identified. Some are dependent on prostaglandin E(2) production (such as induction of cell proliferation, angiogenenis or local immunosuppression, inhibition of apoptosis, increase in cell motility) and others are not (such as carcinogen activation or malondialdehyde production). COX-2 expression has been demonstrated in epithelial cells of colorectal cancers and adenomas and also in interstitial cells. These cells correspond to macrophages and/or fibroblasts and endothelial cells. COX-2 expression in these interstitial cells participates in tumor development. Factors or events that trigger COX-2 expression include oncogene activation, antioncogene inactivation, cytokines, growth factors, some fatty acids, bile salts, and mucins. Finally, selective COX-2 inhibitors may be effective in preventing or treating colorectal adenomas or carcinomas. However, their real efficiency and the cost/benefit balance are currently evaluated, and no definite conclusion can be made at the moment.