Comparative ability of ibuprofen and N-(4-hydroxyphenyl)retinamide to inhibit development of rat mammary adenocarcinomas associated with differential inhibition of gene expression of cyclooxygenase isoforms.

A rodent model of carcinogen-induced mammary tumorigenesis was used to determine the comparative growth inhibitory effects of dietary administration of either 1000 mg/kg of the non-steroidal antiinflammatory drug (NSAID) ibuprofen or 1.5 mmol/kg of the synthetic retinoid N-(4-hydroxyphenyl)-retinamide (4-HPR). In addition, the effects of these compounds on gene expression and protein production of the two isoforms of the cyclooxygenase (COX) gene which are responsible for prostaglandin production were examined. Experimental diets were provided to rats beginning at 7 days prior to administration of a single intragastric dose of 15 mg dimethylbenz[a]anthracene (DMBA) and diets were provided ad libitum until the study was terminated at 16 weeks later. Ibuprofen significantly decreased levels of gene expression of both COX-1 and COX-2 (p < 0.01). Although dietary 4-HPR did significantly diminish levels of COX-1 gene expression (p < 0.01) in rat mammary adenocarcinomas, this synthetic retinoid did not significantly inhibit COX-2 gene expression. COX-1 protein was localized to endothelial cells, infiltrating inflammatory cells, and tumor cells, while COX-2 protein was detected primarily within tumor cells. Although ibuprofen was more effective in inhibiting COX-2 gene expression than 4-HPR, ibuprofen and 4-HPR were equally effective in inhibiting development of carcinogen-induced mammary adenocarcinomas.