JTE-522, a selective cyclooxygenase-2 inhibitor, inhibits induction but not growth and invasion of 1,2-dimethylhydrazine-induced tubular adenocarcinomas of colon in rats.

We have previously demonstrated that JTE-522, a selective cyclooxygenase-2 (COX-2) inhibitor, inhibited development of aberrant crypt foci (ACF) in rats, a putative preneoplastic lesion in colon, and suggested its inhibitory potential in rat colon carcinogenesis. To evaluate the chemopreventive properties of JTE-522, the present study was design to evaluate the inhibitory effects of JTE-522 on rat colon tumorigenesis induced by 1,2-dimethylhydrazine (DMH). Rats at 6 weeks of age were divided into 4 groups. One week after the start of the experiment, all rats received DMH by s.c. injection at a dose of 40 mg/kg body weight once a week for 4 successive weeks. As the initiation and postinitiation treatment groups, groups 1-3 were fed diets containing 0, 50, or 150 ppm JTE-522, respectively, from the start of the study to the end. As the postinitiation treatment group, group 4 was given 150 ppm JTE-522 from 1 week after the last DMH injection to the end of the study. Forty weeks after the start of the experiment, administration of 150 ppm JTE-522 during both initiation and postinitiation stages significantly inhibited the incidences of tubular adenocarcinomas and total carcinomas, as well as total tumors in the colon. The inhibitory effect of JTE-522 was most prominent for tubular adenocarcinomas, but was not observed in the nontubular carcinomas (signet-ring cell and mucinous carcinomas). Almost equal inhibitory effects on tubular adenocarcinomas were also observed in the rats given 150 ppm JTE-522 during the postinitiation stage, suggesting that its major anticancer action is at the postinitiation phase. However, JTE-522 had no effect on the size or invasive extent of tubular adenocarcinomas. Furthermore, microarray analyses revealed that JTE-522 had no effect on gene expression levels in DMH-induced tubular adenocarcinomas. These findings suggest that JTE-522 possesses chemopreventive activity against induction but not progression of tubular adenocarcinomas in rat colon. In view of the significant inhibitory effects of JTE-522 on ACF, its major anticancer action may occur in the postinitiation stage but before the malignant conversion stage of DMH-induced colon carcinogenesis.