The rice bran constituent tricin potently inhibits cyclooxygenase enzymes and interferes with intestinal carcinogenesis in ApcMin mice.

While brown rice is a staple dietary constituent in Asia, rice consumed in the Western world is generally white, obtained from brown rice by removal of the bran. Rice bran contains the flavone tricin, which has been shown to inhibit colon cancer cell growth. We tested the hypothesis that tricin interferes with adenoma formation in the Apc(Min) mouse. Mice received tricin (0.2%) in their American Institute of Nutrition 93G diet throughout their postweaning life span (4-18 weeks). Consumption of tricin reduced numbers of intestinal adenomas by 33% (P < 0.05) compared with mice on control diet. We explored whether tricin may exert its effect via inhibition of cyclooxygenase (COX) enzymes. Its effect on COX activity was assessed in purified enzyme preparations in vitro and its ability to reduce prostaglandin E(2) (PGE(2)) levels in human colon-derived human colon epithelial cell (HCEC) and HCA-7 cells in vitro and in Apc(Min) mice in vivo. Tricin inhibited activity of purified COX-1 and COX-2 enzyme preparations with IC(50) values of approximately 1 micromol/L. At 5 micromol/L, it reduced PGE(2) production in HCEC or HCA-7 cells by 36% (P < 0.01) and 35% (P < 0.05), respectively. COX-2 expression was reduced by tricin weakly in HCEC and unaffected in HCA-7 cells. PGE(2) levels in the small intestinal mucosa and blood of Apc(Min) mice that had received tricin were reduced by 34% (P < 0.01) and 40% (P < 0.05), respectively, compared with control mice. The results suggest that tricin should be further evaluated as a putative colorectal cancer chemopreventive agent.

Comparison of the effects of the chemopreventive agent resveratrol and its synthetic analog trans 3,4,5,4'-tetramethoxystilbene (DMU-212) on adenoma development in the Apc(Min+) mouse and cyclooxygenase-2 in human-derived colon cancer cells.

Naturally occurring molecules with putative cancer chemopreventive properties such as the phytoalexin resveratrol (3,5,4'-trihydroxystilbene) are lead molecules that guide the design of novel agents with improved pharmacologic properties. The synthetic resveratrol analog 3,4,5,4'-tetramethoxystilbene (DMU-212) has been shown to possess stronger antiproliferative properties in human colon cancer cells than resveratrol. We tested the hypothesis that DMU-212 is also a more potent inhibitor of adenoma development in the Apc(Min+) mouse, a model of human intestinal carcinogenesis. Apc(Min+) mice received either stilbene derivative with the diet (0.2%), and adenomas were counted after experiments were terminated. Resveratrol and DMU-212 decreased adenoma load by 27% and 24%, respectively, compared to untreated controls. Cyclooxygenase (COX) enzymes are important mechanistic targets of resveratrol, and we investigated whether DMU-212 interferes with the expression and activity of COX in human colon cells. Incubation of HCA-7 cancer cells for 24-96 hr with either stilbene derivative (1-50 microM) decreased prostaglandin E-2 (PGE-2) production, but only resveratrol decreased COX-2 protein expression. In mice, which received either stilbene derivative (0.2%) for 3 weeks with their diet, PGE-2 levels in the intestinal mucosa were reduced by between 45% and 62% compared to mice on control diet. While resveratrol inhibited enzyme activity in purified COX preparations, DMU-212 failed to do so. The PGE-2 decrease seen with DMU-212 in cells and in vivo is probably mediated via its metabolites. The results suggest that alteration of the resveratrol molecule to generate DMU-212 does not abrogate its ability to decrease adenoma number in Apc(Min+) mice or to interfere with PGE-2 generation in cells.