A number of naturally occurring compounds and several related synthetic agents were confirmed to exert chemopreventive properties against
carcinogenesis in the digestive organs. Phenolic compounds, widely distributed as plant constituents, possess chemopreventive activities in tongue, liver, and large bowel of rodents. Of them, a simple phenolic
protocatechuic acid seems to be a promising compound. Organosulfur compounds contained in the cruciferous vegetables and known to activate detoxifying
enzymes are regarded as a candidate group for
cancer preventive agents. We proved a strong protective effect of S-methylmethanethiosulfonate, a constituent in these vegetables, on
azoxymethane (AOM)-induced large bowel
carcinogenesis. Some oxygenated
carotenoids (
xanthophylls) are reported to have antitumor effects. Naturally occurring
xanthophylls astaxanthin and
canthaxanthin have considerable preventive activities on
4-nitroquinoline-1-oxide (4-NQO)-induced tongue
carcinogenesis and AOM-induced large bowel
carcinogenesis. A novel synthesized retinoidal
butenolide,
KYN-54, which suppresses large bowel as well as tongue
carcinogenesis could be a useful agent for prevention of digestive organ
cancers. Some
trace elements are known to have
anticarcinogenic effects.
Magnesium hydroxide, a
protective agent in colorectal
carcinogenesis, inhibits c-myc expression and
ornithine decarboxylase activity in the mucosal epithelium of the intestine. Our results show that many agents with preventive effects in tongue, liver, and large bowel control
carcinogen-induced hyperproliferation of cells in these organs.
Carcinogens used to induce large bowel
cancers also induce apoptosis in the target sites.
Telomerase activity is increased in the tissues of preneoplastic as well as neoplastic lesions in experimental models such as dimethylbenz[a]
anthracene-induced oral
carcinogenesis in hamsters. These could be useful
biomarkers in studies for
cancer chemoprevention.