Organic isothiocyanates block the production of tumors induced in rodents by diverse carcinogens (polycyclic aromatic hydrocarbons, azo dyes, ethionine, N-2-fluorenylacetamide, and nitrosamines). Protection is afforded by α-naphthyl-, β-naphthyl-, phenyl-, benzyl-, phenethyl-, and other arylalkyl isothiocyanates against tumor development in liver, lung, mammary gland, forestomach, and esophagus. Many isothiocyanates and their glucosinolate precursors (β-thioglucoside, N-hydroxysulfate) occur naturally and sometimes abundantly in plants consumed by humans, e.g., cruciferous vegetables. Nevertheless, the possible contributions of isothiocyanates and glucosinolates to the well recognized protective effects against cancer of high consumptions of vegetables are unclear. The anticarcinogenic effects of isothiocyanates appear to be mediated by tandem and cooperating mechanisms: (a) suppression of carcinogen activation by cytochromes P-450, probably by a combination of down-regulation of enzyme levels and direct inhibition of their catalytic activities, which thereby lower the levels of ultimate carcinogens formed; and (b) induction of Phase 2 enzymes such as glutathione transferases and NAD(P)H: quinone reductase, which detoxify any residual electrophilic metabolites generated by Phase 1 enzymes and thereby destroy their ability to damage DNA. Since isothiocyanates block carcinogenesis by dual mechanisms and are already present in substantial quantities in human diets, these agents are ideal candidates for the development of effective chemoprotection of humans against cancer.
Presented at the 4th International Conference on Anticarcinogenesis & Radiation Protection, April 18–23, 1993, Baltimore, MD. Studies from the laboratory of the authors were supported by a grant from the National Cancer Institute, Department of Health and Human Services (PO1 CA 44530). Y. Z. is a Fellow of the Cancer Research Foundation of America.