Isothiocyanates as cancer chemopreventive agents: Their biological activities and metabolism in rodents and humans

Isothiocyanates (ITCs) are a group of naturally occurring compounds that occur as thioglucoside conjugates, termed glucosinolates, in plants and cruciferous vegetables such as watercress, Brussels sprouts, broccoli, cabbage, kai choi, kale, horseradish, radish and turnip. ITCs inhibit the development of tumors in many of the experimental models investigated, and are being investigated as possible chemopreventive agents for specific human cancers. The goal of this review is to provide a mechanistic understanding for the biological activities of ITCs and to relate the metabolism of ITCs to their action as chemopreventive agents. In vivo animal studies have been conducted to address issues of tissue disposition, pharmacokinetics, and metabolism of ITCs. Methods for analysis of ITCs and their metabolites in urine and plasma have been developed. The metabolism of several naturally occurring ITCs as constituents of foodstuffs or as drugs has also been investigated in human studies. Finally, based on recent epidemiological studies, the role of dietary consumption of vegetables containing ITCs in prevention of human cancers and human cancer susceptibility is discussed.