Chemoprevention of Lung Cancer by Isothiocyanates

Abstract

Naturally occurring and synthetic isothiocyanates are among the most effective chemopreventive agents known. A wide variety of isothiocyanates prevent cancer of various tissues including the rat lung, mammary gland, esophagus, liver, small intestine, colon, and bladder. Mechanistic studies have shown that the chemopreventive activity of isothiocyanates is due to favorable modification of Phase I and Phase II carcinogen metabolism, resulting in increased carcinogen excretion or detoxification and decreased carcinogen DNA interactions. In the majority of studies reported, the isothiocyanate must be present at the time of carcinogen exposure in order to observe inhibition of tumorigenesis. Our studies have focused on the naturally occurring isothiocyanates phenethyl isothiocyanate (PEITC) and benzyl isothiocyanate (BITC) as inhibitors of lung cancer. The carcinogens employed in these studies have been the major lung carcinogens in tobacco smoke — 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and benzo[a]pyrene (BaP). Combinations of chemopreventive agents that inhibit tumorigenesis by NNK and BaP in rodents may be effective in addicted smokers. PEITC is an effective inhibitor of lung tumor induction by NNK in F-344 rats and A/J mice. BITC but not PEITC inhibits BaP induced lung tumorigenesis in A/J mice. PEITC is a selective inhibitor of the metabolic activation of NNK in the rodent lung, and studies in smokers who consumed watercress, a source of PEITC, indicate that the metabolic activation of NNK is also inhibited by PEITC in humans. Combinations of chemopreventive agents active against different carcinogens in tobacco smoke may be useful in the chemoprevention of lung cancer.