Arylalkyl isothiocyanates, naturally-occurring and synthetic, are potent and versatile inhibitors of nitrosamine carcinogenesis. Phenethyl isothiocyanate (PEITC), a constituent of cruciferous vegetables, exhibited selective inhibitory effects against lung tumorigenesis of 4- (methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a tobacco-specific nitrosamine, in both rats and mice. A structural feature of arylalkyl isothiocyanate associated with the inhibitory efficacy was identified as the alkyl chain length. Thus, the newly synthesized 6-phenylhexyl isothiocyanate (PHITC) was at least 100 times more efficacious than PEITC toward the lung tumorigenesis of NNK in mice. At 0.2 mumol, one fiftieth of the NNK dose, PHITC blocked the lung tumor formation by more than 80%. The mechanism of inhibition was attributed to their ability to suppress the activity of cytochrome P-450 isozymes involved in the metabolic activation of NNK. These results suggest that arylalkyl isothiocyanates serve not only as good probes for cytochrome P-450s, but also as potential chemopreventive agents for lung cancer caused by smoking. In this renewal we will (1) synthesize 35S, 14C, and 13C-labeled PEITC and PHITC as probes for cytochrome P-450 enzyme binding studies; (2) compare the tissue distribution and metabolism of PHITC and PEITC in mice and rats; (3) continue structure-efficacy relationship studies by providing new compounds of varied structural features; (4) carry out bioassays to test their inhibitory effects against NNK, benzo(a)pyrene (B(a)P), and N- nitrosodimethylamine (NDMA); (5) test the validity of NNK-hemoglobin adduct as an early marker for the chemopreventive efficacy of synthetic and naturally-occurring isothiocyanates in mice and rats; (6) as a prelude to the human studies, examine the effects of vegetables rich in PEITC, benzyl isothiocyanate (BITC), and allyl isothiocyanate (AITC) on NNK-hemoglobin adduct formation in F344 rats; (7) examine the effects of vegetables which show promise in Aim 6 on NNK-hemoglobin adduct levels in smokers.
