Structure-activity relationships of arylalkyl isothiocyanates for the inhibition of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone metabolism and the modulation of xenobiotic-metabolizing enzymes in rats and mice

• Published in: Carcinogenesis (New York) 1993-06, Vol.14 (6), p.1167-1173
• Main Authors: Guo, Zuyu, Smith, Theresa J., Wang, Erjia, Eklind, Karin I., Chung, Fung-Lung, Yang, Chung S.
• Format: Article
• Language: English
• Subjects: Animals; Anticarcinogenic Agents - chemistry; Biological and medical sciences; Carcinogenesis, carcinogens and anticarcinogens; Carcinogens - metabolism; Chemical agents; Female; Isothiocyanates; Male; Medical sciences; Mice; Microsomes - enzymology; Microsomes, Liver - enzymology; Nitrosamines - metabolism; Oxidation-Reduction; Rats; Rats, Inbred F344; Structure-Activity Relationship; Thiocyanates - chemistry; Tumors
• ISSN: 0143-3334; 1460-2180
• DOI: 10.1093/carcin/14.6.1167

Many arylalkyl isothiocyanates are potent inhibitors of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumorigenesis in rats and mice. In the mouse, 4-phenylbutyl isothiocyanate (PBITC) and 6-phenylhexyl isothiocyanate (PHTTC) exhibited greater inhibition than benzyl isothiocyanate (BITC) and phenethyl isothiocyanate (PEITC). The present study was conducted to investigate the structure-activity relationships of these four arylalkyl isothiocyanates for their inhibition of NNK oxidation and effects on xenobiotic-metabolizing enzymes in rats and mice. A single dose (0.25 or 1.00 mmol/kg) of each isothiocyanate was given to F344 rats 6 or 24 h before death. The rates of NNK oxidation were decreased in microsomes from the liver, lung and nasal mucosa of rats. Generally, PEITC was more potent than BITC but less potent than PBITC and PHlTC. The rates in rat liver microsomes were decreased at 6 h but recovered or increased at 24 h; and the rates in rat lung microsomes were markedly decreased at both 6 and 24 h; and the rates in rat nasal mucosa microsomes were also significantly decreased. The same treatment decreased the rat liver N-nitrosodimethyl-amine demethylase activity dramatically and ethoxyresorufin O-dealkylase and erythromycin N-demethylase activities moderately. However, the rat liver microsomal pentoxy-resorufin O-dealkylase activity was decreased at 6 h but increased at 24 h, with PEITC showing the most marked induction. The rat liver NAD(P)H: quinone oxidoreductase activity was increased 1.4- to 3.3-fold, with PEITC being most effective; and the glutathione S-transferase activity was increased slightly. Similarly, at a single dose of 0.25 mmol/kg (5 μmol/mouse) 24 h before death, PEITC, PBITC, PHlTC but not BITC, decreased NNK oxidation in mouse lung microsomes by 40–85%, with PBITC and PHlTC showing greater inhibition. Furthermore, all four isothiocyanates extensively inhibited NNK oxidation in rat lung and nasal mucosa microsomes as well as mouse lung microsomes in vitro, with PEITC (IC50 of 120–300 nM) being more potent than BITC (IC50 of 500–1400 nM) but less potent than PBITC and PHITC (IC50 of 15–180 nM). PHITC was a very potent competitive inhibitor of NNK oxidation in mouse lung microsomes with apparent K1 values of 11–16 nM. These results indicate that PBITC and PHITC are more potent inhibitors of NNK bioactivation in rats and mice than PEITC. In addition, these arylalkyl isothiocyanates could be effective in protecting a