6-substituted 3,4-benzocoumarins: a new structural class of inducers and inhibitors of CYP1A1-dependent activity.
A new synthetic route was utilized to prepare 6-substituted 3,4-benzocoumarins where the substituents were iodo, fluoro, trifluoromethyl, bromo, chloro, isopropyl, ethyl, t-butyl, methyl, hydrogen, amino, phenyl, or nitro; 3,4-naphthocoumarin was also synthesized. The relative affinities of these congeners for the aryl hydrocarbon (Ah) receptor were determined using rat hepatic cytosol and 2,3,7,8-[3H]tetrachlorodibenzo-p-dioxin ([3H]TCDD) as the radioligand. In addition, the Ah receptor agonist activity of the 6-substituted 3,4-benzocoumarins was determined from their concentration-dependent induction of ethoxyresorufin O-deethylase (EROD) activity. In contrast with many other structural classes of halogenated aromatics, there was not a correlation between the structure-binding versus structure induction relationships for the 6-substituted 3,4-benzocoumarins. These results suggested that some of these congeners may exhibit partial Ah receptor antagonist activities and this was investigated by determining the inhibitory effects of 6-substituted 3,4-benzocoumarins on TCDD-induced EROD activity in rat hepatoma H4II E cells in culture. Only four compounds (6-isopropyl, 6-phenyl, 6-fluoro, and 6-t-butyl) inhibited the TCDD-induced response (21.7 to 64.4% inhibition) and the mechanism of action of the most active inhibitor, 6-t-butyl-3,4-benzocoumarin, was further investigated. In contrast, with other partial Ah receptor antagonists such as alpha-naphthoflavone, cotreatment of rat hepatoma H4II E cells with 1 nM TCDD plus 1 and 10 microM 6-t-butyl-3,4-benzocoumarin did not result in decreased levels of the Ah receptor complex (liganded with TCDD). In addition, there was not significant inhibition of TCDD-induced CYP1A1 mRNA levels or protein as determined by Northern and Western blot analyses. The results suggest that 6-t-butyl-3,4-benzocoumarin or one of its metabolites is a post-translational inhibitor of CYP1A1-dependent enzyme (EROD) activity in this cell line and thus represents a novel Ah receptor-independent inhibition of CYP1A1.
Liu
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H
Department of Veterinary Physiology and Pharmacology, Texas A&M University, College Station 77843-4466.
Santostefano
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Lu
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Y
Safe
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D000818:Animals; D001483:Base Sequence; D001593:Benzyl Compounds / Q000378:metabolism / Q000494:pharmacology; D002467:Cell Nucleus / Q000378:metabolism; D003374:Coumarins / Q000378:metabolism / Q000494:pharmacology*; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology; D015342:DNA Probes; D018076:DNA, Complementary; D004790:Enzyme Induction; D007700:Kinetics; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D000072317:Polychlorinated Dibenzodioxins / Q000378:metabolism; D051381:Rats; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism; D013329:Structure-Activity Relationship
D001593:Benzyl Compounds; D003374:Coumarins; D065607:Cytochrome P-450 Enzyme Inhibitors; D015342:DNA Probes; D018076:DNA, Complementary; D009838:Oligodeoxyribonucleotides; D000072317:Polychlorinated Dibenzodioxins; D018336:Receptors, Aryl Hydrocarbon; D003577:Cytochrome P-450 Enzyme System