6-substituted 3,4-benzocoumarins: a new structural class of inducers and inhibitors of CYP1A1-dependent activity.

Abstract

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.

• Authors: H Liu, M Santostefano, Y Lu, S Safe
• Journal: Archives of biochemistry and biophysics (Arch Biochem Biophys) Vol. 306 Issue 1 Pg. 223-31 (Oct 1993) ISSN: 0003-9861 [Print] United States
• PMID: 8215408 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Benzyl Compounds
• Coumarins
• Cytochrome P-450 Enzyme Inhibitors
• DNA Probes
• DNA, Complementary
• Oligodeoxyribonucleotides
• Polychlorinated Dibenzodioxins
• Receptors, Aryl Hydrocarbon
• Cytochrome P-450 Enzyme System

Topics

• Animals
• Base Sequence
• Benzyl Compounds (metabolism, pharmacology)
• Cell Nucleus (metabolism)
• Coumarins (metabolism, pharmacology)
• Cytochrome P-450 Enzyme Inhibitors
• Cytochrome P-450 Enzyme System (biosynthesis, metabolism)
• Cytosol (enzymology)
• DNA Probes
• DNA, Complementary
• Enzyme Induction
• Kinetics
• Liver (enzymology, metabolism)
• Male
• Molecular Sequence Data
• Oligodeoxyribonucleotides
• Polychlorinated Dibenzodioxins (metabolism)
• Rats
• Receptors, Aryl Hydrocarbon (metabolism)
• Structure-Activity Relationship