Substituted flavones as aryl hydrocarbon (Ah) receptor agonists and antagonists

• Published in: Biochemical pharmacology Vol. 51; no. 8; pp. 1077 - 1087
• Main Authors: Lu, Yu-Fang, Santostefano, Michael, Cunningham, Bernadette D.M., Threadgill, Michael D., Safe, Stephen
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 26.04.1996; Elsevier Science
• Subjects: Ah receptor binding; Animals; Binding, Competitive; Biological and medical sciences; Breast Neoplasms; Cell receptors; Cell structures and functions; CYP1A1 induction/inhibition; Cytochrome P-450 CYP1A1 - biosynthesis; Cytochrome P-450 CYP1A1 - genetics; Cytosol - drug effects; Cytosol - metabolism; flavonoids; Flavonoids - pharmacology; Fundamental and applied biological sciences. Psychology; Humans; Microsomes, Liver - drug effects; Microsomes, Liver - metabolism; Miscellaneous; Molecular and cellular biology; Polychlorinated Dibenzodioxins - antagonists & inhibitors; Polychlorinated Dibenzodioxins - pharmacology; Rats; Receptors, Aryl Hydrocarbon - agonists; Receptors, Aryl Hydrocarbon - antagonists & inhibitors; RNA, Messenger - analysis; Tumor Cells, Cultured - drug effects; Tumor Cells, Cultured - metabolism; Ah receptor binding; EROD; αNF; DRE; HAP; TCDF; Ah; TCDD; flavonoids; MCDF; CYP1A1 induction/inhibition; Agonist; Flavones; Cytochrome P450; Flavonoid; Characterization; Ah receptor; Biological fixation; Structure activity relation; Halogen compound; Plant origin; Established cell line; Antagonist; Structure
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/0006-2952(96)00063-9

The structure-dependent aryl hydrocarbon (Ah) receptor agonist and antagonist activities of the following substituted flavones were investigated: flavone, 4′-methoxy-, 4′-amino-, 4′-chloro-, 4′-bromo-, 4′-nitro-, 4′-chloro-3′-nitro-, 3′-amino-4′-hydroxy-, 3′,4′-dichloro-, and 4′-iodoflavone. The halogenated flavones exhibited competitive Ah receptor binding affinities ( IC 50 = 0.79 to 2.28 nM) that were comparable to that observed for 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) (1.78 nM). The compounds also induced transformation of the rat cytosolic Ah receptor and induced CYP1A1 gene expression in MCF-7 human breast cancer cells. However, despite the high Ah receptor binding affinities for these responses, the halogenated flavones were > 1000 times less active than TCDD for the other responses. Moreover, for other substituted flavones, there was no correlation between Ah receptor binding affinities and their activities as Ah receptor agonists. For example, 4′-aminoflavone induced CYP1A1 mRNA levels in MCF-7 cells but exhibited relatively low Ah receptor binding affinity ( IC 50 = 362 nM) and did not induce transformation of the rat cytosolic Ah receptor. All of the substituted flavones inhibited TCDD-induced transformation of the Ah receptor, and 4′-iodoflavone, an Ah receptor agonist at high concentrations (1–50 μM), inhibited the transformation at concentrations as low as 0.05 and 0.5 μM. Subsequent interaction studies with TCDD and 4′-iodoflavone confirmed that the latter compound inhibits induction of CYP1A1 gene expression by TCDD in MCF-7 cells. The results obtained for the substituted flavones suggest that within this structural class of compounds, various substituent groups can affect markedly the activity of each individual congener as an Ah receptor agonist or antagonist. These substituent-dependent differences in activity may be related to ligand-induced conformational changes in the Ah receptor complex and/or support the proposed existence of more than one form of the Ah receptor.