The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that promotes the expression of phase I and II xenobiotic chemical metabolizing enzyme genes, including the cytochrome P450 (CYP) isoforms CYP1A1 and CYP1A2. α-Naphthoflavone is a flavone that modulates xenobiotic metabolism at several points. It antagonizes AhR, blocking the expression of phase I and II genes at nanomolar concentrations, although it can agonize AhR at higher concentrations (10 μM). α-Naphthoflavone inhibits CYP19 (aromatase), CYP1A1, CYP1A2, and CYP1B1 (IC50s = 500, 60, 6, and 5 nM, respectively), whereas it activates CYP3A4 (Kd = 7.4 μM). Dietary α-naphthoflavone can contribute to carcinogenesis in the presence of synthetic estrogens.
