Aromatase inhibition by flavonoids

Abdel Rahim Ibrahim, Yusuf J Abul-Hajj

Research output: Contribution to journalArticlepeer-review

156 Scopus citations


Several synthetic flavones were found to inhibit the aromatization of androstenedione to estrone catalyzed by human placental microsomes. Twenty-one compounds were tested and the IC50 of the most active were: flavone, 10 μM; 7-hydroxyflavone, 0.5 μM; 7,4′-dihydroxyflavone, 2.0 μM; flavanone, 8.0 μM; and 4′-hydroxyflavanone, 10 μM. Most of the others had IC50 values ranging from 80 to 200 μM. These findings show that 4′-hydroxylation results in either no change or very little change in IC50 for flavanone, isoflavone and isoflavanone as well as other ring A hydroxylated flavones. Derivatives of flavone with a hydroxyl substituent at position 5, 6 and 7 were also screened. 7-Hydroxy-flavone (11) was the most effective competitive inhibitor (IC50=0.5 μM) with an apparent Ki value of 0.25 μM. Compound 11 also induced a change in the absorption spectrum of the aromatase cytochrome P-450 which is indicative of substrate displacement. The relative binding affinities of the flavonoid analogs were determined and only ring A and ring B dihydroxylated analogs were found to bind to the estrogen receptor.

Original languageEnglish (US)
Pages (from-to)257-260
Number of pages4
JournalJournal of Steroid Biochemistry and Molecular Biology
Issue number1
StatePublished - Oct 1990


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