Endocrine-Disrupting Activities of Flavones on Steroid Receptors: Structural Requirements and Synthesis of Novel Flavone with Improved Estrogenic Activity

<b>Background/Objectives:</b> Flavonoids are common ubiquitous components of plants and are consumed by humans and livestock in their diets. Many different activities have been proposed for a variety of flavonoids that play a role in the benefits of a plant-rich diet. On the downside, excessive exposure to some flavonoids comes with a risk of endocrine disruption. Our objective was to define the structural elements of flavones and selected other flavonoids required for endocrine-disrupting activities on each of four steroid receptors, estrogen, androgen, progesterone, and glucocorticoid receptors. <b>Methods:</b> This work presents a systematic screen for the hormone agonist or antagonist activity of a selected panel of flavonoids on estrogen, androgen, progesterone, and glucocorticoid receptors. The screen is focused on the positional requirements of hydroxyl substituents on the flavone backbone. <b>Results:</b> Each receptor exhibited a distinct pattern for structural requirements of the flavones to impact receptor signaling. The most active flavones exhibited antagonist activity on androgen and progesterone receptors with an IC₅₀ of 0.5 and 2 µM, respectively. Flavones only exhibited weak antagonism on glucocorticoid receptors. When active, flavones acted as estrogen receptor agonists. The findings were utilized to design and synthesize a novel flavone, 3-fluoro, 6,4'-dihydroxyflavone <b>14</b>, that displays increased potency as an estrogen agonist (EC₅₀~30 nM). Modeling of the binding of this novel flavone predicts increased preference for ERα versus ERβ relative to the estrogenic phytoestrogen, genistein. <b>Conclusions:</b> The structural requirements for flavones to act as estrogen agonists and antagonists of other steroid receptors are defined. The synthesis of a novel flavone offers potential for topical applications where systemic estrogen activity is undesired. However, the results highlight the potential for endocrine disruption when certain flavones are consumed in quantity as supplements.