genistein and daidzein

While estrogen-related receptors (ERRalpha, ERRbeta, and ERRgamma) share a high amino acid sequence homology with estrogen receptors (ERs), estrogens are not ligands of ERRs. Structure-function studies from this and other laboratories have revealed that ERRs have small ligand-binding pockets and have provided evidence to show that these receptors can activate gene transcription in a constitutive manner. To address the question as to whether there is any agonist for ERRs, our laboratory recently performed virtual ligand screening on ERRalpha that predicted flavone and isoflavone phytoestrogens to be ligands of this receptor. Our mammalian cell transfection and mammalian two-hybrid experiments revealed that three isoflavones (genistein, daidzein, and biochanin A) and one flavone (6,3',4'-trihydroxyflavone) behaved as agonists of ERRs. These phytoestrogens induced the activity of ERRalpha at concentrations that are comparable to those for the activation of ERalpha and ERbeta. In this study, we also used the results of ERRalpha ligand-binding site mutant, F232A, to verify our ERRalpha hypothetical computer model. Our recent ERR research has determined for the first time that flavone and isoflavone phytoestrogens are agonists of ERRs. In addition, our studies have demonstrated that an approach that combines structure-based virtual screening and receptor functional assays can identify novel ligands of orphan nuclear receptors.

Topics: Binding, Competitive; Computer Simulation; Databases, Factual; ERRalpha Estrogen-Related Receptor; Flavones; Flavonoids; Genistein; HeLa Cells; Humans; Isoflavones; Ligands; Luciferases; Models, Molecular; Molecular Structure; Phytoestrogens; Plant Preparations; Receptors, Cytoplasmic and Nuclear; Receptors, Estrogen; Recombinant Fusion Proteins; Structure-Activity Relationship; Transfection

Multidrug resistance (MDR), caused by overexpression of either P-glycoprotein or the multidrug resistance protein (MRP), is characterised by a decreased cellular drug accumulation due to an enhanced drug efflux. In this study, we examined the effects of genistein and structurally related (iso)flavonoids on the transport of rhodamine 123 (Rh123) and daunorubicin in the MRP-overexpressing MDR lung cancer cell lines COR-L23/R and MOR/R. Genistein, genistin, daidzein and quercetin showed major differences in effects on Rh123 vs daunorubicin transport in the MRP-mediated MDR cell lines: the accumulation of daunorubicin was increased, whereas the accumulation of Rh123 was decreased by the flavonoids. The depolarisation of the membrane potential caused by genistein might be involved in the acceleration of the efflux of Rh123 measured in the MRP-overexpressing cell lines. These observations should be taken into account when using fluorescent dyes as probes for determination of transporter activity as a measure of MDR.

Topics: Antimetabolites, Antineoplastic; Daunorubicin; Drug Resistance, Multiple; Genistein; Humans; Isoflavones; Monosaccharide Transport Proteins; Quercetin; Rhodamine 123; Rhodamines; Tumor Cells, Cultured