Isoflavonoids from Erythrina poeppigiana: evaluation of their binding affinity for the estrogen receptor

Glyceollins from soybean: Their pharmacological effects and biosynthetic pathways

Flavonoids are a highly abundant class of secondary metabolites present in plants. Isoflavonoids, in particular, are primarily synthesized in leguminous plants within the subfamily Papilionoideae. Numerous reports have established the favorable role of isoflavonoids in preventing a range of human diseases. Among the isoflavonoid components, glyceollins are synthesized specifically in soybean plants and have displayed promising effects in mitigating the occurrence and progression of breast and ovarian cancers as well as other diseases. Consequently, glyceollins have become a sought-after natural component for promoting women's health. In recent years, extensive research has focused on investigating the molecular mechanism underlying the preventative properties of glyceollins against various diseases. Substantial progress has also been made toward elucidating the biosynthetic pathway of glyceollins and exploring potential regulatory factors. Herein, we provide a review of the research conducted on glyceollins since their discovery five decades ago (1972-2023). We summarize their pharmacological effects, biosynthetic pathways, and advancements in chemical synthesis to enhance our understanding of the molecular mechanisms of their function and the genes involved in their biosynthetic pathway. Such knowledge may facilitate improved glyceollin synthesis and the creation of health products based on glyceollins.

Alpinumisoflavone Activates Disruption of Calcium Homeostasis, Mitochondria and Autophagosome to Suppress Development of Endometriosis

Alpinumisoflavone is an isoflavonoid extracted from the Cudrania tricuspidate fruit and Genista pichisermolliana. It has various physiological functions, such as anti-inflammation, anti-proliferation, and apoptosis, in malignant tumors. However, the effect of alpinumisoflavone is still not known in chronic diseases and other benign reproductive diseases, such as endometriosis. In this study, we examined the cell death effects of alpinumisoflavone on the endometriosis cell lines, End1/E6E7 and VK2/E6E7. Results indicated that alpinumisoflavone inhibited cell migration and proliferation and led to cell cycle arrest, depolarization of mitochondria membrane potential, apoptosis, and disruption of calcium homeostasis in the endometriosis cell lines. However, the cellular proliferation of normal uterine epithelial cells was not changed by alpinumisoflavone. The alteration in Ca²⁺ levels was estimated in fluo-4 AM-stained End1/E6E7 and VK2/E6E7 cells after alpinumisoflavone treatment with or without calcium inhibitor, 2-aminoethoxydiphenyl borate (2-APB). The results indicated that a combination of alpinumisoflavone and a calcium inhibitor reduced the calcium accumulation in the cytosol of endometriosis cells. Additionally, alpinumisoflavone decreased oxidative phosphorylation (OXPHOS) in the endometriotic cells. Moreover, protein expression analysis revealed that alpinumisoflavone inactivated AKT signaling pathways, whereas it increased MAPK, ER stress, and autophagy regulatory proteins in End1/E6E7 and VK2/E6E7 cell lines. In summary, our results suggested that alpinumisoflavone could be a promising effective management agent or an adjuvant therapy for benign disease endometriosis.

Estrogenic flavonoids and their molecular mechanisms of action

Flavonoids are a major group of phytoestrogens associated with physiological effects, and ecological and social impacts. Although the estrogenic activity of flavonoids was reported by researchers in the fields of medical, environmental and food studies, their molecular mechanisms of action have not been comprehensively reviewed. The estrogenic activity of the respective classes of flavonoids, anthocyanidins/anthocyanins, 2-arylbenzofurans/3-arylcoumarins/α-methyldeoxybenzoins, aurones/chalcones/dihydrochalcones, coumaronochromones, coumestans, flavans/flavan-3-ols/flavan-4-ols, flavanones/dihydroflavonols, flavones/flavonols, homoisoflavonoids, isoflavans, isoflavanones, isoflavenes, isoflavones, neoflavonoids, oligoflavonoids, pterocarpans/pterocarpenes, and rotenone/rotenoids, was summarized through a comprehensive literature search, and their structure-activity relationship, biological activities, signaling pathways, and applications were discussed. Although the respective classes of flavonoids contained at least one chemical mimicking estrogen, the mechanisms varied, such as those with estrogenic, anti-estrogenic, non-estrogenic, and biphasic activities, and additional activities through crosstalk/bypassing, which exert biological activities through cell signaling pathways. Such mechanistic variations of estrogen action are not limited to flavonoids and are observed among other broad categories of chemicals, thus this group of chemicals can be termed as the "estrogenome". This review article focuses on the connection of estrogen action mainly between the outer and the inner environments, which represent variations of chemicals and biological activities/signaling pathways, respectively, and form the basis to understand their applications. The applications of chemicals will markedly progress due to emerging technologies, such as artificial intelligence for precision medicine, which is also true of the study of the estrogenome including estrogenic flavonoids.

An overview of techniques and strategies for isolation of flavonoids from the genus Erythrina

Plants in the genus Erythrina is a potential source of chemical constituents, one of which is flavonoids, which have diverse bioactivities. To date, literature on the flavonoids from the genus Erythrina has only highlighted the phytochemical aspects, so this review article will discuss isolation techniques and strategies for the first time. More than 420 flavonoids have been reported in the Erythrina genus, which are grouped into 17 categories. These flavonoid compounds were obtained through isolation techniques and strategies using polar, semi-polar, and non-polar solvents. Various chromatographic techniques have been developed to isolate flavonoids using column flash chromatography, quick column chromatography, centrifugally accelerated thin-layer chromatography, radial chromatography, medium-pressure column chromatography, semi-preparative high-performance liquid chromatography, and preparative high-performance liquid chromatography. Chromatographic processes for isolating flavonoids can be optimized using multivariate statistical applications such as response surface methodology with central composite design, Box-Behnken design, Doehlert design, and mixture design.

Preventive effects of cristacarpin on experimentally induced uveitis by targeting NF-κB

Cristacarpin is a novel prenylated pterocarpan that reportedly exhibits broad anti-cancer activity by enhancing endoplasmic reticulum stress. However, whether and how cristacarpin affects in-flammatory processes remain largely unknown. In the present study, the anti-inflammatory effect of cristacarpin on lipopolysaccharide (LPS)-induced inflammation was investigated using zebrafish embryos, RAW 264.7 macrophages, and mouse uveitis models. In the non-toxic concentration range (from 20 to 100 μM), cristacarpin suppressed pro-inflammatory mediators such as interleukin (IL)-6 and tumor necrosis factor (TNF)-α, while stimulating anti-inflammatory mediators such as IL-4 and IL-10 in LPS-stimulated RAW 264.7 cells and uveitis mouse models. Cristacarpin decreased cell adhesion of macrophages through downregulation of the expression of Ninjurin1 and matrix metalloproteinases. Furthermore, cristacarpin reduced macrophage migration in zebrafish embryos in vivo. Cristacarpin also increased cytosolic levels of inhibitor of nuclear factor-κB and suppressed the nuclear translocation of nuclear factor κ-light-chain-enhancer of activated B cells. Collectively, our results suggest that cristacarpin is a potential therapeutic candidate for developing ocular anti-inflammatory drugs.

Estrogenic and Antioxidant Activities of Pterocarpus soyauxii (Fabaceae) Heartwood Aqueous Extract in Bilateral Oophorectomized Wistar Rat

Phytoestrogens are used to ease postmenopausal symptoms, a property probably due to estrogenic and antioxidant effects. Pterocarpus soyauxii (P. soyauxii) is empirically used in Cameroon to treat among others primary and secondary amenorrhea. The aim of this study is to evaluate estrogenic and antioxidant activities of P. soyauxii heartwood aqueous extract in bilateral oophorectomized Wistar rats. Firstly, a characterization of the extract was carried out. For that, flavonoids, phenols, and tannins levels in P. soyauxii extract were evaluated by colorimetric assays and UHPLC-MS analysis was realized. In vitro antioxidant analysis of P. soyauxii was conducted using DPPH, ABTS, and FRAP assays. Secondly, 2 sets of pharmacologic tests were carried out. The results revealed that P. soyauxii aqueous extract contains, respectively, 229.42 ± 3.62 mg EAG/g, 63.42 ± 2.16 mg EQ/g, and 27.88 ± 0.23 mg ETA/g of polyphenols, flavonoids, and tannins. UHPLC-MS enabled identifying seven components including mono(2-ethylhexyl) phthalate, cembrene, 3′,5′-dimethoxy-4-stilbenol, and linoleic acid. DPPH, ABTS, and FRAP assays revealed that P. soyauxii extract possessed a high antioxidant activity with IC₅₀ value of 730.20 µg/mL, 892.90 µg/mL, and 765.75 mEAG/g of extract, respectively. In the uterotrophic assay, P. soyauxii extract induced significant increase of fresh uterine weight, uterine and vaginal epithelial size, and mammary glands differentiation compared to Ovx control. In the postmenopausal model, compared to the sham control, vagina and uterine dystrophies were observed in Ovx rats treated with distilled water. P. soyauxii aqueous extract expressed estrogenic-like effects on vagina and did not affect uterine epithelial height compared with vehicle groups. On the back of these vaginotrophic effects, the extract displayed antiatherogenic properties by reducing (p < 0.001) AI and LDL cholesterol level as compared to Ovx control group. The extract at 200 mg/kg significantly prevented the increase of MDA (p < 0.01) level and decreased nitrites (p < 0.001) and GSH (p < 0.01) levels compared to Ovx rats. These beneficial effects are related at least in part to the presence of compound such as mono(2-ethylhexyl) phthalate, 3′,5′-dimethoxy-4-stilbenol, and linoleic acid. Overall, P. soyauxii aqueous extract exhibits estrogenic and antioxidant effects which can inhibit postmenopausal symptoms by providing vaginal stratification, improving lipid profile and insulin sensitivity, and reducing oxidative stress without side effects on the endometrium and mammary gland in 84-day Ovx rats.

Scope and Applications of 2,3-Oxidative Aryl Rearrangements for the Synthesis of Isoflavone Natural Products

The reaction of flavanones with hypervalent iodine reagents was investigated with a view to the synthesis of naturally occurring isoflavones. In contrast to several previous reports in the literature, we did not observe the formation of any benzofurans via a ring contraction pathway, but could isolate only isoflavones, resulting from an oxidative 2,3-aryl rearrangement, and flavones, resulting from an oxidation of the flavanones. Although the 2,3-oxidative rearrangement allows a synthetically useful approach toward some isoflavone natural products due to the convenient accessibility of the required starting materials, the overall synthetic utility and generality of the reaction appear to be more limited than previous literature reports suggest.

Total Syntheses of Prenylated Isoflavones from Erythrina sacleuxii and Their Antibacterial Activity: 5-Deoxy-3'-prenylbiochanin A and Erysubin F

The prenylated isoflavones 5-deoxyprenylbiochanin A (7-hydroxy-4'-methoxy-3'-prenylisoflavone) and erysubin F (7,4'-dihydroxy-8,3'-diprenylisoflavone) were synthesized for the first time, starting from mono- or di-O-allylated chalcones, and the structure of 5-deoxy-3'-prenylbiochanin A was corroborated by single-crystal X-ray diffraction analysis. Flavanones are key intermediates in the synthesis. Their reaction with hypervalent iodine reagents affords isoflavones via a 2,3-oxidative rearrangement and the corresponding flavone isomers via 2,3-dehydrogenation. This enabled a synthesis of 7,4'-dihydroxy-8,3'-diprenylflavone, a non-natural regioisomer of erysubin F. Erysubin F (8), 7,4'-dihydroxy-8,3'-diprenylflavone (27), and 5-deoxy-3'-prenylbiochanin A (7) were tested against three bacterial strains and one fungal pathogen. All three compounds are inactive against Salmonella enterica subsp. enterica (NCTC 13349), Escherichia coli (ATCC 25922), and Candida albicans (ATCC 90028), with MIC values greater than 80.0 μM. The diprenylated natural product erysubin F (8) and its flavone isomer 7,4'-dihydroxy-8,3'-diprenylflavone (27) show in vitro activity against methicillin-resistant Staphylococcus aureus (MRSA, ATCC 43300) at MIC values of 15.4 and 20.5 μM, respectively. In contrast, the monoprenylated 5-deoxy-3'-prenylbiochanin A (7) is inactive against this MRSA strain.

Isoflavonoid Profiling and Estrogen-Like Activity of Four Genista Species from the Greek Flora

As part of our ongoing research on phytoestrogens, we investigated the phytochemical profile and estrogen-like activities of eight extracts from the aerial parts of four Genista species of Greek flora using estrogen-responsive cell lines. Ethyl acetate and methanolic extracts of G. acanthoclada, G. depressa,G. hassertiana, and G. millii were obtained with accelerated solvent extraction and their phytochemical profiles were compared using ultra-high-performance liquid chromatography-high-resolution mass spectrometry (uHPLC-HRMS). Fourteen isoflavonoids, previously isolated from G. halacsyi, were used as reference standards for their identification in the extracts. Thirteen isoflavonoids were detected in both extracts of G. acanthoclada and G. hassertiana, while fewer and far fewer were detected in G. millii and G. depressa, respectively. The ethyl acetate extracts of G. hassertiana and G. acanthoclada displayed 2.45- and 1.79-fold higher, respectively, estrogen-like agonist activity in Ishikawa cells compared to MCF-7 cells at pharmacologically relevant concentrations. Both these extracts, but not that of G. depressa, contained mono- and di-O-β-d-glucosides of genistein as well as the aglycone, all three of which are known to display full estrogen-like activity at lower-than-micromolar concentrations. The possibility of using preparations rich in G. hassertiana and/or G. acanthoclada extracts as a potentially safer substitute for low-dose vaginal estrogen for menopausal symptoms is discussed.

Design, synthesis, and biological evaluation of new raloxifene analogues of improved antagonist activity and endometrial safety

Raloxifene agonism of estrogen receptor (ER) in post-menopausal endometrium is not negligible. Based on a rational drug design workflow, we synthesized 14 analogues of raloxifene bearing a polar group in the aromatic ring of the basic side chain (BSC) and/or changes in the bulkiness of the BSC amino group. Analogues with a polar BSC aromatic ring and amino group substituents of increasing volume displayed increasing ER antagonism in Ishikawa cells. Analogues with cyclohexylaminoethoxy (13a) or adamantylaminoethoxy BSC (13b) lacking a polar aromatic ring displayed high ER-binding affinity and ER antagonism in Ishikawa cells higher than raloxifene and similar to fulvestrant (ICI182,780). The endometrial surface epithelium of immature female CD1 mice injected with 13b was comparable to that of vehicle-treated mice, while that of mice treated with estradiol, raloxifene or 13b in combination with estradiol was hyperplastic. These findings indicate that raloxifene analogues with a bulky BSC amino group could provide for higher endometrial safety treatment of the menopausal syndrome.

Flavonoids and other Non-alkaloidal Constituents of Genus Erythrina: Phytochemical Review

BACKGROUND

Genus Erythrina belongs to family Fabaceae, which is widely distributed in tropical and subtropical areas. It has been used in both traditional herbal medicines and pharmacological applications. Original research articles and publications on the overview of alkaloids related to this genus are available, but a supportive systematic review account which highlighted phytochemical aspects of other types of secondary metabolites is currently insufficient.

OBJECTIVE

With the utilization of data and information from SCI-Finder, Google Scholar, the Web of Science, Scopus, Science Direct, PubMed, Chemical Abstracts, ACS journals, Springer, Taylor Francis, Bentham Science and IOP Science, the reliable material sources of this systematic review paper were obtained from the literature published from the 1980s to now.

CONCLUSION

A vast amount of data showed that the non-alkaloidal secondary metabolites were obtained from genus Erythrina with various classes of chemical structures. Herein, approximately five hundred constituents were isolated, comprising flavonoids, terpenoids, saponins, phytosterols, phenols, arylbenzofurans, coumarins, alcohols, ceramides, mono-sugars and fatty acid derivatives. In agreement with the previous phytochemical reports on the plants of the family Fabaceae, flavonoids reached a high amount in the plants of genus Erythrina. Numerous biological activity investigations such as anti-bacteria, anti-cancer, anti-virus using isolated compounds from Erythrina species suggested that secondary metabolites of Erythrina plants are now becoming the promising agents for drug developments.

Effects of some flavonoids on the mycotoxin citrinin reduction by Monascus aurantiacus Li AS3.4384 during liquid-state fermentation

Monascus can produce many beneficial metabolites; however, it can simultaneously also produce citrinin, which seriously limits its application. Therefore, reducing the production of citrinin is of great interest. Herein, Monascus aurantiacus Li AS3.4384 (MAL) was used to optimize the liquid-state fermentation process and investigate the effects of genistein and other flavonoids on citrinin, pigments, and biomass of MAL. Results showed that citrinin decreased by 80%, pigments and biomass increased by approximately 20% in 12 days with addition of 20.0 g/L rice powder as a carbon source and 2.0 g/L genistein during shaking liquid-state fermentation. Further, genistein, daidzein, luteolin, apigenin, quercetin, baicalein, kaempferol myricetin, and genistin exerted different effects on citrinin production by MAL, with genistein causing the highest reduction in citrinin production during liquid-state fermentation, possibly due to the presence of C5-OH, C4′-OH, and C7-OH. Therefore, genistein can be added to the fermentation process of Monascus to reduce citrinin.

Erythrina suberosa: Ethnopharmacology, Phytochemistry and Biological Activities

Plants are a great and irreplaceable source of medicines, fuel, food, energy and even cosmetics. Since prehistory, humans have learned to use plants for survival, growth and proliferation and still today it relies on natural and cultivated vegetables for food and the source of novel compounds with pharmacological activity. Not only herbs and flowers, but also trees are used. Indeed, Erythrina suberosa Roxb. is a deciduous tree of the family Fabaceae, common in Southeast Asia. In India, E. suberosa is called the “corky coral tree” or simply the “Indian coral tree”, given its peculiar red-orange flowers that can flower throughout the year and its corky irregular bark covered by prickles. It is a plant commonly used as an ornamental tree, but it also holds ethnopharmacological and socioeconomic uses. This article explored phytobiological features of E. suberosa, analysing its taxonomy, examining its traditional and common uses and investigating its bioactive components and pharmacological properties.

A Pharmacological Overview of Alpinumisoflavone, a Natural Prenylated Isoflavonoid

Over the last decade, several studies demonstrated that prenylation of flavonoids enhances various biological activities as compared to the respective nonprenylated compounds. In line with this, the natural prenylated isoflavonoid alpinumisoflavone (AIF) has been explored for a number of biological and pharmacological effects (therapeutic potential). In this review, we summarize the current information on health-promoting properties of AIF. Reported data evidenced that AIF has a multitherapeutic potential with antiosteoporotic, antioxidant and anti-inflammatory, antimicrobial, anticancer, estrogenic and antiestrogenic, antidiabetic, and neuroprotective properties. However, research on these aspects of AIF is not sufficient and needs to be reevaluated using more appropriate methods and methodology. Further series of studies are needed to confirm these pharmacological effects, and this review should lay the basis for the design of respective investigations. Overall, despite the drawbacks of studies recorded, AIF exhibits a potential as drug candidate.

Potential cancer chemopreventive and anticancer constituents from the fruits of Ficus hispida L.f. (Moraceae)

ETHNOPHARMACOLOGICAL RELEVANCE

Ficus hispida L.f. (Moraceae) has been used as alternative for traditional medicine in the treatment of various ailments including cancer-cure. The aim of this study was to evaluate the cancer chemopreventive and anticancer activities of crude extracts of F. hispida, with the objective to screen the inhibition of Epstein-Barr virus early antigen, and cytotoxic active components, and provide foundation for potential applications of this promising medical plant.

MATERIALS AND METHODS

Compounds were isolated from the MeOH extract of F. hispida fruits, and their structure elucidation was performed on the basis of extensive spectroscopic analysis. The isolated compounds were evaluated for their inhibitory activities against the Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol 13-acetate (TPA) in Raji cells, and cytotoxic activities against human cancer cell lines (HL60, A549, SKBR3, KB, Hela, HT29, and HepG2) and a normal cell (LO2) using MTT method. For the compound with potent cytotoxic activity, its apoptosis inducing activity was evaluated by the observation of ROS generation level expression, and membrane phospholipid exposure and DNA fragmentation in flow cytometry. The mechanisms of the apoptosis induction were analyzed by Western blotting.

RESULTS

Nineteen compounds, 1-19, including two new isoflavones, 3'-formyl-5,7-dihydroxy-4'-methoxyisoflavone (2) and 5,7-dihydroxy-4'-methoxy-3'- (3-methyl-2-hydroxybuten-3-yl)isoflavone (3), were isolated from the MeOH extract of F. hispida fruits. Five compounds, isowigtheone hydrate (1), 2, 3, 9, and 19, showed potent inhibitory effects on EBV-EA induction with IC₅₀ values in the range of 271-340 molar ratio 32 pmol^-1 TPA. In addition, five phenolic compounds, 1-3, 10, and 13, exhibited cytotoxic activity against two or more cell lines (IC₅₀ 2.5-95.8μM), as well as compounds 1 and 3 were also displayed high selectivity for LO2/HepG2 (SI 23.5 and 11.8, respectively), while the compound 1-induced ROS generation leads to activated caspases-3, -8, and -9 apoptotic process in HL60 cells.

CONCLUSION

This study has established that the MeOH extract of F. hispida fruits contains isoflavones, coumarins, caffeoylquinic acids, along with other compounds including phenolics and steroid glucoside as active principles, and has demonstrated that the chemical constituents of F. hispida may be valuable as potential chemopreventive and anticancer agents.

Flavonoids from Erythrina schliebenii

Prenylated and O-methylflavonoids including one new pterocarpan (1), three new isoflavones (2-4), and nineteen known natural products (5-23) were isolated and identified from the root, stem bark, and leaf extracts of Erythrina schliebenii. The crude extracts and their constituents were evaluated for antitubercular activity against Mycobacterium tuberculosis (H37Rv strain), showing MICs of 32-64 μg mL^-1 and 36.9-101.8 μM, respectively. Evaluation of their toxicity against the aggressive human breast cancer cell line MDA-MB-231 indicated EC₅₀ values of 13.0-290.6 μM (pure compounds) and 38.3 to >100 μg mL^-1 (crude extracts).

Isoflavonoids from Crotalaria albida Inhibit Adipocyte Differentiation and Lipid Accumulation in 3T3-L1 Cells via Suppression of PPAR-γ Pathway

Two 2″-isopropenyl dihydrofuran isoflavonoids (1 and 3), one 2″-isopropenyl dihydrofuran chromone (2), as well as 13 known compounds were isolated from the herbs of Crotalaria albida. Their structures and relative configurations were elucidated via NMR and HRESIMS analyses. The 2″ S absolute configuration of 1 and 2 were deduced by comparing their NOESY spectra with that of 3, which was determined via single crystal X-ray diffraction (CuKα). The 3R absolute configuration of 1 was determined by CD. Compounds 1, 2, and 3 inhibit the adipocyte differentiation and lipid accumulation of 3T3-L1 through down-regulation of PPAR-γ activity.

Prenylated isoflavonoids from plants as selective estrogen receptor modulators (phytoSERMs)

Isoflavonoids are a class of secondary metabolites, which comprise amongst others the subclasses of isoflavones, isoflavans, pterocarpans and coumestans. Isoflavonoids are abundant in Leguminosae, and many of them can bind to the human estrogen receptor (hER) with affinities similar to or lower than that of estradiol. Dietary intake of these so-called phytoestrogens has been associated with positive effects on menopausal complaints, hormone-related cancers, and osteoporosis. Therefore, phytoestrogens are used as nutraceuticals in functional foods or food supplements. Most of the isoflavonoids show agonistic activity towards both hERα and hERβ, the extent of which is modulated by the substitution pattern of their skeleton (i.e.-OH, -OCH(3)). Interestingly, substitutions consisting of a five-carbon prenyl group often seem to result in an antiestrogenic activity. There is growing evidence that the action of some of these prenylated isoflavonoids is tissue-specific, suggesting that they act like selective estrogen receptor modulators (SERMs), such as the well-known chemically synthesized raloxifene and tamoxifen. These so-called phytoSERMS might have high potential for realizing new food and pharma applications. In this review, the structural features of isoflavonoids (i.e. the kind of skeleton and prenylation (e.g. chain or pyran), position of the prenyl group on the skeleton, and the extent of prenylation (single, double)) are discussed in relation to their estrogenic activity. Anti-estrogenic and SERM activity of isoflavonoids was always associated with prenylation, but these activities did not seem to be confined to one particular kind/position of prenylation or isoflavonoid subclass. Few estrogens with agonistic activity were prenylated, but these were not tested for antagonistic activity; possibly, these molecules will turn out to be phytoSERMs as well. Furthermore, the data on the dietary occurrence, bioavailability and metabolism of prenylated isoflavonoids are discussed.

Estrogenic properties of naturally occurring prenylated isoflavones in U2OS human osteosarcoma cells: Structure-activity relationships

Eight isoflavones derivatives, with isoprenyl and/or 7-methoxy substitution, isolated from Erythrina poeppigiana (Fabaceae) have been investigated for their estrogenic properties in receptor subtype-specific reporter gene assays. First we focused on their estrogen receptor alpha and beta (ERalpha and ERbeta) selectivity, second we addressed structure-activity relationships, using bone-derived human osteosarcoma cell line (U2OS cells) stably expressing ERalpha or transiently expressing ERbeta. Our results show that a substitution at position 3' together with a 7-methoxy substitution on the genistein skeleton is associated with a statistically significant activation of the ERalpha- and ERbeta-dependent reporter gene expression in U2OS cells starting from 0.1nM. Particularly, the 7-methoxy-3'-isoprenyl (1) and the 7-methoxy-3'-(3-methyl-2-hydroxybuten-3-yl) (3) derivatives of genistein induces an ERalpha- and ERbeta-coupled luciferase activity at a concentration ten times lower than that of genistein, for which a statistically significant effect was observable at 1nM. On the other hand, isoprenyl substitution at position 6 of the A ring, compound 5, seems to have very little impact on the genistein ability to induce ER-coupled luciferase activity in U2OS cells, while a double prenylation at positions 8 and 3', compound 7, is associated with an almost complete loss of function on the reporter gene activation in U2OS-ERalpha, but in ERbeta expressing system the effectiveness remains on a statistically significant level, demonstrating an "exclusive ERbeta-selectivity" in U2OS human osteosarcoma cells, and therefore 7 can be considered as an isotype-selective ER ligand. Finally all the tested isoflavones derivatives appear to exhibit a slightly pronounced ERbeta preference, depending upon the position and the nature of the substituent moiety on the isoflavone skeleton. The estrogen-like effect of these prenylated isoflavone derivatives could be inhibited by the pure ER antagonist ICI 182 780, indicating that these effects were primarily mediated through ERs.