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Hormone-dependent cancers, such as certain types of breast cancer are characterized by over-expression of estrogen receptors (ERs). Anticancer drug conjugates combining ER ligands with other classes of anticancer agents may not only benefit from dual action at both anti-cancer targets but also from selective delivery of cytotoxic agents to ER-positive tumor cells resulting in less toxicity and adverse effects. Moreover, they could also take advantage of overcoming resistance typical for anti-hormonal monotherapy such as tamoxifen. In this review, we discuss the design, structures and pharmacological effects of numerous series of drug conjugates containing ER ligands such as selective ER modulators (tamoxifen, 4-hydroxytamoxifen, endoxifen), selective ER degraders (ICI-164384) and ER agonists (estradiol) linked to diverse anti-cancer agents including histone-deacetylase inhibitors, DNA-alkylating agents, antimitotic agents and epidermal growth factor receptor inhibitors. [ABSTRACT FROM AUTHOR]

Demyelination in multiple sclerosis (MS) leads to significant, progressive axonal and neuronal degeneration. Currently existing immunosuppressive and immunomodulatory therapies alleviate MS symptoms and slow, but fail to prevent or reverse, disease progression. Restoration of damaged myelin sheath by replenishment of mature oligodendrocytes (OLs) should not only restore saltatory axon conduction, but also provide a major boost to axon survival. Our previous work has shown that therapeutic treatment with the modestly selective generic estrogen receptor (ER) β agonist diarylpropionitrile (DPN) confers functional neuroprotection in a chronic experimental autoimmune encephalomyelitis (EAE) mouse model of MS by stimulating endogenous remyelination. Recently, we found that the more potent, selective ERβ agonist indazole-chloride (Ind-Cl) improves clinical disease and motor performance. Importantly, electrophysiological measures revealed improved corpus callosal conduction and reduced axon refractoriness. This Ind-Cl treatment-induced functional remyelination was attributable to increased OL progenitor cell (OPC) and mature OL numbers. At the intracellular signaling level, transition of early to late OPCs requires ERK1/2 signaling, and transition of immature to mature OLs requires mTOR signaling; thus, the PI3K/Akt/mTOR pathway plays a major role in the late stages of OL differentiation and myelination. Indeed, therapeutic treatment of EAE mice with various ERβ agonists results in increased brain-derived neurotrophic factor (BDNF) and phosphorylated (p) Akt and p-mTOR levels. It is notable that while DPN's neuroprotective effects occur in the presence of peripheral and central inflammation, Ind-Cl is directly neuroprotective, as demonstrated by remyelination effects in the cuprizone-induced demyelination model, as well as immunomodulatory. Elucidating the mechanisms by which ER agonists and other directly remyelinating agents modulate endogenous OPC and OL regulatory signaling is critical to the development of effective remyelinating drugs. The discovery of signaling targets to induce functional remyelination will valuably contribute to the treatment of demyelinating neurological diseases, including MS, stroke, and traumatic brain and spinal cord injury.

Estrogen-regulated pathways are involved in the etiology and progression of epithelial ovarian cancer (EOC), but the relative contribution of estrogen receptor isoforms is unclear. Only a subset of patients responds to antiestrogens including tamoxifen. Based on our previous evidence that miR-206 behaves as an oncosuppressor in EOC, we hypothesized that miR-206 would interfere with G protein-coupled estrogen receptor (GPER)-mediated signaling and cell motility. PFKFB3 and FAK proteins from OC cells challenged with selective estrogen receptor agonist and antagonist were measured by Western blotting. Cell proliferation and motility were analyzed by MTT and Boyden chamber, respectively. Estrogen-dependent cells were transfected with miR-206 mimic or control using Lipofectamine. The migration of SKOV3 and OVCAR5 cells significantly increased following treatment with 17β-estradiol (E2) and the selective GPER agonist G1. However, tamoxifen failed to inhibit E2 effect and even promoted SKOV3 cell migration. Estrogen receptor ligands did not affect SKOV3 proliferation. The GPER antagonist G15 significantly prevented E2-mediated upregulation of PFKFB3 expression, while G1 concentration-dependently upregulated PFKFB3 levels. Consistent with the functional link between PFKFB3 and FAK activation, E2 and G1 increased FAK phosphorylation at Tyr397. Transfection with miR-206 abolished estrogen-induced EOC migration and down-regulated PFKFB3 protein levels. Notably, miR-206 transfection reduced ERα protein abundance, whereas GPER amount was unchanged. By blocking estrogen signaling and G1-induced EOC cell invasiveness with no direct interference with GPER levels, miR-206 mimics have the potential to act as pathway-selective antagonists and deserve further testing as RNA therapeutics in estrogen-dependent EOC. Fig. 10. Regulatory action of miR-206 on the functional expression of estrogen-modulated proteins. Estrogens increased PFKFB3/pFAK proteins levels and the motility of the ovarian cancer cells, via the membrane estrogen receptor GPER. miR-206 blocks GPER-mediated estrogen signaling and cell migration. [Display omitted] [ABSTRACT FROM AUTHOR]

Nuclear receptors such as the estrogen receptors (ERα and ERβ) modulate the effects of the estrogen hormones and are important targets for design of innovative chemotherapeutic agents for diseases such as breast cancer and osteoporosis. Conjugate and bifunctional compounds which incorporate an ER ligand offer a useful method of delivering cytotoxic drugs to tissue sites such as breast cancers which express ERs. A series of novel conjugate molecules incorporating both the ER ligands endoxifen and cyclofenil-endoxifen hybrids covalently linked to the antimitotic and tubulin targeting agent combretastatin A-4 were synthesised and evaluated as ER ligands. A number of these compounds demonstrated pro-apoptotic effects, with potent antiproliferative activity in ER-positive MCF-7 breast cancer cell lines and low cytotoxicity. These conjugates displayed binding affinity towards ERα and ERβ isoforms at nanomolar concentrations e.g., the cyclofenil-amide compound 13e is a promising lead compound of a clinically relevant ER conjugate with IC50 in MCF-7 cells of 187 nM, and binding affinity to ERα (IC50 = 19 nM) and ERβ (IC50 = 229 nM) while the endoxifen conjugate 16b demonstrates antiproliferative activity in MCF-7 cells (IC50 = 5.7 nM) and binding affinity to ERα (IC50 = 15 nM) and ERβ (IC50 = 115 nM). The ER binding effects are rationalised in a molecular modelling study in which the disruption of the ER helix-12 in the presence of compounds 11e, 13e and 16b is presented These conjugate compounds have potential application for further development as antineoplastic agents in the treatment of ER positive breast cancers [ABSTRACT FROM AUTHOR]

The identification of a drug that stimulates endogenous myelination and spares axon degeneration during multiple sclerosis (MS) could potentially reduce the rate of disease progression. Using experimental autoimmune encephalomyelitis (EAE), a mouse model of MS, we have previously shown that prophylactic administration of the estrogen receptor (ER) β ligand 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN) decreases clinical disease, is neuroprotective, stimulates endogenous myelination, and improves axon conduction without altering peripheral cytokine production or reducing central nervous system (CNS) inflammation. Here, we assessed the effects of therapeutic DPN treatment during peak EAE disease, which represents a more clinically relevant treatment paradigm. In addition, we investigated the mechanism of action of DPN treatment-induced recovery during EAE. Given that prophylactic and therapeutic treatments with DPN during EAE improved remyelination-induced axon conduction, and that ER (α and β) and membrane (m)ERs are present on oligodendrocyte lineage cells, a direct effect of treatment on oligodendrocytes is likely. DPN treatment of EAE animals resulted in phosphorylated ERβ and activated the phosphatidylinositol 3-kinase (PI3K)/serine–threonine-specific protein kinase (Akt)/mammalian target of rapamycin (mTOR) signaling pathway, a pathway required for oligodendrocyte survival and axon myelination. These results, along with our previous studies of prophylactic DPN treatment, make DPN and similar ERβ ligands immediate and favorable therapeutic candidates for demyelinating disease.

Demyelination in multiple sclerosis (MS) leads to significant, progressive axonal and neuronal degeneration. Currently existing immunosuppressive and immunomodulatory therapies alleviate MS symptoms and slow, but fail to prevent or reverse, disease progression. Restoration of damaged myelin sheath by replenishment of mature oligodendrocytes (OLs) should not only restore saltatory axon conduction, but also provide a major boost to axon survival. Our previous work has shown that therapeutic treatment with the modestly selective generic estrogen receptor (ER) β agonist diarylpropionitrile (DPN) confers functional neuroprotection in a chronic experimental autoimmune encephalomyelitis (EAE) mouse model of MS by stimulating endogenous remyelination. Recently, we found that the more potent, selective ERβ agonist indazole-chloride (Ind-Cl) improves clinical disease and motor performance. Importantly, electrophysiological measures revealed improved corpus callosal conduction and reduced axon refractoriness. This Ind-Cl treatment-induced functional remyelination was attributable to increased OL progenitor cell (OPC) and mature OL numbers. At the intracellular signaling level, transition of early to late OPCs requires ERK1/2 signaling, and transition of immature to mature OLs requires mTOR signaling; thus, the PI3K/Akt/mTOR pathway plays a major role in the late stages of OL differentiation and myelination. Indeed, therapeutic treatment of EAE mice with various ERβ agonists results in increased brain-derived neurotrophic factor (BDNF) and phosphorylated (p) Akt and p-mTOR levels. It is notable that while DPN’s neuroprotective effects occur in the presence of peripheral and central inflammation, Ind-Cl is directly neuroprotective, as demonstrated by remyelination effects in the cuprizone-induced demyelination model, as well as immunomodulatory. Elucidating the mechanisms by which ER agonists and other directly remyelinating agents modulate endogenous OPC and OL regulatory signaling is critical to the development of effective remyelinating drugs. The discovery of signaling targets to induce functional remyelination will valuably contribute to the treatment of demyelinating neurological diseases, including MS, stroke, and traumatic brain and spinal cord injury. [ABSTRACT FROM AUTHOR]

Fluorinated steroids have found entry into the list of important pharmaceuticals. Fluorinated corticosteroids are being used as topical drugs against rheumatism and inflammatory skin diseases or as inhalation drugs again asthma. A number of fluorinated steroids bind strongly to the estrogen or the progesterone receptor. With the availability of [ 18 F]fluorine as a radiolabel, radiofluorinated steroids are being developed as potential positron emission tomography (PET) imaging agents. This article presents an overview of preparative methods to fluorinated steroids as well as of the uses of these compounds. [ABSTRACT FROM AUTHOR]

Nuclear-receptors are often overexpressed in tumours and can thereby be used as targets when designing novel selective chemotherapeutic agents. To date, many conjugates incorporating an estrogen receptor (ER) ligand have been synthesised in order to direct chemical agents to tissue sites containing ERs. A series of ER ligand conjugates were synthesised incorporating an antagonistic ER ligand scaffold based on endoxifen, covalently-bound via an amide linkage to a variety of combretastatin-based analogues, which may act as antimitotic agents. These novel endoxifen-combretastatin hybrid scaffold analogues were biochemically evaluated in order to determine their antiproliferative and cytotoxicity effects in both the ER-positive MCF-7 and the ER-negative MDA-MB-231 human breast cancer cell lines. ER competitive binding assays were carried out to assess the binding affinity of the lead conjugate 28 towards both the ERα and ERβ isoforms. In results from the NCI 60-cell line screen, the lead conjugate 28 displayed potent and highly selective antiproliferative activity towards the MCF-7 human cancer cell line (IC50 = 5 nM). In the ER-binding assays, the lead conjugate 28 demonstrated potent ER competitive binding in ERα (IC50 value: 0.9 nM) and ERβ (IC50 value: 4.7 nM). Preliminary biochemical results also demonstrate that the lead conjugate 28 may exhibit pure antagonism. This series makes an important addition to the class of ER antagonists and may have potential applications in anticancer therapy.

Highlights: [•] Acute osmotic stress in OVX rats reduces the number of NADPH-d+ cells in the PVN. [•] Under these conditions estradiol increases the number of NADPH-d+ neurons. [•] Both ERα and ERβ are involved in the regulation of the number of NADPH-d+ neurons. [ABSTRACT FROM AUTHOR]

Erythrina lysistemon is an African medicinal plant used as a palliative for problems in women. The crude extract of this plant was shown to exhibit estrogenic effects on the female rat reproductive tract and on cell cuture. Using classic chromatographic methods, two compounds have been isolated as major constituents of this extract: alpinumisoflavone (1) and abyssinone V-4′-methyl ether (2). To determine whether both compounds are actives principles accounting for E. lysistemon effects, we applied the classic 3-day uterotrophic assay. We also carried out a ligand binding assay to determine whether the observed effects are estrogen receptor (ER) mediated. This study showed that whereas compound 1 displayed a fourfold preference for ERα, compound 2 bound ERα and ERβ with a same affinity. The in vivo study showed that compound 1 increased the uterine wet weight by 182.23% ( p < 0.01) and 71.79% ( p < 0.05) at doses of 0.1 and 1 mg/kg BW/day respectively. The uterine epithelium thickened dose-dependently. Vaginal epithelial height also increased by 369.97 and 226.76% respectively ( p < 0.01). Compound 2 acted only on the vagina and increased vaginal epithelial height by 244.56% ( p < 0.01) at 1 mg/kg BW/day. These results suggest that compounds 1 and 2 are endowed with estrogenic properties accounting, at least in part, for E. lysistemon effects. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Demyelination and neurodegeneration is a major contributor in the progression of disability in multiple sclerosis (MS). Thus, the development of therapies that are neuroprotective has elicited considerable interests. Estrogens and estrogen receptor (ER) ligand treatments are promising treatments to prevent MS-induced neurodegeneration and a multicenter phase II clinical trial of estriol as a beneficial therapy in MS is underway. Here, we discuss studies performed in our laboratory that examined the effects of ER ligands in the inflammatory/demyelinating disorder experimental autoimmune encephalomyelitis (EAE), a model of MS. Administration of estriol or 17β-estradiol reduced clinical severity and this clinical disease improvement was associated with favorable changes in cytokine production. There was a significant decrease of neuronal pathology in gray matter along with myelin and axon preservation in white matter of spinal cords of mice with EAE. In subsequent experiments, we contrasted the results of ERα versus ERβ ligand treatment. While ERα ligand treatment was anti-inflammatory, ERβ ligand treatment was not. ERβ ligand treatment nevertheless reduced demyelination and preserved axon numbers in white matter and prevented neuronal abnormalities in gray matter. Clinically, ERα ligand treatment abrogated the disease at the onset, while ERβ ligand treatment had no effect at disease onset, but promoted recovery. Thus, unlike ERα ligand treatment, ERβ ligand treatment was protective at the level of the target organ, independent of anti-inflammatory effects in the peripheral immune system. ERβ ligand treatment should be considered as a potential neuroprotective agent for MS and other neurodegenerative diseases, particularly since breast and uterine cancer are mediated through ERα. [Copyright &y& Elsevier]

Abstract: A series of 4′-hydroxyphenyl-aryl-carbaldehyde oximes (5b) was prepared and found to have high affinity (4nM) and modest selectivity (39-fold) for estrogen receptor-β (ERβ). Substitution of one of the core rings of the scaffold based around these novel ligands further expanded our knowledge in the quest toward achieving high affinity and selectivity for ERβ. An X-ray co-crystal of structure 11 revealed that the oxime moiety was mimicking the C-ring of genistein, as previously predicted by SAR and docking studies. [Copyright &y& Elsevier]

Abstract: Synthesis and derivatization of a series of substituted tetrahydrofluorenone analogs giving potent, ERβ subtype selective ligands are described. Several analogs possessing ERβ binding affinities comparable to 17β-estradiol but with greater than 75-fold selectivity over ERα are reported. [Copyright &y& Elsevier]

Abstract: The anti-inflammatory activity of non-selective estrogens has been attributed to their ability to antagonize the activity of nuclear factor κB (NF-κB), a known mediator of inflammatory responses. Here we report the identification of a potent new class of pathway-selective ER ligands that selectively antagonize NF-κB functional activity, while exhibiting a lack of classical estrogenic effect. [Copyright &y& Elsevier]

Abstract: A new class of estrogen receptor β (ERβ) ligands based on the 2-phenylquinoline scaffold was prepared. Several analogues with C4 substitution displayed high affinity (3–5nM) and significant selectivity (up to 83-fold) for ERβ. The best compound, 13b, was profiled as a selective partial agonist for ERβ at 1μM in a cell-based transcriptional assay. Uterine weight bioassay of 13b indicated no activation of ERα in vivo. [Copyright &y& Elsevier]

The objective of this study was to evaluate the capability of an expert system described in the previous paper (S. Bradbury et al., Toxicol. Sci. 58, 253–269) to identify the potential for chemicals to act as ligands of mammalian estrogen receptors (ERs). The basis of the expert system was a structure activity relationship (SAR) model, based on relative binding affinity (RBA) values for steroidal and nonsteroidal chemicals derived from human ERα (hERα) competitive binding assays. The expert system enables categorization of chemicals into (RBA ranges of < 0.1, 0.1 to 1, 1 to 10, 10 to 100, and >150% relative to 17β-estradiol. In the current analysis, the algorithm was evaluated with respect to predicting RBAs of chemicals assayed with ERs from MCF7 cells, and mouse and rat uterine preparations. The best correspondence between predicted and observed RBA ranges was obtained with MCF7 cells. The agreement between predictions from the expert system and data from binding assays with mouse and rat ER(s) were less reliable, especially for chemicals with RBAs less than 10%. Prediction errors often were false positives, i.e., predictions of greater than observed RBA values. While discrepancies were likely due, in part, to species-specific variations in ER structure and ligand binding affinity, a systematic bias in structural characteristics of chemicals in the hERα training set, compared to the rodent evaluation data sets, also contributed to prediction errors. False-positive predictions were typically associated with ligands that had shielded electronegative sites. Ligands with these structural characteristics were not well represented in the training set used to derive the expert system. Inclusion of a shielding criterion into the original expert system significantly increased the accuracy of RBA predictions. With this additional structural requirement, 38 of 46 compounds with measured RBA values greater than 10% in hERα, MCF7, and rodent uterine preparations were correctly categorized. Of the remaining 129 compounds in the combined data sets, RBA values for 65 compounds were correctly predicted, with 47 of the incorrect predictions being false positives. Based upon this exploratory analysis, the modeling approach, combined with a high-quality training set of RBA values derived from a diverse set of chemical structures, could provide a credible tool for prioritizing chemicals with moderate to high ER binding affinity for subsequent in vitro or in vivo assessments. [ABSTRACT FROM PUBLISHER]

The common reactivity pattern (COREPA) approach is a 3-dimensional, quantitative structure activity relationship (3-D QSAR) technique that permits identification and quantification of specific global and local stereoelectronic characteristics associated with a chemical's biological activity. It goes beyond conventional 3-D QSAR approaches by incorporating dynamic chemical conformational flexibility in ligand-receptor interactions. The approach provides flexibility in screening chemical data sets in that it helps establish criteria for identifying false positives and false negatives, and is not dependent upon a predetermined and specified toxicophore or an alignment of conformers to a lead compound. The algorithm was recently used to screen chemical data sets for rat androgen receptor binding affinity. To further explore the potential application of the algorithm in establishing reactivity patterns for human estrogen receptor α (hERα) binding affinity, the stereoelectronic requirements associated with the binding affinity of 45 steroidal and nonsteroidal ligands to the receptor were defined. Reactivity patterns for relative hERα binding affinity (RBA; 17β-estradiol = 100%) were established based on global nucleophilicity, interatomic distances between electronegative heteroatoms, and electron donor capability of heteroatoms. These reactivity patterns were used to establish descriptor profiles for identifying and ranking compounds with RBA of > 150%, 100–10%, 10–1%, and 1–0.1%. Increasing specificity of reactivity patterns was detected for ligand data sets with RBAs above 10%. Using the results of this analysis, an exploratory expert system was developed for use in ranking relative ER binding affinity potential for large chemical data sets. [ABSTRACT FROM PUBLISHER]

Abstract: A series of estrogen receptor ligands based on a 3-alkyl naphthalene scaffold was synthesized using an intramolecular enolate-alkyne cycloaromatization as the key step. Several of these compounds bearing a C6-OH group were shown to be high affinity ligands. All compounds had similar ERα and ERβ binding affinity ranging from micromolar to low nanomolar. [Copyright &y& Elsevier]