Highly efficient synthesis and characterization of the GPR30-selective agonist G-1 and related tetrahydroquinoline analogs

G Protein-Coupled Estrogen Receptor GPER: Molecular Pharmacology and Therapeutic Applications

The actions of estrogens and related estrogenic molecules are complex and multifaceted in both sexes. A wide array of natural, synthetic, and therapeutic molecules target pathways that produce and respond to estrogens. Multiple receptors promulgate these responses, including the classical estrogen receptors of the nuclear hormone receptor family (estrogen receptors α and β), which function largely as ligand-activated transcription factors, and the 7-transmembrane G protein-coupled estrogen receptor, GPER, which activates a diverse array of signaling pathways. The pharmacology and functional roles of GPER in physiology and disease reveal important roles in responses to both natural and synthetic estrogenic compounds in numerous physiological systems. These functions have implications in the treatment of myriad disease states, including cancer, cardiovascular diseases, and metabolic disorders. This review focuses on the complex pharmacology of GPER and summarizes major physiological functions of GPER and the therapeutic implications and ongoing applications of GPER-targeted compounds.

Immunoblot Detection of the Phosphorylation of the Estrogen Receptor α as an Outcome of GPR30 /GPER1 Activation

Phosphorylation of the serine residues in estrogen receptor (ER) α is important in transcriptional activation. Hence, methods to detect such posttranslational modification events are valuable. We describe, in detail, the analysis of the phosphorylated ERα by electrophoretic separation of proteins and subsequent immunoblotting techniques. In particular, phosphorylation of the ERα is one possible outcome of activation of the putative membrane estrogen receptor (mER), GPR30 or GPER1. Hence, phosphorylation represents a crosstalk event between GPR30 and ERα and may be important in estrogen-regulated physiology.

Synthesis of endo-fused 5-unsubstituted Hexahydro-2H-pyrano[3,2-c]quinolinesvia Sequential Sc(OTf)3-catalyzed Cationic Imino-Diels-Alder Reaction/N-debenzylation using N-benzylanilines, 3,4-dihydro-2H-pyran and Paraformaldehyde under MW Irradiation

BACKGROUND

Hexahydro-2H-pyrano[3,2-c]quinolines are known to have antibacterial, antifungal, and antitumor properties. Great efforts have been made to develop new synthetic methods that lead to the synthesis of valuable libraries. Extensive methodologies, low yields, excessive amounts of catalyst and expensive reactants are some of the limitations of current methodologies.

AIMS AND OBJECTIVE

Developing a useful and efficient method to construct diversely substituted hexahydro-2Hpyrano[ 3,2-c]quinolines into good to excellent yields through a cationic imino-Diels-Alder/N-debenzylation methodology.

METHOD

The cationic imino-Diels-Alder/N-debenzylation methodology was used for the preparation of substituted hexahydro-2H-pyrano[3,2-c]quinolines. It involves the use of Sc(OTf)₃ for activation of cationic imino- Diels-Alder cycloaddition reaction of N-benzylanilines, 3,4-dihydro-2H-pyran and paraformaldehyde in MeCN; and microwave irradiation to shorten reaction time to afford new 6-benzyl-hexahydro-2H-pyrano[3,2- c]quinolines whose catalytic transfer debenzylation reactions with HCO₂NH₄ in the presence of Pd/C (10%) and methanol give the new 5-unsubstituted pyrano[3,2-c]quinolines in excellent yields.

RESULTS

We found that optimal conditions for the preparation of hexahydro-2H-pyrano[3,2-c]quinolines were Sc(OTf)₃ 0.5 % and acetonitrile at 160°C for 15 min; and using paraformaldehyde obtained the 6-benzylhexahydro- 2H-pyrano [3,2-c]quinolines with excellent yields, while the N-debenzylation process using ammonium formate in the presence of Pd/C and methanol resulted in the synthesis of hexahydro-2H-pyrano [3,2-c] quinolines with quantitative yields (95-98%).

CONCLUSION

We describe an efficient method to synthesize hexahydro-2H-pyrano[3,2-c]quinolines via the cationic imino-Diels-Alder/N-debenzylation methodology using Sc(OTf)3 0.5 % as Lewis Acid catalyst. Excellent yields of the products, use of MW irradiation, short times of reactions, and an efficient and highly diversified method are some of the main advantages of this new protocol.

Modifications on the Tetrahydroquinoline Scaffold Targeting a Phenylalanine Cluster on GPER as Antiproliferative Compounds against Renal, Liver and Pancreatic Cancer Cells

The implementation of chemo- and bioinformatics tools is a crucial step in the design of structure-based drugs, enabling the identification of more specific and effective molecules against cancer without side effects. In this study, three new compounds were designed and synthesized with suitable absorption, distribution, metabolism, excretion and toxicity (ADME-tox) properties and high affinity for the G protein-coupled estrogen receptor (GPER) binding site by in silico methods, which correlated with the growth inhibitory activity tested in a cluster of cancer cell lines. Docking and molecular dynamics (MD) simulations accompanied by a molecular mechanics/generalized Born surface area (MMGBSA) approach yielded the binding modes and energetic features of the proposed compounds on GPER. These in silico studies showed that the compounds reached the GPER binding site, establishing interactions with a phenylalanine cluster (F206, F208 and F278) required for GPER molecular recognition of its agonist and antagonist ligands. Finally, a 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) assay showed growth inhibitory activity of compounds 4, 5 and 7 in three different cancer cell lines-MIA Paca-2, RCC4-VA and Hep G2-at micromolar concentrations. These new molecules with specific chemical modifications of the GPER pharmacophore open up the possibility of generating new compounds capable of reaching the GPER binding site with potential growth inhibitory activities against nonconventional GPER cell models.

Preclinical efficacy of the GPER-selective agonist G-1 in mouse models of obesity and diabetes

Human obesity has become a global health epidemic, with few safe and effective pharmacological therapies currently available. The systemic loss of ovarian estradiol (E2) in women after menopause greatly increases the risk of obesity and metabolic dysfunction, revealing the critical role of E2 in this setting. The salutary effects of E2 are traditionally attributed to the classical estrogen receptors ERα and ERβ, with the contribution of the G protein-coupled estrogen receptor (GPER) still largely unknown. Here, we used ovariectomy- and diet-induced obesity (DIO) mouse models to evaluate the preclinical activity of GPER-selective small-molecule agonist G-1 (also called Tespria) against obesity and metabolic dysfunction. G-1 treatment of ovariectomized female mice (a model of postmenopausal obesity) reduced body weight and improved glucose homeostasis without changes in food intake, fuel source usage, or locomotor activity. G-1-treated female mice also exhibited increased energy expenditure, lower body fat content, and reduced fasting cholesterol, glucose, insulin, and inflammatory markers but did not display feminizing effects on the uterus (imbibition) or beneficial effects on bone health. G-1 treatment of DIO male mice did not elicit weight loss but prevented further weight gain and improved glucose tolerance, indicating that G-1 improved glucose homeostasis independently of its antiobesity effects. However, in ovariectomized DIO female mice, G-1 continued to elicit weight loss, reflecting possible sex differences in the mechanisms of G-1 action. In conclusion, this work demonstrates that GPER-selective agonism is a viable therapeutic approach against obesity, diabetes, and associated metabolic abnormalities in multiple preclinical male and female models.

Synthesis and In Vitro Evaluation of Tetrahydroquinoline Derivatives as Antiproliferative Compounds of Breast Cancer via Targeting the GPER

BACKGROUND

Some reports have demonstrated the role of the G Protein-coupled Estrogen Receptor (GPER) in growth and proliferation of breast cancer cells.

OBJECTIVE

In an effort to develop new therapeutic strategies against breast cancer, we employed an in silico study to explore the binding modes of tetrahydroquinoline 2 and 4 to be compared with the reported ligands G1 and G1PABA.

METHODS

This study aimed to design and filter ligands by in silico studies determining their Lipinski's rule, toxicity and binding properties with GPER to achieve experimental assays as anti-proliferative compounds of breast cancer cell lines.

RESULTS

In silico studies suggest as promissory two tetrahydroquinoline 2 and 4 which contain a carboxyl group instead of the acetyl group (as is needed for G1 synthesis), which add low (2) and high hindrance (4) chemical moieties to explore the polar, hydrophobic and hindrance effects. Docking and molecular dynamics simulations of the target compounds were performed with GPER to explore their binding mode and free energy values. In addition, the target small molecules were synthesized and assayed in vitro using breast cancer cells (MCF-7 and MDA-MB-231). Experimental assays showed that compound 2 decreased cell proliferation, showing IC50 values of 50µM and 25µM after 72h of treatment of MCF-7 and MDA-MB-231 cell lines, respectively. Importantly, compound 2 showed a similar inhibitory effect on proliferation as G1 compound in MDA-MB-231 cells, suggesting that both ligands reach the GPER-binding site in a similar way, as was demonstrated through in silico studies.

CONCLUSION

A concentration-dependent inhibition of cell proliferation occurred with compound 2 in the two cell lines regardless of GPER.

A Selective Ligand for Estrogen Receptor Proteins Discriminates Rapid and Genomic Signaling

Estrogen exerts extensive and diverse effects throughout the body of women. In addition to the classical nuclear estrogen receptors (ERα and ERβ), the G protein-coupled estrogen receptor GPER is an important mediator of estrogen action. Existing ER-targeted therapeutic agents act as GPER agonists. Here, we report the identification of a small molecule, named AB-1, with the previously unidentified activity of high selectivity for binding classical ERs over GPER. AB-1 also possesses a unique functional activity profile as an agonist of transcriptional activity but an antagonist of rapid signaling through ERα. Our results define a class of small molecules that discriminate between the classical ERs and GPER, as well as between modes of signaling within the classical ERs. Such an activity profile, if developed into an ER antagonist, could represent an opportunity for the development of first-in-class nuclear hormone receptor-targeted therapeutics for breast cancer exhibiting reduced acquired and de novo resistance.

Gold-Catalyzed Hydroalkoxylation/Povarov Reaction Cascade of Alkynols with N-Aryl Imines: Synthesis of Tetrahydroquinolines

A one-pot gold-catalyzed hydroalkoxylation/Povarov reaction cascade of alkynols with N-aryl imines or in situ generated iminium has been developed. The protocol provides a facile access to a series of fused tricyclic tetrahydroquinolines with a broad substrate scope using readily available materials under mild conditions. The unique mechanistic feature is the dual function of the gold catalyst, which first catalyzed the intramolecular hydroalkoxylation of alkynols, and upon the formation of dihydrofuran species, promoted the following Povarov reaction with high stereoselectivity.

Progress in the Chemistry of Tetrahydroquinolines

Tetrahydroquinoline is one of the most important simple nitrogen heterocycles, being widespread in nature and present in a broad variety of pharmacologically active compounds. This Review summarizes the progress achieved in the chemistry of tetrahydroquinolines, with emphasis on their synthesis, during the period from mid-2010 to early 2018.

Sequential ligand- and structure-based virtual screening approach for the identification of potential G protein-coupled estrogen receptor-1 (GPER-1) modulators

G protein-coupled estrogen receptor-1 (GPER-1) is a seven transmembrane receptor, responsible for mediating rapid estrogen signaling in many physiological responses in reproductive, nervous, endocrine, immune and cardiovascular systems. Due to unavailability of the crystal structure of GPER-1, we have performed sequential ligand-based virtual screening (LBVS) and structure-based screening (SBVS) to identify potential GPER-1 modulators. LBVS and SBVS approaches were validated retrospectively using the Receiver Operating Curve (ROC) plot and the early Enrichment Factor (EF). LBVS was performed based on a GPER-1 agonist, G1, as a query model for screening of the eMolecules library using the Rapid Overlay of Chemical Structure (ROCS) and the electrostatic potential screening (EON) approaches. Top-scored hits from LBVS were further screened by SBVS. SBVS was based on generating homology models of GPER-1 and subsequent molecular docking studies. Using Chemguass4 score, we filtered the final hits with the higher score in comparison to G1 (Chemguass4 score = −11.575). The top-ranked hits were clustered based on similarity in their scaffolds. Prospective validation was performed by evaluating the antiproliferative activity of synthesized compounds (SK0 and SK0P) which were representative of top hits obtained from our virtual screening approach.

This paper presents the application of sequential ligand- and structure-based virtual screening approach for the identification of G protein-coupled estrogen receptor-1 (GPER-1/GPR30) modulators.

Is the membrane estrogen receptor, GPER1, a promiscuous receptor that modulates nuclear estrogen receptor-mediated functions in the brain?

Contribution to Special Issue on Fast effects of steroids. Estrogen signals both slowly to regulate transcription and rapidly to activate kinases and regulate calcium levels. Both rapid, non-genomic signaling as well as genomic transcriptional signaling via intracellular estrogen receptors (ER)s can change behavior. Rapid non-genomic signaling is initiated from the plasma membrane by a G-protein coupled receptor called GPER1 that binds 17β-estradiol. GPER1 or GPR30 is one of the candidates for a membrane ER (mER) that is not only highly expressed in pathology i.e. cancers but also in several behaviorally-relevant brain regions. In the brain, GPER1 signaling, in response to estrogen, facilitates neuroprotection, social behaviors and cognition. In this review, we describe several notable characteristics of GPER1 such as the ability of several endogenous steroids as well as artificially synthesized molecules to bind the GPER1. In addition, GPER1 is localized to the plasma membrane in breast cancer cell lines but may be present in the endoplasmic reticulum or the Golgi apparatus in the hippocampus. Unusually, GPER1 can also translocate to the perinuclear space from the plasma membrane. We explore the idea that subcellular localization and ligand promiscuity may determine the varied downstream signaling cascades of the activated GPER1. Lastly, we suggest that GPER1 can act as a modulator of ERα-mediated action on a convergent target, spinogenesis, in neurons that in turn drives female social behaviors such as lordosis and social learning.

2-Methoxyestradiol causes matrix metalloproteinase 9-mediated transactivation of epidermal growth factor receptor and angiotensin type 1 receptor downregulation in rat aortic smooth muscle cells

Studies have demonstrated the therapeutic potential of estrogen metabolite 2-methoxyestradiol (2ME2) in several cardiovascular disorders, including hypertension. However, the exact mechanism(s) remains unknown. In this study, primary rat aortic smooth muscle cells (RASMCs) were exposed to 2ME2, and angiotensin type 1 receptor (AT1R) expression, function, and associated signaling pathways were evaluated. In RASMCs, 2ME2 downregulated AT1R expression in a concentration- and time-dependent manner, which was correlated with reduced mRNA expression. The 2ME2 effect was through G protein-coupled receptor 30 (GPR30) that inhibits second messenger cAMP. Moreover, 2ME2 exposure phosphorylated ERK1/2 that was sensitive to MEK inhibitor PD98059. Selective epidermal growth factor receptor (EGFR) inhibitor AG1478 blocked 2ME2-induced EGFR transactivation and attenuated subsequent phosphorylation of ERK1/2 preventing AT1R downregulation. The transactivation was dependent on 2ME2-induced release of matrix metalloproteinase 9 (MMP9) and epidermal growth factor demonstrated by ELISA. Furthermore, transfection with small interfering (si) RNA targeting MMP9 impeded ERK1/2 activation and AT1R downregulation in response to 2ME2 and G1 stimulation. Interestingly, under similar conditions, stimulation of GPR30 with the selective agonist G1 elicited similar signaling pathways and downregulated the AT1R expression that was reversed by GPR30 antagonist G15. Furthermore, 2ME2 and G1 inhibited angiotensin II (ANG II) induced Ca2+ release, a response consistent with AT1R downregulation. Collectively, our study demonstrates for the first time that 2ME2 binding to GPR30 induces MMP9 specific transactivation of EGFR that mediates ERK1/2-dependent downregulation of AT1R in RASMCs. The study provides critical insights into the newly discovered role and signaling pathways of 2ME2 in the regulation of AT1R in vascular cells and its potential to be developed as a therapeutic agent that ameliorates hypertension.

Role of GPER in estrogen-dependent nitric oxide formation and vasodilation

Estrogens are potent regulators of vasomotor tone, yet underlying receptor- and ligand-specific signaling pathways remain poorly characterized. The primary physiological estrogen 17β-estradiol (E2), a non-selective agonist of classical nuclear estrogen receptors (ERα and ERβ) as well as the G protein-coupled estrogen receptor (GPER), stimulates formation of the vasodilator nitric oxide (NO) in endothelial cells. Here, we studied the contribution of GPER signaling in E2-dependent activation of endothelial NO formation and subsequent vasodilation. Employing E2 and the GPER-selective agonist G-1, we investigated eNOS phosphorylation and NO formation in human endothelial cells, and endothelium-dependent vasodilation in the aortae of wild-type and Gper-deficient mice. Both E2 and G-1 induced phosphorylation of eNOS at the activation site Ser1177 to similar extents. Endothelial NO production to E2 was comparable to that of G-1, and was substantially reduced after pharmacological inhibition of GPER. Similarly, the clinically used ER-targeting drugs 4OH-tamoxifen, raloxifene, and ICI182,780 (faslodex, fulvestrant™) induced NO formation in part via GPER. We identified c-Src, EGFR, PI3K and ERK signaling pathways to be involved in GPER-dependent NO formation. In line with activation of NO formation in cells, E2 and G-1 induced equally potent vasodilation in the aorta of wild-type mice. Gper deletion completely abrogated the vasodilator response to G-1, while reducing the response to E2 by ∼50%. These findings indicate that a substantial portion of E2-induced endothelium-dependent vasodilation and NO formation is mediated by GPER. Thus, selective targeting of vascular GPER may be a suitable approach to activate the endothelial NO pathway, possibly leading to reduced vasomotor tone and inhibition of atherosclerotic vascular disease.

Influences of non-canonical neurosteroid signaling on developing neural circuits

Developing neural circuits are especially susceptible to environmental perturbation. Endocrine signaling systems such as steroids provide a mechanism to encode physiological changes and integrate function across various biological systems including the brain. 'Neurosteroids' are synthesized and act within the brain across development. There is a long history of steroids sculpting developing neural circuits; more recently, evidence has demonstrated how neurosteroids influence the early potential for neural circuits to organize and transmit precise information via non-canonical receptor types.

Sex steroids regulate skin pigmentation through nonclassical membrane-bound receptors

The association between pregnancy and altered cutaneous pigmentation has been documented for over two millennia, suggesting that sex hormones play a role in regulating epidermal melanocyte (MC) homeostasis. Here we show that physiologic estrogen (17β-estradiol) and progesterone reciprocally regulate melanin synthesis. This is intriguing given that we also show that normal primary human MCs lack classical estrogen or progesterone receptors (ER or PR). Utilizing both genetic and pharmacologic approaches, we establish that sex steroid effects on human pigment synthesis are mediated by the membrane-bound, steroid hormone receptors G protein-coupled estrogen receptor (GPER), and progestin and adipoQ receptor 7 (PAQR7). Activity of these receptors was activated or inhibited by synthetic estrogen or progesterone analogs that do not bind to ER or PR. As safe and effective treatment options for skin pigmentation disorders are limited, these specific GPER and PAQR7 ligands may represent a novel class of therapeutics.

DOI:http://dx.doi.org/10.7554/eLife.15104.001

Factors controlling pigment production in skin are complex and poorly understood. Cells called melanocytes produce a pigment called melanin, which makes the skin darker. It has been known for a long time that skin color often changes during pregnancy, which suggests that sex hormones may be involved. However, the specific hormones and signaling mechanisms responsible for the changes have remained largely undefined.

Estrogen and progesterone are two of the main female sex hormones. Natale et al. now show that estrogen increases pigment production in human melanocytes, and progesterone decreases it.

For hormones to signal to cells, they must bind to and activate particular receptor proteins. Further investigation by Natale et al. revealed that estrogen and progesterone regulate pigment production by binding to receptors that belong to a family called G protein-coupled receptors. These receptors can signal rapidly once activated by sex hormones, and may serve as therapeutic targets for treating pigmentation disorders.

Skin diseases that cause inflammation often also cause changes in skin color. Natale et al. noticed several other G protein-coupled receptors that are likely to control pigmentation through similar mechanisms. Future analyses of the roles that these other receptors perform in melanocytes may therefore reveal how inflammation-based pigmentation changes occur.

DOI:http://dx.doi.org/10.7554/eLife.15104.002

Detection of the Phosphorylation of the Estrogen Receptor α as an Outcome of GPR30 Activation

Phosphorylation of the serine residues in estrogen receptor (ER) α is important in transcriptional activation. Hence, methods to detect such posttranslational modification events are valuable. We describe, in detail, the analysis of the phosphorylated ERα by electrophoretic separation of proteins and subsequent immuno-blotting techniques. In particular, phosphorylation of the ERα is one possible outcome of activation of the putative membrane estrogen receptor (mER), GPR30. Hence, phosphorylation represents a cross talk event between GPR30 and ERα and may be important in estrogen-regulated physiology.

G protein-coupled estrogen receptor inhibits vascular prostanoid production and activity

Complications of atherosclerotic vascular disease, such as myocardial infarction and stroke, are the most common causes of death in postmenopausal women. Endogenous estrogens inhibit vascular inflammation-driven atherogenesis, a process that involves cyclooxygenase (COX)-derived vasoconstrictor prostanoids such as thromboxane A2. Here, we studied whether the G protein-coupled estrogen receptor (GPER) mediates estrogen-dependent inhibitory effects on prostanoid production and activity under pro-inflammatory conditions. Effects of estrogen on production of thromboxane A(2) were determined in human endothelial cells stimulated by the pro-inflammatory cytokine tumour necrosis factor alpha (TNF-α). Moreover, Gper-deficient (Gper(-/-)) and WT mice were fed a pro-inflammatory diet and underwent ovariectomy or sham surgery to unmask the role of endogenous estrogens. Thereafter, contractions to acetylcholine-stimulated endothelial vasoconstrictor prostanoids and the thromboxane-prostanoid receptor agonist U46619 were recorded in isolated carotid arteries. In endothelial cells, TNF-α-stimulated thromboxane A2 production was inhibited by estrogen, an effect blocked by the GPER-selective antagonist G36. In ovary-intact mice, deletion of Gper increased prostanoid-dependent contractions by twofold. Ovariectomy also augmented prostanoid-dependent contractions by twofold in WT mice but had no additional effect in Gper(-/-) mice. These contractions were blocked by the COX inhibitor meclofenamate and unaffected by the nitric oxide synthase inhibitor l-N(G)-nitroarginine methyl ester. Vasoconstrictor responses to U46619 did not differ between groups, indicating intact signaling downstream of thromboxane-prostanoid receptor activation. In summary, under pro-inflammatory conditions, estrogen inhibits vasoconstrictor prostanoid production in endothelial cells and activity in intact arteries through GPER. Selective activation of GPER may therefore be considered as a novel strategy to treat increased prostanoid-dependent vasomotor tone or vascular disease in postmenopausal women.

International Union of Basic and Clinical Pharmacology. XCVII. G Protein-Coupled Estrogen Receptor and Its Pharmacologic Modulators

Estrogens are critical mediators of multiple and diverse physiologic effects throughout the body in both sexes, including the reproductive, cardiovascular, endocrine, nervous, and immune systems. As such, alterations in estrogen function play important roles in many diseases and pathophysiological conditions (including cancer), exemplified by the lower prevalence of many diseases in premenopausal women. Estrogens mediate their effects through multiple cellular receptors, including the nuclear receptor family (ERα and ERβ) and the G protein-coupled receptor (GPCR) family (GPR30/G protein-coupled estrogen receptor [GPER]). Although both receptor families can initiate rapid cell signaling and transcriptional regulation, the nuclear receptors are traditionally associated with regulating gene expression, whereas GPCRs are recognized as mediating rapid cellular signaling. Estrogen-activated pathways are not only the target of multiple therapeutic agents (e.g., tamoxifen, fulvestrant, raloxifene, and aromatase inhibitors) but are also affected by a plethora of phyto- and xeno-estrogens (e.g., genistein, coumestrol, bisphenol A, dichlorodiphenyltrichloroethane). Because of the existence of multiple estrogen receptors with overlapping ligand specificities, expression patterns, and signaling pathways, the roles of the individual receptors with respect to the diverse array of endogenous and exogenous ligands have been challenging to ascertain. The identification of GPER-selective ligands however has led to a much greater understanding of the roles of this receptor in normal physiology and disease as well as its interactions with the classic estrogen receptors ERα and ERβ and their signaling pathways. In this review, we describe the history and characterization of GPER over the past 15 years focusing on the pharmacology of steroidal and nonsteroidal compounds that have been employed to unravel the biology of this most recently recognized estrogen receptor.

G protein-coupled estrogen receptor protects from atherosclerosis

Coronary atherosclerosis and myocardial infarction in postmenopausal women have been linked to inflammation and reduced nitric oxide (NO) formation. Natural estrogen exerts protective effects on both processes, yet also displays uterotrophic activity. Here, we used genetic and pharmacologic approaches to investigate the role of the G protein-coupled estrogen receptor (GPER) in atherosclerosis. In ovary-intact mice, deletion of gper increased atherosclerosis progression, total and LDL cholesterol levels and inflammation while reducing vascular NO bioactivity, effects that were in some cases aggravated by surgical menopause. In human endothelial cells, GPER was expressed on intracellular membranes and mediated eNOS activation and NO formation, partially accounting for estrogen-mediated effects. Chronic treatment with G-1, a synthetic, highly selective small molecule agonist of GPER, reduced postmenopausal atherosclerosis and inflammation without uterotrophic effects. In summary, this study reveals an atheroprotective function of GPER and introduces selective GPER activation as a novel therapeutic approach to inhibit postmenopausal atherosclerosis and inflammation in the absence of uterotrophic activity.

Vascular effects of aldosterone: sorting out the receptors and the ligands

Aldosterone has actions far beyond its role as a renal regulator of sodium reabsorption, and broader mechanisms of action than simply a transcriptional regulator. Aldosterone has a number of vascular effects, including regulation of vascular reactivity and vascular growth and/or development. Aldosterone-mediated effects on vascular reactivity reflect a balance between its endothelial-dependent vasodilator effects and its direct smooth muscle vasoconstrictor effects. The endothelial vasodilator effects of aldosterone are mediated by phosphatidylinositol 3-kinase-dependent activation of nitric oxide synthase. G-Protein oestrogen receptor (GPER) is a recently recognized G-protein coupled receptor (GPCR) that is activated by steroid hormones. It was first recognized as the GPCR mediating the rapid effects of oestrogens. Activation of GPER also mediates at least some of the vascular effects of aldosterone in smooth muscle and endothelial cells. In vascular endothelial cells, aldosterone activation of GPER mediates vasodilation. In contrast, activation of endothelial mineralocorticoid receptors has been linked to enhanced vasoconstrictor and/or impaired vasodilator responses.

Exploration of uracils: pot and step economic production of pyridine core containing templates by multicomponent aza-Diels–Alder reaction

Substituted pyrido[2,3-d]pyrimidines can be obtained with good yields via a multicomponent aza-Diels–Alder reaction from easily available starting materials. The diene behaviour of different uracil derivatives was also elaborately investigated to synthesize desired products.

Activation of the GPR30 receptor promotes lordosis in female mice

BACKGROUND/AIMS

Estrogens are important effectors of reproduction and are critical for upregulating female reproductive behavior or lordosis in females. In addition to the importance of transcriptional regulation of genes by 17β-estradiol-bound estrogen receptors (ER), extranuclear signal transduction cascades such as protein kinase A (PKA) are also important in regulating female sexual receptivity. GPR30 (G-protein coupled receptor 30), also known as GPER1, a putative membrane ER (mER), is a G protein-coupled receptor that binds 17β-estradiol with an affinity that is similar to that possessed by the classical nuclear ER and activates both PKA and extracellular-regulated kinase signaling pathways. The high expression of GPR30 in the ventromedial hypothalamus, a region important for lordosis behavior as well as kinase cascades activated by this receptor, led us to hypothesize that GPR30 may regulate lordosis behavior in female rodents.

METHOD

In this study, we investigated the ability of G-1, a selective agonist of GPR30, to regulate lordosis in the female mouse by administering this agent prior to progesterone in an estradiol-progesterone priming paradigm prior to testing with stud males.

RESULTS

As expected, 17β-estradiol benzoate (EB), but not sesame oil, increased lordosis behavior in female mice. G-1 also increased lordosis behavior in female mice and decreased the number of rejective responses towards male mice, similar to the effect of EB. The selective GPR30 antagonist G-15 blocked these effects.

CONCLUSION

This study demonstrates that activation of the mER GPR30 stimulates social behavior in a rodent model in a manner similar to EB.

Microwave-assisted Expeditious and Efficient Synthesis of Cyclopentene Ring-fused Tetrahydroquinoline Derivatives Using Three-component Povarov Reaction

We report here an efficient and expeditious microwave-assisted synthesis of cyclopentadiene ring-fused tetrahydroquinolines using the three-component Povarov reaction catalyzed by indium (III) chloride. This method has an advantage of shorter reaction time (10 - 15 min) with high and reproducible yields (up to 90%) and is suitable for parallel library synthesis. The optimization process is reported and the results from the microwave route are compared with those of the conventional synthetic route. In almost all cases, the microwave acceleration consistently provided improved yields favoring the cis-diastereomer.

GPER-1 agonist G1 induces vasorelaxation through activation of epidermal growth factor receptor-dependent signalling pathway

Objectives

The G protein-coupled oestrogen receptor-1 (GPER-1) agonist G1 induces endothelium-dependent relaxation. Activation of the epidermal growth factor (EGF) receptor leads to transduction of signals from the plasma membrane for the release of nitric oxide. We tested the hypothesis that G1 induces endothelium-dependent vasorelaxation through activation of the EGF receptor.

Methods

Rat aortic rings were mounted in organ baths. After pretreatment with various inhibitors, aortic rings contracted with 11,9-epoxymethano-prostaglandin F2α or KCl were subjected to relaxation by G1.

Key findings

G1 induced endothelium-dependent vasorelaxation, which was attenuated by pretreatment with either L-Nω-nitroarginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase, or (3aS,4R,9bR)-4-(6-bromo-1,3-benzodioxol-5-yl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinoline HB-EGF, heparin-binding EGF-like growth factor, a GPER-1 antagonist. Neither a general oestrogen receptor antagonist, ICI 182 780, nor a selective oestrogen receptor-α antagonist, methyl-piperidino-pyrazole dihydrochloride (MPP), had an effect on G1-induced vasorelaxation. However, pretreatment with EGF receptor blockers, AG1478 or DAPH, resulted in attenuated G1-induced vasorelaxation. In addition, pretreatment with Src inhibitor 4-amino-3-(4-chlorophenyl)-1-(t-butyl)-1H-pyrazolo[3,4-d]pyrimidine, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine or Akt inhibitor VIII also resulted in attenuated vascular relaxation induced by the cumulative addition of G1. However, neither phosphatidylinositol-3 kinase inhibitors LY294002 and wortmannin nor an extracellular signal-regulated kinase inhibitor 1,4-diamino-2,3-dicyano-1,4-bis(o-aminophenylmercapto) butadiene monoethanolate had effect on vascular relaxation induced by the cumulative addition of G1.

Conclusions

G1 induces endothelium-dependent vasorelaxation through Src-mediated activation of the EGF receptor and the Akt pathway in rat aorta.

Contributions of academic laboratories to the discovery and development of chemical biology tools

The academic setting provides an environment that may foster success in the discovery of certain types of small molecule tools while proving less suitable in others. For example, small molecule probes for poorly understood systems, those that exploit a specific resident expertise, and those whose commercial return is not apparent are ideally suited to be pursued in a university setting. In this review, we highlight five projects that emanated from academic research groups and generated valuable tool compounds that have been used to interrogate biological phenomena: reactive oxygen species (ROS) sensors, GPR30 agonists and antagonists, selective CB2 agonists, Hsp70 modulators, and β-amyloid PET imaging agents. By taking advantage of the unique expertise resident in university settings and the ability to pursue novel projects that may have great scientific value but with limited or no immediate commercial value, probes from academic research groups continue to provide useful tools and generate a long-term resource for biomedical researchers.

Synthesis and characterization of tricarbonyl-Re/Tc(I) chelate probes targeting the G protein-coupled estrogen receptor GPER/GPR30

The discovery of the G protein-coupled estrogen receptor GPER (also GPR30) and the resulting development of selective chemical probes have revealed new aspects of estrogen receptor biology. The potential clinical relevance of this receptor has been suggested from numerous studies that have identified GPER expression in breast, endometrial, ovarian and other cancers. Thus GPER can be considered a candidate biomarker and target for non-invasive imaging and therapy. We have designed and synthesized a series of organometallic tricarbonyl-rhenium complexes conjugated to a GPER-selective small molecule derived from tetrahydro-3H-cyclopenta[c]quinoline. The activity and selectivity of these chelates in GPER-mediated signaling pathways were evaluated. These results demonstrate that GPER targeting characteristics depend strongly on the structure of the chelate and linkage. Ethanone conjugates functioned as agonists, a 1,2,3-triazole spacer yielded an antagonist, and derivatives with increased steric volume exhibited decreased activities. Promising GPER selectivity was observed, as none of the complexes interacted with the nuclear estrogen receptors. Radiolabeling with technetium-99m in aqueous media was efficient and gave radioligands with high radiochemical yields and purity. These chelates have favorable physicochemical properties, show excellent stability in biologically relevant media, exhibit receptor specificity and are promising candidates for continuing development as diagnostic imaging agents targeting GPER expression in cancer.

Identification of a GPER/GPR30 antagonist with improved estrogen receptor counterselectivity

GPER/GPR30 is a seven-transmembrane G protein-coupled estrogen receptor that regulates many aspects of mammalian biology and physiology. We have previously described both a GPER-selective agonist G-1 and antagonist G15 based on a tetrahydro-3H-cyclopenta[c]quinoline scaffold. The antagonist lacks an ethanone moiety that likely forms important hydrogen bonds involved in receptor activation. Computational docking studies suggested that the lack of the ethanone substituent in G15 could minimize key steric conflicts, present in G-1, that limit binding within the ERα ligand binding pocket. In this report, we identify low-affinity cross-reactivity of the GPER antagonist G15 to the classical estrogen receptor ERα. To generate an antagonist with enhanced selectivity, we therefore synthesized an isosteric G-1 derivative, G36, containing an isopropyl moiety in place of the ethanone moiety. We demonstrate that G36 shows decreased binding and activation of ERα, while maintaining its antagonist profile towards GPER. G36 selectively inhibits estrogen-mediated activation of PI3K by GPER but not ERα. It also inhibits estrogen- and G-1-mediated calcium mobilization as well as ERK1/2 activation, with no effect on EGF-mediated ERK1/2 activation. Similar to G15, G36 inhibits estrogen- and G-1-stimulated proliferation of uterine epithelial cells in vivo. The identification of G36 as a GPER antagonist with improved ER counterselectivity represents a significant step towards the development of new highly selective therapeutics for cancer and other diseases.