Estrogen receptor binding tolerance of 16 alpha-substituted estradiol derivatives

In order to examine the tolerance of the estrogen receptor for 16 alpha-substituents in estradiol, we have synthesized various 16 alpha-substituted estrogens and determined their binding affinity for receptor by a competitive radiometric binding assay. The substituents ranged from small, single-atom substituents (halogens), two-atom substituents (halomethyl groups), to larger alkyl groups and ultimately alkyl groups bearing various functionality, including fluorescent (nitrobenzoxadiazole, NBD) and photoreactive (nitroazidophenyl, NAP) groups. The estrogen receptor seems to have a moderate tolerance for bulky substituents: All of the halogen and halomethyl substituents bind with an affinity at least 50% that of estradiol; in the three atom alkyl series, the affinity declined markedly from propargyl (44%) and allyl (38%) to propyl (5%), suggestive of detailed steric constraints or a preference for unsaturation. The larger, more highly functionalized derivatives ranged in affinity from 0.1-7%, with the highest affinity binders being benzyl (5%) and 4-phenoxy-2(E)-butenyl (7%); most of the lowest affinity ones were the bulky fluorescent and photoreactive derivatives. Thus, the estrogen receptor has good tolerance for estradiol derivatives substituted at the 16 alpha-position with nonpolar groups of moderate bulk; however, with groups of larger bulk, affinity is much lower and becomes highly dependent upon the polarity and detailed structure of the substituents.     

Estrogen receptor ligands. Part 6: Synthesis and binding affinity of dihydrobenzodithiins

Dihydrobenzodithiin compounds (1-6) were prepared to explore the expansion of the dihydrobenzoxathiin lead compounds I-III as SERAMs (Selective Estrogen Receptor Alpha Modulators). The dihydrobenzodithiin compounds generally maintained a high degree of selectivity for ERalpha over ERbeta, however, they lacked the in vivo antagonism/agonism activity exhibited by the lead class in an immature rat uterine growth model.     

Estrogen receptor stereochemistry: receptor binding and hormonal responses

Estrogen stimulation of the uterus elicits a spectrum of biochemical responses which are customarily linked together. DES and certain structural analogs, indenestrol A (IA), indenestrol B (IB), indanestrol (I), and pseudo DES (PD), were used as probes to segregate various genomic responses previously considered interrelated, most notably the events of specific protein synthesis, DNA synthesis, and mitosis. These compounds have poor uterotrophic activity; except for I, they interact specifically with mouse uterine estrogen receptors (ER) with high affinity. All translocate stoichiometrically similar amounts of ER complex to the nucleus. IA and IB possess a single chiral carbon atom and exist as a mixture of enantiomers (ENT). We investigated whether the poor biological activity of IA could be explained by differential activity of the enantiomers. The IA ENT were separated to greater than 98% purity using a chirally active HPLC column. Competitive binding assays to cytosolic ER demonstrated a stereochemical chiral preference. This preference was also evident from nuclear ER translocation experiments. IB was as active as DES to induce mouse uterine glucose 6-phosphate dehydrogenase (G-6-PD), while the other compounds had weak activity. Induction of cytosolic progesterone receptor (PR) was stimulated by all the DES compounds. Ornithine decarboxylase (ODC) was stimulated 600% by DES and 180% by IB; the other compounds had no significant activity. Uterine DNA synthesis was increased by DES and IB. Thymidine autoradiography indicated nuclear labeling was occurring primarily in luminal epithelium. Treatment with PD increased uterine cell height but not cell numbers, suggesting the two responses are not necessarily interdependent as previously thought and may require two separate receptor interactions. Such a probe should be useful in studying the individual events involved in estrogen-induced uterine growth. These data also indicate that induction of ER, PR and G-6-PD are not coupled. Therefore, stimulation of a certain uterine response may depend on the structure of the particular ligand receptor complex formed, and its interaction may be regulated by specificity at the genomic acceptor site.     

Dihydrotestosterone derivatives: relative binding affinity versus affinity purification.

Mono esters of a homologous series of diacids of dihydrotestosterone were synthesized and converted to the corresponding n-butyl amides. The relative binding affinities of these amides to androgen receptor were compared with the degree of purification of rat prostate androgen receptor by affinity columns prepared by linking the steroidal acid to amino Sepharose. There was good correlation between binding of the amide model to androgen receptor and the extent of purification by the affinity resin.     

Synthesis,binding affinity and SAR of new benzolactam derivatives as dopamine D3 receptor ligands

A series of new benzolactam derivatives was synthesized and the derivatives were evaluated for their affinities at the dopamine D₁, D₂, and D₃ receptors. Some of these compounds showed high D₂ and/or D₃ affinity and selectivity over the D₁ receptor. The SAR study of these compounds revealed structural characteristics that decisively influenced their D₂ and D₃ affinities. Structural models of the complexes between some of the most representative compounds of this series and the D₂ and D₃ receptors were obtained with the aim of rationalizing the observed experimental results. Moreover, selected compounds showed moderate binding affinity on 5-HT_2A which could contribute to reducing the occurrence of extrapyramidal side effects as potential antipsychotics.     

Synthesis and androgen receptor binding of dihydrotestosterone hemisuccinate homologs

Dihydrotestosterone-succinyl-agarose is the most common form of androgen affinity column. To investigate the effect of variation in the number of methylene groups between the ester and amide functions, a homologous series, varying the number of methylenes between the functional groups, has been synthesized and evaluated. In addition, since structure studies show 17 alpha-methyldihydrotestosterone binds with high affinity, a 17 alpha-carboxymethyl ligand (3) was studied. Relative binding affinities of the dicarboxylates (assayed as the n-butyl amides) range from 0.003 to 0.044 (dihydrotestosterone = 1.00), while there was no detectable binding for 3. Only the suberate binds better than the much-used succinate, and it would be a likely candidate for an affinity ligand.     

Modulation of steroid affinity for the androgen receptor by sucrose

The effects of sucrose on androgen binding to its receptor were investigated. Sucrose decreased the rate of thermal inactivation of unoccupied and occupied androgen receptor (AR) and the rates of [3H]5 alpha-dihydrotestosterone [( 3H]DHT) dissociation from both activated and nonactivated AR complexes. Binding of [3H]DHT to AR in vivo, or in intact cells at 37 degrees C, caused reduction of [3H]DHT dissociation from cytosolic and nuclear complexes, as compared to in vitro labeled receptor complexes. Further, exposure of these complexes to sucrose at 0 degrees C caused an additional reduction of dissociation rates. Thus, the decrease of [3H]DHT dissociation induced by sucrose is independent of the reaction that reduces DHT dissociation from activated and transformed AR. Sucrose also reduced the ability of mersalyl acid to inactivate AR complexes. This effect of sucrose was markedly diminished in the presence of 2M urea. Sucrose did not significantly affect the association rate, sedimentation properties, or nuclear binding ability of AR complexes, but it did decrease the equilibrium dissociation constant. Other monosaccharides and disaccharides also stabilized AR. These data suggest that sucrose induces conformational changes in the steroid binding domain of androgen receptor, thereby reducing the rates of inactivation, steroid dissociation, and the accessibility of sulfhydryl groups to mersalyl.     

Estrogen receptor stereochemistry: ligand binding and hormonal responsiveness

Estrogen stimulation of the uterus produces a spectrum of biochemical responses that are customarily linked together. This report is an overview of a series of studies by our laboratory investigating the role of different ligand structures in eliciting hormonal responses. Diethylstilbestrol (DES) and certain structural analogs, indenestrol A (IA), indenestrol B (IB), and pseudo-DES, were used as probes to segregate various genomic responses previously considered interrelated, most notably the events of specific protein synthesis and DNA synthesis. These compounds have weak uterotrophic activity; however, they interact with high affinity specifically with mouse uterine estrogen receptors (ERs). All of them produce stoichiometrically similar amounts of ER complex in the nucleus. Indenestrol A and IB possess a single chiral carbon atom and exist as a mixture of enantiomers (ENTs). Competitive binding assays of pure ENTs and cytosolic ERs demonstrated a stereochemical chiral preference for the IA isomer but not IB. This preference was also evident from nuclear ER occupancy experiments. Biologic activity of the IA ENTs also demonstrated differences as seen by receptor binding. Ornithine decarboxylase (ODC) activity was stimulated 600% by DES and partially by IA (rac). All of the ODC activity produced by IA (rac) was due to the IA(C3)-S ENT. Uterine DNA synthesis was measured after treatment with the IA compounds. Indenestrol A (rac) increased DNA synthesis to 40% of the level seen with DES. The weak ENTs showed no activity and the active ENTs were weaker than the IA racemic. These compounds should be useful probes for studying the individual responses involved in estrogen-induced uterine growth.(ABSTRACT TRUNCATED AT 250 WORDS)     

Redox-dependent DNA binding of the purified androgen receptor: evidence for disulfide-linked androgen receptor dimers.

Full-length histidine-tagged, dihydrotestosterone-bound human androgen receptor (AR) was purified to homogeneity by affinity and gel-filtration chromatography for antibody production and analysis of AR dimerization and DNA binding properties. A monoclonal antibody was raised that recognized human and rat AR epitope (360)ArgAspTyrTyrAsnPheProLeuAla(368) in the NH(2)-terminal domain and slowed migration of AR-DNA complexes in mobility shift assays. AR binding to androgen response element DNA had a K(d) of 2.0 nM and a Hill coefficient of 2.1, indicating high-affinity, cooperative binding. AR solution dimerization was detected only at >/=0.2 microM AR, and DNA binding increased dimerization up to 30-fold. Slow- and fast-migrating AR-DNA complexes were detected under different reducing conditions that differed 5-fold in their dissociation rates from DNA. Treatment with the sulfhydryl oxidizing reagent diamide formed the faster migrating, slower dissociating complex, indicating it represents disulfide-linked AR dimers bound to DNA. The results indicate that high concentrations of purified AR are required for solution dimerization and that cooperative DNA binding stabilizes two dimer forms that differ in redox state.     

Peptide hormone-membrane interactions: the aggregational and conformational state of lipo-gastrin derivatives and their receptor binding affinity.

The (2RS)-1,2-dipalmitoyl-3-mercaptoglycerol/-, (2RS)-1,2-dimyristoyl-3-mercaptoglycerol/-, and (2RS)-1-myristoyl-2-palmitoyl-3-mercaptoglycerol/maleoyl-bet a-alanyl- [Nle15]-human-gastrin-(2-17) adducts were prepared as lipo-gastrin derivatives of explicitly primary amphiphilic properties. As representative of this class of lipo-gastrins, the dimyristoyl derivative has been thoroughly characterized in its aggregational state since, among the three compounds, theoretically it should exhibit the lowest degree of lipid character. It aggregates in aqueous solution to form monodispersed unilamellar spherical vesicles with dislocation of the peptide moiety at the bilayer surface in predominantly unordered structure. The liposomes are remarkably stable toward solubilization with trifluoroethanol and toward vesicle to micelle transition with neutral and negatively charged surfactants even above their critical micellar concentrations. Asymmetric fusion with the detergent micelles induces polydispersion of the liposomes in terms of shape and size without affecting in significant manner the mode of display of the gastrin portions at the bilayer surface. Only the positively charged hexadecyltrimethylammonium hydroxide provokes the collapse of the vesicles into mixed micelles with concomitant altered dislocation of the gastrin-peptide in the new aggregational state. Despite the lipid properties of the gastrin derivatives, i.e., formation of liposomes, they retain remarkable receptor affinities (IC50 = 1.5 x 10(-9) M for myristoyl-palmitoyl-gastrin, IC50 = 2.0 x 10(-9) M for di-myristoyl-gastrin and IC50 = 3.1 x 10(-9) M for di-palmitoyl-gastrin vs IC50 = 2.8 x 10(-10) M for Nle15-gastrin). Since the displacement of radiolabeled Nle15-gastrin from rat pancreatic acinar cell line membrane preparations by both the parent gastrin hormone and the three lipo-gastrins occurs in parallel manner, the data support a mechanism of receptor occupancy via accumulation of the gastrins at the membrane surface and their two-dimensional diffusion to the target receptor. Thereby the differentiated decrease of affinity in function of fatty acid chain length has to be attributed to the energetically more or less favored transfer of the monomers from the donor vesicles to the acceptor membranes. Moreover, according to this model migration of the lipo-gastrins with their interdigitating di-fatty-acyl moieties should be delayed, again in lipid structure-dependent manner, in comparison to the parent gastrin molecule, which is free to float in the membrane interfacial phase.     

Relative binding affinity of novel steroids to androgen receptors in hamster prostate

The in vivo and in vitro antiandrogenic activity of four aromatic esters 10a-10d, one aliphatic ester 10e based on the pregna-4,16-diene-6, 20-dione structure and two aromatic 17c, 17d and two aliphatic valeroyloxy esters 17a, 17b based on the more saturated 4-pregnene-6,20-dione skeleton was examined. The biological activity of steroids 9, 10a-10e and 17a-17d, was determined using prostate glands from gonadectomized adult male golden hamsters. In the in vitro studies, the relative binding affinity of these steroids to cytoplasmic androgen receptor (AR) of hamster prostate was determined from, the corresponding IC50 values obtained from the competitive binding plots. The standards dihydrotestosterone (DHT) and cyproterone (CA) acetate used have displaced [3H]DHT from the AR with an IC50 value of 3.2 and 4.4 nM respectively. All steroidal compounds synthesized in this study showed a binding affinity for the androgen receptor, present in the cytosol from prostate hamster; compounds 10a-10c showed the highest affinities for this receptor. The in vivo experiments showed that all steroidal derivatives were subcutaneously active, since they decreased the weight of the prostate gland in gonadectomized hamsters treated with DHT, and are antagonists for the androgen receptor since they block the DHT-induced prostate weight gain. The derivatives having the more conjugated 4,16-pregnadiene-6, 20-dione system (10a-10c) exhibited a higher antiandrogenic activity than the corresponding steroids (17a-17d) based on the more saturated 4-pregnene-6,20-dione system.     

4-Azasteroidal 5 alpha-reductase inhibitors without affinity for the androgen receptor

In efforts to develop potent 5 alpha-reductase inhibitors without affinity for the androgen receptor, synthetic 3-oxo-5 alpha-steroids were tested for their ability to inhibit 5 alpha-reductase, using [14C]testosterone as the substrate, and for their ability to inhibit the binding of [3H]5 alpha-dihydrotestosterone to the androgen receptor of rat prostate cytosol. 2',3' alpha-Tetrahydrofuran-2'-spiro-17-(5 alpha-androstan-3-one) is not an inhibitor of 5 alpha-reductase and has a high affinity for the androgen receptor; substitution of the -CH2- at the 4-position with N-H resulted in a good inhibitor of 5 alpha-reductase. The 4-N-CH3 derivative is even more active, whereas the N-CH2-CH3 derivative is inactive. These 4-aza derivatives have much lower affinity for the androgen receptor than the parent compound. The 4-N-H derivatives of several 3-oxo-5 alpha-steroids were found to be 20-100% as potent as their corresponding 4-N-CH3 analogs as inhibitors of 5 alpha-reductase, whereas their androgen receptor affinities were at least 40-fold lower than their 4-N-CH3 analogs. Their 5 beta-isomers did not inhibit either 5 alpha-reductase or the androgen receptor binding of [3H]5 alpha-dihydrotestosterone. Two of these 4-N-H steroids, 17 beta-N,N-diethylcarbamoyl-4-aza-5 alpha-androstan-3-one and 17 beta-N, N-diisopropylcarbamoyl-4-aza-5 alpha-androstan-3-one, are potent 5 alpha-reductase inhibitors with Ki values equal to 29.2 +/- 1.7 and 12.6 +/- 0.8 nM, respectively, but have little affinity for the androgen receptor. The inhibition of 5 alpha-reductase by both compounds is competitive with testosterone. When [3H]testosterone was incubated with minced rat prostate in the presence of either of these two 4-azasteroids, the nuclear concentration of 5 alpha-dihydrotestosterone decreased and that of testosterone increased. The total nuclear uptake of testosterone plus 5 alpha-dihydrotestosterone was not significantly affected. These 4-azasteroids should be useful for investigating the importance of 5 alpha-reductase in androgen action in vivo.     

雌激素受体亚型及其配体调节基因转录机制的研究

本文综述雌激素受体亚型（ERα和ERβ）的结构,功能,组织分布,生理作用及雌激素受体配体调节基因转录的机制,目的是深入系统地了解植物雌激素和选择性雌激素受体调节剂的作用路径及其组织特异性的发生机制,最终为提高雌激素类药物的选择性,优化以临床为基础的药物设计提供一条较为系统的思路。结果表明,ERα和ERβ对不同雌激素类化合物产生不同应答,配体的结构不同,调节基因转录的路径不同和募集的辅调节蛋白的不同是雌激素受体两种亚型组织特异性激活或抑制的主要原因。     

2-Pyridin-2-yl-1H-indole derivatives: synthesis, estrogen receptor binding affinity, and photophysical properties

A series of novel 2-pyridin-2-yl-1H-indole derivatives (4a-f) was prepared by intramolecular cyclodehydration of alpha-anilinyl (or 3-anisidyl)-2-pyridin-2-yl-ethanones (2a-f) and their optical spectroscopy and estrogen receptor (ER) binding properties were studied. These compounds showed long wavelength fluorescent emission, which is sensitive to solvent polarity and pH, while indol-6-ols 4b, e, and f displayed reasonably good binding affinities to ER.     

Estrogen receptor ligands counteract cognitive deficits caused by androgen deprivation in male rats

Androgen deprivation causes impairment of cognitive tasks in rodents and humans, and this deficit can be reverted by androgen replacement therapy. Part of the effects of androgens in the male may be mediated by their local metabolism to estradiol or 3-alpha androstanediol within the brain and the consequent activation of estrogen receptors. In this study we have assessed whether the administration of estradiol benzoate, the estrogen receptor β selective agonist diarylpropionitrile or the estrogen receptor α selective agonist propyl pyrazole triol affect performance of androgen-deprived male Wistar rats in the cross-maze test. In addition, we tested the effect of raloxifene and tamoxifen, two selective estrogen receptor modulators used in clinical practice. The behavior of the rats was assessed 2 weeks after orchidectomy or sham surgery. Orchidectomy impaired acquisition in the cross-maze test. Estradiol benzoate and the selective estrogen receptor β agonist significantly improved acquisition in the cross-maze test compared to orchidectomized animals injected with vehicle. Raloxifene and tamoxifen at a dose of 1 mg/kg, but not at doses of 0.5 or 2 mg/kg, also improved acquisition of orchidectomized animals. Our findings suggest that estrogenic compounds with affinity for estrogen receptor β and selective estrogen receptor modulators, such as raloxifene and tamoxifen, may represent good candidates to promote cognitive performance in androgen-deprived males.     

Synthesis and SAR of novel hydantoin derivatives as selective androgen receptor modulators

A novel series of hydantoin derivatives were identified by in vivo studies as tissue selective androgen receptor modulators. SAR around this series revealed that the function of the ligand could be altered by minor structural modification.     

Steroid derivatives for electrophilic affinity labelling of glucocorticoid binding sites: interaction with the glucocorticoid receptor and biological activity

To investigate the possible use of electrophilic affinity labelling for the characterization of glucocorticoid receptors, different chemically reactive derivatives of deoxycorticosterone (deoxycorticosterone 21-mesylate and deoxycorticosterone 21-(1-imidazole) carboxylate), dexamethasone (dexamethasone 21-mesylate, dexamethasone 21-iodoacetate and dexamethasone 21-bromoacetate) and progesterone (21-chloro progesterone) were tested for their ability to bind irreversibly to the glucocorticoid receptor from goat lactating mammary gland. Using partially purified receptor, only one of the steroids tested, dexamethasone 21-mesylate (DXM-M) was found more effective than dexamethasone (DXM) in preventing exchange of radioactive dexamethasone in the receptor binding site. The affinity of DXM-M for the glucocorticoid receptor, measured by competitive binding assay, was 1/15 that of DXM. Polyacrylamide gel electrophoresis in sodium dodecyl sulphate of the [3H]-DXM-M labeled glucocorticoid receptor revealed a specific covalently radiolabeled fraction corresponding to an apparent molecular weight of 75,000 to 80,000. The biological activity of DXM-M was studied in RPMI 3460-clone 6 Syrian hamster melanoma cells, a cell line which is sensitive to growth inhibition by glucocorticoids. Like DXM, DXM-M inhibits the growth of RPMI 3460-clone 6 cells and it acts as a slowly reversible glucocorticoid agonist at concentrations which correlate with the affinity of DXM-M for the glucocorticoid receptor in vitro.