Biomedical subjects

Shubin Sheng

Publications and source records attributed to Shubin Sheng.

9 recordsLinked to original sources

PubMed2007

Structure-guided optimization of estrogen receptor binding affinity and antagonist potency of pyrazolopyrimidines with basic side chains.

2,3-Diarylpyrazolo[1,5-a]pyrimidines are estrogen receptor (ER) antagonists of modest potency that we have described previously. Guided by the crystal structure of an ER-ligand complex that we have obtained with one of these compounds, we prepared analogs that contain a basic side chain at the 2- or 3-aryl group and quickly found one that, according to the structure-based prediction, shows an increase in binding affinity and antagonist potency and a loss of residual agonist activity.

Cell Line, Tumor↗

PubMed2004

Pyrazolo[1,5-a]pyrimidines: estrogen receptor ligands possessing estrogen receptor beta antagonist activity.

In our search for novel subtype-selective estrogen receptor (ER) ligands, we have examined various heterocyclic units as core structural elements. Here, we have investigated the fused, bicyclic pyrazolo[1,5-a]pyrimidine core, which is a system that allows for analogues to be readily assembled in a library-like fashion. This series of pyrazolo[1,5-a]pyrimidine ER ligands provided us with a new pharmacological profile for an ER ligand: compounds that are passive on both ERs, with a distinct potency selectivity in favor of ERbeta. The most distinctive ligand in this series, 2-phenyl-3-(4-hydroxyphenyl)-5,7-bis(trifluoromethyl)-pyrazolo[1,5-a]pyrimidine, was 36-fold selective for ERbeta in binding. Curiously, on the basis of molecular modeling, the ERbeta binding selectivity of compounds in this series appears to be derived from differing orientations that they adapt in the ligand binding pockets of ERalpha vs ERbeta. In transcription assays this pyrazolopyrimidine was fully effective as an ERbeta antagonist while exhibiting no significant activity on ERalpha. Thus, this ligand functions as a potency- and efficacy-selective ERbeta antagonist that would abrogate estrogen action through ERbeta with minimal effects on its activity through ERalpha; as such, it could be used to study the biological function of ERbeta.

Binding, Competitive↗

PubMed2004

Equol, a natural estrogenic metabolite from soy isoflavones: convenient preparation and resolution of R- and S-equols and their differing binding and biological activity through estrogen receptors alpha and beta.

Equol is a metabolite produced in vivo from the soy phytoestrogen daidzein by the action of gut microflora. It is known to be estrogenic, so human exposure to equol could have significant biological effects. Equol is a chiral molecule that can exist as the enantiomers R-equol and S-equol. To study the biological activity of racemic (+/-)-equol, as well as that of its pure enantiomers, we developed an efficient and convenient method to prepare (+/-)-equol from available isoflavanoid precursors. Furthermore, we optimized a method to separate the enantiomers of equol by chiral HPLC, and we studied for the first time, the activities of the enantiomers on the two estrogen receptors, ERalpha and ERbeta. In binding assays, S-equol has a high binding affinity, preferential for ERbeta (K(i)[ERbeta]=16 nM; beta/alpha=13 fold), that is comparable to that of genistein (K(i)[ERbeta]=6.7 nM; beta/alpha=16), whereas R-equol binds more weakly and with a preference for ERalpha (K(i)[ERalpha]=50 nM; beta/alpha=0.29). All equol isomers have higher affinity for both ERs than does the biosynthetic precursor daidzein. The availability and the in vitro characterization of the equol enantiomers should enable their biological effects to be studied in detail.

Antineoplastic Agents↗

PubMed2004

Allosteric control of ligand selectivity between estrogen receptors alpha and beta: implications for other nuclear receptors.

Allosteric communication between interacting molecules is fundamental to signal transduction and many other cellular processes. To better understand the relationship between nuclear receptor (NR) ligand positioning and the formation of the coactivator binding pocket, we investigated the determinants of ligand selectivity between the two estrogen receptor subtypes ERalpha and ERbeta. Chimeric receptors and structurally guided amino acid substitutions were used to demonstrate that distinct "hot spot" amino acids are required for ligand selectivity. Residues within the ligand binding pocket as well as distal secondary structural interactions contribute to subtype-specific positioning of the ligand and transcriptional output. Examination of other NRs suggests a mechanism of communication between the ligand and coactivator binding pockets, accounting for partial agonist and dimer-specific activity. These results demonstrate the importance of long-range interactions in the transmission of information through the ligand binding domain as well as in determining the ligand selectivity of closely related NR receptor subtypes.

Allosteric Regulation↗

PubMed2003

Novel estrogen receptor ligands based on an anthranylaldoxime structure: role of the phenol-type pseudocycle in the binding process.

The 3,4-diphenylsalicylaldoxime system 1 is an estrogen receptor (ER) ligand of unusual structure, having a hydrogen-bonded pseudocyclic A'-ring in place of the paradigmatic phenolic A-ring that is characteristic of most estrogens. We have investigated the role played by the pseudocycle A' in binding to the ER by preparing 3,4-diphenylbenzaldoxime (4), a compound that completely lacks this ring but still preserves all of the other features of the original molecule 1, as well as a series of 3,4-diphenylanthranylaldoximes (5a-c) in which the nature of the heteroatom participating in the formation of pseudoring A' has been changed from an oxygen (1) to a nitrogen that is either unsubstituted (5a) or substituted with small alkyl groups (a methyl in 5b, or an ethyl in 5c). The importance of hydrogen-bonded pseudocycle A' in the binding process was confirmed by the fact that benzaldoxime 4 showed a greatly reduced binding affinity compared to salicylaldoxime 1. Moreover, the binding affinity improved considerably when the A'-ring contained either an unsubstituted nitrogen (5a) or an N-Me group (5b). On the other hand, the N-Et-substituted anthranyl derivative 5c showed a marked drop in binding affinity. Molecular modeling docking studies on ERalpha confirmed that compounds 5a and 5b fit nicely in the ligand binding pocket, with an especially comfortable fit for the N-Me group of 5b in a small hydrophobic pocket surrounded by nonpolar residues. The limited size of this pocket does not allow accommodation of N-substituents larger than a methyl group, which is consistent with the low binding affinity of the N-Et compound 5c.

Benzene Derivatives↗

PubMed2003

Activities of estrogen receptor alpha- and beta-selective ligands at diverse estrogen responsive gene sites mediating transactivation or transrepression.

Estrogens exert their regulatory transcriptional effects, which can be stimulatory or repressive, at diverse gene sites via two estrogen receptors, ERalpha and ERbeta. Since these two ERs have different tissue distributions, ligands that have the capacity to selectively activate or inhibit these two ERs would be useful in elucidating the biology of these two receptors and might assist in the development of estrogen pharmaceuticals with improved tissue selectivity. We have developed several ligands that showed ERalpha or ERbeta selectivity at promoter-gene sites containing consensus estrogen response elements (EREs): ERalpha-selective agonist (propyl-pyrazole-triol (PPT)), ERalpha-selective antagonist (methyl-piperidino-pyrazole (MPP)), ERbeta-potency selective agonist (diarylpropionitrile (DPN)) and ERbeta-selective antagonist/ERalpha-agonist (R,R-tetrahydrochrysene (R,R-THC)). In this study, we have examined the activity of these compounds at a range of gene sites where ER stimulates gene expression through non-consensus EREs (complement C3), or multiple half-EREs (NHE-RF/EBP50), or by tethering to DNA via other proteins (TGF beta3 and progesterone receptor A/AP-1), and at gene sites where ER represses gene transcription (interleukin-6). At all of these genes, PPT showed full stimulation through ERalpha while displaying no agonism through ERbeta. MPP antagonized estradiol actions on gene transactivation and transrepression through ERalpha, with little or no effect on transcription mediated through ERbeta. DPN displayed subtype-selective agonism, being ca. 30-fold more potent through ERbeta. R,R-THC was a complete antagonist through ERbeta and displayed agonism through ERalpha, the level of which was promoter dependent. Because these ligands maintain their agonist or antagonist character and ER subtype-selectivity at gene sites of diverse nature, where estradiol is either stimulatory or inhibitory, these compounds should prove useful in elucidating the biological functions of ERalpha and ERbeta.

Cell Line, Tumor↗

PubMed2003

Bridged bicyclic cores containing a 1,1-diarylethylene motif are high-affinity subtype-selective ligands for the estrogen receptor.

The actions of estrogens are mediated through the two estrogen receptors, ERalpha and ERbeta. Compounds that interact selectively with ERalpha or ERbeta are of interest because they could be used to explore the biological roles of these ER subtypes and they might be interesting estrogen pharmaceuticals. In a new approach to develop ER subtype-selective ligands, we have embellished the 1,1-diarylethylene motif, common to many nonsteroidal estrogens, with various bridged bicyclic or tricyclic cores, including ones based on bicyclo[3.3.1]nonane, bicyclo[2.2.1]heptane, and selected bi- and tricyclic terpenoids. This design leads to three-dimensional ER ligands of unusual structure that we have used to probe the size and shape of the ligand binding pocket of ERalpha and ERbeta. Many of these compounds have high binding affinities, with the best having a bicyclo[3.3.1]nonane core and binding 3-5 times better than estradiol to both ER subtypes. Some of the compounds show significant affinity selectivity in favor of ERbeta (4- to 5-fold), and in cell-based assays for transcriptional activity most are partial agonists on ERalpha and full antagonists on ERbeta.

Binding, Competitive↗

PubMed2003

Synthesis, binding affinity, and transcriptional activity of hydroxy- and methoxy-substituted 3,4-diarylsalicylaldoximes on estrogen receptors alpha and beta.

An effective, unprecedented replacement of the prototypical phenolic 'A-ring' of estrogens with an oxime and a hydroxy-moiety of the salicylaldoxime derivative 3,4-diphenyl-substituted (1a) opened the way to study structure-activity relationships of a new class of estrogen receptor (ER)-ligands. Herein, we present a study of the ER binding properties and transcriptional activities of analogues of 3,4-diphenylsalicylaldoxime (1a). The introduction of p-OH and p-OMe groups on the phenyl substituents of 1a, as in compounds 1b-g, results in unique structure-activity profiles. The preparation of the hetero-disubstituted compounds (1b-e) was accomplished by a sequential introduction of different 3- and 4-aryl groups, obtained by exploiting the different reactivity of the bromine versus chlorine substituents on the precursor, 2-bromo-3-chloronitrobenzene (5), in the palladium-catalyzed cross-coupling reactions. The results of the biological tests show that the introduction of one hydroxy-group on the 3-phenyl substituent of the lead compound 1a improved the binding affinity on ERbeta (1c), whereas the introduction of the same group on the 4-phenyl substituent of 1a gave a compound (1e) with better affinity properties on ERalpha. The introduction of two hydroxyl groups in the para-position of both phenyl substituents of 1a, as in 1g, lowered the binding on both receptor subtypes. In transcription assays, the ERalpha agonist character of this class of ligands is enhanced by the presence of a p-hydroxy or p-methoxy in the 'distal' phenyl ring, whereas substitution on the other phenyl ring does not substantially modify the partial agonist character of 1a. Thus, results from the binding and transcription assays illustrate that this class of ER ligands has a distinct structure-activity profile on the two ER subtypes, being potent nearly full agonists on ERalpha and weak, partial antagonists on ERbeta.

Cloning, Molecular↗

PubMed2002

Antagonists selective for estrogen receptor alpha.

To develop compounds that are antagonists on ER(alpha), but not ER(beta), we have added basic side-chains typically found in nonsteroidal antiestrogens to pyrazole compounds that bind with much higher affinity to ER(alpha) than to ER(beta). In this way we have developed basic side-chain pyrazoles (BSC-pyrazoles) that are high affinity, potent, selective antagonists on ER(alpha). These BSC-pyrazoles are themselves inactive on ER(alpha) and ER(beta), and they antagonize E2 stimulation by ER(alpha) only. We investigated seven basic side-chain substituents on various alkyl-triaryl-substituted pyrazoles, and the most ER(alpha)-selective compound was methyl-piperidino-pyrazole (MPP). ER(alpha)-selective antagonism was observed on diverse reporter-promoter gene constructs containing estrogen response elements that are consensus, nonconsensus (pS2), or comprised of multiple half-estrogen response elements (NHERF/EBP50) and on genes in which ER works indirectly by tethering to other DNA-bound proteins (TGF(beta)3). In contrast to these BSC-pyrazoles, the antiestrogens trans-hydroxytamoxifen, raloxifene, and ICI 182,780 suppress E2 activity via both ER(alpha) and ER(beta). The most effective BSC-pyrazole, MPP, fully antagonized E2 stimulation of pS2 mRNA in MCF-7 breast cancer cells, consistent with the fact that these cells contain almost exclusively ER(alpha). These compounds should be useful in studying the biological functions of ER(alpha) and ER(beta) and in selectively blocking responses that are mediated through ER(alpha).

Estrogen Antagonists↗