In silico identification of novel inhibitors targeting the DNA-binding domain of the human estrogen receptor alpha

The human estrogen receptor alpha (ERα) is an important regulator in breast cancer development and progression. The frequent ERα mutations in the ligand-binding domain (LBD) can increase the resistance of antiestrogen drugs, highlighting the need to develop new drugs to target ERα-positive breast cancer. In this study, we combined molecular docking, molecular dynamics simulations and binding free energy calculations to develop a structure-based virtual screening workflow to identify hit compounds capable of interfering with the recognition of ERα by the specific response element of DNA. A druggable pocket on the DNA binding domain (DBD) of ERα was identified as the potential binding site. The hits binding modes were further analyzed to reveal the structural characteristics of the DBD-inhibitor complexes. The core structure of the lead molecules was synthesized and was found to inhibit the E2-induced cell proliferation in MCF-7 cell lines. These findings provide an insight into the structural basis of ligand-ERα for alternate sites beyond the LBD-based pocket. The core structure proposed in this study could potentially be used as the lead molecule for further rational optimization of the antiestrogen drug structure with stronger binding of DBD and higher activity.

The Structure-Function Relationship of Angular Estrogens and Estrogen Receptor Alpha to Initiate Estrogen-Induced Apoptosis in Breast Cancer Cells

High-dose synthetic estrogen therapy was the standard treatment of advanced breast cancer for three decades until the discovery of tamoxifen. A range of substituted triphenylethylene synthetic estrogens and diethylstilbestrol were used. It is now known that low doses of estrogens can cause apoptosis in long-term estrogen deprived (LTED) breast cancer cells resistant to antiestrogens. This action of estrogen can explain the reduced breast cancer incidence in postmenopausal women over 60 who are taking conjugated equine estrogens and the beneficial effect of low-dose estrogen treatment of patients with acquired aromatase inhibitor resistance in clinical trials. To decipher the molecular mechanism of estrogens at the estrogen receptor (ER) complex by different types of estrogens-planar [17β-estradiol (E2)] and angular triphenylethylene (TPE) derivatives-we have synthesized a small series of compounds with either no substitutions on the TPE phenyl ring containing the antiestrogenic side chain of endoxifen or a free hydroxyl. In the first week of treatment with E2 the LTED cells undergo apoptosis completely. By contrast, the test TPE derivatives act as antiestrogens with a free para-hydroxyl on the phenyl ring that contains an antiestrogenic side chain in endoxifen. This inhibits early E2-induced apoptosis if a free hydroxyl is present. No substitution at the site occupied by the antiestrogenic side chain of endoxifen results in early apoptosis similar to planar E2 The TPE compounds recruit coregulators to the ER differentially and predictably, leading to delayed apoptosis in these cells. SIGNIFICANCE STATEMENT: In this paper we investigate the role of the structure-function relationship of a panel of synthetic triphenylethylene (TPE) derivatives and a novel mechanism of estrogen-induced cell death in breast cancer, which is now clinically relevant. Our study indicates that these TPE derivatives, depending on the positioning of the hydroxyl groups, induce various conformations of the estrogen receptor's ligand-binding domain, which in turn produces differential recruitment of coregulators and subsequently different apoptotic effects on the antiestrogen-resistant breast cancer cells.

Design and Synthesis of Novel Breast Cancer Therapeutic Drug Candidates Based upon the Hydrophobic Feedback Approach of Antiestrogens

Based upon hydrophobic feedback approaches, we designed and synthesized novel sulfur-containing ERα modulators (4 and 5) as breast cancer therapeutic drug candidates. The tetrahydrothiepine derivative 5a showed the highest binding affinity toward ERα because of its high hydrophobicity, and it acted as an agonist toward MCF-7 cell proliferation. The corresponding alkylamino derivative 5d maintained high binding affinity to ERα and potently inhibited MCF-7 cell proliferation (IC₅₀: 0.09 μM). Docking simulation studies of compound 5d with the ERα BD revealed that the large hydrophobic moiety of compound 5d fit well into the hydrophobic pocket of the ERα LBD and that the sulfur atom of compound 5d formed a sulfur–π interaction with the amino acid residue His524 of the ERα LBD. These interactions play important roles for the binding affinity of compound 5d to the ERα LBD.

3,20-Dihydroxy-13α-19-norpregna-1,3,5(10)-trienes. Synthesis, structures, and cytotoxic, estrogenic, and antiestrogenic effects

New 3,20-dihydroxy-13α-19-norpregna-1,3,5(10)-trienes were synthesized. The effects of these compounds on breast cancer cells and ERα activation were investigated. The scaffold of compounds containing the six-membered ring D' annulated at 16α,17α-positions was constructed via the Lewis acid catalyzed Diels-Alder reaction of butadiene with 3-methoxy-13α-19-norpregna-1,3,5(10),16-tetraen-20-one 5 under a pressure of 600 MPa. The hydrogenation of primary cyclohexene adduct 6 followed by the one-pot reduction-demethylation (DIBAH) gave target epimeric 3,20-dihydroxy steroids 8a and 8b. The Corey-Chaykovsky reaction of the same conjugated ketone 5 gave a 16α,17α-methylene-substituted compound. The reaction of the latter with DIBAH yielded 3,20(R,S)-dihydroxy-16α,17α-methyleno-13α-19-norpregna-1,3,5(10)-triene 10. The hydrogenation of the 16,17-double bond of compound 5 produced a mixture of 17α- and 17β-epimeric ketones, reduction-demethylation of which gave 3,20(S)-dihydroxy-13α,17α-19-norpregna-1,3,5(10)-triene 12a and 3,20(R)-dihydroxy-13α,17β-19-norpregna-1,3,5(10)-triene 12b. All compounds were fully characterized by 1D and 2D NMR, HRMS, and X-ray diffraction. All target compounds showed pronounced cytotoxic effect against MCF-7 breast cancer cells and NCI/ADR-RES doxorubicin-resistant cells at micromolar concentrations. The ERα-mediated luciferase reporter gene assay demonstrated that all compounds, except for compound 10, are ERα inhibitors, while cyclopropane compound 10 proved to be an ERα activator. Docking experiments showed that all compounds are well accommodated to LBD ERα but have some differences in the binding mode.

Synthesis and preliminary evaluation steroidal antiestrogen-geldanamycin conjugates

Three novel steroidal antiestrogen-geldanamycin conjugates were prepared using a convergent strategy. The antiestrogenic component utilized the 11β-(4-functionalized-oxyphenyl) estradiol scaffold, while the geldanamycin component was derived by replacement of the 17-methoxy group with an appropriately functionalized amine. Ligation was achieved in high yield using azide alkyne cyclization reactions. Evaluation of the products against two breast cancer cell lines indicated that the conjugates retained significant antiproliferative activity.

Synthesis and characterization of fluorescent 4-hydroxytamoxifen conjugates with unique antiestrogenic properties

Membrane receptors for steroid hormones are currently a subject of considerable debate. One approach to selectively target these putative receptors has been to couple ligands to substances that restrict cell permeability. Using this approach, an analogue of the estrogen receptor ligand 4-hydroxytamoxifen was attached to fluorescent dyes with differing degrees of predicted cell permeability. The conjugates bound to estrogen receptor in vitro, but all three conjugates, including one predicted to be cell-impermeable, inhibited estradiol-induced transcriptional activation. Fluorescence microscopy revealed cytoplasmic localization for all three conjugates. We further characterized a 4-hydroxytamoxifen analogue conjugated to a BODIPY fluorophore in breast cancer cell lines. Those experiments suggested a similar, but not identical, mode of action to 4-hydroxytamoxifen, as the fluorescent conjugate was equally effective at inhibiting proliferation of both tamoxifen-sensitive and tamoxifen-resistant breast cancer cell lines. While these findings point to significant complicating factors in designing steroid hormone mimics targeted to the plasma membrane, the results also reveal a possible new direction for designing estrogen receptor modulators.

Loss of antagonistic activity of tamoxifen by replacement of one N-methyl of its side chain by fluorinated residues

Efforts to limit the metabolic alteration of the aminoalkyl side chain of tamoxifen by fluorination largely decrease its ER-mediated antagonistic properties in MCF-7 cells (i.e., ability to inhibit growth, to stabilize ER, and to modulate ERE and AP-1 transcriptional activity). This loss is associated with an enhancement of agonistic activity. Loss of interaction between Asp 351 and the nitrogen atom of tamoxifen provoked by the fluorination of its side chain may explain this property.

Antiestrogenically active 2-benzyl-1,1-diarylbut-2-enes: synthesis, structure-activity relationships and molecular modeling study for flexible estrogen receptor antagonists

The nonsteroidal antiestrogen drug tamoxifen is the endocrine treatment of choice for estrogen receptor positive breast cancer, while the related estrogen receptor antagonist raloxifene is an effective therapeutic intervention for osteoporosis. We report the development of a series of hydroxylated 2-benzyl-1,1-diarylbut-2-enes containing a flexible core scaffold structure differing from the 1,1,2-triarylethylene typical of tamoxifen analogues. In this novel structure, a benzylic methylene group acts as a flexible hinge linking the aryl ring C and the ethylene group. The target products were synthesized using a McMurry coupling (titanium tetrachloride/zinc mediated) procedure. In this study, introduction of hydroxyl, ether and ester substitution on ring C was explored in an attempt to correlate possible metabolic activation in Ring C with antiproliferative activity. These Ring C substituted products showed potent antiproliferative activity against the MCF-7 human breast cancer cell line. The compounds were also shown to have high binding affinity for the estrogen receptor (IC(50) values in the low nanomolar range) together with up to 17 fold selectivity for ERalpha/beta. Some compounds demonstrated antiestrogenic activity in the Ishikawa cells at 40 nM without estrogenic stimulation. The products also displayed a pro-apoptotic effect in MCF-7 cells in a flow cytometry based assay. In a computational study, docked structures of the active compounds were compared with the X-ray crystal structures for the complexes of ERalpha with 4-hydroxytamoxifen and ERbeta with raloxifene. The novel ligands are predicted to bind to the ERalpha and ERbeta in an antiestrogenic orientation, with expected differences obtained in the alignment of the benzylic ring C within the ligand binding domain.

[Cytotoxic steroids with antiestrogenic activity of the 11alpha-acyloxyestra-1,3,5(10)-triene series]

Esterification of 3-hydroxyl group in 11-acyloxyestra-1,3,5(10)-trienes with p-[bis(2-chloroethyl)amino]phenylacetic acid led to antitumor steroids displaying antiestrogenic and cytotoxic activities. Our substances exhibit their activities on the model of murine mammary adenocarcinoma Ca-755, with inhibition of the tumor growth being 94-99%. A new approach was used for the 11alpha-hydroxylation of estra-1,3,5(10)-trienes.

[N-ethyl- and [N,N'-diethyl-1,2-bis(2,6-difluoro-3-hydroxyphenyl)-ethylenediamine]dichloroplatinum(II): structure and cytotoxic/estrogenic activity in breast cancer cells

N-Ethyl and N,N'-diethyl derivatives (erythro- and threo-2-PtCl2; meso- and D,L-3-PtCl2) of [meso- and [D,L-1,2-bis(2,6-difluoro-3-hydroxyphenyl)ethylenediamine]dichloroplatinum(II) (meso- and D,L-1-PtCl2) were synthesized and tested for cytotoxicity on the estrogen receptor-positive (ER+) human MCF-7 breast cancer cell line. In this test, only D,L-1-PtCl2 and threo-2-PtCl2 showed strong cytotoxic properties. This revealed the existence of at least one NH2 fragment as a prerequisite for antitumor activity. Furthermore, studies on the three-dimensional structure of the new compounds demonstrated that the aryl and alkyl residues at the five-membered chelate ring have to be arranged in equatorial positions for the triggering of cytotoxic effects, very likely due to the reaction with d(GpG) sequences in DNA resulting in GG-N7,N7 chelates. A contribution of the ER-mediated processes--(a) hindrance of the cellular processing of Pt-modified DNA by overexpression of high mobility group domain proteins and (b) interruption of the vicious circle of mutual growth stimulation of breast cancer cells and granulocytes/macrophages by reduction of the formation of key cytokines--to the anti-breast cancer activity of threo-2-PtCl2 is unlikely, since we did not observe transcription activation in the test on ER+ MCF-7 breast cancer cells stably transfected with luciferase reporter plasmid ERE(wtc)luc.

A Selective Estrogen Receptor Modulator for the Treatment of Hot Flushes

A selective estrogen receptor modulator (SERM) for the potential treatment of hot flushes is described. (R)-(+)-7,9-difluoro-5-[4-(2-piperidin-1-ylethoxy)phenyl]-5H-6-oxachrysen-2-ol, LSN2120310, potently binds ERalpha and ERbeta and is an antagonist in MCF-7 breast adenocarcinoma and Ishikawa uterine cancer cell lines. The compound is a potent estrogen antagonist in the rat uterus. In ovariectomized rats, the compound lowers cholesterol, maintains bone mineral density, and is efficacious in a morphine dependent rat model of hot flush efficacy.

Solid-Phase Organic Synthesis (SPOS) of Modulators of Estrogenic and Androgenic Action

Estrogens and androgens are key growing factors involved in a large series of disorders. Two main strategies are possible for controlling their undesirable agonist effects: (1) blocking their biosynthesis by using selective enzyme inhibitors, and (2) antagonizing their hormonal action on a receptor with an antiestrogen or an antiandrogen. In this review, we will briefly discuss the identification of a series of important therapeutic targets, through the study of steroidogenesis of potent estrogens, estrone and estradiol, and potent androgens, testosterone and dihydrotestosterone, as well as of their nuclear receptors. We will next review the solid-phase synthesis of steroidogenic enzyme (steroid sulfatase and 17beta-hydroxysteroid dehydrogenases) inhibitors and steroid (estrogen and androgen) receptor modulators, all being potential therapeutic agents for the treatment of hormone-sensitive diseases.

Differential response of estrogen receptor subtypes to 1,3-diarylindene and 2,3-diarylindene ligands

Estrogen receptors (ERs) control transcription of genes important for normal human development and reproduction. The signaling networks are complex, and there is a need for a molecular level understanding of the roles of receptor subtypes ERalpha and ERbeta in normal physiology and as therapeutic targets. We synthesized two series of ER ligands, based on a common indene scaffold, in an attempt to develop compounds that can selectively modulate ER-mediated transcription. The 3-ethyl-1,2-diarylindenes, utilizing an amide linker for the 1-aryl extension, bind weakly to the ERs. The 2,3-diarylindenes bind with high affinity to the ER subtypes and demonstrate a range of different biological activities, both in transcriptional reporter gene assays and inhibition of estradiol-stimulated proliferation of MCF-7 cells. Several ligands differentiate between ERalpha and ERbeta subtypes at an estrogen response element (ERE), displaying various levels of partial to full agonist activity at ERalpha, while antagonizing estradiol action at ERbeta.

Estrogen receptor ligands. Part 13: Dihydrobenzoxathiin SERAMs with an optimized antagonist side chain

An optimized side chain for dihydrobenzoxathiin SERAMs was discovered and attached to four dihydrobenzoxathiin platforms. The novel SERAMs show exceptional estrogen antagonist activity in uterine tissue and an MCF-7 breast cancer cell assay.

Synthesis and biological evaluation of stilbene-based pure estrogen antagonists

Replacement of one of the ethyl substituents in diethylstilbestrol by side chains with functional groups converted this potent estrogen into pure antiestrogens with the potential for the treatment of breast cancer. These agents completely suppressed estrogen receptor-mediated gene activation and inhibited the growth of estrogen-sensitive MCF-7 breast cancer cells in submicromolar concentrations. The most potent derivative displayed similar activity as fulvestrant (ICI 182,780) in vitro and in the mouse uterine weight test. Obviously, the stilbene structure can act as a substitute for estradiol in the development of pure estrogen antagonists.

Estrogen receptor ligands. Part 5: The SAR of dihydrobenzoxathiins containing modified basic side chains

Dihydrobenzoxathiin analogs (1-11) with modifications on the basic side chain region were prepared and evaluated for estrogen/anti-estrogen activity in both in vitro and in vivo models. The compounds generally maintained a high degree of selectivity for ERalpha over ERbeta, similar to the original lead compound I. Many of the compounds also maintained high potency in the inhibition of human carcinoma MCF-7 cell growth. However, all were less potent in the inhibition of estradiol-triggered uterine growth. This work demonstrates the sensitive nature of modification to the antagonist basic side chain region.

Diaryl naphthyl methanes a novel class of anti-implantation agents

Diaryl naphthyl methanes and the corresponding 1, 2, 3, 4- and 5, 6, 7, 8-tetrahydro naphthyl methane derivatives have been synthesized as novel estrogen receptor binding ligands. The secondary and tertiary amino alkoxy derivatives of diaryl naphthyl and tetrahydro naphthyl methane interact with the estrogen receptor to elicit promising estrogenic, antiestrogenic and implantation inhibition activities in rats. The most active compounds in this series are 7, 9 and 20, cent percent active in preventing implantation in rats at 2.5 mgkg(-1) dose.

Synthesis, structure, and screening of estrogenic and antiestrogenic activity of new 3,17-substituted-16,17-seco-estratriene derivatives

The starting compound for synthesis of new 16,17-seco-estratriene derivatives was 3-benzyloxy-17-hydroxy-16,17-secoestra-1,3,5(10)-triene-16-nitrile (1b), obtained from estrone in several synthetic steps. 17-Tosyl, -chloro-, bromo-, and -iodo- derivatives 2b, 4b, 5b, and 6b were prepared directly from secocyanoalcohol 1b, while the 17-fluoro-derivative 3b was obtained from tosylate 2b in the reaction with tetrabutyl ammonium fluoride. The corresponding 3-hydroxy derivatives of these compounds were produced by action of hydrogen in presence of Pd/C, except the 3-hydroxy-17-iodo derivative 6a, which was obtained from 3-hydroxy-17-tosyloxy derivative 2a. All the newly synthesized compounds in biological tests on experimental animals exhibited an almost total loss of estrogenic activity, while most of them even prevented the action of endogenous estrogens. On the other hand, most of them, except compounds 3a and 6b, partially hindered the action of estradiol benzoate, behaving as moderate antagonists.

Estrogen receptor-related receptors: orphan receptors desperately seeking a ligand

The nuclear receptor family comprises ligand-dependent and orphan receptors. To the latter group belong the estrogen receptor-related receptors (ERRs) for which conflicting results have been published concerning the nature (constitutive or liganded) of their transcriptional activities. ERRs interfere in various ways, positively and negatively, with estrogen signaling. Moreover recent data analyzing ERR expression in human breast tumors have proposed ERRalpha and ERRgamma as prognostic markers of these cancers. The identification of modulators (positive or negative) of ERR activities would therefore be highly useful in our understanding of estrogen-related pathologies. The purpose of this review is to summarize our knowledge of the nature of ERR activities and progresses in identifying synthetic ERR modulators.

Inhibition of estrone sulfate-induced uterine growth by potent nonestrogenic steroidal inhibitors of steroid sulfatase

The present study describes the biological in vitro and in vivo evaluation of 2-methoxy derivatives of estrogenic inhibitors of steroid sulfatase, namely 3-sulfamoyloxy-17alpha-p-tert-butylbenzyl(or benzyl)-1,3,5 (10)-estratrien-17beta-ols. The addition of the 2-methoxy group conserves the potent inhibitory effect on steroid sulfatase activity (IC(50)s of 0.024 and 0.040 nM) while removing the estrogenic action. Using an ovariectomized mouse model, we show that the first generation of steroid sulfatase inhibitors tested, 3-sulfamoyloxy-17alpha-p-tert-butylbenzyl(or benzyl)estra-1,3,5 (10)-trien-17beta-ols and estrone-3-O-sulfamate, are estrogenic compounds stimulating estrogen-sensitive uterine growth. Interestingly, the 2-methoxy-3-sulfamoyloxy-17alpha-benzylestra-1,3,5 (10)-trien-17beta-ol (7) has no estrogenic activity but efficiently blocks (s.c. and p.o.) uterine growth induced by estrone sulfate, which is converted into estrone and then estradiol by steroid sulfatase and type 1 17beta-hydroxysteroid dehydrogenase, respectively. This report clearly shows that a steroid sulfatase inhibitor can efficiently block estrogen action from the inactive precursor estrone sulfate, in vitro and in vivo.

First dual aromatase-steroid sulfatase inhibitors

Aromatase inhibitors in clinical use block the biosynthesis of estrogens. Hydrolysis of estrone 3-sulfate by steroid sulfatase is an important additional source of tumor estrogen, and blockade of both enzymes should provide a more effective endocrine therapy. Sulfamoylated derivatives of the aromatase inhibitor YM511 inhibited sulfatase and aromatase in JEG-3 cells with respective IC(50) values of 20-227 and 0.82-100 nM (cf. letrozole, 0.89 nM). One dual inhibitor was potent against both enzymes in vivo, validating the concept.

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.

A multidetachable sulfamate linker successfully used in a solid-Phase strategy to generate libraries of sulfamate and phenol derivatives

The sulfamates and phenols constitute two families of compounds with numerous interesting biological properties. Using the ability of a new multidetachable sulfamate linker to generate these two families of compounds from the same resin, we designed and synthesized libraries of estradiol derivatives, sulfamoylated or not. A C-16beta side chain was then judiciously diversified to target two key steroidogenic enzymes, the steroid sulfates and the type 1 17beta-HSD. Four libraries of sulfamate and phenol derivatives were easily obtained by solid-phase parallel synthesis in good crude overall yields (13-62%) and HPLC purities (85-96%). Such strategy using the new two-in-line sulfamate linker could be also extended to other therapeutic targets than steroidogenic enzymes, thus adding to its potential.

Synthesis of some new diaryl and triaryl hydrazone derivatives as possible estrogen receptor modulators

1,2-Bis(4-substituted phenyl)-2-methyl ethanone (2,4-dinitrophenyl)hydrazones and 1-naphthyl-1-(4-substituted phenyl)-methanone (2,4-dinitrophenyl)hydrazones have been synthesized and evaluated for their anti-implantation, uterotrophic, antiuterotrophic, anticancer and antimicrobial activities. Diphenolic hydrazone (compound 6) showed maximum uterotrophic inhibition of 70%, whereas compound 20 exhibited cytotoxicity in the range of 50-70% against MCF-7 and ZR-75-1 human malignant breast cell lines.

Synthesis of (bis)sulfonic acid, (bis)benzamides as follicle-stimulating hormone (FSH) antagonists

Screening efforts identified (bis)sulfonic acid, (bis)benzamides (1-3) as compounds that interact with the follicle stimulating-hormone receptor (FSHR) and inhibit FSH-stimulated cAMP accumulation with IC(50) values in the low micromolar range. Structure-activity relationship studies using novel analogues of 1-3 revealed that two phenylsulfonic acid moieties were necessary for activity and that the carbon-carbon double bond of the stilbene sub-series was the optimum spacer connecting these groups. Selected analogues (2, 14, and 50) were also able to block FSHR-dependent estradiol production in rat primary ovarian granulosa cells and progesterone secretion in a clonal mouse adrenal Y1 cell line. IC(50) values for these compounds in these assays were in the low micromolar range. Optimization of the benzoic acid side chains of 1-3 led to gains in selectivity versus activity at the thyroid stimulating hormone (TSH) receptor (TSHR). For instance, while stilbene (bis)sulfonic acid congener 2 was only 10-fold selective for FSHR over TSHR, analogue 50 with an IC(50) value of 0.9 microM in the FSHR-cAMP assay was essentially inactive at 30 microM in the TSHR-cAMP assay.

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).

D-Secoestrone derivatives. V1. 3-Methoxy-17-oxo-17-phenyl-16,17-secoestra-1,3,5(10)-triene-16-nitrile and 17-hydroxy-3-methoxy-17-phenyl-16,17-secoestra-1,3,5(10)-triene-16-nitrile

The two title 16,17-secoestrone derivatives, 3-methoxy-17-oxo-17-phenyl-16,17-secoestra-1,3,5(10)-triene-16-nitrile, C(25)H(27)NO(2), (I) (17-oxo substituent), and 17-hydroxy-3-methoxy-17-phenyl-16,17-secoestra-1,3,5(10)-triene-16-nitrile, C(25)H(29)NO(2), (II) (17-hydroxy substituent), have quite different conformations in the solid state. These conformational differences can be minimized by molecular mechanics calculations. Thus, the remarkable difference in the biological activity of the two compounds, e.g. the strong oestrogenic characteristics of (I) and the moderate antioestrogenic action of (II), must be caused by the difference in substitution at C17. In (II), the molecules are linked by O-H...N hydrogen bonds, forming spirals along the b direction.

Photochemical synthesis of N-arylbenzophenanthridine selective estrogen receptor modulators (serms)

Selective estrogen receptor modulators are an emerging class of pharmaceutically important molecules. Many compounds in this class contain an aminoethoxyaryl moiety attached to a polycyclic framework at an asymmetric carbon atom. To assess whether this carbon atom can be replaced by nitrogen, we have employed a Ninomiya enamide photocyclization for the rapid synthesis of a novel N-arylbenzophenanthridine framework, 4. Further elaboration of 4 into a new structural class of achiral, nonsteroidal estrogen receptor modulators is described.

Centchroman, a selective estrogen receptor modulator, as a contraceptive and for the management of hormone-related clinical disorders

DL-Centchroman (67/20; INN: Ormeloxifene) synthesized at the Central Drug Research Institute, Lucknow, is a nonsteroidal once-a-week oral contraceptive. It was introduced in Delhi in July, 1991, marketed in India in 1992 as Saheli and Choice-7 (Hindustan Latex Ltd., Thiruvananthapuram) and Centron (Torrent Pharmaceuticals India Ltd., Ahmedabad), and included in the National Family Welfare Programme in 1995.5 According to post-marketing surveillance, approximately 100,000 women were using this pill and approximately 1100,000 menstrual cycles were covered until 1996. It is a unique need-oriented contraceptive being effective when taken immediately after coitus or routinely as a weekly pill and has the advantage of less frequent administration. Its contraceptive action is quickly reversible. It has long terminal serum halflife of 168 hr in women and exhibits duration of anti-implantation/estrogen antagonistic action of 120 hr, despite a short (24.1 hr) serum halflife, in the rat. In lactating women, it is excreted in milk in quantities considered unlikely to cause any deleterious effect on suckling babies. In phase II and III multicentric trials as a contraceptive, children born of method-and-user failure pregnancies showed normal milestones, without any congenital anomaly. Reports of its promising action in the management of certain hormone-related clinical disorders are available. It has an excellent therapeutic index and is considered safe for chronic administration.

Flexible estrogen receptor modulators: design, synthesis, and antagonistic effects in human MCF-7 breast cancer cells

Although many series of estrogen receptor antagonists continue to be produced, the majority are direct structural analogues of existing modulators. To examine the tolerance of the estrogen receptor toward flexible ligands, a series of novel flexible estrogen receptor antagonists were prepared and their antiproliferative effects on human MCF-7 breast tumor cells investigated. Each of these compounds deviated from the traditional triphenylethylene backbone associated with common tamoxifen analogues through the introduction of a flexible methylene (benzylic) spacing group between one of the aryl rings and the ethylene group and through variations in the basic side chain moiety. The compounds prepared, when assayed in conjunction with a tamoxifen standard, demonstrated high potency in antiproliferative assays against an MCF-7 human breast cancer cell line with low cytotoxicity and high binding affinity. A computational study was undertaken to investigate the compounds' potential interactions with specific residues within the human estrogen receptor alpha ligand-binding domain (ER-LBD), predicting these compounds bind in an antiestrogenic fashion within the ER-LBD and interact with those important residues previously identified in the structures of ER-LBD agonist/antagonist cocrystals. These compounds further illustrate the eclectic nature of the estrogen receptor in terms of ligand flexibility tolerance.

Ethyl side-chain modifications in novel flexible antiestrogens--design, synthesis and biological efficacy in assay against the MCF-7 breast tumor cell line

To examine the efficacy of ethyl side-chain modifications in a family of flexible non-steroidal modulators of the estrogen receptor, a series of novel compounds was prepared and their antiproliferative effects on human MCF-7 breast tumor cells evaluated. These flexible antiestrogens consisted of members wherein the ethyl portion of the parent compound, a flexible analogue of tamoxifen, had been modified so as to introduce halogens or a nitro group, or to extend the side-chain length from ethyl to propyl or butyl. The compounds demonstrated potency at low micromolar concentrations in antiproliferative assays against an MCF-7 human breast cancer cell line with low associated cytotoxicity. Tested compounds exhibited nanomolar binding affinity (Ki) for the estrogen receptor (ER) as determined through displacement of radiolabelled estradiol. Semiempirical calculations predict an inherent lower oxidative potential at the allylic position, similar to that calculated for the established analogue toremifene, indicating a lesser propensity of such compounds towards metabolic oxidative carbocation generation and consequent DNA adduct formation. Computational studies predict these compounds to bind in a typical estrogen antagonist mode within the ER-ligand binding domain (LBD). Ethyl side-chain modification in this compound class is well tolerated within the ER and is not detrimental to compound efficacy, with additional potential anti-carcinogenic properties imbued to the molecule.

Triarylpyrazoles with basic side chains: development of pyrazole-based estrogen receptor antagonists

Recently, we developed a novel triaryl-substituted pyrazole ligand system that has high affinity for the estrogen receptor (ER) (Fink, B. E.: Mortenson, D. S.: Stauffer, S. R.; Aron, Z. D.: Katzenellenbogen, J. A. Chem. Biol. 1999, 6, 205). Subsequent work has shown that some analogues in this series are very selective for the ERalpha subtype in terms of binding affinity and agonist potency (Stauffer, S. R.: Coletta, C. J.: Tedesco. R.: Sun, J.: Katzenellenbogen, J. A. J. Med. Chem. 2000, submitted). We now investigate how this pyrazole ER agonist system might be converted into an antagonist or a selective estrogen receptor modifier (SERM) by incorporating a basic or polar side chain like those typically found in antiestrogens and known to be essential determinants of their mixed agonist/antagonist character. We selected an N-piperidinyl-ethyl chain as a first attempt, and introduced it at the four possible sites of substitution on the pyrazole core structure to determine the orientation that the pyrazole might adopt in the ER ligand binding pocket. Of these four, the C(5) piperidinyl-ethoxy-substituted pyrazole 5 had by far the highest affinity. Also, it bound to the ER subtype alpha (ERalpha) with 20-fold higher affinity than to ERbeta. In cell-based transcription assays, pyrazole 5 was an antagonist on both ERalpha and ERbeta, and it was also more potent on ERalpha. Based on structure-binding affinity relationships and on molecular modeling studies of these pyrazoles in a crystal structure of the ERalpha-raloxifene complex, we propose that pyrazoles having a basic substituent on the C(5) phenyl group adopt a binding mode that is different from that of the pyrazole agonists that lack this group. The most favorable orientation appears to be one which places the N(1) phenol in the A-ring binding pocket so that the basic side chain can adopt an orientation similar to that of the basic side chain of raloxifene.

Stereoselectivity of methyl aryldiazoacetate cyclopropanations of 1,1-diarylethylene. Asymmetric synthesis of a cyclopropyl analogue of tamoxifen

[formula: see text] Dirhodium tetrakis(S-(N-dodecylbenzenesulfonyl)prolinate) (Rh2(S-DOSP)4)-catalyzed decomposition of methyl phenyldiazoacetate in the presence of 1,1-diarylethylenes results in intermolecular cyclopropanation with high enantioselectivity (up to 99% ee) and moderate diastereoselectivity (up to 80% de). The reaction was applied to the asymmetric synthesis of a cyclopropyl analogue of tamoxifen.

New estrogenic antagonists bearing dicarba-closo-dodecaborane as a hydrophobic pharmacophore

We have designed and synthesized estrogen antagonists bearing dicarba-closo-dodecaborane (carborane) as a hydrophobic pharmacophore based on the structure of 1-(4-hydroxyphenyl)-1,12-dicarba-closo-dodecaborane, a potent estrogen agonist that we reported previously. Compounds with a long alkyl chain bearing an amide moiety on the carborane skeleton (6, 7) showed estrogen antagonistic activity in a luciferase reporter gene assay using COS-1 cells transfected with a rat ER alpha-expression plasmid and as an appropriate reporter plasmid.

Carboxylic acid analogues of tamoxifen: (Z)-2-[p-(1, 2-diphenyl-1-butenyl)phenoxy]-N,N-dimethylethylamine. Estrogen receptor affinity and estrogen antagonist effects in MCF-7 cells

The triarylethylene estrogen mimetic (E, Z)-4-[1-(p-hydroxyphenyl)-2-phenyl-1-butenyl]phenoxyacetic acid (4) represents a novel class of estrogen receptor (ER) ligands which, like tamoxifen (1), can elicit estrogen agonist and antagonist effects, in turn, in nonreproductive and reproductive tissues. Analogues of 4, incorporating structural features shown previously in triarylethylenes to improve ER affinity and estrogen antagonist properties, were prepared with the ultimate aim of identifying substances with improved estrogenicity exclusive of reproductive tissues. Thus, the side chain of 4 was elongated to give oxybutyric acid 13, which was further altered by (a) repositioning of its p-hydroxyl to the neighboring m-position (12) and (b) ethylenic bond reduction (14). Also, the p-hydroxyl group and oxyacetic acid groups of 4 were, in turn, shifted to the neighboring m-positions, affording 8 and 9. Oxybutyric acid analogue 13 had about 2 times the affinity for human ERalpha as 4, and its antiproliferative effect in MCF-7 cells was greater than that of 1. Dihydro analogue 14, which was conformationally similar to cis-13, had very low ER affinity and antiestrogenicity, and m-hydroxy analogue 12 also had reduced ER affinity and potency, but its MCF-7 cell antiproliferative efficacy was retained. Modest ER affinity and antiproliferative potency were seen with 8, in which phenolic and phenyl rings were trans to one another, but 9, in which these rings were cis, was inactive. Our findings indicate that two-carbon side-chain elongation and/or m-positioning of the hydroxyl group in 4 affords analogues with dominant estrogen antagonist effects in MCF-7 cells.

Novel structural templates for estrogen-receptor ligands and prospects for combinatorial synthesis of estrogens

BACKGROUND

The development of estrogen pharmaceutical agents with appropriate tissue-selectivity profiles has not yet benefited substantially from the application of combinatorial synthetic approaches to the preparation of structural classes that are known to be ligands for the estrogen receptor (ER). We have developed an estrogen pharmacophore that consists of a simple heterocyclic core scaffold, amenable to construction by combinatorial methods, onto which are appended 3-4 peripheral substituents that embody substructural motifs commonly found in nonsteroidal estrogens. The issue addressed here is whether these heterocyclic core structures can be used to prepare ligands with good affinity for the ER.

RESULTS

We prepared representative members of various azole core structures. Although members of the imidazole, thiazole or isoxazole classes generally have weak binding for the ER, several members of the pyrazole class show good binding affinity. The high-affinity pyrazoles bear close conformational relationship to the nonsteroidal ligand raloxifene, and they can be fitted into the ligand-binding pocket of the ER-raloxifene X-ray structure.

CONCLUSIONS

Compounds such as these pyrazoles, which are novel ER ligands, are well suited for combinatorial synthesis using solid-phase methods.

Synthesis and sulfatase inhibitory activities of (E)- and (Z)-4-hydroxytamoxifen sulfamates

We report the development of (E)- and (Z)-4-hydroxytamoxifen sulfamates as estrone sulfatase inhibitors, potential therapeutic agents for the treatment of breast cancer. Both compounds competitively inhibit estrone sulfatase isolated from rat liver with apparent Ki of 35.9 microM for (E)-4-hydroxytamoxifen sulfamate and an apparent Ki of > 500 microM for the (Z) isomer.

2-Phenylbenzo[b]thiophene-based antiestrogens with mammary tumor inhibiting activity

In this study we extended our studies on heterocyclic antiestrogens to 2-phenylbenzo[b]thiophenes which can be considered as isosteric to the 2-phenylindole system. We synthesized a number of 6-hydroxy-2-(4-hydroxyphenyl)benzo[b]thiophenes with carbamoyl and amino functions in the side chain at carbon-3 and analyzed their biological properties. The binding affinities for the estrogen receptor are mainly influenced by the chain length whereas the hormonal profile depends on the nature of the functional group. From this study 3-[10-(2,2,3,3,4,4,4-heptafluorobutyl-methylcarbamoyl) decyl]-6-hydroxy-2-(4-hydroxyphenyl)benzo-[b]thiophene (6e) emerged as an antiestrogen with all the characteristics of a pure antagonist. It did not stimulate gene expression in HeLa cells cotransfected with the expression vector for the human estrogen receptor HEG0 and the luciferase reporter plasmid EREwtc luc nor did it show any estrogenic activity in the mouse uterus weight test. In the latter assay, it completely abrogated the stimulatory effect of estrone. Due to its antiestrogenic potency it strongly inhibited the growth of estrogen-sensitive human MCF-7 breast cancer cells with an IC50 value of 5 nM. These data suggest that an amide function in combination with the fluorination of the terminal carbon atoms is an appropriate modification to abolish the estrogenic action of the 2-phenylbenzothiophene system.

Synthesis and pharmacology of conformationally restricted raloxifene analogues: highly potent selective estrogen receptor modulators

The 2-arylbenzothiophene raloxifene, 1, is a selective estrogen receptor modulator (SERM) which is currently under clinical evaluation for the prevention and treatment of postmenopausal osteoporosis. In vivo structure-activity relationships and molecular modeling studies have indicated that the orientation of the basic amine-containing side chain of 1, relative to the stilbene plane, is an important discriminating factor for the maintenance of tissue selectivity. We have constructed a series of analogues of 1 in which this side chain is held in an orientation which is orthogonal to the stilbene plane, similar to the low-energy conformation predicted for raloxifene. Herein, we report on the synthesis of these compounds and on their activity in a series of in vitro and in vivo biological assays reflective of the SERM profile. In particular, we describe their ability to (1) bind the estrogen receptor, (2) antagonize estrogen-stimulated proliferation of MCF-7 cells in vitro, (3) stimulate TGF-beta3 gene expression in cell culture, (4) inhibit the uterine effects of ethynyl estradiol in immature rats, and (5) potently reduce serum cholesterol and protect against osteopenia in ovariectomized (OVX) rats without estrogen-like stimulation of uterine tissue. These data demonstrate that one of these compounds, LY357489,4, is among the most potent SERMs described to date with in vivo efficacy on bone and cholesterol metabolism in OVX rats at doses as low as 0.01 mg/kg/d.

1-Benzyl-2-phenylindole- and 1,2-diphenylindole-based antiestrogens. Estimation of agonist and antagonist activities in transfection assays

In the 2-phenylindole system, the side chain at the nitrogen atom dominates the endocrine profile both in respect to the reduction of estrogenic action and the increase of antiestrogenic potency. In previous papers we reported on 2-phenylindoles with aliphatic side chains and various functional groups [Biberger, C. and von Angerer, E., J. Steroid Biochem. Molec. Biol., 1996, 58, 31-43 and references therein]. In this study, we incorporated one or two phenyl rings into the side chain in order to lower the flexibility of the side chain. The sulfone group which was used as a polar function was linked to various positions of a benzyl or a phenyl group attached to the indole moiety. The relative binding affinities (RBA) ranged from 1.5 to 8.4% of estradiol. Agonist and antagonist activities were estimated in transfection assays using transiently transfected HeLa cells (cotransfected with the HEG0 vector) and stably transfected MCF-7/2a human breast cancer cells. The reporter plasmid contained the ERE from the Vitellogenin 2A gene, a viral tk promotor and the luciferase gene. Many of the new derivatives showed no or only very low estrogenic activity except for the compound 4e which contained two benzyl elements in the side chain. The antiestrogenic potency was very variable when concentrations 100-fold higher than that of estradiol were applied. The compound with the para-substituted benzyl fragment (4b) proved to be a pure antagonist in the transfection assays. It antagonized the effect of estradiol (10 nM) with an IC50 value of 10(-7) M. It also inhibited strongly the growth of estrogen-sensitive human MCF-7 mammary carcinoma cells (IC50, 3 nM). Its activity was comparable to the one of the corresponding aliphatic 2-phenylindole derivative ZK 164.015. The data from the transcription and proliferation assays suggest that a phenyl ring can be incorporated into the side chain of pure antiestrogens without reducing their potency, provided the aromatic ring is para-substituted and a methylene group between the indole nitrogen and the phenyl group can act as hinge.

A 6beta-(thiaheptanamide) derivative of estradiol as inhibitor of 17beta-hydroxysteroid dehydrogenase type 1

In an effort to develop potent agents for reducing the levels of the active estrogen, estradiol, we developed a new category of 17beta-hydroxysteroid dehydrogenase (17beta-HSD) type 1 inhibitors. The compounds described possess a butyl methyl alkylamide side chain linked to the C6 position of estradiol by a thioether. With a series of epimeric mixtures, an optimal side-chain length of five methylene groups (between the amide group and steroid part) was first determined. Thereafter, both C6 epimers of optimized mixture were obtained after high-pressure liquid chromatography separation. 1H and 13C NMR experiments were performed to confirm the stereochemistry of each epimer. The 6beta-orientation of the side-chain was found to be crucial for enzymatic inhibition. Indeed, for the optimized side-chain length, the compound with a beta-orientation (5: N-butyl,N-methyl 7-(3',17'beta-dihydroxy-1',3',5'( 10')-estratriene-6'beta-yl)-7-thiaheptanamide) was 70-fold more potent than the 6alpha-analog. Compound 5 did not inactivate 17beta-HSD type 1, suggesting a reversible inhibitor. In addition, it was found to be a more potent inhibitor than the substrate estrone itself or a panel of three known inhibitors.

Biodistribution of 123I-labeled 4-hydroxytamoxifen derivatives in rats with dimethylbenzanthracene-induced mammary carcinomas

A 123I-labeled tamoxifen derivative with a high affinity for the antiestrogen-binding site (AEBS) has been prepared. Biodistribution studies in rats showed a good linear correlation between the AEBS contents of tissue in fmol/g and the accumulated amount of radioactivity in percent dose per gram at 24 h.

Steroidal affinity labels of the estrogen receptor. 3. Estradiol 11 beta-n-alkyl derivatives bearing a terminal electrophilic group: antiestrogenic and cytotoxic properties

With the aim of developing a new series of steroidal affinity labels of the estrogen receptor, six electrophilic 11 beta-ethyl (C2), 11 beta-butyl (C4), or 11 beta-decyl (C10) derivatives of estradiol bearing an 11 beta-terminal electrophilic functionality, i.e. bromine (C4), (methylsulfonyl)oxy (C2 and C4), bromoacetamido (C2 and C4), and (p-tolylsulfonyl)oxy (C10), were synthesized. The range of their affinity constants for binding the estrogen receptor was 0.4-37% that of estradiol; the order of increasing affinity (i) relative to the 11 beta-alkyl arm was ethyl < butyl and (ii) relative to the electrophilic functionality was bromoacetamido < bromine < (methylsulfonyl)oxy. Regardless of the conditions used, including prolonged exposure of the receptor to various pH levels (7-9) and temperatures (0-25 degrees C), the extent of receptor affinity labeling by the 11 beta-ethyl and 11 beta-butyl compounds, if any, was under 10%. This was in sharp contrast to results obtained using 11 beta-((tosyloxy)decyl)estradiol which labeled from 60% to 90% of the receptor hormone-binding sites with an EC50 of approximately 10 nM. Estrogenic and antiestrogenic activities of the compounds were determined using the MVLN cell line, which was established from the estrogen-responsive mammary tumor MCF-7 cells by stable transfection of a recombinant estrogen-responsive luciferase gene. The two 11 beta-ethyl compounds were mainly estrogenic, whereas the three 11 beta-butyl and the 11 beta-decyl compounds essentially showed antiestrogenic activity. The fact that the chemical reactivities of 11 beta-ethyl and 11 beta-butyl compounds were not compromised by interaction with the estrogen receptor made the synthesized high-affinity compounds potential cytotoxic agents which might be able to exert either (i) a specific action on estrogen-regulated genes or (ii) a more general action in estrogen-target cells. Therefore the ability of the compounds (1) to irreversibly abolish estrogen-dependent expression of the luciferase gene and (2) to affect the proliferation of MVLN cells were determined. All electrophiles were able to irreversibly suppress expression of the luciferase gene; the antiestrogenic electrophiles were more potent than the estrogenic ones but less efficient than 4-hydroxytamoxifen, a classical and chemically inert triphenylethylene antiestrogen. Only the antiestrogenic electrophiles decreased cell proliferation; however, they were less potent than 4-hydroxytamoxifen. In conclusion, the synthesized electrophilic estradiol 11 beta-ethyl and 11 beta-butyl derivatives (i) were not efficient affinity labels of the estrogen receptor and (ii) did not display significant cytotoxicity in estrogen-sensitive mammary tumor cells. However, since these derivatives displayed high affinity for the estrogen receptor, they could be used to prepare potential cytotoxic agents which might be selective for tumors affecting estrogen-target tissues, by coupling them with a toxic moiety.

Discovery and synthesis of [6-hydroxy-3-[4-[2-(1-piperidinyl)ethoxy]phenoxy]-2-(4-hydroxyphenyl)]b enzo[b]thiophene: a novel, highly potent, selective estrogen receptor modulator

Raloxifene,[2-(4-hydroxyphenyl)-6-hydroxybenzo[b]thien-3-yl] [4-[2-(1-piperidinyl)ethoxy]phenyl]methanone hydrochloride (2), is representative of a class of compounds known as selective estrogen receptor modulators (SERMs) that possess estrogen agonist-like actions on bone tissues and serum lipids while displaying potent estrogen antagonist properties in the breast and uterus. As part of ongoing SAR studies with raloxifene, we found that replacement of the carbonyl group with oxygen ([6-hydroxy-3-[4-[2-(1-piperidinyl)ethoxy]phenoxy]-2-(4-hydroxyphenyl)]b enzo[b]thiophene hydrochloride, 4c) resulted in a substantial (10-fold) increase in estrogen antagonist potency relative to raloxifene in an in vitro estrogen dependent cell proliferation assay (IC50 = 0.05 nM) in which human breast cancer cells (MCF-7) were utilized. In vivo, 4c potently inhibited the uterine proliferative response to exogenous estrogen in immature rats following both sc and oral dosing (ED50 of 0.006 and 0.25 mg/kg, respectively). In ovariectomized aged rats, 4c produced a significant maximal decrease (45%) in total cholesterol at 1.0 mg/kg (p.o.) and showed a protective effect on bone relative to controls with maximal efficacy at 1.0 mg/kg (p.o.). These data identify 4c as a novel SERM with greater potency to antagonize estrogen in uterine tissue and in human mammary cancer cells compared to raloxifene, tamoxifen or ICI-182,780.

Synthesis and biological evaluation of 7-hydroxy-3,4-diphenyl-1,2-dihydroisoquinolines as new 4-hydroxytamoxifen analogues

A phenolic 3,4-diphenyl-1,2-dihydroisoquinoline derivative (4a) as a new 4-hydroxytamoxifen analogue and a related compound (4c) were synthesized from 3,4-diphenyl-1,2,3,4-tetrahydroisoquinolin-4-ols (5a, c), which were prepared by intramolecular Barbier reaction of N-(2-iodobenzyl)phenacylamines. Anti-proliferative activities of 4a,c and 5a,c, as well as 4b and 5b prepared previously, against human mammary carcinoma MCF-7 cell line and human nasopharyngeal carcinoma KB cell line were evaluated. The 3,4-diphenyl-1,2-dihydroisoquinoline derivatives (4a,c) and isoquinolin-4-ols (5a,b) were active against MCF-7 cells and were nearly equipotent to the corresponding nonphenolic compound (1a). The mechanism of the anti-proliferative activity of 4a-c against MCF-7 cells is discussed.

Structure-activity relationships of selective estrogen receptor modulators: modifications to the 2-arylbenzothiophene core of raloxifene

The 2-arylbenzothiophene raloxifene, 1, is a selective estrogen receptor modulator which is currently under clinical evaluation for the prevention and treatment of postmenopausal osteoporosis. A series of raloxifene analogs which contain modifications to the 2-arylbenzothiophene core have been prepared and evaluated for the ability to bind to the estrogen receptor and inhibit MCF-7 breast cancer cell proliferation in vitro. Their ability to function as tissue-selective estrogen agonists in vivo has been assayed in a short-term, ovariectomized (OVX) rat model with end points of serum cholesterol lowering, uterine weight gain, and uterine eosinophil peroxidase activity. These studies have demonstrated that (1) the 6-hydroxy and, to a lesser extent, the 4'-hydroxy substituents of raloxifene are important for receptor binding and in vitro activity, (2) small, highly electronegative 4'-substituents such as hydroxy, fluoro, and chloro are preferred both in vitro and in vivo, (3) increased steric bulk at the 4'-position leads to increased uterine stimulation in vivo, and (4) additional substitution of the 2-aryl moiety is tolerated while additional substitution at the 4-, 5-, or 7-position of the benzothiophene results in reduced biological activity. In addition, compounds in which the 2-aryl group is replaced by alkyl, cycloalkyl, and naphthyl substituents maintain a profile of in vitro and in vivo biological activity qualitatively similar to that of raloxifene. Several novel structural variants including 2-cyclohexyl, 2-naphthyl, and 6-carbomethoxy analogs also demonstrated efficacy in preventing bone loss in a chronic OVX rat model of postmenopausal osteopenia, at doses of 0.1-10 mg/kg.

Novel steroidal 1,4-diketones and pyridazine derivatives as potential antiestrogens

A series of steroidal 1,4-diketone derivatives was synthesized by acid-catalyzed condensation of 2-acetylestradiol-17 beta-acetate with substituted phenylglyoxals. Conversion of the products into the corresponding pyridazine derivatives was achieved by reaction with hydrazine hydrate. The synthesized compounds were evaluated for their uterotrophic, antiuterotrophic, and antifertility activities in mature female albino rats. Among the compounds tested, the phenyl 2, p-bromophenyl 3, and p-methoxyphenyl 5 diketone derivatives displayed uterotrophic activity of 72%, 72%, and 91%, respectively. The gradation of antiestrogenic activity was assessed in vivo by the inhibition of the estrone-stimulated uterine growth. Compounds 2-5 showed moderate antiestrogenic activity of 53-56%. None of the tested compounds elicited antifertility activity as assessed by the post-coital antiimplantation activity test.

Depletion of estrogen receptor in human breast tumor cells by a novel substituted indole that does not bind to the hormone binding domain

Steroidal antiestrogens appear to have at least two major modes of action in breast cancer cells, direct antagonism of estrogen binding to its receptor and depletion of estrogen receptors (ER) due to inhibition of dimerization of the receptor and a resultant destabilization of the receptor protein. In a search for other classes of compounds which would act as dimerization inhibitors, a novel substituted indole (8-{2-[1-(4-chlorobenzoyl)-5-hydroxy-2-methyl-1H-indol-3-yl]-acetylamino} octanoic acid butyl-methyl amide, MDL 101,906) was synthesized. Binding of the ER to its consensus response element (ERE) was apparently decreased in nuclear extracts from MCF-7 human breast cancer cell treated with MDL 101,906. This decreased binding was found to be due to depletion of ER based on direct measurement of ER using an enzyme-linked immunoassay. Other transcription factors were apparently unaffected by MDL 101,906 treatment. Whereas depletion of ER with a steroidal antiestrogen was almost complete after 3 h of treatment of MCF-7 cells, the effect of MDL 101,906 took significantly longer to occur, suggesting a fundamental difference in the mechanisms of action of the two drugs. This was also evident in the lack of binding of MDL 101,906 to the hormone binding domain of ER. MDL 101,906 treatment also caused depletion of ER mRNA in MCF-7 cells. Depletion of ER mRNA was noted by 3 h of drug treatment and was apparently almost complete after 24 h of treatment. Depletion of ER from MCF-7 cells led to a dose-dependent decrease in the expression of luciferase by an ERE-driven luciferase reporter gene assay system. The mechanism of MDL 101,906 appears to be unique and additional studies with this chemical class seem to be warranted to assess the potential for therapeutic utility.