11 beta-amidoalkyl estradiols, a new series of pure antiestrogens

C-Ring Oxidized Estrone Acetate Derivatives: Assessment of Antiproliferative Activities and Docking Studies

C-Ring oxidized estrone acetate derivatives as antiproliferative agents were prepared and tested against five cancer cell lines by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Flow cytometry assays to evaluate cell viability and modifications in cell cycle phases and molecular docking research against estrogen receptor α, steroid sulfatase, and 17β-hydroxysteroid dehydrogenase type 1 were performed. 9α-Hydroxy,11β-nitrooxyestrone acetate was the most cytotoxic molecule against hormone-dependent cancer cells. Furthermore, flow cytometry experiments revealed that this 9α-hydroxy,11β-nitrooxy derivative markedly reduced HepaRG cells viability (~92%) after 24 h of treatment. However, 9α-hydroxyestrone acetate led to selective inhibition of HepaRG cells growth, inducing a G0/G1 cycle arrest, and did not originate a proliferation effect on T47-D cancer cells. Docking studies estimated a generally lower affinity of these compounds to estrogen receptor α than predicted for estrone and 17β-estradiol. Therefore, this structural modification can be of interest to develop new anticancer estrane derivatives devoid of estrogenic action.

Antiestrogens in combination with immune checkpoint inhibitors in breast cancer immunotherapy

Breast cancers (BCs) with expression of estrogen receptor-alpha (ERα) occur in more than 70% of newly-diagnosed patients in the U.S. Endocrine therapy with antiestrogens or aromatase inhibitors is an important intervention for BCs that express ERα, and it remains one of the most effective targeted treatment strategies. However, a substantial proportion of patients with localized disease, and essentially all patients with metastatic BC, become resistant to current endocrine therapies. ERα is present in most resistant BCs, and in many of these its activity continues to regulate BC growth. Fulvestrant represents one class of ERα antagonists termed selective ER downregulators (SERDs). Treatment with fulvestrant causes ERα down-regulation, an event that helps overcome several resistance mechanisms. Unfortunately, full antitumor efficacy of fulvestrant is limited by its poor bioavailability in clinic. We have designed and tested a new generation of steroid-like SERDs. Using ERα-positive BC cells in vitro, we find that these compounds suppress ERα protein levels with efficacy similar to fulvestrant. Moreover, these new SERDs markedly inhibit ERα-positive BC cell transcription and proliferation in vitro even in the presence of estradiol-17β. In vivo, the SERD termed JD128 significantly inhibited tumor growth in MCF-7 xenograft models in a dose-dependent manner (P < 0.001). Further, our findings indicate that these SERDs also interact with ER-positive immune cells in the tumor microenvironment such as myeloid-derived suppressor cells (MDSC), tumor infiltrating lymphocytes and other selected immune cell subpopulations. SERD-induced inhibition of MDSCs and concurrent actions on CD8+ and CD4 + T-cells promotes interaction of immune checkpoint inhibitors with BC cells in preclinical models, thereby leading to enhanced tumor killing even among highly aggressive BCs such as triple-negative BC that lack ERα expression. Since monotherapy with immune checkpoint inhibitors has not been effective for most BCs, combination therapies with SERDs that enhance immune recognition may increase immunotherapy responses in BC and improve patient survival. Hence, ERα antagonists that also promote ER downregulation may potentially benefit patients who are unresponsive to current endocrine therapies.

Synthesis of trans-16-triazolyl-13α-methyl-17-estradiol diastereomers and the effects of structural modifications on their in vitro antiproliferative activities

Novel 16-triazoles in the 13α-estrone series were synthesized via Cu(I)-catalyzed azide-alkyne cycloaddition of the two diastereomeric (on C-16 and on C-17) 16-azido-13α-estra-1,3,5(10)-trien-17-ol 3-benzyl ethers with substituted phenylacetylenes. The new heterocyclic derivatives were evaluated in vitro by means of MTT assays for antiproliferative activity against a panel of human adherent cancer cell lines (HeLa, MCF-7, A431, A2780, T47D, MDA-MB-231 and MDA-MB-361). The inversion of the configurations at C-16 and C-17 selectively affected the growth-inhibitory properties of the tested compounds. The 16β,17α isomers generally proved to be potent on all cell lines, with IC50 values comparable to those of the reference agent cisplatin. Change of the substitution pattern of the phenyl group of the acetylene led to great differences in antiproliferative properties. Exclusively the p-phenyl-substituted triazoles exerted high cytostatic effects. One of the most potent compounds activated caspase-3 and caspase-9 without influencing caspase-8, confirming the induction of apoptosis via the intrinsic pathway.

Current status on development of steroids as anticancer agents

Steroids are important biodynamic agents. Their affinities for various nuclear receptors have been an interesting feature to utilize them for drug development particularly for receptor mediated diseases. Steroid biochemistry and its crucial role in human physiology, has attained importance among the researchers. Recent years have seen an extensive focus on modification of steroids. The rational modifications of perhydrocyclopentanophenanthrene nucleus of steroids have yielded several important anticancer lead molecules. Exemestane, SR16157, fulvestrant and 2-methoxyestradiol are some of the successful leads emerged on steroidal pharmacophores. The present review is an update on some of the steroidal leads obtained during past 25 years. Various steroid based enzyme inhibitors, antiestrogens, cytotoxic conjugates and steroidal cytotoxic molecules of natural as well as synthetic origin have been highlighted. This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

Convergent synthesis of a steroidal antiestrogen-mitomycin C hybrid using "click" chemistry

A convergent synthesis of a novel estrogen receptor-targeted drug hybrid was developed based on structures of the potent anti-proliferative mitomycin C and the steroidal anti-estrogen RU 39411. The steroidal antiestrogen was prepared with an azido-triethylene glycoloxy linker while the mitomycin C derivative (porfirimycin) incorporated a complementary 7-N-terminal alkyne. The two components were ligated using the Huisgen [3 + 2] cycloaddition ("click") reaction. Preliminary biological assays demonstrated that the final hybrid compound retained both potent anti-estrogenic and anti-proliferative activities.

Synthesis and evaluation of 11β-(4-substituted phenyl) estradiol analogs: transition from estrogen receptor agonists to antagonists

INTRODUCTION

As part of our program to develop estrogen receptor (ER) targeted imaging and therapeutic agents we chose to evaluate 11β-substituted estradiol analogs as a representative scaffold. Previous synthetic studies provided an entry into this class of compounds and other work indicated that 11β-(substituted aryl) estradiol analogs were potent antagonists of the ER. Little information existed about the specific structural features involved in the transition from agonism to antagonism for the 11β-aryl estradiol analogs or their potential as scaffolds for drug conjugation.

METHODS

We prepared and characterized a series of 11β-(4-Substituted phenyl) estradiol analogs using modifications of existing synthetic methods. The new compounds, as well as standard steroidal agonists and antagonists, were evaluated as competitive ligands for the ERβ-LBD. Functional assays used the induction of alkaline phosphatase in Ishikawa cells to determine potency of the compounds as ER agonists or antagonists.

RESULTS

The synthetic strategy successfully generated a series of compounds in which the 4-substituent was sequentially modified from hydroxyl to methoxy to azidoethoxy/N,N-dimethylaminoethoxy and eventually to a prototypical 1,4-naphthoquinone-containing moiety. The new compounds all retained high relative binding affinity (RBA) for the ERα-LBD, ranging from 13-83% that of estradiol. No subtype selectivity was observed. More importantly, the transition from agonist to antagonist activity occurs at the 4-methoxy stage where the compound is a mixed antagonist. More notably, antagonism appeared to be more dependent upon the size of the 11β-substituent than upon the nature of the terminal group

CONCLUSIONS

We have developed a synthetic strategy that provides facile access to potent 11β-(4-substituted phenyl) estradiol analogs. The resultant compounds retain high affinity for the ERα-LBD and, more importantly, demonstrate potent antagonist activity in cells. Large functionalities distal to the 11β-phenyl ring had little additional effect on either affinity or efficacy, suggesting the incorporation of diverse imaging or biologically active groups can be attached without significantly compromising the ER-binding capacity. Future studies are in progress to exploit the 11β-aryl estradiol analogs as potential drug delivery systems and imaging agents.

Synthesis and in vivo evaluation of 11-substituted estradiol derivatives as anti-implantation agents

Synthesis of 11-substituted estradiol derivatives (12-17) has been carried out by the Grignard reaction with alkyl, allyl, and benzyl halides on 17beta-hydroxy-3-methoxy-11-oxo-estra-1,3,5(10),8(9)-tetraene (10). The novel compounds (10 and 12-17) were evaluated for their preliminary post-coital contraceptive (anti-implantation) activity in Sprague-Dawley rats. The tested compounds were administered orally and showed significant anti-implantation activity. Compound 13 is the most potent compound in the series which showed 100% contraceptive efficacy at 1.25 mg kg(-1).

Hormone therapy for breast cancer, with an emphasis on the pure antiestrogen fulvestrant: mode of action, antitumor efficacy and effects on bone health

Breast cancer is a major health problem in women of developed Western countries. Whereas estrogen receptor (ER) may be involved in many cases in breast carcinogenesis, its expression in breast tumors may predict a favorable response to hormone therapy. In this review, we report the role played by ER in breast cancer and compare the effects and mechanisms of action of partial (tamoxifen) and pure (fulvestrant) antiestrogens, as well as of aromatase inhibitors. Moreover, as ER also has a critical role in bone metabolism, we review the beneficial and adverse effects of breast cancer hormone therapy on bone health, with a particular emphasis on fulvestrant, the only pure antiestrogen recently approved by the FDA for Phase III clinical trials. We conclude that, because of its therapeutic efficacy and its seemingly minimal effect on bone integrity, fulvestrant represents a new option for the hormonal treatment of breast cancer that deserves further clinical evaluation.

Synthesis and receptor-binding examinations of the normal and 13-epi-D-homoestrones and their 3-methyl ethers

An effective epimerization of the normal estrone 3-methyl and 3-benzyl ethers by using o-phenylenediamine and AcOH made the possibility for facile entry into the 13alpha-estrone series. Combination of this synthetic methodology with an isolation step carried out by means of the Girard-P reagent, the corresponding ethers of 13-epi-estrone were obtained in excellent yields. The 3-hydroxy and 3-methoxy D-homoestrone derivatives in both the normal and the 13alpha-estrone series were then synthesized and tested in vitro in a radioligand-binding assay. The estrogen receptor recognizes these compounds, but their relative binding affinities (RBAs) are lower than that of the reference compound 3,17beta-estradiol. The progesterone receptor-binding affinities of the four D-homo derivatives were also tested showing low values for 13alpha-D-homoestrone and its 3-methyl ether. Pharmacologically, these 13alpha-D-homoestrone derivatives are estrogen receptor-selective molecules.

Synthesis and receptor-binding examination of 16-hydroxymethyl-3,17-estradiol stereoisomers

The four 16-hydroxymethylestra-1,3,5(10)-triene-3,17-diol isomers were synthesized and tested in a radioligand-binding assay. The estrogen receptor recognizes these compounds, but their relative binding affinities are lower than 2.0% relative to that of the reference molecule estra-1,3,5(10)-triene-3,17beta-diol. The affinities of the tested compounds for the androgen and progesterone receptors are very low (K(i)> 100 microm and 1 microM, respectively). The prepared 16-hydroxymethylestra-1,3,5(10)-triene-3,17-diol isomers are therefore estrogen receptor-selective molecules.

Synthesis, structural evaluation, and estrogen receptor interaction of 2,3-diarylpiperazines

To develop novel estrogen receptor (ER) ligands, ring-fused derivatives of the hormonally active (1R,2S)/(1S,2R)-1-(2-chloro-4-hydroxyphenyl)-2-(2,6-dichloro-4-hydroxyphenyl)ethylenediamine 4b were synthesized. (2R,3S)/(2S,3R)-2-(2-Chloro-4-hydroxyphenyl)-3-(2,6-dichloro-4-hydroxyphenyl)piperazine 4 induced ligand-dependent gene expression in MCF-7-2a cells, stably transfected with the plasmid ERE(wtc)luc and was therefore used as a lead structure. The influence of the substitution pattern in the aromatic rings (4-OH (1), 2-F,4-OH (2), 2-Cl,4-OH (3), 2,6-Cl2,3-OH (5), and 2,6-Cl2,4-OH (6)) and the effect of N-ethyl chains on the ER binding and activation of gene expression were studied. The synthesis started from the respective methoxy-substituted (1R,2S)/(1S,2R)-configurated 1,2-diarylethylenediamines 6b to 4b, which were reacted with dimethyl oxalate in order to get 5,6-diarylpiperazine-2,3-diones. Reduction with BH3*tetrahydrofuran and ether cleavage with BBr3 yielded the piperazines 1-6. The N-alkylation of the piperazines 1a-3a, which was employed for obtaining compounds 7-11, was succeeded by acetic anhydride followed by reduction and ether cleavage. Nuclear magnetic resonance (NMR) spectroscopical studies revealed a synclinal conformation of the 1,2-diarylethane pharmacophore and a preference of the substituents at the heterocyclic ring for an equatorial position. This spatial structure prevents an interaction with the ER analogously to that of estradiol (E2). Therefore, the piperazines can displace E2 from its binding site only to a very small extent. Only the N-ethyl (8) and N,N'-diethyl (11) derivatives of piperazine 3 showed relative binding affinity values > 0.1% (8, 0.42%, and 11, 0.17%). Nevertheless, ER-mediated gene activation was verified for the piperazines 4 (20%), 6 (73%), 7 (34%), 8 (74%), and 11 (37%) (concentration, 1 microM; E2, 100% activation) on the MCF-7-2a cell line. O-methylation led to completely inactive compounds and showed the necessity of H bridges from the piperazines to the ER for activating gene expression.

Synthesis and receptor-binding examination of 16-hydroxymethyl-3,17-estradiol stereoisomers

The four 16-hydroxymethylestra-1,3,5(10)-triene-3,17-diol isomers were synthesized and tested in a radioligand-binding assay. The estrogen receptor recognizes these compounds, but their relative binding affinities are lower than 2.0% relative to that of the reference molecule estra-1,3,5(10)-triene-3,17beta-diol. The affinities of the tested compounds for the androgen and progesterone receptors are very low (K(i)> 100 microm and 1 microM, respectively). The prepared 16-hydroxymethylestra-1,3,5(10)-triene-3,17-diol isomers are therefore estrogen receptor-selective molecules.

Biphenyls as surrogates of the steroidal backbone. Part 1: synthesis and estrogen receptor affinity of an original series of polysubstituted biphenyls

In the course of a programme aimed at discovering new ligands of the estrogen receptor, we explored a series of substituted biphenyls. Their synthesis and binding affinity are described.

Steroidal affinity labels of the estrogen receptor alpha. 4. Electrophilic 11beta-aryl derivatives of estradiol

Ten electrophilic estradiol 11beta-aryl derivatives were synthesized, with three different types of 11beta-substituent: (i) pOO(CH(2))(2)X (compounds: 6, X = OSO(2)CH(3); 7, X = I; 13, X = NHCOCH(2)Cl; 15, X = N(CH(3))COCH(2)Br; and 16, X = N(CH(3))COCH(2)Cl); (ii) pOO(CH(2))(5)X (compounds: 17, X = I; 20, X = NHCOCH(2)Br; and 22, X = N(CH(3))COCH(2)Br); and (iii) pOC(triple bond)CCH(2)X (compounds: 27, X = NHCOCH(2)Cl; and 29, X = N(CH(3))COCH(2)Cl). The range of their apparent affinity constants for binding the lamb uterine estrogen receptor alpha (ERalpha) was 3-40% that of estradiol. Six electrophiles, chloroacetamides 13, 16, 27, and 29, iodide 17, and bromoacetamide 20 (whose arm linking the electrophilic carbon to the 11beta-phenyl group includes at least six bonds), were able to irreversibly inhibit the binding of [(3)H]estradiol to ER (25-60% decrease in binding sites), with the following compound effectiveness order: 17 < 13 < 16 approximately 20 approximately 27 approximately 29. Mesylate 6, iodide 7 (whose linking arm includes only three bonds), and bromoacetamides 15 and 22 (which differ from 16 by the Cl to Br change and from 20 by the NH to NCH(3) change, respectively) were much less effective (<10% decrease in binding sites, if any). The fact that the inactivation of estradiol-binding sites by the six electrophiles was totally prevented by estradiol indicated that they were ER affinity labeling agents. When ER was modified by methyl methanethiosulfonate, an SH-specific reagent, the different compounds led to very contrasting results in ER affinity labeling. With modified ER, iodide 17 and chloroacetamides 27 and 29 were practically inactive, chloroacetamides 13 and 16 and bromoacetamide 20 were still active but less effective than on the native ER, whereas tertiary bromoacetamides 15 and 22, found to be practically inactive on native ER, became the most effective electrophiles ( approximately 45% and approximately 65% binding sites inactivated, respectively). The results indicate that in the steroid-filled hormone-binding pocket: (i) nucleophilic residues are localized on the beta-side but relatively remote from the steroid nucleus (distance from C-11 > "seven bonds"); (ii) relatively discrete changes in the electrophilic functionality, such as Cl to Br or NH to NCH(3) of haloacetamido compounds, can markedly modify the positioning of the electrophilic center which could no longer react with the nucleophilic residues; and (iii) cysteine residues (probably homologues of human ERalpha cysteine 381 and/or cysteine 530) are, at least partly, the covalent attachment sites of the electrophiles. Moreover, modification of cysteine residues by methyl methanethiosulfonate changes the structure of the hormone-binding pocket, whose labeling by the various electrophiles is profoundly altered.

Synthesis and estrogenic activities of novel 7-thiosubstituted estratriene derivatives

A diastereomerically pure series of 7alpha-thioestratrienes was prepared and evaluated for its affinity for both the human estrogen receptor alpha and the more recently discovered estrogen receptor beta. The functional estrogenic activities of the compounds were measured in a MCF-7 ERE-tk-luciferase assay. The activities and selectivities of the compounds were sensitive to the nature of the thioether side chain.

Estrogenic antagonists bearing dicarba-closo-dodecaborane as a hydrophobic pharmacophore

Dicarba-closo-dodecaboranes (carboranes), which have spherical geometry and hydrophobicity, are applicable as a hydrophobic pharmacophore of biologically active molecules. We have designed and synthesized estrogenic antagonists based on the structure of the potent agonist 1-hydroxymethyl-12-(4-hydroxyphenyl)-1,12-dicarba-closo-d odecaborane, which we have developed. The compounds showed potent antagonistic activity in luciferase reporter gene assay using COS-1 cells transfected with rat ER alpha-expression plasmid and an appropriate reporter plasmid.

17Alpha-alkan (or alkyn) amide derivatives of estradiol as inhibitors of steroid-sulfatase activity

To develop inhibitors of steroid sulfatase without residual estrogenic activity, we have designed a series of estradiol (E2) derivatives bearing an alkan (or alkyn) amide side chain at position 17alpha. A hydrophobic alkyl group was selected from our previous study where 17alpha-octyl-E2 was found to inhibit strongly the steroid-sulfatase activity. Furthermore, it is known that an alkylamide side chain blocks the estrogen-receptor activation. Starting from ethynylestradiol, the chemical synthesis of target compounds was short and efficient with overall yields of 22-42% (3 or 4 steps). Among these compounds, N-octyl,N-methyl-3-(3',17'beta-dihydroxy-1',3',5'(10')-estratrien- 17'alpha-yl)-propanamide (15) was the most potent inhibitor, with an IC50 value of 0.08 microM for the transformation of estrone sulfate (E1S) to estrone (E1) by homogenated JEG-3 cells. N-butyl, N-hexyl, and N,N-dioctyl propanamide derivatives of E2 (IC50 values of 6.4, 2.8, and >20 microM, respectively) were less potent inhibitors than N-octyl analog 15. Furthermore, the unsaturated propynamide analog of 15 gave lower inhibition (four times) than the saturated compound. Compound 15 is also about 100-fold more effective in interacting with the enzyme than substrate E1S itself. The ability of target compounds to bind the estrogen receptor, to stimulate the proliferation of estrogen-sensitive ZR-75-1 cells, or to inhibit the E2-stimulation of ZR-75-1 cells was also evaluated. Although a mixed estrogenic/anti-estrogenic activity was obtained for tested compounds at 1 microM, no estrogenic activity was observed at 0.03 microM for 15. In conclusion, a promising inhibitor of steroid-sulfatase activity was obtained by introducing a hydrophobic octyl group in a 17alpha-propanamide side chain of E2, but further structure-activity relationships (SAR) studies are necessary to minimize the residual estrogenic activity.

Spironolactone-related inhibitors of type II 17beta-hydroxysteroid dehydrogenase: chemical synthesis, receptor binding affinities, and proliferative/antiproliferative activities

The family of 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) catalyzes the formation and inactivation of testosterone (T), dihydrotestosterone (DHT), and estradiol (E2), thus playing a crucial role in the regulation of active steroid hormones in target tissues. Among the five known 17beta-HSD enzymes, type II catalyzes the oxidation of E2 into estrone (E1), T into androstenedione, DHT into androstanedione, and 20alpha-dihydroprogesterone into progesterone. Specific inhibitors are thus an interesting means to study the regulation and to probe the structure of type II 17beta-HSD. In this context, we have efficiently synthesized a series of 7alpha-thioalkyl and 7alpha-thioaryl derivatives of spironolactone that inhibit type II 17beta-HSD. These new C19-steroidal inhibitors possess two important pharmacophores, namely 17-spiro-gamma-lactone and a bulky side-chain at the 7alpha-position. It was found that a para-substituted benzylthio group at the 7alpha-position enhances the inhibitory potency of spironolactone derivatives on type II 17beta-HSD. In fact, the compound with a para-hydroxy-benzylthio group showed an IC50 value of 0.5 microM against type II 17beta-HSD, whereas the compound with a para-[2-(1-piperidinyl)-ethoxy]-benzylthio group inhibited this enzyme with an IC50 value of 0.7 microM. The latter inhibitor is more selective than the former because it did not show any inhibitory potency against P450 aromatase as well as any affinity towards four steroid receptors (AR, PR, GR, ER). As a result, this inhibitor did not show any proliferative effect on androgen-sensitive Shionogi cells and estrogen-sensitive ZR-75-1 cells. These findings contribute to a better knowledge of the structure of type II 17beta-HSD and offer an interesting tool to study the regulation of this enzyme in several biological systems.

Estrogen receptor-negative/progesterone receptor-positive Evsa-T mammary tumor cells: a model for assessing the biological property of this peculiar phenotype of breast cancers

In 1986 we reported the appearance of a progestin binding protein in the human breast cancer cell line Evsa-T, originally described as lacking both estrogen and progesterone receptors (ER and PR). In this report we show that PR of this cell line displays a binding affinity for [3H]ORG 2058 and a sucrose gradient sedimentation profile similar to those ascribed to PR from MCF-7 or T47D breast cancer cell lines. PR from Evsa-T cells is down-regulated by the progestin R-5020 as well as by the two antiprogestins, ZK 112.993 and ZK 98.299, but does not confer growth sensitivity to these compounds. ER remains undetectable by ligand binding assay, enzyme immunoassay and northern blotting. Our Evsa-T clone could be a valuable model for assessing the mechanisms leading the ER-/PR+ phenotype occurring occasionally in breast cancers and frequently in meningiomas.

Synthesis, uterotrophic, and antiuterotrophic activities of some estradiol derivatives containing thiadiazole, thiazoline, and thiazolidinone moieties

The effect of structural modification on the biological activity of hormones has been studied on five novel series of estradiol analogs bearing a variety of substituents at the 2-position of the steroidal nucleus. The synthesized compounds include 2-[2-(5-substituted amino-1,3,4-thiadiazol-2-yl)vinyl]estradiol 17 beta-acetate 5-9, 2-aroylmethylestradiols 10-12, 2-[2-aryl-2-(substituted thiocarbamoylhydrazono)ethyl]estradiols 13-18 and their cyclic thiazoline 19-24, and thiazolidinone derivatives 25-30. Among the products, the p-hydroxybenzolmethylestradiol 12 exhibited the highest antiestrogenic activity of 63%. It also elicited 34% of the uterotrophic activity of estradiol.

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.

Synthesis and evaluation of estradiol derivatives with 16 alpha-(bromoalkylamide), 16 alpha-(bromoalkyl) or 16 alpha-(bromoalkynyl) side chain as inhibitors of 17 beta-hydroxysteroid dehydrogenase type 1 without estrogenic activity

To develop inhibitors of 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) without residual estrogenic activity, the synthesis of 16 alpha-(bromoalkylamide) derivatives of estradiol was performed starting from a key intermediate aldehyde obtained from commercially available estrone. In addition, series of 16 alpha-(bromoalkyl) and 16 alpha-(bromoalkynyl) derivatives of estradiol were also prepared as model compounds. All new compounds inhibited human placental cytosolic 17 beta-HSD (type 1) with IC50 values ranging from 1.7 to 10.6 microM. From these results, we observed that a primary bromide produces a greater inhibition of 17 beta-HSD activity than secondary bromide, and that a shorter 16 alpha-side chain increases the inhibiting activity. In the estrogen-sensitive ZR-75-1 human breast cancer cell line, the 16 alpha-(bromoalkylamide)-estradiol series had no estrogenic activity at 30 nM, and only the compound with a shorter side chain length showed an estrogenic activity at 1000 nM. Interestingly, at this concentration, the compound with an intermediate side chain length showed an antiestrogenic activity of 74%, whereas the compound with the longer side chain length showed 34% of antiestrogenic activity. In this test, other 17 beta-HSD inhibitors (without bromoalkylamide side chain) were fully estrogenic. Among synthesized compounds, the estradiol derivative 4 (N-butyl, N-methyl, 9-[3',17' beta-(dihydroxy)-1',3',5'(10')-estratrien-16' alpha-yl]-7-bromononamide) was the best compromise for a dual-action inhibitor. This compound inhibited moderately and reversibly the 17 beta-HSD type 1 activity, but possessed no estrogenic activity and exhibited antiestrogenic activity in the ZR-75-1 cell line.

Ethinylestradiol does not enhance the expression of nitric oxide synthase in bovine endothelial cells but increases the release of bioactive nitric oxide by inhibiting superoxide anion production

Estradiol is known to exert a protective effect against the development of atherosclerosis, but the mechanism by which this protection is mediated is unclear. Since animal studies strongly suggest that production of endothelium-derived relaxing factor is enhanced by estradiol, we have examined the effect of estrogens on nitric oxide (NO) synthase (NOS) activity, protein, and mRNA in cultured bovine aortic endothelial cells. In reporter cells rich in guanylate cyclase, it has been observed that long-term treatment (> or = 24 hr) with ethinylestradiol (EE2) dose-dependently increased guanylate cyclase-activating factor activity in the conditioned medium of endothelial cells. However, conversion of L-[14C]arginine to L-[14C]citrulline by endothelial cell homogenate or quantification of nitrite and nitrate released by intact cells in the conditioned medium did not reveal any change in NOS activity induced by EE2 treatment. Similarly, Western and Northern blot analyses did not reveal any change in the endothelial NOS protein and mRNA content in response to EE2. However, EE2 dose- and time-dependently decreased superoxide anion production in the conditioned medium of endothelial cells with an EC50 value (0.1 nM) close to that which increased guanylate cyclase-activating factor activity (0.5 nM). Both of these effects were completely prevented by the antiestrogens tamoxifen and RU54876. Thus, endothelium exposure to estrogens appears to induce a receptor-mediated antioxidant effect that enhances the biological activity of endothelium-derived NO. These effects could account at least in part for the vascular protective properties of these hormones.

New endocrine therapies for breast cancer

How do the new endocrine therapies stand up to the aims of modern endocrine therapy outlined in Table 1? We wish to see increased efficacy, decreased toxicity and improved general health in women taking a new agent. None of the new non-steroidal anti-oestrogens have shown unequivocal evidence of improved efficacy in the clinic to mirror their improved profiles over tamoxifen in preclinical studies. We know that toremifene is equivalent to tamoxifen, but we do not have any phase III data from the other four compounds in development. The specific steroidal antioestrogen, ICI 182,780, looks very promising, but is early in its developmental programme. The new aromatase inhibitors are likely to prove equal to tamoxifen or progestagens, but it is disappointing that improved oestrogen suppression has not led, to date, to improved efficacy. No comment can be made about adjuvant or preventative therapy for any of the new agents, although trials are planned for the new aromatase inhibitors in this clinical situation. Currently, the antiprogestins are disappointing and we will need to wait a considerable time for new agents in preclinical testing to reach the clinic. Many of the new agents are associated with decreased toxicity. It is likely that the NSAEs will be equitoxic with tamoxifen. The steroidal antioestrogen looks particularly non-toxic as do the new aromatase inhibitors, and thus we have an advance in terms of reduced toxicity. The effects of the new agents on the uterus, lipids and bone are in the early stages of testing. Raloxifene, ICI 182,780 and the new aromatase inhibitors are expected to have no proliferative effects on the endometrium, but only the new NSAEs are expected to have beneficial cardiovascular and skeletal effects. If the steroidal anti-oestrogens and new aromatase inhibitors become adjuvant therapies of choice, other agents to prevent osteoporosis and cardiovascular events may also have to be administered.

Clinical uses of antiestrogens

An antiestrogen is a compound that blocks the action of estrogen. Most synthetic antiestrogens have agonistic or antagonistic activity depending on the tissue and the endogenous estrogen mileu. The triphenylethylene derivatives, clomiphene and tamoxifen, are the antiestrogens in greatest clinical use. Their biologic effects, clinical indications, and risks are reviewed. Novel antiestrogens which are beginning to be studied clinically include the benzothiophene derivative, raloxifene and the "pure" antiestrogens such as ICI 182,780. New clinical indications for existing compounds as well as the development of novel antiestrogens may lead to better treatment options for endocrine-dependent conditions.

Correspondence factor analysis of steroid libraries

The receptor binding of a library of 187 steroids to five steroid hormone receptors (estrogen, progestin, androgen, mineralocorticoid, and glucocorticoid) has been analyzed by correspondence factor analysis (CFA) in order to illustrate how the method could be used to derive structure-activity-relationships from much larger libraries. CFA is a cartographic multivariate technique that provides objective distribution maps of the data after reduction and filtering of redundant information and noise. The key to the analysis of very complex data tables is the formation of barycenters (steroids with one or more common structural fragments) that can be introduced into CFA analyses used as mathematical models. This is possible in CFA because the method uses X2-metrics and is based on the distributional equivalence of the rows and columns of the transformed data matrix. We have thus demonstrated, in purely objective statistical terms, the general conclusions on the specificity of various functional and other groups derived from prior analyses by expert intuition and reasoning. A finer analysis was made of a series of A-ring phenols showing the high degree of glucocorticoid receptor and progesterone receptor binding that can be generated by certain C-11-substitutions despite the presence of the phenolic A-ring characteristic of estrogen receptor-specific binding.

Synthesis and biological activities of thioether derivatives related to the antiestrogens tamoxifen and ICI 164384

The catalyzed coupling reaction of activated alcohol and mercaptan was used for the short and efficient synthesis of 14 thioether compounds. Two types of side chains, the methyl butyl alkylamide related to the pure steroidal antiestrogen ICI 164384 and the dimethylamino ethyloxy phenyl related to the clinically used nonsteroidal antiestrogen tamoxifen, were introduced by a thioether link on two types of nuclei (triphenylethane or estradiol). The new thioether derivatives were tested to assess their relative binding affinity for the estrogen receptor and their estrogenic or antiestrogenic activity in the ZR-75-1 (ER+) cell line. The results indicate that of the three types of compounds studied, only the nonsteroidal derivatives with an alkylamide side chain possess antiestrogenic activity. In the steroidal series, displacement of the alkylamide side chain from the 7 to the 6 position produced compounds with chemical characteristics similar to ICI 164384 or EM-139 but without antiestrogenic activity. In the nonsteroidal series of compounds with an aryl side chain, compounds with estrogenic activity were obtained. One compound, a nonsteroidal derivative with a methyl butyl alkylamide side chain 20, possesses a relative binding affinity for the estrogen receptor identical to EM-139 (1.1 and 1.2%, respectively) and a relatively good antiestrogenic activity that is 10-fold lower than EM-139 (IC50 values of 250 and 25 nM, respectively). This nonsteroidal thioether with an alkylamide side chain is free of estrogenic activity.

Mixed estrogenic and anti-estrogenic activities of yuehchukene--a bis-indole alkaloid

Anti-estrogenic effects of yuehchukene were observed in rat uterotrophic, mice vaginal smear and MCF-7 cell growth assays. Whereas yuehchukene per se was estrogenic in these bioassay models, the co-administration of yuehchukene and an optimal dose of 3,17 beta-estradiol (estradiol) could attenuate the maximum estrogenic response due to estradiol alone. The anti-estrogenic effect of yuehchukene in rat uterine hypertrophy was corroborated by a parallel attenuation of ornithine decarboxylase activity in these tissues. Yuehchukene binds to rat, mice and MCF-7 cell estrogen receptors with a relative binding affinity of 1/150 to 1/300. This binding affinity was positively related to estrogenicity as determined by uterotrophic assay and MCF-7 cell growth. However, this estrogenic effect did not correlate with the degree of competitive receptor binding by a weaker agonist. Indole-3-carbinol and methylbutadienylindole could induce ethoxyresorufin O-deethylase and estradiol-2-hydroxylase in rat liver and MCF-7 cells. It is postulated that the 'free' indole moiety of yuehchukene could possess similar induction activity. Thus yuehchukene may have a dual pharmacological function. While the intact molecule is a weak estrogen, the 'free' indole moiety in yuehchukene may induce an enhancement of estradiol-2-hydroxylase, thus terminating the biological activity of the endogenous estrogen pool. There is obvious benefit in attenuating the estrogen level in post-menopausal breast cancer patients without going directly to the use of tamoxifen or aromatase inhibitor. Yuehchukene may serve this purpose. In this context, the pharmacological evaluation of a hydroxylated yuehchukene analogue and the anti-estrogenic effect of methylbutadienylindole acid-condensation products are now being studied in earnest.

N-butyl, N-methyl, 11-[3',17' beta-(dihydroxy)-1',3',5'(10')-estratrien-16' alpha-yl]-9(R/S)-bromo undecanamide: synthesis and 17 beta-HSD inhibiting, estrogenic and antiestrogenic activities

The synthesis of a 16 alpha-(bromoalkylamide) derivative of estradiol (N-butyl, N-methyl, 11-[3',17' beta-(dihydroxy)-1',3',5' (10')-estratrien-16' alpha-yl]-9(R/S)-bromo undecanamide) was performed by two different approaches starting from estrone. Each approach has the same key intermediate, containing an aldehyde group, but differs by the bromination step and the timing of formation of the amide group. This compound was found to cause, at 100 microM, a complete inhibition of 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) responsible for the interconversion of estrone and estradiol. The corresponding IC50 value was 10.6 microM. In the estrogen-sensitive ZR-75-1 human breast cancer cell line, this estradiol derivative has no estrogenic activity at 30 nM and only a minimal estrogenic activity (10% above the basal level) at 1 microM. At this latter concentration, this compound causes a 28% inhibition of 0.1 nM E2-induced cell proliferation (antiestrogenic activity). Thus, the introduction of a side-chain with a secondary bromide and a butyl methyl amide group at the 16 alpha-position of estradiol has two interesting effects; namely an inhibition of cytosolic 17 beta-HSD and a blockade of the estrogenic effect of estradiol.

11 beta-Amidoalkoxyphenyl estradiols, a new series of pure antiestrogens

11 beta-Amidoalkoxyphenyl estradiols, a series of new antiestrogens, have been prepared and compared with tamoxifen (TAM) and 4-hydroxytamoxifen (OH-TAM). In vitro, these compounds were up to 20 times as active as OH-TAM on estradiol (E2)-stimulated MCF-7 cells. Unlike TAM or OH-TAM which were inactive, they displayed potent growth inhibitory effects on MCF-7 cells stimulated by a cocktail of epidermal growth factor and platelet derived growth factor. One of the most active compounds, 5e, was tested in vivo for its antiuterotrophic and antitumoral activities: it proved to be fully antiuterotrophic at 3 mg/kg subcutaneously in mice while being devoid of any uterotrophic activity. It inhibited the E2-induced growth of MCF-7 tumors implanted in nude mice and prevented the partial agonistic activity of TAM on MCF-7 tumor growth in ovariectomized mice. Moreover, on MCF-7 variant tumors, 5e, unlike TAM, did not display any proliferative activity, but inhibited the TAM-induced growth. Overall, these results show that this new series of compounds displays an improved activity profile compared with that of TAM, on tests relevant to human breast cancer treatment.

Skeletal conformations and receptor binding of some 9,11-modified estradiols

The effect of the modification of the 9-11 positions on the skeletal conformation of estradiol (E2) has been analyzed by X-ray crystallography and MM2 molecular mechanics. The 11 beta-hydroxyl and 11-keto analogs of E2 maintained ring conformations which were similar to the natural hormone (E2). Introduction of a double bond at position 9-11 induced a flattening of the entire steroid molecule. An 11 alpha-hydroxyl group brought about significant changes in the alicyclic rings of E2. 9 beta-Estradiol and 11-keto-9 beta-estradiol formed ring conformations which were significantly bent from E2 (below the plane of the A-ring). Examination of the affinity of these C-ring analogs of E2 for the human estrogen receptor has shown extreme variations. A hydroxyl group placed either alpha or beta at the 11-position yielded ligands with vastly different and reduced affinities for the receptor. The low affinity of 11 alpha-hydroxyestradiol (1/300th of E2) may be due to the drastic structural change induced in the alicyclic portion of the molecule, as well as, to the steric or electrostatic effects of the alpha-hydroxyl group upon the receptor protein. An 11 beta-hydroxyl group diminished the receptor binding to 1/60th that of E2 without alicyclic ring distortions, whereas a 9-11 unsaturation reduced the binding to 1/5th although this steroid displayed a flattening of rings B, C, and D. The 11-keto function, which had little effect on the conformation of the estrogen nucleus, reduced the affinity of this ligand to 1/1000th that of E2. The negative bend at the C-ring of 11-keto-9 beta-estradiol and 9 beta-estradiol prevented these ligands from binding receptor. Some of the observed receptor interactions were related to structural alterations in the estrogen ring system induced by modifications on the 9-11 region.

The antioxidant action of a pure antioestrogen: ability to inhibit lipid peroxidation compared to tamoxifen and 17 beta-oestradiol and relevance to its anticancer potential

The pure antioestrogen ICI 164,384, and nafoxidine (structurally related to tamoxifen) were good inhibitors of iron ion-dependent lipid peroxidation. In rat liver microsomes incubated with Fe(III)-ascorbate the overall order of effectiveness of the compounds tested as inhibitors of lipid peroxidation was 4-hydroxytamoxifen > 17 beta-oestradiol > nafoxidine > or = tamoxifen > ICI 164,384. When the microsomes were incubated with Fe(III)-ADP/NADPH, a similar order of effectiveness was observed. In ox-brain phospholipid liposomes incubated with Fe(III)-ascorbate the order was 4-hydroxytamoxifen > 17 beta-oestradiol > ICI 164,384 > tamoxifen > or = nafoxidine. The antioxidant ability of ICI 164,384, a steroidal oestrogen antagonist, is compared to that of tamoxifen (a non-steroidal antioestrogen and partial oestrogen agonist) and 17 beta-oestradiol and is discussed in relation to its anticancer action.

RU 58,668, a new pure antiestrogen inducing a regression of human mammary carcinoma implanted in nude mice

RU 58,668, a new steroidal antiestrogen, has been synthesized. Its in vitro and in vivo pharmacological activities have been compared to those of tamoxifen and ICI 182,780. In vitro, it displayed affinities for human and murine estrogen receptors equivalent to those of 4-hydroxy-tamoxifen, along with moderate affinities for progestin and glucocorticoid receptors. RU 58,668 proved to be a potent antiproliferative agent on MCF-7 cells stimulated by estradiol, or by exogenous or endogenous growth factors (IC50, 0.01 nM). It also inhibited the growth of the insulin-stimulated T47D cell line. In vivo, RU 58,668 displayed a total anti-uterotrophic activity in mice or rats without exhibiting any agonistic effect. Moreover, RU 58,668 was the only antiestrogenic compound tested so far to be able to induce a long term regression of human mammary MCF-7 tumors implanted in nude mice, suggesting its potential use for the treatment of advanced breast cancer.

Progesterone and RU486: opposing effects on human sperm

Progesterone induced a rapid influx of calcium in capacitated human sperm, followed by a long-lasting, dose-dependent increase of intracellular free calcium. Thereafter, progesterone increased the fraction of hyperactivated sperm and the acrosome reaction. On the contrary, the progesterone antagonist RU486 (mifepristone) induced an immediate and transient, dose-dependent decrease of intracellular free calcium and a drop in the values of sperm movement parameters related to hyperactivation. Moreover, RU486 counteracted the effects of progesterone on calcium influx, lateral sperm head displacement, and the acrosome reaction. Therefore, RU486 effects were opposite to those of progesterone. The nature of the membrane receptor(s) involved is unknown. Several steroids bearing 11 beta-phenyl substitutions, with different pharmacological profiles, were also investigated. It was concluded that the steroid structure and chemical groups added to the 11 beta-phenyl influence effects on calcium influx.