Seco-oestradiols and some non-steroidal oestrogens: structural correlates of oestrogenic action

Anti-implantation effect of 2-[piperidinoethoxyphenyl]-3-[4-hydroxyphenyl]-2H-benzo(b)pyran, a potent antiestrogenic agent in rats

OBJECTIVE

To investigate the anti-implantation effect and hormonal profile of 2-[piperidinoethoxyphenyl]-3-[4-hydroxyphenyl]-2H-benzo(b)pyran (K-1) in rats.

DESIGN

In vivo assays for anti-implantation activity were performed in pregnant rats. Assays for estrogenicity/antiesrogenicity were performed in immature ovariectomized female rats. In vitro competitive binding of K-1 to human recombinant ERα, transient transfection assay using ERE-luciferase reporter, and alkaline phosphatase (ALP) activity as a measure of estrogenicity and/antiestrogenicity in human endometrial carcinoma cells were performed.

SETTING

Research laboratory.

ANIMAL(S)

Adult female rats for anti-implantation activity, immature ovariectomized female rats, and immature castrated/intact male rats.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Number of implantations, uterine growth, luciferase reporter activity, ER binding affinity, and ALP activity.

RESULT(S)

Compound K-1 given orally for 1-7 days post coitum at the dose of 100 μg/kg body weight prevented pregnancy in 100% of rats. K-1 was a potent antiestrogenic, and at 50 μg/kg, it could inhibit the effect of 1 μg E(2) in immature rats. Compound was devoid of uterotrophic, androgenic, or antigonadotropic activity. A high affinity binding to ERα was displayed by K-1, with a relative binding affinity of 5% of E(2). In human endometrial carcinoma cells, K-1 did not induce ERα-mediated transcriptional activation that is measured as luciferase reporter activity. K-1 antagonized the E-induced transcriptional activation significantly. K-1 also antagonized E-induced ALP activity in human endometrial cells.

CONCLUSION(S)

K-1 appeared to exert its antifertility action by virtue of its strong antiestrogenic activity.

Modulation of estrogen action during preimplantation period and in immature estradiol-primed rat uterus by anti-implantation agent, ormeloxifene

Studies were undertaken to evaluate the influence of estrogen antagonist-cum anti-implantation agent, ormeloxifene, on 17beta-hydroxysteroid dehydrogenase (17beta-HSD) activity and estrogen action in rat uterus during preimplantation period and to examine its ability to induce progesterone receptor (PR) in immature rat model. A group of female rats received orally a contraceptive dose of 1.25 mg/kg of ormeloxifene on Day 1 postcoitum (pc). Rats were sacrificed on Days 3, 4 and 5 pc, and uterine tissues were processed for enzymatic, estrogen receptor and estradiol (E(2)) estimations. Immature ovariectomized rats received ormeloxifene, subcutaneously for 3 days at various doses in the absence or presence of estradiol, and uterine PR levels were measured using (3)H-R5020 as radioligand. Results revealed that ormeloxifene treatment caused a marked increase in enzyme activity of 17beta-HSD on Days 3, 4 and 5 pc as compared to respective controls. Further, total uterine estrogen receptors as estimated by exchange assay showed a noticeable decrease on Days 4 (35%) and 5 (>80%) pc in ormeloxifene-treated groups. The results correlated well with a decrease in tissue E(2) levels. In immature rats, ormeloxifene caused a dose-dependent increase in cytosolic PR levels; ormeloxifene given along with E(2) (0.1 mug) for 3 days caused a significant reduction in concentration of PRs at 10 mug and higher doses. Ormeloxifene also induced (3)H-progesterone (P) uptake by immature rat uterus. However, in the presence of E(2), it significantly reduced (3)H-P uptake. The in vitro competitive binding experiments did not reveal any displacement of (3)H-R5020 either by ormeloxifene or by its hydroxy derivative from PR. The results suggest that in addition to its competitive antagonism at estrogen receptor level, ormeloxifene enhances the inactivation of intracellular E(2) to estrone, a biologically less active form, thus declining estrogen receptor pool. Moreover, it causes indirect anti-progestational effects in the uterus by virtue of its anti-estrogenic profile rather than by blocking the PRs.

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.

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.

17 alpha (haloacetamidoalkyl) estradiols alkylate the human estrogen receptor at cysteine residues 417 and 530

Results obtained in a previous study suggested that cysteine residues in the estrogen receptor were covalent attachment sites for four 17 alpha-(haloacetamidoalkyl) estradiols (halo, bromo or iodo; alkyl, methyl, ethyl, or propyl). To identify the putative concerned cysteines, we expressed wild-type and various cysteine --> alanine mutants of the human estrogen receptor in COS cells and determined their ability to be alkylated by the four electrophiles. The quadruple mutant, in which all the cysteines (residues 381, 417, 447, and 530) of the hormone-binding site were changed to alanines, showed very little electrophile labeling, whereas the four single mutants (C381A, C417A, C447A, and C530A) were alkylated as efficiently as the wild-type receptor. These results (i) demonstrate that cysteine residues were covalent attachment sites of electrophiles and (ii) indicate that more than one cysteine residue could be alkylated. Analysis of three double mutants (C381A/C530A, C417A/C530A, and C447A/C530A) provided strong evidence that only C417 and C530 were sites for electrophile covalent attachment. Since C530 was also alkylated by tamoxifen aziridine, a nonsteroidal affinity-labeling agent, we propose a selective mode of superimposition of tamoxifen-class antiestrogens with estradiol, which could account for the relative positioning of the two types of ligands in the receptor hormone-binding pocket. According to the structure of the hormone-binding pocket of nuclear receptors, as inferred from crystallographic studies and general sequence alignment of hormone-binding domains, C417 and C530 appear to be (1) located at the extreme border or in structural elements involved in delineation of the hormone-binding pocket, (2) spatially in close proximity to each other, and (3) in positions highly homologous to those of glucocorticoid receptor sites alkylated by affinity- and photoaffinity-labeling agents, respectively.

The estradiol pharmacophore: ligand structure-estrogen receptor binding affinity relationships and a model for the receptor binding site

The accumulated knowledge on the binding of estradiol (E2) and its analogs and the results of affinity-labeling studies have been reviewed and are used herein to derive a binding site model for the estrogen receptor (ER). Estradiol is nonpolar and hydrophobic, except at its molecular termini. Most of its skeletal flexibility resides in the B-ring, and it probably binds in a low-energy conformation. The phenolic OH group in the A-ring contributes about 1.9 kcal/mol to the binding free energy and probably acts primarily as a hydrogen bond donor. The 17 beta-hydroxyl group in the D-ring contributes approximately 0.6 kcal/mol to the binding and probably acts as a hydrogen bond acceptor, either directly or via a water molecule. There also seems to be a degree of flexibility in the region of the receptor that encompasses the D-ring. The aromatic ring contributes about 1.5 kcal/mol, probably through weak polar interactions with receptor residues that contact the beta-face of the steroid. The receptor seems to surround the ligand, so that all four rings contribute significantly to binding. Small hydrophobic substituents enhance binding affinity at positions 4, 12 beta, 14, and 16 alpha; whereas, larger hydrophobic substituents are tolerated at positions 7 alpha, 11 beta, and 17 alpha. In general, the ER is intolerant of polar substituents. Based on E2 analogs bearing affinity-labeling groups, cysteine residues might be present in the binding site in the area of C-4, C-17 alpha, and C-17 beta, and a lysine residue might be located near C-16. Models that represent the limits of deformability of the ligand binding site, the position of preformed pockets, and space occupied by the receptor are presented. The various elements in this model for the binding of steroidal estrogens by the estrogen receptor are consistent with evidence emerging from the crystal structures of related nuclear hormone receptor ligand complexes.

Characterization of centchroman binding protein in plasma of rhesus monkey (Macaca mulatta)

Centchroman, a nonsteroidal antifertility agent was studied for its binding to monkey (Macaca mulatta) plasma proteins using charcoal adsorption and electrophoretic techniques. 14C-centchroman showed a low affinity binding and did not compete for 3H-cortisol or 3H-DHT binding sites in plasma. 14C-centchroman binding protein was heat stable in nature and showed the electrophoretic pattern similar to that of albumin (Rf 0.70). Thus centchroman binds to albumin in monkey plasma which can be suggested as carrier protein for this contraceptive agent.

[3-Substituted 2-phenylindoles: synthesis and biological properties]

Knoevenagel-reaction of indol-3-carbaldehydes 5a,b and 7a,b with nitromethane leads to the nitroethenes 12 and 14, the analogous reaction with malodinitrile to the methylidenemalonic acid dinitriles 16.- Michael-addition of nitromethane at 12 and 14 affords the 1,3-dinitropropanes 13 and 15, reduction of 16 the methylmalonic acid dinitriles 17.- Reaction of indoles 3 with n-BuLi/phenylsulfonylchloride leads to the 3-chloroindoles 18, reaction with NaH/ethyliodide, either cleavage and acylation to derivatives 19.- Compounds 7-11, 14-17, and 19 show affinity to the estrogen receptor. Compounds 7b, 9-11, 17b, and 19b inhibit the growth of MCF-7- and MDA-MB-231-cells. IC50-values are determined and structure-activity relationships are discussed.

Biological profile of 2-[4-(2-N-piperidinoethoxy) phenyl]-3-phenyl (2H) benzo (b) pyran--a potent antiimplantation agent in rat

Compound CDRI-85/287: 2-[4-(2-N-piperidinoethoxy) phenyl]-3-phenyl (2H) benzo (b) pyran has been identified as a potent antiimplantation agent in rat. A single oral dose (2.5 mg/kg body weight) of the compound administered on days 1, 2 or 3 of pregnancy or multiple dosing (0.05 mg/kg daily) on days 5-7 postcoitum effectively prevented pregnancy. When administered on days 5-7 postcoitum, it failed to interrupt pregnancy even at 20 mg/kg dose. The compound is a potent antiestrogen, with very weak uterotrophic activity; it does not induce vaginal cornification in immature ovariectomised rat. Also, it is devoid of progestational, antiprogestational, androgenic, antiandrogenic and antigonadotrophic activities. The results suggest that the compound exerts its antiimplantation acivity in rat by virtue of its antiestrogenic activity [corrected].

Estrogen receptor-binding affinity of tamoxifen analogs with various side chains and their biologic profile in immature rat uterus

Estrogen receptor-binding affinity and estrogenic and antiestrogenic activity have been evaluated for tamoxifen analogs substituted with various side chains. Antagonist activity of the compounds of this series appears to be dependent on the presence of the beta-tert-aminoethoxy moiety. The results also indicate that the dissociation of these compounds from the estrogen receptor-binding site at 25 C is very slow.

The mechanism of action of steroid antagonists: insights from crystallographic studies

Examination of the structures of compounds having high affinity for estrogen, progestin, mineralocorticoid and glucocorticoid receptors strongly suggests that receptor binding is primarily the result of a tight association between the receptor and the steroidal A-ring. High affinity binding to the estrogen receptor appears to be dependent upon the presence of a phenolic ring in the substrate. An inverted 1 beta, 2 alpha conformation of the 4-ene-3-one A-ring appears to be most conductive to high affinity binding to the progesterone receptor. Binding to the mineralocorticoid receptor appears to be correlated to a complementary fit between amino acids of the receptor site and a flat 4-en-3-one A-ring similar to that imposed upon aldosterone by the 11,18-epoxide formation. The glucocorticoid receptor appears to prefer a 4-en-3-one A-ring that is bowed toward the alpha-face as is the case in structures having a 9 alpha-fluoro substituent or additional unsaturation at C(1)-C(2). The binding of androgens to their receptor differs in appearing to have an essential dependence upon functional groups at the A- and D-ring end of the steroid. With the exception of the androgens, the data suggest that specific interactions between the steroid B-, C- and D-rings and the receptor play at best a minor role in receptor binding but are the most important factor in determining agonist versus antagonist behavior subsequent to binding. Antagonists that compete for a steroid receptor site may be expected to have the A-ring composition and conformation necessary for receptor binding but lack the 11 beta-OH and the D-ring conformational features and functional groups that induce or stabilize subsequent receptor functions. Antagonists might also be compounds with A-ring conformations appropriate for binding but other structural features that interfere with subsequent receptor functions essential to activity.

Quantitative structure-activity relationships of estrogenic steroids substituted at C14, C15

The uterotropic activity of thirty 3-methoxyestradiol derivatives is measured and discussed on the basis of X-ray crystallographic results and quantitative structure-activity relationship analyses involving hydrophobic substituent constants pi and f as well as steric parameters Pr and L. In addition, estrogenicity is compared to data of interceptive activity and receptor binding affinity. All the biological data exhibit a high degree of intercorrelation. 17 beta-Hydroxysteroids having 14 alpha configuration reveal a generally better capability of high-affinity binding than those being 14 beta configurated. Between the uterotropic activity and the hydrophobicity of C14, C15 substituents, statistically significant correlations are found which suggest a close contact between the steroidal D-ring subsite and the receptor protein (e.g. for 14 alpha steroids: log UDD = -0.996 pi -0.392; n = 9, r = -0.943, s = 0.235, t = -7.5, alpha less than 0.001). The hydrophobic nature of both 14 alpha and 14 beta medium-sized substituents employed is shown by QSAR regressions to exert a stronger influence than steric effects. Furthermore, there are indications to additional hydrogen bonding and steric repulsion phenomena. As to the receptor-binding models discussed in the literature, it is concluded that the receptor protein has a high conformational flexibility to accommodate very different drug structures all having the common phenolic ring A. But, if an appropriate spacing of steroidal key atoms is recognized by the receptor and, consequently, the steroid-receptor complex is formed, the binding is complemented by hydrophobic interactions also in the D-ring region.

Enhanced antifertility activity of non-steroidal molecules with 3-n-butylamino-2-hydroxypropyloxy side chain

A comparative study of relative binding affinity (RBA) for estradiol-17 beta-receptors, estrogenicity and antifertility activity of compounds 2,2-dimethyl-3-phenyl-4-p-(3-n-butylamino-2-hydroxypropyloxy-pheny l)- 7-methoxycoumarin 4, 2,2-dimethyl-3-phenyl-4-p-(3-n-butylamino-2-hydroxy-propyloxyphenyl++ +)-7-methoxy chromene 5 and trans-2,2-dimethyl-3-phenyl-4-p-(3-n-butylamino-2-hydroxypropyloxyphe nyl)- 7-methoxychroman 6 with the corresponding 4-p-(beta-pyrrolidinoethoxyphenyl) compounds 1-3, is reported. It has been found that the introduction of the novel 3-n-butylamino-2-hydroxypropyloxy moiety in place of the classical tert-beta-aminoethoxy group leads to enhancement of antifertility activity.

Cis isomer of centchroman--a selective ligand for the microsomal antiestrogen binding site

Several compounds structurally related to the triarylethylene antiestrogens, but possessing weak estrogen receptor affinities, were assessed for their ability to interact with the microsomal antiestrogen binding site. While all the compounds tested did interact with this site their relative affinities were somewhat lower than that of tamoxifen. One of these, viz., the cis isomer of centchroman, has however emerged as a selective ligand for the antiestrogen binding site since its estrogen receptor affinity is nearly 50,000 times lower on a relative scale.

Influence of new hydroxylated triphenylethylene (TPE) derivatives on estradiol binding to uterine cytosol

Twelve homologous triphenyl acrylonitrile derivatives with a p-OH or p-CH3 group on one or more of the phenyl rings were synthesized in order to assess the relative influence of each position on binding to the estrogen receptor (ER) and on inhibition of prostaglandin synthetase (PGS). Their relative binding affinities (RBAs) for [3H]estradiol (E2)-labeled ER were compared at 0 and 25 degrees C in mouse and rat uterus cytosol with those of tamoxifen derivatives, cyclofenil and diethylstilbestrol. RBAs in both species were closely correlated (r = 0.92) although the RBAs were about twice as high in the mouse as in the rat. The unsubstituted skeleton had an RBA of much less than 0.1 (estradiol = 100). An OH-group in R1 or R2 (Fig. 1) engendered very low affinity whereas an OH-group in R gave rise to a compound with an RBA equivalent to that of E2, emphasizing the importance of this position in the interaction with ER. Compounds with an additional OH-group in R1 or R2 were significantly better competitors than E2. No further increase in RBA was noted with the trihydroxy derivative. The effect of the introduction of a hydrophobic CH3-group decreased affinity as expected in R, but also in position R1 unless a second OH-group was present in R2. None of the 12 test-compounds competed significantly for binding to the "anti-estrogen binding site" in rat kidney supernatant. Although polar groups were not necessary for inhibition of PGS, inhibition was enhanced by the presence of a hydroxy group in R or R1 (but not R2). Even greater inhibition was obtained by the further introduction of a CH3-group in R1 or R respectively. The conformations of these derivatives are compared to those of known estrogen ligands and anti-inflammatory agents in order to obtain further information on these protein recognition sites.

Substituted derivatives of A-nor-5 alpha-androstane and A-nor-5 alpha-estrane--structure and affinity for hormonal receptors

The interactions of A-nor-5 alpha-androstane and A-nor-5 alpha-estrane derivatives with the estrogen and androgen receptors, have been evaluated by measuring their relative binding affinities (RBAs), under two sets of incubation conditions in order to discriminate between potent agonists from weak agonists with potential antagonist activities. Surprisingly some of these compounds which do not possess a phenolic hydroxyl group interact somewhat markedly with the estrogen receptor. This interaction is characteristic of weak estrogens, with potential anti-estrogenic activity (RBA values decreasing when increasing time and temperature of incubation). Results are in good agreement with data obtained in vivo. Moreover, some of these compounds interact also to some extent with the androgen receptor. Results will be discussed in order to outline some structure-activity relationships in these series.

Structure-activity relationship of estrogens: a study involving cyclofenyl as the model compound

Bis-(p-acetoxyphenyl)cyclohexylidenemethane [cyclofenyl] has been shown to resemble triarylethylene estrogens quite closely in its receptor binding specificity as well as activity profile. Mono-pyrrolidinoethyl ether of cyclofenyl thus acts as a more potent receptor binder but less potent estrogen than its parent. Like triarylethylene antiestrogens, this derivative of cyclofenyl also acts as an antiuterotrophic agent. This finding would substantiate the proposition that the geminal diaryl residue and not the 1,2-diarylethylene moiety is mainly responsible for the receptor binding and activity profile characteristic of triarylethylenes. This understanding can form a basis for the rationalization of the structure-activity-relationship of estrogens at the molecular level.