Syntheses and characterizations of 4-(3,17beta-dihydroxyestra-1,3,5(10)-trien-6alpha- and 6beta-yl)amino-7-nitro-2,1,3-benzoxadiazoles as fluorescent probes

4-(3,17Beta-dihydroxyestra-1,3,5(10)-trien-6alpha- and 6beta-yl)amino-7-nitro-2,1,3-benzoxadiazoles have been synthesized and characterized as fluorescent probes for use in a receptor assay and/or a homogeneous immunoassay for estradiol. The fluorescence intensities are strongly dependent upon the solvent polarity used. The intensities in water were reduced to less than 1% of those in ethyl acetate, and a blue shift was also observed in polar solvents. The quenched fluorescence in aqueous solution was recovered by adding bovine serum albumin or an anti-estradiol antibody. Adding intact estradiol inhibited the fluorescence recovered by the antibody.

Automated synthesis of 16alpha-[18F]fluoroestradiol-3,17beta-disulphamate

After 16alpha-[15F]fluoroestradiol ([18F]FES) has been successfully prepared in an automated module, the synthesis of 16alpha-[18F]fluoroestradiol-3,17beta-disulphamate ([18F]FESDS) is described as a module-assisted one-pot procedure which can provide 10GBq [18F]FESDS with a radiochemical purity better than 99%. The procedure is reliable and reproducible and requires a time of about 90 min. Because of its high sulphatase-inhibitory effect [15F]FESDS is thought to be a new PET tracer to image sites of high sulphatase activity.

Chemical synthesis of 16beta-propylaminoacyl derivatives of estradiol and their inhibitory potency on type 1 17beta-hydroxysteroid dehydrogenase and binding affinity on steroid receptors

The 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) are members of a family of enzymes that catalyze the interconversion of weakly active sexual hormones (ketosteroids) and potent hormones (17beta-hydroxysteroids). Among the known isoforms of 17beta-HSD, the type 1 catalyzes the NAD(P)H-mediated reduction of estrone (E(1)) to estradiol (E(2)), a predominant mitogen for the breast cancer cells. Therefore, the inhibition of this particular enzyme is a logical approach to reduce the concentration of estradiol in breast tumors. To develop inhibitors of type 1 17beta-HSD activity, we hypothesized that molecules containing both hydrophobic and hydrophilic components should be interesting candidates for interacting with both the steroid binding domain and some amino acid residues of the cofactor binding domain of the enzyme. Firstly, a conveniently protected 16beta-(3-aminopropyl)-E(2) derivative was synthesized from commercially available E(1). Then, a representative of all class of NHBoc-protected amino acids (basic, acid, aromatic, aliphatic, hydroxylated) were coupled using standard procedures to the amino group of the precursor. Finally, cleavage of all protecting groups was performed in a single step to generate a series of 16beta-propylaminoacyl derivatives of E(2). The enzymatic screening revealed that none of the novel compounds can inhibit the reductive activity of type 1 17beta-HSD. On the other hand, all of these E(2) derivatives did not show any significant binding affinity on four steroid receptors including the estrogen receptor. Additional efforts aimed at improving the inhibitory potency of these steroidal derivatives on type 1 17beta-HSD without providing estrogenic activities is under investigation using a combinatorial chemistry approach.

Studies on modified estrogens: towards the synthesis of novel 14,15-cyclopropa[a]estra-1,3,5(10),8-tetraenes

To improve the ratio of non-hormonal to hormonal activity, estrogens 3 and 4 were modified at various molecule positions. Isomerization of the 14 alpha,15 alpha-methylene bridge, controlled 3-methoxy group cleavage with respect to the 14 alpha,15 alpha-methylene bridge stereochemistry, reduction of the 8-double bond, and substitution of the oxyfunctionality at C-17 by a methylene and a difluoromethylene moiety were in the focus. As a result of in vivo and in vitro tests, compounds 27 and 29 were selected as potential follow-up candidates of lead 3.

2-Methoxymethylestradiol: a new 2-methoxy estrogen analog that exhibits antiproliferative activity and alters tubulin dynamics

An estradiol metabolite, 2-methoxyestradiol (2-MeOE(2)), has shown antiproliferative effects in both hormone-dependent and hormone-independent breast cancer cells. Previously, a series of 2-hydroxyalkyl estradiol analogs had been synthesized in our laboratories as potential probes for comparison of estrogen receptor (ER)-mediated versus non-ER-mediated effects in breast cancer cells. A methoxy derivative of 2-hydroxymethyl estradiol was prepared for biological evaluation and comparison with 2-MeOE(2). Estrogenic activity of the synthetic analogs was evaluated in two ways, one by examining affinity of the analogs for the estrogen receptor in MCF-7 cells and the other by examining the ability of the analogs to induce estrogen-responsive gene expression. The analog, 2-methoxymethyl estradiol (2-MeOMeE(2)), demonstrated weak affinity for the estrogen receptor (0.9% of estradiol) and weak ability to stimulate estrogen-induced expression of the pS2 gene (0.02% of estradiol). Antitumor activity was evaluated both in vitro and in vivo. The steroidal nucleus seems to be an attractive target for developing novel tubulin polymerization inhibitors. Additionally, such steroidal compounds may have low toxicity compared to the natural products known to interact with tubulin. Interestingly, 2-MeOMeE(2) inhibited tubulin polymerization in vitro at concentrations of 1 and 3 microM and was more effective than 2-MeOE(2). In cells, 2-MeOMeE(2) was effective in suppressing growth and inducing cytotoxicity in MCF-7 and MDA-MB-231 breast cancer cells. The cytotoxic effects of 2-MeOMeE(2) are associated with alterations in tubulin dynamics, with the frequent appearance of misaligned chromosomes, a significant mitotic delay, and the formation of multinucleated cells. In comparison, 2-MeOE(2) was more effective than 2-MeOMeE(2) in producing cytotoxicity and altering tubulin dynamics in intact cells. Assessment of in vivo antitumor activity was performed in athymic mice containing human breast tumor xenografts. Nude mice bearing MDA-MB-435 tumor xenografts were treated i.p. with 50 mg/kg per day of 2-MeOMeE(2) or vehicle control for 45 days. Treatment with 2-MeOMeE(2) resulted in an approximate 50% reduction in mean tumor volume at treatment day 45 when compared to control animals and had no effect on animal weight. Thus, 2-MeOMeE(2) is an estrogen analog with minimal estrogenic properties that demonstrates antiproliferative effects both in vitro and in the human xenograft animal model of human breast cancer.

Selective synthesis of 4-methoxyestrogen from 4-hydroxyestrogen

The introduction of an oxygen atom into the C-6 position of 4-hydroxyestrogen allowed for the selective methylation of the two phenolic hydroxyl groups. When the 6-oxo derivative of 4-hydroxyestrone was benzylated in ethanol, only the 3-monobenzyl ether was obtained without formation of the 4-monobenzyl ether. Moreover, the 6-carbonyl group was further reduced to methylene almost quantitatively in the reaction of 4-acetoxy-6-oxoestrone 3-benzyl ether derivative with sodium borohydride. Therefore, 4-methoxyestrogen was synthesized by essentially combining these two reactions.

Synthesis and biological evaluation of two new radiolabelled estrogens: [125I](E)-3-methoxy-17alpha-iodovinylestra-1,3,5(10),6-tetraen-17beta-ol and

The synthesis of two novel radiolabelled estrogen derivatives, [125I](E)-3-methoxy-17alpha-iodovinylestra-1,3,5(10),6-tetraen-17beta-ol (E[125I]IVDE) and [125I](Z)-3-methoxy-17alpha-iodovinylestra-1,3,5(10),6-tetraen-17beta-ol (Z[125I]IVDE), was carried out aiming to study the influence of the introduction of a C6-C7 double bond on the biological properties of the estradiol molecule. 3-Methoxyestra-1,3,5(10),6-tetraen-17-one was synthesised starting from a suitably protected estrone and subsequently converted into the 17alpha-ethynyl derivative. The radioiodinated derivatives were stereoselectively formed by radioiododestannylation of the corresponding tributylstannyl precursors. The biodistribution of the novel [125I]iodovinylestradiol derivatives was evaluated in immature female mice. Biological data indicated that the Z-isomer, owing to its higher in vivo uptake by the target tissue, has the preferable configuration for further development of similar compounds for estrogen receptor detection.

Synthesis and biological evaluation of 17beta-alkoxyestra-1,3, 5(10)-trienes as potential neuroprotectants against oxidative stress

17beta-O-Alkyl ethers (methyl, ethyl, propyl, butyl, hexyl, and octyl) of estradiol were obtained from 3-O-benzyl-17beta-estradiol with sodium hydride/alkyl halide, followed by the removal of the O-benzyl protecting group via catalytic transfer hydrogenation. An increase compared to estradiol in the protection of neural (HT-22) cells against oxidative stress due to exposure of glutamate was furnished by higher (C-3 to C-8) alkyl ethers, while methyl and ethyl ethers decreased the neuroprotective effect significantly. Lipophilic (butyl and octyl) ethers blocking the phenolic hydroxyl (3-OH) of A-ring were inactive.

Structure-activity relationships of 17alpha-derivatives of estradiol as inhibitors of steroid sulfatase

The steroid sulfatase or steryl sulfatase is a microsomal enzyme widely distributed in human tissues that catalyzes the hydrolysis of sulfated 3-hydroxy steroids to the corresponding free active 3-hydroxy steroids. Since androgens and estrogens may be synthesized inside the cancerous cells starting from dehydroepiandrosterone sulfate (DHEAS) and estrone sulfate (E(1)S) available in blood circulation, the use of therapeutic agents that inhibit steroid sulfatase activity may be a rewarding approach to the treatment of androgeno-sensitive and estrogeno-sensitive diseases. In the present study, we report the chemical synthesis and biological evaluation of a new family of steroid sulfatase inhibitors. The inhibitors were designed by adding an alkyl, a phenyl, a benzyl, or a benzyl substituted at position 17alpha of estradiol (E(2)), a C18-steroid, and enzymatic assays were performed using the steroid sulfatase of homogenized JEG-3 cells or transfected in HEK-293 cells. We observed that a hydrophobic substituent induces powerful inhibition of steroid sulfatase while a hydrophilic one was weak. Although a hydrophobic group at the 17alpha-position increased the inhibitory activity, the steric factors contribute to the opposite effect. As exemplified by 17alpha-decyl-E(2) and 17alpha-dodecyl-E(2), a long flexible side chain prevents adequate fitting into the enzyme catalytic site, thus decreasing capacity to inhibit the steroid sulfatase activity. In the alkyl series, the best compromise between hydrophobicity and steric hindrance was obtained with the octyl group (IC(50) = 440 nM), but judicious branching of side chain could improve this further. Benzyl substituted derivatives of estradiol were better inhibitors than alkyl analogues. Among the series of 17alpha-(benzyl substituted)-E(2) derivatives studied, the 3'-bromobenzyl, 4'-tert-butylbenzyl, 4'-butylbenzyl, and 4'-benzyloxybenzyl groups provided the most potent inhibition of steroid sulfatase transformation of E(1)S into E(1) (IC(50) = 24, 28, 25, and 22 nM, respectively). As an example, the tert-butylbenzyl group increases the ability of the E(2) nucleus to inhibit the steroid sulfatase by 3000-fold, and it also inhibits similarly the steroid sulfatase transformations of both natural substrates, E(1)S and DHEAS. Interestingly, the newly reported family of steroid sulfatase inhibitors acts by a reversible mechanism of action that is different from the irreversible mechanism of the known inhibitor estrone sulfamate (EMATE).

Scintimammography with 11beta-methoxy-(17alpha,20Z)-[123I]iodovinylestrad iol: a complementary role to 99mTc-methoxyisobutyl isonitrile in the characterization of breast tumors

The aim of this study was to investigate a possible relationship between 99mTc-methoxyisobutyl isonitrile (MIBI) uptake and the estrogen receptor (ER) status of breast tumors as determined by 11beta-methoxy-(17alpha,20Z)-[123I]iodovinylestradi ol (MIVE) scintimammography.

METHODS

Thirteen patients referred for MIVE scintimammography after abnormal mammography or finding of a suspect mass on physical examination were injected intravenously with MIVE. Planar images of the breasts and axillary region were taken with both radiopharmaceuticals and compared with pathologic examination of the tumor tissue and in vitro ER quantification.

RESULTS

The presence of cancerous tissue, as indicated by MIBI uptake, is a prerequisite for the accumulation of MIVE by the breast tumors. There was no statistically significant correlation between the MIBI and MIVE tumor uptake ratios. However, the latter correlate well with the presence of ER, as determined by an in vitro assay.

CONCLUSION

MIVE scans add unique information concerning the tumor ER status in breast cancer patients, which could contribute to a better characterization of the tumor and aid in the selection of the most appropriate treatment protocol.

Concepts for the syntheses of biotinylated steroids. Part II: 17beta-estradiol derivatives as immunochemical probes

Biotinylated 17beta-estradiol (E2) derivatives are helpful probes for a better understanding of biospecific E2 interactions with steroid-binding proteins such as the estrogen receptor and anti-steroid antibodies. We describe synthetic strategies for the biotinylation of E2 toward the 3, 6alpha, and 7alpha positions using biotinyl-N-hydroxysuccinimide esters with different spacers, varying in structure and chain length. Key reaction for biotinylation at the 3 position is the regioselective ether formation of the phenolate E2 anion with a linker mesylate without protecting the 17beta-hydroxyl group. The 6alpha position is accessible via a 3,17beta protected 6alpha-hydroxy E2, prepared by stereospecific sodium borohydride reduction of 6-oxo E2. Direct cyanoethylation of the alcohol followed by reduction to the amine allows the biotinylation to 6alpha-O-coupled cyanoethyloxy linker E2 derivatives. Alternatively, 6alpha-O-coupled cyanoalkyloxy polyether linker E2 probes are obtained by a Williamson ether synthesis of the alcohol precursor with omega-t-butyl-dimethylsilyloxy-5-oxa-nonylmesylate. Cyanoethylation of the desilylated compound and further reduction of the nitrile led to the terminal amine. Reductive amination of the 3, 17beta acetylated 6-oxo E2 compound with 6-cyanoethyloxyhexyl ammonium acetate yields in a mixture of 6alpha/beta-N-alkylated E2 nitriles. The epimers are separated by reversed-phase HPLC and the 6alpha-compound subsequently reduced to the terminal amine. The 7alpha-biotinylated E2 compound is derived from 7alpha-(11'-undecyl-N-methyl-N-butylamide) E2, which is already known from literature. Subsequently, the 3 and 17beta positions are protected, and the amide is reduced to the 7alpha-(11'-undecanol) compound. Further cyanoethylation and reduction led to the 11'-amino-ethyloxyundecyl E2. Using (1)H NMR analysis, it could be shown that the biotin moiety of the biotinylated 6alpha- and 7alpha-E2 derivatives has an axial position which results in a vertical orientation of the substituent toward the alpha-face of the planar tetracyclic backbone. Thus, a negligible alteration of the original structure of the upper beta-face offers the feasibility of applying the 6alpha- and 7alpha-derivatives as optimal tracers in competitive immunoassays.

Synthesis of B-ring homologated estradiol analogues that modulate tubulin polymerization and microtubule stability

2-Methoxyestradiol is a cytotoxic human metabolite of estradiol with the ability to bind to the colchicine site of tubulin and inhibit its polymerization, and its 2-ethoxy analogue is even more potent. On the basis of a hypothetical relationship between the structures of colchicine and 2-methoxyestradiol, a B-ring-expanded 2-ethoxyestradiol analogue was synthesized in which the B-ring of the steroid is replaced by the B-ring of colchicine. The synthesis relied on the B-ring expansion of available 6-keto estradiol derivatives as opposed to a total synthesis of the homologated steroid framework. The relative configurations of the acetamido substituents in both epimers of the final product were determined by NOESY NMR and confirmed by X-ray crystallography. The epimer having the 6alpha-acetamido substituent was more active as an inhibitor of tubulin polymerization, and it was also more cytotoxic than the 6beta-epimer. These results are consistent with the proposed structural resemblance of 2-methoxyestradiol and colchicine. Several of the synthetic intermediates proved to be potent inhibitors of tubulin polymerization. On the other hand, a 3,17beta-diacetylated, B-ring-expanded analogue of 2-ethoxyestradiol having a ketone at C-6 resembled paclitaxel (Taxol) in its ability to enhance tubulin polymerization and stabilize microtubules. The corresponding 3-acetate and the 17beta-acetate were both synthesized, and it was determined that the 17beta-acetate, but not the 3-acetate, conferred on the steroid derivative its paclitaxel-like activity.

Radiochemical synthesis and tissue distribution of Tc-99m-labeled 7alpha-substituted estradiol complexes

The diagnosis and staging of breast cancer could be improved by the development of radiopharmaceutical imaging agents that provide a noninvasive determination of the estrogen receptor (ER) status of tumor cells. Agents labeled with (99m)Tc would be especially valuable in this regard. In attempting to achieve this goal, we synthesized four (99m)Tc-labeled 7alpha-substituted estradiol complexes. One complex utilizes the "3+1" mixed ligand design to introduce the Tc metal, whereas the other three took advantage of the cyclopentadienyltricarbonylmetal (CpTM) design. The Tc moieties were attached to the 7alpha position of estradiol with a hexyl tether, a monoether tether, or a polyether tether. The corresponding rhenium compounds have binding affinities for the ER of 20-45% compared with estradiol. Radiochemical yields of the (99m)Tc-labeled compounds ranged from approximately 15% for the CpT-Tc complexes to 95% for the 3 + 1 inorganic complex. Tissue distribution studies in immature female rats showed low nonreceptor-mediated uptake in the target organs and high uptake in nontarget organs such as the liver and fat. These complexes represent the first time that estradiol has been labeled at the 7alpha position with (99m)Tc and provide a further refinement of our understanding of ligand structure-binding affinity correlations for the ER.

Synthesis and evaluation of a new series of 17alpha-[(123)I]iodovinyl estradiols

A series of 17alpha-substituted estradiols was synthesized in which the stereochemical characteristics of carbons 20 and 21 were modified. It was found that the (Z)-isomer demonstrated more favorable receptor binding affinity than the corresponding (E)-isomer.

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.

(17alpha,20E/Z)-iodovinyl- and 16alpha-iodP618-homoestradiol derivatives: synthesis and evaluation for estrogen receptor imaging

Three new 125I-radioiodinated estrogens featuring a 13beta-ethyl instead of the natural 13beta-methyl group, i.e. 18-homoestradiols, were synthesized and evaluated as potential estrogen receptor imaging agents. The 16alpha-iodo-18-methylestradiol and the 125I-labeled analog were synthesized from the corresponding 16beta-bromo analog by the halogen-exchange method. The cis-bromohydrin precursor was obtained by bromination of an estrone enolacetate, followed by epimerization and reduction. The isomeric (17alpha,20E/Z)-iodovinyl-18-methylestradiols were prepared via the vinyltin intermediates. Treatment of 18-methyl-17alpha-ethynylestradiol with tri-n-butyltin hydride, in the presence of azobisisobutyronitrile as catalyst and heating at 90-100 degrees C afforded the (17alpha,20E)-tri-n-butylstannyl isomer as the major product. Changing the catalyst for triethyl borane, at room temperature, mainly gave the 20Z-isomer. The nca 125I-labeled analogs were obtained from their corresponding tin intermediates upon treatment with [125I]NaI in the presence of H2O2. The 16alpha-[125I]iodo- and isomeric (17alpha,20E/Z)-[125I]iodovinyl-18-methylestradiols were evaluated for estrogen receptor-mediated uterine uptake in immature female rats. Homologation of the C13-methyl group did improve the uterine uptake of the iodovinyl derivatives, but also increased blood retention, resulting in lower target uptake ratios. In the case of the 16alpha-iodo analog uterine retention decreased upon C13-homologation.

Solid-phase synthesis of phenolic steroids: from optimization studies to a convenient procedure for combinatorial synthesis of biologically relevant estradiol derivatives

During the course of our studies on therapeutic agents for the treatment of breast cancer, we became interested in the solid-phase combinatorial synthesis of estradiol derivatives that contain a functionalized side chain at either position 16 beta or 7 alpha. Both types of compounds have already demonstrated inhibitory activity toward both biosynthesis and action of estradiol. As a first step, two versatile precursors bearing an azidoalkyl side chain at either position 16 beta or 7 alpha of estradiol were synthesized using standard solution-phase methods. Afterward, the effectiveness of five linkers to attach the phenolic function of these estradiol derivatives to a polystyrene resin was investigated; they were benzylic ether (Merrifield), 4-alkoxy-benzylic ethers (Wang, Sheppard), tetrahydropyranyl ether (Ellman), benzoic ester, and o-nitrobenzyl ether. To test the linker in a synthetic context, a short sequence of reactions, including reduction of the azide and acylation of the corresponding amine, was performed on the polymer-bound estradiol derivative. While all of the tested linkers proved effective in attaching the phenol functionality of the precursor, only the o-nitrobenzyl ether photolabile linker enabled the release of the final products in acceptable purities. Consequently, this linker was used to perform successfully the solid-phase synthesis of four different classes of estradiol derivatives in acceptable yields and excellent purities. This study was preliminary to the combinatorial synthesis of larger libraries of biologically relevant estradiol derivatives.

Synthesis and estrogen receptor binding affinity of a porphyrin-estradiol conjugate for targeted photodynamic therapy of cancer

A tetraphenylporphyrin-C11-beta-estradiol conjugate has been synthesized. Competitive binding assay of the conjugate with estrogen receptor (ER)-ligand-binding domain showed that the conjugate binds specifically to the protein with high affinity. Potential use of this conjugate to selectively deliver cytotoxic porphyrins to ER-positive cells in various carcinomas is discussed.

Preparation of specific antisera to 15alpha-hydroxyestrogens

The synthesis of haptens of 15alpha-hydroxyestrone, 15alpha-hydroxyestradiol, and 15alpha-hydroxyestriol (estetrol) was undertaken, to obtain specific antisera required for enzyme immunoassay. 3-(1-Carboxypropyl) ethers of these 15alpha-hydroxyestrogens were prepared and conjugated with bovine serum albumin and horseradish peroxidase. The specificity of antisera elicited against bovine serum albumin conjugates was checked by the enzyme immunoassay by using horseradish peroxidase-labeled antigen, and proved to be satisfactory in terms of cross-reactivities to related compounds.

Potent inhibition of steroid sulfatase activity by 3-O-sulfamate 17alpha-benzyl(or 4'-tert-butylbenzyl)estra-1,3,5(10)-trienes: combination of two substituents at positions C3 and c17alpha of estradiol

Steroid sulfates are precursors of hormones that stimulate androgen- and estrogen-dependent cancers. Thus, steroid sulfatase, the enzyme that catalyzes conversion of DHEAS and E1S to the corresponding unconjugated steroids DHEA and E1, appears to be one of the key enzymes regulating the level of active androgenic and estrogenic steroids. Since 17alpha-substituted benzylestradiols and 3-O-sulfamate estrone (EMATE) represent two families of steroid sulfatase inhibitors that probably act through different mechanisms, we synthesized compounds 3-O-sulfamate 17alpha-benzylestradiol (4) and 3-O-sulfamate 17alpha-(tert-butylbenzyl)estradiol (5) that contain two kinds of substituents on the same molecule. In our enzymatic assay using a homogenate of human embryonal (293) cells transfected with steroid sulfatase, compounds 4 and 5 were found to be more potent inhibitors than already known steroid sulfatase inhibitors that have only a C17alpha-substituent or only a C3-sulfamate group (EMATE). The IC50 values of 4 and 5 were, respectively, 0.39 and 0.15 nM for the transformation of E1S to E1 and 4.1 and 1.4 nM for the transformation of DHEAS to DHEA. Compound 5 inhibited the steroid sulfatase activity in intact transfected (293) cell culture assays by inactivating the enzyme activity. Compound 5 also inactivates the steroid sulfatase activity at lower concentration than EMATE in microsomes of transfected (293) cells. In this assay, an excess of natural substrate E1S protects enzyme against inactivation by 5 or EMATE. Furthermore, the unsulfamoylated analogue of 5, compound 3, did not inactivate the steroid sulfatase.

Synthesis and evaluation of geldanamycin-estradiol hybrids

Geldanamycin (GDM) binds to the Hsp90 chaperone protein and causes the degradation of several important signalling proteins. A series of novel estradiol-geldanamycin hybrids has been synthesized and evaluated for their ability to induce the selective degradation of the estrogen receptor (ER). The hybrid compounds are active and more selective than the parent causing degradation of ER and HER2, but not other GDM targets.

Synthesis of 6- and 7-hydroxyestradiol 17-sulfates: the potential metabolites of estradiol 17-sulfate by female rat liver microsomes

The potential ring-B hydroxylated metabolites of estradiol 17-sulfate (1) by female rat liver microsomes were chemically prepared as authentic compounds. They are 6alpha- and 6beta-hydroxyestradiol 17-sulfates (7 and 9), and 7alpha- and 7beta-hydroxyestradiol 17-sulfates (12 and 16), whose synthetic procedures are described.

Synthesis and evaluation of 11beta-substituted 21-chloro/iodo-(17alpha,20E/Z)-19-norpregna-1,3,5(10),20-te traene-3, 17beta-diols: high-affinity ligands for the estrogen receptor

We have synthesized six new estrogens substituted at the 11beta-position with a methoxy or vinyl group and at the 17alpha-position with an (E)- or (Z)-chloro/iodovinyl moiety. The products were obtained in good overall yields from the corresponding tri-n-butylstannylvinyl intermediates using the electrophilic halodestannylation methodology. The six new ligands were compared to the 11beta-unsubstituted chloro/iodovinyl derivatives and the 11beta-methoxy (E)- and (Z)-iodovinyl estrogens to evaluate the effects of 11beta-substitution and 20E/Z-stereochemistry. While all the compounds exhibited high affinity for the estrogen receptor, the 20Z-isomers demonstrated higher affinity than the corresponding 20E-isomers. In addition, the presence of the lipophilic 11beta-substituent was favored over either no substituent or a polar (methoxy) group. Within each isomeric series, the presence of the 21-halo substituent had different effects. For the 20E-series, the 21-chloro products had a higher affinity than the 21-iodo analogue, whereas for the 20Z-series the effect was reversed. These results provide additional insights into the interaction of substituted estradiols with the hormone binding domain of the estrogen receptor.

Novel high-affinity steroidal estrogenic ligands: synthesis and receptor binding of 11 beta-vinyl-17 alpha-E/Z-phenylselenovinyl estradiols

Previous studies from our laboratory demonstrated separately the tolerance of the estrogen receptor for the 17 alpha-phenylselenovinyl substituent and the enhancement of affinity imparted by the 11 beta-vinyl moiety. Our recent publication suggested that the two groups could be combined within a single structure and retain high affinity for the estrogen receptor. As a result, we have prepared in good overall yields the E- and Z-isomers of 11 beta-vinyl-17 alpha-phenylselenovinyl estradiol. Evaluation of the new steroids with receptor isolated from lamb cytosol indicated that both isomers are poorer ligands than estradiol at 4 degrees C, but both are better than estradiols. at 25 degrees C. This behavior had not been observed for the 11 beta-unsubstituted 17 alpha-E/Z phenylselenovinyl estradiols. Of particular interest was the observation that, unlike previous isomer pairs, the E-isomer possessed a greater affinity than the Z-isomer. The results suggest that relatively small changes in structure may impart significant differences in the interactions with the receptor and provide the basis for further ligand design.