Synthesis and biologic activities of 11 beta-substituted estradiol as potential antiestrogens

The effect of attachment of a dimethylaminoethoxy or a dimethylaminopropoxy group at the 11 beta-position of estradiol (E2) on its relative binding affinity (RBA) to estrogen receptor (ER) and intrinsic biologic activity is described. The binding of 11 beta-[2-(N,N-dimethylamino) ethoxy]estra-1,3,5(10)-triene-3,17 beta-diol (4) and 11 beta-[3-(N,N- dimethylamino)propoxy]estra-1,3,5(10)-triene-3,17 beta-diol (5) to the ER from immature rat uterine tissue was measured relative to that of [3H]E2 by a competitive binding assay. It was found that the 11 beta-substituted E2 analogs have considerably lower RBA to ER than the corresponding parent compound. The intrinsic activity of compounds 4 and 5 were studied in terms of uterotrophic and antiuterotrophic activity. It was found that the uterotrophic activity of these compounds was drastically reduced compared with E2. However, no antiuterotrophic activity was observed in these compounds at dosages ranging from 1 to 100 micrograms/rat/d.     

Fluorous tolerance of the estrogen receptor alpha as probed by 11-polyfluoroalkylestradiol derivatives

The concern of this work was to try to delineate factors, inherent to fluorination, susceptible to influence estradiol binding to the estrogen receptor alpha (ERalpha). For this purpose, fluorinated chains were linked at 11beta position of the steroid (i.e., C(6)F(13), CH(2)CH(2)C(4)F(9), CH(2)CH(2)C(8)F(17)). Relative binding affinity (RBA) for ERalpha of these compounds and of other related fluorinated derivatives was compared to those of non-fluorinated analogs. Despite being relatively well accepted by the receptor, investigated compounds exhibited lower RBA values at 0 degrees C than their non-fluorinated counterparts. Nevertheless, heavily fluorinated chains were tolerated in so far as they are not too long (C-4) and insulated from the steroidal core by a two methylene spacer unit. Increase of the temperature of our binding assay (25 degrees C) failed to change the RBA values of two selected polyfluorohexyl derivatives while it drastically enhanced the value of the corresponding non-fluorinated analogs. Rigidity of the chain induced by fluorination as well as the oleophilic (fluorophobic) nature of the estradiol binding cavity of ERalpha is proposed to explain these properties.     

Estradiol derivatives bearing sulfur-containing substituents at the 11beta or 7alpha positions: versatile reagents for the preparation of estrogen conjugates

Estradiol derivatives bearing HS-, HSCH(2)-, HSCH(2)CH(2)-, MeS-, MeSCH(2)-, MeSCH(2)CH(2)-, or PhCH(2)SCH(2)CH(2)-groups at the 11beta position or an HS-group at the 7alpha position have been synthesized, and their binding affinity to the estrogen receptor (ER) determined. Nearly all of these substituted estrogens retain high binding affinity, and at the 11beta position, the sulfur atom has an effect on ER binding that is similar to that of a carbon atom. These thiol derivatives are promising intermediates for the preparation of a variety of estradiol conjugates. The methyl sulfides, in particular, might potentially be developed as (11)C-labeled agents for imaging ER-positive tumors by positron emission tomography.     

BODIPY-17α-ethynylestradiol conjugates: Synthesis,fluorescence properties and receptor binding affinities

In vivo imaging of estrogen receptor (ER) densities in human breast cancer is a potential tool to stage disease, guide treatment protocols and follow-up on treatment outcome. Both positron emission tomography (PET) and fluorescence imaging have received ample attention to detect ligand-ER interaction. In this study we prepared BODIPY-estradiol conjugates using 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) as fluorescent probe and estradiol derivatives as ligand and established their relative binding affinity (RBA) for the ERα. The synthesis of the conjugates involves attachment of a BODIPY moiety to the C17α-position of estradiol using Sonogashira or click reactions of iodo-BODIPY or aza-BODIPY with various 17α-ethynylestradiol (EE2) derivatives. The highest RBA for the ERα was observed with the EE2-BODIPY conjugate (7) featuring a linear eight carbon spacer chain. Cell uptake studies and in vivo imaging experiments in an ER-positive mouse tumor model are in progress.     

The relative binding affinity of diethylstilbestrol to uterine nuclear estrogen receptor: effect of serum and serum albumin

The relative binding affinity (RBA) of diethylstilbestrol (DES) was determined in nuclear fractions of the rat uterus. DES displayed a two- to threefold greater affinity (RBA = 245 +/- 36) than estradiol (RBA = 100) for nuclear E receptor. The RBA of DES to nuclear E receptor was lowered significantly in the presence of rat serum (43 +/- 1) or human serum (52 +/- 7). Dilution of human serum resulted in a progressive increase in the RBA of DES which approached that observed in the absence of serum. Addition of purified human serum albumin mimicked the decrease in RBA of DES that was observed with serum. The IC50 of estradiol was not changed in the presence of either rat serum or albumin. These data show that DES possesses a greater affinity for nuclear E receptor than estradiol and that serum albumin can modulate DES binding to uterine E receptor.     

Identification of a series of tetrahydroisoquinoline derivatives as potential therapeutic agents for breast cancer

A series of tetrahydroisoquinoline-N-phenylamide derivatives were designed, synthesized, and tested for their relative binding affinities, and antagonistic activities against estrogen receptor (ER). Compound 1f (relative binding affinity, RBA=5) showed higher binding affinity than tamoxifen (RBA=1), a potent ER antagonist and currently being used for breast cancer therapy. Compound 1f also exerted optimal antagonistic activity against ER in reporter and cell proliferation assays. Interestingly, compound 1j, which only has a minor agonistic effect against ER, acted as a progesterone receptor (PR) antagonist and exerted agonistic activity against AP-1 through ER pathway. Our results show that these new compounds can be employed as leading pharmacophore for further development of potent selective ER and/or PR modulators or antagonists.     

Synthesis and biological activity of 17 beta-substituted estradiol

The dialkylaminoethoxy side chain in triphenylethylene antiestrogens is required for their antiestrogenic activity. Without this side chain the compounds lose their antiestrogenic activity and become essentially estrogenic. Estradiol substituted at the 17 beta-position with dialkylaminoethoxy, dialkylaminoethylamino, or dialkylaminoethylthiol were synthesized and tested for their ability to displace estradiol for its receptor. All of the derivatives tested exhibited low binding affinities to the estrogen receptor, with RBA values ranging between 0 to 1.2 (estradiol = 100). The mouse and rat uterine weight test revealed only low estrogenic activity for this class of compounds. None of the estradiol derivatives synthesized showed antiestrogenic activity.     

Synthesis and biological activities of nucleoside-estradiol conjugates

Nucleosides were coupled to estradiol via a 17alpha-ethynyl spacer group using Pd(II) as a catalyst. The conjugates were evaluated in vitro for estrogen receptor (ER) binding affinity and cytotoxicity against cell lines with and without ER. The highest receptor binding affinities (RBA approximately 3) were observed with conjugates coupled via a relative long spacer group, while none of the conjugates exhibited cytotoxicity against either cell lines.     

11β-Amidoalkyl estradiols, a new series of pure antiestrogens

In order to find new antiestrogens, devoid of any agonistic activity, a series of 11β-amidoalkyl estradiols were prepared. These compounds have been studied in comparison with tamoxifen (TAM): in vitro, for their relative binding affinities (RBA) for mouse and MCF-7 estrogen receptors (ER) and for their antiproliferative effect on MCF-7 (estradiol or EGF/PDGF stimulated) and Ly2 human breast cancer cell lines; in vivo, for their uterotrophic/antiuterotrophic activities in the mouse and for their antitumoral activities on MCF-7 tumors implanted in nude mice.

The most representative compounds are N-methyl-N-isopropyl-(3,17β-dihydroxy-estra-1,3,5(10)-trien-11β-yl)-undecanamide (RU 51625) and its 17-ethynyl derivative (RU 53637). They showed good RBAs for ER and a stronger antiproliferative effect than TAM in vitro. Unlike TAM, these compounds inhibited growth factor stimulated MCF-7 proliferation, and the growth of the TAM resistant cell line Ly2. In vivo, they were completely devoid of uterotrophic activity, when given subcutaneously in mice, but exhibited a slight agonistic effect when administered orally. They showed interesting antitumor activities in nude mice by the percutaneous route, but RU 53637 was significantly more potent than RU 51625 when given orally.     

Electrophoretic characterization of purified bovine, porcine, murine, rat, and human uterine estrogen receptors

The calf uterine estrogen receptor (E2R) in the presence of sodium molybdate has been purified, 7,000-fold by a single passage over an estradiol affinity column. A dominant 70,000-dalton band and two minor bands at 50,000 and 30,000 daltons were observed by electrophoretic analysis. These bands had been eluted using estradiol, sodium sulfocyanate, CHAPS, and HEPES (pH 7.4) with insulin as a carrier protein. The identities of the protein bands were initially confirmed by their failure to bind the affinity column when saturated with estradiol. This single step purification procedure was reproducible and rapid, with yields of 10-20%, providing 25% purity. Diffusion blot analysis, with specific 35S- and 125I-labeled monoclonal antibodies to E2R, confirmed that the 70,000-dalton band represented the estrogen receptor. Specificity was demonstrated by inhibition of binding of purified E2R by both estradiol and diethylstilbestrol but not testosterone, progesterone, corticosterone, aldosterone, or hydrocortisone. The relative binding affinity of the purified receptor was: ethynyl estradiol greater than 17 beta estradiol greater than estriol greater than or equal to estrone greater than or equal to 17 alpha-estradiol greater than mestranol. Pig, human, mouse, and rat uterine estrogen receptors were similarly purified with the affinity column. As with the calf uterine preparations, a dominant 70,000-dalton band with minor bands at 50,000 and 30,000 daltons was identified by diffusion blot analysis in all the species examined.     

Synthesis and biological properties of 7alpha-cyano derivatives of the (17alpha,20E/Z)-[125I]iodovinyl- and 16alpha-[125I]iodo-estradiols

The synthesis, receptor binding affinity, estrogenic potency and tissue distribution of the 7alpha-cyano derivatives of the (17alpha,20E/Z)-[125I]iodovinyl-(CIVE) and 16alpha-[125I]iodo-estradiols (CIE) are reported. The iodovinyl derivatives were prepared via the (17alpha,20E/Z)-tri-n-butylstannyl intermediates, derived from the addition of tri-n-butyl tin hydride to the 17alpha-ethynyl group of the 7alpha-cyano-17alpha-ethynylestradiol, using triethylborane as a catalyst. The no-carrier-added [125I]-CIVE isomers were prepared via the same stereospecific reaction. [125I]-CIE was prepared from 7alpha-cyano-16beta-bromoestradiol via halogen exchange with Na125I. Addition of the 7alpha-cyano group to 16alpha-iodoestradiol did not affect estrogen receptor binding affinity (RBA of CIE is 115). However the estrogenic potential of CIE, as measured by the capacity to stimulate the expression of the pS2 gene, was reduced to 1% as compared to that of estradiol. Addition of a 7alpha-cyano group to the (17alpha,20E/Z)-IVE isomers reduced the RBA to 21 and 36, respectively, while the estrogenic potential was reduced to 2-3% of that of estradiol. Uterus uptake in immature rats of the 125I-labeled CIVE 20E-isomer and the 16alpha-iodo CIE peaked at 0.5h post injection while the (17alpha,20Z)-CIVE isomer showed a maximum only past 5h post injection. Uptake of all three 125I-labeled 7alpha-cyanoestrogens was suppressed by the co-injection of non-radioactive estradiol confirming the role of estrogen receptors in the localization process. Uterus retention pattern differ substantially from those of the analogues 7alpha-methylestrogens, which were previously shown to give high maximum 125I-uptake values at 2h post injection. Overall our data indicate that addition of a 7alpha-cyano group to 123I-labeled estrogens does not improve their potential to serve as SPECT agents for the imaging of estrogen receptor densities in breast cancer.     

The use of the biotinyl estradiol-avidin system for the purification of "nontransformed" estrogen receptor by biohormonal affinity chromatography

Several biotinyl estradiol derivatives have been prepared by coupling estradiol 7 alpha-carboxylic acid to biotin via different linear linkers. All these compounds exhibit a high affinity for the estrogen receptor as determined by competitive binding assays against [3H]estradiol. These compounds also displaced the dye 4-hydroxyazobenzene-2'-carboxylic acid from the biotin-binding sites of avidin free or immobilized on agarose. It was demonstrated that only the derivatives bearing a long spacer chain (greater than 42 A greater than) between estradiol and biotin were able to bind receptor and avidin simultaneously, suggesting some steric hindrance. The biotin-avidin system has been investigated for the purification of the cytosoluble "nontransformed" estrogen receptor stabilized by sodium molybdate. The method relies on: 1) high biohormonal affinity of receptor for biotinyl estradiol derivative; 2) the specific selection by avidin-agarose column of biotinyl estradiol-receptor complexes; and 3) the biohormonal elution step by an excess of radioactive estradiol. Starting from unfractionated cytosol containing molybdate-stabilized nontransformed 8S estrogen receptor with estradiol 7 alpha-(CH2)10-CO-NH-(CH2)2-O-(CH2)2-O-(CH2)2-NH-CO-(CH2)3-NH-biotin, preliminary experiments using avidin-agarose chromatography and then a specific elution step by exchange with free [3H]estradiol, allowed a 500-1,500-fold purification. Further purification of estrogen receptor was obtained by ion exchange chromatography through a DEAE-Sephacel column and led to a congruent to 20% pure protein, assuming one binding site/65,000-Da unit. The hydrodynamic parameters of the purified receptor were essentially identical to those of molybdate-stabilized nontransformed receptor present in crude cytosol. The advantages of this double biotinyl steroid derivative-avidin chromatographic technique over more conventional affinity procedures are discussed and make it applicable to the purification of minute amounts of steroid receptors in a wide variety of tissues.     

Triphenylethylene antiestrogen binding sites (TABS) specificity

The relative binding affinities (RBA) of various compounds for the triphenylethylene antiestrogen binding sites (TABS) were examined. The ability of tamoxifen to inhibit the binding of [3H]tamoxifen to salt extracted (0.4 M KCl) TABS from rat liver nuclei was used as a standard by which other compounds were compared (tamoxifen RBA, 100; Kd approximately 1 nM). Nafoxidine was the most effective triphenylethylene compound used (RBA 333; Kd approximately 0.3 nM) whereas the RBA of zuclomiphene and enclomiphene was not different from tamoxifen. MER-29 was the weakest inhibitor of the triphenylethylene derivatives (RBA 10; Kd approximately 10 nM). Trifluoperazine, chlorpromazine and the anti-calmodulin drugs W-13 and W-12 had RBA's of 25, 1, 1 and 0.1 respectively. The binding affinities of cholesterol and 7-ketocholesterol were significant (Kd approximately 22 nM) while the steroid hormones, estradiol, testosterone, progesterone and corticosterone displayed not observable affinity. Various compounds obtained from Merrill Dow Pharmaceuticals and the Eli Lilly Company which contained alklaminoethoxy side chains linked to aromatic ring structures had RBA's ranging from 1-0.3. We conclude, as other investigators have also concluded, that the similar binding affinities of various triphenylethylene antiestrogens for TABS and their divergent activities as antiestrogens makes it unlikely that TABS are directly involved in estrogen antagonism. The moderate but significant affinity of TABS for trifluoperazine and other drugs thought to be involved in calmodulin regulation indicates that TABS may be a linked in some way to calmodulin function. The binding of cholesterol and 7-ketocholesterol is also significant and may indicate that TABS are involved in cholesterol metabolism.     

Evaluation of 17alpha-E-(trifluoromethylphenyl)vinyl estradiols as novel estrogen receptor ligands

As part of our program to develop novel ligands for the estrogen receptor, we synthesized the series of isomeric 17alpha-(trifluoromethyl)phenylvinyl estradiols using our solid-phase organic synthesis methodology. The compounds were evaluated for their relative binding affinity (RBA) using the ERalpha-LBD and in vivo potency using the immature rat uterotrophic growth assay. The ortho-isomer had the highest RBA values, 48-223, and the highest estrogenicity in vivo. The other isomers had significantly lower affinities and were weaker agonists in the uterotrophic assay. The results suggest that introduction of substituents at the 17alpha-position of estradiol is tolerated by the ER-LBD and permit agonist responses in the intact animal, however, the effect is sensitive to the position of groups on the phenyl ring. This study demonstrates that the 17alpha-position of estradiol is a reasonable site for modification but the position and physicochemical properties of such modifications may significantly affect the affinity and efficacy of the ligand.     

Hepatic stellate cells contain the functional estrogen receptor beta but not the estrogen receptor alpha in male and female rats

In an earlier study, we showed that estradiol (E2) inhibits proliferation and transformation in cultured rat hepatic stellate cells (HSCs) and that the actions of E2 are mediated through estrogen receptors (ERs). This study reports on an investigation of the cellular localization of ER subtypes ERalpha and ERbeta using immunohistochemistry in experimental fibrotic liver rats and of each ER subtype expression in cultured rat HSCs by evaluating the produced mRNA and protein. The results indicate that high levels of ERbeta expression and low or no levels of ERalpha expression were observed in normal and fibrotic livers and in quiescent and activated HSCs from both males and females. The specificity of E2-mediated antiapoptotic induction through the ERbeta was shown by dose-dependent inhibition by the pure ER antagonist ICI 182,780 in HSCs which were undergoing early apoptosis. These findings demonstrate for the first time that rat HSCs possess functional Erbeta, but not Eralpha, to respond directly to E2 exposure.