RBA Values Research Articles

Estrogen receptor binding characteristics of 1,11β-ethanoestradiol: Effect of a 1,11β-bridge on steroidal estrogen

As part of an ongoing program to develop high affinity estrogenic ligands we have synthesized the 11β-vinyl, 11β-ethyl- and 1,11β-ethanoestradiols. Because the 1,11β-ethanoestradiol had not been previously reported in the literature, the investigation of its receptor binding characteristics would provide valuable insight into the effect of 1/11β-substitution. The data obtained in this study indicate that although significant estrogen receptor affinity is present for the 1,11β-ethano derivative, the RBA values, 5–22.4%, were far less than those observed (5–300-fold less) for the corresponding 11β-ethyl and 11β-vinyl estradiols and less than those for the 1-methyl and 11β-methyl estradiols. These results suggest that the orientation that the 11β-substituent must occupy is directed away from the A-ring and that substituents in the 1–11 pocket produce a detrimental effect on receptor interactions.

ChemInform Abstract: Indolo(2,1‐a)isoquinolines. Syntheses, Steroid Hormone Receptor Binding Affinities, and Cytostatic Activity.

AbstractSubstituted phenylalkylamines such as (I) are coupled with bromophenylacetates, e.g. (II), to form the corresponding amides, e.g. (III).

Indolo[2,1-a]isoquinolines. Syntheses, steroid hormone receptor binding affinities, and cytostatic activity

A number of acetoxy-substituted 5,6-dihydroindolo[2,1-a]isoquinolines were synthesized and tested for binding affinity for steroid hormone receptors. All of the derivatives bind to the estrogen receptor with RBA values ranging from 1.5 to 17 (17 beta-estradiol = 100). Some of them show binding affinities for the androgen receptor as well. In the mouse uterine weight test, the tetracycles proved to be weak estrogens with partial antagonistic activity. All of the compounds were tested in vitro for cytostatic activity with hormone-independent MDA-MB 231 and hormone-dependent MCF-7 breast cancer cells. A cytostatic effect was found in both cell lines. The comparison of results exhibited a stronger inhibitory effect on MCF-7 cells only for compounds with high binding affinity for the estrogen receptor. For those derivatives, it can be assumed that the growth inhibition is partly mediated by the estrogen receptor.

Gestodene: A novel synthetic progestin — characterization of binding to receptor and serum proteins

Gestodene, 17α-ethinyl-13-ethyl-17β-hydroxy-4,15-gonadien-3-one, is a new orally active progestational agent, which is available for clinical use in oral contraceptives. The aim of the present study is to make a broad characterization of gestodene at the receptor level and to discuss the results in comparison to those of established progestogens. Kinetic studies of H-gestodene uptake show a rapid increase in the amount of specific binding during the first three hours. After saturation, the amount of specifically bound 3H-gestodege remained almost constant up to 24 hours at 4°C. The dissociation of 3H-gestodene from the cytoplasmic myometrial progesterone receptor, measured by displacement of labeled steroid with dextran-coated charcoal treatment at 4°C at various times, showed a biphasic or two-component first order dissociation curve. As anticipated, sucrose gradient centrifugation analysis of the 3H-gestodene-labeled cytosol of human myometrial tissue showed that the gestodene binding components sedimented in the 4S and 8S region. A 200-fold molar excess of nonradioactive gestodene reduced only the 8S binding of 3H-gestodene. 4S binding of 3H-gestodene was not reduced, which indicate the existence of a second high capacity binding component. In biological test systems, such as the Clauberg test or Kaufmann test, gestodene has proved to be a very effective progestogen. Among nortestosterone derivatives it is one of the most potent and resembles progesterone biologically in its progestogenic effects. This biologically identical gestagenic activity of gestodene and progesterone is reflected by a very similar behavior in vitro in terms of binding to progesterone receptors of human uterus cytosol. Furthermore, competitive studies indicated that gestodene like other synthetic progestagens also displays some affinity for androgen and glucocorticoid receptors but no measurable affinity for the estrogen receptor. Remarkable is the high binding affinity of gestodene to the binding sites of the mineralocorticoid receptor of rat kidney with a RBA value of 350% compared to aldosterone. In contrast to progesterone, gestodene did not bind to CBG, but was bound with a relatively high affinity for SHBG, which is a typical behavior for all 19-nortestosterone derivatives.

Synthesis and biological activity of 17β -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 17β -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 receptor binding of polynuclear organometallic estradiol derivatives

Twelve novel organometallic derivatives of estradiol were synthesized with the aim of utilizing organometallic cold bioprobes as radioisotopic labels substitutes for steroid hormone receptor assays. For this purpose, we envisaged the attachment of several stable cobalt, molybdenum, osmium carbonyl clusters (tetra- and pentanuclear species) at estradiol 17α-, 16α-, 2- or 4- positions. The binding affinity of these new complexes for uterine estradiol receptor has been measured by the competitive binding method. The results show that the 17α- position can tolerate substitution by bulky organometallic groups (especially in the case of cobalt and molybdenum carbonyl clusters). Estradiol derivatives which are functionalized at C-4 and C-16α bind estradiol receptor with reasonable affinity and the RBA values are the same for the complexed and uncomplexed hormones. The 2-position is more sensitive to organometallic substitution and the complexation at the 2-alkyne results in a dramatic decrease of the RBA values. These results show that the attachment of polynuclear moieties in estradiol 17α-, 4- and 16α-, positions gives rise to compounds which are of potential utility in a new non-radioisotopic receptor assay since the metal-carbonyl markers are readily detected by high-sensitivity Fourier-transform infra-red spectroscopy.

2-Alkyl-substituted 1,1-bis(4-acetoxyphenyl)-2-phenylethenes. Estrogen receptor affinity, estrogenic and antiestrogenic properties, and mammary tumor inhibiting activity.

1,1-Bis(4-acetoxyphenyl)-2-phenylethenes that are substituted with H, CH3, C2H5, n-C3H7, i-C3H7, or CH2CF3 in position 2 were synthesized in order to study the influence of the alkyl side chain on estradiol receptor affinity, estrogenic and antiestrogenic properties, and inhibition of the hormone-dependent MXT mammary carcinoma of the mouse. Furthermore, the double bond of 1,1-bis(4-acetoxyphenyl)-2-phenylbut-1-ene was hydrogenated or epoxidated to yield the corresponding ethane and oxirane derivative. Compounds 14 (R = H), 15 (R = CH3), and 16 (R = C2H5) had the best binding affinities. Lengthening the side chain, hydrogenation, or epoxidation decreased the RBA values. In the immature mouse assay, 15 (R = CH3) and 19 (R = CH2CF3) had the highest uterotrophic activity. There was no correlation between receptor affinity and estrogenic properties. Compounds 14 (R = H), 17 (R = n-C3H7), the ethane 20, and the oxirane 21 had some antiuterotrophic activity in a low dosage. The MXT tumor was best inhibited by compounds 15 (R = CH3), 16 (R = C2H5), and 18 (R = i-C3H7) without significant elevation of the uterine weight determined at the end of the experiment. The antitumor effect of 15, 16, and 18 was significantly better than that of tamoxifen. In this series, a certain estrogenic potency in the immature mouse test seems to be necessary for a good antitumor activity, as all compounds with antiuterotrophic and low uterotrophic properties did not exert any significant tumor-inhibiting effect.

ChemInform Abstract: Hydroxy Derivatives of Tamoxifen.

AbstractVerbindungen wie (IV) und (V) werden synthetisiert und mit Tamoxifen (VI) verglichen.

Hydroxy derivatives of tamoxifen

In the exploration of the structural features that affect the RBA (binding affinity for the estrogen receptor of rat uterus relative to that of estradiol) in the tamoxifen [trans-(Z)-1-[4-[2-(dimethylamino)ethoxy]phenyl ]-1,2-diphenyl-1-butene] series, several derivatives variously substituted in the 1-phenyl group have been synthesized. [In the tamoxifen series, the descriptors E and Z, which define the configuration of the geometrical isomers and depend on the location and nature of substituents in the aromatic moieties and the ethyl group, may vary, although the relative configuration (cis or trans) does not. In order to avoid confusion the terms cis and trans will be used in this paper to refer to the relative positions of the 4-[2-(dimethylamino)ethoxy]phenyl and ethyl (or hydroxyethyl, hydroxypropyl, or bromo) substituents attached to the ethene moiety.] The final stage of each synthesis involved acid-catalyzed dehydration of a tertiary alcohol, and, in contrast to the known 3- and 4-hydroxy derivatives which were obtained as near-equimolar cis,trans mixtures, only the trans forms of the 2-hydroxy, 2-methyl, 2,4-dihydroxy, and 4-hydroxy-2-methyl derivatives were obtained. Also, in contrast to the trans forms of the 3- and 4-hydroxy derivatives, which are readily equilibrated to cis,trans mixtures, the trans 2-hydroxy derivative could not be isomerized. Tamoxifen and 2-methyltamoxifen had similar RBA's (approximately 1% of that of E2), but that of 2-hydroxytamoxifen was much lower (0.1%). Introduction of a second hydroxyl group (2,4-dihydroxy derivative) enhanced the RBA, and for the 4-hydroxy-2-methyl derivative, the RBA and growth inhibitory activity against the MCF-7 mammary tumor cell line in vitro were high and comparable to those of 4-hydroxytamoxifen, a metabolite of the parent drug. Tamoxifen derivatives hydroxylated at positions 3 or 4 of the 1-butene moiety and the 5-hydroxy-1-pentene analogue were also synthesized, but they had very low RBA values.

Hydroxy-3-(hydroxyphenyl)indoles. Relationship between structure and estrogen receptor affinity.

AbstractSyntheses and estrogen receptor affinities of the 1,2‐dialkyl(hydroxy)‐3‐(hydroxyphenyl)indoles 11b–19b are described. Derivatives 15b, 16b with a hydroxy group at position 6 of the indole and an ethyl group at C‐2 show a strong binding affinity with an RBA value of 0.72 (estradiol = 100).

Effect of N,N'-diethyl-1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamines on the DMBA-induced mammary carcinoma of the rat

The syntheses and estrogen receptor affinities of meso- and (+/-)-N,N'-dialkyl-1,2-bis(2,6-dichloro-4-hydroxypheny)ethylenediamines (2) are described. They show high binding affinities in both diastereomeric forms but with a preference for the meso isomer, reaching a RBA value of 8.6 (meso-2b; 17 beta-estradiol = 100). Both stereoisomers of 2b exhibit a strong inhibitory effect on the 7,12-dimethylbenz[alpha]anthracene (DMBA) induced hormone-dependent mammary carcinoma of the Sprague-Dawley rat, reducing the tumor area by 74 (meso-2b) and 24% [(+/-)-2b], respectively, after 4 weeks administration of 6 x 6 (mg/kg)/week. The high uterotrophic potency makes a mode of action likely which corresponds to the effect of high doses of estrogens.