Estrogen-receptor interaction.

The interaction of estradiol with uterine cells involves the association of the hormone with an extranuclear receptor protein, followed by temperature dependent translocation of the resulting complex to the nucleus. During this process, the steroid binding unit of the protein undergoes an alteration, called "receptor transformation," that can be recognized by an increase in its sedimentation rate from 3.8S to 5.2S, and by its acquisition of the ability to bind to isolated uterine nuclei and to alleviate a tissue specific deficiency in the RNA synthesizing capacity of such nuclei. Receptor transformation can be effected in the absence of nuclei by warming uterine cytosol with estradiol. This preparation of transformed complex resembles that extracted from nuclei both in its sedimentation rate (5.3S) and in its ability to bind to uterine nuclei and augment RNA synthesis, properties that are not shown by the native complex. It is proposed that receptor transformation is an important step in estrogen action and that a principal role of the hormone is to induce conversion of the receptor protein to a biochemically functional form.

Sulfhydryl groups and estradiol-receptor interaction.

The characteristic ability of rat uteri to take up tritiated estradiol in vitro or to retain estradiol previously incorporated either in vivo or in vitro is destroyed by treating the tissue with various sulfhydryl-blocking reagents. The two radioactive estradiol-receptor complexes, observed in uterine homogenates in the supernatant fraction and in an extract of the nuclear fraction, respectively, are disrupted by brief exposure to organic mercurials in the cold. Sulfhydryl groups of uterine receptor substances apparently play a vital role in estradiol binding, perhaps indirectly through contribution to receptor conformation.

Estrogen receptors in hormone-dependent breast cancers.

The determination of estrogen receptor (estrophilin) in human breast cancers, both primary and metastatic, can furnish information useful to the clinician in his choice of the optimal therapy for the individual patient with advanced disease. Of patients with significant tumor estrophilin levels, most, but not all, will respond favorably to endocrine therapy. Women whose cancers lack sufficient amounts of estrophilin have little or no chance of benefit from endocrine ablation or hormone administration and probably should be treated directly by alternative types of therapy.

Partial antagonism between steroidal and nonsteroidal antiestrogens in human breast cancer cell lines.

Nonsteroidal antiestrogens, such as tamoxifen, are well established in the treatment of breast cancer. The development of new steroidal compounds without partial agonist activity allows deeper insights into the mechanism of antiestrogen action, but thus far, the combined use of steroidal and nonsteroidal antiestrogens has not been studied extensively. We compared the nonsteroidal 4-trans-hydroxytamoxifen (OHT) with the two steroidal antiestrogens, ICI 182780 and RU 58668, in the estrogen receptor-positive human breast cancer cell lines MCF-7 and T47D. The effect of each compound alone or of OHT in combination with one of the steroidal antiestrogens was studied in regard to cell proliferation, expression of estrogen receptors (ERs) and progesterone receptors, and secretion of transforming growth factor beta2 (TGF-beta2). All antiestrogens examined led to enhanced secretion of TGF-beta2, which is correlated with their individual growth-inhibitory potential. OHT partially counteracts the larger growth inhibition of human breast cancer cells exerted by the steroidal antiestrogens ICI 182780 and RU 58668. Also, OHT antagonizes the higher induction of TGF-beta2 seen after treatment of MCF-7 cells with steroidal antiestrogens. The loss of ER and down-regulation of progesterone receptor under treatment with the steroidal antiestrogens is prevented by OHT, whereas the steroidal antiestrogens prevent the ability of hydroxytamoxifen to increase the ER content. These results indicate that TGF-beta2 is a marker of action for both types of compounds, but steroidal and nonsteroidal antiestrogens partially antagonize each other in blocking ER-mediated cellular events. It would appear that no additive or synergistic effect of the two types of antiestrogens can be expected in the treatment of breast cancer.

Comparison of immunocytochemical and steroid-binding assays for estrogen receptor in human breast tumors.

An estrogen receptor immunocytochemical assay which uses monoclonal antibodies to the estrogen receptor protein [Nature (Lond.), 307: 745-747, 1984] was applied to several human tissues, including human breast tumors, and the results were compared to those of steroid-binding assays performed on cytosol extracts of the same tissues. Specific immunoperoxidase staining in fixed, frozen sections was confined to the nucleus of selected cell populations within each tissue examined. In 117 human breast cancers, the presence or absence of nuclear staining was significantly associated with the concentration of cytosolic estrogen receptor. Thirty-eight estrogen receptor immunocytochemical assay-positive tumors were further assessed for several quantifiable features of the staining, including intensity, cellularity, and the proportion of tumor cells stained. Of these, epithelial cellularity showed the highest degree of correlation with the results of steroid-binding assays.

Differences between estrogen- and antiestrogen-estrogen receptor complexes from human breast tumors identified with an antibody raised against the estrogen receptor.

Radiolabeled estrogens 17 beta-[3H]estradiol and diethylstilbestrol ( [3H]DES) and the antiestrogen [3H]monohydroxytamoxifen ( [3H]MHT) all bind with high affinity to the extranuclear estrogen receptor (ER) from the MCF-7 human breast tumor cell line (Kd = 3 X 10(-10), 2 X 10(-10), and 0.63 X 10(-10) M, respectively). A polyclonal antibody raised in a goat to the calf nuclear ER selectively decreased the binding affinity and number of binding sites for 17 beta-[3H]estradiol, but did not appear to affect these binding parameters for [3H]MHT. In the presence of goat antibody, the binding of the nonsteroidal estrogen DES was so perturbed that it was not possible to quantitate the decreased number of binding sites or affinity of this compound as assessed by Scatchard saturation analysis. These results were confirmed in human breast tumor cytosols by sucrose density gradient analysis. The binding of 17 beta-[3H]-estradiol and [3H]DES to the ER was significantly reduced by preincubation with the polyclonal antibody, whereas the binding of [3H]MHT was reduced only when the tumor cytosol was preincubated with a very high concentration of antibody. At these concentrations of antibody, the binding of 17 beta-[3H]estradiol and [3H]DES to the receptor was prevented completely. In contrast, when the antibody was added to the tumor cytosol after the 3H-ligand had bound to the receptor, the binding properties of all 3H-ligands were unaffected. The [3H]MHT-ER antibody complex consistently sedimented as a higher-molecular-weight complex on sucrose density gradients than did the corresponding estrogenic complexes. The decrease in the affinity of estrogenic ligands can be explained in part by an increase in the dissociation rate at 4 degrees of these compounds from the ER. The dissociation rate of MHT was unaffected by the goat antibody. These results imply that there are important differences in the binding of antiestrogen and estrogens to the tumor cytosol ER. A ligand-binding model is proposed that may aid in the understanding of antiestrogen action.

Immunocytochemical assay for estrogen receptor: relationship to outcome of therapy in patients with advanced breast cancer.

We have used an immunoperoxidase technique utilizing a monoclonal antibody to the estradiol receptor to identify immunoreactive estradiol receptor in breast carcinomas and have examined the relationship between the immunoreactive estradiol receptor and response to therapy in patients with advanced breast cancer. Fifty-six patients were found to be assessable for response to endocrine therapy. Twenty-two showed an objective response to some form of endocrine manipulation, and all these had positively stained carcinomas. None of the 17 patients with negatively stained carcinomas responded to endocrine therapy. We conclude that the monoclonal antibody to estradiol receptor can help identify breast cancer patients who may respond to endocrine therapy.

Clinical correlations of steroid receptors and male breast cancer.

Estrogen receptors (ER) were present in tumor specimens from 29 of 34 cases of male breast cancer. There was a significant negative correlation of ER concentration with age. The quantity of ER tended to correlate directly with progesterone receptor levels, disease-free interval, and response duration among responders, but not to a statistically significant extent. In 13 patients for whom response data were available, no significant correlation was observed between ER levels and either frequency or duration of orchiectomy response. Among the six patients with tumor ER levels of less than 30 fmol per mg of protein, however, only two brief responses to orchiectomy occurred that were of little clinical benefit, while three of seven patients with higher ER responded more favorably. Thus, although this suggests that a relationship between low ER and unfavorable orchiectomy response may emerge as more patients are studied, currently available data do not justify basing therapeutic intervention on ER status of a biopsy in a manner analogous to that used for female breast cancer. Nine of 14 male breast cancer patients had positive progesterone receptor assays and several had androgen or glucocorticoid receptors. Tissue from only three of ten men with gynecomastia had measurable ER, and these were limited to the 4S component on sucrose gradients.

Effect of antibodies to estrogen receptor on the binding of 3H-labeled antiestrogens and androstanediol in the uterus.

We report here the effects of antibodies to estrogen receptor (ER) on the binding of tritiated 5 alpha-androstane-3 beta-17 beta-diol and antiestrogens to receptor in calf uterine cytosol. The antibodies, prepared from a rabbit immunized with purified estradiol-receptor complex from calf uterine nuclei, were found to decrease the affinity, but not the number of binding sites, of ER for 5 alpha-androstanediol and tamoxifen [alpha-(4 beta-N-dimethylaminoethoxy)phenyl-alpha'-ethyl-trans-stilbene]. This appeared to be due to the decrease in the association rate of the ligands, while the dissociation rate was not modified. The ER antibodies did not affect the binding of ER to estradiol or to the monohydroxylated metabolite of tamoxifen, nor did they affect the interaction of androgens with the androgen receptor. The formation of a ternary complex among [3H]hydroxytamoxifen [3H-labeled alph-(4 beta-N-dimethylaminoethoxy)phenyl-4-hydroxy-alpha'-ethyl-trans-stilbene], the ER, and the antibodies was demonstrated by sucrose gradient ultracentrifugation. For [3H]tamoxifen and [3H]5 alpha-androstanediol, ternary complexes were also formed with ER bound to monoclonal antibodies linked to Sepharose. These results confirm that ER directly binds androstanediol, tamoxifen, and hydroxytamoxifen. The lower affinity of ligands for ER in the presence of antibodies was only observed for the low affinity ligands and did not appear to be correlated to their antiestrogenic activities.

Estrogen receptors in human prostate: evidence for multiple binding sites.

The existence of estrogen receptors in the human prostate has long been a controversial issue. This may be explained partly by the apparent heterogeneity of estrogen-binding sites in prostatic tissue. We herein report on multiple binding sites for estrogens in cytosol as well as nuclear preparations of human prostatic tissues. One class of binding sites corresponds to the classical, high affinity estrogen receptor; the Kd for [3H]estradiol binding to the receptor was approximately 0.10 nM and the binding was specific for estrogens. The second class of binding sites appeared to have a Kd for [3H]estradiol in the range of 5-10 nM. This second, lower affinity class of binding sites markedly influenced studies of the classical receptor even at low ligand concentrations. Saturation analysis should be performed over a wide range of ligand concentrations (0.05-10 nM) to allow separation of the two binding components. Quantitation of estrogen receptor by a single point assay cannot be carried out accurately unless the low affinity binding component can be blocked. Multiple binding sites for estradiol were observed in the cytosol as well as in the nuclear salt extractable and salt-resistant compartments of normal, benign hyperplastic, and cancerous human prostates. Normal peripheral and cancerous prostates contained significantly (P less than 0.01) higher amounts of cytosol estrogen receptor compared to benign hyperplastic tissue.

Calculating specific binding for prolactin receptor assays.

Specific binding of [125I]iodo-prolactin and receptor is usually calculated by subtracting the amount of bound radioactivity of assays containing excess unlabeled hormone (competed) from that of noncompeted assays. A proportional method to calculate specific binding of prolactin-receptor or other hormone-receptor interactions is introduced as a replacement for the currently used subtraction method. The proportional method calculates specific binding by multiplying the ratio of free radioactivities of noncompeted and competed assays by the radioactivity retained in the competed assay and subtracting this value from the radioactivity retained by the noncompeted assay. In prolactin-receptor assays greater specific binding is seen when data is calculated by this proportional method rather than the subtraction method. The amount of this increase relates directly to the levels of specific and nonspecific binding. Additionally, the binding characteristics of prolactin and receptor in both equilibrium and kinetic studies are significantly different when specific binding is calculated by the proportional method rather than the subtraction method.

Steroid hormones, receptors, and antagonists.

In the thirty-odd years since the first demonstration of estrogen-binding components in reproductive tissues, much has been learned about the molecular details of steroid hormone action. Facts still to be elucidated include the precise mechanism by which interaction with the steroid disrupts the native receptor complex to generate an active transcription factor, just how this activated receptor enhances expression of target genes, and the role of phosphorylation in these events. The concept of receptor-medicated steroid hormone action has provided useful methods for predicting the risk of metastatic recurrence of breast cancers and the response of disseminated disease to endocrine therapy. Application of immunochemical techniques for receptor assay and elucidation of the role of mutant receptors in hormone resistance promise to increase the utility of these diagnostic procedures. A better understanding of the molecular details of steroid hormone antagonism should be helpful in the search for new and more effective agents for the endocrine control of breast cancers.

A new interpretation of antiestrogen action.

Despite differences in their pharmacological behavior, type I and type II antiestrogens have certain important properties in common. Both differ from estradiol in that they enhance the immunoreactivity of estrogen receptors, apparently by inducing conformational change that exposes an additional epitope for a particular monoclonal antibody. Moreover, both types of antihormones not only compete with estradiol for its binding to the receptor but they also react with another domain not recognized by the hormone. The binding capacity for either type of antiestrogen is nearly twice that for estradiol, providing definitive evidence for the existence of specific antiestrogen-binding sites that are postulated to be important in antagonist action. These findings suggest a unified two-site model which helps explain how the same substance can be both an agonist and an antagonist; why there may be species variations in the agonist/antagonist relationship of type I compounds; and why type II agents show only antagonistic properties. It is suggested that interaction with secondary, antagonist-specific binding sites may provide a useful screen in the search for new and improved antihormonal agents.

Synthesis of fluorinated 3beta-hydroxypregn-5-en-20-one derivatives.

Treatment of the unstable 3beta-hydroxy-20, 20-dimethoxypregn-5-ene 3-acetate with acetic anhydride at reflux temperature gave a mixture of 3beta-hydroxy-20-methoxypregna-5, 17(20)-diene and 3beta-hydroxy-20-methoxypregna-5, 20-diene 3-acetates. Fluorination of this mixture with perchloryl fluoride afforded after fractionated crystallization 3beta-hydroxy-17-fluoro-20-methoxypregna-5, 20-diene 3-acetate. Acid hydrolysis of the reaction mixture and subsequent chromatographic separation led to 3beta-hydroxy-17-fluoropregn-5-en-20-one 3-acetate and 3beta-hydroxy-21-fluoropregn-5-en-20-one 3-acetate. 3beta-Hydroxy-17-fluoro-20-methoxy-pregna-5, 20-diene 3-acetate did not react further with perchloryl fluoride even under forcing conditions. Fluorination of 3beta-hydroxy-20-(N-ethyl benzylamino)-pregna-5, 17(20)-diene gave 3beta-hydroxy-17, 21-difluoro-pregn-5-en-20-one, exclusively.

The immunoendocrinology of estrophilin.

Immunoglobulin from the serum of rabbits immunized with highly purified estradiol-receptor complex from calf uterine nuclei has been shown to contain specific antibodies to estrophilin by five criteria. Antibodies to calf nuclear estrophilin cross react with nuclear estradiol-receptor complexes of rat, rabbit and sheep uterus, rat endometrial and pituitary tumor, and MCF-7 human breast cancer cell line. They also react with extranuclear receptor of calf, rat, mouse, rabbit, guinea pig, monkey and sheep uterus, rat mammary, endometrial and pituitary tumor, and human breast cancer. There is no interaction of the antibody with estradiol itself. The nuclear form of estrophilin appears to bind more immunoglobulin molecules than does the cytosol form. The antibodies do not react with either the nuclear or extranuclear dihydrotestosterone-receptor complexes of rat prostate, with the extranuclear progesterone-receptor complexes of rabbit uterus, chick oviduct or rat endometrial tumor, or with rat and mouse alpha-fetoprotein. These findings indicate an immunochemical similarity among estrophilins from several mammalian species, as well as between nuclear and extranuclear forms of the receptor, but not among receptor proteins for different steroid hormones. Immunoglobulin from the serum of a goat immunized with similar antigen shows a considerably higher titer of antibodies to estrophilin. These react with nuclear and extranuclear estradiol-receptor complexes of calf uterus to produce somewhat larger entities than those formed with the rabbit antibody. Unlike the rabbit antibody, interaction with the goat antibody causes a noticeable decrease in estradiol-binding affinity of the extranuclear estrophilin as well as an apparent decrease in the total hormone-binding capacity. Specific antibodies to estrophilin offer promise as valuable reagents for receptor analysis and purification, as well as for the elucidation of many still unresolved questions concerning receptor synthesis, localization and function.