Estradiol Ring Research Articles

Advances in contraception: vaginal contraceptive rings.

The vaginal contraceptive ring is very effective and user dependent. In this article, we will discuss the different types of vaginal contraceptive rings, namely, the etonogestrel/ethinyl estradiol (ENG/EE) ring (NuvaRing, Merck, Rahway, NJ, USA) and the segesterone acetate (SA)/EE (Annovera, Mayne Pharma, Raleigh, NC, USA) ring. The details of dosing and administration, indications, advantages, disadvantages, and cost-effectiveness are presented. This literature review was conducted using PubMed and Google Scholar. The search terms included 'vaginal contraceptive ring', 'etonogestrel/ethinyl estradiol ring', and 'segesterone acetate/ethinyl estradiol ring'. The search was then sorted by year from 2000 until present, and the most recent articles were reviewed. The purpose of this article is to provide a comprehensive reference on the two vaginal contraceptive rings widely used in the United States for clinicians to guide management. Both vaginal contraceptive rings are combination of hormonal contraceptives that suppress ovulation and create physiologic conditions unfavorable for pregnancy. The ENG/EE ring is designed to be replaced monthly, while the SA/EE ring is a single device used over the course of 1 year. Common side effects of both devices include headaches, nausea, vomiting, and vaginitis. Serious adverse reactions can occur with the vaginal contraceptive rings including venous thromboembolism, psychiatric events, and hypersensitivity. Both devices are contraindicated in patients at high risk for arterial or venous thrombotic events, patients with a history of breast cancer or other estrogen/progesterone cancers, and patients with severe liver disease. Overall, the vaginal contraceptive ring is well tolerated and liked by patients. Patients should be well counseled on known severe adverse reactions. The vaginal contraceptive ring is more expensive than other forms of contraception and this should be an important point of discussion with patients.

Financial Burden of Recurrent Urinary Tract Infections in Women: A Time-driven Activity-based Cost Analysis

To utilize Time-Driven Activity-Based Costing to quantify costs of managing recurrent urinary tract infections (RUTI) in women. RUTI was defined as ≥2 UTIs in 6 months or ≥3 UTIs in 12 months. A care-delivery value chain outlined RUTI management (visits, urine studies, and imaging) for acute UTI followed by a form of long-term prevention. Prevention strategies included conservative therapy (Cranberry tablets, d-mannose, or lactobacillus); Estrogen therapy if postmenopausal; Antibiotic use (self-start, postcoital, or continuous regimens); or intravenous antibiotics in case of drug-resistance or intolerance. Costs of each resource were largely obtained from the Medicare Physician Fee Schedule, GoodRx and local pharmacy pricing, and institutional expenses. The capacity cost rate was defined as cost of resources per minute of care. Individual costs were summed to estimate overall expense of initial RUTI workup and annual cost for each long-term prevention strategy. Cost of acute RUTI workup ranged from $390 to $730. Acute antibiotics cost ranged from $10 for oral trimethoprim-sulfamethoxazole to $3970 for intravenous Ertapenem. Annually, mean cost of conservative therapy ranged from $50 for d-mannose to $1290 for vaginal estradiol ring, and antibiotic use for self-start $40, postcoital $60, and continuous $190. Capacity cost rate ranged from $0.003/min for urine culture to $80/min for estrogen ring. Using Time-Driven Activity-Based Costing, costs of RUTI management were efficiently determined. This offers new perspectives for patient counseling and long-term decision making.

Exploring the molecular basis of action of ring D aromatic steroidal antiestrogens.

Salpichrolides are natural plant steroids that contain an unusual six-membered aromatic ring D. We recently reported that some of these compounds, and certain analogs with a simplified side chain, exhibited antagonist effects toward the human estrogen receptor (ER), a nuclear receptor whose endogenous ligand has an aromatic A ring (estradiol). Drugs acting through the inhibition or modulation of ERs are frequently used as a hormonal therapy for ER(+) breast cancer. Previous results suggested that the aromatic D ring was a key structural motif for the observed activity; thus, this modified steroid nucleus may provide a new scaffold for the design of novel antiestrogens. Using molecular dynamics (MD) simulation we have modeled the binding mode of the natural salpichrolide A and a synthetic analog with an aromatic D ring within the ERα. These results taken together with the calculated energetic contributions associated to the different ligand-binding modes are consistent with a preferred inverted orientation of the steroids in the ligand-binding pocket with the aromatic ring D occupying a position similar to that observed for the A ring of estradiol. Major changes in both dynamical behavior and global positioning of H11 caused by the loss of the ligand-His524 interaction might explain, at least in part, the molecular basis of the antagonism exhibited by these compounds. Using steered MD we also found a putative unbinding pathway for the steroidal ligands through a cavity formed by residues in H3, H7, and H11, which requires only minor changes in the overall receptor conformation.

Specificity Determinants of CYP1B1 Estradiol Hydroxylation

Cytochrome P450 (P450)-catalyzed oxidation of the aromatic ring of estradiol can result in 2- or 4-hydroxylation. Which of these products is formed is biologically important, as the 4-hydroxylated metabolite is carcinogenic, whereas the 2-hydroxylated metabolite is not. Most human P450 enzymes, including CYP1A1 and CYP1A2, exhibit a high preference for estradiol 2-hydroxylation, but human CYP1B1 greatly favors 4-hydroxylation. Here we show that heterologous expression of the human, monkey, dog, rat, and mouse CYP1B1 enzymes yields active proteins that differ in their estradiol hydroxylation specificity. The monkey and dog orthologs, like the human enzyme, preferentially catalyze 4-hydroxylation, but the rat and mouse enzymes favor 2-hydroxylation. Analysis of the CYP1B1 sequences in light of these findings suggested that one residue, Val395 in human CYP1B1, could account for the differential hydroxylation specificities. In fact, mutation of this valine in human CYP1B1 to the leucine present in the rat enzyme produces a human enzyme that has the 2-hydroxylation specificity of the rat enzyme. The converse is true when the leucine in the rat enzyme is mutated to the human valine. The role of CYP1B1 in estradiol carcinogenicity thus depends on the identity of this single amino acid residue.

A Randomized Clinical Trial of the Impact of Local Estrogen on Postoperative Tissue Quality After Vaginal Reconstructive Surgery

To evaluate the use and effect of early administration of vaginal estrogen via a continuous low-dose estradiol vaginal ring placed immediately after pelvic reconstructive surgery. This was a randomized controlled trial of 65 postmenopausal women undergoing vaginal reconstructive surgery. The subjects were randomly assigned to receive an estradiol-releasing vaginal ring, placebo vaginal ring, or control without vaginal ring for 12 weeks immediately after vaginal reconstructive surgery. The primary outcome was tissue quality based on vaginal maturation 3 months postoperatively. Secondary outcome measures were subjective and objective signs of atrophy; vaginal pH; the presence of granulation tissue, microscopic inflammation, and major healing abnormalities; and the ability to tolerate an intravaginal ring. At 12 weeks, the estradiol ring group had a significantly improved maturation value (P<0.01) and objective atrophy assessment (P<0.01) compared with the placebo ring and control arms. Granulation tissue was increased in the placebo ring arm (P<0.01). Subjective atrophy scores did not differ among the groups (P=0.39). Early administration of vaginal estrogen after vaginal surgery via an estradiol-releasing ring is feasible and results in improved markers of tissue quality postoperatively compared to placebo and controls.

Management of vulvovaginal atrophy-related sexual dysfunction in postmenopausal women

Menopause and its transition represent significant risk factors for the development of vulvovaginal atrophy-related sexual dysfunction. The objective of this study was to review the hormonal and nonhormonal therapies available for postmenopausal women with vulvovaginal atrophy-related sexual dysfunction, focusing on practical recommendations through a literature review of the most relevant publications in this field. This study is a literature review. Available vaginal estrogen preparations are conjugated equine estrogens, estradiol vaginal cream, a sustained-release intravaginal estradiol ring, or a low-dose estradiol tablet. Vaginal estrogen preparations with the lowest systemic absorption rate may be preferred in women with history of breast cancer and severe vaginal atrophy. Vaginal lubricants and moisturizers applied on a regular basis have an efficacy comparable with that of local estrogen therapy and should be offered to women wishing to avoid the use of vaginal estrogens. Oral, transdermal, or vaginal estrogen preparations are the most effective treatment options for vulvovaginal atrophy-related sexual dysfunction. Selective estrogen receptor modulators such as lasofoxifene and ospemifene showed a positive impact on vaginal tissue in postmenopausal women. Vaginal dehydroepiandrostenedione, vaginal testosterone, and tissue selective estrogen complexes are also emerging as promising new therapies; however, further studies are warranted to confirm their efficacy and safety.

Current Overview of the Management of Urogenital Atrophy in Women with Breast Cancer

Systemic treatments for women with breast cancer frequently induce urogenital symptoms that can negatively impact a women's quality of life. Urogenital atrophy is frequently undiagnosed and untreated, particularly in breast cancer survivors. Symptoms of urogenital atrophy can usually be relieved with vaginal estrogen preparations, but risk of recurrence and safety is undefined in women with a history of breast cancer. Treatment with nonhormonal modalities including vaginal moisturizers or lubricants and lifestyle modification are the first lines of management. Low-dose vaginal 17 β-estradiol (vaginal estradiol tablets 10 μg or vaginal estradiol ring) can be considered for the treatment of symptomatic urogenital atrophy in women with a history of breast cancer after appropriate disclosure to the patient. While effective in treating the urogenital symptoms, the safety of such therapy remains uncertain. The decision to offer vaginal estrogen therapy needs to be individualized and should be made jointly with the oncologist.

Synthesis and biological evaluation of 3,4,6-triaryl-2-pyranones as a potential new class of anti-breast cancer agents

A series of 3,4,6-triaryl-2-pyranones, new class of anti-breast cancer agents, have been synthesized as a structural variants of cyclic triphenylethylenes by replacing the fused benzene ring with pendant phenyl ring to mimic the phenolic A ring of estradiol. Nine of these newly synthesized pyranones exhibited significant anti-proliferative activity in both ER+ve and ER−ve breast cancer cell lines. Four active non-cytotoxic compounds 5c, 5d, 5g and 5h showed specific and selective cytotoxicity and two compounds 5d and 5h induced significant DNA fragmentation in both MCF-7 and MDA-MB-231 cell lines. Based on RBA studies, the molecules probably act in an ER-independent mechanism. The involved pathway was observed as caspase-dependant apoptosis in MCF-7 cells. However, the particular caspases involved and the possible cellular target through which this series of compounds mediate cell death are not known.

Not Too Frail for Love

Four older men have taught me an important lesson. Of course, over the years I have heard many jokes about impotence in old age and am familiar with data on age-related changes in sexual functioning. But there is nothing more powerful than the stories of your patients. Mr. F. was a feisty 87-year-old gentleman whom I looked after in the Veterans Affairs (VA) outpatient clinic during my geriatric fellowship. He had a thick Italian accent, thicker glasses, severe kyphosis, and one of those old-fashioned two-part hearing aids with the little amplifier in his front shirt pocket and a wire traveling up to the earpiece. He looked like a strong breeze could easily topple him. We had just finished a lengthy discussion of his numerous chronic conditions and medications, and I thought that we were done. But as I was getting up to leave the room Mr. F. said, “Hey Doc, I gotta problem. My wife won't ‘put out’ for me any more. What can I do?” I was so surprised by his question that I couldn't give him a good answer. I had had virtually no experience counseling older patients on this delicate but essential issue. A few years later I met Mr. B., a 78-year-old diabetic who exhibited all of the vascular complications known to man, including an above-the-knee amputation. He had been admitted to a VA nursing home to receive wound care for a severe leg ulcer, with the hope of avoiding a second amputation. I happened to meet him during a unique educational experience making rounds with trainees and faculty from programs in geriatrics and urology. Mr. B. sat proudly in his motorized wheelchair in the middle of the nursing home conference room while I questioned him about his urinary symptoms. I inquired as to why he had an indwelling bladder catheter, what type of urinary symptoms he was experiencing, and how he felt about having the catheter. At the end of the interview I asked Mr. B. if he had any questions about the catheter. In his booming voice, in front of all 30 of us, he said, “Yea Doc, will this thing affect my ‘Nature’?” Once again, although by now a bit more mature, I was surprised by his question and uncertain as to how to address it. Almost a decade later, I met Mr. J., the 91-year-old husband of a well-preserved 89-year-old woman with severe dementia to whom he had been married for almost as long as I had been on this earth. Mrs. J. was referred to me for the evaluation of urinary incontinence, and I felt that atrophic vaginitis was an important contributing factor to her symptoms. I had just placed an estradiol ring in her vagina when Mr. J. entered the room. I explained what I had done, and the purpose of the vaginal ring. Stooped over his walker, his severe Parkinson's disease obvious, he slowly looked up at me and asked, in his barely audible, hypophonic voice, “I'm not so sure about this doc.”“What do you mean?” I asked. “Will that thing interfere with our intercourse?” Quite embarrassed by not having thought about this ahead of time, I acknowledged his concern and asked that he contact me if the vaginal ring caused a problem. And just recently, Mr. W., an 82-year-old man with severe congestive heart failure and inoperable musculoskeletal conditions in his spine and legs, referred himself to my continence clinic. It took me and two nursing assistants just to get him from his wheelchair onto the examining table. After a careful history and physical examination, we spent a long time discussing the options for his symptoms of prostatic enlargement and an overactive bladder. As I started to get up, he said: “One final question, Doc: Do you know where I can get some really absorbent bed pads? I'm planning on getting remarried soon, and you know I certainly don't want the sheets getting wet with my new wife sleeping next to me.” I shook his hand, congratulated him, and gave him a brand new incontinence care product catalog and the Website for the National Association for Continence. Geriatricians continue to debate the definition of frailty. As I myself have learned over the years from these four older men, it seems that despite the odds, you can't be too frail for love.

Direct interaction between substrates and endogenous steroids in the active site may change the activity of cytochrome P450 3A4.

CYP3A4 exhibits unusual kinetic characteristics that result from the metabolism of multiple substrate including endogenous steroids and some drugs that coexist at the active site. To clarify the mechanism of the effect of endogenous steroids on the drug metabolism, the interaction between substrates, nevirapine (NVP) and carbamazepine (CBZ), and endogenous steroids was investigated by theoretical calculations. When the activities of NVP 2-hydroxylation and CBZ 10,11-epoxidation by expressed CYP3A4 were measured in the presence of steroids, NVP 2-hydroxylation was found to be remarkably increased by aldosterone and inhibited by estradiol. CBZ 10,11-epoxidation was increased by androstenedione. Three-dimensional computer modeling has shown that the active site of CYP3A4 is especially large, permitting access of two substrate molecules. The interactions between NVP and aldosterone and between CBZ and androstenedione were estimated by theoretical calculations assuming the substrate and steroids to be present in the active site at the same time. It was shown that NVP or CBZ would be stably fixed close to the oxygen atom at the sixth ligand of heme by interaction with steroids, suggesting that NVP and CBZ may be hydroxylated more easily due to the interaction with steroids. Estradiol was also expected to interact with NVP via a pi/pi interaction between a benzene ring, in which the NVP hydroxylation site is located, and a benzene ring of estradiol, suggested to inhibit the reaction. From these results, interactions between the substrate and endogenous steroids in the active site may change the activity of CYP3A4.

Molecular basis for the subtype discrimination of the estrogen receptor-beta-selective ligand, diarylpropionitrile.

Although the two subtypes of the human estrogen receptor (ER), ERalpha and ERbeta, share only 56% amino acid sequence identity in their ligand binding domain (LBD), the residues that surround the ligand are nearly identical; nevertheless, subtype-selective ligands are known. To understand the molecular basis by which diarylpropionitrile (DPN), an ERbeta-selective ligand, is able to discriminate between the two ERs, we examined its activity on ER mutants and chimeric constructs generated by DNA shuffling. The N-terminal region of the ERbeta LBD (through helix 6) appears to be fully responsible for the ERbeta selectivity of DPN. In fact, a single ERalpha point mutation (L384M) was largely sufficient to switch the DPN response of this ER to that of the ERbeta type, but residues in helix 3 are also important in achieving the full ERbeta selectivity of DPN. Using molecular modeling, we found an energetically favorable fit for the S-DPN enantiomer in ERbeta, in which the proximal phenol mimics the A ring of estradiol, and the nitrile engages in stabilizing interactions with residues in the ligand-binding pocket of ERbeta. Our findings highlight that a limited number of critical interactions of DPN with the ERbeta ligand-binding pocket underlie its ER subtype-selective character.

Vaginal estrogen preparations: a review of safety and efficacy for vaginal atrophy.

A theoretical advantage of local (i.e., vaginal) therapy of genitourinary symptoms could be avoidance of systemic adverse effects. Review of efficacy and adverse effects of commonly prescribed vaginal estrogens is of great clinical relevance. A Medline (1966-present) search was performed for randomized controlled trials involving vaginal estrogens. Reference lists of papers were reviewed for additional references. Twenty-two references were randomized controlled trials of vaginal estrogens used by postmenopausal women with signs or symptoms of vaginal atrophy. Subject numbers ranged from 20 to 251. Duration ranged from 2 weeks to 1 year. Different preparations and schedules were used across the trials. All treatments alleviated signs and symptoms of atrophic vaginitis, regardless of whether objective signs of atrophy were required for study entry. Data for urinary symptoms was conflicting; the ring may prevent recurrent urinary tract infections (UTIs). The trials with endometrial scrutiny were less than one year and had mixed results. Nonhormonal lubricant is effective in improving some atrophic signs and symptoms. All preparations were associated with vaginal irritation. Bleeding with vaginal estradiol tablets may be less than that with CEE cream. Vaginal tablets or rings were preferred over other preparations. There were no serious adverse events reported. There was occasional expulsion of estradiol ring in the setting of prior hysterectomy. All preparations are effective in decreasing signs and symptoms of vaginal atrophy, but they differ slightly in their adverse event profiles. Long-term safety of the preparations is best established for estradiol tablets (1 year), but is lacking for all preparations.

Continuous low dose estradiol released from a vaginal ring versus estriol vaginal cream for urogenital atrophy

Objectives: To determine if the efficacy of continuous low dose estradiol released from a vaginal ring is equivalent to estriol vaginal cream regarding improvement of the patient's subjective feeling of vaginal dryness and to determine if there is a preference for either of the two study treatments. Methods: Open-label randomized parallel group trial with active control with a blind evaluation of vaginal cytology and with a cross-over (change-over) phase for preference comparison. One hundred and sixty five postmenopausal women with symptoms of vaginal dryness and signs of vaginal atrophy were randomized to an estradiol ring (Estring ®) or estriol cream (Synapause ®). The duration of each treatment period was 12 weeks. Results: Both study treatments were equally effective regarding the ability to alleviate the symptom feeling of vaginal dryness and the signs of vaginal atrophy. Both treatments were efficient in restoring the vaginal mucosa, recorded as higher maturation values and as decreased vaginal pH. Estring was superior to estriol cream regarding preference of treatment. Both treatments were equivalent for the occurrence of adverse events, including bleeding. Conclusion: data from this change-over study confirm efficacy and safety of both the vaginal ring and cream in the treatment of postmenopausal women with urogenital atrophy symptoms and signs. The patients had a strong preference for the vaginal ring.

Metabolism of 2,2'-dihydroxybiphenyl by Pseudomonas sp. strain HBP1: production and consumption of 2,2',3-trihydroxybiphenyl.

Cells of Pseudomonas sp. strain HBP1 grown on 2-hydroxy- or 2,2'-dihydroxybiphenyl contain NADH-dependent monooxygenase activity that hydroxylates 2,2'-dihydroxybiphenyl. The product of this reaction was identified as 2,2',3-trihydroxybiphenyl by 1H nuclear magnetic resonance and mass spectrometry. Furthermore, the monooxygenase activity also hydroxylates 2,2',3-trihydroxybiphenyl at the C-3' position, yielding 2,2',3,3'-tetrahydroxybiphenyl as a product. An estradiol ring cleavage dioxygenase activity that acts on both 2,2',3-tri- and 2,2',3,3'-tetrahydroxybiphenyl was partially purified. Both substrates yielded yellow meta-cleavage compounds that were identified as 2-hydroxy-6-(2-hydroxyphenyl)-6-oxo-2,4-hexadienoic acid and 2-hydroxy-6-(2,3-dihydroxyphenyl)-6-oxo-2,4-hexadienoic acid, respectively, by gas chromatography-mass spectrometry analysis of their respective trimethylsilyl derivatives. The meta-cleavage products were not stable in aqueous incubation mixtures but gave rise to their cyclization products, 3-(chroman-4-on-2-yl)pyruvate and 3-(8-hydroxychroman-4-on-2-yl)pyruvate, respectively. In contrast to the meta-cleavage compounds, which were turned over to salicylic acid and 2,3-dihydroxybenzoic acid, the cyclization products are not substrates to the meta-cleavage product hydrolase activity. NADH-dependent salicylate monooxygenase activity catalyzed the conversions of salicylic acid and 2,3-dihydroxybenzoic acid to catechol and pyrogallol, respectively. The partially purified estradiol ring cleavage dioxygenase activity that acted on the hydroxybiphenyls also produced 2-hydroxymuconic semialdehyde and 2-hydroxymuconic acid from catechol and pyrogallol, respectively.

Comparison of cytochrome P-450 species which catalyze the hydroxylations of the aromatic ring of estradiol and estradiol 17-sulfate

For identification of microsomal cytochrome P-450 ( P-450) enzymes which catalyze 2- or 4-hydroxylations of estrogens in the rat liver, estradiol (E 2) and estradiol 17-sulfate (E 2-17-S) were selected as the substrates and incubated with various kinds of purified P-450 enzymes: PB-1, PB-2, PB-4 and PB-5 obtained from phenobarbital-treated male rats (Sprague-Dawley); MC-1 and MC-5 from 3-methylcholanthrene-treated male rats; and UT-1, UT-2, UT-4 and UT-5 from untreated animals. The reactions were carried out under the P-450-reconstructed system, and the resulting products were determined by HPLC using electrochemical detection. All the enzymes tested were shown to have varying degrees of catalytic activities for 2-hydroxylation of the two substrates; UT-1 and UT-2 had the highest activity. Of the induced P-450 enzymes, PB-2 and MC-1 showed fairly high catalytic activity for 4-hydroxylation of E 2. The P-450 enzymes obtained from the untreated male rats, especially UT-4, showed the highest catalytic activity for 4-hydroxylation of the two substrates. From these results and also from kinetic experiments, the P-450 enzymes which catalyze 2- and 4-hydroxylations of estrogen were considered to be different species. A part of E 2 was converted to such metabolites as estrone and those having a hydroxyl group at positions 6β, 15α or 16α, each production of which was estimated to be catalyzed by single or multiple P-450s.

Synthesis and characterization of estradiol and estradienonyl derivatives of pentamethylcyclopentadienylruthenium(II)

The ‘C5Me5Ru’ moiety coordinates at the A ring of estradiol to give both the α and β isomers of the ketonic form [Ru(C5Me5)(η5-estradienonyl)](1a and 1b respectively) and the α isomer of the phenolic form [Ru(C5Me5)(η6-estradiol)][PF6]2a; 1a reacts with HPF6 to give quantitatively 2a, but in the presence of NEt31a was regenerated.

Peroxidase-catalyzed displacement of tritium from regiospecifically labeled estradiol and 2-hydroxyestradiol

Estradiol and 2-hydroxyestradiol labeled with 3H at different positions in rings A, B or D were incubated with lactoperoxidase without added H 2O 2 and their oxidative transformation was followed by transfer of 3H into 3H 2O. With estradiol, 3H loss from different positions in the aromatic ring was almost equal and also occurred to a lesser extent from the alicyclic portion of the molecule. Glutathione had less effect on the formation of 3H 2O from the aromatic ring of estradiol than from that of the catechol estrogen where it increased the yield 6-fold. The rate of 3H loss was also very much greater from tritiated 2-hydroxyestradiol than from estradiol and NADPH was inhibitory with both steroids. Conditions for the release of 3H from estradiol and 2-hydroxyestradiol by peroxidase as well as the effect of some biochemical inhibitors were also investigated. The possible contribution of peroxidative formation of 3H 2O during the radiometric assay for catechol estrogen biosynthesis by tissue monooxygenases is discussed.

Molecular Conformation, Receptor Binding, and Hormone Action of Natural and Synthetic Estrogens and Antiestrogens

The X-ray crystallographic structural determinations of synthetic estrogens and antiestrogens provide reliable information on the global minimum energy conformation of these molecules or a local minimum energy conformation that is within 1 or 2 kcal/mole of the global minimum. In favorable cases, state-of-the-art molecular mechanics calculations provide quantitative agreement with X-ray results and information on the relative energy of other local minimum energy conformations not observed crystallographically. Because the conformation of diethylstilbestrol (DES) observed in solvated crystals has an overall conformation and dipole moment more similar to estradiol it is the form more likely to bind to the receptor and produce hormone activity. Either phenol ring of DES can successfully mimic the estradiol A-ring in binding to the receptor. Indenestrol A (INDA) and indenestrol B (INDB) have nearly identical fully extended planar conformations. Either the alpha or gamma rings of these compounds may mimic the A ring of estradiol and compete for the estrogen receptor. Although there are eight distinct ways in which molecules of a racemic mixture of INDA or INDB can bind to the receptor, not all of them may be able to elicit a hormonal response. This may account for the reduced biological activity of the compounds despite their successful competition for receptor binding. The minimum energy conformations of Z-pseudodiethylstilbestrol (ZPD) and E-pseudodiethylstilbestrol (EPD) are bent in a fashion similar to that of indanestrol (INDC). These molecules have good binding affinity suggesting that the receptor does not require a flat molecule. Therefore these conformations would appear to be compatible with receptor binding, but only the Z isomer has an energetically allowed extended conformation that accounts for its observed biological activity relative to DES.

Molecular conformation, receptor binding, and hormone action of natural and synthetic estrogens and antiestrogens.

The X-ray crystallographic structural determinations of synthetic estrogens and antiestrogens provide reliable information on the global minimum energy conformation of these molecules or a local minimum energy conformation that is within 1 or 2 kcal/mole of the global minimum. In favorable cases, state-of-the-art molecular mechanics calculations provide quantitative agreement with X-ray results and information on the relative energy of other local minimum energy conformations not observed crystallographically. Because the conformation of diethylstilbestrol (DES) observed in solvated crystals has an overall conformation and dipole moment more similar to estradiol it is the form more likely to bind to the receptor and produce hormone activity. Either phenol ring of DES can successfully mimic the estradiol A-ring in binding to the receptor. Indenestrol A (INDA) and indenestrol B (INDB) have nearly identical fully extended planar conformations. Either the alpha or gamma rings of these compounds may mimic the A ring of estradiol and compete for the estrogen receptor. Although there are eight distinct ways in which molecules of a racemic mixture of INDA or INDB can bind to the receptor, not all of them may be able to elicit a hormonal response. This may account for the reduced biological activity of the compounds despite their successful competition for receptor binding. The minimum energy conformations of Z-pseudodiethylstilbestrol (ZPD) and E-pseudodiethylstilbestrol (EPD) are bent in a fashion similar to that of indanestrol (INDC). These molecules have good binding affinity suggesting that the receptor does not require a flat molecule. Therefore these conformations would appear to be compatible with receptor binding, but only the Z isomer has an energetically allowed extended conformation that accounts for its observed biological activity relative to DES.

Displacement of estradiol from estrogen receptors by simple alkyl phenols.

Simple alkyl phenols have been tested for their ability to prevent the binding of [3H]estradiol and to displace the prebound hormone from estrogen receptors of uterine cytosols. Tetrahydronaphthol, an analog of the A and B rings of estradiol, is highly effective in preventing the forward bindng of estradiol. p-sec-Amyl phenol (pSAP) with a flexible alkyl chain corresponding to the B ring of estradiol is highly effective at 0 C in displacing estradiol which had been prebound by the receptor. Both compounds were more effective at 0 C than at 23 C. The data are discussed in terms of sequential conformational changes which might be required for the binding and release of the natural hormones and their possible relevance to receptor action.