Structure-activity relationships of estrogens

Aromatase inhibitors for the treatment of breast cancer: An overview (2019-2023)

Aromatase inhibition is considered a legitimate approach for the treatment of ER-positive (ER+) breast cancer as it accounts for more than 70% of breast cancer cases. Aromatase inhibitor therapy has been demonstrated to be highly effective in decreasing tumour size, increasing survival rates, and lowering the chance of cancer recurrence. The present review deliberates the pathophysiology and the role of aromatase in estrogen biosynthesis. Estrogen biosynthesis, various androgens, and their function in the human body have also been discussed. The salient aspects of the aromatase active site, its mode of action, and AIs, along with their intended interactions with presently FDA-approved inhibitors, have been briefly discussed. It has been detailed how different reported AIs were designed, their SAR investigations, in silico analysis, and biological evaluations. Various AIs from multiple origins, such as synthetic and semi-synthetic, have also been discussed.

Perioperative Factors Affecting the Healing of Rectovaginal Fistula

Rectovaginal fistula is rare, but a severe complication in gynecology, which despite the effort of clinicians is still not treated successfully in many cases. According to statistics, the healing rates of surgery in patients with RVF range from 20 to 100%. The treatment effectiveness depends on the etiology of fistula, the age of the patients, the presence of comorbidities, the type of surgery and many other factors. Considering the low efficiency of treatment and the high risk of recurrence, the question of possible methods to improve the results occurs. In our review, we analyzed both modifiable and non-modifiable factors which may influence the treatment, healing rate and future fate of the patients. Taking into account all analyzed risk factors, including age, comorbidities, smoking status, microbiology, medications, stoma and stool features, we are aware that rectovaginal fistula's treatment must be individualized and holistic. In cases of poorly healing RVF, the drainage of feces, the use of antibiotic prophylaxis or the implementation of estrogen therapy may be useful. Moreover, microbiome research in women with RVF and towards estrogen therapy should be performed in order to create treatment algorithms in women with fistulae. Those interventions, in our opinion, may significantly improve the outcome of the patients.

Phytoestrogens, novel dietary supplements for breast cancer

While endocrine therapy is considered as an effective way to treat breast cancer, it still faces many challenges, such as drug resistance and individual discrepancy. Therefore, novel preventive and therapeutic modalities are still in great demand to decrease the incidence and mortality rate of breast cancer. Numerous studies suggested that G protein-coupled estrogen receptor (GPER), a membrane estrogen receptor, is a potential target for breast cancer prevention and treatment. It was also shown that not only endogenous estrogens can activate GPERs, but many phytoestrogens can also function as selective estrogen receptor modulators (SERMs) to interact GPERs. In this review, we discussed the possible mechanisms of GPERs pathways and shed a light of developing novel phytoestrogens based dietary supplements against breast cancers.

Estrogen for the Treatment and Prevention of Breast Cancer: A Tale of 2 Karnofsky Lectures

ABSTRACT

In 1971, Sir Alexander Haddow et al. delivered the inaugural David A. Karnofsky lecture at the American Society for Clinical Oncology. This award was designated American Society for Clinical Oncology's highest, as he had used translational research to identify the first clinical therapy, that is, synthetic estrogens to treat breast cancer. His lecture was entitled "Thoughts on Chemical Therapy." For 40 years, high-dose synthetic estrogens were used as palliative therapy, for some advanced breast cancer patients 5 years following menopause. Mechanisms were unknown. Tamoxifen, a failed "morning-after pill," is an antiestrogen in estrogen receptor-positive breast cancer, which was subsequently used to treat all stages of breast cancer and to prevent breast cancer. In 2008, Jordan was selected to present the 38th Karnofsky lecture entitled: "The Paradoxical Action of Estrogen in Breast Cancer-Survival or Death?" Unexpectedly, through a study of acquired resistance to long-term tamoxifen therapy, estrogen-induced apoptosis in long-term estrogen-deprived breast cancer was deciphered in Jordan's laboratory. These data and the biological rules established under laboratory conditions provided molecular mechanisms to aid in the interpretation of the Women's Health initiative in the United States and the Million Women Study in the United Kingdom. In addition, by establishing laboratory models to understand mechanisms of estrogen-induced apoptosis, new estrogen derivatives were successfully evaluated in the laboratory and tested as candidates for women after the therapeutic failure of antiestrogenic strategies to treat breast cancer. For the future, the knowledge obtained about estrogen-induced apoptosis in cancer holds the promise of discovering new therapies to control or cure cancer in general.

Microwave Microfluidic Sensor for Detection of High Equol Concentrations in Aqueous Solution

This paper presents a Peano fractal geometry complementary split ring resonator (PFCSRR) loaded microstrip transmission line with a microfluidic channel for equol (EQ) sensing in a high and wide range of concentrations in aqueous solution. The proposed sensor was designed based on a CSRR loaded microstrip line with a Peano fractal in the center of a CSRR and validated through simulation and experiment. The microfluidic channel was fabricated using polydimethylsiloxane (PDMS) and installed to cover the sensing area. The free space, empty microfluidic channels, deionized (DI) water, dimethyl sulfoxide (DMSO), and various concentrations of EQ were measured by a microwave sensor through sample-filled microfluidic channels. Detection of high levels of EQ was in the concentration range of 0.01 mM - 100 mM. The materials under test (MUTs) were measured in the frequency range of 1.0 GHz-3.5 GHz based on the magnitude of the transmission coefficient (S₂₁) and resonance frequency (F_r) at room temperature. The S₂₁ and F_r were recorded and analyzed by logarithmic concentrations of EQ for the determinant of the correlations between EQ concentration and S₂₁ and F_r. Principal component analysis (PCA) and K-means clustering were used to analyze and classify groups of MUTs.

Endocrine Disruptors: A Critical Review of In Vitro and In Vivo Testing Strategies for Assessing Their Toxic Hazard to Humans

Currently, there is much concern that a wide range of both synthetic and naturally occurring environmental chemicals can act as endocrine disruptors (EDs), and can adversely affect humans and wildlife. Many in vivo and in vitro tests have been proposed for screening EDs, and several regulatory agencies, including the US Environmental Protection Agency (EPA), have recommended tier-testing schemes. Unfortunately, most of the proposed toxicity tests have substantial problems, including non-specificity and lack of reproducibility. There is also uncertainty concerning their relevance for generating useful hazard data for risk assessment purposes, in view of the diversity of the possible ED mechanisms of action (for example, receptor binding, steroidogenesis and modulation of the homeostatic processes which regulate endogenous responses to hormones). Moreover, most of the suggested test methods have yet to be validated according to internationally accepted criteria, although the OECD and the US EPA have defined tests for validation, and an interlaboratory “prevalidation” exercise has been initiated by the OECD. All this is compounded by the lack of information regarding human exposure levels to EDs, and a lack of direct evidence for a causal link between exposure and the development of adverse human health effects. In addition, the regulatory testing of EDs has important negative implications for animal welfare, as some of the proposed in vivo tests require large group sizes of animals and stressful procedures. From a detailed analysis of the available published literature, it is concluded that it is impossible to assess the relative values of currently available in vitro and in vivo toxicity tests for EDs, or to recommend any test or test battery. Any plans for the widespread testing of EDs are therefore premature and might be unnecessary, at least for detecting possible human effects. Several recommendations are made for rectifying this unsatisfactory situation, including the postponement of screening programmes pending: a) more information on human exposure; b) further details of the mechanisms of action of EDs; and c) the development of improved tests, followed by their proper scientific validation.

Design, synthesis and biological study of hybrid drug candidates of nitric oxide releasing cucurbitacin-inspired estrone analogs for treatment of hepatocellular carcinoma

Development of hybrid drug candidates is well known strategy for designing antitumor agents. Herein, a novel class of nitric oxide donating cucurbitacin inspired estrone analogs (NO-CIEAs) were designed and synthesized as multitarget agents. Synthesized analogs were initially evaluated for their anti-hepatocellular carcinoma activities. Among the tested analogs, NO-CIEAs 17 and 20a exhibited more potent activity against HepG2 cells (IC₅₀ = 4.69 and 12.5 µM, respectively) than the reference drug Erlotinib (IC₅₀ = 25 µM). Interestingly, NO-CIEA 17 exerted also a high potent activity against Erlotinib-resistant HepG2 cell line (HepG2-R) (IC₅₀ = 8.21 µM) giving insight about its importance in drug resistance therapy. Intracellular measurements of NO revealed that NO-CIEAs 17 and 20a showed a significant increase in NO production in tumor cells after 1 h of incubation comparable to the reference prodrug JS-K. Flow cytometric analysis showed that both NO-CIEAs 17 and 20a mainly arrested the HepG2 cells in the G0/G1 phase. Also, In-Cell Based ELISA screening showed that NO-CIEA 17 resulted in a potential inhibitory activity towards the EGFR and MAPK (25% and 29% inhibition compared to untreated control cells, respectively). This data suggests the binding ability of NO-CIEA 17 to the EGFR and ERK to be well correlated along with the docking and cellular studies. Also, treatment of HepG2-R cells with NO-CIEA 17 showed a potential reduction of MRP2 expression in a dose dependent manner providing a significant impact on the chemotherapeutic resistance. Overall, the current study provides a potential new approach for the discovery of a novel antitumor agent against HCC.

Cancer of Reproductive System: Receptors and Targeting Strategies

Carcinogenesis in the different organs of the reproductive system, particularly, prostate, ovarian, and cervical tissues, involves aberrant expression of various physiological receptors belonging to different superfamilies. This chapter provides insights into the physiological receptors that are associated with the genesis, progression, metastasis, management, as well as the prognosis of the cancers of the male and female reproductive systems. It also highlights the structural and binding characteristics of the highly predominant receptors, namely, androgen, estrogen, progesterone, and gonadotropin-releasing hormone (GnRH) receptors, which are overexpressed in these cancers and discusses various strategies to target them.

Detection of 17 β-Estradiol in Environmental Samples and for Health Care Using a Single-Use, Cost-Effective Biosensor Based on Differential Pulse Voltammetry (DPV)

Environmental estrogen pollution and estrogen effects on the female reproductive system are well recognized scientifically. Among the estrogens, 17 β-estradiol is a priority in environmental estrogen pollution, and it is also a major contributor to estrogen which regulates the female reproductive system. 17 β-estradiol is carcinogenic and has a tumor promotion effect relating to breast cancer, lung cancer and others. It also affects psychological well-being such as depression, fatigue and others. Thus, a simple method of detecting 17 β-estradiol will be important for both environmental estrogen pollution and health care. This study demonstrates a single-use, cost-effective 17 β-estradiol biosensor system which can be used for both environmental and health care applications. The bio-recognition mechanism is based on the influence of the redox couple, K₃Fe(CN)₆/K₄Fe(CN)₆ by the interaction between 17 β-estradiol antigen and its α-receptor (ER-α; α-estrogen antibody). The transduction mechanism is an electrochemical analytical technique, differential pulse voltammetry (DPV). The levels of 17 β-estradiol antigen studied were between 2.25 pg/mL and 2250 pg/mL; Phosphate buffered saline (PBS), tap water from the Cleveland regional water district, and simulated urine were used as the test media covering the potential application areas for 17 β-estradiol detection. An interference study by testosterone, which has a similar chemical structure and molecular weight as those of 17 β-estradiol, was carried out, and this 17 β-estradiol biosensor showed excellent specificity without any interference by similar chemicals.

Screening for potential endocrine disruptors in fish: evidence from structural alerts and in vitro and in vivo toxicological assays

BACKGROUND

The European chemicals' legislation REACH aims to protect man and the environment from substances of very high concern (SVHC). Chemicals like endocrine disruptors (EDs) may be subject to authorization. Identification of (potential) EDs with regard to the environment is limited because specific experimental assessments are not standard requirements under REACH. Evidence is based on a combination of in vitro and in vivo experiments (if available), expert judgement, and structural analogy with known EDs.

OBJECTIVES

The objectives of this study are to review and refine structural alerts for the indication of potential estrogenic and androgenic endocrine activities based on in vitro studies; to analyze in vivo mammalian long-term reproduction studies with regard to estrogen- and androgen-sensitive endpoints in order to identify potential indicators for endocrine activity with regard to the environment; to assess the consistency of potential estrogenic and androgenic endocrine activities based on in vitro assays and in vivo mammalian long-term reproduction studies and fish life-cycle tests; and to evaluate structural alerts, in vitro assays, and in vivo mammalian long-term reproduction studies for the indication of potential estrogenic and androgenic endocrine disruptors in fish.

RESULTS

Screening for potential endocrine activities in fish via estrogenic and androgenic modes of action based on structural alerts provides similar information as in vitro receptor-mediated assays. Additional evidence can be obtained from in vivo mammalian long-term reproduction studies. Conclusive confirmation is possible with fish life-cycle tests. Application of structural alerts to the more than 33,000 discrete organic compounds of the EINECS inventory indicated 3585 chemicals (approx. 11%) as potential candidates for estrogenic and androgenic effects that should be further investigated. Endocrine activities of the remaining substances cannot be excluded; however, because the structural alerts perform much better for substances with (very) high estrogenic and androgenic activities, there is reasonable probability that the most hazardous candidates have been identified.

CONCLUSIONS

The combination of structural alerts, in vitro receptor-based assays, and in vivo mammalian studies may support the priority setting for further assessments of chemicals with potential environmental hazards due to estrogenic and androgenic activities.

Organochlorine Residues and Risk of Breast Cancer

Considerable attention has recently been focused on the possible role of estrogenic compounds as etiologic agents in the development of human breast cancer. This review summarizes data from relevant laboratory and epidemiological studies to assess the hypothesis that exposure to organochlo-rines, and specifically 2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane (DDT), increases breast cancer risk. Organochlorine compounds, including pesticides such as DDT and industrial compounds such as the polychlorinated biphenyls (PCBs), have had a long history of use. In general, these compounds are characterized by their high lipophilicity and environmental persistence. DDT was widely used in agriculture and public health programs from 1943 to 1972, when it was removed from use in the Western world. DDT is still used, however, in many developing nations. The International Agency for Research on Cancer concluded that there was adequate evidence that DDT was carcinogenic in laboratory animals, yet epidemiological evidence has not been compelling. The estrogenic activity of o, p'-DDT has been well characterized; however, the affinity of estrogen receptors for this compound is very weak and reported to be 1/2,000–1/10,000 that of 17β-estradiol. Epidemiologically, some investigators have reported elevated levels of 1,1-dichloro-2,2-bis(p-chloro-phenyl)ethylene, a DDT metabolite, and PCBs in breast adipose tissue and blood serum taken from breast cancer patients when compared with controls, while others have reported the absence of such an association. While the etiology of breast cancer is not fully understood, it is generally recognized that estrogenic compounds may increase the risk of disease. Contemporary human exposure to DDT and other organochlorines is very limited and would likely play an insignificant role when compared with other sources of exposure, such as estrogen replacement therapy and phytoestrogens in food.

In vivo and in vitro estrogen bioactivities of alkyl parabens

The alkyl esters of p-hydroxybenzoic acid known as parabens (Pbens) are used as preservatives in food, pharmaceutical and cosmetic formulations. They have been reported as estrogenic. Here, we present evidence for the in vivo and in vitro bioactivities and receptor binding affinities of methylparaben (MePben), ethylparaben (EtPben), propylparaben (PrPben), and butylparaben (BuPben) compared with those of estradiol (E2). Estrogenicity was studied using the uterotrophic assay in immature (Im) and adult ovariectomized (Ovx) CD1 mice, and in immature female Wistar rats (IW). Animals were subcutaneously (sc) treated for three consecutive days with different molar equivalent doses ranging from 3.62 to 1086 mmol/kg body weight of Pbens, E2 (0.036 mmol/kg), or vehicle. Pbens increased uterine weight in Im and Ovx animals and their relative uterotrophic effect to E2 (100) (RUEE2) were from 34 to 91. The relative uterotrophic potencies related to E2 (100) (RUPE2) of these compounds were from 0.003 to 0.007. The E2 ED50 for CD1 animals able to increase the uterine weight was 7 mg/kg (0.9 -55 confidence limits); and that of Pbens ranged from 18 to 74 mg/kg. In IW rats, the ED50 were from 33 to 338 mg/kg. All Pbens, except MePb, competed with [3H]E2 for the estrogen receptor binding sites. The uterotrophic effects of Pbens in Im mice have a positive correlation with the side-chain length of the ester group of these compounds. The E2 and Pbens relative binding affinities (RBA) and Ki values correlated to their estrogenic activity. The NOELs values for Pbens uterotrophic activity in Im were from 0.6 to 6.5 mg/kg per day; and Ovx from 6 to 55 mg/kg. The NOELs IW ranged from 16.5 to 70 mg/kg indicating that Im were more susceptible than Ovx and IW to these effects. The data shown here confirm the estrogenicity of Pbens.

Suppression of liver Apo E secretion leads to HDL/cholesterol immaturity in rats administered ethinylestradiol

Ethinylestradiol (EE), a main component of the combined oral contraceptive pill, is associated with an increased risk of arterial diseases. However, the toxicity mechanism of EE is poorly understood. In this study, we found that the exposure to EE reduced the serum apolipoprotein E (Apo E) level and high-density lipoprotein (HDL)/cholesterol concentration in adult female rats. Diethylstilbestrol showed the same effects and both reductions were suppressed by coadministration of tamoxifen (TAM). Liver perfusion experiments revealed that the secretion rate of Apo E from the liver was significantly reduced. It is concluded that EE damages the maturation of HDL/cholesterol by delaying Apo E secretion from the liver, and this may lead to an increased risk of arterial diseases, such as atheromas.

The influence of equol on the hypothalamic-pituitary-thyroid axis and hepatic lipid metabolic parameters in adult male rats

AIMS

Equol, the principal active metabolite of soy-derived phytoestrogen daidzein, has well-known estrogenic actions. Results of several studies indicate that equol may also have anti-androgenic activities. However, mechanisms of action of equol on hypothalamic-pituitary-thyroid axis (HPTA) and hepatic lipid metabolism in adult male rats have not been determined yet.

MAIN METHODS

Equol at two doses of 100 and 250mg/kgbodyweight(BW)/day was orally gavaged for 5days to groups of 4-month-old male rats. As a positive anti-androgenic control group, animals received 100mg of pure anti-androgenic drug flutamide/kgBW/day. Circulating concentrations of thyroid hormones and lipids, and expression levels of genes underlying HPTA function were determined by radioimmunoassay and TaqMan® real-time reverse transcription polymerase chain reaction, respectively.

KEY FINDINGS

Flutamide significantly decreased relative prostate weight, whereas equol did not. Both equol and flutamide caused a significant increase in relative liver weights, and decreases in plasma levels of total tetraiodothyronine (T4) and triiodothyronine (T3), whereas free T4 and T3 concentrations were not reduced. Equol caused the marked down-regulation of hypothalamic thyrotropin-releasing hormone mRNA expression, whereas flutamide did not. Equol as well as flutamide significantly down-regulated the expression levels of pituitary thyrotropin beta-subunit mRNA, without altering thyrotropin secretion. Equol caused reductions in plasma levels of total cholesterol, high- and low-density lipoproteins and triglycerides, whereas flutamide exerted opposite effects.

SIGNIFICANCE

This is the first study to reveal that in male rats equol did not affect HPTA function and liver lipid metabolism through the anti-androgenic pathway, however, the intrinsic estrogenic actions of equol were observed.

Post-Coital Antifertility Activity of Hibiscus rosa-sinensis Linn. roots

Ancient literature mentions the use of a number of plants/preparations for fertility regulation. Some local contraceptive agents have also been described in Ayurvedic and Unani texts. Documented experiments or clinical data are, however, lacking. Therefore, the present study was undertaken to explore the antifertility and estrogenic activity of ethanolic extract of the roots of Hibiscus rosa-sinensis Linn. A strong anti-implantation (inhibition 100%) and uterotropic activity was observed at the dose level of 400 mg/kg body weight. Histological studies were carried out to confirm this effect.

Estrogen-mediated mechanisms to control the growth and apoptosis of breast cancer cells: a translational research success story

The treatment and prevention of solid tumors have proved to be a major challenge for medical science. The paradigms for success in the treatment of childhood leukemia, Hodgkin's disease, Burkett's lymphoma, and testicular carcinoma with cytotoxic chemotherapy did not translate to success in solid tumors--the majority of cancers that kill. In contrast, significant success has accrued for patients with breast cancer with antihormone treatments (tamoxifen or aromatase inhibitors) that are proved to enhance survivorship, and remarkably, there are now two approved prevention strategies using either tamoxifen or raloxifene. This was considered impossible 40 years ago. We describe the major clinical advances with nonsteroidal antiestrogens that evolved into selective estrogen receptor modulators (SERMs) which successfully exploited the ER target selectively inside a woman's body. The standard paradigm that estrogen stimulates breast cancer growth has been successfully exploited for over 4 decades with therapeutic strategies that block (tamoxifen, raloxifene) or reduce (aromatase inhibitors) circulating estrogens in patients to stop breast tumor growth. But this did not explain why high-dose estrogen treatment that was the standard of care to treat postmenopausal breast cancer for 3 decades before tamoxifen caused tumor regression. This paradox was resolved with the discovery that breast cancer resistance to long-term estrogen deprivation causes tumor regression with physiologic estrogen through apoptosis. The new biology of estrogen action has been utilized to explain the findings in the Women's Health Initiative that conjugated equine estrogen alone given to postmenopausal women, average age 68, will produce a reduction of breast cancer incidence and mortality compared to no treatment. Estrogen is killing nascent breast cancer cells in the ducts of healthy postmenopausal women. The modulation of the ER using multifunctional medicines called SERMs has provided not only significant improvements in women's health and survivorship not anticipated 40 years ago but also has been the catalyst to enhance our knowledge of estrogen's apoptotic action that can be further exploited in the future.

Lipoxin A4 is a novel estrogen receptor modulator

Inflammation is intimately linked with naturally occurring remodeling events in the endometrium. Lipoxins comprise a group of short-lived, nonclassic eicosanoids possessing potent anti-inflammatory and proresolution properties. In the present study, we investigated the role of lipoxin A(4) (LXA(4)) in the endometrium and demonstrated that 15-LOX-2, an enzyme necessary for LX biosynthesis, is expressed in this tissue. Our results establish that LXA(4) possesses robust estrogenic activity through its capacity to alter ERE transcriptional activity, as well as expression of estrogen-regulated genes, alkaline phosphatase activity, and proliferation in human endometrial epithelial cells. Interestingly, LXA(4) also demonstrated antiestrogenic potential, significantly attenuating E2-induced activity. This estrogenic activity was directly mediated through estrogen receptors (ERs). Subsequent investigations determined that the actions of LXA(4) are exclusively mediated through ERα and closely mimic those of the potent estrogen 17β-estradiol (E2). In binding assays, LXA(4) competed with E2 for ER binding, with an IC(50) of 46 nM. Furthermore, LXA(4) exhibited estrogenic activity in vivo, increasing uterine wet weight and modulating E2-regulated gene expression. These findings reveal a previously unappreciated facet of LXA(4) bioactions, implicating this lipid mediator in novel immunoendocrine crosstalk mechanisms.

Hormone replacement therapy and the risk of breast cancer

Hormone replacement therapy (HRT) is given to relieve the climacteric symptoms of menopause. Use of HRT reduced after a report from the Women's Health Initiative linked it to an increased risk of breast cancer. This association has been confirmed in several other studies, including the Million Women Study. The risk of breast cancer is greater for formulations that contain both estrogen and progesterone, compared with estrogen alone. The breast cancer risk associated with HRT is higher for estrogen receptor-positive cancers than for estrogen receptor-negative cancers, and for low-grade cancers compared with high-grade cancers. After cessation of HRT the increased risk of breast cancer dissipates within 2 years. The rapidity of the decline suggests that a proportion of breast cancers that are hormone dependent will regress if the hormonal stimulation is removed. In evaluating a woman who is considering HRT, factors that have been associated with an increased risk include the initiation of hormone use immediately after menopause, a lean body mass and high mammographic breast density.

The dynamic structure of the estrogen receptor

The estrogen receptor (ER) mediates most of the biological effects of estrogens at the level of gene regulation by interacting through its site-specific DNA and with other coregulatory proteins. In recent years, new information regarding the dynamic structural nature of ER has emerged. The physiological effects of estrogen are manifested through ER's two isoforms, ER_α and ER_β. These two isoforms (ER_α and ER_β) display distinct regions of sequence homology. The three-dimensional structures of the DNA-binding domain (DBD) and ligand-binding domain (LBD) have been solved, whereas no three-dimensional natively folded structure for the ER N-terminal domain (NTD) is available to date. However, insights about the structural and functional correlations regarding the ER NTD have recently emerged. In this paper, we discuss the knowledge about the structural characteristics of the ER in general and how the structural features of the two isoforms differ, and its subsequent role in gene regulation.

Internalization of a C17α-alkynylestradiol-porphyrin conjugate into estrogen receptor positive MCF-7 breast cancer cells

We hypothesized that expression of nuclear estrogen receptor (ER) in hormone-sensitive breast cancer cells could be harnessed synergistically with the tumor-accumulating effect of porphyrins to selectively deliver estrogen-porphyrin conjugates into breast tumor cells, and preferentially kill tumor cells upon exposure to visible light. In this study we synthesized a conjugate of C(17α)-alkynylestradiol and pyropheophorbide and demonstrated that this conjugate is internalized by ER-positive MCF-7 cells while pyropheophorbide did not, suggesting an ER-mediated uptake and internalization of the conjugate by incipient nuclear ER in MCF-7 cells. This study is a direct demonstration of our hypothesis about ER-mediated internalization of estrogen-porphyrin conjugates.

Increased expression of histone proteins during estrogen-mediated cell proliferation

BACKGROUND

There is concern about the potential risk posed by compounds with estrogen-like activity present in the environment. As previous studies have shown that combined exposure to such compounds results in dose additivity, it should be possible to assess estrogen exposure with suitable biomarkers of effect.

OBJECTIVES

Our goal was to identify candidate protein biomarkers of effect for estrogenic compounds.

METHODS

In the search for biomarkers, we assessed the effect of several estrogenic compounds on the expression profile of proteins in breast-derived cell lines varying in their estrogen receptor (ER) phenotype using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry. We identified responsive proteins, after separating them by SDS-polyacrylamide gel electrophoresis, and analyzing the trypsin-digested proteins by tandem mass spectrometry.

RESULTS

The estrogenic compounds 17beta-estradiol, genistein, bisphenol A, and endosulfan produced similar protein profile changes in MCF-7 cells (phenotype: ERalpha(+)/ERbeta(+)), but had no effect on MDA-MB-231 (ERalpha(-)/ERbeta(+)), MCF-10F (ERalpha(-)/ERbeta(+)), or MCF-10A (ERalpha(-)/ERbeta(-)) cells. The most responsive proteins in MCF-7 cells were identified as histones H2A, H2B, H3, and H4. Histone levels were not increased in cell lines that showed no proliferative response to estrogens despite their rapid intrinsic growth rate in culture.

CONCLUSION

Our results indicate that ER-mediated cell proliferation results in up-regulation of core histone proteins.

Estrogenic activity of diarylheptanoids from Curcuma comosa Roxb. Requires metabolic activation

Curcuma comosa Roxb. has traditionally been used as a dietary supplement for health promotion in peri- and postmenopausal women in Thailand. We investigated the estrogenic activity of 7 naturally occurring diarylheptanoids from the extracts of C. comosa both in vitro and in vivo. A yeast recombinant system containing human estrogen receptor alpha, coactivator TIF2 and a beta-galactosidase reporter gene was used to determine estrogenic activity of diarylheptanoids metabolically activated with rat liver S9-fraction prior to the assay. The most potent compound was (3R)-1,7-diphenyl-(4E,6E)-4,6-heptadien-3-ol, with a relative potency of 4% compared to 17beta-estradiol. The metabolic activation of diarylheptanoids markedly enhanced their efficiency. The chemical structure required for estrogenic activity of diarylheptanoids was the presence of a keto group at C3 and absence of hydroxyl moiety in ring B. Only diarylheptanoids showing full estrogenic efficiency in vitro were able to elicit uterotrophic activity of in immature ovariectomized rat. This is the first evidence for in vivo estrogenic activity of diarylheptanoids from C. comosa. This novel class of natural phytoestrogens has the potential to be developed for use as dietary supplement in the treatment of menopausal symptoms.

Pharmacophore mapping of flavone derivatives for aromatase inhibition

Aromatase, which catalyses the final step in the steroidogenesis pathway of estrogen, has been target for the design of inhibitor in the treatment of hormone dependent breast cancer for postmenopausal women. The extensive SAR studies performed in the last 30 years to search for potent, selective and less toxic compounds, have led to the development of second and third generation of non-steroidal aromatase inhibitors (AI). Besides the development of synthetic compounds, several naturally occurring and synthetic flavonoids, which are ubiquitous natural phenolic compounds and mediate the host of biological activities, are found to demonstrate inhibitory effects on aromatase. The present study explores the pharmacophores, i.e., the structural requirements of flavones (Fig. 1) for inhibition of aromatase activity, using quantitative structure activity relationship (QSAR) and space modeling approaches. The classical QSAR studies generate the model (R (2) = 0.924, Q (2) = 0.895, s = 0.233) that shows the importance of aromatic rings A and C, along with substitutional requirements in meta and para positions of ring C for the activity. 3D QSAR of Comparative Molecular Field Analysis (CoMFA, R (2) = 0.996, R(2)(cv) = 0.791) and Comparative Molecular Similarity Analysis (CoMSIA, R (2) = 0.992, R(2)(cv) = 0.806) studies show contour maps of steric and hydrophobic properties and contribution of acceptor and donor of the molecule, suggesting the presence of steric hindrance due to ring C and R''-substituent, bulky hydrophobic substitution in ring A, along with acceptors at positions 11, and alpha and gamma of imidazole ring, and donor in ring C favor the inhibitory activity. Further space modeling (CATALYST) study (R = 0.941, Delta( cost ) = 96.96, rmsd = 0.876) adjudge the presence of hydrogen bond acceptor (keto functional group), hydrophobic (ring A) and aromatic rings (steric hindrance) along with critical distance among features are important for the inhibitory activity.

Estrogen receptors: how do they signal and what are their targets

During the past decade there has been a substantial advance in our understanding of estrogen signaling both from a clinical as well as a preclinical perspective. Estrogen signaling is a balance between two opposing forces in the form of two distinct receptors (ER alpha and ER beta) and their splice variants. The prospect that these two pathways can be selectively stimulated or inhibited with subtype-selective drugs constitutes new and promising therapeutic opportunities in clinical areas as diverse as hormone replacement, autoimmune diseases, prostate and breast cancer, and depression. Molecular biological, biochemical, and structural studies have generated information which is invaluable for the development of more selective and effective ER ligands. We have also become aware that ERs do not function by themselves but require a number of coregulatory proteins whose cell-specific expression explains some of the distinct cellular actions of estrogen. Estrogen is an important morphogen, and many of its proliferative effects on the epithelial compartment of glands are mediated by growth factors secreted from the stromal compartment. Thus understanding the cross-talk between growth factor and estrogen signaling is essential for understanding both normal and malignant growth. In this review we focus on several of the interesting recent discoveries concerning estrogen receptors, on estrogen as a morphogen, and on the molecular mechanisms of anti-estrogen signaling.

Pharmacophore Mapping of Selective Binding Affinity of Estrogen Modulators through Classical and Space Modeling Approaches: Exploration of Bridged-Cyclic Compounds with Diarylethylene Linkage

Research on Selective Estrogen Receptor Modulators (SERMs) has been driven by interest in discovering target selective molecules. In view of such significance, the present work explored the pharmacophores of estrogen receptor (ER) subtypes specific binding affinities of diverse compounds belonging to the category of bridged bicyclic-1,1-diarylethylene derivatives. Implementing classical QSAR and CATALYST based space-modeling approaches, it has been explored that attachment of aryl ring systems to unsaturated linkages, availability of phenolic hydroxyl group, global hydrophobicity, and stereochemistry of certain functional groups might be important for governing the subtype specific estrogenic behavior of this group of compounds. Supplementing this deduction, critical interfeature distances between hydrogen bond acceptor, hydrophobic, and ring aromatic features along with steric influence are found to primarily influence the ER-subtypes specific binding of this series of compounds.

Serum free BG-1 cell proliferation assay: A sensitive method for determining organochlorine pesticide estrogen receptor activation at the nanomolar range

Most xenobiotic estrogeniety assay methods rely on direct agonist action on the estrogen receptor (ER) to approximate activation potential. Such methods do have drawbacks since some ER activating pesticides are weak or non-agonistic in ligand-binding assays. This study discusses a method that detects pesticide estrogenic actions regardless of ER ligand binding ability. Using a serum-free BG-1 ovarian cell culture model, we investigated the ability of several organochlorine (OC) pesticides to stimulate known estrogenic actions. We observed concentration dependent ER mediated cell proliferation in BG-1 cells using heptachlor epoxide (HE), beta-hexachlorohexane (beta-HCH), and endosulfan (Endo). In addition, we observed upregulation of the ERE-dependent proteins progesterone receptor and PS2. Gel-shift/EMSA studies for ERE binding further supported these OC's ERE activating abilities. All of these effects were abolished using ICI 164,384(ICI). Using the same culture conditions, we tested the blocking action of growth factor antibodies for erbB2(9G6) and insulin-like growth factor (IGF-Ab) receptors and discovered they inhibited BG-1 proliferation (9G6: HE and beta-HCH/ IGF-Ab: Endo.) This experiment confirms the existence of a possible cross-talk between ER and growth factor receptors in OC ligand-dependent activation and also validates this sensitive method for determining both ligand-dependent and independent estrogenic activity of selected pesticides.

Lessons learnt from structural studies of the oestrogen receptor

Over the last 10 years, structural studies of the ligand-binding domains of nuclear hormone receptors have provided a wealth of information on the nature of ligand-binding and its role in receptor activation. This review examines the insights that studies on oestrogen receptor subtypes ERalpha and ERbeta have provided in terms of (1) basis of receptor activation; (2) recruitment of coregulators; (3) hormone recognition; and (4) subtype-selective ligands. It also highlights the implications for the binding of endocrine disruptors.

Regioselective synthesis and estrogenicity of (±)-8-alkyl-5,7-dihydroxy-4-(4-hydroxyphenyl)-3,4-dihydrocoumarins

Nine new (+/-)-8-alkyl-5,7-dihydroxy-4-(4-hydroxyphenyl)-3,4-dihydrocoumarins have been synthesized from 2,4,6-trimethoxybenzaldehyde via a short, efficient, and regioselective pathway, together with the unsubstituted analogue (+/-)-5,7-dihydroxy-4-(4-hydroxyphenyl)-3,4-dihydrocoumarin. The compounds were tested for estrogenic activity using a yeast-based estrogen screen. Weak estrogenicity was determined for seven members of the series.

QSAR Studies with E-State Index: Predicting Pharmacophore Signals for Estrogen Receptor Binding Affinity of Triphenylacrylonitriles

In connection to developing non-steroidal estrogen analogs, the present study explores the pharmacophore of triphenylacrylonitriles (Fig. 1) for binding affinity to estrogen receptor using Electrotopological State (E-State) indices of constituting atoms. The analysis shows the efficacy of E-State index in developing statistically acceptable model, which defines the electronic environment and topological states of diverse atoms in a molecule. The investigation concluded that electrophilic substitutions at C6 and C18 of the phenyl rings (A and C rings respectively) attached to C2 and C1 of ethylenic moiety, along with presence of hydroxyl substitution at C12 (ring B) and no. of non-hydrogen free terminal atoms of the molecule have influence on the binding affinity to the estrogen receptor.

The consequences of exhaustive antiestrogen therapy in breast cancer: estrogen-induced tumor cell death

Forty years ago, the endocrine treatment for breast cancer was a last resort at palliation before the disease overwhelmed the patient (1). Ovarian ablation was the treatment of choice for the premenopausal patient, whereas either adrenalectomy or, paradoxically, high-dose synthetic estrogen therapy were used for treatment in postmenopausal patients. A reduction or an excess of estrogen provoked objective responses in one out of three women. Unfortunately, there was no way of predicting who would respond to endocrine ablation, and because so few patients responded there was no enthusiasm for developing new endocrine agents. All hopes for a cure for breast cancer turned to appropriate combinations of cytotoxic chemotherapy. Today tamoxifen, a nonsteroidal antiestrogen (2), has proven to be effective in all stages of premenopausal and postmenopausal breast cancer, and several new endocrine strategies, including aromatase inhibitors, luteinizing-hormone releasing hormone (LHRH) superagonists, and a pure antiestrogen (fulvestrant), are now available for breast cancer treatment. Additionally, tamoxifen and raloxifene, a related compound, are used to reduce the risk of breast cancer and osteoporosis, respectively, in high-risk groups (3). Hormonal modulation and strategies to prevent the actions of estrogen in the breast are ubiquitous. However, with successful changes in treatment strategies comes the consequence of change. This minireview will describe the current strategies for the treatment and prevention of breast cancer and present emerging new concepts about the consequences of exhaustive antiestrogen treatment on therapeutic resistance.

Tools for making correct decisions regarding hormone therapy. part I: background and drugs

OBJECTIVE

To review existing scientific data related to the biology of estrogen in the aging process of women, and to understand the pharmacology, physiology, and diversity of sex hormones.

DESIGN

A MEDLINE computer search was performed to identify relevant articles.

RESULT(S)

Estrogen and progesterone have been prescribed for postmenopausal women over the last 60 years. Various formulations have had divergent properties, which are related to dissimilarities in the molecule structure, metabolism, plasma carrier, distribution, receptor binding, and the specific localizations of the different receptors in the various organs.

CONCLUSION(S)

Extensive data are available on the various characteristics of sex-hormone formulations, which are related to clinical consequences. The drugs and means of application have resulted in fundamental differences in activity, such as variance between oral and transdermal applications resulting in different forms of liver involvement. This information could assist in understanding why certain formulations may either prove harmful or beneficial to specific women.

Predicting pharmacophore signals for post-coital antifertility activity of 1-trifluoromethyl-1,2,2-triphenylethylene derivatives: a statistical approximation using E-state index

Considering the worth of developing non-steroidal estrogen analogues, the present research explores the pharmacophores of 1-trifluoromethyl-1,2,2-triphenylethylenes (Fig. 1) for post-coital antifertility activity using electrotopological state atom (E-state) index. The study shows the efficacy of E-state index in developing statistically acceptable model, which explains the electronic environment and topological states of different atoms in a molecule. The exploration concluded that phenyl ring attached to an ethylenic moiety, para substitution by nucleophilic group on the phenyl ring and presence of strong electronegative group as the 4th substituent on the 1st carbon of the ethylenic moiety might be crucial for activity.

Dietary lignins are precursors of mammalian lignans in rats

The mammalian lignans enterolactone (ENL) and enterodiol, commonly found in human plasma and urine, are phytoestrogens that may contribute to the prevention of breast cancer and coronary heart disease. They are formed by the conversion of dietary precursors such as secoisolariciresinol and matairesinol lignans by the colonic microflora. The identification of lignins, cell-wall polymers structurally related to lignans, as precursors of mammalian lignans is reported here for the first time. In study 1, rats were fed rye or wheat bran (15% diet) for 5 d. Untreated brans and brans extracted with solvents to remove lignans were compared. ENL was estimated in urine samples collected for 24 h by time-resolved fluoroimmunoassay. ENL urinary excretion was reduced from 18.6 to 5.3 nmol/d (n=8; P<0.001) when lignans were removed from rye bran and from 30.5 to 6.2 nmol/d (P<0.001) when they were removed from wheat bran. These results suggest that lignins, embedded in the cell wall and retained in the bran during solvent extraction, account for 26-32% of the ENL formed from cereal brans. In study 2, rats were fed a deuterated synthetic lignin (0.2% diet) together with wheat bran (15%) for 3 d. The detection of deuterated ENL by LC-tandem MS in urine (20 nmol/d) clearly confirms the conversion of lignin into mammalian lignans. More research is warranted to determine the bioavailability of lignins in the human diet.

Antidepressant-like effect of different estrogenic compounds in the forced swimming test

The present study evaluated the possible antidepressant-like action of the natural estrogen 17beta-estradiol (E(2), 2.5-10 microg/rat), the synthetic steroidal estrogen ethinyl-estradiol (EE(2), 1.25-10.0 microg/rat), and the nonsteroidal synthetic estrogen, diethyl-stilbestrol (DES, 0.25-1.0 mg/rat) in ovariectomized adult female Wistar rats using the forced swimming test (FST). The behavioral profile induced by the estrogens was compared with that induced by the antidepressants fluoxetine (FLX, 2.5-10 mg/kg) and desipramine (DMI, 2.5-10 mg/kg). In addition, the temporal course of the antidepressant-like action of the estrogenic compounds was analyzed. FLX and DMI induced an antidepressant-like effect characterized by a reduced immobility and increased swimming for FLX and decreased immobility and increased climbing for DMI. Both E(2) and EE(2) produced a decrease in immobility and an increase in swimming, suggesting an antidepressant-like action. DES did not affect the responses in this animal model of depression at any dose tested. The time course analysis of the actions of E(2) (10 microg/rat) and EE(2) (5 microg/rat) showed that both compounds induced an antidepressant-like effect observed 1 h after their injection lasting for 2-3 days.

Problems for risk assessment of endocrine-active estrogenic compounds

Estrogenic industrial compounds such as bisphenol A (BPA) and nonylphenol typically bind estrogen receptor (ER) alpha and ERBeta and induce transactivation of estrogen-responsive genes/reporter genes, but their potencies are usually greater than or equal to 1,000-fold lower than observed for 17Beta-estradiol. Risk assessment of estrogenic compounds on the basis of their potencies in simple reporter gene or binding assays may be inappropriate. For example, selective ER modulators (SERMs) represent another class of synthetic estrogens being developed for treatment of hormone-dependent problems. SERMs differentially activate wild-type ERalpha and variant forms expressing activation function 1 (ER-AF1) and AF2 (ER-AF2) in human HepG2 hepatoma cells transfected with an estrogen-responsive complement C3 promoter-luciferase construct, and these in vitro differences reflect their unique in vivo biologies. The HepG2 cell assay has also been used in our laboratories to investigate the estrogenic activities of the following structurally diverse synthetic and phytoestrogens: 4 -hydroxytamoxifen; BPA; 2 ,4 ,6 -trichloro-4-biphenylol; 2 ,3 ,4 ,5 -tetrachloro-4-biphenylol; p-t-octylphenol; p-nonylphenol; naringenin; kepone; resveratrol; and 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane. The results show that synthetic and phytoestrogens are weakly estrogenic but induce distinct patterns of ER agonist/antagonist activities that are cell context- and promoter-dependent, suggesting that these compounds will induce tissue-specific (in vivo(ER agonist or antagonist activities. These results suggest that other receptors, such as the aryl hydrocarbon receptor, that also bind structurally diverse ligands may exhibit unique responses in vivo that are not predicted by standard in vitro bioassays.

Flavonoids and steroid hormone-dependent cancers

Steroid-hormone dependent cancers, including those of the breast, prostate and colon, are leading causes of morbidity and mortality in western countries. In rural Asian areas, these diseases are relatively uncommon. Dietary factors, including low consumption of fruit, vegetables and soy in the west have been shown in various epidemiologic studies as reasons for these differences. This review discusses flavonoids, one component of these plant foods that is being investigated for their role in chemoprevention. Epidemiological, in vitro, animal and human studies shall be explored to look at mechanisms involved, including steroid hormone activity, effects on cell growth, antioxidant activities, inhibition of chemical carcinogenesis and influences on modulators of cancer risk. Although the in vitro and animal models point to several pathways by which flavonoids may reduce incidence of these cancers, the clinical data are still relatively lacking. More research is needed to determine how best to use foods containing these compounds to reduce steroid hormone-dependent cancer risk.

Mammalian lignan formation in rats fed a wheat bran diet

The dietary origin of lignan phytoestrogens is still poorly understood more than 20 years after their discovery in human urine. Their level in urine has been associated with the consumption of dietary fiber. This paper reports the study of the excretion of enterolactone, assayed by a time-resolved fluoroimmunoassay, in rats fed a diet supplemented with 15% wheat bran, one of the main sources of fiber in Western countries. Enterolactone excretion regularly increased during the two weeks of the diet to reach a value of 45 nmol/day. The level of excretion also increased upon preadaptation to ferulic acid, structurally related to secoisolariciresinol, an established precursor of enterolactone in flaxseeds, and decreased upon preadaptation to potato starch rich in fiber. These results show that the formation of lignans from wheat bran is influenced by the diet, possibly because of an adaptation of the colonic microflora.