Pure antiestrogen RU 58668-loaded nanospheres: morphology, cell activity and toxicity studies

Nanospheres (NS) formulated using biodegradable and biocompatible polymers, poly(D,L-lactide-co-glycolide) (PLGA), poly(D,L-lactide) (PLA) and poly(epsilon-caprolactone) (PCL), loaded with the pure anti-estrogen RU 58668 (RU), a promising estrogen-dependent anticancer agent, have been prepared. They all possess a small size compatible with an intratumoral extravasation behavior and their pegylation reduce significantly their zeta potential. Characterization by freeze fracture electron microscopy have shown that NS are spheric particles with a size ranging between 30 and 50nm and a tendency to agglomerate which is reduced by polyethylene glycol (PEG) grafting. PEG-grafted NS are all non-toxic as revealed by cell viability assay. A specific cellular model has been used to evaluate not only the release extent of the drug but also its biological activity. All formulations tested showed that they release slowly RU as measured by the delayed ability of RU to inhibit estrogen-induced transcription in human breast cancer cells and that they possess only a small amount of surface adsorbed RU.

All trans-retinoic acid acts synergistically with hydroxytamoxifen and transforming-growth factor beta to stimulate apoptosis in MCF-7 breast cancer cells

The anti-estrogen 4-hydroxytamoxifen (TAM) and vitamin A-related compounds, the retinoids, in combination act synergistically to inhibit growth of breast cancer cells in vitro and in vivo. To clarify the mechanism of this synergism, the effect of TAM and all trans-retinoic acid (AT) on proliferation of MCF-7 breast cancer cells was studied in vitro. TAM and AT acted synergistically to cause a time-dependent and dose-dependent inhibition of MCF-7 cell growth. In a temporally related manner, TAM+AT acted synergistically to downregulate Bcl-2 mRNA and Bcl-2 protein expression, and to stimulate apoptosis. TAM and AT each blocked cell cycle progression throughout 7 days of treatment but without any synergistic or additive effect on this process, indicating a selective synergism for apoptosis. The negative growth factor-transforming growth factor beta (TGFbeta) is secreted by these cells and was studied as a potential mediator of the synergistic effects of TAM+AT on apoptosis. TAM+AT acted synergistically to induce a fivefold increase in TGFbeta1 secretion over 72 h. TGFbeta1 alone had no apoptotic effects on these cells; however, TGFbeta1 in combination with AT acted synergistically to inhibit growth, to downregulate Bcl-2 mRNA and Bcl-2 protein expression, and to stimulate apoptosis of these cells in a manner comparable with that noted for TAM+AT. The synergism of both TAM+AT and TGFbeta1+AT for apoptosis was suppressed by estradiol. Co-incubation of TAM+AT with anti-TGFbeta antibody did not block down-regulation of Bcl-2 protein expression or stimulation of apoptosis. The synergistic effects of TAM+AT on apoptosis therefore occur independently of TGFbeta, although TGFbeta may interact with AT in a novel manner to provide another important anti-proliferative mechanism for breast cancer cells.

Tibolone and its metabolites acutely relax rabbit coronary arteries in vitro

OBJECTIVES

To compare the acute effects of estradiol, tibolone and its metabolites on coronary arteries in vitro and to investigate possible vascular mechanisms.

METHODS

Coronary artery ring segments from female rabbits were mounted in myographs for isometric tension recordings. Concentration-response curves to tibolone, 3 alpha-OH-tibolone, 3 beta-OH-tibolone, Delta 4-isomer and 17 beta-estradiol were obtained after precontraction with potassium 30 mmol/l and after addition of N omega-nitro-l-arginine methyl ester 10(-4) mol/l (l-NAME, an inhibitor of endothelial nitric oxide (NO) synthase) or tetraethylammonium chloride 10(-2) mol/l (TEA, an unspecific inhibitor of potassium channels). The effects of the different substances to calcium concentration-response curves were evaluated. Responses are expressed as maximal contraction (E max), concentration giving half maximal contraction (log EC50) or area under curve (AUC).

RESULTS

Tibolone and its metabolites induced a concentration-dependent vasodilatation comparable to that of 17 beta-estradiol with the rank of potency: 3 beta-OH-tibolone approximately = to tibolone>3 alpha-OH-tibolone>Delta 4-isomer (ANOVA). l-NAME partly inhibited the relaxation to all substances. TEA induced a slight rightward shift of the relaxation to 3 alpha-OH-tibolone (log EC50: -5.05 versus -5.20; P<0.05; Student's t-test), but not to the other substances. Calcium concentration-dependent contraction curves were inhibited by all substances compared to controls (AUC, P<0.05, ANOVA).

CONCLUSIONS

Our data indicate that the acute relaxation induced by tibolone and its metabolites in coronary arteries in vitro are probably mediated by endothelium independent inhibition of calcium channels but may also involve an endothelium-dependent mechanism via nitric oxide. The effect of tibolone is comparable to that of 17 beta-estradiol in this set-up.

Kinetic studies of the radical-scavenging activity of estrogens and antiestrogens

Quinoids, quinoid radicals and phenoxyl radicals formed from estrogens (estrone; diethylstilbestrol, DES) and antiestrogens (tamoxifen; toremifene) may be responsible for adverse effects such as carcinogenesis. The radical-scavenging activity of estrogens and antiestrogens was determined quantitatively by the induction period method for the polymerization of methyl methacrylate initiated by thermal decomposition of 2,2'-azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO) under nearly anaerobic conditions. The inhibition rate constant (k(inh), x10(-3) M(-1)s(-1)) for estrone, DES, tamoxifen, toremifene and 2,6-di-t-butyl-4-methyphenol (BHT) was 1-3, 2-4, 6-12, 6-13 and 1-2, respectively. The k(inh) for antiestrogens was two-fold greater than that for estrogens or BHT. In contrast, the stoichiometric factor (n, number of free radicals trapped by one mole of antioxidant moiety) for estrone, DES, tamoxifen, toremifene and BHT was 1.2-1.5, 1.8-2.4, 0.5-0.9, 0.4- 0.5 and 1.5-1.9, respectively. The fully oxidized n values for estrone, DES and BHT would be 2, whereas that for antiestrogens would be 1. However, the n values for estrone and antiestrogens were markedly less than 2 and 1, respectively, suggesting a complex oxidation process resulting in the formation of quinoids, quinoid radicals and phenoxyl radicals during the induction period.

The CXCL12-CXCR4 chemotactic pathway as a target of adjuvant breast cancer therapies

Dose-dense adjuvant breast cancer chemotherapy is a new treatment strategy that aims to improve tumour control by using more frequent cytotoxic dosing together with continuous granulocyte colony-stimulating factor (G-CSF) to minimize neutropaenia. In addition to stimulating neutrophil proliferation, G-CSF mobilizes neutrophils from the bone marrow through proteolytic disruption of the chemokine receptor CXCR4 and its chemotactic ligand CXCL12. As breast cancers also express CXCR4 and oestrogen induces CXCL12, the success of dose-dense treatment could partly reflect inhibition of CXCR4-dependent micrometastatic homing and/or paracrine survival, and suggests a benefit of adjuvant oestrogen suppression for patients with oestrogen-receptor-negative, CXCR4-positive disease.

Transvaginal ultrasonographic assessment of the endometrium in asymptomatic, postmenopausal women using different HRT regimens containing tibolone or estrogen

OBJECTIVE

To assess the effects of hormone replacement therapy (HRT) on endometrial thickness as measured by transvaginal ultrasonography in asymptomatic, postmenopausal women.

STUDY DESIGN

Between 1997 and 2001, 307 women who had no risk factors for endometrial cancer or abnormal vaginal bleeding were enrolled in a study. Patients received 1 of the following HRT modalities: (1) oral equine HRT modalities: (1) oral equine estrogen, (2) oral 17beta-estrogen, (3) transdermal 17beta-estrogen, or (4) oral tibolone. All women taking estrogens were also taking a progestin. Only the patients with endometrial thickness >7 mm underwent endometrial biopsy while taking HRT.

RESULTS

Although we observed an increase in serum estrogen levels as compared to the levels before tibolone therapy, changes in endometrial thickness were not statistically significant in patients taking tibolone.

CONCLUSION

Endometrial thickness with tibolone closely mimics the naturally atrophic postmenopausal state. Thus, tibolone is suggested for those postmenopausal women who have concerns about HRT.

Does tibolone affect serum leptin levels and body weight in postmenopausal women?

OBJECTIVES

Leptin has a significant role in body weight regulation and energy balance. We examined the effect of tibolone on the body weight and serum leptin levels in postmenopausal women.

STUDY DESIGN

Twenty women (aged 43-60 years) participated in this prospective study. All women in this study protocol received 2.5 mg/day of tibolone. Absolute and body mass index (BMI)-corrected serum leptin concentrations and BMI values were measured at baseline, after 3 months, and after 6 months of the tibolone therapy.

RESULTS

Tibolone did not affect absolute and BMI-corrected serum leptin levels, and BMI values during the treatment. A significant linear correlation between BMI values and serum leptin levels was observed (p<0.05, r=0.67).

CONCLUSIONS

Tibolone seems not to affect serum leptin levels, body weight and BMI values of postmenopausal women. There is a significant correlation between serum leptin levels and BMI values.

Effects of amitraz on cytochrome P450-dependent monooxygenases and estrogenic activity in MCF-7 human breast cancer cells and immature female rats

This study investigated the ability of amitraz, a formamidine insecticide, to induce cytochrome P450-dependent monooxygenases and to disrupt estrogenic activity in human breast cancer MCF-7 cells and immature female rats. In MCF-7 cells, treatment with 10 microM amitraz for 24 h increased 7-ethoxyresorufin O-deethylase activity in cell homogenate. Treatment of MCF-7 cells with 1 and 10 microM amitraz for 3 h replaced previously bound [(3)H]17beta-estradiol (E(2)) from estrogen receptors. Treatment with 0.1 and 1 microM amitraz for 2 days inhibited [(3)H]thymidine incorporation into the DNA of MCF-7 cells while the inhibition was blocked in cells co-treated with 1 nM E(2) and amitraz. In immature female rats, treatment with 50 mg/kg amitraz intraperitoneally for 3 days increased cytochrome P450 content, 7-ethoxyresorufin, methoxyresorufin and pentoxyresorufin O-dealkylases, and benzo[a]pyrene hydroxylase activities in liver microsomes. The results of immunoblot analysis revealed that amitraz induced liver microsomal CYP1A1/2, 2B1/2B2, and 3A proteins. Treatment with 10 and 25 mg/kg amitraz for 3 days dose-dependently decreased uterine weight and peroxidase activity in immature female rats while the decreases were blocked in rats co-treated with 10 microg/kg E(2) and 10 or 25 mg/kg amitraz. These in vitro and in vivo findings suggest that amitraz induces multiple forms of P450 and exerts weak antiestrogenic activity.

Endocrinology and hormone therapy in breast cancer: aromatase inhibitors versus antioestrogens

Endocrine therapies act by either blocking or downregulating the oestrogen receptor or by reducing oestrogen concentrations around and within the cancer cell. In postmenopausal women, oestrogen suppression is achieved by inhibition of the enzyme aromatase by aromatase inhibitors (AIs). Modern AIs (anastrozole, letrozole and exemestane) are more potent than earlier ones and suppress oestradiol levels in plasma to virtually undetectable concentrations. Recent comparisons of AIs with the most widely used oestrogen receptor blocking drug tamoxifen indicate that, in general, AIs result in increased response rates and greater durations of response. Here, we summarize data supporting the difference between the two types of treatment and attempt to account for the underlying mechanisms that favour AIs.

Benzoxepin-Derived Estrogen Receptor Modulators: A Novel Molecular Scaffold for the Estrogen Receptor

We present and examine the efficacy of a novel benzoxepin-based scaffold for modulation of the human estrogen receptor. Receptor tolerance of this new molecular scaffold is examined through presentation of experimentally determined antiproliferative effects on human MCF-7 breast tumor cells and measured binding affinities. The effect of functional group substitution on the benzoxepin scaffold is explored through a brief computational structure-activity relationship investigation with molecular simulation.

Thérapeutiques hormonales de la ménopause : impact sur la densité mammographique

Whether qualitative-classified or quantitative-measured, mammographic density, which changes according to physiological variations, is nowadays commonly recognized as a factor increasing the relative risk of breast cancer. The present review aims at clarifying the impact of menopausal hormonal therapies on mammographic density. Neither Tibolone nor Raloxifene seem to have any negative impact on mammographic density. In some instances, oestrogens-progestin hormonal replacement therapies may increase mammographic density and thus reduce sensitivity and specificity of screening mammograms. Shorter intervals between mammographies combined with additional physical examination and breast ultrasonography appear to be the best way to reduce interval cancers.

17β-Estradiol Reduces Cardiomyocyte Apoptosis In Vivo and In Vitro via Activation of Phospho-Inositide-3 Kinase/Akt Signaling

Female gender and estrogen-replacement therapy in postmenopausal women are associated with improved heart failure survival, and physiological replacement of 17β-estradiol (E2) reduces infarct size and cardiomyocyte apoptosis in animal models of myocardial infarction (MI). Here, we characterize the molecular mechanisms of E2 effects on cardiomyocyte survival in vivo and in vitro. Ovariectomized female mice were treated with placebo or physiological E2 replacement, followed by coronary artery ligation (placebo-MI or E2-MI) or sham operation (sham) and hearts were harvested 6, 24, and 72 hours later. After MI, E2 replacement significantly increased activation of the prosurvival kinase, Akt, and decreased cardiomyocyte apoptosis assessed by terminal deoxynucleotidyltransferase dUTP nick-end labeling (TUNEL) staining and caspase 3 activation. In vitro, E2 at 1 or 10 nmol/L caused a rapid 2.7-fold increase in Akt phosphorylation and a decrease in apoptosis as measured by TUNEL staining, caspase 3 activation, and DNA laddering in cultured neonatal rat cardiomyocytes. The E2-mediated reduction in apoptosis was reversed by an estrogen receptor (ER) antagonist, ICI 182,780, and by phospho-inositide-3 kinase inhibitors, LY294002 and Wortmannin. Overexpression of a dominant negative-Akt construct also blocked E2-mediated reduction in cardiomyocyte apoptosis. These data show that E2 reduces cardiomyocyte apoptosis in vivo and in vitro by ER- and phospho-inositide-3 kinase–Akt–dependent pathways and support the relevance of these pathways in the observed estrogen-mediated reduction in myocardial injury.

A comparative study of breast cell proliferation during hormone replacement therapy: effects of tibolon and continuous combined estrogen-progestogen treatment

OBJECTIVE

To use the fine-needle aspiration (FNA) biopsy technique to compare the effects of tibolone, conventional hormone replacement therapy (HRT) and placebo on breast cell proliferation in postmenopausal women.

METHODS

A total of 91 women were randomized to receive either estradiol 2 mg plus norethisterone acetate 1 mg (E2/NETA), tibolone 2.5 mg or placebo for 6 months in a prospective double-blind trial. Breast cell proliferation was assessed using the Ki-67/MIB-1 monoclonal antibody.

RESULTS

From the 83 women who completed the study, a total of 166 FNA biopsies were obtained, and 118 of these aspirates (71%) were evaluable for MIB-1 content. Women with assessable biopsies were younger, had a lower body mass index, and had higher levels of sex hormone binding globulin and insulin-like growth factor-I than women in whom the cell yield was insufficient. During treatment with E2/NETA, there was an increase in proliferation (percentage of MIB-1) from a mean value of 2.2 to 6.4% after 6 months (p < 0.01). No significant changes were recorded during treatment with tibolone or placebo. There was a negative association between proliferation and serum levels of total (r(s) = -0.29, p < 0.05) and free (rs = -0.31, p < 0.03) testosterone.

CONCLUSIONS

Tibolone seems to have little influence on breast cell proliferation.

Tibolone Is Metabolized by the 3α/3β-Hydroxysteroid Dehydrogenase Activities of the Four Human Isozymes of the Aldo-Keto Reductase 1C Subfamily: Inversion of Stereospecificity with a Δ5(10)-3-Ketosteroid

Tibolone is used to treat climacteric complaints and prevent osteoporosis. These beneficial effects are exerted via its 3alpha-and 3beta-hydroxymetabolites. Undesirable stimulation of the breast and endometrium is not apparent. Endometrial stimulation is prevented by the progestogenic activity of its Delta4-ene metabolite. The enzymes responsible for the formation of these active metabolites are unknown. Human aldo-keto reductase (AKR)1C isoforms have been shown to act as 3alpha/3beta-hydroxysteroid dehydrogenases (HSDs) on 5alpha-dihydrotestosterone (5alpha-DHT). We show that AKR1Cs also efficiently catalyze the reduction of the Delta(5(10))-3-ketosteroid tibolone to yield 3alpha- and 3beta-hydroxytibolone. Homogeneous recombinant AKR1C1, AKR1C3, and AKR1C4 gave similar catalytic profiles to those observed with 5alpha-DHT. AKR1C1 catalyzed exclusively the formation of 3beta-hydroxytibolone, AKR1C3 showed weak 3beta/3alpha-HSD activity, and AKR1C4 acted predominantly as a 3alpha-HSD. Whereas AKR1C2 acted as a 3alpha-HSD toward 5alpha-DHT, it functioned exclusively as a 3beta-HSD on tibolone. Furthermore, strong substrate inhibition was observed for the AKR1C2 catalyzed reduction of tibolone. Using NAD+, the 3-hydroxymetabolites were efficiently oxidized by homogeneous recombinant AKR1C2 and AKR1C4. However, because of potent inhibition of this activity by NADPH, AKR1Cs will probably act only as 3-ketosteroid reductases in vivo. Molecular docking simulations using crystal structures of AKR1C1 and AKR1C2 explained why AKR1C2 inverted its stereospecificity from a 3alpha-HSD with 5alpha-DHT to a 3beta-HSD with tibolone. The preference for AKR1C1 and AKR1C2 to form 3beta-hydroxytibolone, and the preference of the liver-specific AKR1C4 to form 3alpha-hydroxytibolone, may explain why 3beta-hydroxytibolone is the major metabolite in human target tissues and why 3alpha-hydroxytibolone is the major circulating metabolite.

Non-classical regulation of estrogen receptor-alpha by ICI182,780

Estrogen receptor-alpha (ER alpha) regulates transcription through a number of molecular mechanisms. Two mechanisms by which ER alpha acts directly in the nucleus have emerged: (1) in classical ER alpha action, estrogen-bound receptor binds estrogen response elements (ERE) and regulates promoters by recruiting coactivators or corepressors to DNA; (2) non-classical action is not dependent on ER alpha binding to EREs; its mechanism is not as clearly defined as classical action. In many instances, non-classical action is mediated by tethering of ER alpha to other DNA-binding proteins, facilitating recruitment of coregulators to transcription regulatory sequences. In some cell types, non-classical stimulation can be enhanced by antagonists and repressed by agonists of ER alpha. Here, we show that non-classical action of ER alpha in 293 cells occurs in a wide range of enhancers and enhancer binding proteins. ER alpha stimulates AP-1 elements, cyclic AMP response elements (CRE), and serum response elements (SRE) in the presence of the antiestrogen ICI182,780. Further, in the presence of ICI182,780, ER alpha stimulates activation domains of Jun, ATF-2, Elk, and CRE-binding protein (CREB). Non-classical ER alpha regulation described here does not appear to be sensitive to point mutations which affect classical and tethered ER alpha action; moreover, in our experiments, non-classical action is uniquely sensitive to nuclear transport inhibition by leptomycin B. Because ICI182,780 appears to affect multiple and diverse transcriptional systems, our results are likely explained by ER alpha-dependent modulation of common components of the transcriptional machinery and may not be completely explained by tethering of ER alpha to specific transcription factors.

Histone deacetylase inhibition and estrogen signalling in human breast cancer cells

Estrogens are steroid hormones, which act through specific nuclear estrogen receptors (ERalpha and ERbeta) and are important regulators of breast cancer growth. These receptors control gene expression by recruiting transcriptional cofactors that exhibit various enzymatic activities such as histone acetyltransferase or histone deacetylase (HDAC) which target histone as well as non-histone substrates. The ERalpha itself and some of the transcriptional regulators have been shown to be acetylated proteins. Research performed over the last decade has highlighted the role of HDAC inhibitors (HDACi) as modulators of transcriptional activity and as a new class of therapeutic agents. In human cancer cells, inhibition of HDACs controls the expression of the ERalpha gene and the transcriptional activity in response to partial antiestrogens such as 4-hydroxytamoxifen. Various HDACi strongly inhibit breast cancer cell proliferation and ERalpha-negative (ER-) appear less sensitive than ERalpha-positive (ER+) cell lines. p21WAF1/CIP1 gene expression, in relation with ERalpha levels, could play a role in this differential response of breast cancer cells to hyperacetylating agents.

Apoptosis in cervical cancer cells: implications for adjunct anti-estrogen therapy for cervical cancer

BACKGROUND

Many tumors show dependence on estrogen for growth and establishment of drug resistance. We examined the effects of estrogen on cervical cancer cells exposed to apoptotic agents including drugs used for treatment.

MATERIALS AND METHODS

We tested the effect of estradiol on apoptosis in three cervical cancer cell lines. Apoptosis was measured by endonucleolytic degradation of DNA. Bcl-2 was measured by Western analysis.

RESULTS

Estradiol reduced the percentage of cells undergoing apoptosis after exposure to the DNA-damaging agents UVB, mitomycin-C and cisplatin. Protection against taxol-induced apoptosis was marginal. Protection was independent of HPV gene expression, and not specific to apoptosis induced by DNA damage, since estradiol significantly reduced the number of apoptotic cells produced after exposure to indole-3-carbinol (I3C), a non-genotoxic phytochemical effective in preventing HPV-induced tumors. Higher concentrations of I3C overcame the anti-apoptotic effect of estradiol. Treatment with I3C resulted in loss of the survival protein Bcl-2, and estradiol partially reversed this effect.

CONCLUSION

Estrogen protects cervical cancer cells treated with DNA-damaging agents; UVB, mitomycin-C and cisplatin, from apoptotic death. For I3C, which induces apoptosis and is anti-estrogenic, the amount of apoptosis versus survival and the level of Bcl-2 depend on the I3C/estradiol ratio.

Differential and Opposing Regulation of PAI-1 Promoter Activity by Estrogen Receptor α and Estrogen Receptor β in Endothelial Cells

To investigate the molecular mechanisms involved in the estrogen-dependent control of plasminogen activator inhibitor-1 (PAI-1) gene expression in vascular cells, we compared the transactivation properties of estrogen receptors (ERalpha and ERbeta) in regulating the activity of a human PAI-1 promoter reporter construct in transfected bovine aortic endothelial cells (BAECs). ERalpha increased PAI-1 promoter activity in BAECs by an estrogen-dependent mechanism, whereas ERbeta suppressed PAI-1 promoter activity by an estrogen-independent mechanism. The suppressive activity of ERbeta was dominant over the inductive activity of ERalpha. Mutation of a putative estrogen response element (ERE) located at position -427 in the proximal promoter abolished the ERalpha action without influencing the suppressive effects of ERbeta. Mutation of either AP1-like site did not eliminate the ERalpha or ERbeta actions at the PAI-1 promoter, suggesting that other promoter elements are involved in these responses. These mutations significantly reduced the -3.4kbp PAI-1 promoter response to serum. We concluded that ERalpha and ERbeta exert differential effects on the PAI-1 promoter activity in transfected BAECs. ERalpha activated the PAI-1 promoter through a proximal ERE (-427) and possibly additional EREs located within the PAI-1 promoter, whereas ERbeta suppressed the promoter construct via an unidentified mechanism. This is the first demonstration of the differential regulation of a vascular gene promoter by ERalpha and ERbeta.

Novel Approach for Evaluation of Estrogenic and Anti-Estrogenic Activities of Genistein and Daidzein using B16 Melanoma Cells and Dendricity Assay

The effects of soy isoflavones, genistein and daidzein, which exhibit estrogenic, anti-estrogenic and/or tyrosine kinase inhibitory activity, on the dendritic morphology of B16 mouse melanoma cells were quantitatively evaluated and compared with those of 17 beta-estradiol (Est) and tyrphostin, a tyrosine kinase inhibitor. Dendricity was significantly stimulated in the order of Est >> genistein > daidzein = tyrphostin, but not by glycosides of genistein and daidzein. In competition experiments, Est counteracted the stimulatory activity of genistein and daidzein, but enhanced the activity of tyrphostin additively, suggesting that genistein and daidzein agonized Est. In addition, when the concentration ratios of genistein/Est and daidzein/Est were higher than 5000 and 50,000, respectively, genistein and daidzein agonized Est. In contrast, when the ratio of daidzein/Est was lower than 500, daidzein antagonized Est. Furthermore, genistein and daidzein competed with each other in stimulatory activity. These observations suggest that: 1) dendricity is stimulated by agonists (genistein and daidzein) of Est and tyrosine kinase inhibitors (genistein and tyrphostin), 2) the concentration ratio of isoflavone aglycone/Est is very important as one regulatory factor for estrogenic and/or anti-estrogenic activity, and 3) daidzein antagonizes not only Est but also genistein. It is concluded that a quantitative and simple dendricity assay using B16 mouse melanoma cells is available to evaluate estrogenic and anti-estrogenic activity in vitro.

Comparative assessment of the inhibition of recombinant human CYP19 (aromatase) by azoles used in agriculture and as drugs for humans

Azoles (imidazoles and triazoles) are used as antifungal agents in agriculture and in medicine, and also for antiestrogen therapy, e.g., for breast cancer treatment. Antifungal activity is based on inhibition of fungal CYP51 (lanosterol 14alpha-demethylase), and estrogen biosynthesis reduction is due to azole inhibition of CYP19 (aromatase). Inhibition of aromatase by antifungal agents is usually an unwanted side effect and may cause endocrine disruption. A fluorimetric assay based on human recombinant CYP19 enzyme with dibenzylfluorescein as a substrate was used to compare the inhibitory potency of 22 azole compounds. Dose responses were established and duplicate datasets were analyzed with a nonlinear mixed-effects model with cumulative normal distribution for the logarithm of concentration. IC50 values (50% inhibitory concentration) of 13 fungicides used in agriculture ranged more than 700-fold, starting from 0.047 microM. The potency of seven human drugs spanned more than 7000-fold, starting from 0.019 microM. Most potent fungicides included prochloraz, flusilazole, and imazalil, and most potent medicinal antifungals were bifonazole, miconazole, and clotrimazole. These in vitro data indicate that the top-ranking azoles used as antifungal agents or drugs are as potent inhibitors of aromatase as are antiestrogen therapeutics used to treat breast cancer. These putative effects of azole agents and drugs on steroid biosynthesis and sex hormone balance should be considered when used in human subjects and also in wildlife exposed to azole fungicides used in agriculture.

Direct action of estradiol on gonadotropin-releasing hormone-1 neuronal activity via a transcription-dependent mechanism

Pulsatile secretion of gonadotropin-releasing hormone-1 (GnRH-1) is essential for reproduction. GnRH-1 induces gonadotropin release and is regulated by 17beta-estradiol (E2). Although a subpopulation of GnRH-1 neurons expresses estrogen receptor (ER) beta, it is unclear whether E2 acts directly on GnRH-1 neurons or indirectly through interneuronal connections. To test the hypothesis that E2 acts directly on GnRH-1 neurons to regulate neuronal activity, we used calcium imaging to monitor intracellular calcium oscillations in GnRH-1 neurons maintained in nasal explants. TTX was used to minimize synaptic input from other cells. Consistent with previous studies, TTX reduced the activity of individual GnRH-1 neurons to a basal level, while the population of cells maintained synchronized calcium oscillations. Exposure of GnRH-1 cells to TTX plus E2 increased the number of calcium peaks/cell, percentage of cells with > or =10 peaks, mean peak amplitude, and percentage of cells that contributed to each calcium pulse in explants maintained in vitro for 7 d (7 div) compared with TTX alone. These effects were induced within 30 min and were not mimicked by 17alpha-estradiol, E2 conjugated to BSA (which does not cross the plasma membrane), or seen at 21 div, when the percentage of GnRH-1 cells expressing ERbeta transcripts declines. In addition, these effects were inhibited by the ER antagonist ICI 182,780 and prevented by inhibition of gene transcription. These data suggest that, via ERbeta, E2 can rapidly act as a hormone-activated transcription complex and are the first to show that E2 directly increases GnRH-1 neuronal activity and synchronization.

Inhibition of estrogen receptor alpha-mediated transcription by antiestrogenic 1,1-dichloro-2,2,3-triarylcyclopropanes

A novel class of pure antiestrogens, 1,1-dichloro-2,2,3-triarylcyclopropanes (DTACs), lack estrogenic activity in a mouse uterotrophic assay and inhibit the growth of estrogen-sensitive MCF-7 breast cancer cells (Day et al., 1991). Here, reporter assays were used to evaluate the effects of the DTACs on estrogen receptor alpha (ERalpha)-mediated transcription from either classic estrogen-response elements (EREs) or nonclassic AP-1 elements. Among the DTACs tested, only the compounds with smaller aromatic substituents, BDRM72 and BDRM81, displayed weak agonist activity on EREs. Their activity was less than that observed for the ER partial agonist, 4-hydroxytamoxifen (ZOHT). In competition experiments, the DTACs blocked estradiol-stimulated transcription from an ERE in a dose-dependent manner and were more effective inhibitors than ZOHT. Each of the DTACs was significantly less active than ZOHT or the pure antiestrogen ICI 182,780 (faslodex) in stimulating transcription from nonclassic AP-1 elements in the presence of ERalpha. DTACs did not modulate either basal or TPA (12-O-tetradecanoylphorbol-13-acetate)-stimulated transcription from an AP-1 element in the absence of ERalpha, indicating that they are not nonspecific inhibitors of transcription and that ERalpha is the drug target. Glutathione S-transferase pull-down assays were used to examine whether DTACs alter the interaction between ERalpha and the p160 coactivator, GRIP1. BDRM35, which has the same dimethylaminomethoxy and phenolic moieties as ZOHT, reduced binding by more than 50%. Thus, disruption of p160 coactivator recruitment by ERalpha may represent one mechanism by which DTACs function as antiestrogens. BDRM35 also suppresses estradiol induction of endogenous target genes c-myc and cyclin D1 in MCF-7 breast cancer cells.

Estrogen Responsiveness of IBEP-2, A New Human Cell Line Derived from Breast Carcinoma

IBEP-2, an established cell line recently derived from breast carcinoma, was characterized with regard to estrogen receptor (ER) expression, cell mitogenic response to estrogenic stimulation and sensitivity to antiestrogens. In addition, we examined ER modulation following binding of agonist and antagonists, and the ER-mediated induction of progesterone receptor (PgR). ER level in IBEP-2 cells, determined by enzyme-linked immunoassay (EIA), was slightly higher than that measured in MCF-7 cells (662 v.s. 595 fmol/mg protein). When tested on IBEP-2 and MCF-7, various agonists stimulated cell growth with EC50's reflecting different estrogenic potencies (E(2) approximately diethylstilbestrol > E(1) > genistein). IBEP-2 appeared slightly more sensitive than MCF-7, especially to E(2) (at least 4-fold difference between EC50 values). By contrast, IBEP-2 and MCF-7 were equally sensitive to the growth inhibitory effect of antiestrogens 4-hydroxy-tamoxifen (OH-Tam) and ICI 182,780. As revealed by immunoblotting and immunofluorescence using anti-ER alpha antibodies, ER expression in IBEP-2 cells was modulated by E(2) and estrogen antagonists like it has been shown in other ER-positive cell lines, that is, E(2) and ICI 182,780 caused ER downregulation, whereas OH-Tam induced ER accumulation. Ligand-induced downregulation of ER involved degradation in proteasomes, since it was suppressed by the proteasome inhibitor MG-132. Exposure of IBEP-2 cells to E(2) resulted in a marked (at least 25-fold) induction of PgR, documented by EIA, immunoblotting and immunofluorescence. PgR induction due to E(2) was not modified by MG-132. Interestingly, MG-132 alone produced an ER-independent increase of PgR expression. IBEP-2 might prove to be valuable to study ER-mediated induction of PgR.

Endometrial assessment in women using tibolone or placebo: 1-year randomized trial and 2-year observational study

OBJECTIVE

To assess the effects of tibolone on the endometrium of postmenopausal women.

DESIGN

A 1-year randomized, double-blind, placebo-controlled clinical trial and a 2-year open clinical trial. The placebo-controlled trial included 40 participants: 20 in the placebo group and 20 in the tibolone group; in the open trial, 17 participants receiving tibolone were assessed over 24 months. Transvaginal ultrasonography was carried out to assess endometrial thickness, and endometrial appearance was assessed on hysteroscopy. In addition, endometrial samples were submitted to histological examination. The occurrence of uterine bleeding and other adverse effects was also assessed.

RESULTS

Results suggest that tibolone does not exert a stimulatory effect on the endometrium: unaltered endometrial thickness, atrophic appearance of most endometria on hysteroscopy, and endometrial histology classified as atrophic, hypotrophic with incipient secretion, or hypotrophic with weak proliferation (one case). Tibolone was effective in the treatment of climacteric symptoms, and only 8.7% of the participants presented uterine bleeding during treatment.

CONCLUSIONS

Tibolone seems to be an effective option for the treatment of climacteric symptoms in postmenopausal women, especially in women who do not want to experience uterine bleeding again.

Antiestrogens Induce Growth Inhibition by Sequential Activation of p38 Mitogen-Activated Protein Kinase and Transforming Growth Factor-β Pathways in Human Breast Cancer Cells

Antiestrogens are successfully used in the treatment of breast cancer. The purpose of this study was to investigate the role of different signal transduction pathways in antiestrogen-induced growth inhibition to gain insights into mechanisms of antiestrogen resistance. We used specific MAPK inhibitors and MCF-7 carcinoma cells as a model to demonstrate that p38 MAPK is an important mediator of antiestrogen growth inhibition in breast cancer. A kinase assay showed that antiestrogens (4-hydroxytamoxifen and ICI 182.780) rapidly induce p38 activity. Overexpression of kinase-deficient mutants of p38 reduced the antiestrogen suppression of Cyclin A transcription. TGFbeta, a negative regulator of breast cancer cell growth, is induced by antiestrogens; therefore, activation of p38 could have been mediated by TGFbeta. We used a TGFbeta and antiestrogen-sensitive reporter gene assay to show that p38 activation precedes TGFbeta activation. These results were further confirmed by quantitative RT-PCR analysis of the antiestrogen-induced transcription of TGFbeta2 and TGFbeta receptor II. Inhibition of p38 reduced the induction of both genes. Finally, Western blot analysis shows that antiestrogens induce phosphorylation of Smad (mothers against decapentaplegic homolog) 2 via p38. Promoter assays with the Smad-dependent reporter p6SBE confirm participation of Smad3 and Smad4 in antiestrogen action. Taken together, our data delineate an antiestrogen signal transduction pathway involving sequential activation of p38 and TGFbeta pathways to mediate growth inhibition.