Selective oestrogen receptor modulators/new antioestrogens: a clinical perspective

Characterizing safety, toxicity, and breast cancer risk reduction using a long-term fulvestrant eluting implant

For individuals at high risk of developing breast cancer, interventions to mitigate this risk include surgical removal of their breasts and ovaries or five years treatment with the anti-estrogen tamoxifen or aromatase inhibitors. We hypothesized that a silicone based anti-estrogen-eluting implant placed within the breast would provide the risk reduction benefit of hormonal therapy, but without the adverse effects that limit compliance. To this end, we demonstrate that when placed adjacent to mammary tissue in the 7,12-dimethylbenz[a]anthracene-induced rat breast cancer model a fulvestrant-eluting implant delays breast cancer with minimal systemic exposure. Using adult female sheep, surgical placement of fulvestrant-eluting implants was safe and did not elicit significant breast tissue pathology when placed at the base of the udder for directed elution into the mammary tissue. At 30 days of elution, fulvestrant was found to penetrate mammary tissue forming a concentration gradient beyond 15 mm from the implant. Consistent with the small animal rat study, minimal systemic fulvestrant biodistribution was found. Together, these studies provide the proof of principle that a breast indwelling fulvestrant-eluting implant can reduce the risk of breast cancer and limit systemic exposure, while penetrating and distributing through breast tissue.

A long-term fulvestrant eluting implant is safe, non-toxic, and reduces the risk of breast cancer in in vivo models

For individuals at high risk of developing breast cancer, interventions to mitigate this risk include surgical removal of their breasts and ovaries or five years treatment with the anti-estrogen tamoxifen or aromatase inhibitors. We hypothesized that a silicone based anti-estrogen-eluting implant placed within the breast would provide the risk reduction benefit of hormonal therapy, but without the adverse effects that limit compliance. To this end, we demonstrate that when placed adjacent to mammary tissue in the DMBA-induced rat breast cancer model a fulvestrant-eluting implant delays breast cancer with minimal systemic exposure. Using adult female sheep, fulvestrant-eluting implants were found to be safe and non-toxic when placed at the base of the udder for directed elution into the mammary tissue. At 30 days of elution, fulvestrant was found to penetrate mammary tissue forming a concentration gradient beyond 15 mm from the implant. Consistent with the small animal rat study, minimal systemic fulvestrant biodistribution was found. Together, these studies provide the proof of principle that a breast indwelling fulvestrant-eluting implant can reduce the risk of breast cancer and limit systemic exposure, while penetrating and distributing through breast tissue.

Fulvestrant inhibits growth of triple negative breast cancer and synergizes with tamoxifen in ERα positive breast cancer by up-regulation of ERβ

The estrogen receptor-alpha (ERα) is used as a predictive marker for anti-estrogen therapy in breast cancer patients. In addition to aromatase inhibitors, ERα can be targeted at the receptor level using the receptor modulator tamoxifen or by the pure anti-estrogen fulvestrant. The role of the second ER, ER-beta (ERβ), as a therapeutic target or prognostic marker in breast cancer is still elusive. Hitherto, it is not known if ERα+/ERβ+ breast cancers would benefit from a treatment strategy combining tamoxifen and fulvestrant or if fulvestrant exert any therapeutic effects in ERα-/ERβ+ breast cancer. Here, we report that fulvestrant up-regulated ERβ in ERα+/ERβ+ breast cancer and in triple negative ERβ+ breast cancers (ERα-/ERβ+). In ERα+/ERβ+ breast cancer, a combination therapy of tamoxifen and fulvestrant significantly reduced tumor growth compared to either treatment alone both in vivo and in vitro. In ERα-/ERβ+ breast cancer fulvestrant had potent effects on cancer growth, in vivo as well as in vitro, and this effect was dependent on intrinsically expressed levels of ERβ. The role of ERβ was further confirmed in cells where ERβ was knocked-in or knocked-down. Inhibition of DNA methyltransferase (DNMT) increased the levels of ERβ and fulvestrant exerted similar potency on DNMT activity as the DNMT inhibitor decitabine. We conclude that fulvestrant may have therapeutic potential in additional groups of breast cancer patients; i) in ERα+/ERβ+ breast cancer where fulvestrant synergizes with tamoxifen and ii) in triple negative/ERβ+ breast cancer patients, a subgroup of breast cancer patients with poor prognosis.

Selective oestrogen receptor antagonists inhibit oesophageal cancer cell proliferation in vitro

BACKGROUND

Oestrogen receptors (ER) have a well-established role to the initiation, progression and regulation of responses to treatment of breast, prostate, and lung cancers. Previous data indicates altered ER expression in oesophageal cancers (OC). However the role of ER subtypes and ER specific inhibitors in the regulation of OC progression remains unclear. This study sought to assess levels of ERα and ERβ in OC. The effects of highly selective ER antagonists on cell proliferation and apoptosis in two OC adenocarcinoma cell lines was also studied.

METHODS

ERα and ERβ expression profiling in paired normal oesophageal mucosa and tumour tissues (n = 34; adenocarcinoma n = 28; squamous cell carcinoma n = 6) was performed using quantitative reverse transcription polymerase chain reaction (qRT-PCR). Correlation between levels of ER with the clinico-pathological features for OC was determined. The effect of selective ER antagonists on proliferation of OE33 and OE19 OC cell lines was studied.

RESULTS

ERα and ERβ mRNA expression was significantly higher (p < 0.05) in tumour tissues relative to their paired normal mucosa and correlated inversely with survival outcome (p < 0.05). Upregulation of ERα mRNA correlated with higher pathological T-stage (p < 0.05) and lymph node metastasis (p < 0.05) while ERβ mRNA upregulation correlated with positive vascular invasion (p < 0.05). A significant concentration-dependent inhibition of proliferation in OE33 and OE19 cell lines was induced by a highly-selective ERα antagonist (MPP) and an ERβ specific antagonist (PHTPP) (p < 0.05). Moreover, anti-oestrogens induced cell death through stimulation of apoptotic caspase activity.

CONCLUSION

These findings indicate that the ER system is involved in OC progression and thus may provide a novel target for the treatment of OC.

Local delivery of hormonal therapy with silastic tubing for prevention and treatment of breast cancer

Broad use of germline testing has identified an increasing number of women at risk for breast cancer with a need for effective chemoprevention. We report a novel method to selectively deliver various anti-estrogens at high drug levels to the breast tissue by implanting a device comprised of silastic tubing. Optimized tubing properties allow elution of otherwise poorly bioavailable anti-estrogens, such as fulvestrant, into mammary tissue in vitro and in vivo with levels sufficient to inhibit estrogen receptor activation and tumor cell proliferation. Implantable silastic tubing delivers fulvestrant selectively to mouse mammary fat tissue for one year with anti-tumor effects similar to those achieved with systemic fulvestrant exposure. Furthermore, local delivery of fulvestrant significantly decreases cell proliferation, as assessed by Ki67 expression, most effectively in tumor sections adjacent to tubing. This approach may thereby introduce a potential paradigm shift and offer a promising alternative to systemic therapy for prevention and early interception of breast cancer.

Effect of estrogen on prostaglandin synthetase in bovine oviduct smooth muscle

Gamete and embryo transport is an important function of the oviduct. This type of transport involves both smooth muscle contraction and epithelial cell secretions, and the former is mediated by prostaglandins (PGs) and their receptors. Our objective was to study the regulation of prostaglandin synthetase (prostaglandin-endoperoxide synthase-1 (PTGS1), prostaglandin-endoperoxide synthase-2 (PTGS2), mPGES-1, mPGES-2, cPGES, and PGFS) by estradiol (E₂) in bovine oviduct smooth muscle. Prostaglandin synthetase mRNA and protein expression were investigated using real-time RT-PCR and Western blot analyses, respectively. Prostaglandin synthetase mRNA and protein expression were increased in oviductal smooth muscle tissue after treatment with different concentrations of estradiol for various time periods. The results indicated that there was no increase in expression observed after treatment with fulvestrant, a selective antagonist of the E₂ receptor, indicating that E₂ interacts with specific E₂ nuclear receptors to upregulate PTGS1, PTGS2, mPGES-1, and PGFS expression. In conclusion, E₂ increases PTGS1, mPGES-1, and PGFS mRNA and protein expression in bovine oviductal smooth muscle when added for different periods of time and at different concentrations. Additionally, E₂ is transported intracellularly and interacts with specific E₂ nuclear receptors to increase PTGS1, PTGS2, mPGES-1 and PGFS expression.

Novel Selective Estrogen Receptor Ligand Conjugates Incorporating Endoxifen-Combretastatin and Cyclofenil-Combretastatin Hybrid Scaffolds: Synthesis and Biochemical Evaluation

Nuclear receptors such as the estrogen receptors (ERα and ERβ) modulate the effects of the estrogen hormones and are important targets for design of innovative chemotherapeutic agents for diseases such as breast cancer and osteoporosis. Conjugate and bifunctional compounds which incorporate an ER ligand offer a useful method of delivering cytotoxic drugs to tissue sites such as breast cancers which express ERs. A series of novel conjugate molecules incorporating both the ER ligands endoxifen and cyclofenil-endoxifen hybrids covalently linked to the antimitotic and tubulin targeting agent combretastatin A-4 were synthesised and evaluated as ER ligands. A number of these compounds demonstrated pro-apoptotic effects, with potent antiproliferative activity in ER-positive MCF-7 breast cancer cell lines and low cytotoxicity. These conjugates displayed binding affinity towards ERα and ERβ isoforms at nanomolar concentrations e.g., the cyclofenil-amide compound 13e is a promising lead compound of a clinically relevant ER conjugate with IC₅₀ in MCF-7 cells of 187 nM, and binding affinity to ERα (IC₅₀ = 19 nM) and ERβ (IC₅₀ = 229 nM) while the endoxifen conjugate 16b demonstrates antiproliferative activity in MCF-7 cells (IC₅₀ = 5.7 nM) and binding affinity to ERα (IC₅₀ = 15 nM) and ERβ (IC₅₀ = 115 nM). The ER binding effects are rationalised in a molecular modelling study in which the disruption of the ER helix-12 in the presence of compounds 11e, 13e and 16b is presented These conjugate compounds have potential application for further development as antineoplastic agents in the treatment of ER positive breast cancers.

Lead Optimization of Benzoxepin-Type Selective Estrogen Receptor (ER) Modulators and Downregulators with Subtype-Specific ERα and ERβ Activity

Estrogen receptor α (ERα) is an important target for the design of drugs such as tamoxifen (2a) and fulvestrant (5). Three series of ER-ligands based on the benzoxepin scaffold structure were synthesized: series I containing an acrylic acid, series II with an acrylamide, and series III with a saturated carboxylic acid substituent. These compounds were shown to be high affinity ligands for the ER with nanomolar IC₅₀ binding values. Series I acrylic acid ligands were generally ERα selective. In particular, compound 13e featuring a phenylpenta-2,4-dienoic acid substituent was shown to be antiproliferative and downregulated ERα and ERβ expression in MCF-7 breast cancer cells. Interestingly, from series III, the phenoxybutyric acid derivative compound 22 was not antiproliferative and selectively downregulated ERβ. A docking study of the benzoxepin ligands was undertaken. Compound 13e is a promising lead for development as a clinically relevant SERD, while compound 22 will be a useful experimental probe for helping to elucidate the role of ERβ in cancer cells.

Phytoestrogens and Mycoestrogens Induce Signature Structure Dynamics Changes on Estrogen Receptor α

Endocrine disrupters include a broad spectrum of chemicals such as industrial chemicals, natural estrogens and androgens, synthetic estrogens and androgens. Phytoestrogens are widely present in diet and food supplements; mycoestrogens are frequently found in grains. As human beings and animals are commonly exposed to phytoestrogens and mycoestrogens in diet and environment, it is important to understand the potential beneficial or hazardous effects of estrogenic compounds. Many bioassays have been established to study the binding of estrogenic compounds with estrogen receptor (ER) and provided rich data in the literature. However, limited assays can offer structure information with regard to the ligand/ER complex. Our current study surveys the global structure dynamics changes for ERα ligand binding domain (LBD) when phytoestrogens and mycoestrogens bind. The assay is based on the structure dynamics information probed by hydrogen deuterium exchange mass spectrometry and offers a unique viewpoint to elucidate the mechanism how phytoestrogens and mycoestrogens interact with estrogen receptor. The cluster analysis based on the hydrogen deuterium exchange (HDX) assay data reveals a unique pattern when phytoestrogens and mycoestrogens bind with ERα LBD compared to that of estradiol and synthetic estrogen modulators. Our study highlights that structure dynamics could play an important role in the structure function relationship when endocrine disrupters interact with estrogen receptors.

Symmetric 4,4'-(piperidin-4-ylidenemethylene)bisphenol derivatives as novel tunable estrogen receptor (ER) modulators

We designed and synthesized 4,4'-(piperidin-4-ylidenemethylene)bisphenol derivatives as novel tunable estrogen receptor (ER) modulators. The introduction of hydrophobic substituents on the nitrogen atom of the piperidine ring enhanced ERα binding affinity. In addition, the introduction of four methyl groups adjacent to the piperidine ring nitrogen atom remarkably enhanced ERα binding affinity. N-Acetyl-2,2,6,6-tetramethylpiperidine derivative 3b showed high ERα binding affinity, high MCF-7 cell proliferation inducing activity, and high metabolic stability in rat liver S9 fractions.

Endogenous oestrogens do not regulate endothelial nitric oxide production in early postnatal rats

Previously we showed that endothelium of 1-2-weeks old rats exerts an anticontractile effect due to spontaneous NO production which correlates with a higher eNOS expression level compared to adult rats. Oestrogens are powerful regulators of eNOS expression and activity in arterial endothelium. This study tested the hypothesis that anticontractile influence of endothelium in young rats is regulated by endogenous oestrogens. Wistar rats were daily treated with ICI 182,780 or letrozole (oestrogen receptor antagonist and aromatase inhibitor, respectively; s.c., 1mg/kg/day) from the second postnatal day, control pups received vehicle injections. At the age of 10-12-days we studied contraction of saphenous arteries using wire myography. ELISA and qPCR were used to evaluate blood sex steroids levels and mRNA expression in arterial tissue, respectively. Ten-12 days old male rats compared to adult male rats demonstrated 78% higher serum 17β-oestradiol concentration and several-fold increase in mRNA contents of oestrogen receptors (ERα and GPER1). However, treatments with ICI 182,780 or letrozole did not affect arterial sensitivity to methoxamine (α1-adrenoceptor agonist) in 10-12-days old males. The blockade of NO-synthase with L-NNA caused tonic contraction and potentiated the response to methoxamine, these effects were similar in control and both treated groups. The sensitivity of endothelium-denuded saphenous arteries to NO-donor DEA/NO did not differ between control and treated groups as well. In addition, treatments with ICI 182,780 or letrozole did not change eNOS expression level in arterial tissue. Our results suggest that endogenous oestrogens do not regulate anticontractile effect of NO during early postnatal development in rats.

Identification of coregulators influenced by estrogen receptor subtype specific binding of the ER antagonists 4-hydroxytamoxifen and fulvestrant

The aim of the present study was to investigate modulation of the interaction of ERα and ERβ with coregulators in the ligand dependent responses induced by the ER antagonistic compounds 4OHT and fulvestrant. Comparison with the modulation index (MI) profiles for the ER agonist estradiol (E2) will elucidate whether differences in the (ant)agonist dependent interaction of ERα and ERβ with coregulators expressed in MI profiles contribute to the differences in (ant)agonist responses. To this end, the selected ER antagonistic compounds were first characterized for intrinsic relative potency and efficacy towards ERα and ERβ using ER selective U2OS reporter gene assays, and subsequently tested for ligand dependent modulation of the interaction of ERα and ERβ with coregulators using the MARCoNI assay. Results obtained indicate a preference of 4OHT to antagonize ERβ and find fulvestrant to be less ER specific. MARCoNI assay responses reveal that ERα and ERβ mediated interaction with coregulators expressed in MI profiles are similar for 4OHT and fulvestrant and generally opposite to the MI profile of the ER agonist E2. Hierarchical clustering based on the MI profiles appeared able to clearly discriminate the two compounds with ER antagonistic properties from the ER agonist E2. Taken together the data reveal that modulation of the interaction of ERs with coregulators discriminates ER agonists from antagonists but does not discriminate between the less specific ER antagonist fulvestrant and the preferential ERβ antagonistic compound 4OHT. It is concluded that differences in modulation of the interaction of ERα and ERβ with coregulators contribute to the differences in ligand dependent responses induced by ER agonists and ER antagonists but the importance of the subtle differences in modulation of the interaction of ERs with coregulators between the ER antagonistic compounds 4OHT and fulvestrant for the ultimate biological effect remains to be established.

Genotoxicity of the some selective estrogen receptor modulators: a review

The objective of this article is to review genotoxicological profile of the major selective estrogen receptor modulators, including clomiphene, tamoxifen, toremifene, raloxifene. These drugs have been used for infertility treatment and breast cancer prevention in high risk-women. However, some studies reported that especially tamoxifen is a genotoxic agent and is related with endometrial cancer. Our review indicate that clomiphene and tamoxifen were found as genotoxic agent in majority of the tests. However published reports showed that toremifene is a weakly genotoxic agent. The genotoxic effects of raloxifene are still poorly known. Further genotoxicity studies should be conducted especially for raloxifene.

Targeting estrogen receptors for the treatment of Alzheimer's disease

The significantly higher incidence of Alzheimer's disease (AD) in women than in men has been attributed to loss of estrogen and a variety of related mechanisms at the molecular, cellular, and hormonal levels, which subsequently elucidate neuroprotective roles of estrogen against AD-related pathology. Recent studies have proposed that beneficial effects of estrogen on AD are directly linked to its ability to reduce amyloid-β peptides and tau aggregates, two hallmark lesions of AD. Despite high expectations, large clinical trials with postmenopausal women indicated that the beneficial effects of estrogen therapies were insignificant and, in fact, elicited adverse effects. Here, we review the current status of AD prevention and treatment using estrogens focusing on recent understandings of their biochemical links to AD pathophysiology. This review also discusses development of selective ligands that specifically target either estrogen receptor α (ERα) or ERβ isoforms, which are potentially promising strategies for safe and efficient treatment of AD.

Endocrine therapy for advanced/metastatic breast cancer

First-line endocrine therapy by estrogen antagonism or suppression of estrogen achieves objective responses (ORs) and clinical benefit (CB) in around 30% and 50% of estrogen receptor-positive metastatic breast cancer patients, respectively. Aromatase inhibitors (AIs) are the most effective treatment in previously untreated postmenopausal women. Tamoxifen is an effective alternative. The optimal endocrine therapy on relapse remains uncertain. Tamoxifen and fulvestrant achieve CB in around 50% of patients and ORs of 10%. CB of exemestane after nonsteroidal AIs is 30% to 50% but ORs are rare. Targeted agents (eg, everolimus) plus endocrine therapy are likely to become increasingly important in overcoming endocrine resistance.

PKA phosphorylation redirects ERα to promoters of a unique gene set to induce tamoxifen resistance

Protein kinase A (PKA)-induced estrogen receptor alpha (ERα) phosphorylation at serine residue 305 (ERαS305-P) can induce tamoxifen (TAM) resistance in breast cancer. How this phospho-modification affects ERα specificity and translates into TAM resistance is unclear. Here, we show that S305-P modification of ERα reprograms the receptor, redirecting it to new transcriptional start sites, thus modulating the transcriptome. By altering the chromatin-binding pattern, Ser305 phosphorylation of ERα translates into a 26-gene expression classifier that identifies breast cancer patients with a poor disease outcome after TAM treatment. MYC-target genes and networks were significantly enriched in this gene classifier that includes a number of selective targets for ERαS305-P. The enhanced expression of MYC increased cell proliferation in the presence of TAM. We demonstrate that activation of the PKA signaling pathway alters the transcriptome by redirecting ERα to new transcriptional start sites, resulting in altered transcription and TAM resistance.

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.

Resistance to antiestrogen arzoxifene is mediated by overexpression of cyclin D1

Resistance to tamoxifen treatment occurs in approximately 50% of the estrogen receptor (ER)alpha-positive breast cancer patients. Resistant patients would benefit from treatment with other available antiestrogens. Arzoxifene is an effective growth inhibitor of ERalpha-positive breast cancer cells, including tamoxifen-resistant tumors. In this study, we show that overexpression of a regular component of the ERalpha transcription factor complex, cyclin D1, which occurs in approximately 40% of breast cancer patients, renders cells resistant to the new promising antiestrogen, arzoxifene. Overexpression of cyclin D1 alters the conformation of ERalpha in the presence of arzoxifene. In this altered conformation, ERalpha still recruits RNA polymerase II to an estrogen response element-containing promoter, inducing transcription of an ERalpha-dependent reporter gene and of endogenous pS2, and promoting arzoxifene-stimulated growth of MCF-7 cells. Arzoxifene is then converted from an ERalpha antagonist into an agonist. This can be explained by a stabilization of the ERalpha/steroid receptor coactivator-1 complex in the presence of arzoxifene, only when cyclin D1 is overexpressed. These results indicate that subtle changes in the conformation of ERalpha upon binding to antiestrogen are at the basis of resistance to antiestrogens.

Effects of celecoxib and ly117018 combination on human breast cancer cells in vitro

Activation and signalling of estrogen receptor (ER) and COX-2 represent two important pathways in breast cancer cell regulation. Activation of either pathway is associated with breast cancer cell proliferation and eventually malignant progression. Raloxifene analogue, Ly117018, a selective estrogen receptor modulator and celecoxib, a specific COX-2 inhibitor have been shown to inhibit breast cancer cell proliferation when used alone in vitro and in vivo. In this study, the combined drug effects on hormone-dependent MCF-7 and hormone-independent MDA-MB-435 cells in vitro were evaluated. Cell proliferation assays excluded drug antagonism and revealed a moderate synergistic growth inhibitory activity of Ly117018 and celecoxib on both cell lines when combined in specific concentrations. Growth inhibition of either compound was not associated with cell cycle arrest. In MCF-7 cells, western blot analysis revealed a decreased phosphorylation of the AKT protein by either agent alone or in combination. In MDA-MB-435 cells, celecoxib alone induced an increase in AKT phosphorylation relative to total AKT protein; this effect was decreased in the presence of Ly117018. These results indicate that these two drugs are non-antagonistic; and when combined in specific concentrations, moderate synergistic antiproliferative activity of celecoxib and Ly117018 were observed in hormone-dependent MCF-7 and hormone-independent MDA-MB-435 cells associated with changes in cell cycle distribution and regulation of AKT protein and phosphorylation. These findings further support a central role of the ER- and COX-2 pathways in human breast cancer cells.

Cancer research meets evolutionary biology

There is increasing evidence that Darwin's theory of evolution by natural selection provides insights into the etiology and treatment of cancer. On a microscopic scale, neoplastic cells meet the conditions for evolution by Darwinian selection: cell reproduction with heritable variability that affects cell survival and replication. This suggests that, like other areas of biological and biomedical research, Darwinian theory can provide a general framework for understanding many aspects of cancer, including problems of great clinical importance. With the availability of raw molecular data increasing rapidly, this theory may provide guidance in translating data into understanding and progress. Several conceptual and analytical tools from evolutionary biology can be applied to cancer biology. Two clinical problems may benefit most from the application of Darwinian theory: neoplastic progression and acquired therapeutic resistance. The Darwinian theory of cancer has especially profound implications for drug development, both in terms of explaining past difficulties, and pointing the way toward new approaches. Because cancer involves complex evolutionary processes, research should incorporate both tractable (simplified) experimental systems, and also longitudinal observational studies of the evolutionary dynamics of cancer in laboratory animals and in human patients. Cancer biology will require new tools to control the evolution of neoplastic cells.

Systematic mapping of posttranslational modifications in human estrogen receptor-alpha with emphasis on novel phosphorylation sites

A systematic study of posttranslational modifications of the estrogen receptor isolated from the MCF-7 human breast cancer cell line is reported. Proteolysis with multiple enzymes, mass spectrometry, and tandem mass spectrometry achieved very high sequence coverage for the full-length 66-kDa endogenous protein from estradiol-treated cell cultures. Nine phosphorylated serine residues were identified, three of which were previously unreported and none of which were previously observed by mass spectrometry by any other laboratory. Two additional modified serine residues were identified in recombinant protein, one previously reported but not observed here in endogenous protein and the other previously unknown. Although major emphasis was placed on identifying new phosphorylation sites, N-terminal loss of methionine accompanied by amino acetylation and a lysine side chain acetylation (or possibly trimethylation) were also detected. The use of both HPLC-ESI and MALDI interfaced to different mass analyzers gave higher sequence coverage and identified more sites than could be achieved by either method alone. The estrogen receptor is critical in the development and progression of breast cancer. One previously unreported phosphorylation site identified here was shown to be strongly dependent on estradiol, confirming its potential significance to breast cancer. Greater knowledge of this array of posttranslational modifications of estrogen receptor, particularly phosphorylation, will increase our understanding of the processes that lead to estradiol-induced activation of this protein and may aid the development of therapeutic strategies for management of hormone-dependent breast cancer.

Prospective serial proton MR spectroscopic assessment of response to tamoxifen for recurrent malignant glioma

OBJECTIVE

Early prediction of imminent failure during chemotherapy for malignant glioma has the potential to guide proactive alterations in treatment before frank tumor progression. We prospectively followed patients with recurrent malignant glioma receiving tamoxifen chemotherapy using proton magnetic resonance spectroscopic imaging ((1)H-MRSI) to identify intratumoral metabolic changes preceding clinical and radiological failure.

METHODS

We performed serial (1)H-MRSI examinations to assess intratumoral metabolite intensities in 16 patients receiving high-dose oral tamoxifen monotherapy for recurrent malignant glioma (WHO grade III or IV) as part of a phase II clinical trial. Patients were followed until treatment failure, death, or trial termination.

RESULTS

Patients were officially classified as responders (7 patients) or non-responders (9 patients) 8 weeks into treatment. At 8 weeks, responders and non-responders had different intratumoral intensities across all measured metabolites except choline. Beyond 8 weeks, metabolite intensities remained stable in all responders, but changed again with approaching disease progression. Choline, lipid, choline/NAA, and lactate/NAA were significantly elevated (P < 0.02), while creatine (P < 0.04) was significantly reduced, compared to stabilized levels on average 4 weeks prior to failure. Lactate was significantly elevated (P = 0.036) fully 8 weeks prior to failure. In one patient who was still responding to tamoxifen at the conclusion of the trial, metabolite intensities never deviated from 8-week levels for the duration of follow-up.

CONCLUSIONS

Characteristic global intratumoral metabolic changes, detectable on serial (1)H-MRSI studies, occur in response to chemotherapy for malignant glioma and may predict imminent treatment failure before actual clinical and radiological disease progression.

Role of mitochondria in tamoxifen-induced rapid death of MCF-7 breast cancer cells

Tamoxifen (Tam) is widely used in chemotherapy of estrogen receptor-positive breast cancer. It inhibits proliferation and induces apoptosis of breast cancer cells by estrogen receptor-dependent modulation of gene expression, but recent reports have shown that Tam (especially at pharmacological concentrations) has also rapid nongenomic effects. Here we studied the mechanisms by which Tam exerts rapid effects on breast cancer cell viability. In serum-free medium 5-7 microM Tam induced death of MCF-7 and MDA-MB-231 cells in a time-dependent manner in less than 60 min. This was associated with release of mitochondrial cytochrome c, a decrease of mitochondrial membrane potential and an increase in production of reactive oxygen species (ROS). This suggests that disruption of mitochondrial function has a primary role in the acute death response of the cells. Accordingly, bongkrekic acid, an inhibitor of mitochondrial permeability transition, was able to protect MCF-7 cells against Tam. Rapid cell death induction by Tam was not associated with immediate activation of caspase-9 or cleavage of poly (ADP-ribose) polymerase. It was not blocked by the caspase inhibitor z-Val-Ala-Asp-fluoromethylketone either. Diphenylene ionodium (DPI), an inhibitor of NADPH oxidase, was able to prevent Tam-induced cell death but not cytochrome c release, which suggests that ROS act distal to cytochrome c. The pure antiestrogen ICI 182780 (1 microM) could partly oppose the effect of Tam in estrogen receptor positive MCF-7 cells, but not in estrogen receptor negative MDA-MB-231 cells. Pre-culturing MCF-7 cells in the absence of 17beta-estradiol (E(2)) or in the presence of a low Tam concentration (1 microM) made the cells even more susceptible to rapid death induction by 5 or 7 microM Tam. This effect was associated with decreased levels of the anti-apoptotic proteins Bcl-X(L) and Bcl-2. In conclusion, our results demonstrate induction of a rapid mitochondrial cell death program in breast cancer cells at pharmacological concentrations of Tam, which are achievable in tumor tissue of Tam-treated breast cancer patients. These mechanisms may contribute to the ability of Tam therapy to induce death of breast cancer cells.

A mass spectrometric approach for the study of the metabolism of clomiphene, tamoxifen and toremifene by liquid chromatography time-of-flight spectroscopy

In this paper, we discuss the capabilities of liquid chromatography coupled to mass spectrometry with a time-of flight system with accurate mass measurement for the detection and characterisation of drug metabolites in biological samples for anti-doping purpose. Urinary excretion samples of three selective oestrogen receptor modulators (SERMs) with a common triphenylethylene structure: clomiphene, toremifene, and tamoxifen, obtained after oral administration of a single dose of each drug, were analysed using a time-of-flight system, after automatic tuning and calibration of the equipment, in positive full scan mode using an electrospray ionisation source. Following this approach we detected most of all significant metabolites reported by others and postulated new metabolites, especially for toremifene, have been characterised: N-demethyl-3-hydroxy-4-methoxy-toremifene and 3- hydroxy-4-methoxy-toremifene; in addtiona to this, in the urinary excretion samples of toremifene some metabolites, without the characteristic chlorine isotope pattern, discarded in previous studies, that are also metabolites of tamoxifen, were identified. The lack of certified reference materials does not allow an accurate determination of the limit of detection (LODs) of all metabolites; however an estimation taking into account the response factor of similar compounds allows to estimate that all metabolites are clearly detectable in a range of concentration comprised between 10 ng mL(-1) and 30 ng mL(-1).

Synergistic cytotoxicity between tamoxifen and the plant toxin persin in human breast cancer cells is dependent on Bim expression and mediated by modulation of ceramide metabolism

Phytochemicals have provided an abundant source of novel therapeutics for the treatment of human cancers. We have previously described a novel plant toxin, persin, derived from avocado leaves, which has unique in vivo actions in the mammary epithelium and Bim-dependent, cytotoxic effects in human breast cancer cells in vitro. Compounds structurally similar to persin, such as the polyunsaturated fatty acid, conjugated linoleic acid, can attenuate steroid hormone receptor signaling and modulate the response of breast cancer cells to antiestrogens. Here, we provide evidence that persin may have similar effects by showing its potent proapoptotic synergy with the antiestrogen 4-hydroxytamoxifen. However, although persin transcriptionally down-regulates estrogen receptor (ER) expression, unlike conjugated linoleic acid, it also shows efficacy in ER-negative breast cancer cells, both alone and in combination with 4-hydroxytamoxifen, whereas normal breast epithelial cells are unaffected, suggesting it may act via a distinct, ER-independent mechanism. These proapoptotic synergistic interactions are associated with increased de novo ceramide synthesis and are dependent on expression of the proapoptotic protein Bim. These data show that persin should be further investigated as a potential novel cancer therapeutic agent because it significantly enhances the sensitivity of breast cancer cells to the cytotoxic effects of tamoxifen, regardless of their ER status, while displaying apparent specificity for the malignant phenotype.

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.

Classification of anti-estrogens according to intramolecular FRET effects on phospho-mutants of estrogen receptor alpha

Anti-estrogen resistance is a major clinical problem in the treatment of breast cancer. In this study, fluorescence resonance energy transfer (FRET) analysis, a rapid and direct way to monitor conformational changes of estrogen receptor alpha (ERalpha) upon anti-estrogen binding, was used to characterize resistance to anti-estrogens. Nine different anti-estrogens all induced a rapid FRET response within minutes after the compounds have liganded to ERalpha in live cells, corresponding to an inactive conformation of the ERalpha. Phosphorylation of Ser(305) and/or Ser(236) of ERalpha by protein kinase A (PKA) and of Ser(118) by mitogen-activated protein kinase (MAPK) influenced the FRET response differently for the various anti-estrogens. PKA and MAPK are both associated with resistance to anti-estrogens in breast cancer patients. Their respective actions can result in seven different combinations of phospho-modifications in ERalpha where the FRET effects of particular anti-estrogen(s) are nullified. The FRET response provided information on the activity of ERalpha under the various anti-estrogen conditions as measured in a traditional reporter assay. Tamoxifen and EM-652 were the most sensitive to kinase activities, whereas ICI-182,780 (Fulvestrant) and ICI-164,384 were the most stringent. The different responses of anti-estrogens to the various combinations of phospho-modifications in ERalpha elucidate why certain anti-estrogens are more prone than others to develop resistance. These data provide new insights into the mechanism of action of anti-hormones and are critical for selection of the correct individual patient-based endocrine therapy in breast cancer.

Targeting malignant glioma survival signalling to improve clinical outcomes

Malignant gliomas are common and aggressive brain tumours in adults. Current treatments for glioblastoma multiforme result in a poor median survival of less than 12 months. The blood-brain barrier restricts the delivery of many chemotherapies to the central nervous system, contributing to the failure of treatment. PI3K/Akt and Ras/MAPK pathways have been identified as important oncogenic pathways in these tumours. The PI3K/Akt pathway mediates cell survival and growth, whereas the Ras/MAPK pathway signals cell differentiation, proliferation and anti-apoptosis. Modern targeted therapies include antibodies to circulating growth factors and cell surface receptors, as well as inhibitors of receptor tyrosine kinases and specific intracellular signalling proteins. Monotherapy with most targeted therapies produces only modest efficacy. Better results are achieved in combination with cytotoxic chemotherapies. Future therapeutics should focus on combination therapy with small lipophilic molecules.

Vasomotor symptoms in menopause: physiologic condition and central nervous system approaches to treatment

OBJECTIVE

The decline in concentrations of gonadal hormones during menopause gives rise to a range of physiologic and psychologic changes that may impact a woman's health and quality of life significantly. Most notable among these are vasomotor symptoms (hot flashes and night sweats) and mood and sleep disturbances.

STUDY DESIGN

This article reviews the physiologic condition underlying menopausal vasomotor symptoms and centrally active, nonhormonal therapies that have demonstrated efficacy for their treatment.

RESULTS

Despite the emergence of a range of nonhormonal treatments for vasomotor symptoms, a need still exists for safe and effective therapeutic options that directly target the underlying thermoregulatory mechanisms for women who want treatment but prefer to avoid hormone therapy or for whom hormone therapy is contraindicated.

CONCLUSION

The availability of centrally active therapies for menopausal vasomotor symptoms with risks and benefits clearly defined by results from well-designed clinical trials has the potential to allay safety concerns that are associated with the treatment of these common symptoms.

Trilostane in advanced breast cancer

Antiestrogens, principally tamoxifen, and aromatase inhibitors have been used as the first- and second-line therapy in patients with advanced postmenopausal breast cancer for many years. However, some patients acquire resistance to these treatments and, at present, further endocrine treatment is achieved by merely substituting the current medication with a different antiestrogen or aromatase inhibitor. Trilostane offers an alternative endocrine treatment due to its unique mode of action. It is an allosteric modulator of the estrogen receptor and targets both the estrogen- and growth factor-dependent pathways through which estradiol stimulates cell proliferation. In clinical trials, trilostane has been shown to be an effective treatment for breast cancer in patients who have relapsed after receiving treatment with one or more forms of endocrine therapy. Ongoing and future clinical trials are examining the potential for the use of trilostane in premenopausal breast cancer, as well as in other malignancies such as prostate cancer.

Characterization of molecular and structural determinants of selective estrogen receptor downregulators

Antiestrogens used for breast cancer therapy can be categorized into two classes that differ in their effect on estrogen receptor (ER) alpha stability. The selective estrogen receptor modulators (SERMs) stabilize ER alpha and the selective estrogen receptor downregulators (SERDs) cause a decrease in cellular ER alpha levels. A clinically relevant antiestrogen, GW7604, appears to work through a SERD-like mechanism, despite sharing the same molecular scaffold as 4-hydroxytamoxifen, a SERM. In order to investigate potential structural features of GW7604 responsible for SERD activity, GW7604 and two analogs were synthesized using a new, improved synthetic route and tested for their effects on ER alpha function and cell proliferation. The two analogs, which have an acrylamide or a methyl vinyl ketone replacing the acrylic acid group of GW7604, display lower binding affinity for ER alpha than GW7604, but show similar antagonism of estradiol-induced activation of ER alpha-mediated transcription as GW7604 and inhibit estradiol-induced proliferation of the MCF-7 cell line with a similar potency as GW7604. Unlike GW7604, neither analog has a significant effect on cellular ER alpha levels, suggesting that the carboxylate is a key determinant in GW7604 action and, for the first time, showing that this group is responsible for inducing ER alpha degradation in breast cancer cells.

A phase II study of carboplatin and chronic high-dose tamoxifen in patients with recurrent malignant glioma

PURPOSE

To determine the response rate, time to disease progression, survival, and toxicity of intravenous carboplatin and chronic oral high-dose tamoxifen in patients with recurrent malignant gliomas.

PATIENTS AND METHODS

Patients with histological confirmation of recurrent malignant gliomas were eligible for this multicenter phase II trial. Treatment consisted of 400 mg/m2 carboplatin intravenously every 4 weeks and oral high dose chronic tamoxifen (80 mg bid in women and 100 mg bid in men).

RESULTS

Twenty seven patients met the eligibility criteria and were evaluable for response. The histological subtypes were: 16 (59%) glioblastoma multiforme (GBM), malignant astrocytoma (5 patients), malignant mixed glioma (5 patients), and glioblastoma/gliosarcoma (1 patient). Twenty-two patients (82%) had an ECOG performance status of 0 or 1. No complete responses were observed, 4 patients (15%) achieved a partial response, and 14 patients (52%) had stable disease. Median time to progression was 3.65 months (95%CI 2.56, 4.83). Median overall survival was 14.09 months (95%CI 7.06, 19.91). One patient with a recurrent GBM had a sustained partial response and is progression free 81 months since starting treatment. Another patient with mixed malignant oligoastrocytoma also had a prolonged partial response (lasting 63 months) and is alive 84 months after treatment for recurrence. The most frequently reported grade 3 or 4 toxicities were fatigue (19%), nausea (11%) and anorexia (11%).

CONCLUSIONS

Carboplatin and high dose tamoxifen has similar response rates to other regimens for recurrent malignant gliomas and are probably equivalent to those found using tamoxifen as monotherapy. Long-lasting periods of disease free survival in some patients (particularly those with malignant mixed oligo astrocytomas) were found.

Endocrine targets for pharmacological intervention in aging in Caenorhabditis elegans

Studies in the nematode Caenorhabditis elegans have been instrumental in defining genetic pathways that are involved in modulating lifespan. Multiple processes such as endocrine signaling, nutritional sensing and mitochondrial function play a role in determining lifespan in the worm and these mechanisms appear to be conserved across species. These discoveries have identified a range of novel targets for pharmacological manipulation of lifespan and it is likely that the nematode model will now prove useful in the discovery of compounds that slow aging. This review will focus on the endocrine targets for intervention in aging and the use of C. elegans as a system for high throughput screens of compounds for their effects on aging.

Adjuvant endocrine therapies for postmenopausal women with early breast cancer: Standards and not

Hormonal manipulations have been used for more than 100 years for the treatment of metastatic breast cancer and after definition of the concept of micro-metastases also in the adjuvant setting. In the postmenopausal population, tamoxifen has played the most important role for almost four decades. Progestins or the first generation of aromatase inhibitors (AIs) were only marginally used in the adjuvant setting due to their prohibitive toxicity. The new generation of anti-estrogen compounds, the selective estrogen receptor down-regulators (SERDs) like fulvestrant have a higher affinity for the estrogen receptor than tamoxifen, but none of its agonist activities, and have shown promising clinical activity in the treatment of advanced breast cancer. The third generation of AIs investigated in six large trials has been reported to be superior to tamoxifen in terms of disease-free survival, but not in terms of survival. These trials will be discussed in terms of results in different subpopulations and of toxicity.

Smad4 inhibits tumor growth by inducing apoptosis in estrogen receptor-alpha-positive breast cancer cells

Estrogen is a mitogen in most estrogen receptor-alpha (ERalpha)-positive breast cancers. We have found that Smad4, a common signal transducer in the transforming growth factor-beta superfamily, acts as an ERalpha transcriptional corepressor. Here, we show that Smad4 induces apoptosis in ERalpha-positive MCF-7 breast cancer cells, but not in ERalpha-negative MDA-MB-231 cells. Smad4 induced expression of short Bim isoforms (by alternative splicing) and Bax and release of cytochrome c in ERalpha-positive cells only, and expression of these apoptotic marker genes was reduced when ERalpha small interfering RNA was introduced. Notably, Smad4 was able to induce apoptosis in MDA-231 cells with acquired ERalpha expression. Furthermore, Smad4 inhibited ERalpha-positive tumor growth by inducing apoptosis in tumor xenografts in nude mice. The sizes of tumors expressing Smad4 were only one-tenth the size of those expressing green fluorescent protein, whereas in ERalpha-negative cells, Smad4 did not reduce the tumor size. Notably, Smad4 also promoted short Bim isoform and Bax expression and release of cytochrome c only in ERalpha-positive MCF-7 tumor xenografts. Bim was sufficient for induction of apoptosis, and the short form was the most potent inducer. Our results demonstrate that Smad4 induces apoptosis by regulating Bim splicing as an initial intrinsic signal in ERalpha-positive cells. Smad4-induced apoptosis in ERalpha-positive breast cancer cells may explain the invasive nature of ERalpha-negative breast tumors, thereby providing a potential target for breast cancer intervention.

ERBB receptors and cancer: the complexity of targeted inhibitors

ERBB receptor tyrosine kinases have important roles in human cancer. In particular, the expression or activation of epidermal growth factor receptor and ERBB2 are altered in many epithelial tumours, and clinical studies indicate that they have important roles in tumour aetiology and progression. Accordingly, these receptors have been intensely studied to understand their importance in cancer biology and as therapeutic targets, and many ERBB inhibitors are now used in the clinic. We will discuss the significance of these receptors as clinical targets, in particular the molecular mechanisms underlying response.