Intrinsic mechanism of estradiol-induced apoptosis in breast cancer cells resistant to estrogen deprivation

Alternating 17β-Estradiol and Aromatase Inhibitor Therapies Is Efficacious in Postmenopausal Women with Advanced Endocrine-Resistant ER+ Breast Cancer

PURPOSE

Strategies to implement estrogen therapy for advanced estrogen receptor-positive (ER+) breast cancer are underdeveloped. Preclinical data suggest that cycling treatment with 17β-estradiol followed by estrogen deprivation can control tumor growth long-term.

PATIENTS AND METHODS

Postmenopausal women with advanced ER+/HER2- breast cancer with recurrence or progression on ≥ 1 antiestrogen or aromatase inhibitor (AI)-based therapy were eligible. Patients received 17β-estradiol (2 mg orally, three times a day) for 8 weeks followed by AI (physician's choice) for 16 weeks, alternating treatments on an 8-week/16-week schedule until disease progression. Patients then optionally received continuous single-agent treatment until a second instance of disease progression. Endpoints included 24-week clinical benefit and objective response per RECIST, and tumor genetic alterations.

RESULTS

Of 19 evaluable patients, clinical benefit rate was 42.1% [95% confidence interval (CI), 23.1%-63.9%] and objective response rate (ORR) was 15.8% (95% CI, 5.7%-37.9%). One patient experienced a grade 3 adverse event related to 17β-estradiol. Among patients who received continuous single-agent treatment until a second instance of disease progression, clinical benefit was observed in 5 of 12 (41.7%) cases. Tumor ER (ESR1) mutations were found by whole-exome profiling in 4 of 7 (57.1%) versus 2 of 9 (22.2%) patients who did versus did not experience clinical benefit from alternating 17β-estradiol/AI therapy. The only two patients to experience objective responses to initial 17β-estradiol had tumor ESR1 mutations.

CONCLUSIONS

Alternating 17β-estradiol/AI therapy may be a promising treatment for endocrine-refractory ER+ breast cancer, including following progression on CDK4/6 inhibitors or everolimus. Further study is warranted to determine whether the antitumor activity of 17β-estradiol differs according to ESR1 mutation status.

Revisiting Estrogen for the Treatment of Endocrine-Resistant Breast Cancer: Novel Therapeutic Approaches

Estrogen receptor (ER)-positive breast cancer is the most common subtype, representing 70-75% of all breast cancers. Several ER-targeted drugs commonly used include the selective estrogen receptor modulator (SERM), tamoxifen (TAM), aromatase inhibitors (AIs) and selective estrogen receptor degraders (SERDs). Through different mechanisms of action, all three drug classes reduce estrogen receptor signaling. Inevitably, resistance occurs, resulting in disease progression. The counterintuitive action of estrogen to inhibit ER-positive breast cancer was first observed over 80 years ago. High-dose estrogen and diethylstilbestrol (DES) were used to treat metastatic breast cancer accompanied by harsh side effects until the approval of TAM in the 1970s. After the development of TAM, randomized trials comparing TAM to estrogen found similar or slightly inferior efficacy but much better tolerability. After decades of research, it was learned that estrogen induces tumor regression only after a period of long-term estrogen deprivation, and the mechanisms of tumor regression were described. Despite the long history of breast cancer treatment with estrogen, this therapeutic modality is now revitalized due to the development of novel estrogenic compounds with improved side effect profiles, newly discovered predictive biomarkers, the development of non-estrogen small molecules and new combination therapeutic approaches.

Subtyping-based platform guides precision medicine for heavily pretreated metastatic triple-negative breast cancer: The FUTURE phase II umbrella clinical trial

Triple-negative breast cancer (TNBC) is a heterogeneous disease and lacks effective treatment. Our previous study classified TNBCs into four subtypes with putative therapeutic targets. Here, we report the final results of FUTURE, a phase II umbrella trial designed to explore whether the subtyping-based strategy may improve the outcomes in metastatic TNBC patients. A total of 141 patients with a median of three previous lines of therapies in the metastatic setting were enrolled in seven parallel arms. Confirmed objective responses were achieved in 42 patients (29.8%; 95% confidence interval [CI], 22.4-38.1). The median values of progression-free survival and overall survival were 3.4 (95% CI: 2.7-4.2) and 10.7 (95% CI: 9.1-12.3) months, respectively. Given Bayesian predictive probability, efficacy boundaries were achieved in four arms. Furthermore, integrated genomic and clinicopathological profiling illustrated associations of clinical and genomic parameters with treatment efficacy, and the efficacy of novel antibody-drug conjugates was explored in preclinical TNBC models of subtypes for which treatment was futile. In general, the FUTURE strategy recruits patients efficiently and provides promising efficacy with manageable toxicities, outlining a direction for further clinical exploration.

Endoplasmic reticulum stress targeted therapy for breast cancer

Recurrence, metastasis, and drug resistance are still big challenges in breast cancer therapy. Internal and external stresses have been proven to substantially facilitate breast cancer progression through molecular and systemic mechanisms. For example, endoplasmic reticulum stress (ERS) results in activation of the unfolded protein response (UPR), which are considered an important cellular stress response. More and more reports indicate its key role in protein homeostasis and other diverse functions involved in the process of breast cancer progression. Therefore, therapies targeting the activation of ERS and its downstream signaling pathways are potentially helpful and novel tools to counteract and fight breast cancer. However, recent advances in our understanding of ERS are focused on characterizing and modulating ERS between healthy and disease states, and so little attention has been paid to studying the role and clinical application of targeting ERS in a certain cancer. In this review, we summarize the function and main mechanisms of ERS in different molecular types of breast cancer, and focus on the development of agents targeting ERS to provide new treatment strategies for breast cancer.

In vitro breast cancer models for studying mechanisms of resistance to endocrine therapy

The development of endocrine resistance is a common reason for the failure of endocrine therapies in hormone receptor-positive breast cancer. This review provides an overview of the different types of in vitro models that have been developed as tools for studying endocrine resistance. In vitro models include cell lines that have been rendered endocrine-resistant by ex vivo treatment; cell lines with de novo resistance mechanisms, including genetic alterations; three-dimensional (3D) spheroid, co-culture, and mammosphere techniques; and patient-derived organoid models. In each case, the key discoveries, different analysis strategies that are suitable, and strengths and weaknesses are discussed. Certain recently developed methodologies that can be used to further characterize the biological changes involved in endocrine resistance are then emphasized, along with a commentary on the types of research outcomes that using these techniques can support. Finally, a discussion anticipates how these recent developments will shape future trends in the field. We hope this overview will serve as a useful resource for investigators that are interested in understanding and testing hypotheses related to mechanisms of endocrine therapy resistance.

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.

Mechanistic Effects of Estrogens on Breast Cancer

PURPOSE

Current concepts regarding estrogen and its mechanistic effects on breast cancer in women are evolving. This article reviews studies that address estrogen-mediated breast cancer development, the prevalence of occult tumors at autopsy, and the natural history of breast cancer as predicted by a newly developed tumor kinetic model.

METHODS

This article reviews previously published studies from the authors and articles pertinent to the data presented.

RESULTS

We discuss the concepts of adaptive hypersensitivity that develops in response to long-term deprivation of estrogen and results in both increased cell proliferation and apoptosis. The effects of menopausal hormonal therapy on breast cancer in postmenopausal women are interpreted based on the tumor kinetic model. Studies of the administration of a tissue selective estrogen complex in vitro, in vivo, and in patients are described. We review the various clinical studies of breast cancer prevention with selective estrogen receptor modulators and aromatase inhibitors. Finally, the effects of the underlying risk of breast cancer on the effects of menopausal hormone therapy are outlined.

DISCUSSION

The overall intent of this review is to present data supporting recent concepts, discuss pertinent literature, and critically examine areas of controversy.

TGFα-EGFR pathway in breast carcinogenesis, association with WWOX expression and estrogen activation

WWOX is a tumor-suppressive steroid dehydrogenase, which relationship with hormone receptors was shown both in animal models and breast cancer patients. Herein, through nAnT-iCAGE high-throughput gene expression profiling, we studied the interplay of estrogen receptors and the WWOX in breast cancer cell lines (MCF7, T47D, MDA-MB-231, BT20) under estrogen stimulation and either introduction of the WWOX gene by retroviral transfection (MDA-MB-231, T47D) or silenced with shRNA (MCF7, BT20). Additionally, we evaluated the consequent biological characteristics by proliferation, apoptosis, invasion, and adhesion assays. TGFα-EGFR signaling was found to be significantly affected in all examined breast cancer cell lines in response to estrogen and strongly associated with the level of WWOX expression, especially in ER-positive MCF7 cells. Under the influence of 17β-estradiol presence, biological characteristics of the cell lines were also delineated. The study revealed modulation of adhesion, invasion, and apoptosis. The obtained results point at a complex role of the WWOX gene in the carcinogenesis of the breast tissue, which seems to be closely related to the presence of estrogen α and/or β receptors.

Estrogen Receptor and the Unfolded Protein Response: Double-Edged Swords in Therapy for Estrogen Receptor-Positive Breast Cancer

Estrogen receptor α (ERα) is a target for the treatment of ER-positive breast cancer patients. Paradoxically, it is also the initial site for estrogen (E₂) to induce apoptosis in endocrine-resistant breast cancer. How ERα exhibits distinct functions, in different contexts, is the focus of numerous investigations. Compelling evidence demonstrated that unfolded protein response (UPR) is closely correlated with ER-positive breast cancer. Treatment with antiestrogens initially induces mild UPR through ERα with activation of three sensors of UPR-PRK-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1α (IRE1α), and activating transcription factor 6 (ATF6)-in the endoplasmic reticulum. Subsequently, these sensors interact with stress-associated transcription factors such as c-MYC, nuclear factor-κB (NF-κB), and hypoxia-inducible factor 1α (HIF1α), leading to acquired endocrine resistance. Paradoxically, E₂ further activates sustained secondary UPR via ERα to induce apoptosis in endocrine-resistant breast cancer. Specifically, PERK plays a key role in inducing apoptosis, whereas IRE1α and ATF6 are involved in endoplasmic reticulum stress-associated degradation after E₂ treatment. Furthermore, persistent activation of PERK deteriorates stress responses in mitochondria and triggers of NF-κB/tumor necrosis factor α (TNFα) axis, ultimately determining cell fate to apoptosis. The discovery of E₂-induced apoptosis has clinical relevance for treatment of endocrine-resistant breast cancer. All of these findings demonstrate that ERα and associated UPR are double-edged swords in therapy for ER-positive breast cancer, depending on the duration and intensity of UPR stress. Herein, we address the mechanistic progress on how UPR leads to endocrine resistance and commits E₂ to inducing apoptosis in endocrine-resistant breast cancer.

Comprehensive metabolomics expands precision medicine for triple-negative breast cancer

Metabolic reprogramming is a hallmark of cancer. However, systematic characterizations of metabolites in triple-negative breast cancer (TNBC) are still lacking. Our study profiled the polar metabolome and lipidome in 330 TNBC samples and 149 paired normal breast tissues to construct a large metabolomic atlas of TNBC. Combining with previously established transcriptomic and genomic data of the same cohort, we conducted a comprehensive analysis linking TNBC metabolome to genomics. Our study classified TNBCs into three distinct metabolomic subgroups: C1, characterized by the enrichment of ceramides and fatty acids; C2, featured with the upregulation of metabolites related to oxidation reaction and glycosyl transfer; and C3, having the lowest level of metabolic dysregulation. Based on this newly developed metabolomic dataset, we refined previous TNBC transcriptomic subtypes and identified some crucial subtype-specific metabolites as potential therapeutic targets. The transcriptomic luminal androgen receptor (LAR) subtype overlapped with metabolomic C1 subtype. Experiments on patient-derived organoid and xenograft models indicate that targeting sphingosine-1-phosphate (S1P), an intermediate of the ceramide pathway, is a promising therapy for LAR tumors. Moreover, the transcriptomic basal-like immune-suppressed (BLIS) subtype contained two prognostic metabolomic subgroups (C2 and C3), which could be distinguished through machine-learning methods. We show that N-acetyl-aspartyl-glutamate is a crucial tumor-promoting metabolite and potential therapeutic target for high-risk BLIS tumors. Together, our study reveals the clinical significance of TNBC metabolomics, which can not only optimize the transcriptomic subtyping system, but also suggest novel therapeutic targets. This metabolomic dataset can serve as a useful public resource to promote precision treatment of TNBC.

Estrogen Receptors-Mediated Apoptosis in Hormone-Dependent Cancers

It is known that estrogen stimulates growth and inhibits apoptosis through estrogen receptor(ER)-mediated mechanisms in many cancer cell types. Interestingly, there is strong evidence that estrogens can also induce apoptosis, activating different ER isoforms in cancer cells. It has been observed that E2/ERα complex activates multiple pathways involved in both cell cycle progression and apoptotic cascade prevention, while E2/ERβ complex in many cases directs the cells to apoptosis. However, the exact mechanism of estrogen-induced tumor regression is not completely known. Nevertheless, ERs expression levels of specific splice variants and their cellular localization differentially affect outcome of estrogen-dependent tumors. The goal of this review is to provide a general overview of current knowledge on ERs-mediated apoptosis that occurs in main hormone dependent-cancers. Understanding the molecular mechanisms underlying the induction of ER-mediated cell death will be useful for the development of specific ligands capable of triggering apoptosis to counteract estrogen-dependent tumor growth.

Estrogen Receptor Complex to Trigger or Delay Estrogen-Induced Apoptosis in Long-Term Estrogen Deprived Breast Cancer

Antiestrogen therapy of breast cancer has been a "gold standard" of treatment of estrogen receptor (ER)-positive breast cancer for decades. Resistance to antiestrogen therapy may develop, however, a vulnerability in long-term estrogen deprived (LTED) breast cancer cells was discovered. LTED breast cancer cells may undergo estrogen-induced apoptosis within a week of treatment with estrogen in vitro. This phenomenon has been also validated in vivo and in the clinic. The molecular ER-mediated mechanism of action of estrogen-induced apoptosis was deciphered, however, the relationship between the structure of estrogenic ligands and the activity of the ER in LTED breast cancer cells remained a mystery until recently. In this review we provide an overview of the structure-activity relationship of various estrogens with different chemical structures and the modulation of estrogen-induced apoptosis in LTED breast cancer cells resistant to antihormone therapy. We provide analysis of evidence gathered over more than a decade of structure-activity relationship studies by our group on the role of the change in the conformation of the estrogen receptor and the biological activities of different classes of estrogens and the receptor as well in LTED breast cancer.

Influence of Estrogen Treatment on ESR1+ and ESR1- Cells in ER+ Breast Cancer: Insights from Single-Cell Analysis of Patient-Derived Xenograft Models

Simple Summary

The benefit of endocrine therapy is normally observed for cancers with 10% or more of cells positive for ER expression. We compared the gene expression profiles in both ESR1⁺ and ESR1^– cells in ER⁺ tumors following estrogen treatment. Our single-cell RNA sequencing analysis of estrogen-stimulated (SC31) and estrogen-suppressed (GS3) patient-derived xenograft models offered an unprecedented opportunity to address the molecular and functional differences between ESR1⁺ and ESR1^– cells. While estrogen should activate ERα and stimulate ESR1⁺ cells, our findings regarding ESR1^– cells were important, indicating that the proliferation of ESR1^– cells in ER⁺ cancer is also influenced by estrogen. Another valuable finding from our studies was that estrogen also upregulated a tumor-suppressor gene, IL-24, only in GS3. Estrogen increased the percentage of cells expressing IL-24, associated with the estrogen-dependent inhibition of GS3 tumor growth.

Abstract

A 100% ER positivity is not required for an endocrine therapy response. Furthermore, while estrogen typically promotes the progression of hormone-dependent breast cancer via the activation of estrogen receptor (ER)-α, estrogen-induced tumor suppression in ER⁺ breast cancer has been clinically observed. With the success in establishing estrogen-stimulated (SC31) and estrogen-suppressed (GS3) patient-derived xenograft (PDX) models, single-cell RNA sequencing analysis was performed to determine the impact of estrogen on ESR1⁺ and ESR1^– tumor cells. We found that 17β-estradiol (E2)-induced suppression of GS3 transpired through wild-type and unamplified ERα. E2 upregulated the expression of estrogen-dependent genes in both SC31 and GS3; however, E2 induced cell cycle advance in SC31, while it resulted in cell cycle arrest in GS3. Importantly, these gene expression changes occurred in both ESR1⁺ and ESR1^– cells within the same breast tumors, demonstrating for the first time a differential effect of estrogen on ESR1^– cells. E2 also upregulated a tumor-suppressor gene, IL-24, in GS3. The apoptosis gene set was upregulated and the G2M checkpoint gene set was downregulated in most IL-24⁺ cells after E2 treatment. In summary, estrogen affected pathologically defined ER⁺ tumors differently, influencing both ESR1⁺ and ESR1^– cells. Our results also suggest IL-24 to be a potential marker of estrogen-suppressed tumors.

Modification of the toxic effects of methylmercury and thimerosal by testosterone and estradiol in SH-SY5Y neuroblastoma cell line

Short-chained alkyl mercury compounds accumulate in particularly in the brain. Exposure to these compounds is associated with various neurotoxic effects. Gender-based differences are observed in neurodevelopmental disorders, and testosterone and estradiol may alter the toxic effect of the compounds. The present study aimed to investigate the toxic effects of methylmercury and thimerosal on SH-SY5Y cells in high testosterone/low estradiol and high estradiol/low testosterone containing cellular environment and estimate whether male and female brains react differently to the toxic effects of methylmercury and thimerosal. Study groups (n = 3) were designed as control: growth medium, thimerosal (T): 1.15-μM thimerosal, methylmercury (M): 2.93-μM methylmercury, high testosterone/low estradiol + thimerosal (TT): 1-μM testosterone + 0.75-μM estradiol + 1.15-μM thimerosal, high estradiol/low testosterone + thimerosal (ET): 0.1-μM testosterone + 7.5-μM estradiol + 1.15-μM thimerosal, high testosterone/low estradiol + methylmercury (TM): 1-μM testosterone + 0.75-μM estradiol + 2.93-μM methylmercury and high estradiol/low testosterone + methylmercury (EM): 0.1-μM testosterone + 7.5-μM estradiol + 2.93-μM methylmercury. While a significant decrease in glutathione levels was observed in M group, it was not seen in EM group. A significant increase in the protein carbonyl levels was detected in T group. A similar increase was observed in the TM and TT groups in which testosterone was dominant. It was determined that methylmercury, but not thimerosal, caused significant DNA damage and in TT group. The results showed that both thimerosal and methylmercury are toxic on SH-SY5Y cells and toxic effects of methylmercury are more severe than thimerosal. It has been determined that testosterone and estradiol alter the toxic effects of thimerosal and methylmercury.

PERK, Beyond an Unfolded Protein Response Sensor in Estrogen-Induced Apoptosis in Endocrine-Resistant Breast Cancer

The discovery of 17β-estradiol (E₂)-induced apoptosis has clinical relevance. Mechanistically, E₂ over activates nuclear estrogen receptor α that results in stress responses. The unfolded protein response (UPR) is initiated by E₂ in the endoplasmic reticulum after hours of treatment in endocrine-resistant breast cancer cells, thereby activating three UPR sensors-PRK-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1α (IRE1α), and activating transcription factor 6 (ATF6) with different functions. Specifically, PERK plays a critical role in induction of apoptosis whereas IRE1α and ATF6 are involved in the endoplasmic reticulum stress-associated degradation (ERAD) of PI3K/Akt/mTOR pathways. In addition to attenuating protein translation, PERK increases the DNA-binding activity of NF-κB and subsequent TNFα expression. In addition, PERK communicates with the mitochondria to regulate oxidative stress at mitochondria-associated endoplasmic reticulum membranes (MAM). Furthermore, PERK is a component enriched in MAMs that interacts with multifunctional MAM-tethering proteins and integrally modulates the exchange of metabolites such as lipids, reactive oxygen species (ROS), and Ca²⁺ at contact sites. MAMs are also critical sites for the initiation of autophagy to remove defective organelles and misfolded proteins through specific regulatory proteins. Thus, PERK conveys signals from nucleus to these membrane-structured organelles that form an interconnected network to regulate E₂-induced apoptosis. Herein, we address the mechanistic progress on how PERK acts as a multifunctional molecule to commit E₂ to inducing apoptosis in endocrine-resistant breast cancer.

Turning scientific serendipity into discoveries in breast cancer research and treatment: a tale of PhD students and a 50-year roaming tamoxifen team

PURPOSE

This retrospective, about a single "mobile" laboratory in six locations on two continents, is intended as a case study in discovery for trainees and junior faculty in the medical sciences. Your knowledge of your topic is necessary to expect the unexpected.

HISTORICAL METHOD

In 1972, there was no tamoxifen, only ICI 46, 474, a non-steroidal anti-estrogen with little chance of clinical development. No one would ever be foolish enough to predict that the medicine, 20 years later, would achieve legendary status as the first targeted treatment for breast cancer, and millions of women would benefit from long-term adjuvant tamoxifen therapy. The secret of tamoxifen's success was a translational research strategy proposed in the mid 1970's. This strategy was to treat only patients with estrogen receptor (ER)-positive breast cancer and deploy 5 or more years of adjuvant tamoxifen therapy to prevent recurrence. Additionally, tamoxifen prevented mammary cancer in animals. Could the medicine prevent breast cancer in women?

RESULTS

Tamoxifen and the failed breast cancer drug raloxifene became the first selective estrogen receptor modulators (SERMs): a new drug group, discovered at the University of Wisconsin, Comprehensive Cancer Center. Serendipity can play a fundamental role in discovery, but there must be a rigorous preparation for the investigator to appreciate the possibility of a pending discovery. This article follows the unanticipated discoveries when PhD students "get the wrong answer." The secret of success of my six Tamoxifen Teams was their technical excellence to create models, to decipher mechanisms, that drove the development of new medicines. Discoveries are listed that either changed women's health or allowed an understanding of originally opaque mechanisms of action of potential therapies. These advances in women's health were supported entirely by government-sponsored peer-reviewed funding and major philanthropy from the Lynn Sage Breast Cancer Foundation, the Avon Foundation, and the Susan G. Komen Breast Cancer Foundation. The resulting lives saved or extended, families aided in a time of crisis and the injection of billions of dollars into national economies by drug development, is proof of the value of Federal or philanthropic investment into unencumbered research aimed at saving millions of lives.

Enhanced IFNα Signaling Promotes Ligand-Independent Activation of ERα to Promote Aromatase Inhibitor Resistance in Breast Cancer

Aromatase inhibitors (AIs) reduce estrogen levels up to 98% as the standard practice to treat postmenopausal women with estrogen receptor-positive (ER+) breast cancer. However, approximately 30% of ER+ breast cancers develop resistance to treatment. Enhanced interferon-alpha (IFNα) signaling is upregulated in breast cancers resistant to AIs, which drives expression of a key regulator of survival, interferon-induced transmembrane protein 1 (IFITM1). However, how upregulated IFNα signaling mediates AI resistance is unknown. In this study, we utilized MCF-7:5C cells, a breast cancer cell model of AI resistance, and demonstrate that these cells exhibit enhanced IFNα signaling and ligand-independent activation of the estrogen receptor (ERα). Experiments demonstrated that STAT1, the mediator of intracellular signaling for IFNα, can interact directly with ERα. Notably, inhibition of IFNα signaling significantly reduced ERα protein expression and ER-regulated genes. In addition, loss of ERα suppressed IFITM1 expression, which was associated with cell death. Notably, chromatin immunoprecipitation experiments validated that both ERα and STAT1 associate with ERE sequences in the IFITM1 promoter. Overall, hyperactivation of IFNα signaling enhances ligand-independent activation of ERα, which promotes ER-regulated, and interferon stimulated gene expression to promote survival in AI-resistant breast cancer cells.

Experimental models of endocrine responsive breast cancer: strengths, limitations, and use

Breast cancers characterized by expression of estrogen receptor-alpha (ER; ESR1) represent approximately 70% of all new cases and comprise the largest molecular subtype of this disease. Despite this high prevalence, the number of adequate experimental models of ER+ breast cancer is relatively limited. Nonetheless, these models have proved very useful in advancing understanding of how cells respond to and resist endocrine therapies, and how the ER acts as a transcription factor to regulate cell fate signaling. We discuss the primary experimental models of ER+ breast cancer including 2D and 3D cultures of established cell lines, cell line- and patient-derived xenografts, and chemically induced rodent models, with a consideration of their respective general strengths and limitations. What can and cannot be learned easily from these models is also discussed, and some observations on how these models may be used more effectively are provided. Overall, despite their limitations, the panel of models currently available has enabled major advances in the field, and these models remain central to the ability to study mechanisms of therapy action and resistance and for hypothesis testing that would otherwise be intractable or unethical in human subjects.

Disrupting interferon-alpha and NF-kappaB crosstalk suppresses IFITM1 expression attenuating triple-negative breast cancer progression

Overexpression of interferon induced transmembrane protein-1 (IFITM1) enhances tumor progression in multiple cancers, but its role in triple-negative breast cancer (TNBC) is unknown. Here, we explore the functional significance and regulation of IFITM1 in TNBC and strategies to target its expression. Immunohistochemistry staining of a tissue microarray demonstrates that IFITM1 is overexpressed in TNBC samples which is confirmed by TCGA analysis. Targeting IFITM1 by siRNA or CRISPR/Cas9 in TNBC cell lines significantly inhibits proliferation, colony formation, and wound healing in vitro. Orthotopic mammary fat pad and mammary intraductal studies reveal that loss of IFITM1 reduces TNBC tumor growth and invasion in vivo. RNA-seq analysis of IFITM1/KO cells reveals significant downregulation of several genes involved in proliferation, migration, and invasion and functional studies identified NF-κB as an important downstream target of IFITM1. Notably, siRNA knockdown of p65 reduces IFITM1 expression and a drug-repurposing screen of FDA approved compounds identified parthenolide, an NFκB inhibitor, as a cytotoxic agent for TNBC and an inhibitor of IFITM1 in vitro and in vivo. Overall, our findings suggest that targeting IFITM1 by suppressing interferon-alpha/NFκB signaling represents a novel therapeutic strategy for TNBC treatment.

Continuous versus intermittent extended adjuvant letrozole for breast cancer: final results of randomized phase III SOLE (Study of Letrozole Extension) and SOLE Estrogen Substudy

BACKGROUND

Late recurrences in postmenopausal women with hormone receptor-positive breast cancers remain an important challenge. Avoidance or delayed development of resistance represents the main objective in extended endocrine therapy (ET). In animal models, resistance was reversed with restoration of circulating estrogen levels during interruption of letrozole treatment. This phase III, randomized, open-label Study of Letrozole Extension (SOLE) studied the effect of extended intermittent letrozole treatment in comparison with continuous letrozole. In parallel, the SOLE estrogen substudy (SOLE-EST) analyzed the levels of estrogen during the interruption of treatment.

PATIENTS AND METHODS

SOLE enrolled 4884 postmenopausal women with hormone receptor-positive, lymph node-positive, operable breast cancer between December 2007 and October 2012 and among them, 104 patients were enrolled in SOLE-EST. They must have undergone local treatment and have completed 4-6 years of adjuvant ET. Patients were randomized between continuous letrozole (2.5 mg/day orally for 5 years) and intermittent letrozole treatment (2.5 mg/day for 9 months followed by a 3-month interruption in years 1-4 and then 2.5 mg/day during all of year 5).

RESULTS

Intention-to-treat population included 4851 women in SOLE (n = 2425 in the intermittent and n = 2426 in the continuous letrozole groups) and 103 women in SOLE-EST (n = 78 in the intermittent and n = 25 in the continuous letrozole groups). After a median follow-up of 84 months, 7-year disease-free survival (DFS) was 81.4% in the intermittent group and 81.5% in the continuous group (hazard ratio: 1.03, 95% confidence interval: 0.91-1.17). Reported adverse events were similar in both groups. Circulating estrogen recovery was demonstrated within 6 weeks after the stop of letrozole treatment.

CONCLUSIONS

Extended adjuvant ET by intermittent administration of letrozole did not improve DFS compared with continuous use, despite the recovery of circulating estrogen levels. The similar DFS coupled with previously reported quality-of-life advantages suggest intermittent extended treatment is a valid option for patients who require or prefer a treatment interruption.

Insights into the Behavior of Triple-Negative MDA-MB-231 Breast Carcinoma Cells Following the Treatment with 17β-Ethinylestradiol and Levonorgestrel

Oral contraceptives (OCs) are widely used due to their efficiency in preventing unplanned pregnancies and treating several human illnesses. Despite their medical value, the toxicity of OCs remains a public concern. Previous studies indicate the carcinogenic potential of synthetic sex hormones and their link to the development and progression of hormone-dependent malignancies such as breast cancer. However, little is known about their influence on the evolution of triple-negative breast carcinoma (TNBC), a malignancy defined by the absence of estrogen, progesterone, and HER2 receptors. This study reveals that the active ingredients of modern OCs, 17β-Ethinylestradiol, Levonorgestrel, and their combination induce differential effects in MDA-MB-231 TNBC cells. The most relevant behavioral changes occurred after the 24 h treatment with 17β-Ethinylestradiol, summarized as follows: (i) decreased cell viability (64.32% at 10 µM); (ii) cell roundness and loss of confluence; (iii) apoptotic aspect of cell nuclei (fragmentation, membrane blebbing); and (iv) inhibited cell migration, suggesting a potential anticancer effect. Conversely, Levonorgestrel was generally associated with a proliferative activity. The association of the two OCs exerted similar effects as 17β-Ethinylestradiol but was less effective. Further studies are necessary to elucidate the hormones' cytotoxic mechanism of action on TNBC cells.

Pharmacology and Molecular Mechanisms of Clinically Relevant Estrogen Estetrol and Estrogen Mimic BMI-135 for the Treatment of Endocrine-Resistant Breast Cancer

Long-term estrogen deprivation (LTED) with tamoxifen (TAM) or aromatase inhibitors leads to endocrine-resistance, whereby physiologic levels of estrogen kill breast cancer (BC). Estrogen therapy is effective in treating patients with advanced BC after resistance to TAM and aromatase inhibitors develops. This therapeutic effect is attributed to estrogen-induced apoptosis via the estrogen receptor (ER). Estrogen therapy can have unpleasant gynecologic and nongynecologic adverse events. Here, we study estetrol (E4) and a model Selective Human ER Partial Agonist (ShERPA) BMI-135. Estetrol and ShERPA TTC-352 are being evaluated in clinical trials. These agents are proposed as safer estrogenic candidates compared with 17β-estradiol (E2) for the treatment of endocrine-resistant BC. Cell viability assays, real-time polymerase chain reaction, luciferase reporter assays, chromatin immunoprecipitation, docking and molecular dynamics simulations, human unfolded protein response (UPR) RT2 PCR profiler arrays, live cell microscopic imaging and analysis, and annexin V staining assays were conducted. Our work was done in eight biologically different human BC cell lines and one human endometrial cancer cell line, and results were compared with full agonists estrone, E2, and estriol, a benchmark partial agonist triphenylethylene bisphenol (BPTPE), and antagonists 4-hydroxytamoxifen and endoxifen. Our study shows the pharmacology of E4 and BMI-135 as less-potent full-estrogen agonists as well as their molecular mechanisms of tumor regression in LTED BC through triggering a rapid UPR and apoptosis. Our work concludes that the use of a full agonist to treat BC is potentially superior to a partial agonist given BPTPE's delayed induction of UPR and apoptosis, with a higher probability of tumor clonal evolution and resistance. SIGNIFICANCE STATEMENT: Given the unpleasant gynecologic and nongynecologic adverse effects of estrogen treatment, the development of safer estrogens for endocrine-resistant breast cancer (BC) treatment and hormone replacement therapy remains a priority. The naturally occurring estrogen estetrol and Selective Human Estrogen-Receptor Partial Agonists are being evaluated in endocrine-resistant BC clinical trials. This work provides a comprehensive evaluation of their pharmacology in numerous endocrine-resistant BC models and an endometrial cancer model and their molecular mechanisms of tumor regression through the unfolded protein response and apoptosis.

The Structure-Function Relationship of Angular Estrogens and Estrogen Receptor Alpha to Initiate Estrogen-Induced Apoptosis in Breast Cancer Cells

High-dose synthetic estrogen therapy was the standard treatment of advanced breast cancer for three decades until the discovery of tamoxifen. A range of substituted triphenylethylene synthetic estrogens and diethylstilbestrol were used. It is now known that low doses of estrogens can cause apoptosis in long-term estrogen deprived (LTED) breast cancer cells resistant to antiestrogens. This action of estrogen can explain the reduced breast cancer incidence in postmenopausal women over 60 who are taking conjugated equine estrogens and the beneficial effect of low-dose estrogen treatment of patients with acquired aromatase inhibitor resistance in clinical trials. To decipher the molecular mechanism of estrogens at the estrogen receptor (ER) complex by different types of estrogens-planar [17β-estradiol (E2)] and angular triphenylethylene (TPE) derivatives-we have synthesized a small series of compounds with either no substitutions on the TPE phenyl ring containing the antiestrogenic side chain of endoxifen or a free hydroxyl. In the first week of treatment with E2 the LTED cells undergo apoptosis completely. By contrast, the test TPE derivatives act as antiestrogens with a free para-hydroxyl on the phenyl ring that contains an antiestrogenic side chain in endoxifen. This inhibits early E2-induced apoptosis if a free hydroxyl is present. No substitution at the site occupied by the antiestrogenic side chain of endoxifen results in early apoptosis similar to planar E2 The TPE compounds recruit coregulators to the ER differentially and predictably, leading to delayed apoptosis in these cells. SIGNIFICANCE STATEMENT: In this paper we investigate the role of the structure-function relationship of a panel of synthetic triphenylethylene (TPE) derivatives and a novel mechanism of estrogen-induced cell death in breast cancer, which is now clinically relevant. Our study indicates that these TPE derivatives, depending on the positioning of the hydroxyl groups, induce various conformations of the estrogen receptor's ligand-binding domain, which in turn produces differential recruitment of coregulators and subsequently different apoptotic effects on the antiestrogen-resistant breast cancer cells.

Novel Pyrrolopyridone Bromodomain and Extra-Terminal Motif (BET) Inhibitors Effective in Endocrine-Resistant ER+ Breast Cancer with Acquired Resistance to Fulvestrant and Palbociclib

Acquired resistance to fulvestrant and palbociclib is a new challenge to treatment of estrogen receptor positive (ER+) breast cancer. ER is expressed in most resistance settings; thus, bromodomain and extra-terminal protein inhibitors (BETi) that target BET-amplified ER-mediated transcription have therapeutic potential. Novel pyrrolopyridone BETi leveraged novel interactions with L92/L94 confirmed by a cocrystal structure of 27 with BRD4. Optimization of BETi using growth inhibition in fulvestrant-resistant (MCF-7:CFR) cells was confirmed in endocrine-resistant, palbociclib-resistant, and ESR1 mutant cell lines. 27 was more potent in MCF-7:CFR cells than six BET inhibitors in clinical trials. Transcriptomic analysis differentiated 27 from the benchmark BETi, JQ-1, showing downregulation of oncogenes and upregulation of tumor suppressors and apoptosis. The therapeutic approach was validated by oral administration of 27 in orthotopic xenografts of endocrine-resistant breast cancer in monotherapy and in combination with fulvestrant. Importantly, at an equivalent dose in rats, thrombocytopenia was mitigated.

Underlying Breast Cancer Risk and Menopausal Hormone Therapy

The recent Collaborative Group on Hormonal Factors in Breast Cancer (CGHFBC) publication calculated the attributable risk of breast cancer from use of estrogen alone and estrogen plus a synthetic progestogen for less than 5 to 15 or more years of use. This CGHFB report calculated attributable risk based on their findings of relative risk from pooled data from 58 studies. Notably, neither the CGHFBC nor other previous studies have examined the effect of underlying risk of breast cancer on attributable risk. This omission prompted us to determine the magnitude of the effect of underlying risk on attributable risk in this perspective. Meaningful communication of the potential risk of menopausal hormonal therapy requires providing women with the estimated risk above their existing underlying risk (ie, attributable risk). Therefore, we have estimated attributable risks from the data published by the CGHFBC, taking into account varying degrees of underlying risk. Based on the Endocrine Society Guideline on Menopausal Hormone Therapy (MHT), we divided groups into 3 categories of risk: low (1.5%), intermediate (3.0%), and high (6.0%) underlying risk of breast cancer over 5 years. In women taking estrogen plus a synthetic progestogen for 5 to 9 years, the attributable risks of MHT increased from 12, to 42, to 85 additional women per 1000 in the low-, intermediate-, and high-risk groups, respectively. The attributable risks for estrogen alone were lower but also increased based on underlying risk. Notably, the attributable risks were amplified with duration of MHT use, which increased both relative risk and breast cancer incidence.

Effect of Physical Training on the Levels of Sex Hormones and the Expression of Their Receptors in Rats With Induced Mammary Cancer in Secondary Prevention Model - Preliminary Study

BACKGROUND/AIM

Breast cancer is the most common malignant tumor among women worldwide. In previous work, we presented results of physical activity in primary prevention in a model of induced mammary gland cancer. In the present study, we assessed the influence of physical activity on sex hormone levels (estradiol and progesterone) and the expression of their receptors (ER, PR), as well as the level of apoptosis of tumor cells in secondary prevention.

MATERIALS AND METHODS

Fifty 1-month-old female Sprague-Dawley rats received intraperitoneal injection of 180 mg/kg body weight of N-methyl-N-nitrosourea (MNU) for tumor induction. Three months after the administration of MNU, rats were divided into four groups: low-intensity, moderate-intensity, and high-intensity physical training groups (combined as PT) and a sedentary control (SC) group. Physical training was conducted 5 days per week with a three-position treadmill according to a precisely described protocol. The entire training was completed by 32 rats from which tissue and blood were collected for further analysis. Immunohistochemistry for ER and PR expression, terminal deoxynucleotidyl transferase dUTP nick-end labeling method for detection of apoptosis, and enzyme-linked fluorescent assay for detection of plasma hormone levels (estradiol and progesterone) were performed. Statistical analysis used p<0.05 as the significance level.

RESULTS

Significantly stronger expression of ER and PR was found in the SC in comparison to the PT group (p=0.035 and p=0.036, respectively). No statistically significant differences were found in estradiol or progesterone concentrations between SC and PT groups. Apoptosis was non-significantly increased in the PT group in comparison with the SC group. Stronger apoptosis in the PT group correlated positively with the level of training intensity (r=0.35, p=0.05).

CONCLUSION

Physical training may reduce ER and PR expression in breast cancer cells, and reduce cell sensitivity to pro-proliferative and anti-apoptotic effects of estrogens, ultimately leading to apoptosis.

Targeting the Unfolded Protein Response in Hormone-Regulated Cancers

Cancer cells exploit many of the cellular adaptive responses to support their survival needs. One of these is the unfolded protein response (UPR), a highly conserved signaling pathway that is mounted in response to endoplasmic reticulum (ER) stress. Recent work showed that steroid hormones, in particular estrogens and androgens, regulate the canonical UPR pathways in breast cancer (BCa) and prostate cancer (PCa). In addition, UPR has pleiotropic effects in advanced disease and development of therapy resistance. These findings implicate the UPR pathway as a novel target in hormonally regulated cancers in the clinic. Here, we review the potential therapeutic value of recently developed small molecule inhibitors of UPR in hormone regulated cancers.

Estrogen-alone therapy and invasive breast cancer incidence by dose, formulation, and route of delivery: findings from the WHI observational study

OBJECTIVE

Research on the relationships between different hormone therapy doses, formulation and routes of delivery, and subsequent breast cancer incidence has been limited. This study directly compared different estrogen doses, formulations, and route of delivery of estrogen alone among women with a hysterectomy in relation to invasive breast cancer incidence.

METHODS

The Women's Health Initiative Observational Study is a large multicenter prospective cohort study conducted at 40 US sites. Analyses included 26,525 postmenopausal women with a hysterectomy, aged 50 to 79 years, at study entry, recruited between September, 1993 and December, 1998, with annual follow-up through September 12, 2005.

RESULTS

Average follow-up was 8.2 years. For conjugated equine estrogen (CEE) users, no difference was observed between low-dose CEE (<0.625 mg) compared with conventional-dose CEE (0.625 mg) for breast cancer (hazard ratio [HR] 0.99, 95% confidence interval [CI] 0.65, 1.48)]. Compared with conventional-dose CEE, transdermal estrogen was associated with a nonsignificant lower risk of invasive breast cancer (HR 0.75, 95% CI 0.47, 1.19). The low prevalence of transdermal use likely limited power for this comparison, and for a comparison of oral estradiol to conventional-dose CEE (HR 1.20, 95% CI 0.84, 1.39).

CONCLUSION

Our results indicate that invasive breast cancer risk did not differ appreciably in women with a hysterectomy using estrogen-alone when directly comparing different doses, formulations, and routes of delivery to the conventional oral CEE. These findings suggest that the lower breast cancer risk found in the WHI estrogen-alone trial may extend to lower doses of CEE. Additional research is needed to confirm these hypotheses.

Suppression of Nuclear Factor-κB by Glucocorticoid Receptor Blocks Estrogen-Induced Apoptosis in Estrogen-Deprived Breast Cancer Cells

Our clinically relevant finding is that glucocorticoids block estrogen (E₂)-induced apoptosis in long-term E₂-deprived (LTED) breast cancer cells. However, the mechanism remains unclear. Here, we demonstrated that E₂ widely activated adipose inflammatory factors such as fatty acid desaturase 1 (FADS1), IL6, and TNFα in LTED breast cancer cells. Activation of glucocorticoid receptor (GR) by the synthetic glucocorticoid dexamethasone upregulated FADS1 and IL6, but downregulated TNFα expression. Furthermore, dexamethasone was synergistic or additive with E₂ in upregulating FADS1 and IL6 expression, whereas it selectively and constantly suppressed TNFα expression induced by E₂ in LTED breast cancer cells. Regarding regulation of endoplasmic reticulum stress, dexamethasone effectively blocked activation of protein kinase RNA-like endoplasmic reticulum kinase (PERK) by E₂, but it had no inhibitory effects on inositol-requiring protein 1 alpha (IRE1α) expression increased by E₂ Consistently, results from reverse-phase protein array (RPPA) analysis demonstrated that dexamethasone could not reverse IRE1α-mediated degradation of PI3K/Akt-associated signal pathways activated by E₂ Unexpectedly, activated GR preferentially repressed nuclear factor-κB (NF-κB) DNA-binding activity and expression of NF-κB-dependent gene TNFα induced by E₂, leading to the blockade of E₂-induced apoptosis. Together, these data suggest that trans-suppression of NF-κB by GR in the nucleus is a fundamental mechanism thereby blocking E₂-induced apoptosis in LTED breast cancer cells. This study provided an important rationale for restricting the clinical use of glucocorticoids, which will undermine the beneficial effects of E₂-induced apoptosis in patients with aromatase inhibitor-resistant breast cancer.

Estrogen therapy induces an unfolded protein response to drive cell death in ER+ breast cancer

Estrogens have been shown to elicit anticancer effects against estrogen receptor α (ER)-positive breast cancer. We sought to determine the mechanism underlying the therapeutic response. Response to 17β-estradiol was assessed in ER+ breast cancer models with resistance to estrogen deprivation: WHIM16 patient-derived xenografts, C7-2-HI and C4-HI murine mammary adenocarcinomas, and long-term estrogen-deprived MCF-7 cells. As another means to reactivate ER, the anti-estrogen fulvestrant was withdrawn from fulvestrant-resistant MCF-7 cells. Transcriptional, growth, apoptosis, and molecular alterations in response to ER reactivation were measured. 17β-estradiol treatment and fulvestrant withdrawal induced transcriptional activation of ER, and cells adapted to estrogen deprivation or fulvestrant were hypersensitive to 17β-estradiol. ER transcriptional response was followed by an unfolded protein response and apoptosis. Such apoptosis was dependent upon the unfolded protein response, p53, and JNK signaling. Anticancer effects were most pronounced in models exhibiting genomic amplification of the gene encoding ER (ESR1), suggesting that engagement of ER at high levels is cytotoxic. These data indicate that long-term adaptation to estrogen deprivation or ER inhibition alters sensitivity to ER reactivation. In such adapted cells, 17β-estradiol treatment and anti-estrogen withdrawal hyperactivate ER, which drives an unfolded protein response and subsequent growth inhibition and apoptosis. 17β-estradiol treatment should be considered as a therapeutic option for anti-estrogen-resistant disease, particularly in patients with tumors harboring ESR1 amplification or ER overexpression. Furthermore, therapeutic strategies that enhance an unfolded protein response may increase the therapeutic effects of ER reactivation.

New insights into acquired endocrine resistance of breast cancer

The translational research strategy of targeting estrogen receptor α (ERα) positive breast cancer and then using long term anti-hormone adjuvant therapy (5-10 years) has reduced recurrences and mortality. However, resistance continues to occur and improvements are required to build on the success of tamoxifen and aromatase inhibitors (AIs) established over the past 40 years. Further translational research has described the evolution of acquired resistance of breast cancer cell lines to long term estrogen deprivation that parallels clinical experience over years. Additionally, recent reports have identified mutations in the ERα obtained from the recurrences of AI treated patients. These mutations allow the ERα to activate without ligands and auto stimulate metastatic tumor growth. Furthermore, the new biology of estrogen-induced apoptosis in acquired resistant models in vitro and in vivo has been interrogated and applied to clinical trials. Inflammation and stress are emerging concepts occurring in the process of acquired resistance and estrogen-induced apoptosis with different mechanisms. In this review, we will present progress in the understanding of acquired resistance, focus on stress and inflammatory responses in the development of acquired resistance, and consider approaches to create new treatments to improve the treatment of breast cancer with endocrine resistance.

Interaction Between MUC1 and STAT1 Drives IFITM1 Overexpression in Aromatase Inhibitor-Resistant Breast Cancer Cells and Mediates Estrogen-Induced Apoptosis

The human oncoprotein, mucin 1 (MUC1), drives tumorigenesis in breast carcinomas by promoting epithelial-to-mesenchymal transition (EMT), epigenetic reprogramming, and evasion of immune response. MUC1 interacts with STAT1, through JAK/STAT signaling, and stimulates transcription of IFN-stimulated genes, specifically IFN-induced transmembrane protein 1 (IFITM1). Our laboratory has previously shown that IFITM1 overexpression in aromatase inhibitor (AI)-resistant breast cancer cells promotes aggressiveness. Here, we demonstrate that differential regulation of MUC1 in AI-sensitive (MCF-7 and T-47D) compared with AI-resistant (MCF-7:5C) cells is critical in mediating IFITM1 expression. A tumor microarray of 94 estrogen receptor-positive human breast tumors correlated coexpression of MUC1 and IFITM1 with poor recurrence-free survival, poor overall survival, and AI-resistance. In this study, we investigated the effects of MUC1/IFITM1 on cell survival and proliferation. We knocked down MUC1 levels with siRNA and pharmacologic inhibitors, which abrogated IFITM1 mRNA and protein expression and induced cell death in AI-resistant cells. In vivo, estrogen and ruxolitinib significantly reduced tumor size and decreased expression of MUC1, P-STAT1, and IFITM1. IMPLICATIONS: MUC1 and IFITM1 overexpression drives AI resistance and can be targeted with currently available therapies.Visual Overview: http://mcr.aacrjournals.org/content/molcanres/17/5/1180/F1.large.jpg.

Hormone signaling via androgen receptor affects breast cancer and prostate cancer in a male patient: A case report

Background

Male breast cancer (MBC) is rare, accounting for only around 1% of all breast cancers. Most MBCs are hormone-driven. Not only the estrogen receptor (ER), but also other steroid hormone receptors, including the androgen receptor (AR) and progesterone receptor (PgR) are expressed in MBC. AR activation in breast cancer cells facilitates downstream gene expression that drives tumorigenesis in a similar manner to ER. AR-mediated signalling works paradoxically in breast cancer and prostate cancer, and cancer cells expressing the AR are endocrine-sensitive.

Case presentation

We describe a case of double cancer of MBC and prostate cancer. A 69-year-old man was referred to our hospital with a lump in his left breast in the 1990s. The patient had cT3N3M0, stage IIIC breast cancer, and underwent a mastectomy and axillary lymph node dissection. Though adjuvant chemotherapy was administered, he experienced pleural metastasis 2 months after the surgery. Two years after the recurrence during endocrine therapy with oral 5-fluorouracil, he complained of frequent urination. Radiological and histological examinations revealed that the patient had cT3N0M0, stage III primary prostate cancer with a prostate-specific antigen (PSA) level of 40.5 ng/mL. Germline mutations in the BRCA1 and BRCA2 genes were not tested. He received multidisciplinary, continuous therapy for both breast and prostate cancer; however, 5 and 3 years after each diagnosis, respectively, he experienced a deep vein thrombosis in his right leg related to the endocrine therapy. Liver metastasis progressed after he stopped breast cancer therapy. However, long-term disease control had been achieved with anti-estrogen therapy for breast cancer and estrogen replacement therapy for prostate cancer.

Conclusions

Several studies have shown that estrogen exposure after estrogen depletion likely causes apoptosis of ER-positive breast cancer cells. Our findings indicate that this also applies to the environment in male body. AR dominant signaling prevents breast cancer recurrence and metastasis, especially in MBC patients.

Comparative Analysis of the Effects of 17-Beta Estradiol on Proliferation, and Apoptosis in Hepatocellular Carcinoma Hep G2 and LCL-PI 11 Cell Lines

Background:

Phytoestrogens are a group of natural compounds with estrogen-like activity and similar structure to estradiol that structurally mimic the mammalian estrogen 17-β estradiol (E2). They have a biphasic effect and exert pleiotropic effects which induce or inhibit estrogen action by activation/inhibition of the estrogen receptors (ERs). These compounds can induce apoptosis at high concentrations. The previous finding indicated that E2 inhibited cell growth and induced apoptosis in hepatocellular carcinoma (HCC) PLC/PRF/5 cell line. The aim of the present study was to investigate the apoptotic and proliferative effects of E2 on hepatocellular carcinoma HepG 2 and LCL-PI 11 cells.

Methods:

The Hep G2 and LCL-PI 11 cells were cultured and treated with E2 for different time periods and then MTT [3-(4, 5-dimethyl-2-thiazolyl) -2, 5-diphenyl -2H- tetrazolium bromide] assay and flow cytometry assay were done to determine cell viability and cell apoptosis respectively.

Results:

E2 had inhibitory and apoptotic effects on Hep G2 cell line, whereas it indicated a biphasic effect on LCL-PI 11 cell line. The half-maximum inhibitory concentration (IC50) value was 3 μM. The inhibitory effect of E2 on Hep G2 cells was observed with all concentrations of E2 (P <0.087), whereas E2 showed a biphasic effect on LCL-PI 11. This compound induced significant apoptosis in Hep G2 cell line at the all treatment times versus control groups, whereas, in the LCL-PI 11 cell, significant apoptotic cells were observed after 72 and 96h (P <0.001).

Conclusion:

E2 can inhibit cell growth and induce apoptosis in hepatocellular carcinoma HepG 2 and LCL-PI 11 cell lines.

Targeting Peroxisome Proliferator-Activated Receptor γ to Increase Estrogen-Induced Apoptosis in Estrogen-Deprived Breast Cancer Cells

Peroxisome proliferator-activated receptor γ (PPARγ) is an important transcription factor that modulates lipid metabolism and inflammation. However, it remains unclear whether PPARγ is involved in modulation of estrogen (E₂)-induced inflammation, thus affecting apoptosis of E₂-deprived breast cancer cells, MCF-7:5C and MCF-7:2A. Here, we demonstrated that E₂ treatment suppressed the function of PPARγ in both cell lines, although the suppressive effect in MCF-7:2A cells was delayed owing to high PPARγ expression. Activation of PPARγ by a specific agonist, pioglitazone, selectively blocked the induction of TNFα expression by E₂, but did not affect other adipose inflammatory genes, such as fatty acid desaturase 1 and IL6. This suppression of TNFα expression by pioglitazone was mainly mediated by transrepression of nuclear factor-κB (NF-κB) DNA-binding activity. A novel finding was that NF-κB functions as an oxidative stress inducer in MCF-7:5C cells but an antioxidant in MCF-7:2A cells. Therefore, the NF-κB inhibitor JSH-23 displayed effects equivalent to those of pioglitazone, with complete inhibition of apoptosis in MCF-7:5C cells, but it increased E₂-induced apoptosis in MCF-7:2A cells. Depletion of PPARγ by siRNA or the PPARγ antagonist T0070907 accelerated E₂-induced apoptosis, with activation of NF-κB-dependent TNFα and oxidative stress. For the first time, we demonstrated that PPARγ is a growth signal and has potential to modulate NF-κB activity and oxidative stress in E₂-deprived breast cancer cell lines. All of these findings suggest that anti-PPARγ therapy is a novel strategy to improve the therapeutic effects of E₂-induced apoptosis in E₂-deprived breast cancer.

Effect of a tissue selective estrogen complex on breast cancer: Role of unique properties of conjugated equine estrogen

The Women's Health Initiative studies reported that the menopausal hormone therapy (MHT) regimen containing conjugated equine estrogen (CEE) and medroxyprogesterone acetate increased, whereas CEE alone reduced breast cancer incidence. These observations suggest the possibility that CEE might exert unique actions on breast and also suggest the need to eliminate the progestogen from MHT regimens. A MHT regimen called a tissue selective estrogen complex (TSEC), containing CEE plus bazedoxifene (BZA), to avoid the need for a progestogen, was developed and FDA approved. Our study addressed two questions regarding this TSEC: (i) whether CEE exert effects on breast cancer which differ from those of estradiol (E2 ) and (ii) whether BZA antagonize the effects of E2 and CEE on breast cancer? Two rodent models (NMU and ACI) were used to compare the effect of CEE with E2 on mammary tumor formation, proliferation and apoptosis. In both the NMU and ACI models, E2 significantly increased tumor incidence and multiplicity whereas in striking contrast CEE did not, even though the estrogenic effects of CEE and E2 on uterine weight were identical. Mechanistically E2 blocked whereas CEE stimulated apoptosis (cleaved caspase-3) in ACI animals and only E2 stimulated proliferation (Ki67). BZA exerted highly potent anti-estrogenic effects on tumors by completely blocking palpable tumor formation. These data suggest that the CEE/BZA TSEC may be a safer, breast-antagonistic, MHT agent for women and might have potential to prevent breast cancer while relieving menopausal symptoms.

Endoxifen, 4-Hydroxytamoxifen and an Estrogenic Derivative Modulate Estrogen Receptor Complex Mediated Apoptosis in Breast Cancer

Estrogen therapy was used to treat advanced breast cancer in postmenopausal women for decades until the introduction of tamoxifen. Resistance to long-term estrogen deprivation (LTED) with tamoxifen and aromatase inhibitors used as a treatment of breast cancer inevitably occurs, but unexpectedly low-dose estrogen can cause regression of breast cancer and increase disease-free survival in some patients. This therapeutic effect is attributed to estrogen-induced apoptosis in LTED breast cancer. Here, we describe modulation of the estrogen receptor (ER) liganded with antiestrogens (endoxifen and 4-hydroxytamoxifen) and an estrogenic triphenylethylene (TPE), ethoxytriphenylethylene (EtOXTPE), on estrogen-induced apoptosis in LTED breast cancer cells. Our results show that the angular TPE estrogen (EtOXTPE) is able to induce the ER-mediated apoptosis only at a later time compared with planar estradiol in these cells. Using real-time polymerase chain reaction, chromatin immunoprecipitation, western blotting, molecular modeling, and X-ray crystallography techniques, we report novel conformations of the ER complex with an angular estrogen EtOXTPE and endoxifen. We propose that alteration of the conformation of the ER complexes, with changes in coactivator binding, governs estrogen-induced apoptosis through the protein kinase regulated by RNA-like endoplasmic reticulum kinase sensor system to trigger an unfolded protein response.

Abiraterone shows alternate activity in models of endocrine resistant and sensitive disease

BACKGROUND

Resistance to endocrine therapy remains a major clinical problem in the treatment of oestrogen-receptor positive (ER+) breast cancer. Studies show androgen-receptor (AR) remains present in 80-90% of metastatic breast cancers providing support for blockade of AR-signalling. However, clinical studies with abiraterone, which blocks cytochrome P450 17A1 (CYP17A1) showed limited benefit.

METHODS

In order to address this, we assessed the impact of abiraterone on cell-viability, cell-death, ER-mediated transactivation and recruitment to target promoters. together with ligand-binding assays in a panel of ER+ breast cancer cell lines that were either oestrogen-dependent, modelling endocrine-sensitive disease, or oestrogen-independent modelling relapse on an aromatase inhibitor. The latter, harboured wild-type (wt) or naturally occurring ESR1 mutations.

RESULTS

Similar to oestrogen, abiraterone showed paradoxical impact on proliferation by stimulating cell growth or death, depending on whether the cells are hormone-dependent or have undergone prolonged oestrogen-deprivation, respectively. Abiraterone increased ER-turnover, induced ER-mediated transactivation and ER-degradation via the proteasome.

CONCLUSIONS

Our study confirms the oestrogenic activity of abiraterone and highlights its differential impact on cells dependent on oestrogen for their proliferation vs. those that are ligand-independent and harbour wt or mutant ESR1. These properties could impact the clinical efficacy of abiraterone in breast cancer.

The relationship between serum E2 levels and recurrence in premenopausal, ER-positive breast cancer patients: A retrospective study

BACKGROUND

Among estrogens, estradiol (E2) has the strongest physiological activity as a stimulator in estrogen receptor (ER)-positive breast cancer. The aim of this study is to investigate E2 dynamics during endocrine therapy and to explore the optimal environment in which tamoxifen (TAM) exhibits better efficacy for ER-positive premenopausal early breast cancer patients.

METHODS

This is a retrospective study enrolled 194 patients with premenopausal ER-positive early-stage breast cancer who aging ≤45 years at onset and receiving luteinizing hormone-releasing hormone-agonist (LHRH-a) and TAM-therapy. Approximately half of the patients also received pre- or post-operative chemotherapy as adjuvant systemic therapy. We studied the relationship between recurrence and serum hormonal dynamics during adjuvant therapy. We monitored the concentrations of E2 and, follicle-stimulating hormone (FSH) in the blood before, during, and after treatment. The median follow-up period was 80 (14-555) months.

RESULTS

Forty-six (23.7%) patients developed recurrent breast cancer after surgery. The prognoses were favorable in the group receiving longer LHRH-a exposure if those patients did not receive chemotherapy as their adjuvant therapy. Paradoxically, patients with high serum E2 levels after LHRH-a showed a low recurrence ratio. This phenomenon might be explained by the similar mechanisms of estrogen therapy after estrogen depletion by aromatase inhibitor (AI) therapy for metastatic breast cancer.

CONCLUSION

Among patients who received endocrine therapy without adjuvant chemotherapy, those with longer LHRH-a exposure had favorable prognoses. A potential association was observed between recurrence and E2 concentrations in women with premenopausal ER-positive early-stage breast cancer.

Modulation of nuclear factor-kappa B activation by the endoplasmic reticulum stress sensor PERK to mediate estrogen-induced apoptosis in breast cancer cells

Stress responses are critical for estrogen (E₂)-induced apoptosis in E₂-deprived breast cancer cells. Nuclear factor-kappa B (NF-κB) is an important therapeutic target to prevent stress responses in chronic inflammatory diseases including cancer. However, whether E₂ activates NF-κB to participate in stress-associated apoptosis in E₂-deprived breast cancer cells is unknown. Here, we demonstrated that E₂ differentially modulates NF-κB activity according to treatment time. E₂ initially has significant potential to suppress NF-κB activation; it completely blocks tumor necrosis factor alpha (TNFα)-induced activation of NF-κB. We found that E₂ preferentially and constantly enhances the expression of the adipogenic transcription factor CCAAT/enhancer binding protein beta (C/EBPβ), which is responsible for the suppression of NF-κB activation by E₂ in MCF-7:5C cells. Interestingly, NF-κB p65 DNA-binding activity is increased when E₂ is administered for 48 h, leading to the induction of TNFα and associated apoptosis. Blocking the nuclear translocation of NF-κB can completely prevent the induction of TNFα and apoptosis induced by E₂. Further examination revealed that protein kinase RNA-like endoplasmic reticulum kinase (PERK), a stress sensor of unfolded protein response (UPR), plays an essential role in the late activation of NF-κB by E₂. This modulation between PERK and NF-κB is mainly mediated by a stress responsive transcription factor, transducer and activator of transcription 3 (STAT3), independently of the classic canonical IκBα signaling pathway. Thus, inhibition of PERK kinase activity completely blocks the DNA binding of both STAT3 and NF-κB, thereby preventing induction of NF-κB-dependent genes and E₂-induced apoptosis. All of these findings suggest that PERK is a key regulator to convey stress signals from the endoplasmic reticulum to the nucleus and illustrate a crucial role for the novel PERK/STAT3/NF-κB/TNFα axis in E₂-induced apoptosis in E₂-deprived breast cancer cells.

A unifying biology of sex steroid-induced apoptosis in prostate and breast cancers

Prostate and breast cancer are the two cancers with the highest incidence in men and women, respectively. Here, we focus on the known biology of acquired resistance to antihormone therapy of prostate and breast cancer and compare laboratory and clinical similarities in the evolution of the disease. Laboratory studies and clinical observations in prostate and breast cancer demonstrate that cell selection pathways occur during acquired resistance to antihormonal therapy. Following sex steroid deprivation, both prostate and breast cancer models show an initial increased acquired sensitivity to the growth potential of sex steroids. Subsequently, prostate and breast cancer cells either become dependent upon the antihormone treatment or grow spontaneously in the absence of hormones. Paradoxically, the physiologic sex steroids now kill a proportion of selected, but vulnerable, resistant tumor cells. The sex steroid receptor complex triggers apoptosis. We draw parallels between acquired resistance in prostate and breast cancer to sex steroid deprivation. Clinical observations and patient trials confirm the veracity of the laboratory studies. We consider therapeutic strategies to increase response rates in clinical trials of metastatic disease that can subsequently be applied as a preemptive salvage adjuvant therapy. The goal of future advances is to enhance response rates and deploy a safe strategy earlier in the treatment plan to save lives. The introduction of a simple evidence-based enhanced adjuvant therapy as a global healthcare strategy has the potential to control recurrence, reduce hospitalization, reduce healthcare costs and maintain a healthier population that contributes to society.

Effect of Genistein and 17-β Estradiol on the Viability and Apoptosis of Human Hepatocellular Carcinoma HepG2 cell line

Background:

One of the most lethal cancers is hepatocellular carcinoma (HCC). Genistein (GE) is a choice compound for treatment of certain types of cancer. Phytoestrogens are plant derivatives that bear a structural similarity to 17-β estradiol (E2) and act in a similar manner. They are a group of lipophillic plant compounds with tumorigenic and antitumorigenic effects. E2 has stimulatory and inhibitory effects on cancer cell lines. This study was designed to investigate the antiproliferative and apoptotic effects of GE and E2 on the HCC HepG2 cell line.

Materials and Methods:

HepG2 cells were cultured and treated with various concentrations of GE and E2 and then 3-[4, 5-dimethyl-2-thiazolyl]-2, 5-diphenyl-2H-tetrazolium bromideand flow cytometry assay were performed to determine cell viability and apoptosis.

Results:

GE and E2 induced apoptosis and inhibited cell growth significantly. Reduction of cell viability by 50% required 20 μM E2 for E2-treatment groups and 20 μMGE for GE-treatment groups. The percentage of the GE-treated apoptotic cells was reduced by about 35%, 42%, and 47% (P < 0.001) and that of E2-treated groups 34%, 39%, and 42% (P < 0.001) after 24, 48, and 72 h, respectively.

Conclusions:

Our experimental work clearly demonstrated that GE and E2 exhibited significant antiproliferative and apoptotic effects on human HCC HepG2 cells.