ERRα Is a Marker of Tamoxifen Response and Survival in Triple-Negative Breast Cancer

Cholesteryl ester transfer protein knock-down in conjunction with a cholesterol-depleting agent decreases tamoxifen resistance in breast cancer cells

The cholesterogenic phenotype, encompassing de novo biosynthesis and accumulation of cholesterol, aids cancer cell proliferation and survival. Previously, the role of cholesteryl ester (CE) transfer protein (CETP) has been implicated in breast cancer aggressiveness, but the molecular basis of this observation is not clearly understood, which this study aims to elucidate. CETP knock-down resulted in a >50% decrease in cell proliferation in both 'estrogen receptor-positive' (ER+; Michigan Cancer Foundation-7 (MCF7) breast cancer cells) and 'triple-negative' breast cancer (TNBC; MDA-MB-231) cell lines. Intriguingly, the abrogation of CETP together with the combination treatment of tamoxifen (5 μM) and acetyl plumbagin (a cholesterol-depleting agent) (5 μM) resulted in twofold to threefold increase in apoptosis in both cell lines. CETP knockdown also showed decreased intracellular CE levels, lipid raft and lipid droplets in both cell lines. In addition, RT2 Profiler PCR array (Qiagen, Germany)-based gene expression analysis revealed an overall downregulation of genes associated in cholesterol biosynthesis, lipid signalling and drug resistance in MCF7 cells post-CETP knock-down. On the contrary, resistance in MDA-MB-231 cells was reduced through increased expression in cholesterol efflux genes and the expression of targetable surface receptors by endocrine therapy. The pilot xenograft mice study substantiated CETP's role as a cancer survival gene as knock-down of CETP stunted the growth of TNBC tumour by 86%. The principal findings of this study potentiate CETP as a driver in breast cancer growth and aggressiveness and thus targeting CETP could limit drug resistance via the reduction in cholesterol accumulation in breast cancer cells, thereby reducing cancer aggressiveness.

Estrogen-related receptor alpha (ERRα) promotes the migration, invasion and angiogenesis of breast cancer stem cell-like cells

Breast cancer progression, metastasis and recurrence are largely driven by breast cancer stem cells (BCSCs), which constitute a subset of tumor cells exhibiting stem cell characteristics. In this study, we evaluated the role of estrogen-related receptor alpha (ERRα) in the migration, invasion and angiogenesis of BCSCs. The inhibition of ERRα using XCT790 or knockdown of ERRα using shRNA inhibited the mammosphere formation efficiency, as well as the migration and invasion of BCSCs derived from the mammospheres of MCF7 and MDA-MB-231 (MB231) cells. Conversely, the overexpression of ERRα significantly increased the migration and invasion of BCSCs derived from the mammosphere. In addition, the XCT790 treatment or shERRα significantly downregulated the epithelial-mesenchymal transition (EMT), as evidenced by the downregulation in the expression of vimentin, Snail, Slug and N-cadherin in the mammospheres of MCF7 and MB231 cells. The chorioallantoic membrane assay showed that the conditioned media from XCT790-treated and shERRα cells significantly inhibited blood vessel formation and vessel length. Furthermore, XCT790 treatment or shERRα also downregulated the expression of molecular markers of angiogenesis, such as VEGF-A and Ang-2 in the mammospheres. Conversely, the overexpression of ERRα in MCF7 cells significantly increased both EMT and angiogenesis. These findings suggest that ERRα inhibits the migration, invasion and angiogenesis of BCSCs, suggesting as a potential target for breast cancer therapy.

Estrogen-Related Receptor Alpha (ERRα) Promotes Cancer Stem Cell-Like Characteristics in Breast Cancer

Cancer stem cells drive tumor initiation, invasion, metastasis and recurrence. In the present study, we have evaluated the role of ERRα in the maintenance of breast cancer stem cells (BCSCs) using breast cancer cell lines. The inhibition of ERRα with the inverse agonist, XCT-790, or the knockdown of ERRα in breast cancer cells significantly reduced the mammosphere formation efficiency and mammosphere size along with a significant reduction in the CD44+/CD24- BCSCs. Treatment with XCT-790 significantly downregulated expression of the transcription factors involved in stem cell maintenance such as Oct4, Klf4, Sox2, Nanog and c-Myc in the mammosphere forming stem cells of MCF7 and MDA-MB-231. In addition, XCT-790 induced cell cycle arrest and apoptosis in the mammosphere-forming cells. The knockdown or inhibition of ERRα downregulated the expression of Notch1 and β-catenin, whereas the overexpression of ERRα in MCF7 cells upregulated the expression of these proteins. Moreover, the inhibition of ERRα synergistically enhanced the efficacy of paclitaxel in inhibiting the BCSCs. These results show that ERRα is crucial for the maintenance of BCSCs and suggest that ERRα could be a potential target for breast cancer treatment.

The Role of Obesity in Breast Cancer Pathogenesis

Research has shown that obesity increases the risk for type 2 diabetes mellitus (Type 2 DM) by promoting insulin resistance, increases serum estrogen levels by the upregulation of aromatase, and promotes the release of reactive oxygen species (ROS) by macrophages. Increased circulating glucose has been shown to activate mammalian target of rapamycin (mTOR), a significant signaling pathway in breast cancer pathogenesis. Estrogen plays an instrumental role in estrogen-receptor-positive breast cancers. The role of ROS in breast cancer warrants continued investigation, in relation to both pathogenesis and treatment of breast cancer. We aim to review the role of obesity in breast cancer pathogenesis and novel therapies mediating obesity-associated breast cancer development. We explore the association between body mass index (BMI) and breast cancer incidence and the mechanisms by which oxidative stress modulates breast cancer pathogenesis. We discuss the role of glutathione, a ubiquitous antioxidant, in breast cancer therapy. Lastly, we review breast cancer therapies targeting mTOR signaling, leptin signaling, blood sugar reduction, and novel immunotherapy targets.

Inhibition of ERK signaling for treatment of ERRα positive TNBC

Breast cancer is the second leading cause of cancer-related deaths in women and triple-negative breast cancer (TNBC), in particular, is an aggressive and highly metastatic type of breast cancer that does not respond to established targeted therapies and is associated with poor prognosis and worse survival. Previous studies identified a subgroup of triple-negative breast cancer patients with high expression of estrogen related receptor alpha (ERRα) that has better prognosis when treated with tamoxifen. We therefore set out to identify common targets of tamoxifen and ERRα in the context of TNBC using phosphoproteomic analysis. In this study, we discovered that phosphorylation of mitogen-activated protein kinase 1 (MAPK1) is regulated by tamoxifen as well as ERRα. Additionally, we showed that inhibition of MAPK signaling together with the use of a selective ERRα inverse agonist, XCT-790, leads to a significant upregulation of apoptosis and paves way for the therapeutic use of MAPK inhibitors for treatment of ERRα expressing TNBC.

The discovery of a novel series of potential ERRα inverse agonists based on p-nitrobenzenesulfonamide template for triple-negative breast cancer in vivo

Oestrogen related receptor α participated in the regulation of oxidative metabolism and mitochondrial biogenesis, and was overexpressed in many cancers including triple-negative breast cancer. A set of new ERRα inverse agonists based on p-nitrobenzenesulfonamide template were discovered and compound 11 with high potent activity (IC50 = 0.80 μM) could significantly inhibit the transcription of ERRα-regulated target genes. By regulating the downstream signalling pathway, compound 11 could suppress the migration and invasion of the ER-negative MDA-MB-231 cell line. Furthermore, compound 11 demonstrated a significant growth suppression of breast cancer xenograft tumours in vivo (inhibition rate 23.58%). The docking results showed that compound 11 could form hydrogen bonds with Glu331 and Arg372 in addition to its hydrophobic interaction with ligand-binding domain. Our data implied that compound 11 represented a novel and effective ERRα inverse agonist, which had broad application prospects in the treatment of triple-negative breast cancer.

Comprehensive Transcriptomic and Proteomic Analyses Identify a Candidate Gene Set in Cross-Resistance for Endocrine Therapy in Breast Cancer

Endocrine therapy (ET) of selective estrogen receptor modulators (SERMs), selective estrogen receptor downregulators (SERDs), and aromatase inhibitors (AIs) has been used as the gold standard treatment for hormone-receptor-positive (HR+) breast cancer. Despite its clinical benefits, approximately 30% of patients develop ET resistance, which remains a major clinical challenge in patients with HR+ breast cancer. The mechanisms of ET resistance mainly focus on mutations in the ER and related pathways; however, other targets still exist from ligand-independent ER reactivation. Moreover, mutations in the ER that confer resistance to SERMs or AIs seldom appear in SERDs. To date, little research has been conducted to identify a critical target that appears in both SERMs/SERDs and AIs. In this study, we conducted comprehensive transcriptomic and proteomic analyses from two cohorts of The Cancer Genome Atlas Breast Invasive Carcinoma (TCGA-BRCA) to identify the critical targets for both SERMs/SERDs and AIs of ET resistance. From a treatment response cohort with treatment response for the initial ET regimen and an endocrine therapy cohort with survival outcomes, we identified candidate gene sets that appeared in both SERMs/SERDs and AIs of ET resistance. The candidate gene sets successfully differentiated progress/resistant groups (PD) from complete response groups (CR) and were significantly correlated with survival outcomes in both cohorts. In summary, this study provides valuable clinical implications for the critical roles played by candidate gene sets in the diagnosis, mechanism, and therapeutic strategy for both SERMs/SERDs and AIs of ET resistance for the future.

Estrogen Related Receptor Alpha (ERRα) a Bridge between Metabolism and Adrenocortical Cancer Progression

Simple Summary

Adrenocortical carcinoma (ACC) is a rare and highly aggressive tumor associated with a very poor prognosis, mostly due to a high risk of recurrence and limited therapeutic options. The identification of “master regulators” of the metabolic changes occurring in cancer cells could offer new targets for innovative therapies. Such a strategy has never been used against ACC progression. In this study, we identify ERRα as key player in ACC metabolism and its targeting can prevent progression to a more aggressive phenotype. The development of new therapeutic strategies to selectively target ERRα in the adrenal with a selective antagonist would hinder ACC progression, avoiding off-target effects.

Abstract

The aim of this study was to investigate the metabolic changes that occur in adrenocortical cancer (ACC) cells in response to the modulation of Estrogen Related Receptor (ERR)α expression and the impact on ACC progression. Proteomics analysis and metabolic profiling highlighted an important role for ERRα in the regulation of ACC metabolism. Stable ERRα overexpression in H295R cells promoted a better mitochondrial fitness and prompted toward a more aggressive phenotype characterized by higher Vimentin expression, enhanced cell migration and spheroids formation. By contrast, a decrease in ERRα protein levels, by molecular (short hairpin RNA) and pharmacological (inverse agonist XCT790) approaches modified the energetic status toward a low energy profile and reduced Vimentin expression and ability to form spheroids. XCT790 produced similar effects on two additional ACC cell lines, SW13 and mitotane-resistant MUC-1 cells. Our findings show that ERRα is able to modulate the metabolic profile of ACC cells, and its inhibition can strongly prevent the growth of mitotane-resistant ACC cells and the progression of ACC cell models to a highly migratory phenotype. Consequently, ERRα can be considered an important target for the design of new therapeutic strategies to fight ACC progression.

Estrogen-Related Receptor α: A Significant Regulator and Promising Target in Bone Homeostasis and Bone Metastasis

Bone homeostasis is maintained with the balance between bone formation and bone resorption, which is involved in the functional performance of osteoblast and osteoclast. Disruption of this equilibrium usually causes bone disorders including osteoporosis, osteoarthritis, and osteosclerosis. In addition, aberrant activity of bone also contributes to the bone metastasis that frequently occurs in the late stage of aggressive cancers. Orphan nuclear receptor estrogen-related receptor (ERRα) has been demonstrated to control the bone cell fate and the progression of tumor cells in bone through crosstalk with various molecules and signaling pathways. However, the defined function of this receptor in bone is inconsistent and controversial. Therefore, we summarized the latest research and conducted an overview to reveal the regulatory effect of ERRα on bone homeostasis and bone metastasis, this review may broaden the present understanding of the cellular and molecular model of ERRα and highlight its potential implication in clinical therapy.

Estrogen-Related Receptors Gene Expression and Copy Number Alteration Association With the Clinicopathologic Characteristics of Breast Cancer

Purpose:

It has been suggested that dysregulation of transcription factors expression or activity plays significant roles in breast cancer (BC) severity and poor prognosis. Therefore, our study aims to thoroughly evaluate the estrogen-related receptor isoforms (ESRRs) expression and copy number alteration (CNA) status and their association with clinicopathologic characteristics in BC.

Methods:

A METABRIC dataset consist of 2509 BC patients’ samples was obtained from the cBioPortal public domain. The gene expression, putative CNA, and relevant tumor information of ESRRs were retrieved. ESRRs messenger RNA (mRNA) expression in BC cell lines was obtained from the Cancer Cell Line Encyclopedia (CCLE). Association and correlation analysis of ESRRs expression with BC clinicopathologic characteristics and molecular subtype were performed. Kaplan–Meier survival analysis was conducted to evaluate the prognostic value of ESRRs expression on patient survival.

Results:

ESRRα expression correlated negatively with patients’ age and overall survival, whereas positively correlated with tumor size, the number of positive lymph nodes, and Nottingham prognostic index (NPI). Conversely, ESRRγ expression was positively correlated with patients’ age and negatively correlated with NPI. ESRRα and ESRRγ expression were significantly associated with tumor grade, expression of hormone receptors, human epidermal growth factor receptor 2 (HER2), and molecular subtype, whereas ESRRβ was only associated with tumor stage. A significant and distinct association of each of ESRRs CNA with various clinicopathologic and prognostic factors was also observed. Kaplan–Meier survival analysis demonstrated no significant difference for survival curves among BC patients with high or low expression of ESRRα, β, or γ. On stratification, high ESRRα expression significantly reduced survival among premenopausal patients, patients with grade I/II, and early-stage disease. In BC cell lines, only ESRRα expression was significantly higher in HER2-positive cells. No significant association was observed between ESRRβ expression and any of the clinicopathologic characteristics examined.

Conclusions:

In this clinical dataset, ESRRα and ESRRγ mRNA expression and CNA show a significant correlation and association with distinct clinicopathologic and prognostic parameters known to influence treatment outcomes; however, ESRRβ failed to show a robust role in BC pathogenesis. ESRRα and ESRRγ can be employed as therapeutic targets in BC-targeted therapy. However, the role of ESRRβ in BC pathogenesis remains unclear.

The ERRα-VDR axis promotes calcitriol degradation and estrogen signaling in breast cancer cells, while VDR-CYP24A1-ERRα overexpression correlates with poor prognosis in patients with basal-like breast cancer

Vitamin D is used to reduce cancer risk and improve the outcome of cancer patients, but the vitamin D receptor (VDR; also known as the calcitriol receptor) pathway needs to be functionally intact to ensure the biological effects of circulating calcitriol, the active form of vitamin D. Besides estrogen receptor alpha (ERα), estrogen-related receptor alpha (ERRα) has also been shown to interfere with the VDR pathway, but its role in the antitumor and transactivation activity of calcitriol is completely unknown in breast cancer (BC). We observed that ERRα functionally supported the proliferation of BC cell lines and acted as a calcitriol-induced regulator of VDR. As such, ERRα deregulated the calcitriol-VDR transcription by enhancing the expression of CYP24A1 as well as of both ERα and aromatase (CYP19A1) in calcitriol-treated cells. ERRα knockdown limited the effect of calcitriol by reducing calcitriol-induced G0/G1 phase cell cycle arrest and by affecting the expression of cyclin D1 and p21/Waf. The interactome analysis suggested that Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-α (PGC-1α) and Proline-, glutamic acid-, and leucine-rich protein 1 (PELP1) are key players in the genomic actions of the calcitriol-VDR-ERRα axis. Evaluation of patient outcomes in The Cancer Genome Atlas (TCGA) dataset showed the translational significance of the biological effects of the VDR-ERRα axis, highlighting that VDR, CYP24A1, and ERRα overexpression correlates with poor prognosis in basal-like BC.

Targeting Different Pathways Using Novel Combination Therapy in Triple Negative Breast Cancer

Triple negative breast cancer (TNBC) is one of the most aggressive subtypes of breast cancer accounting for 15-20% of cases and is defined by the lack of hormonal receptors viz., estrogen receptor (ER), progesterone receptor (PR) and expression of human epidermal growth receptor 2 (HER2). Treatment of TNBC is more challenging than other subtypes of breast cancer due to the lack of markers for the molecularly targeted therapies (ER, PR, and HER-2/ Neu), the conventional chemotherapeutic agents are still the mainstay of the therapeutic protocols of its patients. Despite, TNBC being more chemo-responsive than other subtypes, unfortunately, the initial good response to the chemotherapy eventually turns into a refractory drug-resistance. Using a monotherapy for the treatment of cancer, especially high-grade tumors like TNBC, is mostly worthless due to the inherent genetic instability of tumor cells to develop intrinsic and acquired resistance. Thus, a cocktail of two or more drugs with different mechanisms of action is more effective and could successfully control the disease. Furthermore, combination therapy reveals more, or at least the same, effectiveness with lower doses of every single agent and decreases the likelihood of chemoresistance. Herein, we shed light on the novel combinatorial approaches targeting PARP, EGFR, PI3K pathway, AR, and wnt signaling, HDAC, MEK pathway for efficient treatment of high-grade tumors like TNBC and decreasing the onset of resistance.

Triple-negative breast lobular carcinoma: a luminal androgen receptor carcinoma with specific ESRRA mutations

Primary triple-negative invasive lobular breast carcinomas (TN-ILCs), which do not express hormone receptors and HER2 at diagnosis, are rare and poorly known. In this study, we analyzed the largest TN-ILC series ever reported in the literature, in comparison to phenotypically similar breast tumor subtypes: triple-negative invasive ductal carcinoma (TN-IDC) and hormone receptor-positive invasive lobular carcinoma (HR + ILC). All primary TN-ILCs registered in our database between 2000 and 2018 (n = 38) were compared to tumors from control groups, matched by stage and Elston/Ellis grade, with regard to clinical, pathologic, and immunohistochemical characteristics. A comparative molecular analysis (whole-exome and RNA sequencing using next-generation technology) was also performed. We found that TN-ILC patients were older than those with HR + ILC (P = 0.002) or TN-IDC (P < 0.001). Morphologically, TN-ILCs had aggressive phenotypes, with more pleomorphism (P = 0.003) and higher nuclear grades than HR + ILCs (P = 0.009). Immunohistochemistry showed that TN-ILCs less frequently expressed basal markers (CK5/6, EGFR and SOX10) than TN-IDCs (P < 0.001), while androgen receptor (AR) positivity was more prevalent (P < 0.001). Survival curves analysis did not show differences between TN-ILC and TN-IDC patients, while overall and distant metastasis-free survival were significantly worse compared to those with HR + ILCs (P = 0.047 and P = 0.039, respectively). At a molecular level, we found that TN-ILCs had particular transcriptomic profiles, characterized by increased AR signaling, and associated with frequent alterations in the PI3K network and ERBB2. Interestingly, whole-exome analysis also identified three specific recurrent ESRRA hotspot mutations in these tumors, which have never been described in breast cancer to date and which were absent in the other two tumor subtypes. Our findings highlight that TN-ILC is a unique aggressive breast cancer associated with elderly age, which belong to the luminal androgen receptor subtype as determined by immunohistochemistry and transcriptomic profiling. Moreover, it harbors specific molecular alterations (PI3K, ERBB2 and ESRRA) which may pave the way for new targeted therapeutic strategies.

Molecular Dynamics Simulations Based on 1-Phenyl-4-Benzoyl-1-Hydro-Triazole ERRα Inverse Agonists

Estrogen-related receptor α (ERRα), which is overexpressed in a variety of cancers has been considered as an effective target for anticancer therapy. ERRα inverse agonists have been proven to effectively inhibit the migration and invasion of cancer cells. As few crystalline complexes have been reported, molecular dynamics (MD) simulations were carried out in this study to deepen the understanding of the interaction mechanism between inverse agonists and ERRα. The binding free energy was analyzed by the MM-GBSA method. The results show that the total binding free energy was positively correlated with the biological activity of an inverse agonist. The interaction of the inverse agonist with the hydrophobic interlayer composed of Phe328 and Phe495 had an important impact on the biological activity of inverse agonists, which was confirmed by the decomposition of energy on residues. As Glu331 flipped and formed a hydrogen bond with Arg372 in the MD simulation process, the formation of hydrogen bond interaction with Glu331 was not a necessary condition for the compound to act as an inverse agonist. These rules provide guidance for the design of new inverse agonists.

Down-regulation of estrogen-related receptor alpha (ERRα) inhibits gastric cancer cell migration and invasion in vitro and in vivo

OBJECTIVE

To investigate the correlation between estrogen-related receptor a (ERRα) expression level and gastric cancer (GC).

METHODS

We collected GC and adjacent normal tissues from 50 patients. The parameters of the patients were summarized, and correlation with the expression level of ERRα was calculated. Downregulated ERRα using lentivirus was designed and transfected to SGC-7901 and MGC-803 cells. Cell migration, invasion and wound assays were conducted to determine the correlation between ERRα and capacity for cell migration and invasion. The expression level of the genes involved in epithelial-mesenchymal transition, including E-cadherin, γ-catenin, N-cadherin and vimentin, was determined via real-time or quantitative polymerase chain reaction(qPCR) and Western blot analysis.

RESULTS

The expression of ERRα tends to be higher in GC tissues than in adjacent normal tissues. Analyses ofthe expression level of ERRα and patient parameters show that the ERRα level is significantly correlated with TNM staging and patient survival (P<0.05). The downregulation of ERRα can inhibit cell invasion and migration, which was proven by Transwell and cell wound assays. The levels of E-cadherin and γ-catenin increased by conducting qPCR and Western blot analysis. Meanwhile, the levels of N-cadherin and vimentin decreased when ERRα expression was reduced.

CONCLUSION

ERRα is highly expressed in GC tissues and can promote the migration and invasion of cancer cells. It can be a potential marker for GC diagnosis.

The emerging role of estrogen related receptorα in complications of non-small cell lung cancers

Approximately 85% of lung cancer cases are recognized as non-small cell lung cancer (NSCLC) with a perilous (13–17%) 5-year survival in Europe and the USA. Although tobacco smoking has consistently emerged as the leading cause of NSCLC complications, its consequences are distinctly manifest with respect to sex bias, due to differential gene and sex hormone expression. Estrogen related receptor α (ERRα), a member of the nuclear orphan receptor superfamily is normally expressed in the lungs, and activates various nuclear genes without binding to the ligands, such as estrogens. In NSCLC ERRα expression is significantly higher compared with healthy individuals. It is well established ERα and ERβ‚ have 93% and 60% identity in the DNA and ligand binding domains, respectively. ERα and ERRα have 69% (70% with ERRα-1) and 34% (35% with ERRα-1) identity, respectively; ERRα and ERRβ‚ have 92 and 61% identity, respectively. However, whether there is distinctive ERRα interaction with mammalian estrogens or concurrent involvement in non-ER signalling pathway activation is not known. Relevant to NSCLC, ERRα promotes proliferation, invasion and migration by silencing the tumor suppressor proteins p53 and pRB, and accelerates G₂-M transition during cell division. Epithelial to mesenchymal transition (EMT) and activation of Slug (an EMT associated transcription factor) are the prominent mechanisms by which ERRα activates NSCLC metastasis. Based on these observations, the present article focuses on the feasibility of antiERRα therapy alone and in combination with antiER as a therapeutic strategy for NSCLC complications.

Estrogen-related receptors: novel potential regulators of osteoarthritis pathogenesis

Osteoarthritis (OA) is a chronic inflammatory disease that is associated with articular cartilage destruction, subchondral bone alterations, synovitis, and even joint deformity and the loss of joint function. Although current basic research on the pathogenesis of OA has made remarkable progress, our understanding of this disease still needs to be further improved. Recent studies have shown that the estrogen-related receptor (ERR) family members ERRα and ERRγ may play significant roles in the pathogenesis of OA. In this review, we refer to the latest research on ERRs and the pathogenesis of OA, elucidate the structure and physiopathological functions of the ERR orphan nuclear receptor family, and systematically examine the relationship between ERRs and OA at the molecular level. Moreover, we also discuss and predict the capacity of ERRs as potential targets in the clinical treatment of OA.

Unraveling the multifaceted nature of the nuclear function of mTOR

Positioned at the axis between the cell and its environment, mTOR directs a wide range of cellular activity in response to nutrients, growth factors, and stress. Our understanding of the role of mTOR is evolving beyond the spatial confines of the cytosol, and its role in the nucleus becoming ever more apparent. In this review, we will address various studies that explore the role of nuclear mTOR (nmTOR) in specific cellular programs and how these pathways influence one another. To understand the emerging roles of nuclear mTOR, we discuss data and propose plausible mechanisms to offer novel ideas, hypotheses, and future research directions.

Metformin modulates oncogenic expression of HOTAIR gene via promoter methylation and reverses epithelial-mesenchymal transition in MDA-MB-231 cells

Epithelial-mesenchymal transition (EMT) is a biological event, which critically regulates migration and invasion of cancer cells. EMT is regulated by several protein and nonprotein factors (such as noncoding RNAs). HOTAIR is an oncogenic long noncoding RNA that stimulates EMT in cancers. In the current study, we investigated the effect of metformin on EMT behavior and HOTAIR expression in MDA-MB-231 breast cancer cells. The minimal effective concentrations of metformin (10 and 20 mM) were obtained by the MTT test. Cell migration and invasion in the metformin-containing medium were assayed in the scratch assay and transwell test. Meaningful decreases in both cell migration and invasion were observed in the presence of metformin. Vimentin, snail, β-catenin, and HOTAIR transcripts were quantified by real-time polymerase chain reaction (PCR). Reduction in the expression of vimentin, β-catenin, and HOTAIR was detected as the result of metformin treatment, but the snail showed a constant expression. Western blottingrevealed the downregulation of vimentin and β-catenin proteins. HOTAIR promoter methylation pattern was also investigated in metformin-exposed cells using bisulfite sequencing PCR which the result showed differences in the methylation profile of CpG islands between the treated and untreated cells. In conclusion, metformin modulated oncogenic expression of the HOTAIR gene in the MDA-MB-231 cells. This downregulation was associated with the modification of promoter methylation patterns. Since HOTAIR induces EMT in breast cancer, HOTAIR decline might be one of the mechanisms by which metformin reverses EMT.

The comparison of miRNAs that respond to anti-breast cancer drugs and usnic acid for the treatment of breast cancer

This study was designed to compare usnic acid with anti-breast cancer drug molecules (A-BCDM) routinely used in the treatment of breast cancer. The miRNA information of 17 anti-breast cancer drug used in breast cancer treatment was obtained from the Small Molecule-miRNA Network-Based Inferance (SMIR-NBI) tool. We had been determined common and different expressed miRNAs between 17 A-BCDM & usnic acid and were classified according to the common miRNAs to reveal molecular similarity. As a result of the bioinformatic analyzes, 20 common miRNAs were determined between 17 A-BCDM and usnic acid. The common miRNAs were analyzed with bioinformatic tolls for determining pathways and targets. The most common miRNAs for 6 of 17 A-BCDM and usnic acid were determined as miR-374a-5p and miR-26a-5p. We compared the anti-proliferative effect of usnic acid and one of the 17 A-BCDM that tamoxifen on MDA-MB-231 triple negative breast cancer cell with real-time cell analysis system. The real time PCR assay was carried out with miR-26a-5p for evaluate to expression level of MDA-MB-231 breast cancer cell and MCF-12A non-cancerous epithelial breast cell. As a result of study, usnic acid as novel candidate drug molecule showed high similarity ratio with 5-Fluorouracil, Sulindac Sulfide, Curcumin and Cisplatin A-BCDM used in treatment of breast cancer. miR-26a-5p as common response miRNA of usnic acid and tamoxifen was showed a decreased level of expression by validated qRT-PCR assay. The obtained from study, in addition to 17 A-BCDM, usnic acid has also the potential to be used as a candidate molecule in the treatment of breast cancer. Moreover, miR-26a-5p might be used as a biomarker in the treatment of breast cancer but further analysis is required.

Estrogen Actions in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) lacks estrogen receptor (ER) α, but the expression of estrogen receptors ERβ and G protein-coupled estrogen receptor 1 (GPER-1) is able to trigger estrogen-responsivity in TNBC. Estrogen signaling in TNBC can also be activated and modulated by the constitutively active estrogen-related receptors (ERRs). In this review article, we discuss the role of ERβ and GPER-1 as mediators of E2 action in TNBC as well as the function of ERRs as activators and modulators of estrogen signaling in this cancer entity. For this purpose, original research articles on estrogen actions in TNBC were considered, which are listed in the PubMed database. Additionally, we performed meta-analyses of publicly accessible integrated gene expression and survival data to elucidate the association of ERβ, GPER-1, and ERR expression levels in TNBC with survival. Finally, options for endocrine therapy strategies for TNBC were discussed.

Gremlin-1 augments the oestrogen-related receptor α signalling through EGFR activation: implications for the progression of breast cancer

BACKGROUND

Gremlin-1 (GREM1), one of the bone morphogenetic protein antagonists, is involved in organogenesis, tissue differentiation and kidney development. However, the role of GREM1 in cancer progression and its underlying mechanisms remain poorly understood.

METHODS

The role of GREM1 in breast cancer progression was assessed by measuring cell viability, colony formation, 3D tumour spheroid formation/invasion and xenograft tumour formation. Chromatin immunoprecipitation, a luciferase reporter assay and flow cytometry were performed to investigate the molecular events in which GREM1 is involved.

RESULTS

GREM1 expression was elevated in breast cancer cells and tissues obtained from breast cancer patients. Its overexpression was associated with poor prognosis in breast cancer patients, especially those with oestrogen receptor (ER)-negative tumours. GREM1 knockdown inhibited the proliferation of breast cancer cells and xenograft mammary tumour growth, while its overexpression enhanced their viability, growth and invasiveness. Oestrogen-related receptor α (ERRα), an orphan nuclear hormone receptor, directly interacted with the GREM1 promoter and increased the expression of GREM1. GREM1 also enhanced the promoter activity of ESRRA encoding ERRα, comprising a positive feedback loop. Notably, GREM1 bound to and activated EGFR, a well-known upstream regulator of ERRα.

CONCLUSIONS

Our study suggests that the GREM1-ERRα axis can serve as a potential therapeutic target in the management of cancer, especially ER-negative tumour.

Triple-negative breast cancer: new treatment strategies in the era of precision medicine

Triple-negative breast cancer (TNBC) remains the most aggressive cluster of all breast cancers, which is due to its rapid progression, high probabilities of early recurrence, and distant metastasis resistant to standard treatment. Following the advances in cancer genomics and transcriptomics that can illustrate the comprehensive profiling of this heterogeneous disease, it is now possible to identify different subclasses of TNBC according to both intrinsic signals and extrinsic microenvironment, which have a huge influence on predicting response to established therapies and picking up novel therapeutic targets for each cluster. In this review, we summarize basic characteristics and critical subtyping systems of TNBC, and particularly discuss newly found prospective targets and relevant medications, which were proved promising in clinical trials, thus shedding light on the future development of precision treatment strategies.

Cholesterol as an Endogenous Ligand of ERRα Promotes ERRα-Mediated Cellular Proliferation and Metabolic Target Gene Expression in Breast Cancer Cells

Breast cancer is the 2nd leading cause of cancer-related death among women. Increased risk of breast cancer has been associated with high dietary cholesterol intake. However, the underlying mechanisms are not known. The nuclear receptor, estrogen-related receptor alpha (ERRα), plays an important role in breast cancer cell metabolism, and its overexpression has been linked to poor survival. Here we identified cholesterol as an endogenous ligand of ERRα by purification from human pregnancy serum using a GST-ERRα affinity column and liquid chromatography-tandem mass spectrometry (LC-MS/MS). We show that cholesterol interacts with ERRα and induces its transcriptional activity in estrogen receptor positive (ER+) and triple negative breast cancer (TNBC) cells. In addition, we show that cholesterol enhances ERRα-PGC-1α interaction, induces ERRα expression itself, augments several metabolic target genes of ERRα, and increases cell proliferation and migration in both ER+ and TNBC cells. Furthermore, the stimulatory effect of cholesterol on metabolic gene expression, cell proliferation, and migration requires the ERRα pathway. These findings provide a mechanistic explanation for the increased breast cancer risk associated with high dietary cholesterol and possibly the pro-survival effect of statins in breast cancer patients, highlighting the clinical relevance of lowering cholesterol levels in breast cancer patients overexpressing ERRα.

Distinct Roles of mTOR Targets S6K1 and S6K2 in Breast Cancer

The mechanistic target of rapamycin (mTOR) is a master regulator of protein translation, metabolism, cell growth and proliferation. It forms two complexes, mTOR complex 1 (mTORC1) and 2 (mTORC2). mTORC1 is frequently deregulated in many cancers, including breast cancer, and is an important target for cancer therapy. The immunosuppressant drug rapamycin and its analogs that inhibit mTOR are currently being evaluated for their potential as anti-cancer agents, albeit with limited efficacy. mTORC1 mediates its function via its downstream targets 40S ribosomal S6 kinases (S6K) and eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1). There are two homologs of S6K: S6K1 and S6K2. Most of the earlier studies focused on S6K1 rather than S6K2. Because of their high degree of structural homology, it was generally believed that they behave similarly. Recent studies suggest that while they may share some functions, they may also exhibit distinct or even opposite functions. Both homologs have been implicated in breast cancer, although how they contribute to breast cancer may differ. The purpose of this review article is to compare and contrast the expression, structure, regulation and function of these two S6K homologs in breast cancer.

Dual targeting of estrogen receptor α and estrogen-related receptor α: a novel endocrine therapy for endometrial cancer

Background

Endometrial cancer (EC) is a hormone dependent carcinoma that may involve complex molecular mechanisms. Endocrine therapy by blocking the estrogen and estrogen receptor α (ERα) has been effective in breast cancer, while it is still controversial in EC. Recently, estrogen-related receptor α (ERRα) was proven to be another endocrine therapy target.

Methods

The anti-tumor effect of selective estrogen receptor modulators (SERMs) and XCT790 (XCT) used alone or in combination were evaluated in both of ERα-positive (ERα+) and ERα-negative (ERα-) EC cells. ERα and ERRα mRNA were tested by qPCR, while the protein was detected by Western blot. The proliferation was tested by MTS and cell cycle, apoptosis rate were analyzed by flow cytometry.

Results

A relatively high dose (10 μM) of tamoxifen (TAM) suppressed the expression of ERα and ERRα in two types of EC cells. However, 10 μM raloxifene (RAL) exhibited no effect on ERα and ERRα, while 10 μM XCT down regulated ERRα specifically, but not ERα in all EC cells. When dual targeting on ERα and ERRα by combining TAM with XCT, the proliferation inhibitory effect and apoptosis reached the strongest in all EC cells (P<0.05). Moreover, the inhibitory effect of proliferation was attributed significantly to the G0/G1 arrest (P<0.05). Interestingly, the apoptosis induced by combining TAM with XCT were obviously higher in ERα+ EC cells than ERα- EC cells (P<0.05).

Conclusion

Taken together, the results indicate that dual targeting on ERα and ERRα represents a better anti-tumor effect, which provides a novel endocrine based therapy strategy for EC.

Antitumor effect of XCT790, an ERRα inverse agonist, on ERα-negative endometrial cancer cells

PURPOSE

The estrogen-related receptor (ERR) α is structurally similar to classical estrogen receptors (ERs), but is considered to be an orphan nuclear receptor. We previously found that ERRα regulates uterine endometrial cancer progression. Here, we investigated the efficacy of XCT790, a selective inverse agonist of ERRα, on endometrial cancer cells in vitro and in vivo.

METHODS

HEC-1A and KLE, ERα-negative endometrial cancer cells exhibiting high ERRα expression levels, and HEC-1A cell-derived xenograft model mice were treated with XCT790. Transcriptional activity and cell proliferation were examined using luciferase, WST-8 and colony formation assays, respectively. Cell cycle progression was evaluated using flow cytometry, immunofluorescence cytochemistry and Western blotting. Apoptosis was evaluated using a caspase-3/7 activity assay.

RESULTS

We found that XCT790 significantly inhibited ERRα-induced in vitro transcriptional activity, including that of the vascular endothelial growth factor (VEGF) gene, in a concentration-dependent manner (p < 0.05). We also found that XCT790 suppressed colony formation and cell proliferation in a concentration and time-dependent manner (p < 0.01) without cytotoxicity, and induced apoptosis (p < 0.01). XCT790 was found to cause cell cycle arrest at the mitotic phase. Akt and mTOR phosphorylation was found to be inhibited by XCT790, but PI3K levels were not found to be significantly affected. Combination therapy of XCT790 with paclitaxel elicited a synergistic inhibitory effect. Additionally, we found that XCT790 significantly inhibited in vivo tumor growth and angiogenesis, and induced apoptosis without a reduction in body weight, in xenograft models (p < 0.01).

CONCLUSIONS

From our data we conclude that XCT790 has an anti-tumor effect on endometrial cancer cells in vitro and in vivo. As such, it may serve as a novel therapeutic agent for endometrial cancer.

The PGC-1/ERR network and its role in precision oncology

Transcriptional regulators include a superfamily of nuclear proteins referred to as co-activators and co-repressors, both of which are involved in controlling the functions of several nuclear receptors (NRs). The Nuclear Receptor Signaling Atlas (NURSA) has cataloged the composition of NRs, co-regulators, and ligands present in the human cell and their effort has been identified in more than 600 potential molecules. Given the importance of co-regulators in steroid, retinoid, and thyroid hormone signaling networks, hypothesizing that NRs/co-regulators are implicated in a wide range of pathologies are tempting. The co-activators known as peroxisome proliferator-activated receptor gamma co-activator 1 (PGC-1) and their key nuclear partner, the estrogen-related receptor (ERR), are emerging as pivotal transcriptional signatures that regulate an extremely broad repertoire of mitochondrial and metabolic genes, making them very attractive drug targets for cancer. Several studies have provided an increased understanding of the functional and structural biology of nuclear complexes. However, more comprehensive work is needed to create different avenues to explore the therapeutic potential of NRs/co-activators in precision oncology. Here, we discuss the emerging data associated with the structure, function, and molecular biology of the PGC-1/ERR network and address how the concepts evolving from these studies have deepened our understanding of how to develop more effective treatment strategies. We present an overview that underscores new biological insights into PGC-1/ERR to improve cancer outcomes against therapeutic resistance. Finally, we discuss the importance of exploiting new technologies such as single-particle cryo-electron microscopy (cryo-EM) to develop a high-resolution biological structure of PGC-1/ERR, focusing on novel drug discovery for precision oncology.

Design, Synthesis, Anti-Proliferative, Anti-microbial, Anti-Angiogenic Activity and In Silico Analysis of Novel Hydrazone Derivatives

BACKGROUND

Cancer is the second leading cause of death globally. Hydrazone and hydrazone derivatives have high activity, and for this reason, these compound are greatly used by researchers to synthesize new anti-cancer drug. The aim of this research work is to synthesize novel anticancer agents.

METHODS

New hydrazone derivatives were synthesized via a reaction between 3-formylphenyl methyl carbonate and benzhydrazide, 4-methylbenzoic hydrazide, 4-tert-butylbenzoic hydrazide, 4-nitrobenzoic hydrazide and 3- methoxybenzoic hydrazide, and were successfully characterized using elemental analysis, ¹H-NMR, ¹³C-NMR, FT-IR and LC-MS techniques. The synthesized compounds were evaluated for their antimicrobial (some grampositive and -negative bacteria, filamentous fungi and yeasts), anti-proliferative (T47D and HCC1428-breast cancer cells) and anti-angiogenic (HUVEC-endothelial cells) activities. The anti-proliferative activities of the hydrazone compounds R1-R5 were studied on these cell lines by MTT assay. The anti-angiogenic potential of the compounds was determined by the endothelial tube formation assay. To identify structural features related to the anti-proliferative activity of these compounds, 2D-QSAR was performed.

RESULT

The results indicated that compound R3 exhibited strong anti-angiogenic and anti-proliferative activity on breast cancer cell lines and healthy cell lines. Also, this compound; possessing a tertiary butyl moiety on the hydrazine, exhibited the highest inhibitory effect against all tested microorganisms; in particular, it inhibited Candida albicans at a lower concentration than ketoconazole. Among the investigated compounds, those bearing methyl, tertiary butyl (compound R2, R3) and methoxy (compound R5) moiety were found to be more successful anticandidal derivatives than standard antifungal antibiotics. The QSAR analysis suggested that the tumor specificity of the hydrazone correlated with their molecular weight, lipophilicity, molar refractivity, water solubility, DipolHybrid:(MOPAC) and ExchangeEnergy:(MOPAC). Absorption, Distribution, Metabolism and Elimination (ADME) analysis of the hydrazone compounds showed that they have favorable pharmacokinetic and drug-likeness properties. The ADME results clarify that R3 is the best compound in terms of pharmacokinetic properties. In contrast to other compounds; target prediction analysis of the compound R3 showed inhibitory activity on estrogen-related receptor alpha transcription factor (ESRRA). The target prediction analysis was supported by molinspiration bioactivity score.

CONCLUSION

The R3 compound is considered to be an important candidate for future studies with its suitability for the Lipinski's rule of five for drug-likeness, and effective in vitro and in silico results.

Metastatic and triple-negative breast cancer: challenges and treatment options

The major current conventional types of metastatic breast cancer (MBC) treatments include surgery, radiation, hormonal therapy, chemotherapy, or immunotherapy. Introducing biological drugs, targeted treatment and gene therapy can potentially reduce the mortality and improve the quality of life in patients with MBC. However, combination of several types of treatment is usually recommended. Triple negative breast cancer (TNBC) accounts for 10-20% of all cases of breast carcinoma and is characterized by the low expression of progesterone receptor (PR), estrogen receptor (ER), and human epidermal growth factor receptor 2 (HER2). Consequently, convenient treatments used for MBC that target these receptors are not effective for TNBC which therefore requires special treatment approaches. This review discusses the occurrence of MBC, the prognosis and predictive biomarkers of MBC, and focuses on the novel advanced tactics for treatment of MBC and TNBC. Nanotechnology-based combinatorial approach for the suppression of EGFR by siRNA and gifitinib is described.

Proteasome inhibition induces IKK-dependent interleukin-8 expression in triple negative breast cancer cells: Opportunity for combination therapy

Triple negative breast cancer (TNBC) cells express increased levels of the pro-inflammatory and pro-angiogenic chemokine interleukin-8 (IL-8, CXCL8), which promotes their proliferation and migration. Because TNBC patients are unresponsive to current targeted therapies, new therapeutic strategies are urgently needed. While proteasome inhibition by bortezomib (BZ) or carfilzomib (CZ) has been effective in treating hematological malignancies, it has been less effective in solid tumors, including TNBC, but the mechanisms are incompletely understood. Here we report that proteasome inhibition significantly increases expression of IL-8, and its receptors CXCR1 and CXCR2, in TNBC cells. Suppression or neutralization of the BZ-induced IL-8 potentiates the BZ cytotoxic and anti-proliferative effect in TNBC cells. The IL-8 expression induced by proteasome inhibition in TNBC cells is mediated by IκB kinase (IKK), increased nuclear accumulation of p65 NFκB, and by IKK-dependent p65 recruitment to IL-8 promoter. Importantly, inhibition of IKK activity significantly decreases proliferation, migration, and invasion of BZ-treated TNBC cells. These data provide the first evidence demonstrating that proteasome inhibition increases the IL-8 signaling in TNBC cells, and suggesting that IKK inhibitors may increase effectiveness of proteasome inhibitors in treating TNBC.

The tamoxifen derivative ridaifen-B is a high affinity selective CB2 receptor inverse agonist exhibiting anti-inflammatory and anti-osteoclastogenic effects

Selective estrogen receptor modulators (SERMs) target estrogen receptors (ERs) to treat breast cancer and osteoporosis. Several SERMs exhibit anti-cancer activity not related to ERs. To discover novel anti-cancer drugs acting via ER-independent mechanisms, derivatives of the SERM tamoxifen, known as the "ridaifen" compounds, have been developed that exhibit reduced or no ER affinity, while maintaining cytotoxicity. Tamoxifen and other SERMs bind to cannabinoid receptors with moderate affinity. Therefore, ER-independent effects of SERMs might be mediated via cannabinoid receptors. This study determined whether RID-B, a first generation ridaifen compound, exhibits affinity and/or activity at CB₁ and/or CB₂ cannabinoid receptors. RID-B binds with high affinity (K_i = 43.7 nM) and 17-fold selectivity to CB₂ over CB₁ receptors. RID-B acts as an inverse agonist at CB₂ receptors, modulating G-protein and adenylyl cyclase activity with potency values predicted by CB₂ affinity. Characteristic of an antagonist, RID-B co-incubation produces a parallel-rightward shift in the concentration-effect curve of CB₂ agonist WIN-55,212-2 to inhibit adenylyl cyclase activity. CB₂ inverse agonists are reported to exhibit anti-inflammatory and anti-ostoeclastogenic effects. In LPS-activated macrophages, RID-B exhibits anti-inflammatory effects by reducing levels of nitric oxide (NO), IL-6 and IL-1α, but not TNFα. Only reduction of NO concentration by RID-B is mediated by cannabinoid receptors. RID-B also exhibits pronounced anti-osteoclastogenic effects, reducing the number of osteoclasts differentiating from primary bone marrow macrophages in a cannabinoid receptor-dependent manner. In summary, the tamoxifen derivative RID-B, developed with reduced affinity for ERs, is a high affinity selective CB₂ inverse agonist with anti-inflammatory and anti-osteoclastogenic properties.

Long non-coding RNA SPRY4-IT1 promotes development of hepatic cellular carcinoma by interacting with ERRα and predicts poor prognosis

Hepatocellular carcinoma (HCC) has become one of the most common leading causes of cancer-related deaths worldwide. This study investigates the role of lncRNA, SPRY4-IT1 in the development of HCC. Quantitative real-time PCR (qRT-PCR) was performed and the results showed that SPRY4-IT1 expression was up-regulated in HCC tissues and high expression of SPRY4-IT1 was associated with poor 5-year overall survival in the HCC patient cohort. Clinicopathological analysis showed that the expression of SPRY4-IT1 was significantly correlated with TNM stage in HCC patients. In vitro CCK-8 assay, colony formation assay, cell invasion and migration assays demonstrated that knock-down of SPRY4-IT1 suppressed cell proliferation, colony formation, cell invasion and migration in HCC cells. Flow cytometric analysis showed that knock-down of SPRY4-IT1 induced cell cycle arrest at G0/G1 phase and induced apoptosis. In addition, knock-down of SPRY4-IT1 also suppressed the mRNA and protein expression of estrogen-related receptor α (ERRα). Similarly, knock-down of ERRα inhibited cell proliferation, colony formation, cell invasion and migration in HCC cells. More importantly, ERRα overexpression antagonized the effects of SPRY4-IT1 knock-down on cell proliferation, colony formation, cell invasion and migration in HCC cells. Taken together, our data highlights the pivotal role of SPRY4-IT1 in the tumorigenesis of HCC.

Raptor localization predicts prognosis and tamoxifen response in estrogen receptor-positive breast cancer

Purpose

Deregulated PI3K/mTOR signals can promote the growth of breast cancer and contribute to endocrine treatment resistance. This report aims to investigate raptor and its intracellular localization to further understand its role in ER-positive breast cancer.

Methods

Raptor protein expression was evaluated by immunohistochemistry in 756 primary breast tumors from postmenopausal patients randomized to tamoxifen or no tamoxifen. In vitro, the MCF7 breast cancer cell line and tamoxifen-resistant MCF7 cells were studied to track the raptor signaling changes upon resistance, and raptor localization in ERα-positive cell lines was compared with that in ERα-negative cell lines.

Results

Raptor protein expression in the nucleus was high in ER/PgR-positive and HER2-negative tumors with low grade, features associated with the luminal A subtype. Presence of raptor in the nucleus was connected with ERα signaling, here shown by a coupled increase of ERα phosphorylation at S167 and S305 with accumulation of nuclear raptor. In addition, the expression of ERα-activated gene products correlated with nuclear raptor. Similarly, in vitro we observed raptor in the nucleus of ERα-positive, but not of ER-negative cells. Interestingly, raptor localized to the nucleus could still be seen in tamoxifen-resistant MCF7 cells. The clinical benefit from tamoxifen was inversely associated with an increase of nuclear raptor. High cytoplasmic raptor expression indicated worse prognosis on long-term follow-up.

Conclusion

We present a connection between raptor localization to the nucleus and ERα-positive breast cancer, suggesting raptor as a player in stimulating the growth of the luminal A subtype and a possible target along with endocrine treatment.

Electronic supplementary material

The online version of this article (10.1007/s10549-017-4508-x) contains supplementary material, which is available to authorized users.

A novel compound LingH2-10 inhibits the growth of triple negative breast cancer cells in vitro and in vivo as a selective inverse agonist of estrogen-related receptor α

Unlike other breast cancer subtypes, targeted therapies for triple negative breast cancer (TNBC) have yet to progress past clinical trial stage to approval. Accumulating evidences demonstrated that expression of estrogen-related receptor alpha (ERRα) indicated worse prognosis and correlated with poor outcome in breast cancers including TNBC. Therefore, ERRα modulators/regulators may be potential in the therapeutic treatment of breast cancers. In the current study, we presented a novel compound LingH2-10 that bound to ERRα, as identified using a time-resolved fluorescence resonance energy transfer assay (TR-FRET) with the IC50 value of 0.64±0.12μM. Further, functional activity was determined by transient transfection luciferase reporter assay in order to validate the utility of the binding affinity in a cellular context. LingH2-10 showed selective inhibition on ERRα transcriptional activity with the IC50 value of 0.58±0.09μM in cell-based luciferase reporter assay. Moreover, representative in vitro results showed that LingH2-10 suppressed the proliferation of various human cancer cells, and inhibited the migration of triple negative breast cancer cell MDA-MB-231. In addition, our results demonstrated that well known ERRα target genes such as PDK4, Osteopontin and pS2, were all significantly down modulated by LingH2-10. In vivo experiments showed that LingH2-10 (30mg/kg, every other day) observably suppressed the growth of MDA-MB-231 xenograft tumors by 42.02% compared to untreated xenograft tumors. Taken together, all these data suggested that LingH2-10, as a selective inverse agonist of ERRα, was a lead compound of anti-cancer agents for treating TNBC patients.

ERRα regulates the growth of triple-negative breast cancer cells via S6K1-dependent mechanism

Estrogen-related receptor alpha (ERRα) is an orphan nuclear factor that is a master regulator of cellular energy metabolism. ERRα is overexpressed in a variety of tumors, including ovarian, prostate, colorectal, cervical and breast, and is associated with a more aggressive tumor and a worse outcome. In breast cancer, specifically, high ERRα expression is associated with an increased rate of recurrence and a poor prognosis. Because of the common functions of ERRα and the mTORC1/S6K1 signaling pathway in regulation of cellular metabolism and breast cancer pathogenesis, we focused on investigating the biochemical relationship between ERRα and S6K1. We found that ERRα negatively regulates S6K1 expression by directly binding to its promoter. Downregulation of ERRα expression sensitized ERα-negative breast cancer cells to mTORC1/S6K1 inhibitors. Therefore, our results show that combinatorial inhibition of ERRα and mTORC1/S6K1 may have clinical utility in treatment of triple-negative breast cancer, and warrants further investigation.

The discovery of novel, potent ERR-alpha inverse agonists for the treatment of triple negative breast cancer

The estrogen-related receptor α (ERRα) is an orphan receptor and a novel target for solid tumor therapy, conceivably through effects on the regulation of tumor cell energy metabolism associated with energy stress within solid tumor micro environments. Here we describe the discovery of novel potent inverse agonists of ERRα. In vitro, compound 11 potently inhibits ERRα's transcriptional activity by preventing endogenous PGC-1α and ERRα binding and suppresses the proliferation of different human cancer cell lines and the migration of breast cancer cells (MDA-MB-231). In vivo, compound 11 demonstrates a strong inhibitory effect on the growth of human breast cancer xenografts (MDA-MB-231) and the tumor growth is inhibited by 40.9% after treating with compound 11 (30 mg/kg). The binding mode shows that compound 11 interacts with the binding pocket of ERRα through hydrogen interactions with the residue Gly397 and hydrophobic interactions with the hydrophobic residues. All these results suggest that compound 11 represents a novel potent ERRα inverse agonist and is promising in the discovery of antitumor compounds for the treatment of triple negative breast cancer.

FOXC1 is associated with estrogen receptor alpha and affects sensitivity of tamoxifen treatment in breast cancer

FOXC1 is a member of Forkhead box transcription factors that participates in embryonic development and tumorigenesis. Our previous study demonstrated that FOXC1 was highly expressed in triple‐negative breast cancer. However, it remains unclear what is the relation between FOXC1 and ERα and if FOXC1 regulates expression of ERα. To explore relation between FOXC1 and ERα and discover regulation of ERα expression by FOXC1 in breast cancer, we analyzed data assembled in the Oncomine and TCGA, and found that there was significantly higher FOXC1 expression in estrogen receptor‐negative breast cancer than that in estrogen receptor‐positive breast cancer. Overexpression of FOXC1 reduced expression of ERα and cellular responses to estradiol (E2) and tamoxifen in the MCF‐7 FOXC1 and T47D FOXC1 cells, while knockdown of FOXC1 induced expression of ERα and improved responses to estradiol (E2) and tamoxifen in BT549 FOXC1 shRNA and HCC1806 FOXC1 shRNA cells. In addition, overexpression of FOXC1 reduced expression of progesterone receptor (PR), Insulin receptor substrate 1 (IRS1), and XBP1 (X‐Box Binding Protein 1) and significantly reduced luciferase activity caused by E2 using ERE luciferase reporter assay. These results suggested that FOXC1 regulated expression of ERα and affected sensitivity of tamoxifen treatment in breast cancer, and that FOXC1 may be used as a potential therapeutic target in ERα‐negative breast cancer.

Characterization of a selective inverse agonist for estrogen related receptor α as a potential agent for breast cancer

The estrogen-related receptor α (ERRα) is an orphan nuclear receptor that plays a primary role in the regulation of cellular energy homeostasis and osteogenesis. It is reported that ERRα is widely expressed in a range of tissues and accumulating evidence has supported that the high expression of ERRα correlates with poor prognosis of various human malignancies, including breast, endometrium, colon, prostate and ovary cancers. Herein is described the discovery of a novel selective inverse agonist (HSP1604) of ERRα, but not of ERRβ and ERRγ, as determined using transient transfection luciferase reporter assay and a time-resolved fluorescence resonance energy transfer (TR-FRET) co-activator assay. HSP1604 potently inhibits ERRα transcriptional activity with IC50=1.47±0.17μM in cell-based luciferase reporter assay and also decreases the protein level of ERRα and the mRNA levels of its downstream target genes such as pyruvate dehydrogenase kinase 4 (PDK4), pS2 and osteopontin. HSP1604 has also suppressed the proliferation of different human cancer cell lines and the migration of breast cancer cells with high expression of ERRα. Representative in vivo results show that HSP1604 suppresses the growth of human breast cancer xenograft in nude mice as doses at 30mg/kg or 100mg/kg administered every other day during 28-day period. HSP1604 thus has the potential both as a new agent to inhibit the growth of tumors and as a chemical probe of ERRα biology.

MicroRNA-497 downregulation contributes to cell proliferation, migration, and invasion of estrogen receptor alpha negative breast cancer by targeting estrogen-related receptor alpha

Metastasis has become the main challenge for treatment of estrogen receptor alpha (ERα) negative breast cancer. Here, we found a negative correlation between miR-497 and estrogen-related receptor alpha (ERRα), a nuclear receptor overexpressed in ERα negative breast cancer. Targeted inhibition of ERRα by si-RNA increased miR-497 expression while overexpression of ERRα inhibited miR-497 expression. Further investigation showed that miR-497 targeted ERRα by binding to the 3'UTR region of ERRα. Luciferase assay and ChIP assay confirmed that ERα directly regulated the transcription of miR-497, suggesting that loss of ERα lowered miR-497 level in ERα negative breast cancer. Further, overexpression of miR-497 not only inhibited ERRα expression but also reduced MIF level and MMP9 activity, which led to significant decreases in cell proliferation, migration, and invasion of ERα negative breast cancer. Taken together, our findings suggested that, in ERα negative breast cancer, the low level of ERα reduced miR-497 expression, which promoted ERRα expression that enhanced cell proliferation, migration, and invasion by increasing MIF expression and MMP9 activity.

The PLA2R1-JAK2 pathway upregulates ERRα and its mitochondrial program to exert tumor-suppressive action

Little is known about the biological role of the phospholipase A2 receptor (PLA2R1) transmembrane protein. In recent years, PLA2R1 has been shown to have an important role in regulating tumor-suppressive responses via JAK2 activation, but the underlying mechanisms are largely undeciphered. In this study, we observed that PLA2R1 increases the mitochondrial content, judged by increased levels of numerous mitochondrial proteins, of the mitochondrial structural component cardiolipin, of the mitochondrial DNA content, and of the mitochondrial DNA replication and transcription factor TFAM. This effect of PLA2R1 relies on a transcriptional program controlled by the estrogen-related receptor alpha1 (ERRα) mitochondrial master regulator. Expression of ERRα and of its nucleus-encoded mitochondrial targets is upregulated upon PLA2R1 ectopic expression, and this effect is mediated by JAK2. Conversely, downregulation of PLA2R1 decreases the level of ERRα and of its nucleus-encoded mitochondrial targets. Finally, blocking the ERRα-controlled mitochondrial program largely inhibits the PLA2R1-induced tumor-suppressive response. Together, our data document ERRα and its mitochondrial program as downstream effectors of the PLA2R1-JAK2 pathway leading to oncosuppression.

Inverse agonist of estrogen-related receptor α suppresses the growth of triple negative breast cancer cells through ROS generation and interaction with multiple cell signaling pathways

There is an urgent clinical need for targeted therapy approaches for triple-negative breast cancer (TNBC) patients. Increasing evidences suggested that the expression of estrogen-related receptor alpha (ERRα) was correlate with unfavorable clinical outcomes of breast cancer patients. We here show that inhibition of ERRα by its inverse agonist XCT-790 can suppress the proliferation, decrease G2/M phases, and induce mitochondrial-related apoptosis of TNBC cells. XCT-790 elevates the proteins related to endoplasmic reticulum (ER) stress such as ATF4/6, XBT-1 and CHOP. It also increases the expression of growth inhibition related proteins such as p53 and p21. Further, XCT-790 can increase the generation of reactive oxygen species (ROS) in TNBC cells mainly through inhibition of SOD1/2. While ROS scavenger NAC abolishes XCT-790 induced ER-stress and growth arrest. XCT-790 treatment can rapidly activate the signal molecules including ERK1/2, p38-MAPK, JNK, Akt, p65, and IκBα, while NAC attenuates effects of XCT-790 induced phosphorylation of ERK1/2, p38-MAPK and Akt. Further, the inhibitors of ERK1/2, JNK, Akt, and NF-κB attenuate XCT-790 induced ROS generation. These data suggest that AKT/ROS and ERK/ROS positive feedback loops, NF-κB/ROS, and ROS/p38-MAPK, are activated in XCT-790 treated TNBC cells. In vivo experiments show that XCT-790 significantly suppresses the growth of MDA-MB-231 xenograft tumors, which is associated with up regulation of p53, p21, ER-stress related proteins while down regulation of bcl-2. The present discovery makes XCT-790 a promising candidate drug and lays the foundation for future development of ERRα-based therapies for TNBC patients.

Tamoxifen Action in ER-Negative Breast Cancer

Breast cancer is a highly heterogeneous disease. Tamoxifen is a selective estrogen receptor (ER) modulator and is mainly indicated for the treatment of breast cancer in postmenopausal women and postsurgery neoadjuvant therapy in ER-positive breast cancers. Interestingly, 5–10% of the ER-negative breast cancers have also shown sensitivity to tamoxifen treatment. The involvement of molecular markers and/or signaling pathways independent of ER signaling has been implicated in tamoxifen sensitivity in the ER-negative subgroup. Studies reveal that variation in the expression of estrogen-related receptor alpha, ER subtype beta, tumor microenvironment, and epigenetics affects tamoxifen sensitivity. This review discusses the background of the research on the action of tamoxifen that may inspire future studies to explore effective therapeutic strategies for the treatment of ER-negative and triple-negative breast cancers, the latter being an aggressive disease with worse clinical outcome.