Orphan nuclear receptors as drug targets for the treatment of prostate and breast cancers

Targeting Androgen, Thyroid Hormone, and Vitamin A and D Receptors to Treat Prostate Cancer

The nuclear hormone family of receptors regulates gene expression. The androgen receptor (AR), upon ligand binding and homodimerization, shuttles from the cytosol into the nucleus to activate gene expression. Thyroid hormone receptors (TRs), retinoic acid receptors (RARs), and the vitamin D receptor (VDR) are present in the nucleus bound to chromatin as a heterodimer with the retinoid X receptors (RXRs) and repress gene expression. Ligand binding leads to transcription activation. The hormonal ligands for these receptors play crucial roles to ensure the proper conduct of very many tissues and exert effects on prostate cancer (PCa) cells. Androgens support PCa proliferation and androgen deprivation alone or with chemotherapy is the standard therapy for PCa. RARγ activation and 3,5,3'-triiodo-L-thyronine (T3) stimulation of TRβ support the growth of PCa cells. Ligand stimulation of VDR drives growth arrest, differentiation, and apoptosis of PCa cells. Often these receptors are explored as separate avenues to find treatments for PCa and other cancers. However, there is accumulating evidence to support receptor interactions and crosstalk of regulatory events whereby a better understanding might lead to new combinatorial treatments.

Tumoral periprostatic adipose tissue exovesicles-derived miR-20a-5p regulates prostate cancer cell proliferation and inflammation through the RORA gene

BACKGROUND

From the first steps of prostate cancer (PCa) initiation, tumours are in contact with the most-proximal adipose tissue called periprostatic adipose tissue (PPAT). Extracellular vesicles are important carriers of non-coding RNA such as miRNAs that are crucial for cellular communication. The secretion of extracellular vesicles by PPAT may play a key role in the interactions between adipocytes and tumour. Analysing the PPAT exovesicles (EVs) derived-miRNA content can be of great relevance for understanding tumour progression and aggressiveness.

METHODS

A total of 24 samples of human PPAT and 17 samples of perivesical adipose tissue (PVAT) were used. EVs were characterized by western blot and transmission electron microscopy (TEM), and uptake by PCa cells was verified by confocal microscopy. PPAT and PVAT explants were cultured overnight, EVs were isolated, and miRNA content expression profile was analysed. Pathway and functional enrichment analyses were performed seeking potential miRNA targets. In vitro functional studies were evaluated using PCa cells lines, miRNA inhibitors and target gene silencers.

RESULTS

Western blot and TEM revealed the characteristics of EVs derived from PPAT (PPAT-EVs) samples. The EVs were up taken and found in the cytoplasm of PCa cells. Nine miRNAs were differentially expressed between PPAT and PVAT samples. The RORA gene (RAR Related Orphan Receptor A) was identified as a common target of 9 miRNA-regulated pathways. In vitro functional analysis revealed that the RORA gene was regulated by PPAT-EVs-derived miRNAs and was found to be implicated in cell proliferation and inflammation.

CONCLUSION

Tumour periprostatic adipose tissue is linked to PCa tumour aggressiveness and could be envisaged for new therapeutic strategies.

Integration of Single-Cell RNA Sequencing and Bulk RNA Sequencing to Identify an Immunogenic Cell Death-Related 5-Gene Prognostic Signature in Hepatocellular Carcinoma

Introduction

Immunogenic cell death (ICD) can enhance the potency of immunotherapy in cancer treatment. Nevertheless, it is ambiguous how ICD-related genes (ICDRGs) contribute to hepatocellular carcinoma (HCC).

Methods

Single-cell RNA sequencing (scRNA-seq) data were used to distinguish malignant cells from normal cells in the HCC tumor microenvironment(TME). Bulk RNA sequencing data was employed to acquire the landscape of the 33 ICDRGs. Unsupervised clustering identified two ICD molecular subtypes. The cellular infiltration characteristics and biological behavior in different subtypes were analyzed by ssGSEA. Subsequently, differentially expressed genes (DEGs) between the two subtypes were determined, based on which patients were classified into three gene clusters. Then, the prognostic model was constructed by Lasso-Cox analysis. Finally, we investigated the expression of risk genes in cancer cell line encyclopedia (CCLE) and validated the function of NKX3-2 in vitro experiments.

Results

ICD scores and ICDRGs expression in malignant cells were significantly lower than in normal cells by scRNA-seq analysis. ICD-high subtype was characterized by ICD-related gene overexpression and high levels of immune infiltration abundance and immune checkpoints; Three DEGs-related gene clusters were likewise strongly linked to stromal and immunological activation. In the ICD-related prognostic model consisting of NKX3-2, CHODL, MMP1, NR0B1, and CTSV, the low-risk group patients had a better endpoint and displayed increased susceptibility to immunotherapy and chemotherapeutic drugs like 5-Fluorouracil, afatinib, bortezomib, cediratinib, lapatinib, dasatinib, gefitinib and crizotinib. Moreover, NKX3-2 amplification in HCC samples has been verified by experiments, and its disruption suppressed the proliferation and invasion of tumor cells.

Conclusion

Our study highlighted the potential of the ICDRGs risk score as a prognostic indicator to aid in the accurate diagnosis and immunotherapy sensitivity of HCC.

Targeting the cholesterol-RORα/γ axis inhibits colorectal cancer progression through degrading c-myc

Dysregulated cholesterol metabolism is a hallmark of colorectal cancer (CRC). However, the usage of cholesterol-lowering agents seemed to have no benefit in CRC patients. In this study, we focused on the cholesterol-nuclear receptors (NRs) axis as a strategy. Cholesterol and its derivatives work as ligands for different nuclear receptors, thus promoting cancer progression. The key NR downstream of cholesterol in CRC is unknown. Here, we treated CRC cells with a cholesterol-lowering agent and lipoprotein-depleted conditioned medium, and then detected the change of the putative NRs. The results revealed that RORα/γ (Retinoic acid receptor-related Orphan Receptor α/γ) levels exhibited the most obvious increases in CRC cells subjected them to cholesterol deprivation. RORα/γ agonists significantly inhibited CRC cells proliferation and migration in vitro and in vivo. Also, RORα/γ overexpression repressed CRC cells proliferation and migration in vitro and in vivo and RORα/γ knockdown promoted it. Mechanistically, RORα/γ agonists promoted c-myc degradation by activating the transcription of the ubiquitinase NEDD4. Intriguingly, the combination of RORα/γ agonists and atorvastatin had a synergistic effect on inhibiting CRC cells. These findings demonstrate that the cholesterol- RORα/γ axis is important for maintaining c-myc protein levels. Combination therapy with atorvastatin and RORα/γ agonist is a promising therapeutic strategy for CRC.

TLX, an Orphan Nuclear Receptor With Emerging Roles in Physiology and Disease

TLX (NR2E1), an orphan member of the nuclear receptor superfamily, is a transcription factor that has been described to be generally repressive in nature. It has been implicated in several aspects of physiology and disease. TLX is best known for its ability to regulate the proliferation of neural stem cells and retinal progenitor cells. Dysregulation, overexpression, or loss of TLX expression has been characterized in numerous studies focused on a diverse range of pathological conditions, including abnormal brain development, psychiatric disorders, retinopathies, metabolic disease, and malignant neoplasm. Despite the lack of an identified endogenous ligand, several studies have described putative synthetic and natural TLX ligands, suggesting that this receptor may serve as a therapeutic target. Therefore, this article aims to briefly review what is known about TLX structure and function in normal physiology, and provide an overview of TLX in regard to pathological conditions. Particular emphasis is placed on TLX and cancer, and the potential utility of this receptor as a therapeutic target.

Drugging the 'undruggable'. Therapeutic targeting of protein-DNA interactions with the use of computer-aided drug discovery methods

Transcription factors (TFs) act as major oncodrivers in many cancers and are frequently regarded as high-value therapeutic targets. The functionality of TFs relies on direct protein-DNA interactions, which are notoriously difficult to target with small molecules. However, this prior view of the 'undruggability' of protein-DNA interfaces has shifted substantially in recent years, in part because of significant advances in computer-aided drug discovery (CADD). In this review, we highlight recent examples of successful CADD campaigns resulting in drug candidates that directly interfere with protein-DNA interactions of several key cancer TFs, including androgen receptor (AR), ETS-related gene (ERG), MYC, thymocyte selection-associated high mobility group box protein (TOX), topoisomerase II (TOP2), and signal transducer and activator of transcription 3 (STAT3). Importantly, these findings open novel and compelling avenues for therapeutic targeting of over 1600 human TFs implicated in many conditions including and beyond cancer.

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.

Interplay between orphan nuclear receptors and androgen receptor-dependent or-independent growth signalings in prostate cancer

It is well-established that both the initial and advanced growth of prostate cancer depends critically on androgens and thus on the activated androgen receptor (AR) -mediated signaling pathway. The unique hormone-dependent feature of prostate cancer forms the biological basis of hormone or androgen-deprivation therapy (ADT) that aims to suppress the AR signaling by androgen depletion or AR antagonists. ADT still remains the mainstay treatment option for locally advanced or metastatic prostate cancer. However, most patients upon ADT will inevitably develop therapy-resistance and progress to relapse in the form of castration-resistant disease (castration-resistant prostate cancer or CRPC) or even a more aggressive androgen-independent subtype (therapy-related neuroendocrine prostate cancer or NEPC). Recent advances show that besides AR, some ligand-independent members of nuclear receptor superfamily-designated as orphan nuclear receptors (ONRs), as their endogenous physiological ligands are either absent or not yet identified to date, also play significant roles in the growth regulation of prostate cancer via multiple AR-dependent or -independent (AR-bypass) pathways or mechanisms. In this review, we summarize the recent progress in the newly elucidated roles of ONRs in prostate cancer, with a focus on their interplay in the AR-dependent pathways (intratumoral androgen biosynthesis and suppression of AR signaling) and AR-independent pathways or cellular processes (hypoxia, oncogene- or tumor suppressor-induced senescence, apoptosis and regulation of prostate cancer stem cells). These ONRs with their newly characterized roles not only can serve as novel biomarkers but also as potential therapeutic targets for management of advanced prostate cancer.

The meaning of non-classical estrogen receptors and peroxisome proliferator-activated receptor for boar Leydig cell of immature testis

Communication in biological systems involves diverse-types of cell-cell interaction including cross-talk between receptors expressed by the target cells. Recently, novel sort of estrogen receptors (G protein - coupled estrogen receptor; GPER and estrogen-related receptor; ERR) that signal directly via estrogen binding and/or via mutual interaction-regulated estrogen signaling were reported in various organs including testis. Peroxisome proliferator - activated receptor (PPAR) is responsible for maintaining of lipid homeostasis that is critical for sex steroid production in the testis. Here, we investigated the role of interaction between GPER, ERRβ and PPARγ in steroidogenic Leydig cells of immature boar testis. Testicular fragments cultured ex vivo were treated with GPER or PPARγ antagonists. Then, cell ultrastructure, expression and localization of GPER, ERRβ, PPARγ together with the molecular receptor mechanism, through cyclic AMP and Raf/Ras/extracellular signal activated kinases (ERK), in the control of cholesterol concentration and estrogen production by Leydig cells were studied. In the ultrastructure of antagonist-treated Leydig cells, mitochondria were not branched and not bifurcated as they were found in control. Additionally, in PPARγ-blocked Leydig cells changes in the number of lipid droplets were revealed. Independent of used antagonist, western blot revealed decreased co-expression of GPER, ERRβ, PPARγ with exception of increased expression of ERRβ after PPARγ blockage. Immunohistochemistry confirmed presence of all receptors partially located in the nucleus or cytoplasm of Leydig cells of both control and treated testes. Changes in receptor expression, decreased cholesterol and increased estradiol tissue concentrations occurred through decreased cAMP level (with exception after GPER blockage) as well as Raf/Ras/ERK pathway expression. These all findings indicate that GPER-ERRβ-PPARγ interaction exists in immature boar testis and regulates Leydig cell function. Further detailed studies and considerations on GPER-ERRβ-PPARγ as possible diagnosis/therapy target in disturbances of testis steroidogenic function are needed.

Estrogen-Related Receptor Alpha: An Under-Appreciated Potential Target for the Treatment of Metabolic Diseases

The estrogen-related receptor alpha (ESRRA) is an orphan nuclear receptor (NR) that significantly influences cellular metabolism. ESRRA is predominantly expressed in metabolically-active tissues and regulates the transcription of metabolic genes, including those involved in mitochondrial turnover and autophagy. Although ESRRA activity is well-characterized in several types of cancer, recent reports suggest that it also has an important role in metabolic diseases. This minireview focuses on the regulation of cellular metabolism and function by ESRRA and its potential as a target for the treatment of metabolic disorders.

Exploring the binding mode and thermodynamics of inverse agonists against estrogen-related receptor alpha

Since estrogen-related receptor alpha (ERRα), one of three estrogen-related receptors, displays constitutively active transcriptional activities and important implications in both physiological and pathological processes of breast cancers, ERRα was recently recognized as a new target to fight breast cancers, and regulating the activity of ERRα with inverse agonists has thus become a promising new therapeutic strategy. A few inverse agonists cyclohexylmethyl-(1-p-tolyl-1H-indol-3-ylmethyl)-amine (compound 1), thiadiazoacrylamide (XCT790), and 1-(2,5-diethoxy-benzyl)-3-phenyl-area analogues (compounds 2 and 3) were reported to be capable of targeting ERRα. However, the detailed mechanism by which the inverse agonists deactivate ERRα remains unclear, especially in the aspects of quantitative binding and hot spot residues. Therefore, to gain insights into the interaction modes between inverse agonists and ERRα ligand binding domain, all-atom molecular dynamics (MD) simulations were firstly carried out for the complexes of inverse agonists and ERRα. The binding free energies were then calculated with MM-PBSA method to quantitatively discuss the binding of the inverse agonists with ERRα. The binding affinities were finally decomposed to per-residue contributions to identify the hot spot residues as well as assess their role in the binding mechanism. MD simulations show that the inverse agonists stretch downwards into the ERRα ligand binding pocket (LBP) formed by H3 and H11 helices, and upon the binding H12 adopts a well-defined position in the coactivator groove, where PGC-1α binds to ERRα. Binding energy analysis indicates that compound 3 and XCT790 bind more tightly to ERRα than compounds 1 and 2, and the energy difference mainly results from the contribution of van der Waals interaction. Both binding mode analysis and affinity decomposition per-residue indicate that compound 1, XCT790, and compound 3 have similar binding spectra to ERRα, primarily interacting with the residues of H3, H5, H6/H7 loop, and H11 helix, while compound 2 lacks a significant interaction with the H5 region. The hot spot residues significantly binding to the three inverse agonists in common include Leu324, Phe328, Phe382, Leu398, Phe495, and Leu500. It is essential for an effective inverse agonist to strongly bind with the aromatic ring cluster consisting of Phe328(H3), Phe495(H11), and Phe382(H5/H6 loop) as well as Leu500.

All-atom MD simulations were for the first time carried out for the complexes of inverse agonists and ERRα, and their binding free energies were also calculated with MM-PBSA to quantitatively discuss the binding of the inverse agonists with ERRα.

Telocytes in the mouse testicular interstitium: implications of G-protein-coupled estrogen receptor (GPER) and estrogen-related receptor (ERR) in the regulation of mouse testicular interstitial cells

Telocytes (TCs), a novel type of interstitial cells, are involved in tissue homeostasis maintenance. This study aimed to investigate TC presence in the interstitium of mouse testis. Additionally, inactivation of the G-coupled membrane estrogen receptor (GPER) in the testis was performed to obtain insight into TC function, regulation, and interaction with other interstitial cells. Mice were injected with a GPER antagonist (G-15; 50 μg/kg bw), and the GPER-signaling effect on TC distribution, ultrastructure, and function, as well as the interstitial tissue interaction of GPER with estrogen-related receptors (ERRs), was examined. Microscopic observations of TC morphology were performed with the use of scanning and transmission electron microscopes. Telocyte functional markers (CD34; c-kit; platelet-derived growth factor receptors α and β, PDGFRα and β; vascular endothelial growth factor, VEGF; and vimentin) were analyzed by immunohistochemistry/immunofluorescence and Western blot. mRNA expression of CD34 as well as ERR α, β, and γ was measured by qRT-PCR. Relaxin and Ca2+ concentrations were analyzed by immunoenzymatic and colorimetric assays, respectively. For the first time, we reveal the presence of TCs in the interstitium together with the peritubular area of mouse testis. Telocytes were characterized by specific features such as a small cell body and extremely long prolongations, constituting a three-dimensional network mainly around the interstitial cells. Expression of all TC protein markers was confirmed. Based on scanning electron microscopic observation in GPER-blocked testis, groups of TCs were frequently seen. No changes were found in TC ultrastructure in GPER-blocked testis when compared to the control. However, tendency to TC number change (increase) after the blockage was observed. Concomitantly, no changes in mRNA CD34 expression and increase in ERR expression were detected in GPER-blocked testes. In addition, Ca2+ was unchanged; however, an increase in relaxin concentration was observed. Telocytes are an important component of the mouse testicular interstitium, possibly taking part in maintaining its microenvironment as well as contractile and secretory functions (via themselves or via controlling of other interstitial cells). These cells should be considered a unique and useful target cell type for the prevention and treatment of testicular interstitial tissue disorders based on estrogen-signaling disturbances.

Retinoic acid-related orphan receptor alpha (RORA) variants and risk of breast cancer

BACKGROUND

Breast cancer is the most common type of cancer and the second leading cause of cancer death in females. Despite numerous studies in this field, the etiology and clinical behavior of breast tumors have not been understood yet. Retinoid orphan nuclear receptor alpha (RORA) is a member of the orphan nuclear factor family involved in the regulation of lipid and steroid metabolism, immune response and circadian rhythms. Recent evidences support its role as a tumor suppressor gene.

OBJECTIVES

To find the associations between RORA polymorphisms and breast cancer.

METHODS

In the present study, we evaluated the association between two functional polymorphisms in RORA (rs11639084 and rs4774388) and breast cancer risk in a population of 122 Iranian breast cancer patients as well as 200 healthy subjects by means of tetra primer-amplification refractory mutation system-PCR (4P-ARMS-PCR) method.

RESULTS

The rs4774388 has been shown to be associated with breast cancer risk in recessive inheritance model (OR (95% CI ) = 0.51 (0.26-0.97) and P = 0.041). However, the allele and genotype frequencies of rs11639084 were not different in patients and control (P > 0.05). Haplotype analysis revealed no significant association of any estimated block of rs11639084/rs4774388 in breast cancer patients versus healthy controls.

CONCLUSIONS

The results of this study support a putative role for RORA in breast cancer pathogenesis.

Interplay between estrogen-related receptors and steroidogenesis-controlling molecules in adrenals. In vivo and in vitro study

Estrogen-related receptors (ERRs) α, β and γ appear to be novel molecules implicated in estrogen signaling. We blocked and activated ERRs in mouse (C57BL/6) adrenals and adrenocortical cells (H295R) using pharmacological agents XCT 790 (ERRα antagonist) and DY131 (ERRβ/γ agonist), respectively. Mice were injected with XCT 790 or DY131 (5 μg/kg bw) while cells were exposed to XCT 790 or DY131 (0.5 μg/L). Irrespectively of the agent used, changes in adrenocortical cell morphology along with changes in lutropin, cholesterol levels and estrogen production were found. Diverse and complex ERRs regulation of multilevel-acting steroidogenic proteins (perilipin; PLIN, cytochrome P450 side-chain cleavage; P450scc, translocator protein; TSPO, steroidogenic acute regulatory protein; StAR, hormone sensitive lipase; HSL and HMG-CoA reductase; HMGCR) was revealed. Blockage of ERRα decreased P450scc, StAR and TSPO expressions. Activation of ERRβ/γ increased P450scc, StAR and HMGCR while decreased HSL expressions. PLIN expression increased either after XCT 790 or DY131 treatment. Additionally, treatment with both XCT 790 or DY131 decreased activity of Ras/Raf, Erk and Akt indicating their involvement in control of morphology and steroidogenic function of cortex cells. ERRs are important in maintaining morpho-function of cortex cells through action in specific, opposite, or common manner on steroidogenic molecules.

Discovery and characterization of small molecules targeting the DNA-binding ETS domain of ERG in prostate cancer

Genomic alterations involving translocations of the ETS-related gene ERG occur in approximately half of prostate cancer cases. These alterations result in aberrant, androgen-regulated production of ERG protein variants that directly contribute to disease development and progression. This study describes the discovery and characterization of a new class of small molecule ERG antagonists identified through rational in silico methods. These antagonists are designed to sterically block DNA binding by the ETS domain of ERG and thereby disrupt transcriptional activity. We confirmed the direct binding of a lead compound, VPC-18005, with the ERG-ETS domain using biophysical approaches. We then demonstrated VPC-18005 reduced migration and invasion rates of ERG expressing prostate cancer cells, and reduced metastasis in a zebrafish xenograft model. These results demonstrate proof-of-principal that small molecule targeting of the ERG-ETS domain can suppress transcriptional activity and reverse transformed characteristics of prostate cancers aberrantly expressing ERG. Clinical advancement of the developed small molecule inhibitors may provide new therapeutic agents for use as alternatives to, or in combination with, current therapies for men with ERG-expressing metastatic castration-resistant prostate cancer.

Molecular pathways involved in the transport of nuclear receptors from the nucleus to cytoplasm

Nuclear receptors (NRs) are transcription regulators that direct the expression of many genes linked to cellular processes, such as proliferation, differentiation, and apoptosis. Additionally, some cellular events are also modulated by signaling pathways induced by NRs outside of the nucleus. Hence, the subcellular transport of NRs is dynamic and is modulated by several signals, protein-protein interactions, and posttranslational modifications. Particularly, the exit of NRs from the nucleus to cytoplasm and/or other compartments is transcendental, as it is this export event, which determines their abundance in the cells' compartments, the activation or attenuation of nuclear or extranuclear pathways, and the magnitude and duration of their effects inside or outside of the nucleus. Consequently, an adequate control of the distribution of NRs is critical for homeostasis, because a deregulation in the nucleo-cytoplasmic transport of NRs could be involved in diseases including cancer as well as metabolic and vascular alterations. In this review, we investigated the pathways and molecular and biological aspects that have been described for the nuclear export of NRs so far and their functional relevance in some diseases. This information suggests that the transport of NRs out of the nucleus is a key mechanism for the identification of new therapeutic targets for alterations associated with the deregulation of the function of NRs.

DAX1 promotes cervical cancer cell growth and tumorigenicity through activation of Wnt/β-catenin pathway via GSK3β

DAX1 is well known for its fundamental role in several types of cancer, while its biological role in cervical cancer remains largely unexplored. The expression of DAX1 in cervical carcinoma tissue was examined using immunohistochemistry and western blot. The effects of DAX1 silencing on the cell growth, tumor formation, and CSC (cancer stem cell) characteristics were also investigated. DAX1 expressed a gradual increase from normal cervix to high-grade squamous intraepithelial lesions, and consequently to cervical cancer. Silence of DAX1 significantly inhibited the cell growth, tumorigenicity, and tumorsphere formation. Furthermore, the TOP/FOP-Flash reporter assay revealed that Wnt/β-catenin pathway was significantly inactivated in DAX1-silenced cervical cancer cells with the downregulation of Wnt/β-catenin targeting genes, including cyclinD1 and c-myc. Moreover, dual-luciferase reporter and chromatin immunoprecipitation (ChIP) assay confirmed that DAX1 transcriptionally repressed glycogen synthase kinase 3β (GSK3β), an inhibitor of the Wnt/β-catenin pathway, by physically interacting with -666~-444 motif on the GSK3β promoter. Additionally, the blockage of GSK3β by CHIR-99021 resulted in a significant increase of CSC characteristics induced by the silence of DAX1. Our data demonstrated that DAX1 is overexpressed in cervical cancer, and that it promotes cell growth and tumorigenicity through activating Wnt/β-catenin pathway mediated by GSK3β.

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.

Chlorinated biphenyls effect on estrogen-related receptor expression, steroid secretion, mitochondria ultrastructure but not on mitochondrial membrane potential in Leydig cells

To characterize polychlorinated biphenyls (PCBs) action on Leydig cells, PCBs congeners, low-chlorinated (delor 103; d103) and high-chlorinated ones (delor 106; d106) were selected. The cells were treated according to PCBs dose (d103 or d106 0.2 ng/ml in low doses:, or 2 ng/ml in high doses) and type (d103 + d106 in low doses or 103 + 106 in high doses). After 24 h treatment with PCBs, a distinct increase in estrogen-related receptors (ERRs type α, β and γ) expression was revealed. However, the dose- and type-dependent PCBs effect was mostly exerted on ERRα expression. A similar increase in ERRs expression was demonstrated by estradiol but not testosterone, which was without an effect on ERRs. PCBs caused no decrease in the membrane potential status of Leydig cells (either in dose or type schedule) but had severe effects on the mitochondria number and structure. Moreover, PCBs markedly increased calcium (Ca2+) concentration and sex steroid secretion (both androgens and estrogens were elevated). These findings suggest a similar estrogenic action of PCBs congeners (d103 and d106) on Leydig cell function. We report dose- and type-specific effects of PCBs only on Leydig cell ERRs expression. Both delors showed common effects on the mitochondria ultrastructural and functional status. Based on our results, ERRα seems to be the most sensitive to hormonal modulation. The increases in Ca2+ and sex steroid secretion may be due to the activation of ERRs by PCBs binding and/or direct effect of PCBs on ERRs mRNA/protein expression. Nevertheless, to confirm the existence of possible relationships between ERRs signaling (including PCBs as ligands) and mitochondria function in Leydig cells, further intensive studies are needed.

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.

Emerging roles of orphan nuclear receptors in regulation of innate immunity

Innate immunity constitutes the first line of defense against pathogenic and dangerous insults. However, it is a double-edged sword, as it functions in both clearance of infection and inflammatory damage. It is therefore important that innate immune responses are tightly controlled to prevent harmful excessive inflammation. Nuclear receptors (NRs) are a family of transcription factors that play critical roles in various physiological responses. Orphan NRs are a subset of NRs for which the ligands and functions are unclear. Accumulating evidence has revealed that orphan NRs play essential roles in innate immune responses to prevent pathogenic inflammatory responses and to enhance antimicrobial host defenses. In this review, we describe current knowledge on the roles and mechanisms of orphan NRs in the regulation of innate immune responses. Discovery of new functions of orphan NRs would facilitate development of novel preventive and therapeutic strategies against human inflammatory diseases.

The emerging roles of orphan nuclear receptors in prostate cancer

Orphan nuclear receptors are members of the nuclear receptor (NR) superfamily and are so named because their endogenous physiological ligands are either unknown or may not exist. Because of their important regulatory roles in many key physiological processes, dysregulation of signalings controlled by these receptors is associated with many diseases including cancer. Over years, studies of orphan NRs have become an area of great interest because their specific physiological and pathological roles have not been well-defined, and some of them are promising drug targets for diseases. The recently identified synthetic small molecule ligands, acting as agonists or antagonists, to these orphan NRs not only help to understand better their functional roles but also highlight that the signalings mediated by these ligand-independent NRs in diseases could be therapeutically intervened. This review is a summary of the recent advances in elucidating the emerging functional roles of orphan NRs in cancers, especially prostate cancer. In particular, some orphan NRs, RORγ, TR2, TR4, COUP-IFII, ERRα, DAX1 and SHP, exhibit crosstalk or interference with androgen receptor (AR) signaling in either normal or malignant prostatic cells, highlighting their involvement in prostate cancer progression as androgen and AR signaling pathway play critical roles in this process. We also propose that a better understanding of the mechanism of actions of these orphan NRs in prostate gland or prostate cancer could help to evaluate their potential value as therapeutic targets for prostate cancer.

Estrogen-Related Receptors in Breast Cancer and Prostate Cancer

Estrogen-signaling pathways are implicated in the development of breast cancer and prostate cancer. Various studies have focused on additional signaling pathways, mediated by estrogen-related receptors (ERRs). ERRs are constitutively active receptors that share a high degree of homology with the classical estrogen receptors (ERs). However, they do not bind to estrogen, while ERs do. ERRs are involved in the development of alternative pathways that lead to the development of cancer and are regarded as potential therapeutic targets for the treatment of breast cancer and prostate cancer that do not respond to conventional therapies. In this review, we first present general structural features of ERRs. Then, we focus on breast cancer and prostate cancer, which are primarily hormone-dependent cancers, and summarizes recent progress in elucidating the involvement of each ERR in these two types of malignancies.