PAX3-FOXO1A Expression in Rhabdomyosarcoma Is Driven by the Targetable Nuclear Receptor NR4A1

Orphan Nuclear Receptor 4A1 (NR4A1) and NR4A2are Endogenous Regulators of CD71 and TheirLigands Induce Ferroptosis in Breast Cancer

Ferroptosis is an iron-dependent cell death pathway that involves multiple genes including the transferrin receptor (TFRC/CD71), glutathione peroxidase 4 (GPX4) and SLC7A11. This study is based on the hypothesis that orphan nuclear receptor 4A1 (NR4A1) and NR4A2 maintain low levels of ferroptosis in triple negative breast cancer (TNBC) cells and that bis-indole derived (CDIM) compounds act as NR4A1/2 ligands that induce ferroptosis by enhancing CD71 expression. 1,1-Bis(3'-indolyl)-1-(3,5-disubstitutedphenyl)methane (DIM-3,5) analogs were investigated for their cytotoxicity and effects on NR4A1 and NR4A2 regulated genes and induction of ferroptosis by cytotoxicity, western blot and RT-PCR. Several assays also determined enhanced lipoperoxidation, reactive oxygen species and malondialdehyde formation in TNBC cells. Knockdown of NR4A1, NR4A2, Sp1 and Sp4 was carried out by RNA interference. Molecular mechanisms of NR4A1/2-mediated regulation of CD71 expression were determined using CD71-luciferase promoter constructs, overexpression of Sp1 and chromatin immunoprecipitation (ChIP) assays. Initial studies show that DIM-3,5 act as an inverse NR4A1/NR4A2 agonist that downregulated the pro-oncogenic responses/gene products regulated by both receptors in TNBC cells. DIM-3,5 analogs also induced ROS, malondialdehyde and lipoperoxide formation in TNBC cells and this was accompanied by indicators of ferroptosis that include decreased expression of GPX4 and SLC7A11 and induction of CD71. Induction of CD71, an important biomarker of ferroptosis was observed after treatment of TNBC cells with DIM-3,5 analogs, knockdown of NR4A1, NR4A2, Sp1 or Sp4 demonstrating that induction of CD71 was coregulated by both receptors. Moreover, both promoter and ChIP analysis indicated that NR4A1 and NR4A2 acted as ligand-dependent cofactors of Sp1/4-mediated expression of CD71 in TNBC cells. CD71, a key biomarker of ferroptosis is an NR4A1/2/Sp regulated gene that can be directly targeted by DIM-3,5 inverse NR4A1/2 agonists to induce ferroptosis in TNBC cells.

Perfluorooctane Sulfonate (PFOS) and Related Compounds Induce Nuclear Receptor 4A1 (NR4A1)-Dependent Carcinogenesis

Polyfluoroalkyl substances (PFAS) are widely used industrial compounds that have been identified as contaminants in almost every component of the global ecosystem, and in human studies, higher levels of PFAS have been correlated with increased incidence of multiple diseases. Based on the results of human and laboratory animal studies, we hypothesize that the orphan nuclear receptor 4A1 (NR4A1) may be a critical target for some PFAS such as the legacy linear polyfluorooctanesulfonate (PFOS) and other sulfonates. We show that PFOS and related compounds bound the ligand binding domain (LBD) of NR4A1 and induced the growth of several cancer cell lines and enhanced tumor growth in an athymic nude mouse model. Using NR4A1-responsive rhabdomyosarcoma Rh30 cells as a model, PFOS induced NR4A1-dependent cell proliferation and Rh30 cell migration and invasion. Moreover, in Rh30 cells, PFOS also induces several NR4A1-regulated genes including the PAX3-FOXO1 oncogene and downstream gene products, and in a chromatin immunoprecipitation assay, PFOS does not decrease NR4A1 binding to the promoter. These results demonstrate that PFOS is an NR4A1 ligand and enhances tumorigenesis through the activation of this receptor.

Dual nuclear receptor 4A1 (NR4A1/NR4A2) ligands inhibit glioblastoma growth and target TWIST1

1,1-Bis(3'-indolyl)-1-(3,5-disubstitutedphenyl)methane (DIM-3,5) compounds are dual receptor ligands that bind both orphan nuclear receptor 4A1 (NR4A1) and NR4A2. Knockdown of NR4A1 or NR4A2 by RNA interference in glioblastoma (GBM) cells decreased growth and induced apoptosis and comparable effects were observed for DIM-3,5 analogs, which exhibit inverse agonist activity and inhibit NR4A1- and NR4A2-mediated pro-oncogenic activity. Knockdown of NR4A1 or NR4A2 or treatment with DIM-3,5 analogs also decreased expression of TWIST1 mRNA and protein in GBM cells by 40%-90%.The proximal region of the TWIST1 gene promoter contains functional GC-rich binding sites that bind Sp1 and Sp4, and knockdown of these transcription factors also decreased TWIST1 expression in GBM cells. Further analysis by chromatin immunoprecipitation, protein-protein coimmunoprecipitation, and binding assays demonstrated that NR4A1/NR4A2 coregulate TWIST1 gene expression as ligand-dependent cofactors of Sp1 and Sp4, which interact with cis proximal GC-rich sites in the TWIST1 gene promoter. In vivo studies show that DIM-3,5 dual NR4A1/2 inverse agonists also reduced intratumoral TWIST1 expression while significantly prolonging survival of mice in a syngeneic mouse model of GBM, demonstrating that these ligands are promising new agents for targeting TWIST1 and treating GBM. SIGNIFICANCE STATEMENT: The TWIST1 gene is a pro-oncogenic factor that regulates epithelial-to-mesenchymal transition in glioblastoma cells. This paper shows that the orphan nuclear receptor 4A1 (NR4A1) and NR4A2 regulate TWIST1 expression, which can be targeted by bis-indole-derived dual NR4A1/2 inverse agonists.

Activation of Genes by Nuclear Receptor/Specificity Protein (Sp) Interactions in Cancer

The human nuclear receptor (NR) superfamily consists of 48 genes that are ligand-activated transcription factors that play a key role in maintaining cellular homeostasis and in pathophysiology. NRs are important drug targets for both cancer and non-cancer endpoints as ligands for these receptors can act as agonists, antagonists or inverse agonists to modulate gene expression. With two exceptions, the classical mechanism of action of NRs involves their interactions as monomers, dimers or heterodimers with their cognate response elements (cis-elements) in target gene promoters. Several studies showed that a number of NR-regulated genes did not directly bind their corresponding cis-elements and promoter analysis identified that NR-responsive gene promoters contained GC-rich sequences that bind specificity protein 1 (Sp1), Sp3 and Sp4 transcription factors (TFs). This review is focused on identifying an important sub-set of Sp-regulated genes that are indirectly coregulated through interactions with NRs. Subsequent studies showed that many NRs directly bind Sp1 (or Sp3 and Sp4), the NR/Sp complexes bind GC-rich sites to regulate gene expression and the NR acts as a ligand-modulated nuclear cofactor. In addition, several reports show that NR-responsive genes contain cis-elements that bind both Sp TFs and NRs, and mutation of either cis-element results in loss of NR-responsive (inducible and/or basal). Regulation of these genes involves interactions between DNA-bound Sp TFs with proximal or distal DNA-bound NRs, and, in some cases, other nuclear cofactors are required for gene expression. Thus, many NR-responsive genes are regulated by NR/Sp complexes, and these genes can be targeted by ligands that target NRs and also by drugs that induce degradation of Sp1, Sp3 and Sp4.

Discovery of a novel exceptionally potent and orally active Nur77 ligand NB1 with a distinct binding mode for cancer therapy

The orphan nuclear receptor Nur77 is emerging as an attractive target for cancer therapy, and activating Nur77's non-genotypic anticancer function has demonstrated strong therapeutic potential. However, few Nur77 site B ligands have been identified as excellent anticancer compounds. There are no co-crystal structures of effective anticancer agents at Nur77 site B, which greatly limits the development of novel Nur77 site B ligands. Moreover, the lack of pharmaceutical ligands restricts Nur77's therapeutic proof of concept. Herein, we developed a first-in-class Nur77 site B ligand (NB1) that significantly inhibited cancer cells by mediating the Nur77/Bcl-2-related apoptotic effect at mitochondria. The X-ray crystallography suggests that NB1 is bound to the Nur77 site B with a distinct binding mode. Importantly, NB1 showed favorable pharmacokinetic profiles and safety, as evidenced by its good oral bioavailability in rats and lack of mortality, bodyweight loss, and pathological damage at the 512.0 mg/kg dose in mice. Furthermore, oral administration of NB1 demonstrated remarkable in vivo anticancer efficacy in an MDA-MB-231 xenograft model. Together, our work discovers NB1 as a new generation Nur77 ligand that activates the Nur77/Bcl-2 apoptotic pathway with a safe and effective cancer therapeutic potency.

A novel NR4A2-HuR axis promotes pancreatic cancer growth and tumorigenesis that is inhibited by NR4A2 antagonists

Pancreatic ductal adenocarcinoma (PDAC) patients' express higher levels of the orphan Nuclear Receptor 4A2 (NR4A2, NURR1) compared to normal pancreas and NR4A2 is a prognostic factor for patient survival. Knockdown of NR4A2 by RNA interference (RNAi) inhibited cell proliferation, invasion, and migration. RNA sequencing performed in NR4A2(+/+) and NR4A2(-/-) MiaPaCa2 cells demonstrated that NR4A2 played a significant role in cellular metabolism. Human antigen R (HuR) and isocitrate dehydrogenase 1 (IDH1) were identified as NR4A2 target genes. HuR is a pro-oncogenic RNA binding protein and silencing of HuR by RNAi significantly downregulated expression of NR4A2. Expression of HuR and IDH1 were significantly downregulated after treatment with NR4A2 inverse agonist, 1,1-bis(3'-indolyl)-1-(p-chlorophenyl)methane resulting in significant inhibition of tumor growth in an athymic nude mouse xenograft model. This study demonstrates that NR4A2 and HuR regulate genes and signaling pathways that enhance tumorigenesis and targeting NR4A2 and HuR expression with an NR4A2 inverse agonist represents a novel regimen for treating PDAC.

Natural products and synthetic analogs as selective orphan nuclear receptor 4A (NR4A) modulators

Although endogenous ligands for the orphan nuclear receptor 4A1 (NR4A1, Nur77), NR4A2 (Nurr1), and NR4A3 (Nor-1) have not been identified, several natural products and synthetic analogs bind NR4A members. These studies are becoming increasingly important since members of the NR4A subfamily of 3 receptors are potential drug targets for treating cancer and non-cancer endpoints and particularly those conditions associated with inflammatory diseases. Ligands that bind NR4A1, NR4A2, and NR4A3 including Cytosporone B, celastrol, bis-indole derived (CDIM) compounds, tryptophan/indolic, metabolites, prostaglandins, resveratrol, piperlongumine, fatty acids, flavonoids, alkaloids, peptides, and drug families including statins and antimalarial drugs. The structural diversity of NR4A ligands and their overlapping and unique effects on NR4A1, NR4A2, and NR4A3 suggest that NR4A ligands are selective NR4A modulators (SNR4AMs) that exhibit tissue-, structure-, and response-specific activities. The SNR4AM activities of NR4A ligands are exemplified among the Cytosporone B analogs where n-pentyl-2-[3,5-dihydroxy-2-(nonanoyl)]phenyl acetate (PDNPA) binds NR4A1, NR4A2 and NR4A3 but activates only NR4A1 and exhibits significant functional differences with other Cytosporone B analogs. The number of potential clinical applications of agents targeting NR4A is increasing and this should spur future development of SNR4AMs as therapeutics that act through NR4A1, NR4A2 and NR4A3.

Bis-indole-derived NR4A1 antagonists inhibit colon tumor and splenic growth and T-cell exhaustion

There is evidence that the orphan nuclear receptor 4A1 (NR4A1, Nur77) is overexpressed in exhausted CD8 + T cells and regulates PD-L1 in tumors. This study investigated the effects of potent bis-indole-derived NR4A1 antagonists on reversing T-cell exhaustion and downregulating PD-L1 in colon tumors/cells. NR4A1 antagonists inhibited colon tumor growth and downregulated expression of PD-L1 in mouse colon MC-38-derived tumors and cells. TILs from MC-38 cell-derived colon tumors and splenic lymphocytes exhibited high levels of the T-cell exhaustion markers including PD-1, 2B4, TIM3+ and TIGIT and similar results were observed in the spleen, and these were inhibited by NR4A1 antagonists. In addition, treatment with NR4A1 antagonists induced cytokine activation markers interferon γ, granzyme B and perforin mRNAs and decreased TOX, TOX2 and NFAT in TIL-derived CD8 + T cells. Thus, NR4A1 antagonists decrease NR4A1-dependent pro-oncogenic activity and PD-L1 expression in colon tumors and inhibit NR4A1-dependent T-cell exhaustion in TILs and spleen and represent a novel class of mechanism-based drugs that enhance immune surveillance in tumors.

Flavonoids Quercetin and Kaempferol Are NR4A1 Antagonists and Suppress Endometriosis in Female Mice

Nuclear receptor 4A1 (NR4A1) plays an important role in endometriosis progression; levels of NR4A1 in endometriotic lesions are higher than in normal endometrium, and substituted bis-indole analogs (NR4A1) antagonists suppress endometriosis progression in mice with endometriosis. In addition, the flavonoids kaempferol and quercetin are natural products that directly bind NR4A1 and significantly repress the intrinsic NR4A1-dependent transcriptional activity in human endometriotic epithelial and stromal cells and Ishikawa endometrial cancer cells. NR4A1 knockdown and inhibition of NR4A1 by kaempferol and quercetin suppressed proliferation of human endometriotic epithelial cells and Ishikawa cells by inhibiting epidermal growth factor receptor/c-Myc/survivin-mediated growth-promoting and survival pathways, The mammalian target of rapamycin (mTOR) signaling and αSMA/CTGF/COL1A1/FN-mediated fibrosis signaling but increasing Thioredoxin domain Containing 5/SESN2-mediated oxidative/estrogen receptors stress signaling. In human endometriotic stromal cells, NR4A1 knockdown and inhibition of NR4A1 by kaempferol and quercetin primarily inhibited mTOR signaling by suppressing proliferation of human endometrial stromal cells. In addition, kaempferol and quercetin treatment also effectively suppressed the growth of endometriotic lesions in mice with endometriosis compared with the vehicle without any body weight changes. Therefore, kaempferol and quercetin are NR4A1 antagonists with potential as nutritional therapy for endometriosis.

Genomic and Epigenetic Changes Drive Aberrant Skeletal Muscle Differentiation in Rhabdomyosarcoma

Rhabdomyosarcoma (RMS), the most common soft-tissue sarcoma in children and adolescents, represents an aberrant form of skeletal muscle differentiation. Both skeletal muscle development, as well as regeneration of adult skeletal muscle are governed by members of the myogenic family of regulatory transcription factors (MRFs), which are deployed in a highly controlled, multi-step, bidirectional process. Many aspects of this complex process are deregulated in RMS and contribute to tumorigenesis. Interconnected loops of super-enhancers, called core regulatory circuitries (CRCs), define aberrant muscle differentiation in RMS cells. The transcriptional regulation of MRF expression/activity takes a central role in the CRCs active in skeletal muscle and RMS. In PAX3::FOXO1 fusion-positive (PF+) RMS, CRCs maintain expression of the disease-driving fusion oncogene. Recent single-cell studies have revealed hierarchically organized subsets of cells within the RMS cell pool, which recapitulate developmental myogenesis and appear to drive malignancy. There is a large interest in exploiting the causes of aberrant muscle development in RMS to allow for terminal differentiation as a therapeutic strategy, for example, by interrupting MEK/ERK signaling or by interfering with the epigenetic machinery controlling CRCs. In this review, we provide an overview of the genetic and epigenetic framework of abnormal muscle differentiation in RMS, as it provides insights into fundamental mechanisms of RMS malignancy, its remarkable phenotypic diversity and, ultimately, opportunities for therapeutic intervention.

Heparanase-1 is downregulated in chemoradiotherapy orbital rhabdomyosarcoma and relates with tumor growth as well as angiogenesis

AIM

To determine the role of heparanase-1 (HPSE-1) in orbital rhabdomyosarcoma (RMS), and to investigate the feasibility of HPSE-1 targeted therapy for RMS.

METHODS

Immunohistochemistry was performed to analyze HPSE-1 expression in 51 cases of orbital RMS patients (including 28 cases of embryonal RMS and 23 cases of alveolar RMS), among whom there were 27 treated and 24 untreated with preoperative chemoradiotherapy. In vitro, studies were conducted to examine the effect of HPSE-1 silencing on RMS cell proliferation and tube formation of human umbilical vein endothelial cells (HUVECs). RD cells (an RMS cell line) and HUVECs were infected with HPSE-1 shRNA lentivirus at a multiplicity of infection (MOI) of 10 and 30 separately. Real-time PCR and Western blot were applied to detect the mRNA and protein expression levels of HPSE-1. Cell viability of treated or control RD cells was evaluated by cell counting kit-8 (CCK-8) assay. Matrigel tube formation assay was used to evaluate the effect of HPSE-1 RNAi on the tube formation of HUVECs.

RESULTS

Immunohistochemistry showed that the expression rate of HPSE-1 protein was 92.9% in orbital embryonal RMS and 91.3% in orbital alveolar RMS. Tissue from alveolar orbital RMS did not show relatively stronger staining than that from the embryonal orbital RMS. However, despite the types of RMS, comparing the cases treated chemoradiotherapy with those untreated, we have observed that chemoradiotherapy resulted in weaker staining in patients' tissues. The expression levels of HPSE-1 declined significantly in both the mRNA and protein levels in HPSE-1 shRNA transfected RD cells. The CCK-8 assay showed that lentivirus-mediated HPSE-1 silencing resulted in significantly reduced RD cells viability in vitro. Silencing HPSE-1 expression also inhibited VEGF-induced tube formation of HUVECs in Matrigel.

CONCLUSION

HPSE-1 silencing may be a promising therapy for the inhibition of orbital RMS progression.

Nuclear receptor 4A1 (NR4A1) antagonists target paraspeckle component 1 (PSPC1) in cancer cells

Paraspeckles compound 1 (PSPC1) is a multifunctional protein that plays an important role in cancer cells, where PSPC1 is a master regulator of pro-oncogenic responses that includes activation of TGFβ (TGFβ1), TGFβ-dependent EMT, and metastasis. The pro-oncogenic activities of PSPC1 closely resembled those observed for the orphan nuclear receptor 4A1 (NR4A1, Nur77) and knockdown of NR4A1 decreased expression of PSPC1 in MDA-MB-231 breast, H1299 lung, and SNU449 liver cancer cells. Similar results were observed in these same cell lines after treatment with bisindole-derived (CDIMs) NR4A1 antagonists. Moreover, PSPC1-dependent regulation of TGFβ, genes associated with cancer stem cells and epithelial to mesenchymal transition (EMT) were also downregulated after NR4A1 silencing or treatment of breast, lung, and liver cancer cells with CDIM/NR4A1 antagonists. Results of chromatin immunoprecipitation (ChIP) assays suggest that NR4A1 regulates PSPC1 through interaction with an NBRE sequence in the PSPC1 gene promoter. These results coupled with in vivo studies showing that NR4A1 antagonists inhibit breast tumor growth and downregulate PSPC1 in tumors indicate that the pro-oncogenic nuclear PSPC1 factor can be targeted by CDIM/NR4A1 antagonists.

Orphan nuclear receptor 4A1 (NR4A1) and novel ligands

The nuclear receptor (NR) superfamily of transcription factors encodes expression of 48 human genes that are important for maintaining cellular homeostasis and in pathophysiology, and this has been observed for all sub-families including orphan receptors for which endogenous ligands have not yet been identified. The orphan NR4A1 (Nur77 and TR3) and other members of this sub-family (NR4A2 and NR4A3) are immediate early genes induced by diverse stressors, and these receptors play an important role in the immune function and are up-regulated in some inflammatory diseases including solid tumors. Although endogenous ligands for NR4A have not been identified, several different classes of compounds have been characterized as NR4A1 ligands that bind the receptor. These compounds include cytosporone B and structurally related analogs, bis-indole derived (CDIM) compounds, the triterpenoid celastrol and a number of other chemicals including polyunsaturated fatty acids. NR4A1 ligands bind different regions/surfaces of NR4A1 and exhibit selective NR4A1 modulator (SNR4AM) activities that are dependent on ligand structure and cell/tissue context. NR4A1 ligands exhibit pharmacologic activities in studies on cancer, endometriosis metabolic and inflammatory diseases and are promising agents with clinical potential for treating multiple diseases.

Flavonoids kaempferol and quercetin are nuclear receptor 4A1 (NR4A1, Nur77) ligands and inhibit rhabdomyosarcoma cell and tumor growth

BACKGROUND

Flavonoids exhibit both chemopreventive and chemotherapeutic activity for multiple tumor types, however, their mechanisms of action are not well defined. Based on some of their functional and gene modifying activities as anticancer agents, we hypothesized that kaempferol and quercetin were nuclear receptor 4A1 (NR4A1, Nur77) ligands and confirmed that both compounds directly bound NR4A1 with KD values of 3.1 and 0.93 μM, respectively.

METHODS

The activities of kaempferol and quercetin were determined in direct binding to NR4A1 protein and in NR4A1-dependent transactivation assays in Rh30 and Rh41 rhabdomyosarcoma (RMS) cells. Flavonoid-dependent effects as inhibitors of cell growth, survival and invasion were determined in XTT and Boyden chamber assays respectively and changes in protein levels were determined by western blots. Tumor growth inhibition studies were carried out in athymic nude mice bearing Rh30 cells as xenografts.

RESULTS

Kaempferol and quercetin bind NR4A1 protein and inhibit NR4A1-dependent transactivation in RMS cells. NR4A1 also regulates RMS cell growth, survival, mTOR signaling and invasion. The pro-oncogenic PAX3-FOXO1 and G9a genes are also regulated by NR4A1 and, these pathways and genes are all inhibited by kaempferol and quercetin. Moreover, at a dose of 50 mg/kg/d kaempferol and quercetin inhibited tumor growth in an athymic nude mouse xenograft model bearing Rh30 cells.

CONCLUSION

These results demonstrate the clinical potential for repurposing kaempferol and quercetin for clinical applications as precision medicine for treating RMS patients that express NR4A1 in order to increase the efficacy and decrease dosages of currently used cytotoxic drugs.

Transcription factors specificity protein and nuclear receptor 4A1 in pancreatic cancer

Specificity protein (Sp) transcription factors (TFs) Sp1, Sp3 and Sp4, and the orphan nuclear receptor 4A1 (NR4A1) are highly expressed in pancreatic tumors and Sp1 is a negative prognostic factor for pancreatic cancer patient survival. Results of knockdown and overexpression of Sp1, Sp3 and Sp4 in pancreatic and other cancer lines show that these TFs are individually pro-oncogenic factors and loss of one Sp TF is not compensated by other members. NR4A1 is also a pro-oncogenic factor and both NR4A1 and Sp TFs exhibit similar functions in pancreatic cancer cells and regulate cell growth, survival, migration and invasion. There is also evidence that Sp TFs and NR4A1 regulate some of the same genes including survivin, epidermal growth factor receptor, PAX3-FOXO1, α5- and α6-integrins, β1-, β3- and β4-integrins; this is due to NR4A1 acting as a cofactor and mediating NR4A1/Sp1/4-regulated gene expression through GC-rich gene promoter sites. Several studies show that drugs targeting Sp downregulation or NR4A1 antagonists are highly effective inhibitors of Sp/NR4A1-regulated pathways and genes in pancreatic and other cancer cells, and the triterpenoid celastrol is a novel dual-acting agent that targets both Sp TFs and NR4A1.

The Histone Methyltransferase Gene G9A Is Regulated by Nuclear Receptor 4A1 in Alveolar Rhabdomyosarcoma Cells

The histone methyltransferase G9A (EHMT2) gene catalyzes methylation of histone 3 lysine 9 (H3K9), and this gene silencing activity contributes to the tumor promoter-like activity of G9A in several tumor types including alveolar rhabdomyosarcoma (ARMS). Previous studies show the orphan nuclear receptor 4A1 (NR4A1, Nur77) is overexpressed in rhabdomyosarcoma and exhibits pro-oncogenic activity. In this study, we show that knockdown of NR4A1 in ARMS cells decreased expression of G9A mRNA and protein. Moreover, treatment of ARMS cells with several bis-indole-derived NR4A1 ligands (antagonists) including 1,1-bis(3'-indolyl)-1-(4-hydroxyphenyl)methane (CDIM8), 3,5-dimethyl (3,5-(CH3)2), and 3-bromo-5-methoxy (3-Br-5-OCH3) analogs also decreased G9A expression. Furthermore, NR4A1 antagonists also decreased G9A expression in breast, lung, liver, and endometrial cancer cells confirming that G9A is an NR4A1-regulated gene in ARMS and other cancer cell lines. Mechanistic studies showed that the NR4A1/Sp1 complex interacted with the GC-rich 511 region of the G9A promoter to regulate G9A gene expression. Moreover, knockdown of NR4A1 or treatment with NR4A1 receptor antagonists decreased overall H3K9me2, H3K9me2 associated with the PTEN promoter, and PTEN-regulated phospho-Akt. In vivo studies showed that the NR4A1 antagonist (3-Br-5-OCH3) inhibited tumor growth in athymic nude mice bearing Rh30 ARMS cells and confirmed that G9A was an NR4A1-regulated gene that can be targeted by NR4A1 receptor antagonists.

The Paradoxical Roles of Orphan Nuclear Receptor 4A (NR4A) in Cancer

The three-orphan nuclear receptor 4A genes are induced by diverse stressors and stimuli, and there is increasing evidence that NR4A1 (Nur77), NR4A2 (Nurr1), and NR4A3 (Nor1) play an important role in maintaining cellular homeostasis and in pathophysiology. In blood-derived tumors (leukemias and lymphomas), NR4A expression is low and NR4A1-/-/NR4A3-/- double knockout mice rapidly develop acute myelocytic leukemia, suggesting that these receptors exhibit tumor suppressor activity. Treatment of leukemia and most lymphoma cells with drugs that induce expression of NR4A1and NR4A3 enhances apoptosis, and this represents a potential clinical application for treating this disease. In contrast, most solid tumor-derived cell lines express high levels of NR4A1 and NR4A2, and both receptors exhibit pro-oncogenic activities in solid tumors, whereas NR4A3 exhibits tumor-specific activities. Initial studies with retinoids and apoptosis-inducing agents demonstrated that their cytotoxic activity is NR4A1 dependent and involved drug-induced nuclear export of NR4A1 and formation of a mitochondrial proapoptotic NR4A1-bcl-2 complex. Drug-induced nuclear export of NR4A1 has been reported for many agents/biologics and involves interactions with multiple mitochondrial and extramitochondrial factors to induce apoptosis. Synthetic ligands for NR4A1, NR4A2, and NR4A3 have been identified, and among these compounds, bis-indole derived (CDIM) NR4A1 ligands primarily act on nuclear NR4A1 to inhibit NR4A1-regulated pro-oncogenic pathways/genes and similar results have been observed for CDIMs that bind NR4A2. Based on results of laboratory animal studies development of NR4A inducers (blood-derived cancers) and NR4A1/NR4A2 antagonists (solid tumors) may be promising for cancer therapy and also for enhancing immune surveillance.

Construction of a Prognostic Immune Signature for Squamous-Cell Lung Cancer to Predict Survival

Background

Limited treatment strategies are available for squamous-cell lung cancer (SQLC) patients. Few studies have addressed whether immune-related genes (IRGs) or the tumor immune microenvironment can predict the prognosis for SQLC patients. Our study aimed to construct a signature predict prognosis for SQLC patients based on IRGs.

Methods

We constructed and validated a signature from SQLC patients in The Cancer Genome Atlas (TCGA) using bioinformatics analysis. The underlying mechanisms of the signature were also explored with immune cells and mutation profiles.

Results

A total of 464 eligible SQLC patients from TCGA dataset were enrolled and were randomly divided into the training cohort (n = 232) and the testing cohort (n = 232). Eight differentially expressed IRGs were identified and applied to construct the immune signature in the training cohort. The signature showed a significant difference in overall survival (OS) between low-risk and high-risk cohorts (P < 0.001), with an area under the curve of 0.76. The predictive capability was verified with the testing and total cohorts. Multivariate analysis revealed that the 8-IRG signature served as an independent prognostic factor for OS in SQLC patients. Naive B cells, resting memory CD4 T cells, follicular helper T cells, and M2 macrophages were found to significantly associate with OS. There was no statistical difference in terms of tumor mutational burden between the high-risk and low-risk cohorts.

Conclusion

Our study constructed and validated an 8-IRG signature prognostic model that predicts clinical outcomes for SQLC patients. However, this signature model needs further validation with a larger number of patients.

Bis-indole derived nuclear receptor 4A1 (NR4A1) antagonists inhibit TGFβ-induced invasion of embryonal rhabdomyosarcoma cells

Transforming growth factor β (TGFβ) enhances invasion of breast and lung cancer cells through phosphorylation-dependent nuclear export of the nuclear receptor 4A1 (NR4A1, Nur77). This response is inhibited by the NR4A1 antagonist 1,1-bis(3'-indoly)-1-(p-hydroxyphenyl) methane (CDIM8) and we hypothesized that similar effects would be observed in Rhabdomyosarcoma (RMS) cells. Although some kinase inhibitors block TGFβ-induced invasion of embryonal RMS (ERMS) cells, the mechanism differs from breast and lung cancer cells since NR4A1 is extranuclear in ERMS cells. However, CDIM8 blocks basal and TGFβ-induced invasion of RD and SMS-CTR ERMS cell lines but not Rh30 alveolar RMS (ARMS) cells. Moreover, this response in ERMS cells was independent of SMAD7 degradation or activation of SMAD2/SMAD3. β-Catenin silencing decreased ERMS cell invasion and CDIM8 induced proteasome-independent downregulation of β-catenin. The novel mechanism of CDIM8-mediated inhibition of basal and TGFβ-induced ERMS cell invasion was due to activation of the Bcl-2-NR4A1 complex, mitochondrial disruption, induction of the tumor suppressor-like cytokine interleukin-24 (IL-24) which in turn downregulates β-catenin expression. Thus, the NR4A1 antagonist inhibits TGFβ-induced invasion of ERMS cells through initial targeting of cytosolic NR4A1.

Bis-Indole-Derived Nuclear Receptor 4A1 (NR4A1, Nur77) Ligands as Inhibitors of Endometriosis

Endometriosis is an inflammatory disease that primarily affects women during their reproductive years, and since current hormonal therapies are of concern, new hormone-independent treatment regimens are needed. The orphan nuclear receptor 4A1 (NR4A1, Nur77) is expressed in patient-derived (stromal) endometriotic cells and also epithelial cell lines, and we observed that knockdown of NR4A1 in patient-derived ectopic endometrium-isolated ovarian endometrioma (ESECT)-7 and ESECT-40 cells decreased cell proliferation and induced apoptosis. Moreover, the treatment of these cells with bis-indole derived NR4A1 ligands 1,1-bis(3'-indolyl)-1-(p-hydroxyphenyl)methane (DIM-C-pPhOH) and its buttressed 3-chloro-5-methoxy analog (DIM-C-pPhOH-3-Cl-5-OCH3) inhibited cell growth and induced apoptosis and related genes. The compounds exhibit NR4A1 antagonist activities in both functional and transactivation assays whereas these effects were not observed in normal endometrial cells. We also observed that NR4A1 knockdown and treatment with NR4A1 antagonists decreased fibrosis, α-smooth muscle actin, and related pro-fibrotic genes in ESECT-7 and ESECT-40 cells, and similar results were observed in epithelial-derived endometriotic cell lines. Moreover, in an endometriosis mouse model with auto-transplantation and also in severe combined immune deficiency mice transplanted with human endometriotic cells treatment with 25 mg/kg/day DIM-C-pPhOH-3-Cl-5-OCH3 significantly inhibited growth and expansion of endometriotic lesions. Thus, bis-indole-derived NR4A1 ligands represent a novel class of drugs as nonhormonal therapy for endometriosis.

A Bis-Indole-Derived NR4A1 Antagonist Induces PD-L1 Degradation and Enhances Antitumor Immunity

PD-L1 is expressed in tumor cells and its interaction with PD-1 plays an important role in evading immune surveillance; this can be overcome using PD-L1 or PD-1 immunotherapy antibodies. This study reports a novel approach for targeting PD-L1. In human breast cancer cell lines and 4T1 mouse mammary tumor cells, PD-L1 expression was regulated by the nuclear receptor NR4A1/Sp1 complex bound to the proximal germinal center (GC)-rich region of the PD-L1 gene promoter. Treatment of breast cancer cells with bis-indole-derived NR4A1 antagonists including 1,1-bis(3'-indolyl)-1-(3-chloro-4-hydroxy-5-methoxyphenyl)methane (Cl-OCH3) decreased expression of PD-L1 mRNA, promoter-dependent luciferase activity, and protein. In in vivo studies using a syngeneic mouse model bearing orthotopically injected 4T1 cells, Cl-OCH3 decreased tumor growth and weight and inhibited lung metastasis. Cl-OCH3 also decreased expression of CD3+/CD4+/CD25+/FoxP3+ regulatory T cells and increased the Teff/Treg ratio. Therefore, the potent anticancer activities of NR4A1 antagonists are also accompanied by enhanced antitumor immunity in PD-L1-expressing triple-negative breast cancer and thus represent a novel class of drugs that mimic immunotherapy. SIGNIFICANCE: These findings show that the orphan nuclear receptor NR4A1 controls PD-L1 expression and identify a chemical probe capable of disrupting this regulatory axis.

Inhibition of NR4A1 Promotes ROS Accumulation and IL24-Dependent Growth Arrest in Rhabdomyosarcoma

Nuclear receptor 4A1 (NR4A1, Nur77) is overexpressed in rhabdomyosarcoma (RMS), and inactivation of NR4A1 (siNR4A1) or treatment with the NR4A1 antagonist 1,1-bis(3'-indoly)-1-(p-hydroxy-phenyl)methane (DIM-C-pPhOH) has antiproliferative and proapoptotic effects on RMS cells. However, the mechanism by which NR4A1 inhibition exerts these effects is poorly defined. Here, we report that NR4A1 silencing or inhibition resulted in accumulation of reactive oxygen species (ROS) and ROS-dependent induction of the tumor suppressor-like cytokine IL24 in RMS cells. Mechanistically, NR4A1 was found to regulate the expression of the proreductant genes thioredoxin domain-containing 5 (TXNDC5) and isocitrate dehydrogenase 1 (IDH1), which are downregulated in RMS cells following NR4A1 knockdown or inhibition. Silencing TXNDC5 and IDH1 also induced ROS accumulation and IL24 expression in RMS cells, suggesting that NR4A1 antagonists mediate their antiproliferative and apoptotic effects through modulation of proreductant gene expression. Finally, cotreatment with the antioxidant glutathione or IL24-blocking antibody reversed the effects of NR4A1 inhibition, demonstrating the importance of both ROS and IL24 in mediating the cellular responses. IMPLICATIONS: Overall, these data elucidate the mechanism by which NR4A1 inhibition functions to inhibit the proliferation, survival, and migration of RMS cells.

Potent inhibition of breast cancer by bis-indole-derived nuclear receptor 4A1 (NR4A1) antagonists

BACKGROUND

Nuclear receptor 4A1 (NR4A1) is overexpressed in mammary tumors, and the methylene-substituted bis-indole derivative 1,1-bis(3'-indolyl)-1-(p-hydroxyphenyl)methane (DIM-C-pPhOH) acts as an NR4A1 antagonist (inverse agonist) and inhibits NR4A1-regulated pro-oncogenic pathways/genes in breast and other cancer cells.

METHODS

Buttressed analogs of DIM-C-pPhOH were synthesized by condensation of the substituted p-hydroxybenzaldehydes with indole. Breast cancer cell growth, survival, and migration assays were carried out by cell counting, Annexin V staining, and Boyden chamber assays, respectively. Changes in RNA and protein expression were determined by RT-PCR and western blots, respectively. Analysis of RNAseq results was carried out using Ingenuity Pathway Analysis, and in vivo potencies of NR4A1 antagonists were determined in athymic nude mice bearing MDA-MB-231 cells in an orthotopic model.

RESULTS

Ingenuity Pathway analysis of common genes modulated by NR4A1 knockdown or treatment with DIM-C-pPhOH showed that changes in gene expression were consistent with the observed decreased functional responses, namely inhibition of growth and migration and increased apoptosis. DIM-C-pPhOH is rapidly metabolized and the effects and potencies of buttressed analogs of DIM-C-pPhOH which contain one or two substituents ortho to the hydroxyl groups were investigated using NR4A1-regulated gene/gene products as endpoints. The buttressed analogs were more potent than DIM-C-pPhOH in both in vitro assays and as inhibitors of mammary tumor growth. Moreover, using 1,1-bis(3'-indolyl)-1-(3-chloro-4-hydroxy-5-methoxyphenyl)methane (DIM-C-pPhOh-3-Cl-5-OCH3) significant tumor growth inhibition was observed at doses as low as 2 mg/kg/d which was at least an order of magnitude more potent than DIM-C-pPhOH.

CONCLUSIONS

These buttressed analogs represent a more potent set of second generation NR4A1 antagonists as inhibitors of breast cancer.

Reactive Oxygen Species (ROS)-Inducing Triterpenoid Inhibits Rhabdomyosarcoma Cell and Tumor Growth through Targeting Sp Transcription Factors

Methyl 2-trifluoromethyl-3,11-dioxo-18β-olean-1,12-dien-3-oate (CF3DODA-Me) is derived synthetically from glycyrrhetinic acid, a major component of licorice, and this compound induced reactive oxygen species (ROS) in RD and Rh30 rhabdomyosarcoma (RMS) cells. CF3DODA-Me also inhibited growth and invasion and induced apoptosis in RMS cells, and these responses were attenuated after cotreatment with the antioxidant glutathione, demonstrating the effective anticancer activity of ROS in RMS. CF3DODA-Me also downregulated expression of specificity protein (Sp) transcription factors Sp1, Sp3, and Sp4 and prooncogenic Sp-regulated genes including PAX3-FOXO1 (in Rh30 cells). The mechanism of CF3DODA-Me-induced Sp-downregulation involved ROS-dependent repression of c-Myc and cMyc-regulated miR-27a and miR-17/20a, and this resulted in induction of the miRNA-regulated Sp repressors ZBTB4, ZBTB10, and ZBTB34. The cell and tumor growth effects of CF3DODA-Me further emphasize the sensitivity of RMS cells to ROS inducers and their potential clinical applications for treating this deadly disease. IMPLICATIONS: CF3DODA-Me and HDAC inhibitors that induce ROS-dependent Sp downregulation could be developed for clinical applications in treating rhabdomyosarcoma.

TGFβ-Induced Lung Cancer Cell Migration Is NR4A1-Dependent

TGFβ induces migration of lung cancer cells (A549, H460, and H1299), dependent on activation of c-Jun N-terminal kinase (JNK1), and is inhibited by the JNK1 inhibitor SP600125. Moreover, TGFβ-induced migration of the cells is also blocked by the nuclear export inhibitor leptomycin B (LMB) and the orphan nuclear receptor 4A1 (NR4A1) ligand 1,1-bis(3'-indolyl)-1-(p-hydroxyphenyl)methane (CDIM8), which retains NR4A1 in the nucleus. Subsequent analysis showed that the TGFβ/TGFβ receptor/PKA/MKK4 and -7/JNK pathway cascade phosphorylates and induces nuclear export of NR4A1, which in turn forms an active complex with Axin2, Arkadia (RNF111), and RNF12 (RLIM) to induce proteasome-dependent degradation of SMAD7 and enhance lung cancer cell migration. Thus, NR4A1 also plays an integral role in mediating TGFβ-induced lung cancer invasion, and the NR4A1 ligand CDIM8, which binds nuclear NR4A1, represents a novel therapeutic approach for TGFβ-induced blocking of lung cancer migration/invasion. IMPLICATIONS: Effective treatment of TGFβ-induced lung cancer progression could involve a number of agents including the CDIM/NR4A1 antagonists that block not only TGFβ-induced migration, but several other NR4A1-regulated prooncogenic genes/pathways in lung cancer cell lines.

Interleukin-24 (IL24) Is Suppressed by PAX3-FOXO1 and Is a Novel Therapy for Rhabdomyosarcoma

Alveolar rhabdomyosarcoma (ARMS) patients have a poor prognosis, and this is primarily due to overexpression of the oncogenic fusion protein PAX3-FOXO1. Results of RNA-sequencing studies show that PAX3-FOXO1 represses expression of interleukin-24 (IL24), and these two genes are inversely expressed in patient tumors. PAX3-FOXO1 also regulates histone deacetylase 5 (HDAC5) in ARMS cells, and results of RNA interference studies confirmed that PAX3-FOXO1-mediated repression of IL24 is HDAC5-dependent. Knockdown of PAX3-FOXO1 decreases ARMS cell proliferation, survival, and migration, and we also observed similar responses in cells after overexpression of IL24, consistent with results reported for this tumor suppressor-like cytokine in other solid tumors. We also observed in double knockdown studies that the inhibition of ARMS cell proliferation, survival, and migration after knockdown of PAX3-FOXO1 was significantly (>75%) reversed by knockdown of IL24. Adenoviral-expressed IL24 was directly injected into ARMS tumors in athymic nude mice, and this resulted in decreased tumor growth and weight. Because adenoviral IL24 has already successfully undergone phase I in clinical trials, this represents an alternative approach (alone and/or combination) for treating ARMS patients who currently undergo cytotoxic drug therapies.

Characteristics of Nur77 and its ligands as potential anticancer compounds (Review)

Nuclear receptor subfamily 4 group A member 1 (NR4A1; also termed Nur77/TR3/NGFIB), a member of the nuclear receptor superfamily, is expressed as an early response gene to regulate the expression of multiple target genes. Nur77 has the typical structure of a nuclear receptor, including an N‑terminal domain, a DNA binding domain, and a ligand‑binding domain. The expression and localization of Nur77 are closely associated with its roles in cell proliferation and apoptosis. Nur77 was first identified as an orphan receptor, the endogenous ligand of which has not yet been identified; however, an increasing number of compounds targeting Nur77 have been reported to have beneficial effects in the treatment of cancer and other diseases. This review provides a brief overview of the identification, structure, expression and localization, transcriptional role and non‑genomic function of Nur77, and summarizes the ligands that have been shown to interact with Nur77, including cytosporone B, cisplatin, TMPA, PDNPA, CCE9, THPN, Z‑ligustilide, celastrol and bisindole methane compounds, which may potentially be used to treat cancer in humans.

Bis-Indole-Derived NR4A1 Ligands and Metformin Exhibit NR4A1-Dependent Glucose Metabolism and Uptake in C2C12 Cells

Treatment of C2C12 muscle cells with metformin or the NR4A1 ligand 1,1-bis(3'-indolyl)-1-(p-hydroxyphenyl)methane (DIM-C-pPhOH) induced NR4A1 and Glut4 messenger RNA and protein expression. Similar results were observed with buttressed (3- or 3,5-substituted) analogs of DIM-C-pPhOH, including 1,1-bis(3'-indolyl)-1-(3-chloro-4-hydroxy-5-methoxyphenyl)methane (DIM-C-pPhOH-3-Cl-5-OCH3), and the buttressed analogs were more potent than DIM-C-pPhOH NR4A1 agonists. Metformin and the bis-indole substituted analogs also induced expression of several glycolytic genes and Rab4, which has previously been linked to enhancing cell membrane accumulation of Glut4 and overall glucose uptake in C2C12 cells, and these responses were also observed after treatment with metformin and the NR4A1 ligands. The role of NR4A1 in mediating the responses induced by the bis-indoles and metformin was determined by knockdown of NR4A1, and this resulted in attenuating the gene and protein expression and enhanced glucose uptake responses induced by these compounds. Our results demonstrate that the bis-indole-derived NR4A1 ligands represent a class of drugs that enhance glucose uptake in C2C12 muscle cells, and we also show that the effects of metformin in this cell line are NR4A1-dependent.