The aryl hydrocarbon receptor as a target for estrogen receptor-negative breast cancer chemotherapy

The potential of aryl hydrocarbon receptor as receptors for metabolic changes in tumors

Cancer cells can alter their metabolism to meet energy and molecular requirements due to unfavorable environments with oxygen and nutritional deficiencies. Therefore, metabolic reprogramming is common in a tumor microenvironment (TME). Aryl hydrocarbon receptor (AhR) is a ligand-activated nuclear transcription factor, which can be activated by many exogenous and endogenous ligands. Multiple AhR ligands can be produced by both TME and tumor cells. By attaching to various ligands, AhR regulates cancer metabolic reprogramming by dysregulating various metabolic pathways, including glycolysis, lipid metabolism, and nucleotide metabolism. These regulated pathways greatly contribute to cancer cell growth, metastasis, and evading cancer therapies; however, the underlying mechanisms remain unclear. Herein, we review the relationship between TME and metabolism and describe the important role of AhR in cancer regulation. We also focus on recent findings to discuss the idea that AhR acts as a receptor for metabolic changes in tumors, which may provide new perspectives on the direction of AhR research in tumor metabolic reprogramming and future therapeutic interventions.

Interplay between Estrogen, Kynurenine, and AHR Pathways: An immunosuppressive axis with therapeutic potential for breast cancer treatment

Breast cancer is one of the most common malignancies among women worldwide. Estrogen exposure via endogenous and exogenous sources during a lifetime, together with environmental exposure to estrogenic compounds, represent the most significant risk factor for breast cancer development. As breast tumors establish, multiple pathways are deregulated. Among them is the aryl hydrocarbon receptor (AHR) signaling pathway. AHR, a ligand-activated transcription factor associated with the metabolism of polycyclic aromatic hydrocarbons and estrogens, is overexpressed in breast cancer. Furthermore, AHR and estrogen receptor (ER) cross-talk pathways have been observed. Additionally, the Tryptophan (Trp) catabolizing enzymes indolamine-2,3-dioxygenase (IDO) and tryptophan-2,3-dioxygenase (TDO) are overexpressed in breast cancer. IDO/TDO catalyzes the formation of Kynurenine (KYN) and other tryptophan-derived metabolites, which are ligands of AHR. Once KYN activates AHR, it stimulates the expression of the IDO enzyme, increases the level of KYN, and activates non-canonical pathways to control inflammation and immunosuppression in breast tumors. The interplay between E2, AHR, and IDO/TDO/KYN pathways and their impact on the immune system represents an immunosuppressive axis on breast cancer. The potential modulation of the immunosuppressive E2-AHR-IDO/TDO/KYN axis has aroused great expectations in oncotherapy. The present article will review the mechanisms implicated in generating the immunosuppressive axis E2-AHR-IDO/TDO/KYN in breast cancer and the current state of knowledge as a potential therapeutic target.

The effects of environmental aryl hydrocarbon receptor ligands on signaling and cell metabolism in cancer

Dioxin and dioxin-like compounds are chlorinated organic pollutants formed during the manufacturing of other chemicals. Dioxins are ligands of the aryl hydrocarbon receptor (AHR), that induce AHR-mediated biochemical and toxic responses and are persistent in the environment. 2,3,7,8- tetrachlorodibenzo para dioxin (TCDD) is the prototypical AHR ligand and its effects represent dioxins. TCDD induces toxicity, immunosuppression and is a suspected tumor promoter. The role of TCDD in cancer however is debated and context-dependent. Environmental particulate matter, polycyclic aromatic hydrocarbons, perfluorooctane sulfonamide, endogenous AHR ligands, and cAMP signaling activate AHR through TCDD-independent pathways. The effect of activated AHR in cancer is context-dependent. The ability of FDA-approved drugs to modulate AHR activity has sparked interest in their repurposing for cancer therapy. TCDD by interfering with endogenous pathways, and overstimulating other endogenous pathways influences all stages of cancer. Herein we review signaling mechanisms that activate AHR and mechanisms by which activated AHR modulates signaling in cancer including affected metabolic pathways.

Deciphering the roles of aryl hydrocarbon receptor (AHR) in regulating carcinogenesis

Aryl hydrocarbon receptor (AHR) is a ligand-dependent receptor that belongs to the superfamily of basic helix-loop-helix (bHLH) transcription factors. The activation of the canonical AHR signaling pathway is known to induce the expression of cytochrome P450 enzymes, facilitating the detoxification metabolism in the human body. Additionally, AHR could interact with various signaling pathways such as epidermal growth factor receptor (EGFR), signal transducer and activator of transcription 3 (STAT3), hypoxia-inducible factor-1α (HIF-1α), nuclear factor ekappa B (NF-κβ), estrogen receptor (ER), and androgen receptor (AR) signaling pathways. Over the past 30 years, several studies have reported that various chemical, physical, or biological agents, such as tobacco, hydrocarbon compounds, industrial and agricultural chemical wastes, drugs, UV, viruses, and other toxins, could affect AHR expression or activity, promoting cancer development. Thus, it is valuable to overview how these factors regulate AHR-mediated carcinogenesis. Current findings have reported that many compounds could act as AHR ligands to drive the expressions of AHR-target genes, such as CYP1A1, CYP1B1, MMPs, and AXL, and other targets that exert a pro-proliferation or anti-apoptotic effect, like XIAP. Furthermore, some other physical and chemical agents, such as UV and 3-methylcholanthrene, could promote AHR signaling activities, increasing the signaling activities of a few oncogenic pathways, such as the phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) and mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathways. Understanding how various factors regulate AHR-mediated carcinogenesis processes helps clinicians and scientists plan personalized therapeutic strategies to improve anti-cancer treatment efficacy. As many studies that have reported the roles of AHR in regulating carcinogenesis are preclinical or observational clinical studies that did not explore the detailed mechanisms of how different chemical, physical, or biological agents promote AHR-mediated carcinogenesis processes, future studies should focus on conducting large-scale and functional studies to unravel the underlying mechanism of how AHR interacts with different factors in regulating carcinogenesis processes.

Aryl Hydrocarbon Receptor as an Anticancer Target: An Overview of Ten Years Odyssey

Aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor belonging to the basic helix-loop-helix (bHLH)/per-Arnt-sim (PAS) superfamily, is traditionally known to mediate xenobiotic metabolism. It is activated by structurally diverse agonistic ligands and regulates complicated transcriptional processes through its canonical and non-canonical pathways in normal and malignant cells. Different classes of AhR ligands have been evaluated as anticancer agents in different cancer cells and exhibit efficiency, which has thrust AhR into the limelight as a promising molecular target. There is strong evidence demonstrating the anticancer potential of exogenous AhR agonists including synthetic, pharmaceutical, and natural compounds. In contrast, several reports have indicated inhibition of AhR activity by antagonistic ligands as a potential therapeutic strategy. Interestingly, similar AhR ligands exert variable anticancer or cancer-promoting potential in a cell- and tissue-specific mode of action. Recently, ligand-mediated modulation of AhR signaling pathways and the associated tumor microenvironment is emerging as a potential approach for developing cancer immunotherapeutic drugs. This article reviews advances of AhR in cancer research covering publication from 2012 to early 2023. It summarizes the therapeutic potential of various AhR ligands with an emphasis on exogenous ligands. It also sheds light on recent immunotherapeutic strategies involving AhR.

Potential Role of Host Microbiome in Areca Nut-Associated Carcinogenesis and Addiction

Areca nut (AN) is widely consumed all over the world, bringing great harm to human health and economy. Individuals with AN chewing are at high risk of cardiovascular disease and impaired immune system and metabolic system. Despite a growing number of studies having reported on the adverse effects brought by AN chewing, the exact mechanism of it is limited and the need for additional exploration remains. In recent years, the interaction between microorganisms, especially intestinal microorganism and host, has been extensively studied. AN chewing might disrupt the oral and intestinal microbiota communities through direct connect with the microbes it contains, altering PH, oxygen of oral and intestinal microenvironment, and disturbing the immune homeostasis. These mechanisms provide insights into the interplay between areca nut and host microbiota. Emerging studies have proposed that bidirectional interaction between polyphenols and intestinal microbes might play a potential role in the divergence of polyphenol, extracted from AN, among individuals with or without AN-induced cancer development and progression. Although some AN chewers have been aware of the harmful effects brought by AN, they cannot abolish this habit because of the addiction of AN. Increasing studies have tried to revealed that gut microbiota might influence the onset/development of addictive behaviors. Altogether, this review summarizes the possible reasons for the disturbance of host microbiota caused by areca nut chewing and clarifies the complex interaction between human microbiome and major constituents and the addiction and carcinogenicity of AN, tempting to provide novel insights into the development and utilization of it, and to control the adverse consequences caused by AN chewing.

The Role of the Aryl Hydrocarbon Receptor (AhR) and Its Ligands in Breast Cancer

Breast cancer is a complex disease which is defined by numerous cellular and molecular markers that can be used to develop more targeted and successful therapies. The aryl hydrocarbon receptor (AhR) is overexpressed in many breast tumor sub-types, including estrogen receptor -positive (ER+) tumors; however, the prognostic value of the AhR for breast cancer patient survival is not consistent between studies. Moreover, the functional role of the AhR in various breast cancer cell lines is also variable and exhibits both tumor promoter- and tumor suppressor- like activity and the AhR is expressed in both ER-positive and ER-negative cells/tumors. There is strong evidence demonstrating inhibitory AhR-Rα crosstalk where various AhR ligands induce ER degradation. It has also been reported that different structural classes of AhR ligands, including halogenated aromatics, polynuclear aromatics, synthetic drugs and other pharmaceuticals, health promoting phytochemical-derived natural products and endogenous AhR-active compounds inhibit one or more of breast cancer cell proliferation, survival, migration/invasion, and metastasis. AhR-dependent mechanisms for the inhibition of breast cancer by AhR agonists are variable and include the downregulation of multiple genes/gene products such as CXCR4, MMPs, CXCL12, SOX4 and the modulation of microRNA levels. Some AhR ligands, such as aminoflavone, have been investigated in clinical trials for their anticancer activity against breast cancer. In contrast, several publications have reported that AhR agonists and antagonists enhance and inhibit mammary carcinogenesis, respectively, and differences between the anticancer activities of AhR agonists in breast cancer may be due in part to cell context and ligand structure. However, there are reports showing that the same AhR ligand in the same breast cancer cell line gives opposite results. These differences need to be resolved in order to further develop and take advantage of promising agents that inhibit mammary carcinogenesis by targeting the AhR.

Epigenetics and environment in breast cancer: New paradigms for anti-cancer therapies

Breast cancer remains the most frequently diagnosed cancer in women worldwide. Delayed presentation of the disease, late stage at diagnosis, limited therapeutic options, metastasis, and relapse are the major factors contributing to breast cancer mortality. The development and progression of breast cancer is a complex and multi-step process that incorporates an accumulation of several genetic and epigenetic alterations. External environmental factors and internal cellular microenvironmental cues influence the occurrence of these alterations that drives tumorigenesis. Here, we discuss state-of-the-art information on the epigenetics of breast cancer and how environmental risk factors orchestrate major epigenetic events, emphasizing the necessity for a multidisciplinary approach toward a better understanding of the gene-environment interactions implicated in breast cancer. Since epigenetic modifications are reversible and are susceptible to extrinsic and intrinsic stimuli, they offer potential avenues that can be targeted for designing robust breast cancer therapies.

Emodin inhibits U87 glioblastoma cells migration by activating aryl hydrocarbon receptor (AhR) signaling pathway

Aryl hydrocarbon receptor (AhR) is a ligand-activated receptor to mediates the biological reactions of many environmental and natural compounds, which is highly expressed in glioblastoma. Although it has been reported that AhR agonist emodin can suppress some kinds of tumors, its inhibitory effect on glioblastoma migration and its relationship with AhR remain unclear. Based on the complexity of tumor pathogenesis and the tissue specificity of AhR, we hope can further understand the effect of emodin on glioblastoma and explore its mechanism. We found that the inhibitory effect of emodin on the migration of U87 glioblastoma cells increased with time, and the cell migration ability was inhibited by about 25% after 36 h exposure. In this process, emodin promoted the expression of the tumor suppressor IL24 by activating the AhR signaling pathway. Reducing the expression of AhR or IL24 by interfering RNA could block or relieve the inhibitory effect of emodin on the U87 cells migration, which indicates the inhibition of emodin on the migration of glioblastoma is mediated by the AhR-IL24 axis. Our data proved the AhR-IL24 signal axis is an important pathway for emodin to inhibit the migration of glioblastoma, and the AhR signaling pathway can be used as a key target to research the regulation effect and its mechanism of compounds on glioblastoma migration.

Aryl Hydrocarbon Receptor and Its Diverse Ligands and Functions: An Exposome Receptor

The aryl hydrocarbon receptor (AhR) is a transcriptional factor that regulates multiple functions following its activation by a variety of ligands, including xenobiotics, natural products, microbiome metabolites, and endogenous molecules. Because of this diversity, the AhR constitutes an exposome receptor. One of its main functions is to regulate several lines of defense against chemical insults and bacterial infections. Indeed, in addition to its well-established detoxication function, it has several functions at physiological barriers, and it plays a critical role in immunomodulation. The AhR is also involved in the development of several organs and their homeostatic maintenance. Its activity depends on the type of ligand and on the time frame of the receptor activation, which can be either sustained or transient, leading in some cases to opposite modes of regulations as illustrated in the regulation of different cancer pathways. The development of selective modulators and their pharmacological characterization are important areas of research. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Aryl hydrocarbon receptor interacting protein (AIP) significantly influences prognosis of pancreatic carcinoma

INTRODUCTION

Aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor. Aryl hydrocarbon receptor interacting protein (AIP) in one of AHR ligands. The aim of this study is to analyze the prognostic influence of AIP in pancreatic carcinoma.

MATERIAL AND METHODS

Retrospective case series with immunohistochemical analysis of AIP. We have estimated a multivariate Cox's model for the outcome (progression free and overall survival).

RESULTS

204 patients were included in the study. As expected prognosis was poor and 67.8% died of disease. As for AIP 9.8% of the cases showed nuclear staining of the epithelial tumor cells and 59.4% a cytoplasmic one. Stroma was stained in 53.1% of the cases. Univariate survival analysis revealed a significantly worse prognosis of patients with cytoplasmic AIP expression (stroma and epithelium), but nuclear expression was associated to a better prognosis. In the multivariate analysis stromal AIP expression was an independent prognosticator of progression free survival, together with pT stage, histological grade and history of diabetes.

DISCUSSION

AIP Is a conserved cochaperone protein binding to many proteins. AIP has been proposed as a potential tumor suppressor gene. To date, no study has analyzed the immunohistochemical expression of AIP in pancreatic carcinoma. Our results indicate that both epithelial and stromal cytoplasmic expression of AIP is associated to bad prognosis, while nuclear translocation seems to improve prognosis.

CONCLUSION

Although we must deepen into the complex signaling pathways underlying this potential association, our results open a way to inhibiting AHR as a potential target against pancreatic carcinoma.

Amino alcohol acrylonitriles as broad spectrum and tumour selective cytotoxic agents

We have identified specific dichlorophenylacrylonitriles as lead compounds in the development of novel anticancer compounds, notably, (Z)-N-(4-(2-cyano-2-(3,4-dichlorophenyl)vinyl)phenyl)acetamide (1) and ANI-7 (2). Herein we specifically probe the SAR associated with the terminal aromatic ring and associated cytoxicity in a broad range of human cancer cell lines. Synthesis of three focused libraries revealed a poor tolerance for electron withdrawing and donating moieties (Library A). A clear preference for hydrophobic substituents on a terminal piperazine moiety (Library B) with good levels of broad spectrum cytotoxicity, e.g. 13a (GI50 2.5-6.0 μM), as did the introduction of a methylene spacer with 13i (4-CH3PhCH2; GI50 1.5-4.5 μM). Removal of the aromatic moiety and installation of simple hydrophobic groups (Library C), in particular an adamantyl moiety, afforded highly active broad spectrum cytotoxic agents with GI50 values ranging from 1.7 μM (14k; 1-adamantyl) to 5.6 μM (14i; pyrrolidine). Within these libraries we note lung cancer selectivity, relative to normal cells, of 13h (fluoro substituted acrylonitrile, GI50 1.6 μM, 9.3-fold selective); the colorectal selectivity of 14h (methylpiperidine analogue, GI50 0.36 μM, 6.9-fold selective) and the breast cancer selectivity of 13f (nitrile substituted acrylonitrile, GI50 2.3-6.0 μM, up to 20-fold selective). The latter was confirmed as a novel AhR ligand and a CYP1A1 activating compound, that likely induces cell death following bioactivation; a phenomenon previously described in breast cancer cell populations.

Natural Products: Implication in Cancer Prevention and Treatment through Modulating Various Biological Activities

Cancer is one of the most leading causes of death worldwide. It is one of the primary global diseases that cause morbidity and mortality in millions of people. It is usually caused by different carcinogenic agents that damage the genetic material and alter the cell signaling pathways. Carcinogens are classified into two groups as genotoxic and non-genotoxic agents. Genotoxic carcinogens are capable of directly altering the genetic material, while the non-genotoxic carcinogens are capable of producing cancer by some secondary mechanisms not related to direct gene damage. There is undoubtedly the greatest need to utilize some novel natural products as anticancer agents, as these are within reach everywhere. Interventions by some natural products aimed at decreasing the levels and conditions of these risk factors can reduce the frequency of cancer incidences. Cancer is conventionally treated by surgery, radiation therapy and chemotherapy, but such treatments may be fast-acting and causes adverse effects on normal tissues. Alternative and innovative methods of cancer treatment with the least side effects and improved efficiency are being encouraged. In this review, we discuss the different risk factors of cancer development, conventional and innovative strategies of its management and provide a brief review of the most recognized natural products used as anticancer agents globally.

Targeting the aryl hydrocarbon receptor with a novel set of triarylmethanes

The aryl hydrocarbon receptor (AhR) is a chemical sensor upregulating the transcription of responsive genes associated with endocrine homeostasis, oxidative balance and diverse metabolic, immunological and inflammatory processes, which have raised the pharmacological interest on its modulation. Herein, a novel set of 32 unsymmetrical triarylmethane (TAM) class of structures has been synthesized, characterized and their AhR transcriptional activity evaluated using a cell-based assay. Eight of the assayed TAM compounds (14, 15, 18, 19, 21, 22, 25, 28) exhibited AhR agonism but none of them showed antagonist effects. TAMs bearing benzotrifluoride, naphthol or heteroaromatic (indole, quinoline or thiophene) rings seem to be prone to AhR activation unlike phenyl substituted or benzotriazole derivatives. A molecular docking analysis with the AhR ligand binding domain (LBD) showed similarities in the binding mode and in the interactions of the most potent TAM identified 4-(pyridin-2-yl (thiophen-2-yl)methyl)phenol (22) compared to the endogenous AhR agonist 5,11-dihydroindolo[3,2-b]carbazole-12-carbaldehyde (FICZ). Finally, in silico predictions of physicochemical and biopharmaceutical properties for the most potent agonistic compounds were performed and these exhibited acceptable druglikeness and good ADME profiles. To our knowledge, this is the first study assessing the AhR modulatory effects of unsymmetrical TAM class of compounds.

A novel naphthalimide that selectively targets breast cancer via the arylhydrocarbon receptor pathway

We report that the naphthalimide analogue 2-(2-aminophenyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (NAP-6) is a highly potent and selective breast cancer targeting molecule. These effects are mediated via the aryl hydrocarbon receptor (AHR) pathway and the subsequent induction of CYP1 metabolising monooxygenases in breast cancer cell line models. Indeed the triple negative breast cancer cell line MDA-MB-468 with a GI₅₀ value of 100 nM is greater than 500-fold more sensitive to NAP-6 compared with other tumour derived cell models. Within 1 h exposure of these cells to NAP-6, CYP1A1 expression increases 25-fold, rising to 250-fold by 24 h. A smaller concurrent increase in CYP1A2 and CYP1B1 is also observed. Within 24 h these cells present with DNA damage as evident by enhanced H2AXγ expression, cell cycle checkpoint activation via increased CHK2 expression, S-phase cell cycle arrest and cell death. Specific small molecule inhibitors of the AHR and CYP1 family ameliorate these events. A positive luciferase reporter assay for NAP-6 induced XRE binding further confirms the role of the AHR in this phenomenon. Non-sensitive cell lines fail to show these biological effects. For the first time we identify 2-(2-aminophenyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione as a new AHR ligand that selectively targets breast cancer.

Critical Review on the Presence of Phthalates in Food and Evidence of Their Biological Impact

Phthalates are a huge class of chemicals with a wide spectrum of industrial uses, from the manufacture of plastics to food contact applications, children's toys, and medical devices. People and animals can be exposed through different routes (i.e., ingestion, inhalation, dermal, or iatrogenic exposure), as these compounds can be easily released from plastics to water, food, soil, air, making them ubiquitous environmental contaminants. In the last decades, phthalates and their metabolites have proven to be of concern, particularly in products for pregnant women or children. Moreover, many authors reported high concentrations of phthalates in soft drinks, mineral waters, wine, oil, ready-to-eat meals, and other products, as a possible consequence of their accumulation along the food production chain and their accidental release from packaging materials. However, due to their different physical and chemical properties, phthalates do not have the same human and environmental impacts and their association to several human diseases is still under debate. In this review we provide an overview of phthalate toxicity, pointing out the health and legal issues related to their occurrence in several types of food and beverage.

Amino Alcohol Acrylonitriles as Activators of the Aryl Hydrocarbon Receptor Pathway: An Unexpected MTT Phenotypic Screening Outcome

Lead (Z)-N-(4-(2-cyano-2-(3,4-dichlorophenyl)vinyl)phenyl)acetamide, 1 showed MCF-7 GI₅₀ =30 nM and 400-fold selective c.f. MCF10A (normal breast tissue). Acetamide moiety modification (13 a-g) to introduce additional hydrophobicity was favoured with MCF-7 breast cancer cell activity enhanced at 1.3 nM. Other analogues were potent against the HT29 colon cancer cell line at 23 nM. Textbook SAR data was observed in the MCF-7 cell line, in an MTT assay, via the ortho (17 a), meta (17 b) and para (13 f). The amino alcohol -OH moiety was pivotal, but no stereochemical preference noted. But, these data did not fit our homology modelling expectations. Aberrant MTT ((3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) screening results and metabolic interference confirmed by sulforhodamine B (SRB) screening. Interfering analogues resulted in 120 and 80-fold CYP1A1 and CYP1A2 amplification, with no upregulation of SULT1A1. This is consistent with activation of the AhR pathway. Piperidine per-deuteration reduced metabolic inactivation. 3-OH / 4-OH piperidine analogues showed differential MTT and SRB activity supporting MTT assay metabolic inactivation. Data supports piperidine 3-OH, but not the 4-OH, as a CYP substrate. This family of β-amino alcohol substituted 3,4-dichlorophenylacetonitriles show broad activity modulated via the AhR pathway. By SRB analysis the most potent analogue was 23 b, (Z)-3-(4-(3-(4-phenylpiperidin-1-yl)-2-hydroxypropoxy)phenyl)-2-(3,4-dichlorophenyl)-acrylonitrile.

The putative endogenous AHR ligand ITE reduces JAG1 and associated NOTCH1 signaling in triple negative breast cancer cells

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor. Triple negative breast cancer (TNBC) is the most aggressive breast cancer subtype. TNBC expresses AHR and AHR ligands have anti-cancer activity in TNBC. The aggressiveness of TNBC is due in part to JAG1-NOTCH1 signaling. ITE is a putative endogenous AHR ligand. We show that ITE reduces the expression of JAG1 the amount of Notch 1 intracellular domain (NICD1) and the phosphorylation of STAT3 (at tyrosine 705) in TNBC MDA-MB-231 cells. The STAT3 inhibitor STATTIC also reduced JAG1. STAT3, thus, mediates regulation of JAG1 in MDA-MB-231 cells. Reducing the expression of JAG1 with short interfering RNA decreases the growth, migration and invasiveness of MDA-MB-231 cells. JAG1, therefore, has cellular effects in MDA-MB-231 cells under basal conditions. We consequently evaluated if exposing cells to greater amounts of JAG1 would counteract ITE cellular effects in MDA-MB-231 cells. The results show that JAG1 does not counteract the cellular effects of ITE. JAG1, thus, has no effect on growth or invasiveness in MDA-MB-231 cells treated with ITE. JAG1, therefore, has context dependent roles in MDA-MB-231 cells (basal versus ITE treatment). The results also show that other pathways, not inhibition of the JAG1-NOTCH1 pathway, are important for mediating the growth and invasive inhibitory effect of ITE on MDA-MB-231 cells.

The aryl hydrocarbon receptor (AhR) as a breast cancer drug target

Breast cancer is the most common cancer in women, with more than 1.7 million diagnoses worldwide per annum. Metastatic breast cancer remains incurable, and the presence of triple-negative phenotypes makes targeted treatment impossible. The aryl hydrocarbon receptor (AhR), most commonly associated with the metabolism of xenobiotic ligands, has emerged as a promising biological target for the treatment of this deadly disease. Ligands for the AhR can be classed as exogenous or endogenous and may have agonistic or antagonistic activity. It has been well reported that agonistic ligands may have potent and selective growth inhibition activity in a number of oncogenic cell lines, and one (aminoflavone) has progressed to phase I clinical trials for breast cancer sufferers. In this study, we examine the current state of the literature in this area and elucidate the promising advances that are being made in hijacking the cytosolic-to-nuclear pathway of the AhR for the possible future treatment of breast cancer.

Compounds of PAH mixtures dependent interaction between multiple signaling pathways in granulosa tumour cells

Mechanism of PAH mixtures, using granulosa tumour cells, was investigated. Cells were exposed to a mixture of all 16 priority PAHs (M1) or a mixture of five PAHs not classified as human carcinogens (M2). The effect of siAHR, siAHRR and siNFKB2 on the expression of CYP1A1, CYP1B1, GSTM1, ERα, AR and cell proliferation was described. M1 decreased AhR and CYP1A1, while increased AhRR and ARNT expression. M2 also decreased AhR and CYP1A1 but had no effect on AhRR expression. siAHRR reversed the inhibitory effect of M1 on AhR and CYP1A1,while inhibitory effect of M2 was still observed. siNFKB2 reversed inhibitory effect of both mixtures on AhR and CYP1A1 expression and stimulatory effect of M1 on AhRR expression. siAHR reversed stimulatory effect of both mixtures on ERα expression. Stimulatory effect of M1 on cell proliferation was not observed in siAHR, was still observed in siESR1 cells. M2 had no effect on cell proliferation, however stimulatory effect was appeared in siAHR and siESR1cells. In conclusion: M1 by activation of AhRR and NFkB p52, but M2 only by activation of NFκB attenuated AhR signalling and ligand-induced CYP1A1 expression. Interaction between AhR and ER following M1 and M2 exposure is primarily initiated through AhR.

Putative tumor suppressor cytoglobin promotes aryl hydrocarbon receptor ligand-mediated triple negative breast cancer cell death

Nearly 40 000 women die annually from breast cancer in the United States. Clinically available targeted breast cancer therapy is largely ineffective in triple negative breast cancer (TNBC), characterized by tumors that lack expression of the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (Her2). TNBC is associated with a poor prognosis. Previous reports show that aryl hydrocarbon receptor (AhR) partial agonist 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (5F 203) selectively inhibits the growth of breast cancer cells, including those of the TNBC subtype. We previously demonstrated that 5F 203 induced the expression of putative tumor suppressor gene cytoglobin (CYGB) in breast cancer cells. In the current study, we determined that 5F 203 induces apoptosis and caspase-3 activation in MDA-MB-468 TNBC cells and in T47D ER+ PR + Her2 - breast cancer cells. We also show that caspases and CYGB promote 5F 203-mediated apoptosis in MDA-MB-468 cells. 5F 203 induced lysosomal membrane permeabilization (LMP) and cathepsin B release in MDA-MB-468 and T47D cells. In addition, silencing CYGB attenuated the ability of 5F 203 to induce caspase-3/-7 activation, proapoptotic gene expression, LMP, and cathepsin B release in MDA-MB-468 cells. Moreover, 5F 203 induced CYGB protein expression, proapoptotic protein expression, and caspase-3 cleavage in MDA-MB-468 cells and in MDA-MB-468 xenograft tumors grown orthotopically in athymic mice. These data provide a basis for the development of AhR ligands with the potential to restore CYGB expression as a novel strategy to treat TNBC.

Long-term airborne dioxin exposure and breast cancer risk in a case-control study nested within the French E3N prospective cohort

BACKGROUND

Dioxins, Group 1 carcinogens, are emitted by industrial chlorinated combustion processes and suspected to increase breast cancer risk through receptor-mediated pathways.

OBJECTIVES

We estimated breast cancer risk associated with airborne dioxin exposure, using geographic information system (GIS) methods and historical exposure data.

METHODS

We designed a case-control study (429 breast cancer cases diagnosed between 1990 and 2008, matched to 716 controls) nested within the E3N (Etude Epidémiologique auprès de femmes de la Mutuelle Générale de l'Education Nationale) cohort. Airborne dioxin exposure was assessed using a GIS-based metric including participants' residential history, technical characteristics of 222 dioxin sources, residential proximity to dioxin sources, exposure duration and wind direction. Odds ratios (OR) and 95% confidence intervals (CI) associated with quintiles of cumulative exposure were estimated using multivariate logistic regression models.

RESULTS

We observed no increased risk of breast cancer for higher dioxin exposure levels overall and according to hormone-receptor status. We however observed a statistically significant OR for Q2 versus Q1 overall (1.612, 95% CI: 1.042-2.493) and for estrogen-receptor (ER) positive breast cancer (1.843, 95% CI: 1.033-3.292).

CONCLUSIONS

Overall, as well as according to hormone-receptor status, no increased risk was observed for higher airborne dioxin exposure. The increased risk for low exposure levels might be compatible with non-monotonic dose-response relationship. Confirmation of our findings is required. Our GIS-based metric may provide an alternative in absence of ambient dioxin monitoring and may allow assessing exposure to other pollutants.

High AHR expression in breast tumors correlates with expression of genes from several signaling pathways namely inflammation and endogenous tryptophan metabolism

Increasing epidemiological and animal experimental data provide substantial support for the role of aryl hydrocarbon receptor (AhR) in mammary tumorigenesis. The effects of AhR have been clearly demonstrated in rodent models of breast carcinogenesis and in several established human breast cancer cell lines following exposure to AhR ligands or AhR overexpression. However, relatively little is known about the role of AhR in human breast cancers. AhR has always been considered to be a regulator of toxic and carcinogenic responses to environmental contaminants such as TCDD (dioxin) and benzo[a]pyrene (BaP). The aim of this study was to identify the type of breast tumors (ERα-positive or ERα-negative) that express AHR and how AhR affects human tumorigenesis. The levels of AHR, AHR nuclear translocator (ARNT) and AHR repressor (AHRR) mRNA expression were analyzed in a cohort of 439 breast tumors, demonstrating a weak association between high AHR expression and age greater than fifty years and ERα-negative status, and HR-/ERBB2 breast cancer subtypes. AHRR mRNA expression was associated with metastasis-free survival, while AHR mRNA expression was not. Immunohistochemistry revealed the presence of AhR protein in both tumor cells (nucleus and/or cytoplasm) and the tumor microenvironment (including endothelial cells and lymphocytes). High AHR expression was correlated with high expression of several genes involved in signaling pathways related to inflammation (IL1B, IL6, TNF, IL8 and CXCR4), metabolism (IDO1 and TDO2 from the kynurenine pathway), invasion (MMP1, MMP2 and PLAU), and IGF signaling (IGF2R, IGF1R and TGFB1). Two well-known ligands for AHR (TCDD and BaP) induced mRNA expression of IL1B and IL6 in an ERα-negative breast tumor cell line. The breast cancer ER status likely influences AhR activity involved in these signaling pathways. The mechanisms involved in AhR activation and target gene expression in breast cancers are also discussed.

(Z)-2-(3,4-Dichlorophenyl)-3-(1H-Pyrrol-2-yl)Acrylonitrile Exhibits Selective Antitumor Activity in Breast Cancer Cell Lines via the Aryl Hydrocarbon Receptor Pathway

We have previously reported the synthesis and breast cancer selectivity of (Z)-2-(3,4-dichlorophenyl)-3-(1H-pyrrol-2-yl)acrylonitrile (ANI-7) in cancer cell lines. To further evaluate the selectivity of ANI-7, we have expanded upon the initial cell line panel to now include the breast cancer cell lines (MCF7, MCF7/VP16, BT474, T47D, ZR-75-1, SKBR3, MDA-MB-468, BT20, MDA-MB-231); normal breast cells (MCF-10A); and cell lines derived from colon (HT29), ovarian (A2780), lung (H460), skin (A431), neuronal (BE2C), glial (U87, SJG2), and pancreatic (MIA) cancers. We now show that ANI-7 is up to 263-fold more potent at inhibiting the growth of breast cancer cell lines (MCF7, MCF7/VP16, BT474, T47D, ZR-75-1, SKBR3, MDA-MB-468) than normal breast cells (MCF-10A) or cell lines derived from other tumor types. Measures of growth inhibition, cell cycle analysis, morphologic assessment, Western blotting, receptor binding, gene expression, small interfering RNA technology, reporter activity, and enzyme inhibition assays were exploited to define the mechanism of action of ANI-7. In this work, we report that ANI-7 mediates its effects via the activation of the aryl hydrocarbon receptor (AhR) pathway and the subsequent induction of CYP1-metabolizing mono-oxygenases. The metabolic conversion of ANI-7 induces DNA damage, checkpoint activation, S-phase cell cycle arrest, and cell death in sensitive breast cancer cell lines. Basal expression of AhR, the AhR nuclear translocator, and the CYP1 family members do not predict for sensitivity; however, inherent expression of the phase II-metabolizing enzyme sulfur transferase 1A1 does. For the first time, we identify (Z)-2-(3,4-dichlorophenyl)-3-(1H-pyrrol-2-yl)acrylonitrile as a new AhR ligand.

Intestine-Specific Homeobox Gene ISX Integrates IL6 Signaling, Tryptophan Catabolism, and Immune Suppression

The intestine-specific homeobox transcription factor intestine-specific homeobox (ISX) is an IL6-inducible proto-oncogene implicated in the development of hepatocellular carcinoma, but its mechanistic contributions to this process are undefined. In this study, we provide evidence that ISX mediates a positive feedback loop integrating inflammation, tryptophan catabolism, and immune suppression. We found that ISX-mediated IL6-induced expression of the tryptophan catabolic enzymes Indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase in hepatocellular carcinoma cells, resulting in an ISX-dependent increase in the tryptophan catabolite kynurenine and its receptor aryl hydrocarbon receptor (AHR). Activation of this kynurenine/AHR signaling axis acted through a positive feedback mechanism to increase ISX expression and enhance cellular proliferation and tumorigenic potential. RNAi-mediated attenuation of ISX or AHR reversed these effects. In an IDO1-dependent manner, ectopic expression of ISX induced expression of genes encoding the critical immune modulators CD86 (B7-2) and programmed death ligand-1 (PD-L1), through which ISX conferred a significant suppressive effect on the CD8⁺ T-cell response. In hepatocellular carcinoma specimens, expression of IDO1, kynurenine, AHR, and PD-L1 correlated negatively with survival. Overall, our results identified a feed-forward mechanism of immune suppression in hepatocellular carcinoma organized by ISX, which involves kynurenine-AHR signaling and PD-L1, offering insights into immune escape by hepatocellular carcinoma, which may improve its therapeutic management. Cancer Res; 77(15); 4065-77. ©2017 AACR.

A Molecular Mechanism To Switch the Aryl Hydrocarbon Receptor from a Transcription Factor to an E3 Ubiquitin Ligase

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that is known as a mediator of toxic responses. Recently, it was shown that the AhR has dual functions. Besides being a transcription factor, it also possesses an intrinsic E3 ubiquitin ligase function that targets, e.g., the steroid receptors for proteasomal degradation. The aim of this study was to identify the molecular switch that determines whether the AhR acts as a transcription factor or an E3 ubiquitin ligase. To do this, we used the breast cancer cell line MCF7, which expresses a functional estrogen receptor alpha (ERα) signaling pathway. Our data suggest that aryl hydrocarbon receptor nuclear translocator (ARNT) plays an important role in the modulation of the dual functions of the AhR. ARNT knockdown dramatically impaired the transcriptional activation properties of the ligand-activated AhR but did not affect its E3 ubiquitin ligase function. The availability of ARNT itself is modulated by another basic helix-loop-helix (bHLH)-Per-ARNT-SIM (PAS) protein, the repressor of AhR function (AhRR). MCF7 cells overexpressing the AhRR showed lower ERα protein levels, reduced responsiveness to estradiol, and reduced growth rates. Importantly, when these cells were used to produce estrogen-dependent xenograft tumors in SCID mice, we also observed lower ERα protein levels and a reduced tumor mass, implying a tumor-suppressive-like function of the AhR in MCF7 xenograft tumors.

Role of the aryl hydrocarbon receptor in carcinogenesis and potential as an anti-cancer drug target

The aryl hydrocarbon receptor (AhR) was initially identified as the receptor that binds and mediates the toxic effects induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and structurally related halogenated aromatics. Other toxic compounds including some polynuclear aromatic hydrocarbons act through the AhR; however, during the last 25 years, it has become apparent that the AhR plays an essential role in maintaining cellular homeostasis. Moreover, the scope of ligands that bind the AhR includes endogenous compounds such as multiple tryptophan metabolites, other endogenous biochemicals, pharmaceuticals and health-promoting phytochemicals including flavonoids, indole-3-carbinol and its metabolites. It has also been shown that like other receptors, the AhR is a drug target for multiple diseases including cancer, where both AhR agonists and antagonists effectively block many of the critical hallmarks of cancer in multiple tumor types. This review describes the anti-cancer activities of AhR ligands and demonstrates that it is time to separate the AhR from TCDD and exploit the potential of the AhR as a novel target for cancer chemotherapy.

The Aryl Hydrocarbon Receptor (AhR) as a Drug Target for Cancer Chemotherapy

The aryl hydrocarbon receptor (AhR) is overexpressed in some patients with different tumor types, and the receptor can be a negative or positive prognostic factor. There is also evidence from both in vivo and in vitro cell culture models that the AhR can exhibit tumor-specific pro-oncogenic and tumor suppressor-like functions and therefore can be treated with AhR antagonists or agonists, respectively. Successful clinical applications of AhR ligands will require the synthesis and development of selective AhR modulators (SAhRMs) with tumor-specific AhR agonist or antagonist activity, and some currently available compounds such as indole-3-carbinol and diindolylmethane-(DIM) and synthetic AhR antagonists are potential drug candidates. There is also evidence that some AhR-active pharmaceuticals, including tranilast, flutamide, hydroxytamoxifen and omeprazole or their derivatives, may be effective AhR-dependent anticancer agents for single or combination cancer chemotherapies for treatment of breast and pancreatic cancers.

Aryl Hydrocarbon Receptor Ligand 5F 203 Induces Oxidative Stress That Triggers DNA Damage in Human Breast Cancer Cells

Breast tumors often show profound sensitivity to exogenous oxidative stress. Investigational agent 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (5F 203) induces aryl hydrocarbon receptor (AhR)-mediated DNA damage in certain breast cancer cells. Since AhR agonists often elevate intracellular oxidative stress, we hypothesize that 5F 203 increases reactive oxygen species (ROS) to induce DNA damage, which thwarts breast cancer cell growth. We found that 5F 203 induced single-strand break formation. 5F 203 enhanced oxidative DNA damage that was specific to breast cancer cells sensitive to its cytotoxic actions, as it did not increase oxidative DNA damage or ROS formation in nontumorigenic MCF-10A breast epithelial cells. In contrast, AhR agonist and procarcinogen benzo[a]pyrene and its metabolite, 1,6-benzo[a]pyrene quinone, induced oxidative DNA damage and ROS formation, respectively, in MCF-10A cells. In sensitive breast cancer cells, 5F 203 activated ROS-responsive kinases: c-Jun-N-terminal kinase (JNK) and p38 mitogen activated protein kinase (p38). AhR antagonists (alpha-naphthoflavone, CH223191) or antioxidants (N-acetyl-l-cysteine, EUK-134) attenuated 5F 203-mediated JNK and p38 activation, depending on the cell type. Pharmacological inhibition of AhR, JNK, or p38 attenuated 5F 203-mediated increases in intracellular ROS, apoptosis, and single-strand break formation. 5F 203 induced the expression of cytoglobin, an oxidative stress-responsive gene and a putative tumor suppressor, which was diminished with AhR, JNK, or p38 inhibition. Additionally, 5F 203-mediated increases in ROS production and cytoglobin were suppressed in AHR100 cells (AhR ligand-unresponsive MCF-7 breast cancer cells). Our data demonstrate 5F 203 induces ROS-mediated DNA damage at least in part via AhR, JNK, or p38 activation and modulates the expression of oxidative stress-responsive genes such as cytoglobin to confer its anticancer action.

Estimated dietary dioxin exposure and breast cancer risk among women from the French E3N prospective cohort

Introduction

Dioxins are environmental and persistent pollutants mostly emitted from combustion facilities (e.g. waste incinerators, metal and cement industries). Known to be endocrine disrupting chemicals, dioxins are suspected to increase breast cancer (BC) risk. Although diet is considered the primary source of dioxin exposure, no previous study has been published on dietary dioxin exposure in relation to BC risk. We aimed to assess dietary dioxin exposure among women from the E3N cohort and estimate BC risk associated with this exposure.

Methods

The study included 63,830 women from the E3N cohort who completed a diet history questionnaire (DHQ) in 1993 and were followed until 2008. Dietary dioxin exposure was estimated by combining consumption data from the E3N DHQ and food dioxin contamination data from a French national monitoring program. Hazard ratios (HR) and 95% confidence intervals (CI) were estimated by Cox models adjusted for BC risk factors.

Results

Mean dietary dioxin exposure was estimated at 1.3 ± 0.4 pg/kg body weight (BW)/day. A 0.4 pg/kg BW/d increase in dioxin intake was not associated with overall BC risk (HR = 1.00; 95% CI: 0.96, 1.05). A significant decrease in risk of estrogen receptor negative (ER-)/progesterone receptor negative (PR-) tumors was observed among post-menopausal women in the upper quartile of estimated dioxin intake (HR for Q4 vs. Q1: 0.65; 95% CI: 0.45, 0.96; P for trend across quartiles = 0.0463).

Conclusions

Overall, no association between estimated dietary dioxin exposure and BC risk was found among E3N women. Further studies should include both dietary and environmental exposures to determine whether low-dose dioxin exposure is associated with BC risk.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-015-0536-9) contains supplementary material, which is available to authorized users.

Aryl hydrocarbon receptor ligands in cancer: friend and foe

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that is best known for mediating the toxicity and tumour-promoting properties of the carcinogen 2,3,7,8-tetrachlorodibenzo-p-dioxin, commonly referred to as ‘dioxin’. AHR influences the major stages of tumorigenesis — initiation, promotion, progression and metastasis — and physiologically relevant AHR ligands are often formed during disease states or during heightened innate and adaptive immune responses. Interestingly, ligand specificity and affinity vary between rodents and humans. Studies of aggressive tumours and tumour cell lines show increased levels of AHR and constitutive localization of this receptor in the nucleus. This suggests that the AHR is chronically activated in tumours, thus facilitating tumour progression. This Review discusses the role of AHR in tumorigenesis and the potential for therapeutic modulation of its activity in tumours.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) inhibits human ovarian cancer cell proliferation

PURPOSE

The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, mediates a broad spectrum of biological processes, including ovarian growth and ovulation. Recently, we found that an endogenous AhR ligand (ITE) can inhibit ovarian cancer proliferation and migration via the AhR. Here, we tested whether 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, an exogenous AhR ligand) may exert similar anti-ovarian cancer activities using human ovarian cancer and non-cancerous human ovarian surface epithelial cells.

METHODS

Two human ovarian cancer cell lines (SKOV-3 and OVCAR-3) and one human ovarian surface epithelial cell line (IOSE-385) were used. Cell proliferation and migration activities were determined using crystal violet and FluoroBlok insert system assays, respectively. AhR protein expression was assessed by Western blotting. Expression of cytochrome P450, family 1, member A1 (CYP1A1) and member B1 (CYP1B1) mRNA was assessed by qPCR. Small interfering RNAs (siRNAs) were used to knock down AhR expression.

RESULTS

We found that TCDD dose-dependently suppressed OVCAR-3 cell proliferation, with a maximum effect (~70% reduction) at 100 nM. However, TCDD did not affect SKOV-3 and IOSE-385 cell proliferation and migration. The estimated IC50 of TCDD for inhibiting OVCAR-3 cell proliferation was 4.6 nM. At 10 nM, TCDD time-dependently decreased AhR protein levels, while it significantly increased CYP1A1 and CYP1B1 mRNA levels in SKOV-3, OVCAR-3 and IOSE-385 cells, indicating activation of AhR signaling. siRNA-mediated AhR knockdown readily blocked TCDD-mediated suppression of OVCAR-3 cell proliferation.

CONCLUSION

Our data indicate that TCDD can suppress human ovarian cancer cell proliferation via the AhR signaling pathway and that TCDD exhibits an anti-proliferative activity in at least a subset of human ovarian cancer cells.

Tranilast: a review of its therapeutic applications

Tranilast (N-[3',4'-dimethoxycinnamoyl]-anthranilic acid) is an analog of a tryptophan metabolite. Initially, tranilast was identified as an anti-allergic agent, and used in the treatment of inflammatory diseases, such as bronchial asthma, atypical dermatitis, allergic conjunctivitis, keloids and hypertrophic scars. Subsequently, the results showed that it could be also effective in the management of a wide range of conditions. The beneficial effects of tranilast have also been seen in a variety of disease states, such as fibrosis, proliferative disorders, cancer, cardiovascular problems, autoimmune disorders, ocular diseases, diabetes and renal diseases. Moreover, several trials have shown that it has very low adverse effects and it is generally well tolerated by patients. In this review, we have attempted to accurately summarize previously published studies relating to the use of tranilast for a range of disorders and discuss the drug's possible mode of action. The major mode of the drug's efficacy appears to be the suppression of the expression and/or action of the TGF-β pathway, but the drug affects other factors as well. The findings presented in this review demonstrate the potential of tranilast for the control of a vast array of pathological situations, furthermore, it is a prescribed drug without severe side effects.

Computational prediction and analysis of breast cancer targets for 6-methyl-1, 3, 8-trichlorodibenzofuran

Breast cancer is one of the most known cancer types caused to the women around the world. Dioxins on the other hand are a wide range of chemical compounds known to cause the effects on human health. Among them, 6-Methyl-1,3,8-trichlorodibenzofuran (MCDF) is a relatively non toxic prototypical alkyl polychlorinated dibenzofuran known to act as a highly effective agent for inhibiting hormone-responsive breast cancer growth in animal models. In this study, we have developed a multi-level computational approach to identify possible new breast cancer targets for MCDF. We used PharmMapper Server to predict breast cancer target proteins for MCDF. Search results showed crystal Structure of the Antagonist Form of Glucocorticoid Receptor with highest fit score and AutoLigand analysis showed two potential binding sites, site-A and site-B for MCDF. A molecular docking was performed on these two sites and based on binding energy site-B was selected. MD simulation studies on Glucocorticoid receptor-MCDF complex revealed that MCDF conformation was stable at site-B and the intermolecular interactions were maintained during the course of simulation. In conclusion, our approach couples reverse pharmacophore analysis, molecular docking and molecular dynamics simulations to identify possible new breast cancer targets for MCDF.

MicroRNAs in cancer therapeutic response: Friend and foe

Cancer initiation and development engage extremely complicated pathological processes which involve alterations of a large number of cell signaling cascades and functional networks in temporal and spatial orders. During last decades, microRNAs (miRNAs), a class of non-coding RNAs, have emerged as critical players in cancer pathogenesis and progression by modulating many pathological aspects related to tumor development, growth, metastasis, and drug resistance. The major function of miRNAs is to post-transcriptionally regulate gene expression depending on recognition of complementary sequence residing in target mRNAs. Commonly, a particular miRNA recognition sequence could be found in a number of genes, which allows a single miRNA to regulate multiple functionally connected genes simultaneously and/or chronologically. Furthermore, a single gene can be targeted and regulated by multiple miRNAs. However, previous studies have demonstrated that miRNA functions are highly context-dependent, which leads to distinct pathological outcomes in different types of cancer as well as at different stages by alteration of the same miRNA. Here we summarize recent progress in studies on miRNA function in cancer initiation, metastasis and therapeutic response, focusing on breast cancer. The varying functions of miRNAs and potential application of using miRNAs as biomarkers as well as therapeutic approaches are further discussed in the context of different cancers.

Targeting mast cells tryptase in tumor microenvironment: a potential antiangiogenetic strategy

Angiogenesis is a complex process finely regulated by the balance between angiogenesis stimulators and inhibitors. As a result of proangiogenic factors overexpression, it plays a crucial role in cancer development. Although initially mast cells (MCs) role has been defined in hypersensitivity reactions and in immunity, it has been discovered that MCs have a crucial interplay on the regulatory function between inflammatory and tumor cells through the release of classical proangiogenic factors (e.g., vascular endothelial growth factor) and nonclassical proangiogenic mediators granule-associated (mainly tryptase). In fact, in several animal and human malignancies, MCs density is highly correlated with tumor angiogenesis. In particular, tryptase, an agonist of the proteinase-activated receptor-2 (PAR-2), represents one of the most powerful angiogenic mediators released by human MCs after c-Kit receptor activation. This protease, acting on PAR-2 by its proteolytic activity, has angiogenic activity stimulating both human vascular endothelial and tumor cell proliferation in paracrine manner, helping tumor cell invasion and metastasis. Based on literature data it is shown that tryptase may represent a promising target in cancer treatment due to its proangiogenic activity. Here we focused on molecular mechanisms of three tryptase inhibitors (gabexate mesylate, nafamostat mesylate, and tranilast) in order to consider their prospective role in cancer therapy.

Aryl hydrocarbon receptor in breast cancer—a newly defined prognostic marker

Aryl hydrocarbon receptor (AhR) has been reported to exert various anticancer effects upon breast carcinoma cells in vitro but its details have remained largely unknown. Therefore, we first examined the AhR status in 90 invasive ductal carcinoma patients using immunohistochemistry. We then performed in vitro studies including wound healing assay, invasion assay, and matrix metalloproteinase (MMP) protein array in order to further elucidate the roles of AhR signaling in breast carcinoma. The status of AhR immunoreactivity was inversely correlated with histological grade (P = 0.0135) and Ki-67 labeling index (LI; P = 0.0087) of the patients. In addition, results of both uni- and multivariate analyses revealed that AhR in carcinoma cells turned out an independent prognostic factor with a protective relative risk (P = 0.0179). An administration of 10 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a ligand of AhR, significantly decreased Ki-67 LI in an AhR-dependent fashion in MCF-7, T47D, ZR75-1, and MDA-MB-231. Wound healing and invasion assays performed in T47D and ZR75-1 further demonstrated that 10 nM TCDD inhibited estrogen-induced migration and invasion of cells. MMP proteins associated with AhR in breast carcinoma cells were also firstly identified. These results demonstrated that AhR in breast carcinoma cells is considered a newly defined histological prognostic parameter of the breast cancer patients and effects of AhR activation on proliferation and MMPs expression may be related to the relatively good clinical outcome of AhR-positive breast cancer patients.

In silico identification of an aryl hydrocarbon receptor antagonist with biological activity in vitro and in vivo

The aryl hydrocarbon receptor (AHR) is critically involved in several physiologic processes, including cancer progression and multiple immune system activities. We, and others, have hypothesized that AHR modulators represent an important new class of targeted therapeutics. Here, ligand shape-based virtual modeling techniques were used to identify novel AHR ligands on the basis of previously identified chemotypes. Four structurally unique compounds were identified. One lead compound, 2-((2-(5-bromofuran-2-yl)-4-oxo-4H-chromen-3-yl)oxy)acetamide (CB7993113), was further tested for its ability to block three AHR-dependent biologic activities: triple-negative breast cancer cell invasion or migration in vitro and AHR ligand-induced bone marrow toxicity in vivo. CB7993113 directly bound both murine and human AHR and inhibited polycyclic aromatic hydrocarbon (PAH)- and TCDD-induced reporter activity by 75% and 90% respectively. A novel homology model, comprehensive agonist and inhibitor titration experiments, and AHR localization studies were consistent with competitive antagonism and blockade of nuclear translocation as the primary mechanism of action. CB7993113 (IC50 3.3 × 10(-7) M) effectively reduced invasion of human breast cancer cells in three-dimensional cultures and blocked tumor cell migration in two-dimensional cultures without significantly affecting cell viability or proliferation. Finally, CB7993113 effectively inhibited the bone marrow ablative effects of 7,12-dimethylbenz[a]anthracene in vivo, demonstrating drug absorption and tissue distribution leading to pharmacological efficacy. These experiments suggest that AHR antagonists such as CB7993113 may represent a new class of targeted therapeutics for immunomodulation and/or cancer therapy.

The aryl hydrocarbon receptor ligand omeprazole inhibits breast cancer cell invasion and metastasis

BACKGROUND

Patients with ER-negative breast tumors are among the most difficult to treat and exhibit low survival rates due, in part, to metastasis from the breast to various distal sites. Aryl hydrocarbon receptor (AHR) ligands show promise as antimetastatic drugs for estrogen receptor (ER)-negative breast cancer.

METHODS

Triple negative MDA-MB-231 breast cancer cells were treated with eight AHR-active pharmaceuticals including 4-hydroxtamoxifen, flutamide leflunomide, mexiletine, nimodipine, omeprazole, sulindac and tranilast, and the effects of these compounds on cell proliferation (MTT assay) and cell migration (Boyden chamber assay) were examined. The role of the AHR in mediating inhibition of MDA-MB-231 cell invasion was investigated by RNA interference (RNAi) and knockdown of AHR or cotreatment with AHR agonists. Lung metastasis of MDA-MB-231 cells was evaluated in mice administered cells by tail vein injection and prometastatic gene expression was examined by immunohistochemistry.

RESULTS

We showed that only the proton pump inhibitor omeprazole decreased MDA-MB-231 breast cancer cell invasion in vitro. Omeprazole also significantly decreased MDA-MB-231 cancer cell metastasis to the lung in a mouse model (tail vein injection), and in vitro studies showed that omeprazole decreased expression of at least two prometastatic genes, namely matrix metalloproteinase-9 (MMP-9) and C-X-C chemokine receptor 4 (CXCR4). Results of RNA interference studies confirmed that omeprazole-mediated downregulation of CXCR4 (but not MMP-9) was AHR-dependent. Chromatin immunoprecipitation assays demonstrated that omeprazole recruited the AHR to regions in the CXCR4 promoter that contain dioxin response elements (DREs) and this was accompanied by the loss of pol II on the promoter and decreased expression of CXCR4.

CONCLUSIONS

AHR-active pharmaceuticals such as omeprazole that decrease breast cancer cell invasion and metastasis may have important clinical applications for late stage breast cancer chemotherapy.

Roles of xenobiotic receptors in vascular pathophysiology

The pregnane X receptor (PXR) and constitutive androstane receptor (CAR), 2 closely related and liver-enriched members of the nuclear receptor superfamily, and aryl hydrocarbon receptor (AhR), a nonnuclear receptor transcription factor (TF), are major receptors/TFs regulating the expression of genes for the clearance and detoxification of xenobiotics. They are hence defined as "xenobiotic receptors". Recent studies have demonstrated that PXR, CAR and AhR also regulate the expression of key proteins involved in endobiotic responses such as the metabolic homeostasis of lipids, glucose, and bile acid, and inflammatory processes. It is suggested that the functions of PXR, CAR and AhR may be closely implicated in the pathogeneses of metabolic vascular diseases, such as hyperlipidemia, atherogenesis, and hypertension. Therefore, manipulation of the activities of these receptors may provide novel strategies for the treatment of vascular diseases. Here, we review the pathophysiological roles of PXR, CAR and AhR in the vascular system.

Zinc finger nuclease-mediated knockout of AHR or ARNT in human breast cancer cells abolishes basal and ligand-dependent regulation of CYP1B1 and differentially affects estrogen receptor α transactivation

In this study, we used zinc finger nuclease-mediated knockout of the aryl hydrocarbon receptor (AHR) or AHR nuclear translocator (ARNT) in MCF7 and AHR knockout in MDA-MB-231 human breast cancer cells to investigate cross talk among AHR, ARNT, and estrogen receptor α (ERα). Knockout of AHR or ARNT prevented the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-dependent induction of all AHR target genes examined. Knockout of AHR or ARNT also significantly reduced basal cytochrome P4501B1 (CYP1B1) expression levels, which were restored with overexpression of either protein but not with a DNA binding-deficient AHR mutant. Basal and TCDD-, 17β-estradiol (E2)-, or TCDD + E2-dependent recruitment of AHR, ARNT, ERα, NCoA3, and RNA polymerase II to CYP1B1 as well as CYP1B1 mRNA levels were abolished in MCF7-AHR((ko)) and MDA-MB-231 AHR(ko) cells. However, reduced but significant E2-dependent recruitment of ERα, NCoA3, and RNA polymerase II to CYP1B1 and weak increases in CYP1B1 mRNA levels were observed in MCF7 ARNT((ko)) cells. Interestingly, E2-dependent increases in trefoil factor 1, but not growth regulation by estrogen in breast cancer 1 (GREB1) mRNA levels, were dependent on ARNT expression. Moreover, the TCDD-dependent increases in the proteolytic degradation of ERα were prevented by the loss of AHR or ARNT. Our data show that AHR and ARNT play critical roles in the basal, TCDD, and E2-induced regulation of CYP1B1 but also reveal distinct roles for both proteins in ERα transactivation.

Beta-naphthoflavone (DB06732) mediates estrogen receptor-positive breast cancer cell cycle arrest through AhR-dependent regulation of PI3K/AKT and MAPK/ERK signaling

Beta-naphthoflavone (BNF, DB06732) is an agonist of aryl hydrocarbon receptor (AhR) and a putative chemotherapeutic agent that has antitumor activity against mammary carcinomas in vivo. However, the mechanism by which BNF exerts this antitumor effect remains unclear. Thus, we explored mechanisms of BNF's antitumor effects in human breast cancer cells. This study showed that BNF suppressed cell proliferation and induced cell cycle arrest in the G0/G1 phase with downregulation of cyclin D1/D3 and CDK4 and upregulation of p21(Cip1/Waf1), leading to a senescence-like phenotype in estrogen receptor (ER)-positive MCF-7 cells, but not in ER-negative MDA-MB-231 cells. In addition, BNF inhibited PI3K/AKT signaling, and the PI3K inhibitor, LY294,002, exhibited the same inhibitory effects on cyclinD1/D3, CDK4 and the cell cycle as BNF. Interestingly, BNF activated mitogen-activated protein kinase-extracellular signal-regulated kinase (MAPK-ERK) signaling, and more notably, MEK inhibitor PD98059 significantly blocked the BNF-induced cell cycle arrest and upregulation of p21(Cip1/Waf1). Furthermore, specific ERα and AhR siRNA studies indicate that ERα is required in BNF-induced p21(Cip1/Waf1) expression, and BNF-mediated cell cycle arrest and modulation of AKT and ERK signaling is AhR-dependent. Taken together, AhR-dependent inhibition of the PI3K/AKT pathway, activation of MAPK/ERK and modulation of ERα is a novel mechanism underlying BNF-mediated antitumor effects in breast cancer, which may represent a promising strategy to be exploited in future clinical trials.

Aryl hydrocarbon receptor ligands inhibit igf-ii and adipokine stimulated breast cancer cell proliferation

Obesity increases human cancer risk and the risk for cancer recurrence. Adipocytes secrete paracrine factors termed adipokines that stimulate signaling in cancer cells that induce proliferation. The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that plays roles in tumorigenesis, is regulated by exogenous lipophilic chemicals, and has been explored as a therapeutic target for cancer therapy. Whether exogenous AHR ligands modulate adipokine stimulated breast cancer cell proliferation has not been investigated. We provide evidence that adipocytes secrete insulin-like growth factor 2 (IGF-2) at levels that stimulate the proliferation of human estrogen receptor (ER) positive breast cancer cells. Using highly specific AHR ligands and AHR short interfering RNA (AHR-siRNA), we show that specific ligand-activated AHR inhibits adipocyte secretome and IGF-2-stimulated breast cancer cell proliferation. We also report that a highly specific AHR agonist significantly (P < 0.05) inhibits the expression of E2F1, CCND1 (known as Cyclin D1), MYB, SRC, JAK2, and JUND in breast cancer cells. Collectively, these data suggest that drugs that target the AHR may be useful for treating cancer in human obesity.

Role of the aryl hydrocarbon receptor in carcinogenesis and potential as a drug target

The aryl hydrocarbon receptor (AHR) is highly expressed in multiple organs and tissues, and there is increasing evidence that the AHR plays an important role in cellular homeostasis and disease. The AHR is expressed in multiple tumor types, in cancer cell lines, and in tumors from animal models, and the function of the AHR has been determined by RNA interference, overexpression, and inhibition studies. With few exceptions, knockdown of the AHR resulted in decreased proliferation and/or invasion and migration of cancer cell lines, and in vivo studies in mice overexpressing the constitutively active AHR exhibited enhanced stomach and liver cancers, suggesting a pro-oncogenic role for the AHR. In contrast, loss of the AHR in transgenic mice that spontaneously develop colonic tumors and in carcinogen-induced liver tumors resulted in increased carcinogenesis, suggesting that the receptor may exhibit antitumorigenic activity prior to tumor formation. AHR ligands also either enhanced or inhibited tumorigenesis, and these effects were highly tumor specific, demonstrating that selective AHR modulators that exhibit agonist or antagonist activities represent an important new class of anticancer agents that can be directed against multiple tumors.

Antiandrogenic activity of humic substances

For long, natural organic matter (NOM) composed mainly of humic substances (HS) were regarded as inert in the ecosystems with respect to their possible chemical interaction with exposed organisms. However recently, NOM have been shown to elicit various adverse effects generally attributed to synthetic xenobiotics, including estrogenic effects translating into shifts of the gender ratios in populations. However, the anti/androgenic pathway was not yet evaluated. Here, we applied an anti/androgenic sensitive cell line MDA stably transfected with the firefly luciferase gene under transcriptional control of the androgen responsive element. With five out of twelve tested NOM preparations, particularly with soil and coal isolates, we identified a relatively high, concentration-dependent antiandrogenic effect. This appears to be the first study to show this endocrine disrupting pathway for a ubiquitous biogeochemical matrix, a potential activity which should not be neglected in forthcoming studies on synthetic endocrine disruptors in the environment.

Aryl hydrocarbon receptor (AHR)-active pharmaceuticals are selective AHR modulators in MDA-MB-468 and BT474 breast cancer cells

Leflunomide, flutamide, nimodipine, mexiletine, sulindac, tranilast, 4-hydroxytamoxifen, and omeprazole are pharmaceuticals previously characterized as aryl hydrocarbon receptor (AHR) agonists in various cell lines and animal models. In this study, the eight AHR-active pharmaceuticals were investigated in highly aggressive aryl hydrocarbon (Ah)-responsive BT474 and MDA-MB-468 breast cancer cell lines, and their effects on AHR protein, CYP1A1 (protein and mRNA), CYP1B1 (mRNA), and cell migration were determined. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) was used as a positive control. The AHR agonist activities of the pharmaceuticals depended on structure, response, and cell context. Most compounds induced one or more AHR-mediated responses in BT474 cells, whereas in Ah-responsive MDA-MB-468 cells effects of the AHR-active pharmaceuticals were highly variable. 4-Hydroxytamoxifen, mexiletine, and tranilast did not induce CYP1A1 in MDA-MB-468 cells; moreover, in combination with TCDD, mexiletine was a potent AHR antagonist, tranilast was a partial antagonist, and 4-hydroxytamoxifen also exhibited some AHR antagonist activity. Omeprazole and, to a lesser extent, sulindac and leflunomide were full and partial AHR agonists, respectively, in both breast cancer cell lines. These data indicate that the AHR-active pharmaceuticals are selective AHR modulators, and applications of these drugs for targeting the AHR must be confirmed by studies using the most relevant cell context.

The aryl hydrocarbon receptor mediates leflunomide-induced growth inhibition of melanoma cells

A novel role of the dihydroorotatedehydrogenase (DHODH) inhibitor leflunomide as a potential anti-melanoma therapy was recently reported (Nature 471:518-22, 2011). We previously reported that leflunomide strongly activates the transcriptional activity of the Aryl Hydrocarbon Receptor (AhR). We therefore tested whether the AhR regulates the anti-proliferative effects of leflunomide in melanoma. We first evaluated the expression of AhR in melanoma cells and found that AhR is highly expressed in A375 melanoma as well as in several other cancer cell types. To evaluate whether AhR plays a role in regulating the growth inhibitory effects of leflunomide in A375 cells, we generated a stable cell line from parental A375 cells expressing a doxycycline (DOX) inducible AhR shRNA. Using these cells in the absence or presence of DOX (normal AhR levels or AhR-knockdown, respectively) we found that the anti-proliferative effects of leflunomide, but not its metabolite A771726, were strongly dependent upon AhR expression. It has been well established that supplementation of cells with exogenous uridine completely rescues the anti-proliferative effects due to DHODH inhibition. Thus, we performed uridine rescue experiments in A375 cells to determine whether the anti-proliferative effects of leflunomide are solely due to DHODH inhibition as previously reported. Interestingly, saturating levels of uridine only modestly rescued A375 cells from the anti-proliferative effects of both leflunomide and A771726, indicating additional mechanism(s), apart from DHODH inhibition are responsible for the anti-proliferative effects of leflunomide in melanoma cells. Uridine also did not rescue MDA-MB-435S melanoma cell proliferation after leflunomide treatment. Our results reveal that the AhR is a molecular target of leflunomide and support the feasibility of the clinical application of leflunomide for treating melanoma. Furthermore, analysis of expression data from 967 cancer cell lines revealed that AhR is expressed in multiple different cancer types supporting the intriguing possibility of targeting the AhR for therapy in a number of cancers.