Omeprazole Inhibits Pancreatic Cancer Cell Invasion through a Nongenomic Aryl Hydrocarbon Receptor Pathway

The aryl hydrocarbon receptor: a rehabilitated target for therapeutic immune modulation

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor originally identified as the target mediating the toxic effects of environmental pollutants including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and dioxins. For years, AHR activation was actively avoided during drug development. However, the AHR was later identified as an important physiological regulator of the immune response. These findings triggered a paradigm shift that resulted in identification of the AHR as a regulator of both innate and adaptive immunity and outlined a pathway for its modulation by the diet, commensal flora and metabolism in the context of autoimmunity, cancer and infection. Moreover, the AHR was revealed as a candidate target for the therapeutic modulation of the immune response. Indeed, the first AHR-activating drug (tapinarof) was recently approved for the treatment of psoriasis. Clinical trials are underway to evaluate the effects of tapinarof and other AHR-targeting therapeutics in inflammatory diseases, cancer and infections. This Review outlines the molecular mechanism of AHR action, and describes how it regulates the immune response. We also discuss links to disease and AHR-targeting therapeutics that have been tested in past and ongoing clinical trials.

Naringenin Exhibits Antiglioma Activity Related to Aryl Hydrocarbon Receptor Activity and IL-6, CCL2, and TNF-α Expression

BACKGROUND

Glioblastoma (GBM) is a highly aggressive brain tumor characterized by rapid cell proliferation, invasive behavior, and chemoresistance. The aryl hydrocarbon receptor (AhR) is implicated in chemoresistance and immune evasion, making it a promising therapeutic target. Natural compounds such as flavonoids have gained attention for their anti-inflammatory, antioxidant, and anticancer properties. Among them, naringenin, a citrus-derived flavonoid, exerts antiproliferative, pro-apoptotic, and immunomodulatory effects.

OBJECTIVES

This study investigated the antiglioma effects of the flavonoid naringenin on the viability, growth, and migration of glioma cells and its potential role as an AhR modulator.

METHODS

Human (U87) and rat (C6) glioma cell lines were exposed to naringenin (10-300 µM) alone or in combination with the AhR agonist indole-3-carbinol (50 µM) for 24 to 48 h. Cell viability, scratch wound, and cell migration assays were performed. The expression of inflammatory markers was also analyzed by RT-qPCR.

RESULTS

Naringenin exerted dose- and time-dependent inhibition of cell viability and migration. The treatment decreased the gene expression of interleukin-6 (IL-6) and chemokine (CCL2), alongside increased tumor necrosis factor-alpha (TNF-α) expression, an effect reversed by the AhR agonist.

CONCLUSIONS

These findings highlight naringenin's potential as an antiglioma agent and its role in AhR signaling.

Aryl Hydrocarbon Receptor Knockout Accelerates PanIN Formation and Fibro-Inflammation in a Mutant Kras -Driven Pancreatic Cancer Model

OBJECTIVES

The pathogenesis of pancreas cancer (PDAC) remains poorly understood, hindering efforts to develop a more effective therapy for PDAC. Recent discoveries show the aryl hydrocarbon receptor (AHR) plays a crucial role in the development of several cancers and can be targeted for therapeutic effect. However, its involvement in the pathogenesis of PDAC remains unclear. To address this gap, we evaluated the role of AHR in the development of PDAC precancerous lesions in vivo .

MATERIALS AND METHODS

We created a global AHR-null, mutant Kras -driven PDAC mouse model (A -/- KC) and evaluated the changes in PDAC precursor lesion formation (PanIN-1, 2, and 3) and associated fibro-inflammation between KC and A -/- KC at 5 months of age. We then examined the changes in the immune microenvironment followed by single-cell RNA-sequencing analysis to evaluate concomitant transcriptomic changes.

RESULTS

We identified a significant increase in PanIN-1 lesion formation and PanIN-1 associated fibro-inflammatory infiltrate in A -/- KC versus KC mice. This was associated with significant changes in the adaptive immune system, particularly a decrease in the CD4+/CD8+ T-cell ratio, as well as a decrease in the T-regulatory/Th17 T-cell ratio suggesting unregulated inflammation.

CONCLUSIONS

These findings show the loss of AHR results in heightened Kras -induced PanIN formation, through modulation of immune cells within the pancreatic tumor microenvironment.

The aryl hydrocarbon receptor as a tumor modulator: mechanisms to therapy

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that is widely recognized to play important, but complex, modulatory roles in a variety of tumor types. In this review, we comprehensively summarize the increasingly controversial role of AhR as a tumor regulator and the mechanisms by which it alters tumor progression based on the cancer cell type. Finally, we discuss new and emerging strategies to therapeutically modulate AhR, focusing on novel agents that hold promise in current human clinical trials as well as existing FDA-approved drugs that could potentially be repurposed for cancer therapy.

Targeting aryl hydrocarbon receptor to prevent cancer in barrier organs

The skin, lung, and gut are important barrier organs that control how the body reacts to environmental stressors such as ultraviolet (UV) radiation, air pollutants, dietary components, and microorganisms. The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that plays an important role in maintaining homeostasis of barrier organs. AhR was initially discovered as a receptor for environmental chemical carcinogens such as polycyclic aromatic hydrocarbons (PAHs). Activation of AhR pathways by PAHs leads to increased DNA damage and mutations which ultimately lead to carcinogenesis. Ongoing evidence reveals an ever-expanding role of AhR. Recently, AhR has been linked to immune systems by the interaction with the development of natural killer (NK) cells, regulatory T (Treg) cells, and T helper 17 (Th17) cells, as well as the production of immunosuppressive cytokines. However, the role of AhR in carcinogenesis is not as straightforward as we initially thought. Although AhR activation has been shown to promote carcinogenesis in some studies, others suggest that it may act as a tumor suppressor. In this review, we aim to explore the role of AhR in the development of cancer that originates from barrier organs. We also examined the preclinical efficacy data of AhR agonists and antagonists on carcinogenesis to determine whether AhR modulation can be a viable option for cancer chemoprevention.

The Role of Endocrine Disruption Chemical-Regulated Aryl Hydrocarbon Receptor Activity in the Pathogenesis of Pancreatic Diseases and Cancer

The aryl hydrocarbon receptor (AHR) serves as a ligand-activated transcription factor crucial for regulating fundamental cellular and molecular processes, such as xenobiotic metabolism, immune responses, and cancer development. Notably, a spectrum of endocrine-disrupting chemicals (EDCs) act as agonists or antagonists of AHR, leading to the dysregulation of pivotal cellular and molecular processes and endocrine system disruption. Accumulating evidence suggests a correlation between EDC exposure and the onset of diverse pancreatic diseases, including diabetes, pancreatitis, and pancreatic cancer. Despite this association, the mechanistic role of AHR as a linchpin molecule in EDC exposure-related pathogenesis of pancreatic diseases and cancer remains unexplored. This review comprehensively examines the involvement of AHR in EDC exposure-mediated regulation of pancreatic pathogenesis, emphasizing AHR as a potential therapeutic target for the pathogenesis of pancreatic diseases and cancer.

Potential AhR-independent mechanisms of 2,3,7,8-Tetrachlorodibenzo-p-dioxin inhibition of human glioblastoma A172 cells migration

The toxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is generally believed to be mediated by aryl hydrocarbon receptor (AhR), but some evidence suggests that the effects of TCDD can also be produced through AhR-independent mechanisms. In previous experiments, we found that mainly AhR-dependent mechanism was involved in the migration inhibition of glioblastoma U87 cells by TCDD. Due to the heterogeneity of glioblastomas, not all tumor cells have significant AhR expression. The effects and mechanisms of TCDD on the migration of glioblastomas with low AhR expression are still unclear. We employed a glioblastoma cell line A172 with low AhR expression as a model, using wound healing and Transwell® assay to detect the effect of TCDD on cell migration. We found that TCDD can inhibit the migration of A172 cells without activating AhR signaling pathway. Further, after being pre-treated with AhR antagonist CH223191, the inhibition of TCDD on A172 cells migration was not changed, indicating that the effect of TCDD on A172 cells is not dependent on AhR activation. By transcriptome sequencing analysis, we propose dysregulation of the expression of certain migration-related genes, such as IL6, IL1B, CXCL8, FOS, SYK, and PTGS2 involved in cytokines, MAPK, NF-κB, and IL-17 signaling pathways, as potential AhR-independent mechanisms that mediate the inhibition of TCDD migration in A172 cells.

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.

The Role of Microbiota in Pancreatic Cancer

Pancreatic cancer (PC) has an unfavorable prognosis with few effective therapeutic options. This has led researchers to investigate the possible links between microbiota and PC. A disrupted gut microbiome can lead to chronic inflammation, which is involved in the pathogenesis of PC. In addition, some bacterial strains can produce carcinogens that promote the growth of cancer cells. Research has also focused on pancreatic and oral microbiota. Changes in these microbiota can contribute to the development and progression of PC. Furthermore, patients with periodontal disease have an increased risk of developing PC. The potential use of microbiota as a prognostic marker or to predict patients' responses to chemotherapy or immunotherapy is also being explored. Overall, the role of microbiota-including the gut, pancreatic, and oral microbiota-in PC is an active research area. Understanding these associations could lead to new diagnostic and therapeutic targets for this deadly disease.

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.

Aryl hydrocarbon receptor knockout accelerates PanIN formation and fibro-inflammation in a mutant Kras-driven pancreatic cancer model

Objectives

The pathogenesis of pancreas cancer (PDAC) remains poorly understood, hindering efforts to develop a more effective therapy for PDAC. Recent discoveries show the aryl hydrocarbon receptor (AHR) plays a crucial role in the pathogenesis of several cancers, and can be targeted for therapeutic effect. However, its involvement in PDAC remains unclear. Therefore, we evaluated the role of AHR in the development of PDAC in vivo.

Methods

We created a global AHR-null, mutant Kras-driven PDAC mouse model (A-/-KC) and evaluated the changes in PDAC precursor lesion formation (Pan-IN 1, 2, and 3) and associated fibro-inflammation between KC and A-/-KC at 5 months of age. We then examined the changes in the immune microenvironment followed by single-cell RNA-sequencing analysis to evaluate concomitant transcriptomic changes.

Results

We found a significant increase in PanIN-1 lesion formation and PanIN-1 associated fibro-inflammatory infiltrate in A-/-KC vs KC mice. This was associated with significant changes in the adaptive immune system, particularly a decrease in the CD4+/CD8+ T-cell ratio, as well as a decrease in the T-regulatory/Th17 T-cell ratio suggesting unregulated inflammation.

Conclusion

These findings show the loss of AHR results in heightened Kras-induced PanIN formation, through modulation of immune cells within the pancreatic tumor microenvironment.

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.

Proposal to Consider Chemical/Physical Microenvironment as a New Therapeutic Off-Target Approach

The molecular revolution could lead drug discovery from chance observation to the rational design of new classes of drugs that could simultaneously be more effective and less toxic. Unfortunately, we are witnessing some failure in this sense, and the causes of the crisis involve a wide range of epistemological and scientific aspects. In pharmacology, one key point is the crisis of the paradigm the “magic bullet”, which is to design therapies based on specific molecular targets. Drug repurposing is one of the proposed ways out of the crisis and is based on the off-target effects of known drugs. Here, we propose the microenvironment as the ideal place to direct the off-targeting of known drugs. While it has been extensively investigated in tumors, the generation of a harsh microenvironment is also a phenotype of the vast majority of chronic diseases. The hostile microenvironment, on the one hand, reduces the efficacy of both chemical and biological drugs; on the other hand, it dictates a sort of “Darwinian” selection of those cells armed to survive in such hostile conditions. This opens the way to the consideration of the microenvironment as a convenient target for pharmacological action, with a clear example in proton pump inhibitors.

Omeprazole suppresses aggressive cancer growth and metastasis in mice through promoting Snail degradation

Omeprazole is a proton pump inhibitor that has recently been reported to exhibit anticancer activity against several types of cancer. However, the anticancer mechanisms of omeprazole remain elusive. Snail is an oncogenic zinc finger transcription factor; aberrant activation of Snail is associated with the occurrence and progression of cancer. In this study, we investigated whether Snail acted as a direct anticancer target of omeprazole. We showed that omeprazole displayed a high binding-affinity to recombinant Snail protein (K_d = 0.076 mM), suggesting that omeprazole directly and physically binds to the Snail protein. We further revealed that omeprazole disrupted CREB-binding protein (CBP)/p300-mediated Snail acetylation and then promoted Snail degradation through the ubiquitin-proteasome pathway in HCT116 cells. Omeprazole treatment markedly suppressed Snail-driven epithelial-mesenchymal transition (EMT) in aggressive HCT116, SUM159, and 4T1 cancer cells in vitro and reduced EMT-associated tumor invasion and metastasis in cancer cell xenograft models. Omeprazole also inhibited tumor growth by limiting Snail-dependent cell cycle progression. Overall, this study, for the first time, identifies Snail as a target of omeprazole and reveals a novel mechanism underlying the therapeutic effects of omeprazole against cancer. This study strongly suggests that omeprazole may be an excellent auxiliary drug for treating patients with malignant tumors.

Hypothesis: Emerging Roles for Aryl Hydrocarbon Receptor in Orchestrating CoV-2-Related Inflammation

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is the pathogenic agent of Coronavirus-Induced Disease-2019 (COVID-19), a multi-organ syndrome which primarily targets the respiratory system. In this review, considering the large amount of data pointing out the role of the Aryl hydrocarbon Receptor (AhR) in the inflammatory response and in the modulation of innate and adaptive immunity, we describe some mechanisms that strongly suggest its involvement in the management of COVID-19′s inflammatory framework. It regulates both the expression of Angiotensin Converting Enzyme-2 (ACE-2) and its stabilizing partner, the Broad neutral Amino acid Transporter 1 (B⁰AT1). It induces Indolamine 2,3 dioxygenase (IDO-1), the enzyme which, starting from Tryptophan (Trp), produces Kynurenine (Kyn, Beta-Anthraniloyl-L-Alanine). The accumulation of Kyn and the depletion of Trp arrest T cell growth and induce apoptosis, setting up an immune-tolerant condition, whereas AhR and interferon type I (IFN-I) build a mutual inhibitory loop that also involves NF-kB and limits the innate response. AhR/Kyn binding boosts the production of Interleukin-6 (IL-6), thus reinforcing the inflammatory state and counteracting the IDO-dependent immune tolerance in the later stage of COVID-19. Taken together, these data depict a framework where sufficient clues suggest the possible participation of AhR in the management of COVID-19 inflammation, thus indicating an additional therapeutic target for this disease.

Esomeprazole alleviates fibrosis in systemic sclerosis by modulating AhR/Smad2/3 signaling

Systemic sclerosis (SSc) is a connective tissue disease with the involvement of complex signaling pathways, such as TGF-β/Smad2/3. SSc can lead to severe multiple organ fibrosis, but no effective therapy is currently available because of its unclear pathogenesis. Exploring new treatments is the focus of recent research on SSc. Recent studies have implied a potential antifibrotic role of esomeprazole (ESO), but with currently unidentified mechanisms. Signaling of AhR, a ligand-dependent transcription factor, has been described as a key controller of fibrosis, tumorigenesis, and immune balance. Recently, it has been reported that ESO may be an exogenous agonist of AhR signaling, while no previous study has revealed the effects of ESO on SSc and its underlying mechanisms. In this study, we demonstrate that ESO suppresses the migration of SSc dermal fibroblasts, downregulates profibrotic markers, including COLIA1, α-SMA CTGF and MMP1, and limits collagen production potentially via the activation of AhR signaling. More importantly, ESO could block Smad2/3 phosphorylation concurrently with the reduction in collagen via AhR signaling. Moreover, our results from the bleomycin (BLM)-induced SSc model in skin and lung shows that ESO ameliorates fibrosis in vivo, which in keeping with our in vitro results. We conclude that ESO is a potential therapeutic drug for SSc fibrosis.

IDO1/TDO dual inhibitor RY103 targets Kyn-AhR pathway and exhibits preclinical efficacy on pancreatic cancer

Indoleamine 2,3-dioxygenase 1 (IDO1) catalyzing the conversion of tryptophan (Trp) to kynurenine (Kyn) in kynurenine pathway (KP) is involved in the immunosuppression in pancreatic cancer (PC), but the value of IDO1 as an independent prognostic marker for PC is uncertain. Moreover, the correlation between tryptophan 2,3-dioxygenase (TDO), an isozyme of IDO1, and PC is largely unknown. Using TCGA database, the correlation between IDO1 and/or TDO expression and PC patients' survival was analyzed. The expressions of IDO1 and TDO in PC cells and PC mice were examined. The effects of IDO1, TDO or dual inhibition on IDO1 and TDO effector pathway (Aryl hydrocarbon receptor, AhR) and on migration and invasion of PC cells were investigated. The block effect of IDO1/TDO dual inhibitor RY103 on KP was evaluated. The preclinical efficacy of RY103 and its immunomodulatory effect on KPIC orthotopic PC mice and Pan02 tumor-bearing mice were explored. Results showed that IDO1/TDO co-expression is an independent prognostic marker for PC. RY103 can significantly block KP and target Kyn-AhR pathway to blunt the migration and invasion of PC cells, exhibit preclinical efficacy and ameliorate IDO1/TDO-mediated immunosuppression in PC mice.

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.

Effect of the acid suppressor omeprazole on the proliferation, migration, invasion and cell cycle of esophageal squamous cell carcinoma cells via the aryl hydrocarbon receptor pathway

Esophageal cancer is a malignant tumor type with one of the highest mortality rates worldwide. The aryl hydrocarbon receptor (AHR), which has been investigated in recent years, has been confirmed to be associated with the occurrence and development of esophageal cancer. AHR has a variety of different ligands, which regulate its activity following binding. The widely known acid inhibitor omeprazole (OME) also affects AHR and its downstream proteins (such as the cytochrome P450 family) by non-ligand binding; however, the mechanisms have remained to be fully elucidated. Therefore, the aim of the present study was to investigate the role of OME in esophageal squamous cell carcinoma (ESCC), whether the mechanism proceeds via the AHR pathway and how OME regulates AHR to affect the occurrence and development of esophageal carcinoma. The AHR-selective regulator OME was used to treat the ESCC cell lines TE1 and KYSE150. Western blot analysis was used to verify the effect of OME on AHR and proliferating cell nuclear antigen (PCNA) protein expression levels, while Cell Counting Kit (CCK)-8, wound-healing and Transwell assays were used to determine the proliferation, migration and invasion of the ESCCs, respectively, following treatment with OME. In addition, flow cytometry was used to investigate the cell cycle distribution of the ESCCs following incubation with OME. AHR was highly expressed in the ESCCs and following treatment with OME, the protein expression levels of AHR and PCNA were downregulated. The CCK-8 assay indicated that the proliferation of the ESCCs was also reduced following treatment with OME. Furthermore, flow cytometry revealed a notable block of the cells in G₁/G₀ phase, while the results of the wound-healing and Transwell assays respectively suggested that cell migration and invasion were reduced. In conclusion, OME inhibited the proliferation, migration and invasion of ESCC cells and blocked the cell cycle via the AHR pathway, which may provide a therapeutic effect on esophageal squamous cell cancer.

AhR and Cancer: From Gene Profiling to Targeted Therapy

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that has been shown to be an essential regulator of a broad spectrum of biological activities required for maintaining the body’s vital functions. AhR also plays a critical role in tumorigenesis. Its role in cancer is complex, encompassing both pro- and anti-tumorigenic activities. Its level of expression and activity are specific to each tumor and patient, increasing the difficulty of understanding the activating or inhibiting roles of AhR ligands. We explored the role of AhR in tumor cell lines and patients using genomic data sets and discuss the extent to which AhR can be considered as a therapeutic target.

Environmental chemicals, breast cancer progression and drug resistance

Breast cancer (BC) is one of the most common causes of cancer in the world and the second leading cause of cancer deaths among women. Mortality is associated mainly with the development of metastases. Identification of the mechanisms involved in metastasis formation is, therefore, a major public health issue. Among the proposed risk factors, chemical environment and pollution are increasingly suggested to have an effect on the signaling pathways involved in metastatic tumor cells emergence and progression. The purpose of this article is to summarize current knowledge about the role of environmental chemicals in breast cancer progression, metastasis formation and resistance to chemotherapy. Through a scoping review, we highlight the effects of a wide variety of environmental toxicants, including persistent organic pollutants and endocrine disruptors, on invasion mechanisms and metastatic processes in BC. We identified the epithelial-to-mesenchymal transition and cancer-stemness (the stem cell-like phenotype in tumors), two mechanisms suspected of playing key roles in the development of metastases and linked to chemoresistance, as potential targets of contaminants. We discuss then the recently described pro-migratory and pro-invasive Ah receptor signaling pathway and conclude that his role in BC progression is still controversial. In conclusion, although several pertinent pathways for the effects of xenobiotics have been identified, the mechanisms of actions for multiple other molecules remain to be established. The integral role of xenobiotics in the exposome in BC needs to be further explored through additional relevant epidemiological studies that can be extended to molecular mechanisms.

Aryl hydrocarbon receptors as potential therapeutic targets

Aryl hydrocarbon receptors (AhR) are regulators of the expression of cytochrome P-450 isoforms, mediating a wide variety of the effects of substances from the endogenous or exogenous origin, including those produced from the microbiome. An exciting new aspect of their activity is their localization in the brain and their potential to modulate the action of the immune system. AhR is emerging as an essential toxicological and therapeutic target for neuromodulation. Further studies are needed for elucidating their utility as drug-targets.

Dopamine is an aryl hydrocarbon receptor agonist

Tryptophan metabolites exhibit aryl hydrocarbon receptor (AhR) agonist activity and recent studies show that the phenylalanine metabolites serotonin and carbidopa, a drug used in treating Parkinson's disease, activated the AhR. In this study, we identified the neuroactive hormone dopamine as an inducer of drug-metabolizing enzymes CYP1A1, CYP1B1, and UGT1A1 in colon and glioblastoma cells and similar results were observed for carbidopa. In contrast, carbidopa but not dopamine exhibited AhR activity in BxPC3 pancreatic cancer cells whereas minimal activity was observed for both compounds in Panc1 pancreatic cancer cells. In contrast with a previous report, the induction responses and cytotoxicity of carbidopa was observed only at high concentrations (100 µM) in BxPC3 cells. Our results show that similar to serotonin and several tryptophan metabolites, dopamine is also an AhR-active compound.

Aryl Hydrocarbon Receptor (AHR) Ligands as Selective AHR Modulators (SAhRMs)

The aryl hydrocarbon receptor (AhR) was first identified as the intracellular protein that bound and mediated the toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) and dioxin-like compounds (DLCs). Subsequent studies show that the AhR plays an important role in maintaining cellular homeostasis and in pathophysiology, and there is increasing evidence that the AhR is an important drug target. The AhR binds structurally diverse compounds, including pharmaceuticals, phytochemicals and endogenous biochemicals, some of which may serve as endogenous ligands. Classification of DLCs and non-DLCs based on their persistence (metabolism), toxicities, binding to wild-type/mutant AhR and structural similarities have been reported. This review provides data suggesting that ligands for the AhR are selective AhR modulators (SAhRMs) that exhibit tissue/cell-specific AhR agonist and antagonist activities, and that their functional diversity is similar to selective receptor modulators that target steroid hormone and other nuclear receptors.

Epigenetic Regulations of AhR in the Aspect of Immunomodulation

Environmental factors contribute to autoimmune disease manifestation, and as regarded today, AhR has become an important factor in studies of immunomodulation. Besides immunological aspects, AhR also plays a role in pharmacological, toxicological and many other physiological processes such as adaptive metabolism. In recent years, epigenetic mechanisms have provided new insight into gene regulation and reveal a new contribution to autoimmune disease pathogenesis. DNA methylation, histone modifications, chromatin alterations, microRNA and consequently non-genetic changes in phenotypes connect with environmental factors. Increasing data reveals AhR cross-roads with the most significant in immunology pathways. Although study on epigenetic modulations in autoimmune diseases is still not well understood, therefore future research will help us understand their pathophysiology and help to find new therapeutic strategies. Present literature review sheds the light on the common ground between remodeling chromatin compounds and autoimmune antibodies used in diagnostics. In the proposed review we summarize recent findings that describe epigenetic factors which regulate AhR activity and impact diverse immunological responses and pathological changes.

Omeprazole Inhibits Glioblastoma Cell Invasion and Tumor Growth

Background: The aryl hydrocarbon receptor (AhR) is expressed in gliomas and the highest staining is observed in glioblastomas. A recent study showed that the AhR exhibited tumor suppressor-like activity in established and patient-derived glioblastoma cells and genomic analysis showed that this was due, in part, to suppression of CXCL12, CXCR4 and MMP9. Methods: Selective AhR modulators (SAhRMs) including AhR-active pharmaceuticals were screened for their inhibition of invasion using a spheroid invasion assay in patient-derived AhR-expressing 15-037 glioblastoma cells and in AhR-silenced 15-037 cells. Invasion, migration and cell proliferation were determined using spheroid invasion, Boyden chambers and scratch assay, and XTT metabolic assays for cell growth. Changes in gene and gene product expression were determined by real-time PCR and Western blot assays, respectively. In vivo antitumorigenic activity of omeprazole was determined in SCID mice bearing subcutaneous patient-derived 15-037 cells. Results: Results of a screening assay using patient-derived 15-037 cells (wild-type and AhR knockout) identified the AhR-active proton pump inhibitor omeprazole as an inhibitor of glioblastoma cell invasion and migration only AhR-expressing cells but not in cells where the AhR was downregulated. Omeprazole also enhanced AhR-dependent repression of the pro-invasion CXCL12, CXCR4 and MMP9 genes, and interactions and effectiveness of omeprazole plus temozolomide were response-dependent. Omeprazole (100 mg/kg/injection) inhibited and delayed tumors in SCID mice bearing patient-derived 15-037 cells injected subcutaneously. Conclusion: Our results demonstrate that omeprazole enhances AhR-dependent inhibition of glioblastoma invasion and highlights a potential new avenue for development of a novel therapeutic mechanism-based approach for treating glioblastoma.

New Treatments in Renal Cancer: The AhR Ligands

Kidney cancer rapidly acquires resistance to antiangiogenic agents, such as sunitinib, developing an aggressive migratory phenotype (facilitated by c-Metsignal transduction). The Aryl hydrocarbon receptor (AhR) has recently been postulated as a molecular target for cancer treatment. Currently, there are two antitumor agent AhR ligands, with activity against renal cancer, that have been tested clinically: aminoflavone (AFP 464, NSC710464) and the benzothiazole (5F 203) prodrug Phortress. Our studies investigated the action of AFP 464, the aminoflavone pro-drug currently used in clinical trials, and 5F 203 on renal cancer cells, specifically examining their effects on cell cycle progression, apoptosis and cell migration. Both compounds caused cell cycle arrest and apoptosis but only 5F 203 potently inhibited the migration of TK-10, Caki-1 and SN12C cells as well as the migration signal transduction cascade, involving c-Met signaling, in TK-10 cells. Current investigations are focused on the development of nano-delivery vehicles, apoferritin-encapsulated benzothiazoles 5F 203 and GW610, for the treatment of renal cancer. These compounds have shown improved antitumor effects against TK-10 cells in vitro at lower concentrations compared with a naked agent.

Oncobiosis and Microbial Metabolite Signaling in Pancreatic Adenocarcinoma

Pancreatic adenocarcinoma is one of the most lethal cancers in both men and women, with a median five-year survival of around 5%. Therefore, pancreatic adenocarcinoma represents an unmet medical need. Neoplastic diseases, such as pancreatic adenocarcinoma, often are associated with microbiome dysbiosis, termed oncobiosis. In pancreatic adenocarcinoma, the oral, duodenal, ductal, and fecal microbiome become dysbiotic. Furthermore, the pancreas frequently becomes colonized (by Helicobacter pylori and Malassezia, among others). The oncobiomes from long- and short-term survivors of pancreatic adenocarcinoma are different and transplantation of the microbiome from long-term survivors into animal models of pancreatic adenocarcinoma prolongs survival. The oncobiome in pancreatic adenocarcinoma modulates the inflammatory processes that drive carcinogenesis. In this review, we point out that bacterial metabolites (short chain fatty acids, secondary bile acids, polyamines, indole-derivatives, etc.) also have a role in the microbiome-driven pathogenesis of pancreatic adenocarcinoma. Finally, we show that bacterial metabolism and the bacterial metabolome is largely dysregulated in pancreatic adenocarcinoma. The pathogenic role of additional metabolites and metabolic pathways will be identified in the near future, widening the scope of this therapeutically and diagnostically exploitable pathogenic pathway in pancreatic adenocarcinoma.

Tranilast induces MiR-200c expression through blockade of RelA/p65 activity in leiomyoma smooth muscle cells

OBJECTIVE

To determine the mechanism by which tranilast induces miR-200c expression in leiomyoma smooth muscle cells (LSMCs).

DESIGN

Experimental study.

SETTING

Academic research laboratory.

PATIENT(S)

Women undergoing hysterectomy for leiomyoma.

INTERVENTION(S)

Blockade of RelA/p65.

MAIN OUTCOME MEASURE(S)

Effects of tranilast and blockade of RelA/p65 on miR-200c expression.

RESULT(S)

Tranilast, an inflammation inhibitor, dose-dependently induced miR-200c in LSMCs and myometrium smooth muscle cells (MSMCs), with a more profound effect in LSMCs than in MSMCs. The treatment of LSMCs with Bay 117082, an inhibitor of IκB phosphorylation, further enhanced miR-200c induction by tranilast. The knockdown of RelA/p65 by small interfering RNA also induced miR-200c expression in LSMCs. Although tranilast had no effect on total RelA/p65 protein levels in LSMCs, it significantly induced RelA/p65 phosphorylation at S536 while reducing its activity as well as its nuclear translocation. ChIP assay indicated that tranilast reduces the binding ability of RelA/p65 to miR-200c promoter, resulting in miR-200c induction. Tranilast also inhibited interleukin-8 (IL8) expression in LSMCs. The induction of miR-200c by tranilast partially mediates the inhibitory effect of tranilast on the expression of IL8 and cyclin-dependent kinase 2 in LSMCs.

CONCLUSION(S)

Induction of miR-200c by tranilast in LSMCs is mediated through a transcriptional mechanism involving inhibition of the nuclear factor κB signaling pathway. These results highlight the significance of inflammation in the pathogenesis of leiomyoma and the potential utility of antiinflammatory drugs for treatment of leiomyomas.

New drugs are not enough‑drug repositioning in oncology: An update

Drug repositioning refers to the concept of discovering novel clinical benefits of drugs that are already known for use treating other diseases. The advantages of this are that several important drug characteristics are already established (including efficacy, pharmacokinetics, pharmacodynamics and toxicity), making the process of research for a putative drug quicker and less costly. Drug repositioning in oncology has received extensive focus. The present review summarizes the most prominent examples of drug repositioning for the treatment of cancer, taking into consideration their primary use, proposed anticancer mechanisms and current development status.

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.

Targeting Aryl hydrocarbon receptor for next-generation immunotherapies: Selective modulators (SAhRMs) versus rapidly metabolized ligands (RMAhRLs)

Aryl Hydrocarbon Receptor (AhR) constitutes a major network hub of genomic and non-genomic signaling pathways, connecting host's immune cells to environmental factors. It shapes innate and adaptive immune processes to environmental stimuli with species-, cell- and tissue-type dependent specificity. Although an ever increasing number of studies has thrust AhR into the limelight as attractive target for the development of next-generation immunotherapies, concerns exist on potential safety issues associated with small molecule modulation of the receptor. Selective AhR modulators (SAhRMs) and rapidly metabolized AhR ligands (RMAhRLs) are two classes of receptor agonists that are emerging as interesting lead compounds to bypass AhR-related toxicity in favor of therapeutic effects. In this article, we discuss SAhRMs and RMAhRLs reported in literature, covering concepts underlying their definitions, specific binding modes, structure-activity relationships and AhR-mediated functions.

The aryl hydrocarbon receptor is a tumor suppressor-like gene in glioblastoma

The aryl hydrocarbon receptor (AhR) plays an important role in maintaining cellular homeostasis and also in pathophysiology. For example, the interplay between the gut microbiome and microbially derived AhR ligands protects against inflammation along the gut-brain axis. The AhR and its ligands also inhibit colon carcinogenesis, but it has been reported that the AhR and its ligand kynurenine enhance glioblastoma (GBM). In this study, using both established and patient-derived GBM cells, we re-examined the role of kynurenine and the AhR in GBM, observing that kynurenine does not modulate AhR-mediated gene expression and does not affect invasion of GBM cells. Therefore, using an array of approaches, including ChIP, quantitative real-time PCR, and cell migration assays, we primarily focused on investigating the role of the AhR in GBM at the functional molecular and genomic levels. The results of transient and stable CRISPR/Cas9-mediated AhR knockdown in GBM cells indicated that loss of AhR enhances GBM tumor growth in a mouse xenograft model, increases GBM cell invasion, and up-regulates expression of pro-invasion/pro-migration genes, as determined by ingenuity pathway analysis of RNA-Seq data. We conclude that the AhR is a tumor suppressor-like gene in GBM; future studies are required to investigate whether the AhR could be a potential drug target for treating patients with GBM who express this receptor.

Dietary natural flavonoids treating cancer by targeting aryl hydrocarbon receptor

The role of aryl hydrocarbon receptor (AhR) as a ligand-activated transcription factor in the field of cancer has gradually been unveiled. A strong body of evidence indicated that AhR is implicated in cell proliferation and apoptosis, immune metabolism and other processes, which further affected tumor growth, survival, migration, and invasion. Therefore, AhR targeted therapy may become a new method for cancer treatment and provide a new direction for clinical tumor treatment. Astonishingly, the largest source of exposure of animals and humans to AhR ligands (synthetic and natural) comes from the diet. Myriad studies have described that various natural dietary chemicals can directly activate and/or inhibit the AhR signaling pathway. Of note, numerous natural products contribute to AhR active, of which dietary flavonoids are the largest class of natural AhR ligands. As interest in AhR and its ligands increases, it seems sensible to summarize current research on these ligands. In this review, we highlight the role of AhR in tumorigenesis and focus on the double effect of AhR in cancer therapy. We explored the molecular mechanism of AhR ligands on cancer through a few AhR agonists/antagonists currently in clinical practice. Ultimately, we summarize and highlight the latest progression of dietary flavonoids as AhR ligands in cancer inhibition, including the limitations and deficiencies of it in clinical research. This review will offer a comprehensive understanding of AhR and its dietary ligands which may dramatically pave the way for targeted cancer treatment.

Tetrandrine enhances the ubiquitination and degradation of Syk through an AhR-c-src-c-Cbl pathway and consequently inhibits osteoclastogenesis and bone destruction in arthritis

Recently, we reported that tetrandrine, a natural alkaloid, could inhibit the osteoclastogenesis and bone erosion through enhancing the ubiquitination and degradation of spleen tyrosine kinase (Syk). Herein, we addressed whether and how aryl hydrocarbon receptor (AhR) mediate the effect of tetrandrine. In vitro, tetrandrine was shown to repress RANKL-induced osteoclastogenesis and the expression of osteoclast-related marker genes, which was almost completely reversed by either AhR antagonist CH223191 or siRNA. In pre-osteoclasts, tetrandrine enhanced the ubiquitination and degradation of Syk through the AhR/c-src/c-Cbl signaling pathway, downregulated the expression of phospho-Syk and phospho-PLCγ2, and inhibited the nuclear translocation of NFATc1, a master transcription factor for osteoclastogenesis. Notably, tetrandrine acted through the non-genomic pathway of the ligand-activated AhR, as evidenced by the fact that the effect of tetrandrine did not change in the absence of AhR nuclear translocator. In collagen-induced arthritis rats, oral administration of tetrandrine decreased the number of phospho-Syk-positive cells and osteoclasts, and reduced the bone erosion in the areas of the proximal tibial epiphysis excluding the cortical bone. A combined use with CH223191 almost abolished the effect of tetrandrine. These findings revealed that tetrandrine enhanced the ubiquitination and degradation of Syk and consequently repressed the osteoclastogenesis and bone destruction through the AhR-c-src-c-Cbl pathway.

An Increased Level of Aryl Hydrocarbon Receptor in Patients with Pancreatic Cancer

BACKGROUND Aryl-carbon receptor (AhR), a ligand-activated transcription factor, is best known for its ability to mediate the effects of environmental toxins such as 2,3,7,8-tetrachlorodibenzo-p-dioxin. AhR is expressed in several tumor cells and regulates the expression of genes in the signal transduction pathways. In this study, we examined the soluble levels of AhR in patients with pancreatic cancer. METHODS 123 samples, including 59 (48%) samples of pancreatic ductal adenocarcinoma based on histological evidence and 64 (52%) healthy control samples, were evaluated to determine plasma levels of AhR by Enzyme-linked immunoassay. RESULTS The median of AhR among patients was 0.280 ng/mL, which differed considerably from 0.07 ng/mL in the control group (p < 0.001). Significant differences of the AhR were observed between the plasma samples of the patients compared with the healthy group, with respect to male sex (p < 0.001), age groups (p = 0.001), diabetic status (p < 0.001), body mass index (BMI) categories (p = 0.035), and constantly smokers (p < 0.001). We also observed significant differences between the level of AhR expression between men and women (p = 0.01) and ever to never smokers (p = 0.009) in the case group. In addition, the age of 65 and a BMI of 25 or less were significant factors in plasma AhR levels ([1.61 95%CI 1.08-2.38] and [1.84 95%CI 1.22-2.77], respectively). CONCLUSION The results of this study can add diagnostic information to pancreatic cancer involving AhR and the potential efficacy of this receptor in therapeutic strategies.

A one-pot metal-free protocol for the synthesis of chalcogenated furans from 1,4-enediones and thiols

Transition-metal-free synthesis of chalcogenated furans through the sequential thiol-Michael/Paal–Knorr reaction of 1,4-enediones in the presence of a catalytic amount of p-toluene sulfonic acid has been developed.

Systems Oncology: Bridging Pancreatic and Castrate Resistant Prostate Cancer

Large investments by pharmaceutical companies in the development of new antineoplastic drugs have not been resulting in adequate advances of new therapies. Despite the introduction of new methods, technologies, translational medicine and bioinformatics, the usage of collected knowledge is unsatisfactory. In this paper, using examples of pancreatic ductal adenocarcinoma (PaC) and castrate-resistant prostate cancer (CRPC), we proposed a concept showing that, in order to improve applicability of current knowledge in oncology, the re-clustering of clinical and scientific data is crucial. Such an approach, based on systems oncology, would include bridging of data on biomarkers and pathways between different cancer types. Proposed concept would introduce a new matrix, which enables combining of already approved therapies between cancer types. Paper provides a (a) detailed analysis of similarities in mechanisms of etiology and progression between PaC and CRPC, (b) diabetes as common hallmark of both cancer types and (c) knowledge gaps and directions of future investigations. Proposed horizontal and vertical matrix in cancer profiling has potency to improve current antineoplastic therapy efficacy. Systems biology map using Systems Biology Graphical Notation Language is used for summarizing complex interactions and similarities of mechanisms in biology of PaC and CRPC.

Regulation of the Immune Response by the Aryl Hydrocarbon Receptor

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that is activated by small molecules provided by the diet, microorganisms, metabolism, and pollutants. AhR is expressed by a number of immune cells, and thus AhR signaling provides a molecular pathway that integrates the effects of the environment and metabolism on the immune response. Studies have shown that AhR signaling plays important roles in the immune system in health and disease. As its activity is regulated by small molecules, AhR also constitutes a potential target for therapeutic immunomodulation. In this review we discuss the role of AhR in the regulation of the immune response in the context of autoimmunity, infection, and cancer, as well as the potential opportunities and challenges of developing AhR-targeted therapeutics.

Inhibition of pancreatic cancer Panc1 cell migration by omeprazole is dependent on aryl hydrocarbon receptor activation of JNK

Several aryl hydrocarbon receptor (AhR)-active pharmaceuticals were screened as inhibitors of pancreatic cancer cell invasion and identified two compounds, omeprazole, that inhibited invasion. Inhibition of highly invasive Panc1 cell invasion by omeprazole involves an AhR-dependent non-genomic pathway, and omeprazole-mediated inhibition of Panc1 cell invasion was dependent on Jun-N-terminal kinase (JNK) and mitogen-activated kinase kinase 7 (MKK7). The failure of omeprazole to induce nuclear translocation of the AhR was not due to overexpression of cytosolic AhR partner proteins Hsp90 or XAP2, and results of DNA sequencing show that the AhR expressed in Panc1 cells was not mutated. Results of RNAseq studies indicate that omeprazole induced an AhR-dependent downregulation of several pro-invasion factors including activated leukocyte cell adhesion molecule (ALCAM), long chain fatty acid CoA-synthase (CSL4), stathmin 3 (STMN3) and neuropillin 2 (NRP2), and the specific functions of these genes are currently being investigated.

Towards Resolving the Pro- and Anti-Tumor Effects of the Aryl Hydrocarbon Receptor

We have postulated that the aryl hydrocarbon receptor (AHR) drives the later, more lethal stages of some cancers when chronically activated by endogenous ligands. However, other studies have suggested that, under some circumstances, the AHR can oppose tumor aggression. Resolving this apparent contradiction is critical to the design of AHR-targeted cancer therapeutics. Molecular (siRNA, shRNA, AHR repressor, CRISPR-Cas9) and pharmacological (AHR inhibitors) approaches were used to confirm the hypothesis that AHR inhibition reduces human cancer cell invasion (irregular colony growth in 3D Matrigel cultures and Boyden chambers), migration (scratch wound assay) and metastasis (human cancer cell xenografts in zebrafish). Furthermore, these assays were used for a head-to-head comparison between AHR antagonists and agonists. AHR inhibition or knockdown/knockout consistently reduced human ER⁻/PR⁻/Her2⁻ and inflammatory breast cancer cell invasion, migration, and metastasis. This was associated with a decrease in invasion-associated genes (e.g., Fibronectin, VCAM1, Thrombospondin, MMP1) and an increase in CDH1/E-cadherin, previously associated with decreased tumor aggression. Paradoxically, AHR agonists (2,3,7,8-tetrachlorodibenzo-p-dioxin and/or 3,3′-diindolylmethane) similarly inhibited irregular colony formation in Matrigel and blocked metastasis in vivo but accelerated migration. These data demonstrate the complexity of modulating AHR activity in cancer while suggesting that AHR inhibitors, and, under some circumstances, AHR agonists, may be useful as cancer therapeutics.

Suppression of aberrant choroidal neovascularization through activation of the aryl hydrocarbon receptor

The aryl hydrocarbon receptor (AhR) is a ligand activated transcription factor, initially discovered for its role in regulating xenobiotic metabolism. There is extensive evidence supporting a multi-faceted role for AhR, modulating physiological pathways important in cell health and disease. Recently we demonstrated that the AhR plays a role in the pathogenesis of age-related macular degeneration (AMD), the leading cause of vision loss in the elderly. We found that loss of AhR exacerbates choroidal neovascular (CNV) lesion formation in a murine model. Herein we tested the therapeutic impact of AhR activation on CNV lesion formation and factors associated with aberrant neovascularization. We screened a panel of synthetic drugs and endogenous AhR ligands, assessed their ability to activate AhR in choroidal endothelial cells, and inhibit angiogenesis in vitro. Drugs with an anti-angiogenic profile were then administered to a murine model of CNV. Two compounds, leflunomide and flutamide, significantly inhibited CNV formation concurrent with positive modifying effects on angiogenesis, inflammation, extracellular matrix remodeling, and fibrosis. These results validate the role of the AhR pathway in regulating CNV pathogenesis, identify mechanisms of AhR-based therapies in the eye, and argue in favor of developing AhR as a drug target for the treatment of neovascular AMD.

Investigation of the aryl hydrocarbon receptor and the intrinsic tumoral component of the kynurenine pathway of tryptophan metabolism in primary brain tumors

INTRODUCTION

There is mounting evidence supporting the role of tryptophan metabolism via the kynurenine pathway (KP) in the pathogenesis of primary brain tumors. Under normal physiological conditions, the KP is the major catabolic pathway for the essential amino acid tryptophan. However, in cancer cells, the KP becomes dysregulated, depletes local tryptophan, and contributes to an immunosuppressive tumor microenvironment.

METHODS

We examined the protein expression levels (in 73 gliomas and 48 meningiomas) of the KP rate-limiting enzymes indoleamine 2,3-dioxygenase (IDO) 1, IDO2, and tryptophan 2,3-dioxygenase (TDO2), as well as, the aryl hydrocarbon receptor (AhR), a carcinogenic transcription factor activated by KP metabolites. In addition, we utilized commercially available small-molecules to pharmacologically modulate IDO1, IDO2, TDO2, and AhR in patient-derived glioma and meningioma cell lines (n = 9 each).

RESULTS

We observed a positive trend between the grade of the tumor and the average immunohistochemical staining score for IDO1, IDO2, and TDO2, with TDO2 displaying the strongest immunostaining. AhR immunostaining was present in all grades of gliomas and meningiomas, with the greatest staining intensity noted in glioblastomas. Immunocytochemical staining showed a positive trend between nuclear localization of AhR and histologic grade in both gliomas and meningiomas, suggesting increased AhR activation with higher tumor grade. Unlike enzyme inhibition, AhR antagonism markedly diminished patient-derived tumor cell viability, regardless of tumor type or grade, following in vitro drug treatments.

CONCLUSIONS

Collectively, these results suggest that AhR may offer a novel and robust therapeutic target for a patient population with highly limited treatment options.

Rethinking the Combination of Proton Exchanger Inhibitors in Cancer Therapy

Microenvironmental acidity is becoming a key target for the new age of cancer treatment. In fact, while cancer is characterized by genetic heterogeneity, extracellular acidity is a common phenotype of almost all cancers. To survive and proliferate under acidic conditions, tumor cells up-regulate proton exchangers and transporters (mainly V-ATPase, Na⁺/H⁺ exchanger (NHE), monocarboxylate transporters (MCTs), and carbonic anhydrases (CAs)), that actively extrude excess protons, avoiding intracellular accumulation of toxic molecules, thus becoming a sort of survival option with many similarities compared with unicellular microorganisms. These systems are also involved in the unresponsiveness or resistance to chemotherapy, leading to the protection of cancer cells from the vast majority of drugs, that when protonated in the acidic tumor microenvironment, do not enter into cancer cells. Indeed, as usually occurs in the progression versus malignancy, resistant tumor clones emerge and proliferate, following a transient initial response to a therapy, thus giving rise to more malignant behavior and rapid tumor progression. Recent studies are supporting the use of a cocktail of proton exchanger inhibitors as a new strategy against cancer.

Carbidopa: a selective Ah receptor modulator (SAhRM)

The aryl hydrocarbon receptor (AhR) was discovered as the intracellular receptor that bound with high affinity to the environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and the AhR is required for mediating the toxicity induced by TCDD. Subsequent studies show that the AhR binds structurally diverse chemicals including plant-derived compounds that promote health and several AhR-active pharmaceuticals that exhibit anticancer activity. In this issue, there is a report that carbidopa, a drug used for treating Parkinson's disease, is also an AhR ligand, and this compound inhibits pancreatic cancer cell and tumor growth. These results are consistent with activities of other AhR-active compounds that inhibit carcinogenesis. Like carbidopa, these chemicals are selective AhR modulators with potential clinical applications that are AhR-dependent.

Carbidopa is an activator of aryl hydrocarbon receptor with potential for cancer therapy

Carbidopa is used with l-DOPA (l-3,4-dihydroxyphenylalanine) to treat Parkinson's disease (PD). PD patients exhibit lower incidence of most cancers including pancreatic cancer, but with the notable exception of melanoma. The decreased cancer incidence is not due to l-DOPA; however, the relevance of Carbidopa to this phenomenon has not been investigated. Here, we tested the hypothesis that Carbidopa, independent of l-DOPA, might elicit an anticancer effect. Carbidopa inhibited pancreatic cancer cell proliferation both in vitro and in vivo. Based on structural similarity with phenylhydrazine, an inhibitor of indoleamine-2,3-dioxygenase-1 (IDO1), we predicted that Carbidopa might also inhibit IDO1, thus providing a molecular basis for its anticancer effect. The inhibitory effect was confirmed using human recombinant IDO1. To demonstrate the inhibition in intact cells, AhR (aryl hydrocarbon receptor) activity was monitored as readout for IDO1-mediated generation of the endogenous AhR agonist kynurenine in pancreatic and liver cancer cells. Surprisingly, Carbidopa did not inhibit but instead potentiated AhR signaling, evident from increased CYP1A1 (cytochrome P450 family 1 subfamily A member 1), CYP1A2, and CYP1B1 expression. In pancreatic and liver cancer cells, Carbidopa promoted AhR nuclear localization. AhR antagonists blocked Carbidopa-dependent activation of AhR signaling. The inhibitory effect on pancreatic cancer cells in vitro and in vivo and the activation of AhR occurred at therapeutic concentrations of Carbidopa. Chromatin immunoprecipitation assay further confirmed that Carbidopa promoted AhR binding to its target gene CYP1A1 leading to its induction. We conclude that Carbidopa is an AhR agonist and suppresses pancreatic cancer. Hence, Carbidopa could potentially be re-purposed to treat pancreatic cancer and possibly other cancers as well.

Loss of NR2E3 represses AHR by LSD1 reprogramming, is associated with poor prognosis in liver cancer

The aryl hydrocarbon receptor (AHR) plays crucial roles in inflammation, metabolic disorder, and cancer. However, the molecular mechanisms regulating AHR expression remain unknown. Here, we found that an orphan nuclear NR2E3 maintains AHR expression, and forms an active transcriptional complex with transcription factor Sp1 and coactivator GRIP1 in MCF-7 human breast and HepG2 liver cancer cell lines. NR2E3 loss promotes the recruitment of LSD1, a histone demethylase of histone 3 lysine 4 di-methylation (H3K4me2), to the AHR gene promoter region, resulting in repression of AHR expression. AHR expression and responsiveness along with H3K4me2 were significantly reduced in the livers of Nr2e3^rd7 (Rd7) mice that express low NR2E3 relative to the livers of wild-type mice. SP2509, an LSD1 inhibitor, fully restored AHR expression and H3K4me2 levels in Rd7 mice. Lastly, we demonstrated that both AHR and NR2E3 are significantly associated with good clinical outcomes in liver cancer. Together, our results reveal a novel link between NR2E3, AHR, and liver cancer via LSD1-mediated H3K4me2 histone modification in liver cancer development.

Repositioning of proton pump inhibitors in cancer therapy

Drug repositioning, as a smart way to exploit new molecular targets of a known drug, has been gaining increasing attention in the discovery of anti-cancer drugs. Proton pump inhibitors (PPIs) as benzimidazole derivatives, which are essentially H⁺-K⁺-ATPases inhibitors, are commonly used in the treatment of acid-related diseases such as gastric ulcer. In recent years, exploring the new application of PPIs in anti-cancer field has become a hot research topic. Interestingly, cancer cells display an alkaline intracellular pH and an acidic extracellular pH. The extracellular acidity of tumors can be corrected by PPIs that are selectively activated in an acid milieu. It is generally believed that PPIs might provoke disruption of pH homeostasis by targeting V-ATPase on cancer cells, which is the theoretical basis for PPIs to play an anti-cancer role. Numerous studies have shown specialized effects of the PPIs on tumor cell growth, metastasis, chemoresistance, and autophagy. PPIs may really represent new anti-cancer drugs due to better safety and tolerance, the potential selectivity in targeting tumor acidity, and the ability to inhibit mechanism pivotal for cancer homeostasis. In this review, we focus on the new therapeutic applications of PPIs in multiple cancers, explaining the rationale behind this approach and providing practical evidence.

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.