The Aryl Hydrocarbon Receptor and Tumor Immunity

New Insights Into Gut-Bacteria-Derived Indole and Its Derivatives in Intestinal and Liver Diseases

The interaction between host and microorganism widely affects the immune and metabolic status. Indole and its derivatives are metabolites produced by the metabolism of tryptophan catalyzed by intestinal microorganisms. By activating nuclear receptors, regulating intestinal hormones, and affecting the biological effects of bacteria as signaling molecules, indole and its derivatives maintain intestinal homeostasis and impact liver metabolism and the immune response, which shows good therapeutic prospects. We reviewed recent studies on indole and its derivatives, including related metabolism, the influence of diets and intestinal commensal bacteria, and the targets and mechanisms in pathological conditions, especially progress in therapeutic strategies. New research insights into indoles will facilitate a better understanding of their druggability and application in intestinal and liver diseases.

Pharmacological blockage of the AHR-CYP1A1 axis: a call for in vivo evidence

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that can be activated by structurally diverse compounds arising from the environment and the microbiota and host metabolism. Expanding evidence has been shown that the modulation of the canonical pathway of AHR occurs during several chronic diseases and that its abrogation might be of clinical interest for metabolic and inflammatory pathological processes. However, most of the evidence on the pharmacological abrogation of the AHR-CYP1A1 axis has been reported in vitro, and therefore, guidance for in vivo studies is needed. In this review, we cover the state-of-the-art of the pharmacodynamic and pharmacokinetic properties of AHR antagonists and CYP1A1 inhibitors in different in vivo rodent (mouse or rat) models of disease. This review will serve as a road map for those researchers embracing this emerging therapeutic area targeting the AHR. Moreover, it is a timely opportunity as the first AHR antagonists have recently entered the clinical stage of drug development.

Monitoring of emerging contaminants of concern in the aquatic environment: a review of studies showing the application of effect-based measures

Water scarcity is increasingly a global cause of concern mainly due to widespread changes in climate conditions and increased consumptive water use driven by the exponential increase in population growth. In addition, increased pollution of fresh water sources due to rising production and consumption of pharmaceuticals and organic chemicals will further exacerbate this concern. Although surface water contamination by individual chemicals is often at very low concentration, pharmaceuticals for instance are designed to be efficacious at low concentrations, creating genuine concern for their presence in freshwater sources. Furthermore, the additive impact of multiple compounds may result in toxic or other biological effects that otherwise will not be induced by individual chemicals. Globally, different legislative frameworks have led to pre-emptive efforts which aim to ensure good water ecological status. Reports detailing the use and types of effect-based measures covering specific bioassay batteries that can identify specific mode of actions of chemical pollutants in the aquatic ecosystem to evaluate the real threat of pollutants to aquatic lives and ultimately human lives have recently emerged from monitoring networks such as the NORMAN network. In this review, we critically evaluate some studies within the last decade that have implemented effect-based monitoring of pharmaceuticals and organic chemicals in aquatic fauna, evaluating the occurrence of different chemical pollutants and the impact of these pollutants on aquatic fauna with special focus on pollutants that are contaminants of emerging concern (CEC) in urban wastewater. A critical discussion on studies that have used effect-based measures to assess biological impact of pharmaceutical/organic compound in the aquatic ecosystem and the endpoints measurements employed is presented. The application of effect-based monitoring of chemicals other than assessment of water quality status is also discussed.

Involvement of Kynurenine Pathway in Hepatocellular Carcinoma

Simple Summary

The kynurenine pathway (KP) is a biochemical pathway that synthesizes the vital coenzyme, nicotinamide adenine dinucleotide (NAD⁺). In cancer, the KP is significantly activated, leading to tryptophan depletion and the production of downstream metabolites, which skews the immune response towards tumour tolerance. More specifically, advanced stage cancers that readily metastasize evidence the most dysregulation in KP enzymes, providing a clear link between the KP and cancer morbidity. Consequently, this provides the rationale for an attractive new drug discovery opportunity for adjuvant therapeutics targeting KP-mediated immune tolerance, which would greatly complement current pharmacological interventions. In this review, we summarize recent developments in the roles of the KP and clinical trials examining KP inhibition in liver cancer.

Abstract

As the second and third leading cancer-related death in men and the world, respectively, primary liver cancer remains a major concern to human health. Despite advances in diagnostic technology, patients with primary liver cancer are often diagnosed at an advanced stage. Treatment options for patients with advanced hepatocarcinoma (HCC) are limited to systemic treatment with multikinase inhibitors and immunotherapy. Furthermore, the 5-year survival rate for these late-stage HCC patients is approximately 12% worldwide. There is an unmet need to identify novel treatment options and/or sensitive blood-based biomarker(s) to detect this cancer at an early stage. Given that the liver harbours the largest proportion of immune cells in the human body, understanding the tumour–immune microenvironment has gained increasing attention as a potential target to treat cancer. The kynurenine pathway (KP) has been proposed to be one of the key mechanisms used by the tumour cells to escape immune surveillance for proliferation and metastasis. In an inflammatory environment such as cancer, the KP is elevated, suppressing local immune cell populations and enhancing tumour growth. In this review, we collectively describe the roles of the KP in cancer and provide information on the latest research into the KP in primary liver cancer.

The aryl hydrocarbon receptor: A diagnostic and therapeutic target in glioma

Glioblastoma multiforme (GBM) is a deadly disease; 5-year survival rates have shown little improvement over the past 30 years. In vivo positron emission tomography (PET) imaging is an important method of identifying potential diagnostic and therapeutic molecular targets non-invasively. The aryl hydrocarbon receptor (AhR) is a transcription factor that regulates multiple genes involved in immune response modulation and tumorigenesis. The AhR is an attractive potential drug target and studies have shown that its activation by small molecules can modulate innate and adaptive immunity beneficially and prevent AhR-mediated tumour promotion in several cancer types. In this review, we provide an overview of the role of the AhR in glioma tumorigenesis and highlight its potential as an emerging biomarker for glioma therapies targeting the tumour immune response and PET diagnostics.

Immunosuppressive metabolites in tumoral immune evasion: redundancies, clinical efforts, and pathways forward

Tumors accumulate metabolites that deactivate infiltrating immune cells and polarize them toward anti-inflammatory phenotypes. We provide a comprehensive review of the complex networks orchestrated by several of the most potent immunosuppressive metabolites, highlighting the impact of adenosine, kynurenines, prostaglandin E2, and norepinephrine and epinephrine, while discussing completed and ongoing clinical efforts to curtail their impact. Retrospective analyses of clinical data have elucidated that their activity is negatively associated with prognosis in diverse cancer indications, though there is a current paucity of approved therapies that disrupt their synthesis or downstream signaling axes. We hypothesize that prior lukewarm results may be attributed to redundancies in each metabolites' synthesis or signaling pathway and highlight routes for how therapeutic development and patient stratification might proceed in the future.

The Tumor Microenvironment-Dependent Transcription Factors AHR and HIF-1α Are Dispensable for Leukemogenesis in the Eµ-TCL1 Mouse Model of Chronic Lymphocytic Leukemia

Simple Summary

Chronic lymphocytic leukemia (CLL) is the most common leukemia in Western countries, mostly affecting the elderly. The survival of leukemic cells depends on multiple soluble factors and on the stimulation of the BCR signaling pathway. Microenvironment-dependent transcription factors also contribute to CLL biology. Here, we generated new transgenic murine conditional knock-out models of CLL to study the role of the two transcription factors HIF-1α and AHR. Unexpectedly, we observed that both factors are dispensable for leukemia development in these models.

Abstract

Chronic lymphocytic leukemia (CLL) is the most frequent leukemia in the elderly and is characterized by the accumulation of mature B lymphocytes in peripheral blood and primary lymphoid organs. In order to proliferate, leukemic cells are highly dependent on complex interactions with their microenvironment in proliferative niches. Not only soluble factors and BCR stimulation are important for their survival and proliferation, but also the activation of transcription factors through different signaling pathways. The aryl hydrocarbon receptor (AHR) and hypoxia-inducible factor (HIF)-1α are two transcription factors crucial for cancer development, whose activities are dependent on tumor microenvironment conditions, such as the presence of metabolites from the tryptophan pathway and hypoxia, respectively. In this study, we addressed the potential role of AHR and HIF-1α in chronic lymphocytic leukemia (CLL) development in vivo. To this end, we crossed the CLL mouse model Eµ-TCL1 with the corresponding transcription factor-conditional knock-out mice to delete one or both transcription factors in CD19+ B cells only. Despite AHR and HIF-1α being activated in CLL cells, deletion of either or both of them had no impact on CLL progression or survival in vivo, suggesting that these transcription factors are not crucial for leukemogenesis in CLL.

A Comprehensive Pan-Cancer Analysis of 33 Human Cancers Reveals the Immunotherapeutic Value of Aryl Hydrocarbon Receptor

Background

Previous studies have reported the potential of aryl hydrocarbon receptor (AhR) in cancer immunotherapy. However, the mechanisms underpinning its therapeutic value have yet to be comprehensively investigated. Thus, this research aimed to explore the underlying association between AhR and cancer immunotherapy in 33 human cancers.

Methods

The gene expression data and clinical characteristics of 33 cancers were retrieved from The Cancer Genome Atlas database. The immunotherapeutic cohorts included GSE67501 and GSE78220 as well as IMvigor210, which were obtained from the Gene Expression Omnibus database and included in a previously published study respectively. Clinical parameters, including patient age, gender, survival, and tumor stage were analyzed to assess the prognostic value of AhR. The activity of AhR was generated by single sample gene set enrichment analysis and used to evaluate the difference between the AhR transcriptome and protein expression level. To better understand the role of AhR in cancer immunotherapy, the correlation between AhR and tumor microenvironment, as well as its relation to immune processes/elements, such as immune cell infiltration, immune inhibitors and stimulators, and the major histocompatibility complex were analyzed. The relevant underlying pathways associated with AhR signaling in cancer were also explored. Furthermore, the correlation between AhR and two immunotherapeutic biomarkers (tumor mutational burden and microsatellite instability) was investigated. Finally, the relationship between AhR and immunotherapeutic response was explored using three independent immunotherapeutic cohorts.

Results

Although AhR was not closely associated with age (5/33), gender (3/33), or tumor stage (3/21) in any of the studied human cancers, it exhibited potential prognostic value for predicting patient survival. Consistency has been observed between AhR activity and expression in some cancers (7/33). Generally, AhR presented a robust correlation with immune cell infiltration, immune modulators, and immunotherapeutic markers. Moreover, high AhR expression was significantly related to immune-relevant pathways. However, no significant correlation was observed between AhR and the immunotherapeutic response.

Conclusions

This research investigated the immunotherapeutic value of AhR in 33 human cancers, providing evidence regarding the function of AhR and its role in clinical treatment. However, considering that a bioinformatics approach was adopted, the current results are preliminary and require further validation.

Tryptophan Metabolites at the Crossroad of Immune-Cell Interaction via the Aryl Hydrocarbon Receptor: Implications for Tumor Immunotherapy

The Aryl hydrocarbon receptor (AhR) is a critical regulator of both innate and adaptive immune responses, with potent immunomodulatory effects that makes this receptor an attractive molecular target for novel therapeutics. Accumulating evidence indicates that diverse—both host’s and microbial—tryptophan metabolites profoundly regulate the immune system in the host via AhR, promoting either tolerance or immunity, largely as a function of the qualitative and quantitative nature of the metabolites being contributed by either source. Additional findings indicate that host and microbiota-derived tryptophan metabolic pathways can influence the outcome of immune responses to tumors. Here, we review recent studies on the role and modalities of AhR activation by various ligands, derived from either host-cell or microbial-cell tryptophan metabolic pathways, in the regulation of immune responses. Moreover, we highlight potential implications of those ligands and pathways in tumor immunotherapy, with particular relevance to checkpoint-blockade immune intervention strategies.

Lipopolysaccharide-Enhanced Responses against Aryl Hydrocarbon Receptor in FcgRIIb-Deficient Macrophages, a Profound Impact of an Environmental Toxin on a Lupus-Like Mouse Model

Fc gamma receptor IIb (FcgRIIb) is the only inhibitory-FcgR in the FcgR family, and FcgRIIb-deficient (FcgRIIb^−/−) mice develop a lupus-like condition with hyper-responsiveness against several stimulations. The activation of aryl hydrocarbon receptor (Ahr), a cellular environmental sensor, might aggravate activity of the lupus-like condition. As such, 1,4-chrysenequinone (1,4-CQ), an Ahr-activator, alone did not induce supernatant cytokines from macrophages, while the 24 h pre-treatment by lipopolysaccharide (LPS), a representative inflammatory activator, prior to 1,4-CQ activation (LPS/1,4-CQ) predominantly induced macrophage pro-inflammatory responses. Additionally, the responses from FcgRIIb^−/− macrophages were more prominent than wild-type (WT) cells as determined by (i) supernatant cytokines (TNF-α, IL-6, and IL-10), (ii) expression of the inflammation associated genes (NF-κB, aryl hydrocarbon receptor, iNOS, IL-1β and activating-FcgRIV) and cell-surface CD-86 (a biomarker of M1 macrophage polarization), and (iii) cell apoptosis (Annexin V), with the lower inhibitory-FcgRIIb expression. Moreover, 8-week-administration of 1,4-CQ in 8 week old FcgRIIb^−/− mice, a genetic-prone lupus-like model, enhanced lupus characteristics as indicated by anti-dsDNA, serum creatinine, proteinuria, endotoxemia, gut-leakage (FITC-dextran), and glomerular immunoglobulin deposition. In conclusion, an Ahr activation worsened the disease severity in FcgRIIb^−/− mice possibly through the enhanced inflammatory responses. The deficiency of inhibitory-FcgRIIb in these mice, at least in part, prominently enhanced the pro-inflammatory responses. Our data suggest that patients with lupus might be more vulnerable to environmental pollutants.

Role of aryl hydrocarbon receptor in central nervous system tumors: Biological and therapeutic implications

Aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor, whose canonical pathway mainly regulates the genes involved in xenobiotic metabolism. However, it can also regulate several responses in a non-canonical manner, such as proliferation, differentiation, cell death and cell adhesion. AhR plays an important role in central nervous system tumors, as it can regulate several cellular responses via different pathways. The polymorphisms of the AHR gene have been associated with the development of gliomas. In addition, the metabolism of tumor cells promotes tumor growth, particularly in tryptophan synthesis, where some metabolites, such as kynurenine, can activate the AhR pathway, triggering cell proliferation in astrocytomas, medulloblastomas and glioblastomas. Furthermore, as part of the changes in neuroblastomas, AHR is able to downregulate the expression of proto-oncogene c-Myc, induce differentiation in tumor cells, and cause cell cycle arrest and apoptosis. Collectively, these data suggested that the modulation of the AhR pathway may downregulate tumor growth, providing a novel strategy for applications for the treatment of certain tumors through the control of the AhR pathway.

AHR signaling pathway reshapes the metabolism of AML/MDS cells and potentially leads to cytarabine resistance

Emerging evidence suggests that aryl hydrocarbon receptor (AHR) promotes the initiation, invasion, progression, and metastasis of cancer cells. However, its effects in patients with myelodysplastic syndrome/acute myeloid leukemia (MDS/AML) remain undefined. In this study, we aimed to investigate the effects of AHR activation on malignant cells in patients with MDS/AML. We found that AHR was expressed aberrantly in patients with MDS/AML. Further studies demonstrated that inhibiting AHR decreased the mitochondrial dehydrogenase content and the mitochondrial membrane potential (MMP) in MDS/AML cells. Activating AHR with L-kynurenine (Kyn) increased AHR expression, which was accompanied by an increase in mitochondrial dehydrogenase content and MMP in MDS/AML cells. Moreover, the expression level of mitochondria-associated mitochondrial transcription factor A was increased after activating AHR with L-Kyn when compared with that in the control group but decreased after inhibiting the AHR signal. Activating AHR in MDS/AML cells enhanced the resistance to cytarabine. These findings indicated that activating the AHR signaling pathway reshaped the metabolism in MDS/AML cells, thus contributing to the resistance to cytarabine.

The Participation of the Intrinsically Disordered Regions of the bHLH-PAS Transcription Factors in Disease Development

The basic helix–loop–helix/Per-ARNT-SIM (bHLH-PAS) proteins are a family of transcription factors regulating expression of a wide range of genes involved in different functions, ranging from differentiation and development control by oxygen and toxins sensing to circadian clock setting. In addition to the well-preserved DNA-binding bHLH and PAS domains, bHLH-PAS proteins contain long intrinsically disordered C-terminal regions, responsible for regulation of their activity. Our aim was to analyze the potential connection between disordered regions of the bHLH-PAS transcription factors, post-transcriptional modifications and liquid-liquid phase separation, in the context of disease-associated missense mutations. Highly flexible disordered regions, enriched in short motives which are more ordered, are responsible for a wide spectrum of interactions with transcriptional co-regulators. Based on our in silico analysis and taking into account the fact that the functions of transcription factors can be modulated by posttranslational modifications and spontaneous phase separation, we assume that the locations of missense mutations inducing disease states are clearly related to sequences directly undergoing these processes or to sequences responsible for their regulation.

Metabolic regulation of T lymphocyte motility and migration

In order to fulfill their effector and patrolling functions, lymphocytes traffic through the body and need to adapt to different tissue microenvironments. First, mature lymphocytes egress the bone marrow and the thymus into the vascular system. Circulating lymphocytes can exit the vasculature and penetrate into the tissues, either for patrolling in search for pathogens or to eliminate infection and activate the adaptive immune response. The cytoskeletal reorganization necessary to sustain migration require high levels of energy thus presenting a substantial bioenergetic challenge to migrating cells. The metabolic regulation of lymphocyte motility and trafficking has only recently begun to be investigated. In this review we will summarize current knowledge of the crosstalk between cell metabolism and the cytoskeleton in T lymphocytes, and discuss the concept that lymphocyte metabolism may reprogram in response to migratory stimuli and adapt to the different environmental cues received during recirculation in tissues.

Immune metabolism in PD-1 blockade-based cancer immunotherapy

Energy metabolism plays an important role in proliferating cells. Recent reports indicate that metabolic regulation or metabolic products can control immune cell differentiation, fate and reactions. Cancer immunotherapy based on blockade of programmed cell death protein 1 (PD-1) has been used worldwide, but a significant fraction of patients remain unresponsive. Therefore, clarifying the mechanisms and overcoming the unresponsiveness are urgent issues. Because cancer immunity consists of interactions between the cancer and host immune cells, there has recently been a focus on the metabolic interactions and/or competition between the tumor and the immune system to address these issues. Cancer cells render their microenvironment immunosuppressive, driving T-cell dysfunction or exhaustion, which is advantageous for cancer cell survival. However, accumulating mechanistic evidence of T-cell and cancer cell metabolism has gradually revealed that controlling the metabolic pathways of either type of cell can overcome T-cell dysfunction and reprogram the metabolic balance in the tumor microenvironment. Here, we summarize the role of immune metabolism in T-cell-based immune surveillance and cancer immune escape. This new concept has boosted the development of combination therapy and predictive biomarkers in cancer immunotherapy with immune checkpoint inhibitors.

Lack of association between multiple polymorphisms in aryl hydrocarbon receptor (AhR) gene and cancer susceptibility

BACKGROUND

The aryl hydrocarbon receptor (AhR) is commonly known as an environmental sensor. Polymorphisms in AhR gene have been implicated in susceptibility to cancer. However, the results were controversial. This study was conducted to quantitatively summarize the association between AhR polymorphisms and cancer risk by meta-analysis.

METHODS

Relevant reports were searched in four databases (Embase, PubMed, Wanfang, and China National Knowledge Infrastructure). We used pooled odds ratio (OR) and 95% confidence interval (95% CI) to evaluate the strength of the association in both standard and cumulative meta-analysis. Subgroup and sensitivity analysis was also performed, and between-study heterogeneity and publication bias were checked.

RESULTS

A total of seventeen studies referring to three AhR polymorphisms (rs2066853, rs7796976, and rs2074113) were identified, and 9557 cases and 10038 controls were included. There was no statistically significant association of AhR rs2066853 polymorphism with cancer risk in the overall population, and the negative results were repeated in subgroup analysis by the ethnicity and cancer type. Concerning AhR rs7796976 or rs2074113 polymorphism, no significant correlation was detected. Moreover, these non-significant findings were stable in sensitivity analysis, and the cumulative meta-analysis indicated a trend of no significant link between this three AhR polymorphisms and cancer risk as more data accumulated over time.

CONCLUSION

This meta-analysis provides evidence that the rs2066853, rs7796976, or rs2074113 polymorphism in AhR gene is not a susceptible predictor of cancer. Further clinical and functional investigation between AhR polymorphisms and cancer susceptibility are needed.

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.

Roles of aryl hydrocarbon receptor in endothelial angiogenic responses†

Aryl hydrocarbon receptor (AhR) is a transcription factor, which can be activated by a plethora of structure-diverse ligands. Historically, AhR is known for its involvements in regulation of metabolism of xenobiotics. However, normal physiological roles of AhR have been defined in other essential biological processes, including vascular growth and function, reproduction, and immunoresponses. In contrast, aberrant expression and activation of the AhR signaling pathway occur in a variety of human diseases, many of which (e.g., preeclampsia, atherosclerosis, and hypertension) could be associated with endothelial dysfunction. Indeed, emerging evidence has shown that either exogenous or endogenous AhR ligands can induce endothelial dysfunction in either an AhR-dependent or AhR-independent manner, possibly reliant on the blood vessel origin (artery and vein) of endothelial cells. Given that the AhR signaling pathway has broad impacts on endothelial and cardiovascular function, AhR ligands, AhR, and their downstream genes could be considered novel therapeutic targets for those endothelial-related diseases. This review will discuss the current knowledge of AhR's mediation on endothelial function and potential mechanisms underlying these actions with a focus on placental endothelial cells.

Nutritional Therapy to Modulate Tryptophan Metabolism and Aryl Hydrocarbon-Receptor Signaling Activation in Human Diseases

The aryl hydrocarbon receptor (AhR) is a nuclear protein which, upon association with certain endogenous and exogenous ligands, translocates into the nucleus, binds DNA and regulates gene expression. Tryptophan (Trp) metabolites are one of the most important endogenous AhR ligands. The intestinal microbiota is a critical player in human intestinal homeostasis. Many of its effects are mediated by an assembly of metabolites, including Trp metabolites. In the intestine, Trp is metabolized by three main routes, leading to kynurenine, serotonin, and indole derivative synthesis under the direct or indirect involvement of the microbiota. Disturbance in Trp metabolism and/or AhR activation is strongly associated with multiple gastrointestinal, neurological and metabolic disorders, suggesting Trp metabolites/AhR signaling modulation as an interesting therapeutic perspective. In this review, we describe the most recent advances concerning Trp metabolism and AhR signaling in human health and disease, with a focus on nutrition as a potential therapy to modulate Trp metabolites acting on AhR. A better understanding of the complex balance between these pathways in human health and disease will yield therapeutic opportunities.

The aryl hydrocarbon receptor promotes inflammation-induced dedifferentiation and systemic metastatic spread of melanoma cells

The aryl hydrocarbon receptor (AHR) is a ligand binding-transcription factor of the basic helix-loop-helix family regulating multiple cellular functions such as differentiation, cell cycle, apoptosis, and inflammatory reactions. In neoplastic diseases, the AHR has been described to modulate proliferation and differentiation in dichotomous ways, either inhibiting or augmenting the growth of tumors. The precise role of AHR in melanoma is mostly unknown. Here, we report a functional effect of AHR activation on inflammation-induced melanoma cell dedifferentiation and the development of lung metastases in a mouse model. Via in silico analyses of "The Cancer Genome Atlas" human melanoma cohort, we detected a correlation between AHR expression levels and a dedifferentiated melanoma cell phenotype with an invasive gene signature, which we were able to functionally recapitulate in a panel of human melanoma cell lines. Both human and mouse melanoma cell lines upregulated AHR expression after inflammatory stimulation with tumor necrosis factor-α (TNF-α). Activation of AHR in human and mouse melanoma cell lines with the endogenous ligand formylindolo(3,2-b)carbazole (FICZ) promoted inflammation-induced dedifferentiation in vitro. Importantly, mouse melanoma cells with CRISPR/Cas9-mediated disruption of the AHR gene showed impaired in vivo tumor growth after transplantation in the skin as well as decreased numbers of spontaneous lung metastases. Taken together, our results demonstrate a functional role for AHR expression in melanoma development and metastatic progression. This provides a scientific basis for future experiments that further dissect the underlying molecular mechanisms and assess the potential for AHR inhibition as part of multimodal melanoma treatment strategies.

Salinomycin promotes T-cell proliferation by inhibiting the expression and enzymatic activity of immunosuppressive indoleamine-2,3-dioxygenase in human breast cancer cells

Indoleamine 2,3 dioxygenase (IDO) is upregulated in many tumor types, including breast cancer, and plays a reputable role in promoting tumor immune tolerance. The importance of the immunosuppressive mechanism of IDO by suppressing T-cell function has garnered profound interest in the development of clinical IDO inhibitors. Herein, we established a screening method with cervical HeLa cells to induce IDO expression using interferon-γ (IFN-γ). After screening our chemical library, we found that salinomycin potently inhibited IFN-γ-stimulated kynurenine synthesis with IC₅₀ values of 3.36-4.66 μM in both human cervical and breast cancer cells. Salinomycin lowered the IDO1 and IDO2 expression with no impact on the expression of tryptophan-2,3-dioxygenase. Interestingly, salinomycin potently repressed the IDO1 enzymatic activity by directly targeting the proteins in cells. Molecular docking revealed an alignment that favors nucleophilic attack of salinomycin in the catalytic domain of IDO1. Activation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway by IFN-γ was significantly suppressed by salinomycin, via inhibiting the Jak1, Jak2, and STAT1/3 phosphorylation. Moreover, it inhibited IFN-γ-induced activation of the nuclear factor (NF)-κB pathway by inhibiting IκB degradation and NF-κB phosphorylation without affecting BIN1 expression. Furthermore, salinomycin significantly restored the proliferation of T cells co-cultured with IFN-γ-treated breast cancer cells and potentiated antitumor activity of cisplatin in vivo. These findings suggest that salinomycin suppresses kynurenine synthesis by inhibiting the catalytic activity of IDO1 and its expression by inhibiting the JAK/STAT and NF-κB pathways. Salinomycin warrants further investigation as a novel dual-functional IDO inhibitor for cancer immunotherapy.

Neuroendocrine tumours and their microenvironment

Tumours can escape the immune system by expressing programmed death-ligand-1 (PD-L1), which allows them to bind to PD-1 on T-cells and avoid recognition by the immune system. Regulatory T-cells (Tregs), indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO) also play a role in immune suppression. Knowledge about the interaction of neuroendocrine tumours (NETs) with their immune microenvironment and the role of immunotherapy in patients with NET is scarce. Here, we investigated the immune microenvironment of serotonin-producing (SP) and non-serotonin-producing NETs (NSP-NETs). Tumours of 33 patients with SP-NET and 18 patients with NSP-NET were studied. Immunohistochemical analyses were performed for PD-L1, T-cells, IDO, TDO, mismatch repair proteins (MMRp) and activated fibroblasts. PD-L1 expression was seen in < 1% of tumour and T-cells. T-cells were present in 33% of NETs, varying between 1 and 10% T-cells per high power field. IDO was expressed in tumour cells in 55% of SP-NETs and 22% of NSP-NETs (p = 0.039). TDO was expressed in stromal cells in 64% of SP-NETs and 13% of NSP-NETs (p = 0.001). No tumours had loss of MMRp. TDO-expressing stromal cells also strongly expressed α-SMA and were identified as cancer-associated fibroblasts (CAFs). Factors that are associated with a response to checkpoint inhibitor treatment were absent or only present to a limited extent in the tumour microenvironment of NETs. The expression of IDO and TDO in a substantial part of NETs and the presence of CAFs suggest two mechanisms that could be responsible for the cold immune microenvironment, which should be explored to enhance anti-tumour immunity and clinical responses.

Targeting glutamine metabolism enhances tumor-specific immunity by modulating suppressive myeloid cells

Myeloid cells comprise a major component of the tumor microenvironment (TME) that promotes tumor growth and immune evasion. By employing a small-molecule inhibitor of glutamine metabolism, not only were we able to inhibit tumor growth, but we markedly inhibited the generation and recruitment of myeloid-derived suppressor cells (MDSCs). Targeting tumor glutamine metabolism led to a decrease in CSF3 and hence recruitment of MDSCs as well as immunogenic cell death, leading to an increase in inflammatory tumor-associated macrophages (TAMs). Alternatively, inhibiting glutamine metabolism of the MDSCs themselves led to activation-induced cell death and conversion of MDSCs to inflammatory macrophages. Surprisingly, blocking glutamine metabolism also inhibited IDO expression of both the tumor and myeloid-derived cells, leading to a marked decrease in kynurenine levels. This in turn inhibited the development of metastasis and further enhanced antitumor immunity. Indeed, targeting glutamine metabolism rendered checkpoint blockade-resistant tumors susceptible to immunotherapy. Overall, our studies define an intimate interplay between the unique metabolism of tumors and the metabolism of suppressive immune cells.

IDO, TDO, and AHR overexpression is associated with poor outcome in diffuse large B-cell lymphoma patients in the rituximab era

Although Indoleamine 2,3-dioxygenase (IDO), tryptophan-2,3-dioxygenase (TDO), and aryl hydrocarbon receptor (AHR) are involved in cancer immune escape, their prognostic impact on diffuse large B-cell lymphoma (DLBCL) is unknown.To examine the prognostic impact of IDO, TDO, and AHR on patients with DLBCL.This was a retrospective study on treatment-naïve patients with newly diagnosed DLBCL at the Henan Province People's Hospital between 01/2012 and 06/2015. Patients with inflammatory reactive lymph nodes were included as controls. All cases were reviewed by 2 pathologists. IDO, TDO, and AHR positivity was determined through immunochemistry. Survival was examined using the Kaplan-Meier method and multivariable Cox analyses.The positive expression of TDO (50.0% vs 16.7%, P = .005) and AHR (60.0% vs 8.3%, P < .001) were higher in DLBCL than in inflammatory control. The overall survival of IDO, TDO, and AHR positive expression in DLBCL patients was 34.6, 26.7, and 32.2 months, respectively, which is significantly shorter than that of the corresponding negative patients (49.0 months, P = .04; 58.2 months, P < .001; 58.0 months, P < .001; respectively). The multivariable analysis showed that TDO expression and Ann-Arbor stage were independently associated with PFS (TDO: HR = 8.347, 95%CI: 2.992-23.289, P < .001; stage: HR = 2.729, 95%CI: 1.571-4.739, P < .001) and OS (TDO: HR = 9.953, 95%CI: 3.228-30.686, P < .001; stage: HR = 2.681, 95%CI: 1.524-4.719, P = .001) in DLBCL patients.Overexpression of IDO, TDO, and AHR is associated with poor survival of patients with DLBCL and could be involved in the immune escape of cancer cells. Further studies are necessary to determine whether these proteins can be targeted by treatment regimens.

Live-cell screening platform using human-induced pluripotent stem cells expressing fluorescence-tagged cytochrome P450 1A1

Human-induced pluripotent stem cells (hiPSCs) are invaluable sources for drug screening and toxicity tests because of their differentiation potential and proliferative capacity. Recently, the CRISPR-Cas9-mediated homologous recombination system has enabled reporter knock-ins at desired loci in hiPSCs, and here, we generated a hiPSC reporter line expressing mCherry-tagged cytochrome P450 1A1 (CYP1A1), which can be utilized to screen for the modulators of aryl hydrocarbon receptor (AHR) in live cells. CYP1A1-mCherry hiPSCs exhibited typical characteristics of pluripotent stem cells such as marker expression, differentiation potential, and normal karyotype. After differentiation into hepatocyte-like cells (HLCs), CYP1A1-mCherry fusion protein was expressed and localized at the endoplasmic reticulum, and induced by AHR agonists. We obtained 23 hits modulating CYP1A1 expression from high-content screening with 241 hepatotoxicity chemicals and nuclear receptor ligands, and identified three upregulating chemicals and two downregulating compounds. Responses of hiPSC-HLCs against an AHR agonist were more similar to human primary hepatocytes than of HepG2 hepatocellular carcinoma cells. This platform has the advantages of live-cell screening without sacrificing cells (unlike previously available CYP1A1 reporter cell lines), as well as an indefinite supply of cells, and can be utilized in a wide range of screening related to AHR- and CYP1A1-associated diseases in desired cell types.

Induction of leukemic stem cell differentiation by aryl hydrocarbon receptor agonist and synergy with gilteritinib in FLT3-ITD + acute myeloid leukemia

Leukemic stem cells (LSCs) are a major cause of treatment failure and recurrence of acute myeloid leukemia (AML). Targeting LSC is essential to developing a potential cure for patients with relapsed/refractory AML. Here we investigated the effect of aryl hydrocarbon receptor (AhR) signaling on AML stem/progenitor proportion and examined the combined effect of AhR agonist and tyrosine kinase inhibitor. The AhR agonist, 6-formylindolo[3,2-b]carbazole (FICZ), significantly decreased the LSC proportion and clonogenicity and increased differentiation markers in AML primary cells. Synergistic/additive effects of FICZ and gilteritinib, FMS-like tyrosine kinase 3 (FLT3) inhibitor, were confirmed in AML cells with FLT3-ITD. We present evidence that combination of both agents inhibits FLT3 downstream molecules and degrades clonogenicity. Collectively, our results suggest that FICZ not only compels LSC differentiation, but also enhances the efficacy of gilteritinib when combined. Clinical application of this combined approach may pave a new therapeutic strategy for patients with FLT3 mutated AML.

The Role of Aryl Hydrocarbon Receptor (AhR) in Brain Tumors

Primary brain tumors, both malignant and benign, are diagnosed in adults at an incidence rate of approximately 23 people per 100 thousand. The role of AhR in carcinogenesis has been a subject of debate, given that this protein may act as either an oncogenic protein or a tumor suppressor in different cell types and contexts. Lately, there is growing evidence that aryl hydrocarbon receptor (AhR) plays an important part in the development of brain tumors. The role of AhR in brain tumors is complicated, depending on the type of tumor, on ligands that activate AhR, and other features of the pathological process. In this review, we summarize current knowledge about AhR in relation to brain tumors and provide an overview of AhR’s potential as a therapeutic target.

Interferon-Induced IDO1 Mediates Radiation Resistance and Is a Therapeutic Target in Colorectal Cancer

Colorectal cancer is a major cause of mortality worldwide. Chemotherapy and radiation remain standard treatment for locally advanced disease, with current immune-targeting therapies applying to only a small subset of patients. Expression of the immuno-oncology target indoleamine 2,3 dioxygenase 1 (IDO1) is associated with poor colorectal cancer clinical outcomes but is understudied as a potential treatment target. In this study, we examined the interaction between the IDO1 pathway and radiotherapy in colorectal cancer. We used human and mouse colorectal cancer cell lines, organoids, mouse syngeneic colorectal cancer tumor graft models, and colorectal cancer tissues from patients who received radiotherapy. IDO1 activity was blocked using the clinical IDO1 inhibitor epacadostat and by genetic disruption. We found that radiation induced IDO1 overexpression in colorectal cancer through type I and II IFN signaling. IDO1 enzymatic activity directly influenced colorectal cancer radiation sensitivity. IDO1 inhibition sensitized colorectal cancer to radiation-induced cell death, whereas the IDO1 metabolite kynurenine promoted radioprotection. IDO1 inhibition also potentiated Th1 cytokines and myeloid cell-modulating factors in the tumor microenvironment and promoted an abscopal effect on tumors outside the radiation field. Conversely, IDO1 blockade protected the normal small intestinal epithelium from radiation toxicity and accelerated recovery from radiation-induced weight loss, indicating a role in limiting side effects. These data demonstrated that IDO1 inhibition potentiates radiotherapy effectiveness in colorectal cancer. The findings also provide rationale and mechanistic insight for the study of IDO1 inhibitors as adjuvant therapy to radiation in patients with locally advanced sporadic and colitis-associated colorectal cancer.

Kynurenic acid and cancer: facts and controversies

Kynurenic acid (KYNA) is an endogenous tryptophan metabolite exerting neuroprotective and anticonvulsant properties in the brain. However, its importance on the periphery is still not fully elucidated. KYNA is produced endogenously in various types of peripheral cells, tissues and by gastrointestinal microbiota. Furthermore, it was found in several products of daily human diet and its absorption in the digestive tract was evidenced. More recent studies were focused on the potential role of KYNA in carcinogenesis and cancer therapy; however, the results were ambiguous and the biological activity of KYNA in these processes has not been unequivocally established. This review aims to summarize the current views on the relationship between KYNA and cancer. The differences in KYNA concentration between physiological conditions and cancer, as well as KYNA production by both normal and cancer cells, will be discussed. The review also describes the effect of KYNA on cancer cell proliferation and the known potential molecular mechanisms of this activity.

From Association to Causality: the Role of the Gut Microbiota and Its Functional Products on Host Metabolism

Many genomic studies have revealed associations between the gut microbiota composition and host metabolism. These observations led to the idea that a causal relationship could exist between the microbiota and metabolic diseases, a concept supported by studies showing compositional changes in the microbial community in metabolic diseases and transmissibility of host phenotype via microbiota transfer. Accumulating data suggest that the microbiota may affect host metabolic phenotypes through the production of metabolites. These bioactive microbial metabolites, sensitive fingerprints of microbial function, can act as inter-kingdom signaling messengers via penetration into host blood circulation and tissues. These fingerprints may be used for diagnostic purposes, and increased understanding of strain specificity in producing microbial metabolites can identify bacterial strains or specific metabolites that can be used for therapeutic purposes. Here, we will review data supporting the causal role of the gut microbiota in metabolism and discuss mechanisms and potential clinical implications.

Symurban Nanocrystals for Advanced Anti-Pollution Skincare

Several of most common dermatoses worldwide, e.g., psoriasis and atopic dermatitis, are worsened in their clinical picture when the skin is regularly exposed to an increased air pollution level, e.g., particulate matter. This is explainable by the activation of the aryl hydrocarbon receptor (AhR) in the skin, which results in an increased release of proinflammatory cytokines and matrix metalloproteinases. Symurban is a competitive AhR antagonist and thus allows the effective protection of skin. In order to improve its dermal bioavailability as a poorly soluble active agent (0.25 µg/mL), nanocrystals were prepared and evaluated. Nanocrystals are pure active crystals reduced in particle size to the submicron range of 100 to 1000 nm. They feature the properties of nanocrystals, such as increased saturation solubility and dissolution velocity, without having to be declared as nanomaterial. Production methods and parameters were systematically investigated. Wet bead milling at 2000 rpm for 30 min yielded the best results. A z-average of 280 nm was achieved for a 10% Symurban suspension with a polydispersity index of 0.20, indicating a narrow size distribution. For the long-term stabilization of the nanocrystal suspension, the performance of 15 surfactants of different categories and HLB values were investigated and evaluated. It was found that non-ionic surfactants in general were better able to stabilize the system than anionic or amphoteric surfactants. Highest stability of over 12 months at 25 °C was achieved with 2% Plantacare 810 UP, an ECOCERT surfactant with high skin tolerance. The suspension was also chemically long-term stable with >97% of remaining Symurban over 12 months. The saturation solubility of Symurban as nanocrystals was significantly increased from 0.25 to 2.9 μg/mL, which corresponds to a factor of >11. In a case study of one male volunteer with healthy skin conditions, penetration profiles of Symurban nanocrystal hydrogel and commercial anti-pollution serum containing an identical amount of Symurban were determined and compared. After 20 min of exposure, the relative Symurban concentration in the deeper skin layers (tape 19-30) was more than two times higher for nanocrystal hydrogel (16%) than the commercial serum (7%). These results suggest that nanocrystals are a promising delivery system for the poorly soluble anti-pollution agent Symurban.

Indirect regulation of TFPI-2 expression by miR-494 in breast cancer cells

TFPI-2 has been shown to be involved in breast cancer pathogenesis by inhibiting extracellular matrix degradation, and low levels are associated with disease progression. As microRNA-494 (miR-494) protects against breast cancer progression, we investigated whether miR-494 is involved in the regulation of TFPI-2 in MCF-7 breast cancer cells. TFPI-2 mRNA and protein levels increased after transfection with miR-494 mimic, and TFPI-2 mRNA and miR-494 levels correlated positively in tumors from breast cancer patients. No specific binding sites for miR-494 in the 3'-untranslated region (UTR) of TFPI2 were identified; however, miR-494 was predicted in silico to bind 3'-UTR of the transcription factors AHR and ELF-1, which have potential binding sites in the TFPI2 promoter. ELF-1 mRNA was downregulated whereas AHR mRNA levels were upregulated after transfection with miR-494 mimic. Knockdown of ELF-1 and AHR increased and reduced TFPI-2 mRNA levels, respectively. Increased luciferase activity was seen when TFPI-2 promoter constructs containing the potential AHR or ELF-1 binding sites were co-transfected with miR-494 mimic. In conclusion, TFPI-2 mRNA levels were upregulated by miR-494 in MCF-7 breast cancer cells most likely by an indirect association where miR-494 targeted the transcription factors AHR and ELF-1. This association was supported in a breast cancer cohort.

Short-term and long-term outcomes of indigo naturalis treatment for inflammatory bowel disease

BACKGROUND AND AIM

Indigo naturalis (IN) is a traditional Chinese herbal medicine reported to be effective in inducing remission in ulcerative colitis (UC). We conducted a retrospective observational study to investigate the efficacy and safety of IN for induction and maintenance therapy in patients with inflammatory bowel disease.

METHODS

Data were collected from the electric medical records of patients with inflammatory bowel disease who had started IN treatment between March 2015 and April 2017 at Kyushu University Hospital. Clinical response and remission rates were assessed based on the clinical activity index determined by Rachmilewitz index or Crohn's disease (CD) activity index. Cumulative IN continuation rates were estimated using the Kaplan-Meier method. Overall adverse events (AEs) during follow-up were also analyzed.

RESULTS

Seventeen UC patients and eight CD patients were enrolled. Clinical response and remission rates at week 8 were 94.1% and 88.2% in UC patients and 37.5% and 25.0% in CD patients, respectively. Clinical remission rates, as assessed through non-responders imputation analyses at weeks 52 and 104, were 76.4% and 70.4% in UC patients and 25.0% and 25.0% in CD patients, respectively. Ten patients (40%) experienced AEs during follow-up. Three patients (12%) experienced severe AEs, including acute colitis requiring hospitalization in two patients and acute colitis with intussusception requiring surgery in one patient.

CONCLUSIONS

Indigo naturalis showed favorable therapeutic efficacy in UC, whereas its therapeutic efficacy in CD appeared to be modest. The risk of severe AEs should be recognized for IN treatment.

Inflammasome expression is higher in ovarian tumors than in normal ovary

Chronic inflammation fundamentally influences cancer risk and development. A mechanism of chronic inflammation is the formation of inflammasome complexes which results in the sustained secretion of the pro-inflammatory cytokines IL1β and IL18. Inflammasome expression and actions vary among cancers. There is no information on inflammasome expression in ovarian cancer (OvCa). To determine if ovarian tumors express inflammasome components, mRNA and protein expression of NLRP3 (nucleotide-binding domain, leucine-rich repeat family, pyrin domain containing 3), caspase-1, IL1β, and IL18 expression in hen and human OvCa was assessed. Chicken (hen) OvCa a valid model of spontaneous human OvCa. Hens were selected into study groups with or without tumors using ultrasonography; tumors were confirmed by histology, increased cellular proliferation, and expression of immune cell marker mRNA. mRNA expression was higher for hallmarks of inflammasome activity (caspase-1, 5.9x increase, p = 0.04; IL1β, 4x increase, p = 0.04; and IL18, 7.8x increase, p = 0.0003) in hen OvCa compared to normal ovary. NLRP3, caspase-8 and caspase-11 mRNA did not differ significantly between tumor and non-tumor containing ovaries. Similar results occurred for human OvCa. Protein expression by immunohistochemistry paralleled mRNA expression and was qualitatively higher in tumors. Increased protein expression of caspase-1, IL1β, and IL18 occurred in surface epithelium, tumor cells, and immune cells. The aryl hydrocarbon receptor (AHR), a potential tumor suppressor and NLRP3 regulator, was higher in hen (2.4x increase, p = 0.002) and human tumors (1.8x increase, p = 0.038), suggesting a role in OvCa. Collectively, the results indicate that inflammasome expression is associated with hen and human OvCa, although the NLR sensor type remains to be determined.

The Aryl Hydrocarbon Receptor Is Expressed in Thyroid Carcinoma and Appears to Mediate Epithelial-Mesenchymal-Transition

Aryl hydrocarbon receptor (AhR) is expected to promote initiation, progression and invasion of cancer cells regulating proliferation, differentiation, gene expression, inflammation, cell motility and migration. Furthermore, an immunosuppressant function of AhR has been recognized. This study evaluated AhR expression and its role in thyroid cancer progression. AhR expression was assessed by qPCR in 107 thyroid cancer samples (90 PTCs, 11 MTCs, 6 ATCs), and by immunohistochemistry in 41 PTCs. To estimate receptor activation, the expression of target genes CYP1A1 and CYP1B1 was measured. AhR functional effects were evaluated in kynurenine-stimulated FTC-133 and BcPap cell lines by analyzing the expression of genes involved in EMT and cell motility. AhR mRNA expression resulted significantly higher in all the analyzed thyroid cancer samples compared to normal thyroid and a statistically significant correlation with CYP1B1 was detected. Kynurenine-stimulated FTC-133 and BcPap showed the activation of a specific AhR-driven EMT program characterized by E-cadherin decrease and SLUG, N-cadherin and fibronectin increase, resulting in boost of cell motility and invasion. This study confirmed the importance of the IDO1-Kyn-AhR pathway in thyroid cancer tumorigenesis, suggesting an AhR pivotal role in mediating an immunosuppressive microenvironment and favoring the acquisition of a mesenchymal phenotype that could promote invasiveness and metastasis.

Transcriptome analysis reveals significant differences between primary plasma cell leukemia and multiple myeloma even when sharing a similar genetic background

Primary plasma cell leukemia (pPCL) is a highly aggressive plasma cell dyscrasia characterised by short remissions and very poor survival. Although the 17p deletion is associated with poor outcome and extramedullary disease in MM, its presence does not confer the degree of aggressiveness observed in pPCL. The comprehensive exploration of isoform expression and RNA splicing events may provide novel information about biological differences between the two diseases. Transcriptomic studies were carried out in nine newly diagnosed pPCL and ten MM samples, all of which harbored the 17p deletion. Unsupervised cluster analysis clearly distinguished pPCL from MM samples. In total 3584 genes and 20033 isoforms were found to be deregulated between pPCL and MM. There were 2727 significantly deregulated isoforms of non-differentially expressed genes. Strangely enough, significant differences were observed in the expression of spliceosomal machinery components between pPCL and MM, in respect of the gene, isoform and the alternative splicing events expression. In summary, transcriptome analysis revealed significant differences in the relative abundance of isoforms between pPCL and MM, even when they both had the 17p deletion. The mRNA processing pathway including RNA splicing machinery emerged as one of the most remarkable mechanisms underlying the biological differences between the two entities.

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.

Application of RNA-sequencing to identify transcriptome modification by DCLK1 in colorectal cancer cells

Doublecortin like kinase 1 (DCLK1) is a cancer stem cell marker for the colorectal cancer (CRC). It plays critical roles in the oncogenesis, progression and metastasis of CRC. DCLK1 can be an intriguing therapeutic target for CRC treatment. However, the molecular mechanism of how DCLK1 functions is unclear currently. In our research, we aim to apply RNA-Sequencing (RNA Seq) technology, a high throughput massively Next Generation Sequencing approach, to monitor transcriptome changes due to DCLK1 over-expression in the CRC cells. In order to achieve our goal, RNA from quadruplicate samples from two clones of isogenic DCLK1 stable over-expression cells and the parental wild type HCT116 cells was sent for RNA Seq on the Illumina NextSeq500 platform. Differentially expressed (DE) genes were evaluated by t-test (P <0.05 and fold-change ±1.5 or greater) using two methods: (1) FWER; and (2) Benjamani and Hochberg FDR (false discovery rate) which corrects for multiple comparisons. Gene networks and functional analysis were evaluated using Ingenuity Pathways Analysis (IPA). We identified 1463 DE genes common for both DCLK1 overexpression clone A and clone B cells. IPA results indicated that 72 canonical pathways were significantly modified by DCLK1 over-expression (P<0.05), among which 9 out of the top 10 pathways are involved in the cell cycle regulation, indicating that DCLK1 might play its tumorigenesis role via activation of pathways facilitating cell proliferation, repression of pathways inhibiting cells proliferation and function against pathways facilitating cell apoptosis. Cell cycle analysis results confirmed the IPA findings, which demonstrated that DCLK1 over-expression cells had much less G0/G1 cells but much more S and G2/M cells (P<0.05). In conclusion, DCLK1 over-expression significantly modified transcriptome profile of CRC cancer cells. Control of the cell cycle regulation might be one of the critical mechanism for DCLK1 function. Our findings provide more direct evidence for the development of DCLK1 as a therapeutic target for CRC treatment, and will be of great benefit for the discovery of novel therapeutic target within the DCLK1 molecular network for the treatment of colorectal cancer patients.

Differences in the early stage gene expression profiles of lung adenocarcinoma and lung squamous cell carcinoma

The discovery of lung carcinoma subtype-specific gene expression changes has the potential to elucidate the molecular differences and provide personalized therapeutic targets for these pathologies. The aim of the present study was to characterize the genetic profiles of the early stages (IA/IB) of two non-small cell lung cancer subtypes, adenocarcinoma (AD) and squamous cell carcinoma (SC). RNA-Seq gene expression data from The Cancer Genome Atlas was analyzed to compare the gene expression differences between AD and SC. The gene sets specific to each subtype were further analyzed to identify the enriched Gene Ontology terms, Kyoto Encyclopedia of Genes and Genomes pathways and biological functions. The results demonstrated that a unique set of genes (145 upregulated and 27 downregulated) was altered in AD, but not in SC; another set of genes (146 upregulated and 103 downregulated) was significantly altered in SC, but not in AD. Genes highly upregulated specifically in AD included albumin (1,732-fold), protein lin-28 homolog A, which is a positive regulator of cyclin-dependent kinase 2 (150-fold) and gastric lipase (81-fold). Genes highly upregulated specifically in SC included amelotin (618-fold), alcohol dehydrogenase 7 (57-fold), aclerosteosis (55-fold) and claudin-22 (54-fold). Several cancer/testis antigen family genes were notably upregulated in SC, but not in AD, whereas mucins were upregulated only in AD. Functional pathway analysis demonstrated that the dysregulation of genes associated with retinoid X receptors was common in AD and SC, genes associated with ‘lipid metabolism’ and ‘drug metabolism’ were dysregulated only in SC, whereas genes associated with ‘molecular transport’ and ‘cellular growth and proliferation’ were significantly enriched in AD specifically. These results reveal fundamental differences in the gene expression profiles of early-stage AD and SC. In addition, the present study identified molecular pathways that are uniquely associated with the pathogenesis of these subtypes.

Subcellular Localization Signals of bHLH-PAS Proteins: Their Significance, Current State of Knowledge and Future Perspectives

The bHLH-PAS (basic helix-loop-helix/ Period-ARNT-Single minded) proteins are a family of transcriptional regulators commonly occurring in living organisms. bHLH-PAS members act as intracellular and extracellular "signals" sensors, initiating response to endo- and exogenous signals, including toxins, redox potential, and light. The activity of these proteins as transcription factors depends on nucleocytoplasmic shuttling: the signal received in the cytoplasm has to be transduced, via translocation, to the nucleus. It leads to the activation of transcription of particular genes and determines the cell response to different stimuli. In this review, we aim to present the current state of knowledge concerning signals that affect shuttling of bHLH-PAS transcription factors. We summarize experimentally verified and published nuclear localization signals/nuclear export signals (NLSs/NESs) in the context of performed in silico predictions. We have used most of the available NLS/NES predictors. Importantly, all our results confirm the existence of a complex system responsible for protein localization regulation that involves many localization signals, which activity has to be precisely controlled. We conclude that the current stage of knowledge in this area is still not complete and for most of bHLH-PAS proteins an experimental verification of the activity of further NLS/NES is needed.

Aryl Hydrocarbon Receptor Modulates Carcinogenesis and Maintenance of Skin Cancers

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that responds to a wide range of chemicals, including chemical carcinogens such as dioxins and carcinogenic polyaromatic hydrocarbons, and induces a battery of genes associated with detoxification, proliferation, and immune regulation. Recent reports suggest that AHR plays an important role in carcinogenesis and maintenance of various types of skin cancers. Indeed, AHR is a susceptibility gene for squamous cell carcinoma and a prognostic factor for melanoma and Merkel cell carcinoma. In addition, the carcinogenic effects of ultraviolet (UV) and chemical carcinogens, both of which are major environmental carcinogenetic factors of skin, are at least partly mediated by AHR, which regulates UV-induced inflammation and apoptosis, the DNA repair system, and metabolic activation of chemical carcinogens. Furthermore, AHR modulates the efficacy of key therapeutic agents in melanoma. AHR activation induces the expression of resistance genes against the inhibitors of V600E mutated B-Raf proto-oncogene, serine/threonine kinase (BRAF) in melanoma and upregulation of programmed cell death protein 1 (PD-1) in tumor-infiltrating T cells surrounding melanoma. Taken together, these findings underscore the importance of AHR in the biology of skin cancers. Development of therapeutic agents that modulate AHR activity is a promising strategy to advance chemoprevention and chemotherapy for skin cancers.

The Transcription Factor Elf3 Is Essential for a Successful Mesenchymal to Epithelial Transition

The epithelial to mesenchymal transition (EMT) and the mesenchymal to epithelial transition (MET) are two critical biological processes that are involved in both physiological events such as embryogenesis and development and also pathological events such as tumorigenesis. They present with dramatic changes in cellular morphology and gene expression exhibiting acute changes in E-cadherin expression. Despite the comprehensive understanding of EMT, the regulation of MET is far from being understood. To find novel regulators of MET, we hypothesized that such factors would correlate with Cdh1 expression. Bioinformatics examination of several expression profiles suggested Elf3 as a strong candidate. Depletion of Elf3 at the onset of MET severely impaired the progression to the epithelial state. This MET defect was explained, in part, by the absence of E-cadherin at the plasma membrane. Moreover, during MET, ELF3 interacts with the Grhl3 promoter and activates its expression. Our findings present novel insights into the regulation of MET and reveal ELF3 as an indispensable guardian of the epithelial state. A better understanding of MET will, eventually, lead to better management of metastatic cancers.

bHLH-PAS Proteins: Their Structure and Intrinsic Disorder

The basic helix–loop–helix/Per-ARNT-SIM (bHLH–PAS) proteins are a class of transcriptional regulators, commonly occurring in living organisms and highly conserved among vertebrates and invertebrates. These proteins exhibit a relatively well-conserved domain structure: the bHLH domain located at the N-terminus, followed by PAS-A and PAS-B domains. In contrast, their C-terminal fragments present significant variability in their primary structure and are unique for individual proteins. C-termini were shown to be responsible for the specific modulation of protein action. In this review, we present the current state of knowledge, based on NMR and X-ray analysis, concerning the structural properties of bHLH–PAS proteins. It is worth noting that all determined structures comprise only selected domains (bHLH and/or PAS). At the same time, substantial parts of proteins, comprising their long C-termini, have not been structurally characterized to date. Interestingly, these regions appear to be intrinsically disordered (IDRs) and are still a challenge to research. We aim to emphasize the significance of IDRs for the flexibility and function of bHLH–PAS proteins. Finally, we propose modern NMR methods for the structural characterization of the IDRs of bHLH–PAS proteins.

Passenger hotspot mutations in cancer driven by APOBEC3A and mesoscale genomic features

Cancer drivers require statistical modeling to distinguish them from passenger events, which accumulate during tumorigenesis but provide no fitness advantage to cancer cells. The discovery of driver genes and mutations relies on the assumption that exact positional recurrence is unlikely by chance; thus, the precise sharing of mutations across patients identifies drivers. Examining the mutation landscape in cancer genomes, we found that many recurrent cancer mutations previously designated as drivers are likely passengers. Our integrated bioinformatic and biochemical analyses revealed that these passenger hotspot mutations arise from the preference of APOBEC3A, a cytidine deaminase, for DNA stem-loops. Conversely, recurrent APOBEC-signature mutations not in stem-loops are enriched in well-characterized driver genes and may predict new drivers. This demonstrates that mesoscale genomic features need to be integrated into computational models aimed at identifying mutations linked to diseases.

Indoleamine-2,3-Dioxygenase in Thyroid Cancer Cells Suppresses Natural Killer Cell Function by Inhibiting NKG2D and NKp46 Expression via STAT Signaling Pathways

Natural killer (NK) cells are key players in the immune system. They use receptors on their cell surface to identify target cells. However, to escape being killed by the immune system, cancer cells such as thyroid cancer cells, use various methods to suppress the function of NK cells. Thus, this study aims to elucidate how thyroid cancer cells downregulate NK cell function in a co-culture system. We found that thyroid cancer cells suppress NK cell cytotoxicity and inhibit the expression of activating receptors, such as NKG2D and NKp46, by regulating indoleamine 2,3-dioxygenase (IDO). Also, thyroid cancer cells produce kynurenine using IDO, which causes NK cell dysfunction. Kynurenine enters NK cells via the aryl hydrocarbon receptor (AhR) on the surfaces of the NK cells, which decreases NK cell function and NK receptor expression via the signal transducer and activator of transcription (STAT) 1 and STAT3 pathways. In addition, STAT1 and STAT3 directly regulated the expression of NKG2D and NKp46 receptors by binding to the promoter region. Conclusively, NK cell function may be impaired in thyroid cancer patients by IDO-induced kynurenine production. This implies that IDO can be used as a target for thyroid cancer therapeutics aiming at improving NK cell function.

Old Receptor, New Tricks-The Ever-Expanding Universe of Aryl Hydrocarbon Receptor Functions. Report from the 4th AHR Meeting, 29⁻31 August 2018 in Paris, France

In a time where "translational" science has become a mantra in the biomedical field, it is reassuring when years of research into a biological phenomenon suddenly points towards novel prevention or therapeutic approaches to disease, thereby demonstrating once again that basic science and translational science are intimately linked. The studies on the aryl hydrocarbon receptor (AHR) discussed here provide a perfect example of how years of basic toxicological research on a molecule, whose normal physiological function remained a mystery for so long, has now yielded a treasure trove of actionable information on the development of targeted therapeutics. Examples are autoimmunity, metabolic imbalance, inflammatory skin and gastro-intestinal diseases, cancer, development and perhaps ageing. Indeed, the AHR field no longer asks, "What does this receptor do in the absence of xenobiotics?" It now asks, "What doesn't this receptor do?".