The AhR is involved in the regulation of LoVo cell proliferation through cell cycle-associated proteins

Comparative Inhibitory Effects of Natural Biflavones from Ginkgo against Human CYP1B1 in Recombinant Enzymes and MCF-7 Cells

Human cytochrome P450 1B1 (CYP1B1) is an extrahepatic enzyme overexpressed in many tumors and associated with angiogenesis. Ginkgetin, isoginkgetin, sciadopitysin, and amentoflavone, the primary biflavones found in Ginkgo biloba, have excellent anti-inflammatory and anti-tumor effects. However, the effect of biflavones on CYP1B1 activities remains unknown. In this study, 7-ethoxyresorufin O-deethylation (EROD) was used to characterize the activities of CYP1 families. The impacts of four ginkgo biflavones on CYP1B1 activity and the cellular protein expression of CYP1B1 were systematically investigated. The results showed that amentoflavone with six hydroxyl substituents exhibited the most potent selective inhibitory effect on CYP1B1 activity with IC₅₀ of 0.054 µM in four biflavones. Sciadopitysin, with three hydroxyl and three methoxy substituents, had the weakest inhibitory activity against CYP1B1. Ginkgetin and isoginkgetin, both with four hydroxyl and two methoxy substituents, showed similar inhibitory intensity towards CYP1B1 with IC₅₀ values of 0.289 and 0.211 µM, respectively. Kinetic analysis showed that ginkgetin and amentoflavone inhibited CYP1B1 in a non-competitive mode, whereas sciadopitysin and isoginkgetin induced competitive or mixed types of inhibition. Notably, four ginkgo biflavones were also confirmed to suppress the protein expressions of CYP1B1 and AhR in MCF-7. Furthermore, molecular docking studies indicated more hydrogen bonds formed between amentoflavone and CYP1B1, which might explain the strongest inhibitory action towards CYP1B1. In summary, these findings suggested that biflavones remarkably inhibited both the activity and protein expression of CYP1B1 and the inhibitory activities enhanced with the increasing hydroxyl substitution, providing new insights into the anti-tumor potentials of biflavones.

Icariside I - A novel inhibitor of the kynurenine-AhR pathway with potential for cancer therapy by blocking tumor immune escape

BACKGROUND

Although therapeutic antibodies against immune checkpoints such as PD-1/PD-L1 have achieved unprecedented success in clinical tumor patients, there are still many patients who are ineffective or have limited responses to immune checkpoint blockade (ICB). Discovery of novel strategies for cancer immunotherapy including natural small molecules is needed.

METHODS

Owing to its extremely low content in Epimedium genus, we firstly constructed a microbial cell factory to enzymatically biosynthesize icariside I, a natural flavonoid monosaccharide from Herbal Epimedium. Using a combination of targeted MS-based metabolomics, flow cytometric analysis, and biological assays, the therapeutic potentials of icariside I were subsequently investigated in vivo and in vitro.

RESULTS

We find that icariside I markedly downregulates a series of intermediate metabolites such as kynurenine, kynurenic acid and xanthurenic acid and corresponding key enzymes involved in kynurenine-AhR pathway in both tumor cells and tumor-bearing mice. In vivo, oral administration of icariside I downregulates SLC7A8 and PAT4 transporters and AhR, thus inhibiting nuclear PD-1 in CTLs. Moreover, icariside I significantly upregulates CD8 + T cells in both peripheral blood and tumor tissues of tumor-bearing mice. Consequently, interferon-γ (IFN-γ) secreted by CD8 + T cells suppresses tumor growth through activation of JAK1-STAT1 signaling, thus inducing tumor cell apoptosis.

CONCLUSIONS

These results suggest that icariside I could be an effective small molecule drug for tumor immunotherapy by blocking kynurenine-AhR pathway and tumor immune escape.

Targeting AhR as a Novel Therapeutic Modality against Inflammatory Diseases

For decades, activation of Aryl Hydrocarbon Receptor (AhR) was excluded from consideration as a therapeutic approach due to the potential toxic effects of AhR ligands and the induction of the cytochrome P450 enzyme, Cyp1a1, following AhR activation. However, it is now understood that AhR activation not only serves as an environmental sensor that regulates the effects of environmental toxins, but also as a key immunomodulator where ligands induce a variety of cellular and epigenetic mechanisms to attenuate inflammation. Thus, the emergence of further in-depth research into diverse groups of compounds capable of activating this receptor has prompted reconsideration of its use therapeutically. The aim of this review is to summarize the body of research surrounding AhR and its role in regulating inflammation. Specifically, evidence supporting the potential of targeting this receptor to modulate the immune response in inflammatory and autoimmune diseases will be highlighted. Additionally, the opportunities and challenges of developing AhR-based therapies to suppress inflammation will be discussed.

Induction of cell apoptosis by biliverdin reductase inhibitor in MCF-7 and MDA-MB-468 breast cancer cell lines: Experimental and in silico studies

Biliverdin reductase, biliverdin and bilirubin are known as important components of cellular signaling pathways that play major roles in cell proliferation and apoptosis, although their physiological relevance is still under evaluation. This study was designed to investigate the expression and activity of BVR-A and its apoptotic effect in the breast cancer cell lines, MCF-7 and MDA-MB-468. The expression of BVR-A was examined by real-time PCR and western blot analysis. Bilirubin concentration was measured by HPLC and molecular docking was performed to identify an appropriate inhibitor for BVR-A. To detect cell apoptosis, annexin V-PI staining, caspase-3, -8, and -9 activities were evaluated. Cell viability was reduced by biliverdin, in a dose-dependent manner, and an intrinsic apoptotic response occurred which was evidenced by caspase-3 and -9 activities. The intra- and extracellular concentrations of bilirubin were higher in MCF-7 cells than those of MDA-MB-468 cells. The expression of BVR-A, at mRNA and protein levels, in MCF-7 was also higher than that of MDA-MB-468 cells. Treatment of both cell lines with biliverdin plus DTNB, a BVR-A inhibitor, increased the cell death significantly when compared with biliverdin alone. Using annexin V-PI staining and assessment of caspase-3 activity, it was confirmed that biliverdin together with DTNB increases apoptosis in breast cancer cells. In conclusion, biliverdin has an important role in cell apoptosis and inhibition of biliverdin reductase increases the apoptotic effect of biliverdin.

Diet-Host-Microbiota Interactions Shape Aryl Hydrocarbon Receptor Ligand Production to Modulate Intestinal Homeostasis

The aryl hydrocarbon receptor (AhR) is a ligand-activated basic-helix-loop-helix transcription factor that binds structurally diverse ligands and senses cues from environmental toxicants and physiologically relevant dietary/microbiota-derived ligands. The AhR is an ancient conserved protein and is widely expressed across different tissues in vertebrates and invertebrates. AhR signaling mediates a wide range of cellular functions in a ligand-, cell type-, species-, and context-specific manner. Dysregulation of AhR signaling is linked to many developmental defects and chronic diseases. In this review, we discuss the emerging role of AhR signaling in mediating bidirectional host-microbiome interactions. We also consider evidence showing the potential for the dietary/microbial enhancement ofhealth-promoting AhR ligands to improve clinical pathway management in the context of inflammatory bowel diseases and colon tumorigenesis.

β-Naphthoflavone Activation of the Ah Receptor Alleviates Irradiation-Induced Intestinal Injury in Mice

Radiotherapy induced gastrointestinal syndrome results from the acute damage of intestinal stem cells, impaired crypts reconstruction, and subsequent breakdown of the mucosal barrier. The toxicity of ionizing radiation is associated with oxidative stress in the intestinal epithelial cells (IECs). Moreover, the rapid proliferation of IECs is a risk factor for radiation damage. β-naphthoflavone (BNF) is an agonist of the aryl hydrocarbon receptor (AhR) and possesses potential antioxidative activity. We investigated BNF radioprotection in IECs experiencing γ-ray exposure, contributed to mitigation of radiation enteritis. BNF significantly enhanced cell viability and suppressed cell apoptosis in an AhR activation-dependent manner. The mechanism of BNF reducing the IECs radiosensitivity was associated with cell cycle arrest and suppression of cell proliferation. In contrast, AhR antagonist CH-223191 significantly blocked BNF-induced cell cycle arrest. Cyp1a1 mRNA levels are induced after irradiation in a dose-dependent manner, and CYP1A1 protein expression increased in the irradiated intestinal tract as well. BNF also reduces DNA strand breaks induced by irradiation. These studies demonstrate that BNF pretreatment prolonged median survival time of mice upon exposure to a lethal dose of radiation and alleviated irradiation-induced toxicity within the bowel.

6-Formylindolo[3,2-b]carbazole reduces apoptosis induced by benzo[a]pyrene in a mitochondrial-dependent manner

Benzo[a]pyrene (B[a]P), a potent carcinogen, has been proved that it can induce apoptosis via activation of the aryl hydrocarbon receptor (AhR) pathway. The metabolite of tryptophan 6-formylindolo[3,2-b]carbazole (FICZ), an endogenous activator of AhR, plays bifunctional roles in cell growth and apoptosis. However, whether and how FICZ can reduce the toxicity of B[a]P and the mechanism underlying this remain unclear. In this study, FICZ interfered with the toxicity of B[a]P in mouse hepatocarcinoma cell line Hepa1-6. The results of the MTT assay indicated that FICZ and B[a]P made opposite effects on cell proliferation. The scratch-wound healing assay showed that B[a]P (1 µM for 24 hr) exposure triggered cell migration and that was inhibited by FICZ (10 nM). In addition, FICZ ameliorated B[a]P-induced apoptosis by inhibiting reactive oxygen species generation and caspase-3 activation, as well as increasing reduced glutathione level in mitochondria. Furthermore, gene expression analyses indicated that FICZ competed with B[a]P, which reduced the transcriptional activation of the cyp1a1 and cyp1b1 genes, as well as Bcl2 and P53. Accordingly, the interaction between FICZ and B[a]P in the AhR pathway inhibited apoptosis in a mitochondrial-dependent manner, suggesting that endogenous compound may reduce the toxicity of exogenous pollutant in vivo and providing an available way to improve health condition related to the hepatic metabolic disorder.

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.

Bilirubin as a signaling molecule

For long time bilirubin was only considered as a potentially dangerous sign of liver diseases, but it now appears clear that it is also a powerful signaling molecule. Together with potent antioxidant activities that were only reported in the last few decades, many other biological effects have now been clearly described. These include especially profound inhibitory effects on almost all effectors of the immune system, with their clinical consequences in the bilirubin-mediated protection against autoimmune and inflammatory diseases. Separate from these, bilirubin activates various nuclear and cytoplasmic receptors, resembling the endocrine activities of actual hormonal substances. This is true for the "classical" hepatic nuclear receptors, including the aryl hydrocarbon receptor, or the constitutive androstane receptor; and also for some lesser-explored receptors such as peroxisome proliferator-activated receptors α and γ; Mas-related G protein-coupled receptor; or other signaling molecules including fatty acid binding protein 1, apolipoprotein D, or reactive oxygen species. All of these targets have broad metabolic effects, which in turn may offer protection against obesity, diabetes mellitus, and other metabolic diseases. The (mostly experimental) data are also supported by clinical evidence. In fact, data from the last three decades have convincingly demonstrated the protective effects of mildly elevated serum bilirubin concentrations against various "diseases of civilization." Additionally, even tiny, micromolar changes of serum bilirubin concentrations have been associated with substantial alteration in the risks of these diseases. It is highly likely that all of the biological activities of bilirubin have yet to be exhaustively explored, and thus we can expect further clinical discoveries about this evolutionarily old molecule into the future.

The Opposite Effect of L-kynurenine and Ahr Inhibitor Ch223191 on Apoptotic Protein Expression in Pancreatic Carcinoma Cells (Panc-1)

BACKGROUND

L-kynurenine, derivate of L-tryptophan, is synthetized by indoleamine 2,3-dioxygenase (IDO). The effects of L-kynurenine depend on its binding to an aryl hydrocarbon receptor (AhR).

OBJECTIVE

The aim of this study was to investigate the changes within the apoptotic pathway in PANC-1 cells subjected to L-kynurenine or L-tryptophan considering the production of anti-apoptotic proteins from the IAPs and Bcl-2 family, as well as the regulation of NF-κB signaling.

METHODS

The investigated substances were added alone or in combination with the AhR inhibitor (CH223191) to cultures of PANC-1 cells. Cytoplasmic and nuclear proteins were analyzed by immunoblotting and cells were incubated with the investigated substances to determine cytotoxicity and proliferative effects.

RESULTS

Incubation of PANC-1 cells with L-kynurenine or L-tryptophan resulted in the increase in antiapoptotic cIAP-1, cIAP-2, XIAP and Bcl-2 expression and a decrease in pro-apoptotic Bax. These changes were accompanied by the reduction of active caspases -9, -3 and PARP-1. The treatment leads to translocation and enhanced production of nuclear NF-κB p50 and Bcl-3. Incubation of the cells with AhR blocker either alone or together with L-kynurenine or L-tryptophan resulted in the opposite effect, leading to the downregulation of IAPs and Bcl-2, upregulation of Bax and caspases expression.

CONCLUSION

1) L-kynurenine and its precursor promote anti-apoptotic effects through the modulation of IDOdependent pathway and regulation of IAPs, Bcl-2 and NF-κB family members in pancreatic carcinoma cells 2) inhibition of AhR by CH223191 exerts an apoptosis-promoting effect, and this observation might suggest the potential use of this compound in pancreatic cancer therapy.

[Aryl-hydrocarbon receptor as a potential target for anticancer therapy]

Aryl-hydrocarbon receptor (Aryl Hydrocarbon Receptor, AHR) is a ligand-dependent transcription factor, whose functions are related to xenobiotic detoxification, response to inflammation, and maintenance of tissue homeostasis. Recent investigations suggest that AHR also plays an important role in the processes of carcinogenesis. Increased expression of AHR is observed in several types of tumors and tumor cell lines. In addition, it turned out that the composition of pharmaceutical drugs used in oncotherapy includes some ligands AHR. These facts allow us to consider an aryl-hydrocarbon receptor as a potential target for anticancer therapy, especially for the treatment of severe cancers whose treatment options are very limited or do not exist at all. In this review the examples of AHR ligands' effect on tumor cell cultures and on model mice lines with AHR-dependent response are discussed.

The tryptophan derivative 6-formylindolo[3,2-b]carbazole, FICZ, a dynamic mediator of endogenous aryl hydrocarbon receptor signaling, balances cell growth and differentiation

The aryl hydrocarbon receptor (AHR) is not essential to survival, but does act as a key regulator of many normal physiological events. The role of this receptor in toxicological processes has been studied extensively, primarily employing the high-affinity ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, regulation of physiological responses by endogenous AHR ligands remains to be elucidated. Here, we review developments in this field, with a focus on 6-formylindolo[3,2-b]carbazole (FICZ), the endogenous ligand with the highest affinity to the receptor reported to date. The binding of FICZ to different isoforms of the AHR seems to be evolutionarily well conserved and there is a feedback loop that controls AHR activity through metabolic degradation of FICZ via the highly inducible cytochrome P450 1A1. Several investigations provide strong evidence that FICZ plays a critical role in normal physiological processes and can ameliorate immune diseases with remarkable efficiency. Low levels of FICZ are pro-inflammatory, providing resistance to pathogenic bacteria, stimulating the anti-tumor functions, and promoting the differentiation of cancer cells by repressing genes in cancer stem cells. In contrast, at high concentrations FICZ behaves in a manner similar to TCDD, exhibiting toxicity toward fish and bird embryos, immune suppression, and activation of cancer progression. The findings are indicative of a dual role for endogenously activated AHR in barrier tissues, aiding clearance of infections and suppressing immunity to terminate a vicious cycle that might otherwise lead to disease. There is not much support for the AHR ligand-specific immune responses proposed, the differences between FICZ and TCDD in this context appear to be explained by the rapid metabolism of FICZ.

Chemistry and Properties of Indolocarbazoles

The indolocarbazoles are an important class of nitrogen heterocycles which has evolved significantly in recent years, with numerous studies focusing on their diverse biological effects, or targeting new materials with potential applications in organic electronics. This review aims at providing a broad survey of the chemistry and properties of indolocarbazoles from an interdisciplinary point of view, with particular emphasis on practical synthetic aspects, as well as certain topics which have not been previously accounted for in detail, such as the occurrence, formation, biological activities, and metabolism of indolo[3,2- b]carbazoles. The literature of the past decade forms the basis of the text, which is further supplemented with older key references.

Adaptive changes in global gene expression profile of lung carcinoma A549 cells acutely exposed to distinct types of AhR ligands

Exposure to persistent ligands of aryl hydrocarbon receptor (AhR) has been found to cause lung cancer in experimental animals, and lung adenocarcinomas are often associated with enhanced AhR expression and aberrant AhR activation. In order to better understand the action of toxic AhR ligands in lung epithelial cells, we performed global gene expression profiling and analyze TCDD-induced changes in A549 transcriptome, both sensitive and non-sensitive to CH223191 co-treatment. Comparison of our data with results from previously reported microarray and ChIP-seq experiments enabled us to identify candidate genes, which expression status reflects exposure of lung cancer cells to TCDD, and to predict processes, pathways (e.g. ER stress, Wnt/β-cat, IFNɣ, EGFR/Erbb1), putative TFs (e.g. STAT, AP1, E2F1, TCF4), which may be implicated in adaptive response of lung cells to TCDD-induced AhR activation. Importantly, TCDD-like expression fingerprint of selected genes was observed also in A549 cells exposed acutely to both toxic (benzo[a]pyrene, benzo[k]fluoranthene) and endogenous AhR ligands (2-(1H-Indol-3-ylcarbonyl)-4-thiazolecarboxylic acid methyl ester and 6-formylindolo[3,2-b]carbazole). Overall, our results suggest novel cellular candidates, which could help to improve monitoring of AhR-dependent transcriptional activity during acute exposure of lung cells to distinct types of environmental pollutants.

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.

A Novel Perspective on the Biology of Bilirubin in Health and Disease

Unconjugated bilirubin (UCB) is known to be one of the most potent endogenous antioxidant substances. While hyperbilirubinemia has long been recognized as an ominous sign of liver dysfunction, recent data strongly indicate that mildly elevated bilirubin (BLB) levels can be protective against an array of diseases associated with increased oxidative stress. These clinical observations are supported by new discoveries relating to the role of BLB in immunosuppression and inhibition of protein phosphorylation, resulting in the modulation of intracellular signaling pathways in vascular biology and cancer, among others. Collectively, the evidence suggests that targeting BLB metabolism could be considered a potential therapeutic approach to ameliorate a variety of conditions.