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(1) Background: Kidney transplantation is the best therapy for patients with end-stage renal disease, but the risk of rejection complicates it. Indoleamine 2,3-dioxygenase 1 (IDO1), an enzyme involved in immune response modulation, has been suggested to play a role in transplant immunological injury. The aim of the study was to explore the expression of IDO1 in the interstitial foci of transplanted kidneys and its potential association with rejection episodes. (2) Methods: This retrospective study analysed kidney transplant biopsies from 121 patients, focusing on IDO1 expression in interstitial foci. Immunohistochemistry was used to detect IDO1, and patients were categorised based on IDO1 presence (IDO1-IF positive or negative). The incidence of rejection was compared between these groups. (3) Results: Patients with IDO1 expression in interstitial foci (IDO1-IF(+)) exhibited higher incidences of rejection 46/80 (57.5%) vs. 10/41 (24.34%) patients compared to IDO1-IF(−) patients, which was statistically significant with p = 0.0005. The analysis of antibody-mediated rejection showed that IDO1-IF(+) patients developed AMR at 12/80 (15%), while only 1 IDO1-IF(−) negative patient did (2,44%), with p = 0.035. T-cell-mediated rejection was also more common in IDO1-IF(+) patients 43/80 (53.75%) than in IDO1-IF(−) patients 7/41 (17.07%), with p = 0.0001. (4) Conclusions: IDO1 expression in interstitial foci of renal transplant biopsies is associated with a higher incidence of rejection, suggesting that IDO1 could serve as a potential biomarker for transplant rejection. These findings highlight the importance of IDO1 in immune regulation and its potential utility in improving the management of kidney transplant recipients. [ABSTRACT FROM AUTHOR]

Simple Summary: Mammary carcinomas have been diagnosed with increasing frequency in pet rabbits. Prognostic biomarkers are limited, and the only available treatment is surgical excision. Additional treatment options are needed, e.g., for animals in which metastases to internal organs preclude complete tumor removal. Human breast cancer may express the immunosuppressive enzyme indoleamine 2,3-dioxygenase 1 (IDO1), that represents a prognostic biomarker and a possible therapeutic target. Since previous studies revealed similarities between human breast cancer and pet rabbit mammary carcinomas, this study investigated IDO1 immunostaining in 96 mammary carcinomas of 96 pet rabbits with an average age of 5.5 years. All rabbits with reported sex were female. Variable percentages of IDO1-positive tumor cells were detected in 90 (94%) carcinomas. Furthermore, IDO1 immunostaining was observed in the secretory epithelial cells of the adjacent non-neoplastic mammary tissue. This study provides further information on the molecular features of mammary carcinomas in rabbits. It also shows similarities in IDO1 expression between rabbit mammary carcinomas and human breast cancer. These findings can have a mutual benefit. They could lead the development of novel treatment options for rabbits with mammary carcinomas. In addition, they further support the value of rabbits with mammary carcinomas for breast cancer research. For mammary carcinomas in pet rabbits, prognostic biomarkers are poorly defined, and treatment is limited to surgical excision. Additional treatment options are needed for rabbit patients for which surgery is not a suitable option. In human breast cancer, the immunosuppressive enzyme indoleamine 2,3-dioxygenase 1 (IDO1) represents a prognostic biomarker and possible therapeutic target. This retrospective immunohistochemical study examined IDO1 in 96 pet rabbit mammary carcinomas with known mitotic count, hormone receptor status, and percentage of stromal tumor infiltrating lymphocytes (TILs). Tumors were obtained from 96 pet rabbits with an average of 5.5 years. All rabbits with reported sex (n = 88) were female or female-spayed. Of the carcinomas, 94% expressed IDO1, and 86% had sparse TILs consistent with cold tumors. Statistically significant correlations existed between a higher percentage of IDO1-positive tumor cells, lower mitotic counts, and increased estrogen receptor expression. The threshold for significance was IDO1 staining in >10% of tumor cells. These results lead to the assumption that IDO1 expression contributes to tumorigenesis and may represent a prognostic biomarker and possible therapeutic target also in pet rabbit mammary carcinomas. They also support the value of rabbits for breast cancer research. [ABSTRACT FROM AUTHOR]

Indoleamine 2,3‐dioxygenase 1 (IDO1), the key enzyme in the catabolism of the essential amino acid tryptophan (Trp) through kynurenine pathway, induces immune tolerance and is considered as a critical immune checkpoint, but its impacts as a metabolism enzyme on glucose and lipid metabolism are overlooked. We aim to clarify the potential role of IDO1 in aerobic glycolysis in pancreatic cancer (PC). Analysis of database revealed the positive correlation in PC between the expressions of IDO1 and genes encoding important glycolytic enzyme hexokinase 2 (HK2), pyruvate kinase (PK), lactate dehydrogenase A (LDHA) and glucose transporter 1 (GLUT1). It was found that IDO1 could modulate glycolysis and glucose uptake in PC cells, Trp deficiency caused by IDO1 overexpression enhanced glucose uptake by stimulating GLUT1 translocation to the plasma membrane of PC cells. Besides, Trp deficiency caused by IDO1 overexpression suppressed the apoptosis of PC cells via promoting glycolysis, which reveals the presence of IDO1–glycolysis–apoptosis axis in PC. IDO1 inhibitors could inhibit glycolysis, promote apoptosis, and exhibit robust therapeutic efficacy when combined with GLUT1 inhibitor in PC mice. Our study reveals the function of IDO1 in the glucose metabolism of PC and provides new insights into the therapeutic strategy for PC. [ABSTRACT FROM AUTHOR]

Kidney transplantation is a crucial treatment for end-stage kidney disease, with immunosuppressive drugs helping to reduce acute rejection rates. However, kidney graft longevity remains a concern. This study explores the role of indoleamine 2,3-dioxygenase 1 (IDO1) in kidney transplant immunology. IDO1 breaks down tryptophan, affecting immune cell behavior, primarily T-cells. The research focuses on both cellular and antibody-mediated immune responses, often causing graft damage. The study assessed IDO1 expression in renal transplant biopsies from patients with graft function decline, examining its connection to clinical parameters. A total of 121 biopsy samples were evaluated for IDO1 expression using immunohistochemistry. Patients were categorized as IDO1(+) positive or IDO1(−) negative based on immunoreactivity in tubular epithelium. Results showed a significant link between IDO1 expression and rejection incidence. IDO1(+) positive patients had lower rejection rates (32.9%) compared to IDO1(−) negative ones (62.2%) [p = 0.0017], with substantial differences in antibody-mediated rejection (AMR) (5.2% vs. 20%) [p = 0.0085] and T-cell mediated rejection (TCMR) (31.6% vs. 57.8%). These associations suggest that IDO1 may play a protective role in kidney transplant rejection. IDO1 modulation could offer novel therapeutic avenues to enhance graft survival. The study underscores IDO1 as a potential marker for rejection risk assessment, with its potential applications in personalized interventions and improved patient outcomes. Further research is needed to fully comprehend the mechanisms behind IDO1's immunomodulatory functions and its potential clinical translation. [ABSTRACT FROM AUTHOR]

Abstract Indoleamine 2,3‐dioxygenase 1 (IDO1), the key enzyme in the catabolism of the essential amino acid tryptophan (Trp) through kynurenine pathway, induces immune tolerance and is considered as a critical immune checkpoint, but its impacts as a metabolism enzyme on glucose and lipid metabolism are overlooked. We aim to clarify the potential role of IDO1 in aerobic glycolysis in pancreatic cancer (PC). Analysis of database revealed the positive correlation in PC between the expressions of IDO1 and genes encoding important glycolytic enzyme hexokinase 2 (HK2), pyruvate kinase (PK), lactate dehydrogenase A (LDHA) and glucose transporter 1 (GLUT1). It was found that IDO1 could modulate glycolysis and glucose uptake in PC cells, Trp deficiency caused by IDO1 overexpression enhanced glucose uptake by stimulating GLUT1 translocation to the plasma membrane of PC cells. Besides, Trp deficiency caused by IDO1 overexpression suppressed the apoptosis of PC cells via promoting glycolysis, which reveals the presence of IDO1–glycolysis–apoptosis axis in PC. IDO1 inhibitors could inhibit glycolysis, promote apoptosis, and exhibit robust therapeutic efficacy when combined with GLUT1 inhibitor in PC mice. Our study reveals the function of IDO1 in the glucose metabolism of PC and provides new insights into the therapeutic strategy for PC.

For mammary carcinomas in pet rabbits, prognostic biomarkers are poorly defined, and treatment is limited to surgical excision. Additional treatment options are needed for rabbit patients for which surgery is not a suitable option. In human breast cancer, the immunosuppressive enzyme indoleamine 2,3-dioxygenase 1 (IDO1) represents a prognostic biomarker and possible therapeutic target. This retrospective immunohistochemical study examined IDO1 in 96 pet rabbit mammary carcinomas with known mitotic count, hormone receptor status, and percentage of stromal tumor infiltrating lymphocytes (TILs). Tumors were obtained from 96 pet rabbits with an average of 5.5 years. All rabbits with reported sex (n = 88) were female or female-spayed. Of the carcinomas, 94% expressed IDO1, and 86% had sparse TILs consistent with cold tumors. Statistically significant correlations existed between a higher percentage of IDO1-positive tumor cells, lower mitotic counts, and increased estrogen receptor expression. The threshold for significance was IDO1 staining in >10% of tumor cells. These results lead to the assumption that IDO1 expression contributes to tumorigenesis and may represent a prognostic biomarker and possible therapeutic target also in pet rabbit mammary carcinomas. They also support the value of rabbits for breast cancer research.

Indoleamine 2,3-dioxygenase 1 (IDO1) is a tryptophan metabolizing enzyme chronically activated in many cancer patients and its expression and activity correlate with a poor prognosis. In fact, it acts as an immune regulator and contributes to tumor-induced immunosuppression by determining tryptophan deprivation and producing immunosuppressive metabolites named kynurenines. These findings made IDO1 an attractive target for cancer immunotherapy and small-molecule inhibitors, such as epacadostat, have been developed to block its enzymatic activity. Although epacadostat was effective in preclinical models and in early phase trials, it gave negative results in a metastatic melanoma randomized phase III study to test the benefit of adding epacadostat to the reference pembrolizumab therapy. However, the reason for the epacadostat failure in this clinical trial has never been understood. Our data suggest that a possible explanation of epacadostat ineffectiveness may rely on the ability of this drug to enhance the other IDO1 immunoregulatory mechanism, involving intracellular signaling function. These findings open up a new perspective for IDO1 inhibitors developed as new anticancer drugs, which should be carefully evaluated for their ability to block not only the catalytic but also the signaling activity of IDO1. [ABSTRACT FROM AUTHOR]

Indoleamine 2,3-dioxygenase 1 (IDO1) is a tryptophan metabolizing enzyme chronically activated in many cancer patients and its expression and activity correlate with a poor prognosis. In fact, it acts as an immune regulator and contributes to tumor-induced immunosuppression by determining tryptophan deprivation and producing immunosuppressive metabolites named kynurenines. These findings made IDO1 an attractive target for cancer immunotherapy and small-molecule inhibitors, such as epacadostat, have been developed to block its enzymatic activity. Although epacadostat was effective in preclinical models and in early phase trials, it gave negative results in a metastatic melanoma randomized phase III study to test the benefit of adding epacadostat to the reference pembrolizumab therapy. However, the reason for the epacadostat failure in this clinical trial has never been understood. Our data suggest that a possible explanation of epacadostat ineffectiveness may rely on the ability of this drug to enhance the other IDO1 immunoregulatory mechanism, involving intracellular signaling function. These findings open up a new perspective for IDO1 inhibitors developed as new anticancer drugs, which should be carefully evaluated for their ability to block not only the catalytic but also the signaling activity of IDO1.

By far, no revolutionary breakthrough in the treatment of Parkinson's disease (PD) was found. It is indeed a knotty problem to select a satisfactory strategy for treating some patients with advanced stage PD. Development of novel therapeutic targets against PD has been an urgent task faced by global PD researchers. Targets in the tryptophan-kynurenine pathway (KP) were then considered. Metabolites in the KP are liposoluble. Some neurotoxic metabolites, including 3-hydroxykynurenine and its downstream 3-hydroxyanthranilic acid and quinolinic acid, are mainly produced peripherally. They can easily cross the blood-brain barrier (BBB) and exert their neurotoxic effects in the central neuron system (CNS), which is considered as a potential pathophysiological mechanism of neurodegenerative diseases. Hence, agents against the targets in the KP have two characteristics: (1) being independent from the dopaminergic system and (2) being seldom affected by the BBB. Inspiringly, one agent, namely, the inhibitor of indoleamine 2,3-dioxygenase 1, has been currently reported to present satisfactory efficacy comparable to levodopa, implying that the KP might be a potential novel target for PD. This review collected and summarized the updated information regarding the association of the KP with PD, which is helpful for understanding the clinical value of the KP in the PD scenario. [ABSTRACT FROM AUTHOR]

Combining chemo-therapeutics with immune checkpoint inhibitors facilitates killing cancer cells and activating the immune system through inhibiting immune escape. However, their treatment effects remain limited due to the compromised accumulation of both drugs and inhibitors in certain tumor tissues. Herein, a new poly (acrylamide-co-acrylonitrile-co-vinylimidazole-co-bis(2-methacryloyl) oxyethyl disulfide) (PAAVB) polymer-based intelligent platform with controllable upper critical solution temperature (UCST) was used for the simultaneous delivery of paclitaxel (PTX) and curcumin (CUR). Additionally, a hyaluronic acid (HA) layer was coated on the surface of PAAVB NPs to target the CD44-overexpressed tumor cells. The proposed nanomedicine demonstrated a gratifying accumulation in tumor tissue and uptake by cancer cells. Then, the acidic microenvironment and high level of glutathione (GSH) in cancer cells could spontaneously decrease the UCST of polymer, leading to the disassembly of the NPs and rapid drug release at body temperature without extra-stimuli. Significantly, the released PTX and CUR could induce the immunogenic cell death (ICD) to promote adaptive anti-tumor immunogenicity and inhibit immunosuppression through suppressing the activity of indoleamine 2,3-dioxygenase 1 (IDO1) enzyme respectively. Therefore, the synergism of this intelligent nanomedicine can suppress primary breast tumor growth and inhibit their lung metastasis.

Deletion of brain-derived neurotrophic factor (BDNF) and upregulation of indoleamine 2,3-dioxygenase 1 (IDO1) are associated with depression severity in animals. The neurotransmitter hypothesis of depression at the transcriptomic level can be tested using BDNF- and IDO1-knockout mouse models and RNA-seq. In this study, BDNF+/−, IDO1−/−, and chronic ultra-mild stress (CUMS)-induced depression mouse models and controls were developed, and the differentially expressed genes were analyzed. Furthermore, the ceRNA package was used to search the lncRNA2Target database for potential lncRNAs. Finally, a protein–protein interaction (PPI) network was constructed using STRINGdb. By comparing the control and CUMS model groups, it was found that pathway enrichment analysis and ceRNA network analysis revealed that most differentially expressed genes (DEGs) were associated with protection of vulnerable neuronal circuits. In addition, we found the enriched pathways were associated with nervous system development and synapse organization when comparing the control and BDNF+/−model groups. When replicating the neurotransmitter disruption features of clinical patients, such comparisons revealed the considerable differences between CUMS and knockdown BDNF models, and the BDNF+/−model may be superior to the classic CUMS model. The data obtained in the present study implicated the potential DEGs and their enriched pathway in three mouse models related to depression and the regulation of the ceRNA network-mediated gene in the progression of depression. Together, our findings may be crucial for uncovering the mechanisms underlying the neurotransmitter hypothesis of depression in animals. [ABSTRACT FROM AUTHOR]

Deletion of brain-derived neurotrophic factor (BDNF) and upregulation of indoleamine 2,3-dioxygenase 1 (IDO1) are associated with depression severity in animals. The neurotransmitter hypothesis of depression at the transcriptomic level can be tested using BDNF- and IDO1-knockout mouse models and RNA-seq. In this study, BDNF+/−, IDO1−/−, and chronic ultra-mild stress (CUMS)-induced depression mouse models and controls were developed, and the differentially expressed genes were analyzed. Furthermore, the ceRNA package was used to search the lncRNA2Target database for potential lncRNAs. Finally, a protein–protein interaction (PPI) network was constructed using STRINGdb. By comparing the control and CUMS model groups, it was found that pathway enrichment analysis and ceRNA network analysis revealed that most differentially expressed genes (DEGs) were associated with protection of vulnerable neuronal circuits. In addition, we found the enriched pathways were associated with nervous system development and synapse organization when comparing the control and BDNF+/−model groups. When replicating the neurotransmitter disruption features of clinical patients, such comparisons revealed the considerable differences between CUMS and knockdown BDNF models, and the BDNF+/−model may be superior to the classic CUMS model. The data obtained in the present study implicated the potential DEGs and their enriched pathway in three mouse models related to depression and the regulation of the ceRNA network-mediated gene in the progression of depression. Together, our findings may be crucial for uncovering the mechanisms underlying the neurotransmitter hypothesis of depression in animals.

Tryptophan metabolism plays a crucial role in facilitating various cellular processes essential for maintaining normal cellular function. Indoleamine 2,3-dioxygenase 1 (IDO1) catalyzes the conversion of tryptophan (Trp) into kynurenine (Kyn), thereby initiating the degradation of Trp. The resulting Kyn metabolites have been implicated in the modulation of immune responses. Currently, the role of IDO1-mediated tryptophan metabolism in the process of viral infection remains relatively unknown. In this study, we discovered that classical swine fever virus (CSFV) infection of PK-15 cells can induce the expression of IDO1, thereby promoting tryptophan metabolism. IDO1 can negatively regulate the NF-κB signaling by mediating tryptophan metabolism, thereby facilitating CSFV replication. We found that silencing the IDO1 gene enhances the expression of IFN-α, IFN-β, and IL-6 by activating the NF-κB signaling pathway. Furthermore, our observations indicate that both silencing the IDO1 gene and administering exogenous tryptophan can inhibit CSFV replication by counteracting the cellular autophagy induced by Rapamycin. This study reveals a novel mechanism of IDO1-mediated tryptophan metabolism in CSFV infection, providing new insights and a theoretical basis for the treatment and control of CSFV.IMPORTANCEIt is well known that due to the widespread use of vaccines, the prevalence of classical swine fever (CSF) is shifting towards atypical and invisible infections. CSF can disrupt host metabolism, leading to persistent immune suppression in the host and causing significant harm when co-infected with other diseases. Changes in the host's metabolic profiles, such as increased catabolic metabolism of amino acids and the production of immunoregulatory metabolites and their derivatives, can also influence virus replication. Mammals utilize various pathways to modulate immune responses through amino acid utilization, including increased catabolic metabolism of amino acids and the production of immunoregulatory metabolites and their derivatives, thereby limiting viral replication. Therefore, this study proposes that targeting the modulation of tryptophan metabolism may represent an effective approach to control the progression of CSF., Competing Interests: The authors declare no conflict of interest.

Objective: To determine the expression and functional roles of indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase (TDO2) in leiomyoma.Design: Experimental study.Setting: Academic research laboratory.Patient(s): Women undergoing hysterectomy for leiomyoma.Intervention(s): Blockade of IDO1 and TDO2.Main Outcome Measure(s): Expression of IDO1 and TDO2 in leiomyoma and the effects of their inhibitors on the extracellular matrix.Result(s): Leiomyoma expressed significantly higher levels of IDO1 and TDO2 messenger ribonucleic acid (mRNA; 60.3%, 35/58 pairs and 98.3%, 57/58 pairs, respectively) and protein (54%, 27/50 pairs and 92%, 46/50 pairs, respectively) as well as the enzyme activity marker kynurenine (78.3%, 36/46 pairs for IDO1/TDO2) compared with levels in matched myometrium. The expression of TDO2 but not IDO1 mRNA was significantly higher in fibroids from African American compared with that in Caucasian and Hispanic patients. The TDO2 but not the IDO1 protein and mRNA levels were more abundant in fibroids bearing the MED12 mutation compared with results in wild-type leiomyomas. Treatment of leiomyoma smooth muscle cell and myometrial smooth muscle cell spheroids with the TDO2 inhibitor 680C91 but not the IDO1 inhibitor epacadostat significantly repressed cell proliferation and the expression of collagen type I (COL1A1) and type III (COL3A1) in a dose-dependent manner; these effects were more pronounced in leiomyoma smooth muscle cells compared with myometrial smooth muscle cell spheroids.Conclusion(s): These results underscore the physiological significance of the tryptophan degradation pathway in the pathogenesis of leiomyomas and the potential utility of anti-TDO2 drugs for treatment of leiomyomas. [ABSTRACT FROM AUTHOR]

Indoleamine 2,3-dioxygenase 1 (IDO1), a tryptophan catabolising enzyme, is known as a tumour cell survival factor that causes immune escape in several types of cancer. Flavonoids of Sophora flavescens have a variety of biological benefits for humans; however, cancer immunotherapy effect has not been fully investigated. The flavonoids (1–6) isolated from S. flavescens showed IDO1 inhibitory activities (IC50 4.3–31.4 µM). The representative flavonoids (4–6) of S. flavescens were determined to be non-competitive inhibitors of IDO1 by kinetic analyses. Their binding affinity to IDO1 was confirmed using thermal stability and surface plasmon resonance (SPR) assays. The molecular docking analysis and mutagenesis assay revealed the structural details of the interactions between the flavonoids (1–6) and IDO1. These results suggest that the flavonoids (1–6) of S. flavescens, especially kushenol E (6), as IDO1 inhibitors might be useful in the development of immunotherapeutic agents against cancers.

IDO1-mediated immune escape can lead to the malignant progression of tumors. However, the precise mechanism of IDO1 remains unclear. This study showed that IDO1 can bind to GBP1 and increase the extracellular secretion of IDO1 with the assistance of GBP1, thereby promoting the malignant proliferation and metastasis of lung cancer. In vitro study showed that the high expression levels of IDO1 and GBP1 in lung cancer cells promoted cell invasion and migration. In vivo study revealed that knock-down of IDO1 and GBP1 inhibited tumor growth and metastasis. In addition, Astragaloside IV reduces the extracellular secretion of IDO1 by blocking the interaction of IDO1 and GBP1, thereby reducing T cell exhaustion and inhibiting tumor progression. These results suggest that blocking the extracellular secretion of IDO1 may prevent T cell exhaustion and thereby enhance the effect of PD-1 inhibitors on cancer treatment.

IDO1-mediated immune escape can lead to the malignant progression of tumors. However, the precise mechanism of IDO1 remains unclear. This study showed that IDO1 can bind to GBP1 and increase the extracellular secretion of IDO1 with the assistance of GBP1, thereby promoting the malignant proliferation and metastasis of lung cancer. In vitro study showed that the high expression levels of IDO1 and GBP1 in lung cancer cells promoted cell invasion and migration. In vivo study revealed that knock-down of IDO1 and GBP1 inhibited tumor growth and metastasis. In addition, Astragaloside IV reduces the extracellular secretion of IDO1 by blocking the interaction of IDO1 and GBP1, thereby reducing T cell exhaustion and inhibiting tumor progression. These results suggest that blocking the extracellular secretion of IDO1 may prevent T cell exhaustion and thereby enhance the effect of PD-1 inhibitors on cancer treatment. [ABSTRACT FROM AUTHOR]

Knowledge of a protein's spatial dynamics at the subcellular level is key to understanding its function(s), interactions, and associated intracellular events. Indoleamine 2,3‐dioxygenase 1 (IDO1) is a cytosolic enzyme that controls immune responses via tryptophan metabolism, mainly through its enzymic activity. When phosphorylated, however, IDO1 acts as a signaling molecule in plasmacytoid dendritic cells (pDCs), thus activating genomic effects, ultimately leading to long‐lasting immunosuppression. Whether the two activities—namely, the catalytic and signaling functions—are spatially segregated has been unclear. We found that, under conditions favoring signaling rather than catabolic events, IDO1 shifts from the cytosol to early endosomes. The event requires interaction with class IA phosphoinositide 3‐kinases (PI3Ks), which become activated, resulting in full expression of the immunoregulatory phenotype in vivo in pDCs as resulting from IDO1‐dependent signaling events. Thus, IDO1's spatial dynamics meet the needs for short‐acting as well as durable mechanisms of immune suppression, both under acute and chronic inflammatory conditions. These data expand the theoretical basis for an IDO1‐centered therapy in inflammation and autoimmunity. Synopsis: The cytosolic enzyme IDO1 can also act as a signaling molecule in plasmacytoid dendritic cells. Under conditions favoring signaling, IDO1 interacts with PI3K subunits and localizes to early endosomes, a step necessary for immunoregulatory IDO1 signaling in pDCs. [ABSTRACT FROM AUTHOR]

Background: Prunella vulgaris L. (P. vulgaris) has traditionally been used to treat swelling and inflammation of the thyroid gland. This study aimed to evaluate the effects of P. vulgaris on experimental autoimmune thyroiditis (EAT) and explore the roles of indoleamine 2,3-dioxygenase 1 (IDO1) and regulatory T cells (Tregs) in these P. vulgaris-mediated effects. Methods: The main bioactive compounds in P. vulgaris were analysed by high-performance liquid chromatography. An EAT model was established by immunization of Lewis rats with thyroglobulin via subcutaneous injection. Thyroid volume was assessed by ultrasound, and lymphatic infiltration in the thyroid was evaluated by haematoxylin and eosin staining. The serum levels of thyroglobulin antibody (TgAb) and cytokines were measured by indirect enzyme-linked immunosorbent assay. The percentage of CD4+CD25+Foxp3+ Tregs was detected by flow cytometry. The mRNA and protein levels of IDO1 were measured by qRT-PCR and Western blotting, respectively. The levels of tryptophan (Trp) and kynurenine (Kyn) in serum and faecal samples were assessed with a fluorometric kit and spectrophotometry. Results: The main bioactive compound in P. vulgaris was rosmarinic acid. The TgAb level and thyroid volume in EAT rats were significantly decreased after administration of P. vulgaris (P < 0.01). The inflammation score in EAT rats that were administered P. vulgaris was significantly lower than that in the EAT controls (P < 0.01). In addition, P. vulgaris promoted the expansion of splenic Tregs and increased the production of IL-10 and TGF-β (P < 0.01) in EAT rats. Moreover, P. vulgaris induced IDO1 mRNA and protein expression in the spleen and intestine in P. vulgaris-treated EAT rats (P < 0.01). Finally, Trp levels were reduced and Kyn levels and the Kyn/Trp ratio were increased in the serum of P. vulgaris-treated EAT rats. Conclusion: We were the first to demonstrate the role of IDO1-induced Treg expansion in P. vulgaris-mediated attenuation of EAT. Our study provides insight into the immunopathogenesis of autoimmune thyroiditis and shows the potential therapeutic value of P. vulgaris.

Abstract Background Indoleamine 2,3-dioxygenase 1 (IDO1) catalyzes the first and rate-limiting step in converting tryptophan to kynurenine. Chimeric antigen receptor (CAR) T cells are T cells with recombinant receptors targeting tumor-associated antigens. The Food and Drug Administration has approved CAR T cells that target CD19 for treatment of advanced B cell leukemia and lymphoma. However, CAR T cell therapy in solid tumors has been hampered by multiple obstacles. Preclinical and clinical studies suggest that combinatorial immune checkpoint blockade and IDO1 inhibition provide durable therapeutic efficacy against cancer. Yet, the combination of IDO1 inhibition and CAR T has not been attempted. Methods We analyze IDO1 downregulation by miR-153 in colon cancer cells and the association of IDO1 and miR-153 expression with colorectal patient survival. We generate CAR T cells targeting the epidermal growth factor receptor variant III and measure their tumor killing effects against colon cancer cells with or without miR-153 overexpression by killing assays and in xenografts. Results IDO1 is highly expressed in colorectal tumors and is inversely associated with patient survival. miR-153 directly inhibits IDO1 expression by targeting its 3′ untranslated region in colon cancer cells; yet, miR-153 overexpression does not affect cancer cell survival, apoptosis, and colony formation. When colon cancer cells are targeted by CAR T cells, miR-153 overexpression within tumor cells significantly enhances T cell killing in vitro and suppresses xenograft tumor growth in mice. Conclusions These findings indicate that miR-153 inhibits IDO1 expression in colon cancer cells and is a tumor-suppressive miRNA that enhances CAR T cell immunotherapy. This study supports the combinatorial use of IDO1 inhibitors and CAR T cells in treating solid tumors.

L-tryptophan (Trp), an essential amino acid for mammals, is the precursor of a wide array of immunomodulatory metabolites produced by the kynurenine and serotonin pathways. The kynurenine pathway is a paramount source of several immunoregulatory metabolites, including L-kynurenine (Kyn), the main product of indoleamine 2,3-dioxygenase 1 (IDO1) that catalyzes the rate-limiting step of the pathway. In the serotonin pathway, the metabolite N-acetylserotonin (NAS) has been shown to possess antioxidant, antiinflammatory, and neuroprotective properties in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). However, little is known about the exact mode of action of the serotonin metabolite and the possible interplay between the 2 Trp metabolic pathways. Prompted by the discovery that NAS neuroprotective effects in EAE are abrogated in mice lacking IDO1 expression, we investigated the NAS mode of action in neuroinflammation. We found that NAS directly binds IDO1 and acts as a positive allosteric modulator (PAM) of the IDO1 enzyme in vitro and in vivo. As a result, increased Kyn will activate the ligand-activated transcription factor aryl hydrocarbon receptor and, consequently, antiinflammatory and immunoregulatory effects. Because NAS also increased IDO1 activity in peripheral blood mononuclear cells of a significant proportion of MS patients, our data may set the basis for the development of IDO1 PAMs as first-in-class drugs in autoimmune/neuroinflammatory diseases. [ABSTRACT FROM AUTHOR]

Indoleamine 2,3-dioxygenase 1 (IDO1), a tryptophan catabolising enzyme, is known as a tumour cell survival factor that causes immune escape in several types of cancer. Flavonoids of Sophora flavescens have a variety of biological benefits for humans; however, cancer immunotherapy effect has not been fully investigated. The flavonoids (1–6) isolated from S. flavescens showed IDO1 inhibitory activities (IC50 4.3–31.4 µM). The representative flavonoids (4–6) of S. flavescens were determined to be non-competitive inhibitors of IDO1 by kinetic analyses. Their binding affinity to IDO1 was confirmed using thermal stability and surface plasmon resonance (SPR) assays. The molecular docking analysis and mutagenesis assay revealed the structural details of the interactions between the flavonoids (1–6) and IDO1. These results suggest that the flavonoids (1–6) of S. flavescens, especially kushenol E (6), as IDO1 inhibitors might be useful in the development of immunotherapeutic agents against cancers. [ABSTRACT FROM AUTHOR]

The kynurenine pathway (KP) is highly regulated in the immune system, where it promotes immunosuppression in response to infection or inflammation. Indoleamine 2,3-dioxygenase 1 (IDO1), the main enzyme of KP, has a broad spectrum of activity on immune cells regulation, controlling the balance between stimulation and suppression of the immune system at sites of local inflammation, relevant to a wide range of autoimmune and inflammatory diseases. Various autoimmune diseases, among them endocrinopathies, have been identified to date, but despite significant progress in their diagnosis and treatment, they are still associated with significant complications, morbidity, and mortality. The precise cellular and molecular mechanisms leading to the onset and development of autoimmune disease remain poorly clarified so far. In breaking of tolerance, the cells of the innate immunity provide a decisive microenvironment that regulates immune cells’ differentiation, leading to activation of adaptive immunity. The current review provided a comprehensive presentation of the known role of IDO1 and KP activation in the regulation of the innate and adaptive arms of the immune system. Significant attention has been paid to the immunoregulatory role of IDO1 in the most prevalent, organ-specific autoimmune endocrinopathies—type 1 diabetes mellitus (T1DM) and autoimmune thyroiditis.

Graphical abstract Highlights • 38 Indazole derivatives were synthesized. • Compound 35 displayed the most IDO1 inhibitory potency. • Compound 35 was identified as an IDO1/TDO dual inhibitor. • Compound 35 decreased the INFγ-induced IDO1 expression. • Compound 35 exhibited in vivo antitumor activity in CT26 model. Abstract Indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase (TDO) are constitutively overexpressed in many types of cancer cells and exert important immunosuppressive functions. In this article, a series of 4,6-substituted-1 H -indazole derivatives were synthesized and evaluated the inhibitory activities against IDO1 and TDO, as well as their structure-activity relationships (SARs). Among these, compound 35 displayed the most IDO1 inhibitory potency with an IC 50 value of 0.74 μM in an enzymatic assay and 1.37 μM in HeLa cells. Quantitative analysis of the Western blot results indicated that 35 significantly decreased the INFγ-induced IDO1 expression in a concentration-dependent manner. In addition, 35 showed promising TDO inhibition with an IC 50 value of 2.93 μM in the enzymatic assay and 7.54 μM in A172 cells. Moreover, compound 35 exhibited in vivo antitumor activity in the CT26 xenograft model. These findings suggest that 1 H -indazole derivative 35 is a potent IDO1/TDO dual inhibitor, and has the potential to be developed for IDO1/TDO-related cancer treatment. [ABSTRACT FROM AUTHOR]

In mammals, amino acid metabolism has evolved to act as a critical regulator of innate and adaptive immune responses. Rheumatoid arthritis (RA) is the most common form of inflammatory arthropathy sustained by autoimmune responses. We examine here the current knowledge of tryptophan and arginine metabolisms and the main immunoregulatory pathways in amino acid catabolism, in both RA patients and experimental models of arthritis. We found that l-tryptophan (Trp) metabolism and, in particular, the kynurenine pathway would exert protective effects in all experimental models and in some, but not all, RA patients, possibly due to single nucleotide polymorphisms in the gene coding for indoleamine 2,3-dioxygenase 1 (IDO1; the enzyme catalyzing the rate-limiting step of the kynurenine pathway). The function, i.e., either protective or pathogenetic, of the l-arginine (Arg) metabolism in RA was less clear. In fact, although immunoregulatory arginase 1 (ARG1) was highly induced at the synovial level in RA patients, its true functional role is still unknown, possibly because of few available preclinical data. Therefore, our analysis would indicate that amino acid metabolism represents a fruitful area of research for new drug targets for a more effective and safe therapy of RA and that further studies are demanding to pursue such an important objective.

Although significant progress has been made in understanding autoimmunity, no immunotherapy to effectively halt immune-mediated destruction of β cells in type 1 diabetes (T1D) is currently available. For successful immunotherapy it will be necessary to identify novel drug targets as well as robust immunologic biomarkers to predict disease heterogeneity and patient responsiveness. Inhibition of immune checkpoint mechanisms represents a novel and effective strategy in tumor immunotherapy. Because they are fundamental to rewiring immune circuits, the underlying mechanisms could be therapeutically enhanced and used as biomarkers in T1D. We examine here current knowledge of immune checkpoint molecules in T1D. One specific immune checkpoint mechanism, namely tryptophan metabolism, may meet the need for a valid drug target and robust biomarker in the quest for effective and personalized immunotherapy in T1D. Highlights T1D is a heterogeneous autoimmune disease for which an effective cure by immunotherapy has not yet been identified. Immune checkpoint molecules are regulators of the immune system that maintain self-tolerance and prevent autoimmunity. Indoleamine 2,3-dioxygenase 1 (IDO1) is an immune checkpoint enzyme that is defective in patients affected by T1D and is characterized by genetic polymorphism. Restoration of full IDO1 activity can be obtained in vitro by using a blocker of the interleukin-6 receptor (tocilizumab) in peripheral blood mononuclear cells from patients with T1D characterized by a specific IDO1 genotype (rs7820268 C>T). Personalized drug targeting of IDO1 may lead to an effective cure by immunotherapy in patients with T1D. [ABSTRACT FROM AUTHOR]

In our endeavor towards the development of potent multi-target ligands for the treatment of Alzheimer’s disease, miconazole was identified to show BuChE-IDO1 dual-target inhibitory effects. Morris water maze test indicated that miconazole obviously ameliorated the cognitive function impaired by scopolamine. Furthermore, it showed good safety in primary hepatotoxicity evaluation. Based on these results, we designed, synthesized, and evaluated a series of miconazole derivatives as BuChE-IDO1 dual-target inhibitors. Out of the 12 compounds, 5i and 5j exhibited the best potency in enzymatic evaluation, thus were selected for subsequent behavioral study, in which the two compounds exerted much improved effect than tacrine. Meanwhile, 5i and 5j displayed no apparent hepatotoxicity. The results suggest that miconazole analogue offers an attractive starting point for further development of new BuChE-IDO1 dual-target inhibitors against Alzheimer’s disease. [ABSTRACT FROM AUTHOR]

Long non-coding RNAs (LncRNAs) have been recently regarded as systemic regulators in multiple biologic processes including tumorigenesis. In this study, we observed the expression of lncRNA lnc-sox5 was significantly increased in colorectal cancer (CRC). Despite the CRC cell growth, cell cycle and cell apoptosis was not affected by lnc-sox5 knock-down, lnc-sox5 knock-down suppressed CRC cell migration and invasion. In addition, xenograft animal model suggested that lnc-sox5 knock-down significantly suppressed the CRC tumorigenesis. Our results also showed that the expression of indoleamine 2,3-dioxygenase 1 (IDO1) was significantly reduced by lnc-sox5 knock-down and therefore modulated the infiltration and cytotoxicity of CD3+CD8+T cells. Taken together, these results suggested that lnc-sox5 unbalances tumor microenvironment to regulate colorectal cancer progression. [ABSTRACT FROM PUBLISHER]

Indoleamine 2,3-dioxygenase 1 (IDO1)-mediated kynurenine pathway of tryptophan degradation is identified as an important immune effector pathway in the tumor cells to escape a potentially effective immune response. IDO1 is an attractive target for anticancer therapy and the discovery of IDO1 inhibitors has been intensely ongoing in both academic research laboratories and pharmaceutical organizations. Our study discovered that 1 H -indazole was a novel key pharmacophore with potent IDO1 inhibitory activity. A series of new 1 H -indazole derivatives were synthesized and determined the enzyme inhibitory activities, and the compound 2g exhibited the highest activity with an IC 50 value of 5.3 μM. The structure–activity relationships (SARs) analysis of the 1 H -indazole derivatives as novel IDO1 inhibitors indicated that the 1 H -indazole scaffold is necessary for IDO1 inhibition, and the substituent groups at the both 4-position and 6-position largely affect inhibitory activity. The docking model exhibited that the effective interactions of 1 H -indazoles with ferrous ion of heme and key residues of hydrophobic Pocket A and B ensured the IDO1 inhibitory activities. The study suggested that the 1 H -indazole was a novel interesting scaffold for IDO inhibition for further development. [ABSTRACT FROM AUTHOR]

Tryptophan-2,3-dioxygenase (TDO) and indoleamine-2, 3-dioxygenase 1 (IDO1) are the important tumor immune checkpoints and TDO and IDO1 inhibition may present a potential approach to activate the T cell-mediated antitumor immune response during cancer treatment. Herein, we designed and synthesized a series of nitro-aryl 1 H -indazole derivatives. SARs analysis showed that the nitro-aryl at the C-4 position of 1 H -indazole was beneficial for TDO inhibition and directly tumoricidal effect and the substituents at C-6 position of 1 H -indazole significantly affected the activity and selectivity of IDO1/TDO. Among these derivatives, HT-28 and HT-30 demonstrated nanomolar potency and excellent selectivity against TDO with IC 50 values of 0.62 μM and 0.17 μM respectively, and HT-37 showed the IDO1 and TDO dual-target inhibitory activity with IC 50 values of 0.91 μM and 0.46 μM against IDO1 and TDO. Moreover, HT-28 showed the significant tumoricidal effect on six tumor cell lines, while HT-30 and HT-37 had almost no cytotoxic activity on these tumor cells. In the CT-26 allograft BALB/c mice, HT-28 had the significant in vivo antitumor activity at a lower dose. IHC staining assay indicated that HT-28 could reduce the expression of Foxp3 and enhance the expression of CD8 and TNF-α in tumor tissue. In summary, we developed a difunctional monomer with immune-chemotherapy effect to obtain the better in anti-tumor activity. [Display omitted] • HT-28 is a difunctional monomer with immune-chemotherapies. • HT-28 demonstrates nanomolar potency and excellent selectivity against TDO. • HT-28 inhibits in vivo tumor growth and increases the immune response. • The nitro-aryl of C-4 is beneficial for TDO inhibition and directly tumoricidal effect. • The substituents at C-6 position significantly affect the activity of IDO1/TDO. [ABSTRACT FROM AUTHOR]

Abstract: Cinnabarinic acid (CA) is an endogenous metabolite of the kynurenine pathway which acts as an orthosteric agonist of type-4 metabotropic glutamate receptor (mGlu4). We now report that systemic administration of CA (0.1–10 mg/kg, i.p.) was highly protective against experimental autoimmune encephalomyelitis (EAE) induced by the myelin oligodendrocyte glycoprotein (MOG35-55) peptide, which models multiple sclerosis in mice. Full protection against EAE required daily injections of CA since the time of immunization, similarly to what reported for the mGlu4 enhancer N-phenyl-7-(hydroxyimino)cyclopropa[b]chromen-1acarboxamide (PHCCC). CA treatment boosted an immune response dominated by regulatory T (Treg) cells at the expenses of Th17 cells. In addition, exogenous CA enhanced endogenous CA formation in lymphocytes, suggesting the occurrence of a positive feedback loop sustaining immune tolerance. To examine whether activation of mGlu4 could account for the protective activity of CA against EAE, we used mGlu4 knockout mice. As expected, these mice displayed a more severe form of EAE in response to immunization. CA was still protective against EAE in mGlu4-deficient mice, although its action was significantly reduced both at high and low CA doses. This suggests that the action of CA against neuroinflammation involves multiple mechanisms including the activation of mGlu4. These data further suggest that CA is one possible bridge between activation of the kynurenine pathway and immune tolerance aimed at restraining neuroinflammation. [Copyright &y& Elsevier]

Screening of a fragment library identified 2-hydrazinobenzothiazole as a potent inhibitor of indoleamine 2,3-dioxygenase 1 (IDO1), an enzyme expressed by tumours that suppresses the immune system. Spectroscopic studies indicated that 2-hydrazinobenzothiazole interacted with the IDO1 haem and in silico docking predicted that the interaction was through hydrazine. Subsequent studies of hydrazine derivatives identified phenylhydrazine (IC50 =0.25±0.07μM) to be 32-fold more potent than 2-hydrazinobenzothiazole (IC50 =8.0±2.3μM) in inhibiting rhIDO1 and that it inhibited cellular IDO1 at concentrations that were noncytotoxic to cells. Here, phenylhydrazine is shown to inhibit IDO1 through binding to haem. [ABSTRACT FROM AUTHOR]

By far, no revolutionary breakthrough in the treatment of Parkinson's disease (PD) was found. It is indeed a knotty problem to select a satisfactory strategy for treating some patients with advanced stage PD. Development of novel therapeutic targets against PD has been an urgent task faced by global PD researchers. Targets in the tryptophan-kynurenine pathway (KP) were then considered. Metabolites in the KP are liposoluble. Some neurotoxic metabolites, including 3-hydroxykynurenine and its downstream 3-hydroxyanthranilic acid and quinolinic acid, are mainly produced peripherally. They can easily cross the blood-brain barrier (BBB) and exert their neurotoxic effects in the central neuron system (CNS), which is considered as a potential pathophysiological mechanism of neurodegenerative diseases. Hence, agents against the targets in the KP have two characteristics: (1) being independent from the dopaminergic system and (2) being seldom affected by the BBB. Inspiringly, one agent, namely, the inhibitor of indoleamine 2,3-dioxygenase 1, has been currently reported to present satisfactory efficacy comparable to levodopa, implying that the KP might be a potential novel target for PD. This review collected and summarized the updated information regarding the association of the KP with PD, which is helpful for understanding the clinical value of the KP in the PD scenario.

Abstract: Interferon gamma (IFNγ) is a cytokine involved in many anti-viral and immunoregulatory processes. One of the major mechanisms through which IFNγ exerts these effects is by inducing expression of indoleamine 2,3 dioxygenase-1 (IDO1), an enzyme that catalyses the first, rate-limiting step of the kynurenine pathway. In this pathway, tryptophan can be catabolised to many products, including picolinic acid and nicotinamide adenine dinucleotide. However, in endothelial cells, the pathway ends at the production of kynurenine. This is due to little or no expression of enzymes that metabolise kynurenine. Production of kynurenine has been used as an indicator of human IDO1 activity, and hence as an hIDO1 bioassay. Due to IFNγ's ability to induce IDO1 expression, kynurenine production can also be a measure of human IFNγ (hIFNγ) bioactivity. Previously, the levels of hIFNγ have been commonly determined by anti-viral assays, high performance liquid chromatography and ELISA. Apart from their technical complexity, these assays are costly and only the anti-viral assay measures bioactive IFNγ. Here, we report the development of an improved IFNγ spectrophotometric bioassay using a human brain endothelial cell line (HBEC 5i). The method is sensitive, easy to perform and cost efficient. [Copyright &y& Elsevier]

The kynurenine pathway (KP) is highly regulated in the immune system, where it promotes immunosuppression in response to infection or inflammation. Indoleamine 2,3-dioxygenase 1 (IDO1), the main enzyme of KP, has a broad spectrum of activity on immune cells regulation, controlling the balance between stimulation and suppression of the immune system at sites of local inflammation, relevant to a wide range of autoimmune and inflammatory diseases. Various autoimmune diseases, among them endocrinopathies, have been identified to date, but despite significant progress in their diagnosis and treatment, they are still associated with significant complications, morbidity, and mortality. The precise cellular and molecular mechanisms leading to the onset and development of autoimmune disease remain poorly clarified so far. In breaking of tolerance, the cells of the innate immunity provide a decisive microenvironment that regulates immune cells' differentiation, leading to activation of adaptive immunity. The current review provided a comprehensive presentation of the known role of IDO1 and KP activation in the regulation of the innate and adaptive arms of the immune system. Significant attention has been paid to the immunoregulatory role of IDO1 in the most prevalent, organ-specific autoimmune endocrinopathies—type 1 diabetes mellitus (T1DM) and autoimmune thyroiditis. [ABSTRACT FROM AUTHOR]