Rationale: Immunosuppressive tumor microenvironment (iTME) plays an important role in carcinogenesis, and some macrophage subsets are associated with iTME generation. However, the sub-population characterization of macrophages in oral carcinogenesis remains largely unclear. Here, we investigated the immunosuppressive status with focus on function of a macrophage subset that expressed indoleamine 2,3 dioxygenase 1 (Macro-IDO1) in oral carcinogenesis. Methods: We built a single cell transcriptome atlas from 3 patients simultaneously containing oral squamous cell carcinoma (OSCC), precancerous oral leukoplakia (preca-OLK) and paracancerous tissue (PCA). Through single-cell RNA sequencing and further validation using multicolor immunofluorescence staining and the in vitro/in vivo experiments, the immunosuppressive cell profiles were built and the role of a macrophage subset that expressed indoleamine 2,3 dioxygenase 1 (Macro-IDO1) in the malignant transformation of oral leukoplakia was evaluated. Results: The iTME formed at preca-OLK stage, as evidenced by increased exhausted T cells, Tregs and some special subsets of macrophages and fibroblasts. Macro-IDO1 was predominantly enriched in preca-OLK and OSCC, distributed near exhausted T cells and possessed tumor associated macrophage transformation potentials. Functional analysis revealed the established immunosuppressive role of Macro-IDO1 in preca-OLK and OSCC: enriching the immunosuppression related genes; having an established level of immune checkpoint score; exerting strong immunosuppressive interaction with T cells; positively correlating with the CD8-exhausted. The immunosuppression related gene expression of macrophages also increased in preca-OLK/OSCC compared to PCA. The use of the IDO1 inhibitor reduced 4NQO induced oral carcinogenesis in mice. Mechanistically, IFN-γ-JAK-STAT pathway was associated with IDO1 upregulation in OLK and OSCC. Conclusions: These results highlight that Macro-IDO1-enriched in preca-OLK possesses a strong immunosuppressive role and contributes to oral carcinogenesis, providing a potential target for preventing precancerous legions from transformation into OSCC.

Tryptophan (Trp) metabolism plays a vital role in cancer immunity. Indoleamine 2.3-dioxygenase 1 (IDO1), is a crucial enzyme in the metabolic pathway by which Trp is degraded to kynurenine (Kyn). IDO1-mediated Trp metabolites can inhibit tumor immunity and facilitate immune evasion by cancer cells; thus, targeting IDO1 is a potential tumor immunotherapy strategy. Recently, numerous IDO1 inhibitors have been introduced into clinical trials as immunotherapeutic agents for cancer treatment. However, drawbacks such as low oral bioavailability, slow onset of action, and high toxicity are associated with these drugs. With the continuous development of nanotechnology, medicine is gradually entering an era of precision healthcare. Nanodrugs carried by inorganic, lipid, and polymer nanoparticles (NPs) have shown great potential for tumor therapy, providing new ways to overcome tumor diversity and improve therapeutic efficacy. Compared to traditional drugs, nanomedicines offer numerous significant advantages, including a prolonged half-life, low toxicity, targeted delivery, and responsive release. Moreover, based on the physicochemical properties of these nanomaterials (eg, photothermal, ultrasonic response, and chemocatalytic properties), various combination therapeutic strategies have been developed to synergize the effects of IDO1 inhibitors and enhance their anticancer efficacy. This review is an overview of the mechanism by which the Trp-IDO1-Kyn pathway acts in tumor immune escape. The classification of IDO1 inhibitors, their clinical applications, and barriers for translational development are discussed, the use of IDO1 inhibitor-based nanodrug delivery systems as combination therapy strategies is summarized, and the issues faced in their clinical application are elucidated. We expect that this review will provide guidance for the development of IDO1 inhibitor-based nanoparticle nanomedicines that can overcome the limitations of current treatments, improve the efficacy of cancer immunotherapy, and lead to new breakthroughs in the field of cancer immunotherapy.

Despite the immune system\'s role in the detection and eradication of abnormal cells, cancer cells often evade elimination by exploitation of various immune escape mechanisms. Among these mechanisms is the ability of cancer cells to upregulate amino acid-metabolizing enzymes, or to induce these enzymes in tumor-infiltrating immunosuppressive cells. Amino acids are fundamental cellular nutrients required for a variety of physiological processes, and their inadequacy can severely impact immune cell function. Amino acid-derived metabolites can additionally dampen the anti-tumor immune response by means of their immunosuppressive activities, whilst some can also promote tumor growth directly. Based on their evident role in tumor immune escape, the amino acid-metabolizing enzymes glutaminase 1 (GLS1), arginase 1 (ARG1), inducible nitric oxide synthase (iNOS), indoleamine 2,3-dioxygenase 1 (IDO1), tryptophan 2,3-dioxygenase (TDO) and interleukin 4 induced 1 (IL4I1) each serve as a promising target for immunotherapeutic intervention. This review summarizes and discusses the involvement of these enzymes in cancer, their effect on the anti-tumor immune response and the recent progress made in the preclinical and clinical evaluation of inhibitors targeting these enzymes.

Although therapies based on mesenchymal stromal cells (MSCs) are being implemented in clinical settings, many aspects regarding these procedures require further optimization. Domestic dogs suffer from numerous immune-mediated diseases similar to those found in humans. This study aimed to assess the immunomodulatory activity of canine (c) Wharton jelly (WJ)-derived MSCs and refer them to human (h) MSCs isolated from the same tissue. Canine MSC(WJ)s appeared to be more prone to in vitro aging than their human counterparts. Both canine and human MSC(WJ)s significantly inhibited the activation as well as proliferation of CD4+ and CD8+ T cells. The treatment with IFNγ significantly upregulated indoleamine-2,3-dioxygenase 1 (IDO1) synthesis in human and canine MSC(WJ)s, and the addition of poly(I:C), TLR3 ligand, synergized this effect in cells from both species. Unstimulated human and canine MSC(WJ)s released TGFβ at the same level (p > 0.05). IFNγ significantly increased the secretion of TGFβ in cells from both species (p < 0.05); however, this response was significantly stronger in human cells than in canine cells. Although the properties of canine and human MSC(WJ)s differ in detail, cells from both species inhibit the proliferation of activated T cells to a very similar degree and respond to pro-inflammatory stimulation by enhancing their anti-inflammatory activity. These results suggest that testing MSC transplantation in naturally occurring immune-mediated diseases in dogs may have high translational value for human clinical trials.

This review discusses the potential of targeting the kynurenine pathway (KP) in the treatment of inflammatory diseases. The KP, responsible for the catabolism of the amino acid tryptophan (TRP), produces metabolites that regulate various physiological processes, including inflammation, cell cycle, and neurotransmission. These metabolites, although necessary to maintain immune balance, may accumulate excessively during inflammation, leading to systemic disorders. Key KP enzymes such as indoleamine 2,3-dioxygenase 1 (IDO1), indoleamine 2,3-dioxygenase 2 (IDO2), tryptophan 2,3-dioxygenase (TDO), and kynurenine 3-monooxygenase (KMO) have been considered promising therapeutic targets. It was highlighted that both inhibition and activation of these enzymes may be beneficial, depending on the specific inflammatory disorder. Several inflammatory conditions, including autoimmune diseases, for which modulation of KP activity holds therapeutic promise, have been described in detail. Preclinical studies suggest that this modulation may be an effective treatment strategy for diseases for which treatment options are currently limited. Taken together, this review highlights the importance of further research on the clinical application of KP enzyme modulation in the development of new therapeutic strategies for inflammatory diseases.

UNASSIGNED: Introduction: The influenza virus primarily targets the respiratory tract, yet both the respiratory and intestinal systems suffer damage during infection. The connection between lung and intestinal damage remains unclear.
UNASSIGNED: Our experiment employs 16S rRNA technology and Liquid Chromatography-Mass Spectrometry (LC-MS) to detect the impact of influenza virus infection on the fecal content and metabolites in mice. Additionally, it investigates the effect of influenza virus infection on intestinal damage and its underlying mechanisms through HE staining, Western blot, Q-PCR, and flow cytometry.
UNASSIGNED: Our study found that influenza virus infection caused significant damage to both the lungs and intestines, with the virus detected exclusively in the lungs. Antibiotic treatment worsened the severity of lung and intestinal damage. Moreover, mRNA levels of Toll-like receptor 7 (TLR7) and Interferon-b (IFN-b) significantly increased in the lungs post-infection. Analysis of intestinal microbiota revealed notable shifts in composition after influenza infection, including increased Enterobacteriaceae and decreased Lactobacillaceae. Conversely, antibiotic treatment reduced microbial diversity, notably affecting Firmicutes, Proteobacteria, and Bacteroidetes. Metabolomics showed altered amino acid metabolism pathways due to influenza infection and antibiotics. Abnormal expression of indoleamine 2,3-dioxygenase 1 (IDO1) in the colon disrupted the balance between helper T17 cells (Th17) and regulatory T cells (Treg cells) in the intestine. Mice infected with the influenza virus and supplemented with tryptophan and Lactobacillus showed reduced lung and intestinal damage, decreased Enterobacteriaceae levels in the intestine, and decreased IDO1 activity.
UNASSIGNED: Overall, influenza infection caused damage to lung and intestinal tissues, disrupted intestinal microbiota and metabolites, and affected Th17/Treg balance. Antibiotic treatment exacerbated these effects. Supplementation with tryptophan and Lactobacillus improved lung and intestinal health, highlighting a new understanding of the lung-intestine connection in influenza-induced intestinal disease.

Tryptophan (Trp) is an essential amino acid, whose metabolism is a key gatekeeper of intestinal homeostasis. Yet, its systemic effects, particularly on atherosclerosis, remain unknown. Here we show that high-fat diet (HFD) increases the activity of intestinal indoleamine 2, 3-dioxygenase 1 (IDO), which shifts Trp metabolism from the production of microbiota-derived indole metabolites towards kynurenine production. Under HFD, the specific deletion of IDO in intestinal epithelial cells leads to intestinal inflammation, impaired intestinal barrier, augmented lesional T lymphocytes and atherosclerosis. This is associated with an increase in serotonin production and a decrease in indole metabolites, thus hijacking Trp for the serotonin pathway. Inhibition of intestinal serotonin production or supplementation with indole derivatives alleviates plaque inflammation and atherosclerosis. In summary, we uncover a pivotal role of intestinal IDO in the fine-tuning of Trp metabolism with systemic effects on atherosclerosis, paving the way for new therapeutic strategies to relieve gut-associated inflammatory diseases.

Early detection of cancer via biomarkers is vital for improving patient survival rates. In the case of skin cancers, low-molecular-weight biomarkers can penetrate the skin barrier, enabling non-invasive sampling at an early stage. This study focuses on detecting tryptophan (Trp) and kynurenine (Kyn) on the surface of reconstructed 3D melanoma and melanocyte models. This is examined in connection with IDO-1 and IL-6 expression in response to IFN-γ or UVB stimulation, both crucial factors of the melanoma tumor microenvironment (TME). Using a polystyrene scaffold, full-thickness human skin equivalents containing fibroblasts, keratinocytes, and melanocytes or melanoma cells were developed. The samples were stimulated with IFN-γ or UVB, and Trp and Kyn secretion was measured using HPLC-PDA and HPLC-MS. The expression of IDO-1 and IL-6 was measured using RT-qPCR. Increased Trp catabolism to Kyn was observed in IFN-γ-stimulated melanoma and melanocyte models, along with higher IDO-1 expression. UVB exposure led to significant changes in Kyn levels but only in the melanoma model. This study demonstrates the potential of skin surface Trp and Kyn monitoring to capture TME metabolic changes. It also lays the groundwork for future in vivo studies, aiding in understanding and monitoring skin cancer progression.

Artesunate (ART), a natural product isolated from traditional Chinese plant Artemisia annua, has not been extensively explored for its anti-melanoma properties. In our study, we found that ART inhibited melanoma cell proliferation and induced melanoma cell ferroptosis. Mechanistic study revealed that ART directly targets Ido1, thereby suppressing Hic1-mediated transcription suppression of Hmox1, resulting in melanoma cell ferroptosis. In CD8+ T cells, ART does not cause cell ferroptosis due to the low expression of Hmox1. It also targets Ido1, elevating tryptophan levels, which inhibits NFATc1-mediated PD1 transcription, consequently activating CD8+ T cells. Our study uncovered a potent and synergistic anti-melanoma efficacy arising from ART-induced melanoma cell ferroptosis and concurrently enhancing CD8+ T cell-mediated immune response both in vivo and in vitro through directly targeting Ido1. Our study provides a novel mechanistic basis for the utilization of ART as an Ido1 inhibitor and application in clinical melanoma treatment.

BACKGROUND: Indoleamine 2,3- dioxygenase 1 (IDO1) is an immunosuppressive enzyme that has been correlated with shorter disease-specific survival in patients with urothelial carcinoma (UC). IDO1 may counteract the antitumor effects of immune checkpoint inhibitors. Epacadostat is a potent and highly selective inhibitor of IDO1. In the phase I/II ECHO-202/KEYNOTE-037 study, epacadostat plus pembrolizumab resulted in a preliminary objective response rate (ORR) of 35% in a cohort of patients with advanced UC.
METHODS: ECHO-307/KEYNOTE-672 was a double-blinded, randomized, phase III study. Eligible adults had confirmed locally advanced/unresectable or metastatic UC of the urinary tract and were ineligible to receive cisplatin-based chemotherapy. Participants were randomly assigned (1:1) to receive epacadostat (100 mg twice daily) plus pembrolizumab (200 mg every 3 weeks) or placebo plus pembrolizumab for up to 35 pembrolizumab infusions. The primary endpoint was investigator-assessed ORR per Response Evaluation Criteria in Solid Tumors (version 1.1).
RESULTS: A total of 93 patients were randomized (epacadostat plus pembrolizumab, n = 44; placebo plus pembrolizumab, n = 49). Enrollment was stopped early due to emerging data from the phase III ECHO-301/KEYNOTE-252 study. The median duration of follow-up was 64 days in both arms. Based on all available data at cutoff, ORR (unconfirmed) was 31.8% (95% CI, 22.46-55.24%) for epacadostat plus pembrolizumab and 24.5% (95% CI, 15.33-43.67%) for placebo plus pembrolizumab. Circulating kynurenine levels numerically increased from C1D1 to C2D1 in the placebo-plus-pembrolizumab arm and decreased in the epacadostat-plus-pembrolizumab arm. Epacadostat-plus-pembrolizumab combination treatment was well tolerated with a safety profile similar to the placebo arm. Treatment discontinuations due to treatment-related adverse events were more frequent with epacadostat (11.6% vs. 4.1%).
CONCLUSIONS: Treatment with epacadostat plus pembrolizumab resulted in a similar ORR and safety profile as placebo plus pembrolizumab in cisplatin-ineligible patients with previously untreated locally advanced/unresectable or metastatic UC. At a dose of 100 mg twice daily, epacadostat did not appear to completely normalize circulating kynurenine levels when administered with pembrolizumab. Larger studies with longer follow-up and possibly testing higher doses of epacadostat, potentially in different therapy settings, may be warranted.
BACKGROUND: ClinicalTrials.gov identifier: NCT03361865, retrospectively registered December 5, 2017.