Extensive profiling of the expression of the indoleamine 2,3-dioxygenase 1 protein in normal and tumoral human tissues

Increased coexpression of PD-L1 and IDO1 is associated with poor overall survival in patients with NK/T-cell lymphoma

Immunotherapy with programmed cell death 1 ligand 1 (PD-L1) blockade was effective in patients with NK/T-cell lymphoma. In addition to PD-L1, indoleamine 2,3-dioxygenase-1 (IDO1) is one of the most promising immunotherapeutic targets. High proportions of PD-L1 and IDO1 proteins were observed by immunohistochemistry (IHC) from 230 newly diagnosed patients with NK/T lymphoma with tissue samples from three cancer centers and were associated with poor overall survival (OS) in patients with NK/T lymphoma. Importantly, the coexpression of PD-L1 and IDO1 was related to poor OS and short restricted mean survival time in patients with NK/T lymphoma and was an independent prognostic factor in the training cohorts, and which was also validated in 58 NK/T lymphoma patients (GSE90597). Moreover, a nomogram model constructed with PD-L1 and IDO1 expression together with age could provide concise and precise predictions of OS rates and median survival time. The high-risk group in the nomogram model had a positive correlation with CD4 + T-cell infiltration in the validation cohort, as did the immunosuppressive factor level. Therefore, high PD-L1 and IDO1 expression was associated with poor OS in patients with NK/T lymphoma. PD-L1 and IDO1 might be potential targets for future immune checkpoint blockade (ICB) therapy for NK/T lymphoma.

Immunometabolism in cancer: basic mechanisms and new targeting strategy

Maturing immunometabolic research empowers immune regulation novel approaches. Progressive metabolic adaptation of tumor cells permits a thriving tumor microenvironment (TME) in which immune cells always lose the initial killing capacity, which remains an unsolved dilemma even with the development of immune checkpoint therapies. In recent years, many studies on tumor immunometabolism have been reported. The development of immunometabolism may facilitate anti-tumor immunotherapy from the recurrent crosstalk between metabolism and immunity. Here, we discuss clinical studies of the core signaling pathways of immunometabolism and their inhibitors or agonists, as well as the specific functions of these pathways in regulating immunity and metabolism, and discuss some of the identified immunometabolic checkpoints. Understanding the comprehensive advances in immunometabolism helps to revise the status quo of cancer treatment. An overview of the new landscape of immunometabolism. The PI3K pathway promotes anabolism and inhibits catabolism. The LKB1 pathway inhibits anabolism and promotes catabolism. Overactivation of PI3K/AKT/mTOR pathway and IDO, IL4I1, ACAT, Sirt2, and MTHFD2 promote immunosuppression of TME formation, as evidenced by increased Treg and decreased T-cell proliferation. The LKBI-AMPK pathway promotes the differentiation of naive T cells to effector T cells and memory T cells and promotes anti-tumor immunity in DCs.

Cellular metabolism regulates the differentiation and function of T-cell subsets

T cells are an important component of adaptive immunity and protect the host from infectious diseases and cancers. However, uncontrolled T cell immunity may cause autoimmune disorders. In both situations, antigen-specific T cells undergo clonal expansion upon the engagement and activation of antigens. Cellular metabolism is reprogrammed to meet the increase in bioenergetic and biosynthetic demands associated with effector T cell expansion. Metabolites not only serve as building blocks or energy sources to fuel cell growth and expansion but also regulate a broad spectrum of cellular signals that instruct the differentiation of multiple T cell subsets. The realm of immunometabolism research is undergoing swift advancements. Encapsulating all the recent progress within this concise review in not possible. Instead, our objective is to provide a succinct introduction to this swiftly progressing research, concentrating on the metabolic intricacies of three pivotal nutrient classes-lipids, glucose, and amino acids-in T cells. We shed light on recent investigations elucidating the roles of these three groups of metabolites in mediating the metabolic and immune functions of T cells. Moreover, we delve into the prospect of "editing" metabolic pathways within T cells using pharmacological or genetic approaches, with the aim of synergizing this approach with existing immunotherapies and enhancing the efficacy of antitumor and antiinfection immune responses.

Kynurenine Pathway in Respiratory Diseases

The kynurenine pathway is the primary route for tryptophan catabolism and has received increasing attention as its association with inflammation and the immune system has become more apparent. This review provides a broad overview of the kynurenine pathway in respiratory diseases, from the initial observations to the characterization of the different cell types involved in the synthesis of kynurenine metabolites and the underlying immunoregulatory mechanisms. With a focus on respiratory infections, the various attempts to characterize the kynurenine/tryptophan (K/T) ratio as an inflammatory marker are reviewed. Its implication in chronic lung inflammation and its exacerbation by respiratory pathogens is also discussed. The emergence of preclinical interventional studies targeting the kynurenine pathway opens the way for the future development of new therapies.

The role of dendritic cells in cancer immunity and therapeutic strategies

Dendritic cells (DCs) are asserted as the most potent antigen-presenting cells (APCs) that orchestrate both innate and adaptive immunity, being extremely effective in the induction of robust anti-cancer T cell responses. Hence, the modulation of DCs function represents an attractive target for improving cancer immunotherapy efficacy. A better understanding of the immunobiology of DCs, the interaction among DCs, immune effector cells and tumor cells in tumor microenvironment (TME) and the latest advances in biomedical engineering technology would be required for the design of optimal DC-based immunotherapy. In this review, we focus on elaborating the immunobiology of DCs in healthy and cancer environments, the recent advances in the development of enhancing endogenous DCs immunocompetence via immunomodulators as well as DC-based vaccines. The rapidly developing field of applying nanotechnology to improve DC-based immunotherapy is also highlighted.

The dynamic role of immune checkpoint molecules in diagnosis, prognosis, and treatment of head and neck cancers

Head and neck cancer (HNC) is the sixth most common cancer type, accounting for approximately 277,597 deaths worldwide. Recently, the Food and Drug Administration (FDA) has approved immune checkpoint blockade (ICB) agents targeting programmed death-1 (PD-1) and programmed death-ligand 1 (PD-L1) as a treatment regimen for head and neck squamous cell carcinomas (HNSCC). Studies have reported the role of immune checkpoint inhibitors as targeted therapeutic regimens that unleash the immune response against HNSCC tumors. However, the overall response rates to immunotherapy vary between 14-32% in recurrent or metastatic HNSCC, with clinical response and treatment success being unpredictable. Keeping this perspective in mind, it is imperative to understand the role of T cells, natural killer cells, and antigen-presenting cells in modulating the immune response to immunotherapy. In lieu of this, these immune molecules could serve as prognostic and predictive biomarkers to facilitate longitudinal monitoring and understanding of treatment dynamics. These immune biomarkers could pave the path for personalized monitoring and management of HNSCC. In this review, we aim to provide updated immunological insight on the mechanism of action, expression, and the clinical application of immune cells' stimulatory and inhibitory molecules as prognostic and predictive biomarkers in HNC. The review is focused mainly on CD27 and CD137 (members of the TNF-receptor superfamily), natural killer group 2 member D (NKG2D), tumor necrosis factor receptor superfamily member 4 (TNFRSF4 or OX40), S100 proteins, PD-1, PD-L1, PD-L2, T cell immunoglobulin and mucin domain 3 (TIM-3), cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), lymphocyte-activation gene 3 (LAG-3), indoleamine-pyrrole 2,3-dioxygenase (IDO), B and T lymphocyte attenuator (BTLA). It also highlights the importance of T, natural killer, and antigen-presenting cells as robust biomarker tools for understanding immune checkpoint inhibitor-based treatment dynamics. Though a comprehensive review, all aspects of the immune molecules could not be covered as they were beyond the scope of the review; Further review articles can cover other aspects to bridge the knowledge gap.

Effects of IFN-γ on the immunological microenvironment and TAM polarity in stage IA non-small cell lung cancer and its mechanisms

OBJECTIVE

To investigate the effect of interferon-γ (IFN-γ) on the immune microenvironment and the polarity of tumor-associated macrophages (TAMs) in stage IA non-small cell lung cancer (NSCLC) and its mechanisms.

METHODS

Human non-small cell lung cancer A549 cells were treated with a series of IFN-γ concentrations (0, 50, 100, 150, 200, 250, and 300 ng/mL). Tumor tissues from patients with stage IA NSCLC were cultured using the air-liquid interface culture technique to establish a tumor microenvironment (TME) organ model. The NSCLC model was constructed by subcutaneously embedding small tumor pieces into the back of nonobese diabetic severe combined immune deficiency (NOD SCID) mice. The size and weight of the tumors were recorded, and the tumor volume was calculated. CCK-8 assays were used to investigate cell proliferation, flow cytometry and TUNEL staining were used to evaluate cell apoptosis, colony formation was investigated by cloning experiments, and cell invasion and migration were evaluated by Transwell assays and scratch tests. The expression of apoptosis-related proteins (Bax, Bcl-2 and C-caspase 3), M2 polarization-related markers (CD163, CD206 and IDO1), and marker proteins of cytotoxic T cells and helper T cells (CD8 and CD4) was detected by Western blot. The expression of Ki-67 and IDO1 was detected by immunohistochemistry, and the levels of IL-6, IL-10, IL-13 and TNF-α were measured by ELISA. The expression of CD68 was measured by RT‒qPCR, and the phagocytosis of TAMs was evaluated by a Cell Trace CFSE kit and cell probe staining.

RESULTS

The proliferation activity of A549 cells increased with increasing IFN-γ concentration and peaked when the concentration reached 200 ng/mL, and the proliferation activity of A549 cells was suppressed thereafter. After treatment with 200 ng/mL IFN-γ, the apoptosis rate of cells decreased, the number of cell colonies increased, the invasion and migration of cells were promoted, the expression of Bax and C-caspase 3 was downregulated, and the expression of Bcl-2 was upregulated in cells and the TME model. In the TME model, CD163, CD206, IDO1 and Ki-67 were upregulated, CD8 and CD4 were downregulated, apoptosis was reduced, the levels of IL-6 and TNF-α were decreased, and the levels of IL-10 and IL-13 were increased. IL-4 induced TAMs to express CD163 and CD206, reduced the levels of IL-6 and TNF-α, increased the levels of IL-10 and IL-13, and weakened the phagocytic function of TAMs. IFN-γ treatment further enhanced the effect of IL-4 and enhanced the viability of A549 cells. IDO1 decreased the viability of T cells and NK cells, while suppressing the effect of IFN-γ. In mice, compared with NSCLC mice, the tumor volume and weight of the IFN-γ group were increased, the expression of CD163, CD206, IDO1, Ki-67 and Bcl-2 in tumor tissue was upregulated, the expression of Bax and C-caspase 3 was downregulated, and apoptosis was reduced. The levels of IL-6 and TNF-α were decreased, and the levels of IL-10 and IL-13 were increased in the serum of mice.

CONCLUSION

In stage IA NSCLC, a low concentration of IFN-γ promotes the polarization of TAMs to the M2 phenotype in the TME model by upregulating the expression of IDO1, promoting the viability of cancer cells, inhibiting the viability of T cells and NK cells, and thus establishing an immune microenvironment conducive to tumor progression.

Comprehensive analysis the prognostic and immune characteristics of mitochondrial transport-related gene SFXN1 in lung adenocarcinoma

BACKGROUND

Mitochondria, which serve as the fundamental organelle for cellular energy and metabolism, are closely linked to the growth and survival of cancer cells. This study aims to identify and assess Sideroflexin1 (SFXN1), an unprecedented mitochondrial gene, as a potential prognostic biomarker for lung adenocarcinoma (LUAD).

METHODS

The mRNA and protein levels of SFXN1 were investigated based on the Cancer Genome Atlas (TCGA) LUAD dataset, and then validated by real-time quantitative PCR, Western Blotting and immunohistochemistry from our clinical samples. The clinical correlation and prognostic value were evaluated by the TCGA cohort and verified via our clinical dataset (n = 90). The somatic mutation, drug sensitivity data, immune cell infiltration and single-cell RNA sequencing data of SFXN1 were analyzed through public databases.

RESULTS

SFXN1 was markedly upregulated at both mRNA and protein levels in LUAD, and high expression of SFXN1 were correlated with larger tumor size, positive lymph node metastasis, and advanced clinical stage. Furthermore, SFXN1 upregulation was significantly associated with poor clinical prognosis. SFXN1 co-expressed genes were also analyzed, which were mainly involved in the cell cycle, central carbon metabolism, DNA repair, and the HIF-1α signaling pathway. Additionally, SFXN1 expression correlated with the expression of multiple immunomodulators, which act to regulate the tumor immune microenvironment. Results also demonstrated an association between SFXN1 expression and increased immune cell infiltration, such as activated CD8 + T cells, natural killer cells (NKs), activated dendritic cells (DCs), and macrophages. LUAD patients with high SFXN1 expression exhibited heightened sensitivity to multiple chemotherapies and targeted drugs and predicted a poor response to immunotherapy. SFXN1 represented an independent prognostic marker for LUAD patients with an improved prognostic value for overall survival when combined with clinical stage information.

CONCLUSIONS

SFXN1 is frequently upregulated in LUAD and has a significant impact on the tumor immune environment. Our study uncovers the potential of SFXN1 as a prognostic biomarker and as a novel target for intervention in LUAD.

Identification of kynurenine and quinolinic acid as promising serum biomarkers for drug-induced interstitial lung diseases

BACKGROUND

Drug-induced interstitial lung disease (DILD) is a lung injury caused by various types of drugs and is a serious problem in both clinical practice and drug development. Clinical management of the condition would be improved if there were DILD-specific biomarkers available; this study aimed to meet that need.

METHODS

Biomarker candidates were identified by non-targeted metabolomics focusing on hydrophilic molecules, and further validated by targeted approaches using the serum of acute DILD patients, DILD recovery patients, DILD-tolerant patients, patients with other related lung diseases, and healthy controls.

RESULTS

Serum levels of kynurenine and quinolinic acid (and kynurenine/tryptophan ratio) were elevated significantly and specifically in acute DILD patients. The diagnostic potentials of these biomarkers were superior to those of conventional lung injury biomarkers, Krebs von den Lungen-6 and surfactant protein-D, in discriminating between acute DILD patients and patients with other lung diseases, including idiopathic interstitial pneumonia and lung diseases associated with connective tissue diseases. In addition to identifying and evaluating the biomarkers, our data showed that kynurenine/tryptophan ratios (an indicator of kynurenine pathway activation) were positively correlated with serum C-reactive protein concentrations in patients with DILD, suggesting the potential association between the generation of these biomarkers and inflammation. Our in vitro experiments demonstrated that macrophage differentiation and inflammatory stimulations typified by interferon gamma could activate the kynurenine pathway, resulting in enhanced kynurenine levels in the extracellular space in macrophage-like cell lines or lung endothelial cells. Extracellular quinolinic acid levels were elevated only in macrophage-like cells but not endothelial cells owing to the lower expression levels of metabolic enzymes converting kynurenine to quinolinic acid. These findings provide clues about the molecular mechanisms behind their specific elevation in the serum of acute DILD patients.

CONCLUSIONS

The serum concentrations of kynurenine and quinolinic acid as well as kynurenine/tryptophan ratios are promising and specific biomarkers for detecting and monitoring DILD and its recovery, which could facilitate accurate decisions for appropriate clinical management of patients with DILD.

Tryptophan Metabolism and Gut Microbiota: A Novel Regulatory Axis Integrating the Microbiome, Immunity, and Cancer

Tryptophan metabolism and gut microbiota form an integrated regulatory axis that impacts immunity, metabolism, and cancer. This review consolidated current knowledge on the bidirectional interactions between microbial tryptophan processing and the host. We focused on how the gut microbiome controls tryptophan breakdown via the indole, kynurenine, and serotonin pathways. Dysbiosis of the gut microbiota induces disruptions in tryptophan catabolism which contribute to disorders like inflammatory conditions, neuropsychiatric diseases, metabolic syndromes, and cancer. These disruptions affect immune homeostasis, neurotransmission, and gut-brain communication. Elucidating the mechanisms of microbial tryptophan modulation could enable novel therapeutic approaches like psychobiotics and microbiome-targeted dietary interventions. Overall, further research on the microbiota-tryptophan axis has the potential to revolutionize personalized diagnostics and treatments for improving human health.

Membrane Localization and Phosphorylation of Indoleamine 2,3-Dioxygenase 2 (IDO2) in A549 Human Lung Adenocarcinoma Cells: First Steps in Exploring Its Signaling Function

Indoleamine 2,3-dioxygenase 2 (IDO2) is a paralog of Indoleamine 2,3-dioxygenase 1 (IDO1), a tryptophan-degrading enzyme producing immunomodulatory molecules. However, the two proteins are unlikely to carry out the same functions. IDO2 shows little or no tryptophan catabolic activity and exerts contrasting immunomodulatory roles in a context-dependent manner in cancer and autoimmune diseases. The recently described potential non-enzymatic activity of IDO2 has suggested its possible involvement in alternative pathways, resulting in either pro- or anti-inflammatory effects in different models. In a previous study on non-small cell lung cancer (NSCLC) tissues, we found that IDO2 expression revealed at the plasma membrane level of tumor cells was significantly associated with poor prognosis. In this study, the A549 human cell line, basally expressing IDO2, was used as an in vitro model of human lung adenocarcinoma to gain more insights into a possible alternative function of IDO2 different from the catalytic one. In these cells, immunocytochemistry and isopycnic sucrose gradient analyses confirmed the IDO2 protein localization in the cell membrane compartment, and the immunoprecipitation of tyrosine-phosphorylated proteins revealed that kinase activities can target IDO2. The different localization from the cytosolic one and the phosphorylation state are the first indications for the signaling function of IDO2, suggesting that the IDO2 non-enzymatic role in cancer cells is worthy of deeper understanding.

Sphingomyelin-derived nanovesicles for the delivery of the IDO1 inhibitor epacadostat enhance metastatic and post-surgical melanoma immunotherapy

Epacadostat (EPA), the most advanced IDO1 inhibitor, in combination with PD-1 checkpoint inhibitor, has failed in a recent Phase III clinical trial for treating metastatic melanoma. Here we report an EPA nanovesicle therapeutic platform (Epacasome) based on chemically attaching EPA to sphingomyelin via an oxime-ester bond highly responsive to hydrolase cleavage. Via clathrin-mediated endocytosis, Epacasome displays higher cellular uptake and enhances IDO1 inhibition and T cell proliferation compared to free EPA. Epacasome shows improved pharmacokinetics and tumour accumulation with efficient intratumoural drug release and deep tumour penetration. Additionally, it outperforms free EPA for anticancer efficacy, potentiating PD-1 blockade with boosted cytotoxic T lymphocytes (CTLs) and reduced regulatory T cells and myeloid-derived suppressor cells responses in a B16-F10 melanoma model in female mice. By co-encapsulating immunogenic dacarbazine, Epacasome further enhances anti-tumor effects and immune responses through the upregulation of NKG2D-mediated CTLs and natural killer cells responses particularly when combined with the PD-1 inhibitor in the late-stage metastatic B16-F10-Luc2 model in female mice. Furthermore, this combination prevents tumour recurrence and prolongs mouse survival in a clinically relevant, post-surgical melanoma model in female mice. Epacasome demonstrates potential to synergize with PD-1 blockade for improved response to melanoma immunotherapy.

Interplay between Estrogen, Kynurenine, and AHR Pathways: An immunosuppressive axis with therapeutic potential for breast cancer treatment

Breast cancer is one of the most common malignancies among women worldwide. Estrogen exposure via endogenous and exogenous sources during a lifetime, together with environmental exposure to estrogenic compounds, represent the most significant risk factor for breast cancer development. As breast tumors establish, multiple pathways are deregulated. Among them is the aryl hydrocarbon receptor (AHR) signaling pathway. AHR, a ligand-activated transcription factor associated with the metabolism of polycyclic aromatic hydrocarbons and estrogens, is overexpressed in breast cancer. Furthermore, AHR and estrogen receptor (ER) cross-talk pathways have been observed. Additionally, the Tryptophan (Trp) catabolizing enzymes indolamine-2,3-dioxygenase (IDO) and tryptophan-2,3-dioxygenase (TDO) are overexpressed in breast cancer. IDO/TDO catalyzes the formation of Kynurenine (KYN) and other tryptophan-derived metabolites, which are ligands of AHR. Once KYN activates AHR, it stimulates the expression of the IDO enzyme, increases the level of KYN, and activates non-canonical pathways to control inflammation and immunosuppression in breast tumors. The interplay between E2, AHR, and IDO/TDO/KYN pathways and their impact on the immune system represents an immunosuppressive axis on breast cancer. The potential modulation of the immunosuppressive E2-AHR-IDO/TDO/KYN axis has aroused great expectations in oncotherapy. The present article will review the mechanisms implicated in generating the immunosuppressive axis E2-AHR-IDO/TDO/KYN in breast cancer and the current state of knowledge as a potential therapeutic target.

COVID-19. Biology, pathophysiology, and immunology: a pathologist view

Even if the SARS-CoV-2 pandemic has been declared over, several risks and clinical problems remain to be faced, including long-COVID sequelae and possible outbreaks of pathogenic variants. Intense research on COVID-19 has provided in these few years a striking amount of data covering different fields and disciplines, which can help to provide a knowledge shield against new potential infective spreads, and may also potentially be applied to other fields of medicine, including oncology and neurology. Nevertheless, areas of uncertainty still remain regarding the pathogenic mechanisms that subtend the multifaceted manifestations of the disease. To better clarify the pathogenesis of the disease, a systematic multidisciplinary evaluation of the many mechanisms involved in COVID-19 is mandatory, including clinical, physiological, radiological, immunological and pathological studies. In COVID-19 syndrome the pathological studies have been mainly performed on autopsy cases, and only a few studies are available on biopsies. Nevertheless, these studies have provided relevant information that can substantially contribute to decipher the complex scenario characterizing the different forms of COVID-19 and long-COVID-19. In this review the data provided by pathological investigations are recapitulated and discussed, in the light of different hypothesis and data provided by clinical, physiological and immunological data.

Increased expression of IDO1 is associated with improved survival and increased number of TILs in patients with high-grade serous ovarian cancer

BACKGROUND

The enzyme indoleamine 2,3-dioxygenase 1 (IDO1) plays a crucial role in regulating the immune system's response to tumors, but its exact role in cancer, especially in high-grade serous ovarian cancer (HGSOC), remains controversial. We aimed to investigate the prognostic impact of IDO1 expression and its correlation with tumor-infiltrating lymphocytes (TILs) in HGSOC.

METHODS

Immunohistochemical (IHC) staining and bioimage analysis using the QuPath software were employed to assess IDO1 protein expression in a well-characterized cohort of 507 patients with primary HGSOC. Statistical evaluation was performed using SPSS, and in silico validation considering IDO1 mRNA expression in bulk and single-cell gene expression datasets was conducted. Additionally, IDO1 expression in interferon-gamma (IFNG) stimulated HGSOC cell lines was analyzed.

RESULTS

Our findings revealed that IDO1 protein and mRNA expression serve as positive prognostic markers for overall survival (OS) and progression-free survival (PFS) in HGSOC. High IDO1 expression was associated with a significant improvement in OS by 21 months (p < 0.001) and PFS by 6 months (p = 0.016). Notably, elevated IDO1 expression correlated with an increased number of CD3+ (p < 0.001), CD4+ (p < 0.001), and CD8+ TILs (p < 0.001). Furthermore, high IDO1 mRNA expression and protein level were found to be associated with enhanced responsiveness to pro-inflammatory cytokines, particularly IFNG.

CONCLUSIONS

Our study provides evidence that IDO1 expression serves as a positive prognostic marker in HGSOC and is associated with an increased number of CD3+, CD4+ and CD8+ TILs. Understanding the intricate relationship between IDO1, TILs, and the tumor microenvironment may hold the key to improving outcomes in HGSOC.

The High-Risk Human Papillomavirus Type Influences the Tissue Microenvironment in Cervical Intraepithelial Neoplasia Grade 2

High-risk, cancer-causing human papillomavirus (HPV) types are associated with cervical precancer and cancer. A high proportion of high-risk HPV precancer lesions undergo immune-mediated regression. The purpose of this study was to determine if the tissue microenvironment of HPV16 and 18 (HPV16/18) cervical intraepithelial neoplasia grade 2 lesions differed from other high-risk types (HPV 'other'). Consistent with other studies, we found that progression to higher-grade disease was more frequent in HPV16/18 lesions when compared with HPV 'other' lesions. HPV16/18 lesions were significantly more likely to be indoleamine 2,3,-dioxygenase 1 (IDO1)-positive and were associated with reduced CD8 and FoxP3 T cells in the lesion. In the stroma, reduced Tbet- and CD32-positive cells and increased Blimp1-positive cells were significantly associated with HPV16/18 lesions when compared with HPV 'other' types. On analysis of the IDO1-positive tissues, lesional IDO1 was associated with significantly decreased numbers of CD4-, CD8-, and FoxP3-positive cells in the stroma compared with IDO1-negative tissues. These data suggest that IDO1 expression may impair infiltration of CD4, CD8, and FoxP3 cells into the stroma beneath the precancer lesion. Increased expression of IDO1 may contribute to immune avoidance and an increased frequency of disease progression in HPV16- and 18-positive lesions.

Development of a DNA aptamer targeting IDO1 with anti-tumor effects

Immune checkpoint blockade has become an effective approach to reverse the immune tolerance of tumor cells. Indoleamine 2,3-dioxygenase 1 (IDO1) is frequently upregulated in many types of cancers and contributes to the establishment of an immunosuppressive cancer microenvironment, which has been thought to be a potential target for cancer therapy. However, the development of IDO1 inhibitors for clinical application is still limited. Here, we isolated a DNA aptamer with a strong affinity and inhibitory activity against IDO1, designated as IDO-APT. By conjugating with nanoparticles, in situ injection of IDO-APT to CT26 tumor-bearing mice significantly suppresses the activity of regulatory T cells and promotes the function of CD8⁺ T cells, leading to tumor suppression and prolonged survival. Therefore, this functional IDO1-specific aptamer with potent anti-tumor effects may serve as a potential therapeutic strategy in cancer immunotherapy. Our data provide an alternative way to target IDO1 in addition to small molecule inhibitors.

Combined Inhibition of Indolamine-2,3-Dioxygenase 1 and C-X-C Chemokine Receptor Type 2 Exerts Antitumor Effects in a Preclinical Model of Cervical Cancer

Cervical cancer is a public health problem diagnosed in advanced stages, and its main risk factor is persistent high-risk human papillomavirus infection. Today, it is necessary to study new treatment strategies, such as immunotherapy, that use different targets of the tumor microenvironment. In this study, the K14E7E2 mouse was used as a cervical cancer model to evaluate the inhibition of indolamine-2,3-dioxygenase 1 (IDO-1) and C-X-C chemokine receptor type 2 (CXCR-2) as potential anti-tumor targets. DL-1MT and SB225002 were administered for 30 days in two regimens (R1 and R2) based on combination and single therapy approaches to inhibit IDO-1 and CXCR-2, respectively. Subsequently, the reproductive tracts were resected and analyzed to determine the tumor areas, and IHCs were performed to assess proliferation, apoptosis, and CD8 cellular infiltration. Our results revealed that combined inhibition of IDO-1 and CXCR-2 significantly reduces the areas of cervical tumors (from 196.0 mm2 to 58.24 mm2 in R1 and 149.6 mm2 to 52.65 mm2 in R2), accompanied by regions of moderate dysplasia, decreased papillae, and reduced inflammation. Furthermore, the proliferation diminished, and apoptosis and intra-tumoral CD8 T cells increased. In conclusion, the combined inhibition of IDO-1 and CXCR-2 is helpful in the antitumor response against preclinical cervical cancer.

Involvement of the kynurenine pathway in breast cancer: updates on clinical research and trials

Breast cancer (BrCa) is the leading cause of cancer incidence and mortality in women worldwide. While BrCa treatment has been shown to be highly successful if detected at an early stage, there are few effective strategies to treat metastatic tumours. Hence, metastasis remains the main cause in most of BrCa deaths, highlighting the need for new approaches in this group of patients. Immunotherapy has been gaining attention as a new treatment for BrCa metastasis and the kynurenine pathway (KP) has been suggested as one of the potential targets. The KP is the major biochemical pathway in tryptophan (TRP) metabolism, catabolising TRP to nicotinamide adenine dinucleotide (NAD+). The KP has been reported to be elevated under inflammatory conditions such as cancers and that its activity suppresses immune surveillance. Dysregulation of the KP has previously been reported implicated in BrCa. This review aims to discuss and provide an update on the current mechanisms involved in KP-mediated immune suppression and cancer growth. Furthermore, we also provide a summary on 58 studies about the involvement of the KP and BrCa and five clinical trials targeting KP enzymes and their outcome.

Indoleamine 2,3-Dioxygenase (IDO) Activity: A Perspective Biomarker for Laboratory Determination in Tumor Immunotherapy

Indoleamine 2,3-dioxygenase 1 (IDO1) is a heme enzyme involved in catalyzing the conversion of tryptophan (Trp) into kynurenine (Kyn) at the first rate-limiting step in the kynurenine pathway of L-tryptophan metabolism. It has been found to be involved in several biological functions such as aging, immune microorganism, neurodegenerative and infectious diseases, and cancer. IDO1 plays an important role in immune tolerance by depleting tryptophan in the tumor microenvironment and inhibiting the proliferation of effector T cells, which makes it an important emerging biomarker for cancer immunotherapy. Therefore, the research and development of IDO1 inhibitors are of great importance for tumor therapy. Of interest, IDO activity assays are of great value in the screening and evaluation of inhibitors. Herein, we mainly review the biological functions of IDO1, immune regulation, key signaling molecules in the response pathway, and the development of IDO1 inhibitors in clinical trials. Furthermore, this review provides a comprehensive overview and, in particular, a discussion of currently available IDO activity assays for use in the evaluation of IDO inhibitors in human blood. We believe that the IDO activity is a promising biomarker for the immune escape and laboratory evaluation of tumor immunotherapy.

A Phase II Study of Epacadostat and Pembrolizumab in Patients with Advanced Sarcoma

PURPOSE

Epacadostat, an indole 2,3 dioxygenase 1 (IDO1) inhibitor, proposed to shift the tumor microenvironment toward an immune-stimulated state, showed early promise in melanoma but has not been studied in sarcoma. This study combined epacadostat with pembrolizumab, which has modest activity in select sarcoma subtypes.

PATIENTS AND METHODS

This phase II study enrolled patients with advanced sarcoma into five cohorts including (i) undifferentiated pleomorphic sarcoma (UPS)/myxofibrosarcoma, (ii) liposarcoma (LPS), (iii) leiomyosarcoma (LMS), (iv) vascular sarcoma, including angiosarcoma and epithelioid hemangioendothelioma (EHE), and (v) other subtypes. Patients received epacadostat 100 mg twice daily plus pembrolizumab at 200 mg/dose every 3 weeks. The primary endpoint was best objective response rate (ORR), defined as complete response (CR) and partial response (PR), at 24 weeks by RECIST v.1.1.

RESULTS

Thirty patients were enrolled [60% male; median age 54 years (range, 24-78)]. The best ORR at 24 weeks was 3.3% [PR, n = 1 (leiomyosarcoma); two-sided 95% CI, 0.1%-17.2%]. The median PFS was 7.6 weeks (two-sided 95% CI, 6.9-26.7). Treatment was well tolerated. Grade 3 treatment-related adverse events occurred in 23% (n = 7) of patients. In paired pre- and post-treatment tumor samples, no association was found between treatment and PD-L1 or IDO1 tumor expression or IDO-pathway-related gene expression by RNA sequencing. No significant changes in serum tryptophan or kynurenine levels were observed after baseline.

CONCLUSIONS

Combination epacadostat and pembrolizumab was well tolerated and showed limited antitumor activity in sarcoma. Correlative analyses suggested that inadequate IDO1 inhibition was achieved.

Regulation of IDO2 by the Aryl Hydrocarbon Receptor (AhR) in Breast Cancer

Indoleamine 2,3-dioxygenase 2 (IDO2) is a tryptophan-catabolizing enzyme and a homolog of IDO1 with a distinct expression pattern compared with IDO1. In dendritic cells (DCs), IDO activity and the resulting changes in tryptophan level regulate T-cell differentiation and promote immune tolerance. Recent studies indicate that IDO2 exerts an additional, non-enzymatic function and pro-inflammatory activity, which may play an important role in diseases such as autoimmunity and cancer. Here, we investigated the impact of aryl hydrocarbon receptor (AhR) activation by endogenous compounds and environmental pollutants on the expression of IDO2. Treatment with AhR ligands induced IDO2 in MCF-7 wildtype cells but not in CRISPR-cas9 AhR-knockout MCF-7 cells. Promoter analysis with IDO2 reporter constructs revealed that the AhR-dependent induction of IDO2 involves a short-tandem repeat containing four core sequences of a xenobiotic response element (XRE) upstream of the start site of the human ido2 gene. The analysis of breast cancer datasets revealed that IDO2 expression increased in breast cancer compared with normal samples. Our findings suggest that the AhR-mediated expression of IDO2 in breast cancer could contribute to a pro-tumorigenic microenvironment in breast cancer.

Immune Checkpoint Inhibitors in Renal Cell Carcinoma: Molecular Basis and Rationale for Their Use in Clinical Practice

Renal cell carcinoma (RCC) is the seventh most common cancer in men and the ninth most common cancer in women worldwide. There is plenty of evidence about the role of the immune system in surveillance against tumors. Thanks to a better understanding of immunosurveillance mechanisms, immunotherapy has been introduced as a promising cancer treatment in recent years. Renal cell carcinoma (RCC) has long been thought chemoresistant but highly immunogenic. Considering that up to 30% of the patients present metastatic disease at diagnosis, and around 20–30% of patients undergoing surgery will suffer recurrence, we need to identify novel therapeutic targets. The introduction of immune checkpoint inhibitors (ICIs) in the clinical management of RCC has revolutionized the therapeutic approach against this tumor. Several clinical trials have shown that therapy with ICIs in combination or ICIs and the tyrosine kinase inhibitor has a very good response rate. In this review article we summarize the mechanisms of immunity modulation and immune checkpoints in RCC and discuss the potential therapeutic strategies in renal cancer treatment.

Design, synthesis, biological evaluation of urea substituted 1,2,5-oxadiazole-3-carboximidamides as novel indoleamine 2,3-dioxygenase-1 (IDO1) inhibitors

Indoleamine 2,3-dioxygenase-1 (IDO1) has been considered as an attractive target for oncology immunotherapy due to its immunosuppressive effects on the tumor microenvironment. The most advanced IDO1 inhibitor epacadostat in combination with anti-PD-1 antibody failed to show desirable objective response. Epacadostat is now reevaluated in phase III clinical trials, but its pharmacokinetic (PK) properties are unsatisfactory. To further unravel the antitumor efficacy of IDO1 inhibitors, we designed a series of epacadostat analogues by introducing various urea-containing side chains. In particular, the most active compound 3 showed superior inhibitory potency against recombinant hIDO1 and hIDO1 in HeLa cells induced by interferon γ (IFNγ) relative to epacadostat (3, biochemical hIDO1 IC₅₀ = 67.4 nM, HeLa hIDO1 IC₅₀ = 17.6 nM; epacadostat, biochemical hIDO1 IC₅₀ = 75.9 nM, HeLa hIDO1 IC₅₀ = 20.6 nM). Moreover, compound 3 exhibited improved physicochemical properties and rat PK profile with better oral exposure and bioavailability compared with epacadostat. Importantly, this compound exhibited comparable antitumor efficacy with epacadostat in LLC syngeneic xenograft models. Hence, compound 3 represents a promising lead compound for discovery of more effective IDO1 inhibitors.

IDO1/COX2 Expression Is Associated with Poor Prognosis in Colorectal Cancer Liver Oligometastases

Background: IDO1 and COX2 have emerged as promising immunotherapy targets. It is unclear whether IDO1 and COX2 expression levels in colorectal cancer (CRC) patients with liver oligometastases could be independent predictors of overall survival (OS) and progression-free survival (PFS). The purpose of this study was to investigate the correlation of IDO1 and COX2 expression levels with OS and PFS in CRC patients with liver oligometastases. Methods: The expression levels of IDO1 and COX2 were assessed by immunohistochemistry in 107 specimens from patients with liver oligometastases. The correlation between the expression of IDO1 and COX2 and the clinicopathological parameters and OS/PFS in patients was examined. Results: The expression level of IDO1/COX2 was significantly correlated with age and was not associated with gender, BMI, T stage, N stage, primary tumor size, liver metastasis size, CEA, CA19-9, CD3 TILs or CD8 TILs. In univariate analysis, we found that IDO1/COX2 expression, CEA and N stage all yielded significantly poor OS and PFS outcomes. In our multivariate Cox model, IDO1/COX2 coexpression, CEA and N stage were found to be significantly correlated with OS; IDO1/COX2 coexpression and CEA were significantly correlated with PFS. Conclusions: IDO1/COX2 coexpression plays a pivotal role and may act as a potential prognostic biomarker for survival in CRC patients with liver oligometastases.

A cost-effective machine learning-based method for preeclampsia risk assessment and driver genes discovery

BACKGROUND

The placenta, as a unique exchange organ between mother and fetus, is essential for successful human pregnancy and fetal health. Preeclampsia (PE) caused by placental dysfunction contributes to both maternal and infant morbidity and mortality. Accurate identification of PE patients plays a vital role in the formulation of treatment plans. However, the traditional clinical methods of PE have a high misdiagnosis rate.

RESULTS

Here, we first designed a computational biology method that used single-cell transcriptome (scRNA-seq) of healthy pregnancy (38 wk) and early-onset PE (28-32 wk) to identify pathological cell subpopulations and predict PE risk. Based on machine learning methods and feature selection techniques, we observed that the Tuning ReliefF (TURF) score hybrid with XGBoost (TURF_XGB) achieved optimal performance, with 92.61% accuracy and 92.46% recall for classifying nine cell subpopulations of healthy placentas. Biological landscapes of placenta heterogeneity could be mapped by the 110 marker genes screened by TURF_XGB, which revealed the superiority of the TURF feature mining. Moreover, we processed the PE dataset with LASSO to obtain 497 biomarkers. Integration analysis of the above two gene sets revealed that dendritic cells were closely associated with early-onset PE, and C1QB and C1QC might drive preeclampsia by mediating inflammation. In addition, an ensemble model-based risk stratification card was developed to classify preeclampsia patients, and its area under the receiver operating characteristic curve (AUC) could reach 0.99. For broader accessibility, we designed an accessible online web server ( http://bioinfor.imu.edu.cn/placenta ).

CONCLUSION

Single-cell transcriptome-based preeclampsia risk assessment using an ensemble machine learning framework is a valuable asset for clinical decision-making. C1QB and C1QC may be involved in the development and progression of early-onset PE by affecting the complement and coagulation cascades pathway that mediate inflammation, which has important implications for better understanding the pathogenesis of PE.

The signaling function of IDO1 incites the malignant progression of mouse B16 melanoma

Indoleamine 2,3 dioxygenase 1 (IDO1), a leader tryptophan-degrading enzyme, represents a recognized immune checkpoint molecule. In neoplasia, IDO1 is often highly expressed in dendritic cells infiltrating the tumor and/or in tumor cells themselves, particularly in human melanoma. In dendritic cells, IDO1 does not merely metabolize tryptophan into kynurenine but, after phosphorylation of critical tyrosine residues in the non-catalytic small domain, it triggers a signaling pathway prolonging its immunoregulatory effects by a feed-forward mechanism. We here investigated whether the non-enzymatic function of IDO1 could also play a role in tumor cells by using B16-F10 mouse melanoma cells transfected with either the wild-type Ido1 gene (Ido1^WT ) or a mutated variant lacking the catalytic, but not signaling activity (Ido1^H350A ). As compared to the Ido1^WT -transfected counterpart (B16^WT), B16-F10 cells expressing Ido1^H350A (B16^H350A) were characterized by an in vitro accelerated growth mediated by increased Ras and Erk activities. Faster growth and malignant progression of B16^H350A cells, also detectable in vivo, were found to be accompanied by a reduction in tumor-infiltrating CD8⁺ T cells and an increase in Foxp3⁺ regulatory T cells. Our data, therefore, suggest that the IDO1 signaling function can also occur in tumor cells and that alternative therapeutic approach strategies should be undertaken to effectively tackle this important immune checkpoint molecule.

The Prognostic Role of Serine Racemase in Patients With Pancreatic Cancer: A New Marker in Cancer Metabolism

OBJECTIVES

Serine racemase (SRR) participates in serine metabolism in central nervous systems. Serine racemase is only studied in colorectal cancer, and its role in pancreatic cancer (PC) is unknown. This study aims to investigate the role of SRR in PC.

METHODS

Totally 182 patients with PC were enrolled in this study. Slices from patients were stained for SRR and CD8+ T cells. Kaplan-Meier methods were used to do survival analysis according to SRR expression from immunohistochemical staining. Univariate and multivariate Cox regression analysis was performed to clarify the independent prognostic value of SRR. Bioinformatic tools were used to explore and validate the expression, prognostic value, possible mechanism, and immune interaction of SRR in PC.

RESULTS

The expression of SRR was lower in tumor tissue than normal tissue, also potentially decreased with the increasing tumor grade. Low SRR expression was an independent risk factor for overall survival (hazards ratio, 1.875; 95% confidence interval, 1.175-2.990; P = 0.008) in patients with PC. Serine racemase was positively correlated with CD8+ T cells infiltration and possibly associated with CCL14 and CXCL12 expression.

CONCLUSIONS

Serine racemase plays a prognostic role in PC and may be a potentially therapeutic target.

Expression of IDO1 and PD-L2 in Patients with Benign Lymphadenopathies and Association with Autoimmune Diseases

The expression patterns of IDO1 and PD-L2 have not been thoroughly investigated in benign lymphadenopathies. The aim with this study was to elucidate how IDO1 and PD-L2 are expressed in benign lymphadenopathies in patients with autoimmune diseases (AD) compared to patients without AD. Formalin-fixed paraffin-embedded lymph nodes from 22 patients with AD and 57 patients without AD were immunohistochemically stained to detect IDO1 and PD-L2. The material was previously stained with EBER in situ hybridization to detect cells harboring the Epstein-Barr virus (EBV). IDO1 and PD-L2 were generally expressed by leukocytes to low degrees, while follicular IDO1+ cells were very rare. IDO1+ cells in single germinal centers were detected in five patients, and there was a high co-occurrence of follicular EBV+ cells in these cases (three of five patients). There were also significant correlations between interfollicular EBV+ cells and interfollicular IDO1+ cells (Spearman rho = 0.32, p = 0.004) and follicular IDO1+ cells (Spearman rho = 0.34, p = 0.004). High or low amounts of IDO1+ or PD-L2+ cells were not statistically significantly associated with patients with AD. However, the lymphadenopathy with the highest amount of interfollicular IDO1+ cells, which was also the only lymphadenopathy in which endothelial cells expressed IDO1, was in a patient with sarcoidosis. This study further supports that the EBV induces the expression of IDO1 and our findings should be recognized by future studies on IDO1 and PD-L2 in inflammatory and malignant conditions.

Partners in crime: The feedback loop between metabolic reprogramming and immune checkpoints in the tumor microenvironment

The tumor microenvironment (TME) is a complex and constantly changing cellular system composed of heterogeneous populations of tumor cells and non-transformed stromal cells, such as stem cells, fibroblasts, endothelial cells, pericytes, adipocytes, and innate and adaptive immune cells. Tumor, stromal, and immune cells consume available nutrients to sustain their proliferation and effector functions and, as a result of their metabolism, produce a wide array of by-products that gradually alter the composition of the milieu. The resulting depletion of essential nutrients and enrichment of by-products work together with other features of the hostile TME to inhibit the antitumor functions of immune cells and skew their phenotype to promote tumor progression. This review briefly describes the participation of the innate and adaptive immune cells in recognizing and eliminating tumor cells and how the gradual metabolic changes in the TME alter their antitumor functions. In addition, we discuss the overexpression of the immune checkpoints and their ligands as a result of nutrient deprivation and by-products accumulation, as well as the amplification of the metabolic alterations induced by the immune checkpoints, which creates an immunosuppressive feedback loop in the TME. Finally, the combination of metabolic and immune checkpoint inhibitors as a potential strategy to treat cancer and enhance the outcome of patients is highlighted.

The promise of targeting heme and mitochondrial respiration in normalizing tumor microenvironment and potentiating immunotherapy

Cancer immunotherapy shows durable treatment responses and therapeutic benefits compared to other cancer treatment modalities, but many cancer patients display primary and acquired resistance to immunotherapeutics. Immunosuppressive tumor microenvironment (TME) is a major barrier to cancer immunotherapy. Notably, cancer cells depend on high mitochondrial bioenergetics accompanied with the supply of heme for their growth, proliferation, progression, and metastasis. This excessive mitochondrial respiration increases tumor cells oxygen consumption, which triggers hypoxia and irregular blood vessels formation in various regions of TME, resulting in an immunosuppressive TME, evasion of anti-tumor immunity, and resistance to immunotherapeutic agents. In this review, we discuss the role of heme, heme catabolism, and mitochondrial respiration on mediating immunosuppressive TME by promoting hypoxia, angiogenesis, and leaky tumor vasculature. Moreover, we discuss the therapeutic prospects of targeting heme and mitochondrial respiration in alleviating tumor hypoxia, normalizing tumor vasculature, and TME to restore anti-tumor immunity and resensitize cancer cells to immunotherapy.

IDO1 and inflammatory neovascularization: bringing new blood to tumor-promoting inflammation

In parallel with the genetic and epigenetic changes that accumulate in tumor cells, chronic tumor-promoting inflammation establishes a local microenvironment that fosters the development of malignancy. While knowledge of the specific factors that distinguish tumor-promoting from non-tumor-promoting inflammation remains inchoate, nevertheless, as highlighted in this series on the 'Hallmarks of Cancer', it is clear that tumor-promoting inflammation is essential to neoplasia and metastatic progression making identification of specific factors critical. Studies of immunometabolism and inflamometabolism have revealed a role for the tryptophan catabolizing enzyme IDO1 as a core element in tumor-promoting inflammation. At one level, IDO1 expression promotes immune tolerance to tumor antigens, thereby helping tumors evade adaptive immune control. Additionally, recent findings indicate that IDO1 also promotes tumor neovascularization by subverting local innate immunity. This newly recognized function for IDO1 is mediated by a unique myeloid cell population termed IDVCs (IDO1-dependent vascularizing cells). Initially identified in metastatic lesions, IDVCs may exert broader effects on pathologic neovascularization in various disease settings. Mechanistically, induction of IDO1 expression in IDVCs by the inflammatory cytokine IFNγ blocks the antagonistic effect of IFNγ on neovascularization by stimulating the expression of IL6, a powerful pro-angiogenic cytokine. By contributing to vascular access, this newly ascribed function for IDO1 aligns with its involvement in other cancer hallmark functionalities, (tumor-promoting inflammation, immune escape, altered cellular metabolism, metastasis), which may stem from an underlying role in normal physiological functions such as wound healing and pregnancy. Understanding the nuances of how IDO1 involvement in these cancer hallmark functionalities varies between different tumor settings will be crucial to the future development of successful IDO1-directed therapies.

Tryptophan and its metabolites in normal physiology and cancer etiology

Within the growing field of amino acid metabolism, tryptophan (Trp) catabolism is an area of increasing interest. Trp is essential for protein synthesis, and its metabolism gives rise to biologically active catabolites including serotonin and numerous metabolites in the kynurenine (Kyn) pathway. In normal tissues, the production of Trp metabolites is directly regulated by the tissue-specific expression of Trp-metabolizing enzymes. Alterations of these enzymes in cancers can shift the balance and lead to an increased production of specific byproducts that can function as oncometabolites. For example, increased expression of the enzyme indoleamine 2,3-dioxygenase, which converts Trp into Kyn, leads to an increase in Kyn levels in numerous cancers. Kyn functions as an oncometabolite in cancer cells by promoting the activity of the transcription factor aryl hydrocarbon receptor, which regulates progrowth genes. Moreover, Kyn also inhibits T-cell activity and thus allows cancer cells to evade clearance by the immune system. Therefore, targeting the Kyn pathway has become a therapeutic focus as a novel means to abrogate tumor growth and immune resistance. This review summarizes the biological role and regulation of Trp metabolism and its catabolites with an emphasis on tumor cell growth and immune evasion and outlines areas for future research focus.

Lung Cancer Immunotherapy: Beyond Common Immune Checkpoints Inhibitors

Immunotherapy is an ever-expanding field in lung cancer treatment research. Over the past two decades, there has been significant progress in identifying immunotherapy targets and creating specific therapeutic agents, leading to a major paradigm shift in lung cancer treatment. However, despite the great success achieved with programmed death protein 1/ligand 1 (PD-1/PD-L1) monoclonal antibodies and with anti-PD-1/PD-L1 plus anti-cytotoxic T-lymphocyte antigen 4 (CTLA-4), only a minority of lung cancer patients respond to treatment, and of these many subsequently experience disease progression. In addition, immune-related adverse events sometimes can be life-threatening, especially when anti-CTLA-4 and anti-PD-1 are used in combination. All of this prompted researchers to identify novel immune checkpoints targets to overcome these limitations. Lymphocyte activation gene-3 (LAG-3), T cell immunoglobulin (Ig) and Immunoreceptor Tyrosine-Based Inhibitory Motif (ITIM) domain (TIGIT), T cell immunoglobulin and mucin-domain containing-3 (TIM-3) are promising molecules now under investigation. This review aims to outline the current role of immunotherapy in lung cancer and to examine efficacy and future applications of the new immune regulating molecules.

Identification and Characterization of a Novel Dual Inhibitor of Indoleamine 2,3-dioxygenase 1 and Tryptophan 2,3-dioxygenase

Kynurenine (Kyn), a metabolite of tryptophan (Trp), is a key regulator of mammal immune responses such as cancer immune tolerance. Indoleamine-2,3-dioxygenase (IDO) and tryptophan-2,3-dioxygenase (TDO) are main enzymes regulating the first and rate-limiting step of the Kyn pathway. To identify new small molecule inhibitors of TDO, we selected A172 glioblastoma cell line constitutively expressed TDO. Characterization of this cell line using kinase inhibitor library resulted in identification of MEK/ERK pathway-dependent TDO expression. After knowing the properties for TDO expression, we further proceeded to screen chemical library for TDO inhibitors. We previously determined that S-benzylisothiourea derivatives are enzymatic inhibitors of indoleamine 2,3-dioxygenase 1 (IDO1) and suggested that the isothiourea moiety could be an important pharmacophore for binding to heme. Based on this premise, we screened an in-house library composed of various isothiourea derivatives and identified a bisisothiourea derivative, PVZB3001, as an inhibitor of TDO. Interestingly, PVZB3001 also inhibited the enzymatic activity of IDO1 in both cell-based and cell-free assays but did not inhibit other heme enzymes. Molecular docking studies suggested the importance of isothiourea moieties at the ortho position of the phenyl ring for the inhibition of catalytic activity. PVZB3001 showed competitive inhibition against TDO, and this was supported by the docking simulation. PVZB3001 recovered natural killer (NK) cell viability and functions by inhibiting Kyn accumulation in conditioned medium of both IDO1- and TDO-expressing cells. Furthermore, oral administration of IDO1-overexpressing tumor-bearing mice with PVZB3001 significantly inhibited tumor growth. Thus, we identified a novel selective dual inhibitor of IDO1 and TDO using the Kyn production assay with a glioblastoma cell line. This inhibitor could be a useful pharmacological tool for modulating the Kyn pathway in a variety of experimental systems.

Interleukin-6 and indoleamine-2,3-dioxygenase as potential adjuvant targets for Papillomavirus-related tumors immunotherapy

High-risk Human papillomavirus (HPV) infections represent an important public health issue. Nearly all cervical malignancies are associated with HPV, and a range of other female and male cancers, such as anogenital and oropharyngeal. Aiming to treat HPV-related tumors, our group developed vaccines based on the genetic fusion of the HSV-1 glycoprotein D (gD) with the HPV-16 E7 oncoprotein (gDE7 vaccines). Despite the promising antitumor results reached by gDE7 vaccines in mice, combined therapies may increase the therapeutic effects by improving antitumor responses and halting immune suppressive mechanisms elicited by tumor cells. Considering cancer immunosuppressive mechanisms, indoleamine-2,3-dioxygenase (IDO) enzyme and interleukin-6 (IL-6) stand out in HPV-related tumors. Since IL-6 sustained the constitutive IDO expression, here we evaluated the therapeutic outcomes achieved by the combination of active immunotherapy based on a gDE7 protein-based vaccine with adjuvant treatments involving blocking IDO, either by use of IDO inhibitors or IL-6 knockout mice. C57BL/6 wild-type (WT) and transgenic IL-6-/- mice were engrafted with HPV16-E6/E7-expressing TC-1 cells and treated with 1-methyl-tryptophan isoforms (D-1MT and DL-1MT), capable to inhibit IDO. In vitro, the 1MT isoforms reduced IL-6 gene expression and IL-6 secretion in TC-1 cells. In vivo, the multi-targeted treatment improved the antitumor efficacy of the gDE7-based protein vaccine. Although the gDE7 immunization achieves partial tumor mass control in combination with D-1MT or DL-1MT in WT mice or when administered in IL-6-/- mice, the combination of gDE7 and 1MT in IL-6-/- mice further enhanced the antitumor effects, reaching total tumor rejection. The outcome of the combined therapy was associated with an increased frequency of activated dendritic cells and decreased frequencies of intratumoral polymorphonuclear myeloid-derived suppressor cells and T regulatory cells. In conclusion, the present study demonstrated that IL-6 and IDO negatively contribute to the activation of immune cells, particularly dendritic cells, reducing gDE7 vaccine-induced protective immune responses and, therefore, opening perspectives for the use of combined strategies based on inhibition of IL-6 and IDO as immunometabolic adjuvants for immunotherapies against HPV-related tumors.

Tyk2 is a tumor suppressor in colorectal cancer

Janus kinase Tyk2 is implicated in cancer immune surveillance, but its role in solid tumors is not well defined. We used Tyk2 knockout mice (Tyk2^Δ/Δ) and mice with conditional deletion of Tyk2 in hematopoietic (Tyk2^ΔHem) or intestinal epithelial cells (Tyk2^ΔIEC) to assess their cell type-specific functions in chemically induced colorectal cancer. All Tyk2-deficient mouse models showed a higher tumor burden after AOM-DSS treatment compared to their corresponding wild-type controls (Tyk2^+/+ and Tyk2^fl/fl), demonstrating tumor-suppressive functions of Tyk2 in immune cells and epithelial cancer cells. However, specific deletion of Tyk2 in hematopoietic cells or in intestinal epithelial cells was insufficient to accelerate tumor progression, while deletion in both compartments promoted carcinoma formation. RNA-seq and proteomics revealed that tumors of Tyk2^Δ/Δ and Tyk2^ΔIEC mice were immunoedited in different ways with downregulated and upregulated IFNγ signatures, respectively. Accordingly, the IFNγ-regulated immune checkpoint Ido1 was downregulated in Tyk2^Δ/Δ and upregulated in Tyk2^ΔIEC tumors, although both showed reduced CD8⁺ T cell infiltration. These data suggest that Tyk2^Δ/Δ tumors are Ido1-independent and poorly immunoedited while Tyk2^ΔIEC tumors require Ido1 for immune evasion. Our study shows that Tyk2 prevents Ido1 expression in CRC cells and promotes CRC immune surveillance in the tumor stroma. Both of these Tyk2-dependent mechanisms must work together to prevent CRC progression.

Identification of a Novel Pseudo-Natural Product Type IV IDO1 Inhibitor Chemotype

Natural product (NP)-inspired design principles provide invaluable guidance for bioactive compound discovery. Pseudo-natural products (PNPs) are de novo combinations of NP fragments to target biologically relevant chemical space not covered by NPs. We describe the design and synthesis of apoxidoles, a novel pseudo-NP class, whereby indole- and tetrahydropyridine fragments are linked in monopodal connectivity not found in nature. Apoxidoles are efficiently accessible by an enantioselective [4+2] annulation reaction. Biological evaluation revealed that apoxidoles define a new potent type IV inhibitor chemotype of indoleamine 2,3-dioxygenase 1 (IDO1), a heme-containing enzyme considered a target for the treatment of neurodegeneration, autoimmunity and cancer. Apoxidoles target apo-IDO1, prevent heme binding and induce unique amino acid positioning as revealed by crystal structure analysis. Novel type IV apo-IDO1 inhibitors are in high demand, and apoxidoles may provide new opportunities for chemical biology and medicinal chemistry research.

Tryptophan 2,3-dioxygenase may be a potential prognostic biomarker and immunotherapy target in cancer: A meta-analysis and bioinformatics analysis

Background

Tryptophan 2,3-dioxygenase (TDO2) is one of the emerging immune checkpoints. Meanwhile, TDO2 is also a key enzyme in the tryptophan (Trp)–kynurenine (Kyn) signaling pathway. Many studies have evaluated that TDO2 is highly expressed in various malignant tumor patients and plays a prognostic role. However, the sample size of a single prognostic study was small, and the results were still controversial.

Methods

We used Stata software and referenced the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) statement to conduct a meta-analysis on TDO2 and its clinical features and prognosis. We searched the PubMed, Cochrane Library, and Web of Science databases to find publications concerning TDO2 expression in malignant tumor patients up to June 2021. We used the Newcastle–Ottawa Scale (NOS) to evaluate the bias risk of the included literature. Risk ratios (RRs) and hazard ratios (HRs) were used for clinical outcomes, specifically overall survival (OS) and progression-free survival (PFS). In addition, we used data from The Cancer Genome Atlas (TCGA) to verify our conclusions.

Results

Nine studies including 667 patients with malignant tumors were identified. Our results suggested that overexpression of TDO2 was statistically correlated with poor OS and poor PFS (HR = 2.58, 95% CI = 1.52–4.40, p = 0.0005; HR = 2.38, 95% CI = 0.99–5.73, p = 0.05). In terms of clinicopathological characteristics, the overexpression level of TDO2 was statistically correlated with TNM (tumor–node–metastasis) stage (RR = 0.65, 95% CI = 0.48–0.89, p = 0.002) and regional lymph node metastasis (RR = 0.76, 95% CI = 0.59–0.99, p = 0.04). Subgroup analysis revealed the potential sources of heterogeneity. In addition, bioinformatics studies suggested that the level of TDO2 was high in malignant tumors and higher in cancer tissue than in matched paracarcinoma tissue. Gene enrichment analysis showed that TDO2 was closely related to immune response.

Conclusion

Overall, TDO2 may be a biomarker for the survival and prognosis of patients with malignant tumors and a potential therapeutic target in the future.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=260442, identifier (CRD42021260442)

Indoleamine 2,3-dioxygenase 1 (IDO1): an up-to-date overview of an eclectic immunoregulatory enzyme

Indoleamine 2,3-dioxygenase 1 (IDO1) catalyzes the initial rate-limiting step in the degradation of the essential amino acid tryptophan along the kynurenine pathway. When discovered more than 50 years ago, IDO1 was thought to be an effector molecule capable of mediating a survival strategy based on the deprivation of bacteria and tumor cells of the essential amino acid tryptophan. Since 1998, when tryptophan catabolism was discovered to be crucially involved in the maintenance of maternal T-cell tolerance, IDO1 has become the focus of several laboratories around the world. Indeed, IDO1 is now considered as an authentic immune regulator not only in pregnancy, but also in autoimmune diseases, chronic inflammation, and tumor immunity. However, in the last years, a bulk of new information-including structural, biological, and functional evidence-on IDO1 has come to light. For instance, we now know that IDO1 has a peculiar conformational plasticity and, in addition to a complex and highly regulated catalytic activity, is capable of performing a nonenzymic function that reprograms the expression profile of immune cells toward a highly immunoregulatory phenotype. With this state-of-the-art review, we aimed at gathering the most recent information obtained for this eclectic protein as well as at highlighting the major unresolved questions.

Research progress on microRNA-1258 in the development of human cancer

microRNAs (miRNAs) are small endogenous RNAs composed of 20-22 nucleotides that do not encode proteins, which regulate the expression of downstream genes by targeting the 3' untranslated region of mRNA. Plentiful research has demonstrated that miRNAs participate in the initiation and development of diverse diseases and malignant tumors. miR-1258 exerts great influence on tumors, including tumor growth, distant metastasis, migration, invasion, chemosensitivity, cell glycolysis, apoptosis, and stemness. Interestingly, miR-1258 is a miRNA with explicit functions and has been investigated to act as a tumor suppressor in studies on various types of tumors. With accumulating research on miR-1258, it has been found to be used as a biomarker in the early diagnosis and prognosis prediction of tumor patients. In this review, we outline the development of miR-1258 research, describe its regulatory network, and discuss its roles in cancer. Additionally, we generalize the potential clinical applications of miR-1258. This review offers emerging perspectives and orientations for further comprehending the function of miR-1258 as a diagnostic and prognostic biomarker and potent therapeutic target in cancer.

Combination of apatinib with apo-IDO1 inhibitor for the treatment of colorectal cancer

Colorectal cancer (CRC) is the third most common cancer in the world. Recently, many clinical studies have demonstrated the therapeutic potential of immune checkpoint therapy combined with inhibitors of vascular endothelial growth factor receptor 2 (VEGFR2) in colon cancer. Compound B37, identified in our previous experiment, is an apo-form indoleamine-2,3-dioxygenase 1 inhibitor (apo-IDO1 inhibitor), which has been shown to significantly suppress tumor growth combined with an anti-PD1 antibody. We speculated whether this apo-IDO inhibitor (B37) combined with a VEGFR2 inhibitor (apatinib) would further improve its anti-tumor activity. Therefore, a syngeneic mouse colon cancer model (mouse colon cancer cell line CT26) was established to investigate the anti-tumor activity of B37 combined with apatinib. As expected, the combination of B37 and apatinib (VEGFR2 inhibitor) improved the therapeutic effect compared with apo-IDO1 inhibitor and apatinib monotherapy, as shown by the reduced growth of transplanted tumors, weakened proliferation, and increased apoptosis of cancer cells. Specifically, there was a 24.8% reduction in tumor volume using apatinib and 31.3% reduction using B37. The combination-treated group showed remarkable inhibition of tumor growth (52.2%). For tumor weight, there was a 29.2% reduction in the apatinib-treated group and 35.0% reduction in the B37-treated group. The combination-treated group showed a 56.3% reduction. Moreover, the combination therapy reprogrammed the immune microenvironment by increasing infiltration of CD4⁺ and CD8⁺ T cells, decreasing the ratio of regulatory T cells, and promoting the killing ability of T cells manifested by elevated expression of IFN-γ and granzyme B in the combination-treated group. Our study indicates that the combination of apo-IDO1 inhibitor and apatinib is a promising strategy for CRC therapy.

Expression of immune checkpoint regulators, programmed death-ligand 1 (PD-L1/PD-1), cytotoxic T lymphocyte antigen 4 (CTLA-4), and indolaimine-2, 3-deoxygenase (IDO) in uterine mesenchymal tumors

BACKGROUND

Immune checkpoints including programmed death-ligand 1/programmed death-1/ (PD-L1/PD-1), cytotoxic T lymphocyte antigen 4 (CTLA-4), and indolaimine-2, 3-deoxygenase (IDO) have recently emerged as effective candidates for treatment against a range of human malignancies. We have investigated their expression in the uterine mesenchymal tumors.

METHODS

Sixty-eight mesenchymal tumors were categorized into 6 diagnostic groups. We assessed PD-L1, PD-1, CTLA-4, and IDO expression on paraffin embedded tissue blocks of the uterine tumors using the respective antibodies. Immunohistochemical (IHC) stains were classified as positive when the reactions were present in at least 1% of the cell membranes for PD-L1/PD-1 or in cytoplasm for CTLA-4 and IDO, regardless of intensity. Student's t-test and McNemar's chi-square tests were carried out to analyze the results.

RESULTS

The mesenchymal neoplasms had expressed the immune checkpoints in the tumor and/or the lymphoid cells at the rate of 49% and 54% respectively. The tumor cells were positive in 10 (18%, PD-L1), 0 (0%, PD-1), 18 (32%, CTLA-4), and 13 (23%, IDO) cases while the infiltrating lymphoid cells were positive in 10 (18%, PD-L1), 23 (40%, PD-1), 18 (32%, CTLA-4), and 13 (23%, IDO) cases. Overall, comparison of paired tumor vs lymphoid cells resulted in p-values of ≤ 0.04.

CONCLUSIONS

Nearly 50% of the uterine tumors express at least one of the immune checkpoints in tumor and/or the infiltrating lymphoid cells. However, expression of the proteins in the two cellular components are mutually exclusive. Namely, when tumor cells express an immune checkpoint, the infiltrating lymphoid cells do not, and vice versa. Since the leiomyosarcomas are reportedly resistant to the immunotherapy when PD-L1 is expressed in the tumor cells, it can be posited that presence of the IHC positive lymphoid cells may be a better indicator of response to the treatment.

Systemic tryptophan homeostasis

Tryptophan is an essential amino acid, which is not only a building block for protein synthesis, but also a precursor for the biosynthesis of co-enzymes and neuromodulators, such as NAD/NADP(H), kynurenic acid, melatonin and serotonin. It also plays a role in immune homeostasis, as local tryptophan catabolism impairs T-lymphocyte mediated immunity. Therefore, tryptophan plasmatic concentration needs to be stable, in spite of large variations in dietary supply. Here, we review the main checkpoints accounting for tryptophan homeostasis, including absorption, transport, metabolism and elimination, and we discuss the physiopathology of disorders associated with their dysfunction. Tryptophan is catabolized along the kynurenine pathway through the action of two enzymes that mediate the first and rate-limiting step of the pathway: indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase (TDO). While IDO1 expression is restricted to peripheral sites of immune modulation, TDO is massively expressed in the liver and accounts for 90% of tryptophan catabolism. Recent data indicated that the stability of the TDO protein is regulated by tryptophan and that this regulation allows a tight control of tryptophanemia. TDO is stabilized when tryptophan is abundant in the plasma, resulting in rapid degradation of dietary tryptophan. In contrast, when tryptophan is scarce, TDO is degraded by the proteasome to avoid excessive tryptophan catabolism. This is triggered by the unmasking of a degron in a non-catalytic tryptophan-binding site, resulting in TDO ubiquitination by E3 ligase SKP1-CUL1-F-box. Deficiency in TDO or in the hepatic aromatic transporter SLC16A10 leads to severe hypertryptophanemia, which can disturb immune and neurological homeostasis.

Tobacco carcinogen induces tryptophan metabolism and immune suppression via induction of indoleamine 2,3-dioxygenase 1

Indoleamine 2,3-dioxygenase 1 (IDO1), the enzyme that catabolizes tryptophan (Trp) metabolism to promote regulatory T cells (Tregs) and suppress CD8⁺ T cells, is regulated by several intrinsic signaling pathways. Here, we found that tobacco smoke, a major public health concern that kills 8 million people each year worldwide, induced IDO1 in normal and malignant lung epithelial cells in vitro and in vivo. The carcinogen nicotine-derived nitrosaminoketone (NNK) was the tobacco compound that upregulated IDO1 via activation of the transcription factor c-Jun, which has a binding site for the IDO1 promoter. The NNK receptor α7 nicotinic acetylcholine receptor (α7nAChR) was required for NNK-induced c-Jun activation and IDO1 upregulation. In A/J mice, NNK reduced CD8⁺ T cells and increased Tregs. Clinically, smoker patients with non-small-cell lung cancer (NSCLC) exhibited high IDO1 levels and low Trp/kynurenine (Kyn) ratios. In NSCLC patients, smokers with lower IDO1 responded better to anti-PD1 antibody treatment than those with higher IDO1. These data indicate that tobacco smoke induces IDO1 to catabolize Trp metabolism and immune suppression to promote carcinogenesis, and lower IDO1 might be a potential biomarker for anti-PD1 antibodies in smoker patients, whereas IDO1-high smoker patients might benefit from IDO1 inhibitors in combination with anti-PD1 antibodies.

Identification of Potential Allosteric Site Binders of Indoleamine 2,3-Dioxygenase 1 from Plants: A Virtual and Molecular Dynamics Investigation

Ligand and structure-based computational screenings were carried out to identify flavonoids with potential anticancer activity. Kushenol E, a flavonoid with proven anticancer activity and, at the same time, an allosteric site binder of the enzyme indoleamine 2,3-dioxygenase-1 (IDO1), was used as the reference compound. Molecular docking and molecular dynamics simulations were performed for the screened flavonoids with known anticancer activity. The following two of these flavonoids were identified as potential inhibitors of IDO1: dichamanetin and isochamanetin. Molecular dynamics simulations were used to assess the conformational profile of IDO1-flavonoids complexes, as well as for calculating the bind-free energies.

Targeting immunometabolism mediated by the IDO1 Pathway: A new mechanism of immune resistance in endometrial cancer

Immunotherapy is acquiring a primary role in treating endometrial cancer (EC) with a relevant benefit for many patients. Regardless, patients progressing during immunotherapy or those who are resistant represent an unmet need. The mechanisms of immune resistance and escape need to be better investigated. Here, we review the major mechanisms of immune escape activated by the indolamine 2,3-dioxygenase 1 (IDO1) pathway in EC and focus on potential therapeutic strategies based on IDO1 signaling pathway control. IDO1 catalyzes the first rate-limiting step of the so-called “kynurenine (Kyn) pathway”, which converts the essential amino acid l-tryptophan into the immunosuppressive metabolite l-kynurenine. Functionally, IDO1 has played a pivotal role in cancer immune escape by catalyzing the initial step of the Kyn pathway. The overexpression of IDO1 is also associated with poor prognosis in EC. These findings can lead to advantages in immunotherapy-based approaches as a rationale for overcoming the immune escape. Indeed, besides immune checkpoints, other mechanisms, including the IDO enzymes, contribute to the EC progression due to the immunosuppression induced by the tumor milieu. On the other hand, the IDO1 enzyme has recently emerged as both a promising therapeutic target and an unfavorable prognostic biomarker. This evidence provides the basis for translational strategies of immune combination, whereas IDO1 expression would serve as a potential prognostic biomarker in metastatic EC.

IDO1 is highly expressed in macrophages of patients in advanced tumour stages of oral squamous cell carcinoma

PURPOSE

Strategies for Indolamine-2,3-dioxygenase 1 (IDO1) inhibition in cancer immunotherapy once produced encouraging results, but failed in clinical trials. Recent evidence indicates that immune cells in the tumour microenvironment, especially macrophages, contribute to immune dysregulation and therefore might play a critical role in drug resistance.

METHODS

In this study, we investigated the significance of IDO1 expressing immune cells in primary tumours and corresponding lymph node metastases (LNMs) in oral squamous cell carcinoma (OSCC) by immunohistochemistry. The link between IDO1 and macrophages was investigated by flow cytometry in tumour tissue, healthy adjacent tissue and peripheral blood mononuclear cells (PBMCs). IDO1 activity (measured as Kynurenine/Tryptophan ratio) was assessed by ELISAs.

RESULTS

High IDO1 expression in tumour-infiltrating immune cells was significantly correlated with advanced stages [Spearman's rank correlation (SRC), p = 0.027] and reduced progression-free survival (multivariate Cox regression, p = 0.034). IDO1 was significantly higher expressed in PBMCs of patients in advanced stages than in healthy controls (ANOVA, p < 0.05) and IDO1⁺ macrophages were more abundant in intratumoural areas than peritumoural (t test, p < 0.001). IDO1 expression in PBMCs was significantly correlated with IDO1 activity in serum (SRC, p < 0.05). IDO1 activity was significantly higher in patients with LNMs (t test, p < 0.01).

CONCLUSION

All in all, IDO1 expressing immune cells, especially macrophages, are more abundant in advanced stages of OSCC and are associated with reduced progression-free survival. Further investigations are needed to explore their role in local and systemic immune response. The IDO1 activity might be a suitable biomarker of metastasis in OSCC patients.

Design, synthesis and biological evaluation of erlotinib-based IDO1 inhibitors

Erlotinib is a highly specific and reversible epidermal growth factor receptor tyrosine kinase inhibitor for the targeted therapy of non-small-cell lung cancer (NSCLC) However, the efficacy of erlotinib is limited because the development of drug resistance during chemotherapy. Indoleamine 2,3-dioxygenase-1 (IDO1) is a rate-limiting tryptophan catabolic enzyme that is activated in many human cancers. In this study, we designed a series of erlotinib-based 1,2,3-triazole compounds by combining erlotinib with phenyl or benzyl azide. Attentive FP prediction model was used to predict the bioactivity of those compounds. We discovered that most of the erlotinib-based 1,2,3-triazole compounds are capable of suppressing IDO1 activities in vitro experiments. Among them, compound 14b (IC50 = 0.59 ± 0.05 μM) had the strongest inhibitory effect on IDO1. In addition, compound 14b significantly inhibited tumor growth comparable to the antitumor activity of erlotinib and the IDO1 inhibitor epacadostat in murine tumor models.