Tryptophan: A Rheostat of Cancer Immune Escape Mediated by Immunosuppressive Enzymes IDO1 and TDO

Mass spectrometric monitoring of redox transformation and arylation of tryptophan

Tryptophan (Trp) is an essential amino acid obtained from human diet. It is involved not only in de novo biosynthesis of proteins but also in complex metabolic pathways. Redox transformation of tryptophan is under-explored in comparison with kynurenine, serotonin and indole pyruvate pathways. We described herein a mass spectrometric approach that can not only detect electron transfer-associated changes in masses and charges, but also identify electron-directed bond cleavages and radical-radical cross-coupling reactions in redox transformation of tryptophan. Photoactive TiO2 that is widely applied in cosmetic products is used as electron donor and receptor because of the capability to generate photoelectrons and holes. It was demonstrated tryptophan undergoes redox transformation through the removal of an electron from amino nitrogen atom by hole oxidization along with an electron capture in the indole ring. The back and forth electron-shuttle converts electric energy into chemical energy that enforces bond cleavages. Sodium-coupled electron transfer (SCET) was found in complementary with proton-coupled electron transfer in tryptophan. The movement of sodium ions avoids electric charge buildup caused by electron transfer. Various redox products were detected on both light irradiated TiO2 and skins, among which β-carboline shows extensive radical scavenging ability for diverse cross-coupling with indole derivatives. Light-independent redox products have been detected in vivo such as in mouse brain, indicating the presence of in vivo electron transfer-directed redox transformation. It has also been revealed that tryptophan can be arylated on Cα and Cβ atoms in response to the exposure of halogenated aromatics.

IDO1-mediated AhR activation up-regulates pentose phosphate pathway via NRF2 to inhibit ferroptosis in lung cancer

Ferroptosis is a type of cell death marked by iron-dependent lipid peroxide accumulation. Indoleamine 2,3-dioxygenase 1 (IDO1), a key enzyme in the catabolism of tryptophan through kynurenine pathway, participates in the development of multiple tumor types. However, the role of IDO1 in tumor ferroptosis is unclear. In this study, we identified IDO1 as a key regulator of ferroptosis in lung cancer. With Erastin-treated lung cancer cells, we found that IDO1 inhibited ferroptosis, reduced the generation of lipid peroxide and ROS. Mechanistically, IDO1 promoted the expression of nuclear factor erythroid 2-related factor 2 (NRF2) through activating aryl hydrocarbon receptor (AhR) pathway. IDO1 up-regulated the expression of solute carrier family 7 member 11 (SLC7A11) and the activity of pentose phosphate pathway (PPP) via AhR-NRF2 axis, promoted the production of reduced nicotinamide adenine dinucleotide phosphate (NADPH) and glutathione (GSH), thereby inhibiting ferroptosis. Moreover, combined treatment with IDO1 inhibitor and Erastin inhibited tumor growth, down-regulated SLC7A11 expression and PPP activity, promoted tumor ferroptosis in lung cancer-bearing mice. In conclusion, this study revealed the function of IDO1 in lung cancer ferroptosis and provided a new strategy for lung cancer therapy.

Research progress in bifunctional small molecules for cancer immunotherapy

Immunotherapy has become one of the most revolutionary modalities for cancer treatment with the approval of many anti-PD-L1 (programmed cell death-ligand 1)/PD-1 (programmed cell death-1) monoclonal antibodies (mAbs). However, anti-PD-L1/PD-1 mAbs suffer from several drawbacks including limited clinical efficacy (∼20 %), poor pharmacokinetics, and the development of immune resistance. Hence, the search for PD-1/PD-L1-based combination therapies and other PD-L1-based bifunctional small molecule modulators [e.g. PD-L1/HDAC (Histone Deacetylase), PD-L1/CXCL12 (C-X-C chemokine ligand 12), PD-L1/Tubulin, PD-L1/IDO1 (Indoleamine 2,3 dioxygenase 1), PD-L1/PARP (Poly(ADP-ribose) polymerase), PD-L1/STING (Stimulator of interferon genes), and PD-L1/NAMPT (Nicotinamide phosphoribosyltransferase)-targeting dual inhibitors] has been intensified with considerable strides achieved in the past couple of years. Herein, we summarize the latest development of bifunctional small molecules as immunotherapy for tumor treatment, including those PD-L1-based, A2AR (Adenosine 2A receptor)-based, IDO1-based, Toll-like receptor (TLR)-based, SHP2 (Src homology 2 domain-containing phosphatase 2)-based, and HPK1 (Hematopoietic progenitor kinase 1)-based dual-acting compounds. In addition, we also summarize the tumorigenesis and synergy mechanism of various targets. Finally, the challenges and future directions for bifunctional small molecules for cancer immunotherapy are also discussed in detail.

N-formylkynurenine but not kynurenine enters a nucleophile-scavenging branch of the immune-regulatory kynurenine pathway

Tryptophan catabolism along the kynurenine pathway (KP) mediates key physiological functions ranging from immune tolerance to lens UV protection, but the contributory roles and chemical fates of individual KP metabolites are incompletely understood. This particularly concerns the first KP metabolite, N-formylkynurenine (NFK), canonically viewed as a transient precursor to the downstream kynurenine (KYN). Here, we challenge that canon and show that hydrolytic enzymes act as a rheostat switching NFK's fate between the canonical KP and a novel non-enzymatic branch of tryptophan catabolism. In the physiological environment (37 °C, pH 7.4), NFK deaminated into electrophilic NFK-carboxyketoalkene (NFK-CKA), which rapidly (<2 min) formed adducts with nucleophiles such as cysteine and glutathione, the key intracellular antioxidants. Serum hydrolases suppressed NFK deamination as they hydrolysed NFK to KYN ∼3 times faster than NFK deaminates. Whilst KYN did not deaminate, its deaminated product (KYN-CKA) rapidly reacted with cysteine but not glutathione. The new NFK transformations of a yet to be discovered function highlight NFK's significance beyond hydrolysis to KYN and suggests the dominance of its chemical transformations over those of KYN. Enzyme compartmentalisation and abundance offer insights into the regulation of non-enzymatic KP metabolite transformations such as KYN involved in immune regulation, protein modification, lens aging or neuropathology.

Targeting the kynurenine pathway: another therapeutic opportunity in the metabolic crosstalk between cancer and immune cells

The pivotal role of metabolic reprogramming in cancer-related drug resistance, through the tryptophan-catabolized kynurenine pathway (KP), has been particularly underscored in recent research. This pathway, driven by indoleamine 2,3-dioxygenase 1 (IDO1), facilitates immune evasion and promotes tumor progression by fostering an immunosuppressive environment. In Phase III investigation of the combination of IDO1 inhibition with immune checkpoint inhibitors (ICIs), the combination therapy was not efficacious. In this review, we revisit current advances, explore future directions, and emphasize the importance of dual inhibition of the KP rate-limiting enzymes IDO1 and tryptophan 2,3-dioxygenase-2 (TDO2) in appropriate patient populations. We propose that dual inhibition may maximize the therapeutic potential of KP inhibition. Additionally, we delve into the complex cellular interactions in cancer and metabolic dependencies within the tumor microenvironment (TME). Insights from preclinical studies, recent clinical trials, and promising therapeutic combinations will be discussed to elucidate and promote a clear path forward for the direction of KP research into cancer-related outcomes.

Role of amino acid metabolism in tumor immune microenvironment of colorectal cancer

This review investigates the role of amino acid metabolism in the tumor microenvironment of colorectal cancer (CRC) and explores potential targeted therapeutic strategies. The paper synthesized current research on amino acid metabolism in the colorectal cancer tumor microenvironment, focusing on amino acids such as tryptophan, methionine, glutamine, and arginine. It examined their impact on tumor growth, immune evasion, and patient prognosis, as well as the metabolic reprogramming of tumor cells and complex tumor microenvironment interactions. Aberrant amino acid metabolism was a hallmark of colorectal cancer, influencing tumor proliferation, survival, and invasiveness. Key findings included: Tryptophan metabolism via the kynurenine and serotonin pathways significantly affected immune response and tumor progression in CRC. Methionine influenced T cell function and DNA methylation, playing a critical role in tumor development. Glutamine was extensively used by tumor cells for energy metabolism and supported immune cell function. Arginine metabolism impacted CD8+ T cell functionality and tumor growth. The review also discussed the dual roles of immune cells in the tumor microenvironment and the potential of targeting amino acid metabolic pathways for CRC treatment. In conclusion, amino acid metabolism significantly impacts the colorectal cancer tumor microenvironment and immunity. Understanding these metabolic pathways provides valuable insights into CRC pathogenesis and identifies potential therapeutic targets. Future research should focus on developing treatments that disrupt these metabolic processes to improve patient outcomes in CRC.

Improving the Anti-Tumor Effect of Indoleamine 2,3-Dioxygenase Inhibitor CY1-4 by CY1-4 Nano-Skeleton Drug Delivery System

Background: CY1-4, 9-nitropyridine [2',3':4,5] pyrimido [1,2-α] indole -5,11- dione, is an indoleamine 2,3-dioxygenase (IDO) inhibitor and a poorly water-soluble substance. It is very important to increase the solubility of CY1-4 to improve its bioavailability and therapeutic effect. In this study, the mesoporous silica nano-skeleton carrier material Sylysia was selected as the carrier to load CY1-4, and then the CY1-4 nano-skeleton drug delivery system (MSNM@CY1-4) was prepared by coating the hydrophilic polymer material Hydroxypropyl methylcellulose (HPMC) and the lipid material Distearoylphosphatidyl-ethanolamine-poly(ethylene glycol)2000 (DSPE-PEG2000) to improve the anti-tumor effect of CY1-4. Methods: The solubility and dissolution of MSNM@CY1-4 were investigated, and its bioavailability, anti-tumor efficacy, IDO inhibitory ability and immune mechanism were evaluated in vivo. Results: CY1-4 was loaded in MSNM@CY1-4 in an amorphous form, and MSNM@CY1-4 could significantly improve the solubility (up to about 200 times) and dissolution rate of CY1-4. In vivo studies showed that the oral bioavailability of CY1-4 in 20 mg/kg MSNM@CY1-4 was about 23.9-fold more than that in 50 mg/kg CY1-4 suspension. In B16F10 tumor-bearing mice, MSNM@CY1-4 significantly inhibited tumor growth, prolonged survival time, significantly inhibited IDO activity in blood and tumor tissues, and reduced Tregs in tumor tissues and tumor-draining lymph nodes to improve anti-tumor efficacy. Conclusions: The nano-skeleton drug delivery system (MSNM@CY1-4) constructed in this study is a potential drug delivery platform for improving the anti-tumor effect of oral poorly water-soluble CY1-4.

Koala ocular disease grades are defined by chlamydial load changes and increases in Th2 immune responses

Introduction

This study employs bulk RNA sequencing, PCR, and ELISA assays to analyze the pathological factors affecting the outcomes of C. pecorum ocular infections in koalas. It investigates the immune responses and gene expression profiles associated with various stages of koala ocular chlamydiosis.

Methods

A cohort of 114 koalas from Queensland, Australia were assessed, with 47% displaying clinical signs of ocular disease. Animals were classified into three cohorts: acute active disease (G1), chronic active disease (G2), and chronic inactive disease (G3), along with subclinical Chlamydia pecorum positive (H2) and healthy (H1) cohorts.

Results

Analysis of clinical, microbiological, humoral immune and cellular immune biomarkers revealed varying chlamydial loads and anti-chlamydial IgG levels across disease grades, with a negative correlation observed between ocular chlamydial load and anti-chlamydial IgG. Koala ocular mucosa gene expression analysis from 27 koalas identified shared expression pathways across disease cohorts, with a significant upregulation of IFNγ expression and tryptophan metabolism in all disease stages.

Discussion

These findings help elucidate immune response dynamics and molecular pathways underlying koala ocular chlamydiosis, providing insights crucial for disease management strategies.

Double-Edge Effects of Leucine on Cancer Cells

Leucine is an essential amino acid that cannot be produced endogenously in the human body and therefore needs to be obtained from dietary sources. Leucine plays a pivotal role in stimulating muscle protein synthesis, along with isoleucine and valine, as the group of branched-chain amino acids, making them one of the most popular dietary supplements for athletes and gym-goers. The individual effects of leucine, however, have not been fully clarified, as most of the studies so far have focused on the grouped effects of branched-chain amino acids. In recent years, leucine and its metabolites have been shown to stimulate muscle protein synthesis mainly via the mammalian target of the rapamycin complex 1 signaling pathway, thereby improving muscle atrophy in cancer cachexia. Interestingly, cancer research suggests that leucine may have either anti-cancer or pro-tumorigenic effects. In the current manuscript, we aim to review leucine's roles in muscle protein synthesis, tumor suppression, and tumor progression, specifically summarizing the molecular mechanisms of leucine's action. The role of leucine is controversial in hepatocellular carcinoma, whereas its pro-tumorigenic effects have been demonstrated in breast and pancreatic cancers. In summary, leucine being used as nutritional supplement for athletes needs more attention, as its pro-oncogenic effects may have been identified by recent studies. Anti-cancer or pro-tumorigenic effects of leucine in various cancers should be further investigated to achieve clear conclusions.

METABOLIC AND BIOENERGETIC ALTERATIONS ARE ASSOCIATED WITH INFECTION SUSCEPTIBILITY IN SURVIVORS OF SEVERE TRAUMA: AN EXPLORATORY STUDY

ABSTRACT

Background : Trauma and blood loss are frequently associated with organ failure, immune dysfunction, and a high risk of secondary bacterial lung infections. We aim to test if plasma metabolomic flux and monocyte bioenergetics are altered in association with trauma and related secondary infections. Methods : Plasma samples were collected from trauma patients at three time points: days 0, 3, and 7 postadmission. Metabolites (140) were measured in plasma from trauma survivors ( n = 24) and healthy control individuals (HC, n = 10). Further analysis within the trauma cohort included subsets of trauma/infection-negative (TIneg, n = 12) and trauma/infection-positive patients (TIpos, n = 12). The bioenergetic profile in monocytes was determined using mitochondrial and glycolytic stress tests. Results : In the trauma cohort, significant alterations were observed in 29 metabolites directly affecting 11 major metabolic pathways, while 34 metabolite alterations affected 8 pathways in 9, versus TIneg patients. The most altered metabolic pathways included protein synthesis, the urea cycle/arginine metabolism, phenylalanine, tyrosine, tryptophan biosynthesis, and carnitine compound family. In monocytes from trauma patients, reduced mitochondrial indices and loss of glycolytic plasticity were consistent with an altered profile of plasma metabolites in the tricarboxylic acid cycle and glycolysis. Conclusions : Our study highlights that the metabolic profile is significantly and persistently affected by trauma and related infections. Among trauma survivors, metabolic alterations in plasma were associated with reduced monocyte bioenergetics. These exploratory findings establish a groundwork for future clinical studies aimed at enhancing our understanding of the interplay between metabolic/bioenergetic alterations associated with trauma and secondary bacterial infections.

ADAM10 modulates the efficacy of T-cell-mediated therapy in solid tumors

T-cell-mediated therapeutic strategies are the most potent effectors of cancer immunotherapy. However, an essential barrier to this therapy in solid tumors is disrupting the anti-cancer immune response, cancer-immunity cycle, T-cell priming, trafficking and T-cell cytotoxic capacity. Thus, reinforcing the anti-cancer immune response is needed to improve the effectiveness of T-cell-mediated therapy. Tumor-associated protease ADAM10, endothelial cells (ECs) and cytotoxic CD8+ T cells engage in complex communication via adhesion, transmigration and chemotactic mechanisms to facilitate an anti-cancer immune response. The precise impact of ADAM10 on the intricate mechanisms underlying these interactions remains unclear. This paper broadly explores how ADAM10, through different routes, influences the efficacy of T-cell-mediated therapy. ADAM10 cleaves CD8+ T-cell-targeting genes and impacts their expression and specificity. In addition, ADAM10 mediates the interactions of adhesion molecules with T cells and influences CD8+ T-cell activity and trafficking. Thus, understanding the role of ADAM10 in these events may lead to innovative strategies for advancing T-cell-mediated therapies.

Molecular mechanisms and therapeutic significance of Tryptophan Metabolism and signaling in cancer

Tryptophan (Trp) metabolism involves three primary pathways: the kynurenine (Kyn) pathway (KP), the 5-hydroxytryptamine (serotonin, 5-HT) pathway, and the indole pathway. Under normal physiological conditions, Trp metabolism plays crucial roles in regulating inflammation, immunity, and neuronal function. Key rate-limiting enzymes such as indoleamine-2,3-dioxygenase (IDO), Trp-2,3-dioxygenase (TDO), and kynurenine monooxygenase (KMO) drive these metabolic processes. Imbalances in Trp metabolism are linked to various cancers and often correlate with poor prognosis and adverse clinical characteristics. Dysregulated Trp metabolism fosters tumor growth and immune evasion primarily by creating an immunosuppressive tumor microenvironment (TME). Activation of the KP results in the production of immunosuppressive metabolites like Kyn, which modulate immune responses and promote oncogenesis mainly through interaction with the aryl hydrocarbon receptor (AHR). Targeting Trp metabolism therapeutically has shown significant potential, especially with the development of small-molecule inhibitors for IDO1, TDO, and other key enzymes. These inhibitors disrupt the immunosuppressive signals within the TME, potentially restoring effective anti-tumor immune responses. Recently, IDO1 inhibitors have been tested in clinical trials, showing the potential to enhance the effects of existing cancer therapies. However, mixed results in later-stage trials underscore the need for a deeper understanding of Trp metabolism and its complex role in cancer. Recent advancements have also explored combining Trp metabolism inhibitors with other treatments, such as immune checkpoint inhibitors, chemotherapy, and radiotherapy, to enhance therapeutic efficacy and overcome resistance mechanisms. This review summarizes the current understanding of Trp metabolism and signaling in cancer, detailing the oncogenic mechanisms and clinical significance of dysregulated Trp metabolism. Additionally, it provides insights into the challenges in developing Trp-targeted therapies and future research directions aimed at optimizing these therapeutic strategies and improving patient outcomes.

Immunoprognostic analysis of indoleamine 2,3-dioxygenase 1 in patients with cervical cancer

The incidence of cervical cancer is increasing. Immunotherapies show better patient outcomes than monotherapies; however, the mainstay treatment for cervical cancer remains surgery and chemotherapy. Indoleamine 2,3-dioxygenase 1 (IDO1) acts on multiple tryptophan substrates, exhibiting antitumor, immunomodulatory, and antioxidant activities. Despite the association of elevated IDO1 expression with unfavorable outcomes in various cancers, its precise function in cervical cancer remains ambiguous. Here, we explored the prognostic significance of IDO1 in cervical carcinoma. Gene expression datasets were obtained from The Cancer Genome Atlas. Gene Expression Omnibus datasets were used for differential expression and functional correlation analyses. Using Human Protein Atlas alongside Tumor-Immune System Interaction Database, we assessed the association of IDO1 with survival rates. Given the link between cervical cancer prognosis and immune invasion, CIBERSORT was used to assess the connection between immune cells and IDO1, while the percentage of tumor-penetrating immune cells based on IDO1 expression in cervical cancer patients was analyzed using Tumor-Immune System Interaction Database. Incorporating a clinicopathological characteristic-based risk score model with IDO1 risk score, we devised a nomogram to predict cervical cancer patient survival. The effects of IDO1 in immune regulation and its prognostic significance were validated using data from patients with cervical cancer obtained from The Cancer Imaging Archive database. Compared with that in normal cervical tissues, IDO1 expression was significantly upregulated in cervical cancer tissues and significantly correlated with cervical cancer progression and prognosis. IDO1 expression showed a positive association with monocyte and macrophage abundance, while exhibiting a negative correlation with that of endothelial cells and eosinophils. Cox regression analyses highlighted IDO1 as the core immune gene implicated in cervical cancer. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses revealed an association of IDO1 with the metabolic pathways of tryptophan, phenylalanine, and tyrosine. Univariate and multivariate analyses revealed that elevated IDO1 expression correlates markedly with cervical cancer outcomes, suggesting it as a promising therapeutic target. The Cancer Imaging Archive data analysis revealed that the impact of anti-PD1 and CTLA4 therapy is more pronounced in cervical cancer patients exhibiting elevated IDO1 expression. IDO1 is a potential target for immunotherapy for cervical cancer.

Hypoxia-Targeted Immunotherapy with PD-1 Blockade in Head and Neck Cancer

Intratumoral hypoxia is associated with tumor progression, aggressiveness, and therapeutic resistance in several cancers. Hypoxia causes cancer cells to experience replication stress, thereby activating DNA damage and repair pathways. MutT homologue-1 (MTH1, also known as NUDT1), a member of the Nudix family, maintains the genomic integrity and viability of tumor cells in the hypoxic tumor microenvironment. Although hypoxia is associated with poor prognosis and can cause therapeutic resistance by regulating the microenvironment, it has not been considered a treatable target in cancer. This study aimed to investigate whether hypoxia-induced MTH1 is a useful target for immunotherapy and whether hypoxic conditions influence the antitumor activity of immune cells. Our results showed that MTH1 expression was elevated under hypoxic conditions in head and neck cancer cell lines. Furthermore, we identified a novel MTH1-targeting epitope peptide that can activate peptide-specific CD4+ helper T cells with cytotoxic activity. The proliferation and cytotoxic activity of T cells were maintained under hypoxic conditions, and PD-1 blockade further augmented the cytotoxicity. These results indicate that MTH1-targeted immunotherapy combined with checkpoint blockade can be an effective strategy for the treatment of hypoxic tumors.

Surface-Enhanced Raman Scattering Monitoring of Tryptophan Dynamics in 3D Pancreatic Tumor Models

In the intricate landscape of the tumor microenvironment, both cancer and stromal cells undergo rapid metabolic adaptations to support their growth. Given the relevant role of the metabolic secretome in fueling tumor progression, its unique metabolic characteristics have gained prominence as potential biomarkers and therapeutic targets. As a result, rapid and accurate tools have been developed to track metabolic changes in the tumor microenvironment with high sensitivity and resolution. Surface-enhanced Raman scattering (SERS) is a highly sensitive analytical technique and has been proven efficient toward the detection of metabolites in biological media. However, profiling secreted metabolites in complex cellular environments such as those in tumor-stroma 3D in vitro models remains challenging. To address this limitation, we employed a SERS-based strategy to investigate the metabolic secretome of pancreatic tumor models within 3D cultures. We aimed to monitor the immunosuppressive potential of stratified pancreatic cancer-stroma spheroids as compared to 3D cultures of either pancreatic cancer cells or cancer-associated fibroblasts, focusing on the metabolic conversion of tryptophan into kynurenine by the IDO-1 enzyme. We additionally sought to elucidate the dynamics of tryptophan consumption in correlation with the size, temporal evolution, and composition of the spheroids, as well as assessing the effects of different drugs targeting the IDO-1 machinery. As a result, we confirm that SERS can be a valuable tool toward the optimization of cancer spheroids, in connection with their tryptophan metabolizing capacity, potentially allowing high-throughput spheroid analysis.

Harnessing CD8+ T cell dynamics in hepatitis B virus-associated liver diseases: Insights, therapies and future directions

Hepatitis B virus (HBV) infection playsa significant role in the etiology and progression of liver-relatedpathologies, encompassing chronic hepatitis, fibrosis, cirrhosis, and eventual hepatocellularcarcinoma (HCC). Notably, HBV infection stands as the primary etiologicalfactor driving the development of HCC. Given the significant contribution ofHBV infection to liver diseases, a comprehensive understanding of immunedynamics in the liver microenvironment, spanning chronic HBV infection,fibrosis, cirrhosis, and HCC, is essential. In this review, we focused on thefunctional alterations of CD8+ T cells within the pathogenic livermicroenvironment from HBV infection to HCC. We thoroughly reviewed the roles ofhypoxia, acidic pH, metabolic reprogramming, amino acid deficiency, inhibitory checkpointmolecules, immunosuppressive cytokines, and the gut-liver communication in shapingthe dysfunction of CD8+ T cells in the liver microenvironment. Thesefactors significantly impact the clinical prognosis. Furthermore, we comprehensivelyreviewed CD8+ T cell-based therapy strategies for liver diseases,encompassing HBV infection, fibrosis, cirrhosis, and HCC. Strategies includeimmune checkpoint blockades, metabolic T-cell targeting therapy, therapeuticT-cell vaccination, and adoptive transfer of genetically engineered CD8+ T cells, along with the combined usage of programmed cell death protein-1/programmeddeath ligand-1 (PD-1/PD-L1) inhibitors with mitochondria-targeted antioxidants.Given that targeting CD8+ T cells at various stages of hepatitis Bvirus-induced hepatocellular carcinoma (HBV + HCC) shows promise, we reviewedthe ongoing need for research to elucidate the complex interplay between CD8+ T cells and the liver microenvironment in the progression of HBV infection toHCC. We also discussed personalized treatment regimens, combining therapeuticstrategies and harnessing gut microbiota modulation, which holds potential forenhanced clinical benefits. In conclusion, this review delves into the immunedynamics of CD8+ T cells, microenvironment changes, and therapeuticstrategies within the liver during chronic HBV infection, HCC progression, andrelated liver diseases.

Potential of Targeting TDO2 as the Lung Adenocarcinoma Treatment

Tryptophan catabolism plays an important role in the metabolic reconnection in cancer cells to support special demands of tumor initiation and progression. The catabolic product of the tryptophan pathway, kynurenine, has the capability of suppressing the immune reactions of tumor cells. In this study, we conducted internal and external cohort studies to reveal the importance of tryptophan 2,3-dioxygenase (TDO) for lung adenocarcinoma (LUAD). Our study further demonstrated that the TDO2 expression was associated with the proliferation, survival, and invasion of LUAD cells, and targeting TDO2 for LUAD tumors could be a potential therapeutic strategy.

Comparative secretome metabolic dysregulation by six engineered dietary nanoparticles (EDNs) on the simulated gut microbiota

The potential use of engineered dietary nanoparticles (EDNs) in diet has been increasing and poses a risk of exposure. The effect of EDNs on gut bacterial metabolism remains largely unknown. In this study, liquid chromatography-mass spectrometry (LC-MS) based metabolomics was used to reveal significantly altered metabolites and metabolic pathways in the secretome of simulated gut microbiome exposed to six different types of EDNs (Chitosan, cellulose nanocrystals (CNC), cellulose nanofibrils (CNF) and polylactic-co-glycolic acid (PLGA); two inorganic EDNs including TiO2 and SiO2) at two dietary doses. We demonstrated that all six EDNs can alter the composition in the secretome with distinct patterns. Chitosan, followed by PLGA and SiO2, has shown the highest potency in inducing the secretome change with major pathways in tryptophan and indole metabolism, bile acid metabolism, tyrosine and phenol metabolism. Metabolomic alterations with clear dose response were observed in most EDNs. Overall, phenylalanine has been shown as the most sensitive metabolites, followed by bile acids such as chenodeoxycholic acid and cholic acid. Those metabolites might be served as the representative metabolites for the EDNs-gut bacteria interaction. Collectively, our studies have demonstrated the sensitivity and feasibility of using metabolomic signatures to understand and predict EDNs-gut microbiome interaction.

Glioblastoma Therapy: Past, Present and Future

Glioblastoma (GB) stands out as the most prevalent and lethal form of brain cancer. Although great efforts have been made by clinicians and researchers, no significant improvement in survival has been achieved since the Stupp protocol became the standard of care (SOC) in 2005. Despite multimodality treatments, recurrence is almost universal with survival rates under 2 years after diagnosis. Here, we discuss the recent progress in our understanding of GB pathophysiology, in particular, the importance of glioma stem cells (GSCs), the tumor microenvironment conditions, and epigenetic mechanisms involved in GB growth, aggressiveness and recurrence. The discussion on therapeutic strategies first covers the SOC treatment and targeted therapies that have been shown to interfere with different signaling pathways (pRB/CDK4/RB1/P16ink4, TP53/MDM2/P14arf, PI3k/Akt-PTEN, RAS/RAF/MEK, PARP) involved in GB tumorigenesis, pathophysiology, and treatment resistance acquisition. Below, we analyze several immunotherapeutic approaches (i.e., checkpoint inhibitors, vaccines, CAR-modified NK or T cells, oncolytic virotherapy) that have been used in an attempt to enhance the immune response against GB, and thereby avoid recidivism or increase survival of GB patients. Finally, we present treatment attempts made using nanotherapies (nanometric structures having active anti-GB agents such as antibodies, chemotherapeutic/anti-angiogenic drugs or sensitizers, radionuclides, and molecules that target GB cellular receptors or open the blood-brain barrier) and non-ionizing energies (laser interstitial thermal therapy, high/low intensity focused ultrasounds, photodynamic/sonodynamic therapies and electroporation). The aim of this review is to discuss the advances and limitations of the current therapies and to present novel approaches that are under development or following clinical trials.

Amino acid metabolism, redox balance and epigenetic regulation in cancer

Amino acids act as versatile nutrients driving cell growth and survival, especially in cancer cells. Amino acid metabolism comprises numerous metabolic networks and is closely linked with intracellular redox balance and epigenetic regulation. Reprogrammed amino acid metabolism has been recognized as a ubiquitous feature in tumour cells. This review outlines the metabolism of several primary amino acids in cancer cells and highlights the pivotal role of amino acid metabolism in sustaining redox homeostasis and regulating epigenetic modification in response to oxidative and genetic stress in cancer cells.

Metabolic Signature of Warburg Effect in Cancer: An Effective and Obligatory Interplay between Nutrient Transporters and Catabolic/Anabolic Pathways to Promote Tumor Growth

Aerobic glycolysis in cancer cells, originally observed by Warburg 100 years ago, which involves the production of lactate as the end product of glucose breakdown even in the presence of adequate oxygen, is the foundation for the current interest in the cancer-cell-specific reprograming of metabolic pathways. The renewed interest in cancer cell metabolism has now gone well beyond the original Warburg effect related to glycolysis to other metabolic pathways that include amino acid metabolism, one-carbon metabolism, the pentose phosphate pathway, nucleotide synthesis, antioxidant machinery, etc. Since glucose and amino acids constitute the primary nutrients that fuel the altered metabolic pathways in cancer cells, the transporters that mediate the transfer of these nutrients and their metabolites not only across the plasma membrane but also across the mitochondrial and lysosomal membranes have become an integral component of the expansion of the Warburg effect. In this review, we focus on the interplay between these transporters and metabolic pathways that facilitates metabolic reprogramming, which has become a hallmark of cancer cells. The beneficial outcome of this recent understanding of the unique metabolic signature surrounding the Warburg effect is the identification of novel drug targets for the development of a new generation of therapeutics to treat cancer.

Identification of paeoniflorin from Paeonia lactiflora pall. As an inhibitor of tryptophan 2,3-dioxygenase and assessment of its pharmacological effects on depressive mice

ETHNOPHARMACOLOGICAL RELEVANCE

The radix of Paeonia lactiflora Pall. (PaeR) is a traditional Chinese medicine (TCM) clinically used for treating depression. Although it has been established that PaeR can protect the liver and alleviate depressive-like behaviors, its bioactive chemicals and antidepressant mechanism remain unclear. Our pilot study showed that PaeR reduced the expression of the L-tryptophan- catabolizing enzyme tryptophan 2,3-dioxygenase (TDO) in the livers of stress-induced depression-like mice.

AIM OF THE STUDY

This study aimed to screen potential TDO inhibitors from PaeR and investigate the potential therapeutic use of TDO inhibition for treating depression.

MATERIALS AND METHODS

Molecular docking, magnetic ligand fishing, and secrete-pair dual luminescence assay were conducted for in vitro ligand discovery and high-throughput screening of TDO inhibitors. Stable TDO overexpression was achieved in HepG2 cell lines to evaluate the TDO inhibitory activities of drugs in vitro by RT-PCR and Western blot analyses of TDO at mRNA and protein levels. In vivo validation of TDO inhibitory potency and evaluation of TDO inhibition as a potential therapeutic strategy for major depressive disorder (MDD) were performed using mice subjected to "3 + 1″ combined stresses for at least 30 days to induce depression-like behaviors. A well-known TDO inhibitor, LM10, was evaluated in parallel.

RESULTS

The PaeR extract significantly ameliorated depressive-like behaviors of stressed mice, attributed to inhibition of TDO expression and tryptophan modulation metabolism. After a comprehensive analysis of molecular docking, ligand fishing, and luciferase assay, paeoniflorin was screened as a TDO inhibitor from the PaeR extract. This compound, structurally different from LM10, potently inhibited human and mouse TDO in cell- and animal-based assays. The effects of TDO inhibitors on MDD symptoms were evaluated in a stress-induced depression-like mouse model. In mice, both inhibitors had beneficial effects on stress-induced depressive-like behavioral despair and unhealthy physical status. Moreover, both inhibitors increased the liver serotonin/tryptophan ratio and decreased the kynurenine/tryptophan ratio after oral administration, demonstrating in vivo inhibition of TDO activity. Our data substantiated the potential of TDO inhibition as a therapeutic strategy to improve behavioral activity and decrease despair symptoms in major depressive disorder.

CONCLUSIONS

This study introduced a hitherto undocumented comprehensive screening strategy to identify TDO inhibitors in PaeR extract. Our findings also highlighted the potential of PaeR as a source of antidepressant constituents and pinpointed the inhibition of TDO as a promising therapeutic approach for managing major depressive disorder.

COVID-19-associated liver injury: Adding fuel to the flame

COVID-19 is mainly characterized by respiratory disorders and progresses to multiple organ involvement in severe cases. With expansion of COVID-19 and SARS-CoV-2 research, correlative liver injury has been revealed. It is speculated that COVID-19 patients exhibited abnormal liver function, as previously observed in the SARS and MERS pandemics. Furthermore, patients with underlying diseases such as chronic liver disease are more susceptible to SARS-CoV-2 and indicate a poor prognosis accompanied by respiratory symptoms, systemic inflammation, or metabolic diseases. Therefore, COVID-19 has the potential to impair liver function, while individuals with preexisting liver disease suffer from much worse infected conditions. COVID-19 related liver injury may be owing to direct cytopathic effect, immune dysfunction, gut-liver axis interaction, and inappropriate medication use. However, discussions on these issues are infancy. Expanding research have revealed that angiotensin converting enzyme 2 (ACE2) expression mediated the combination of virus and target cells, iron metabolism participated in the virus life cycle and the fate of target cells, and amino acid metabolism regulated immune response in the host cells, which are all closely related to liver health. Further exploration holds great significance in elucidating the pathogenesis, facilitating drug development, and advancing clinical treatment of COVID-19-related liver injury. This article provides a review of the clinical and laboratory hepatic characteristics in COVID-19 patients, describes the etiology and impact of liver injury, and discusses potential pathophysiological mechanisms.

Lactobacillus gallinarum-derived metabolites boost anti-PD1 efficacy in colorectal cancer by inhibiting regulatory T cells through modulating IDO1/Kyn/AHR axis

OBJECTIVE

Gut microbiota is a key player in dictating immunotherapy response. We aimed to explore the immunomodulatory effect of probiotic Lactobacillus gallinarum and its role in improving anti-programmed cell death protein 1 (PD1) efficacy against colorectal cancer (CRC).

DESIGN

The effects of L. gallinarum in anti-PD1 response were assessed in syngeneic mouse models and azoxymethane/dextran sulfate sodium-induced CRC model. The change of immune landscape was identified by multicolour flow cytometry and validated by immunohistochemistry staining and in vitro functional assays. Liquid chromatography-mass spectrometry was performed to identify the functional metabolites.

RESULTS

L. gallinarum significantly improved anti-PD1 efficacy in two syngeneic mouse models with different microsatellite instability (MSI) statuses (MSI-high for MC38, MSI-low for CT26). Such effect was confirmed in CRC tumourigenesis model. L. gallinarum synergised with anti-PD1 therapy by reducing Foxp3+ CD25+ regulatory T cell (Treg) intratumoural infiltration, and enhancing effector function of CD8+ T cells. L. gallinarum-derived indole-3-carboxylic acid (ICA) was identified as the functional metabolite. Mechanistically, ICA inhibited indoleamine 2,3-dioxygenase (IDO1) expression, therefore suppressing kynurenine (Kyn) production in tumours. ICA also competed with Kyn for binding site on aryl hydrocarbon receptor (AHR) and antagonised Kyn binding on CD4+ T cells, thereby inhibiting Treg differentiation in vitro. ICA phenocopied L. gallinarum effect and significantly improved anti-PD1 efficacy in vivo, which could be reversed by Kyn supplementation.

CONCLUSION

L. gallinarum-derived ICA improved anti-PD1 efficacy in CRC through suppressing CD4+Treg differentiation and enhancing CD8+T cell function by modulating the IDO1/Kyn/AHR axis. L. gallinarum is a potential adjuvant to augment anti-PD1 efficacy against CRC.

Inhibition of STAT-mediated cytokine responses to chemically-induced colitis prevents inflammation-associated neurobehavioral impairments

Depression can be associated with chronic systemic inflammation, and production of peripheral proinflammatory cytokines and upregulation of the kynurenine pathway have been implicated in pathogenesis of depression. However, the mechanistic bases for these comorbidities are not yet well understood. As tryptophan 2,3-dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO), which convert tryptophan to kynurenine, are rate-limiting enzymes of the kynurenine pathway, we screened TDO or IDO inhibitors for effects on the production of proinflammatory cytokines in a mouse macrophage cell line. The TDO inhibitor 680C91 attenuated LPS-induced pro-inflammatory cytokines including IL-1β and IL-6. Surprisingly, this effect was TDO-independent, as it occurred even in peritoneal macrophages from TDO knockout mice. Instead, the anti-inflammatory effects of 680C91 were mediated through the suppression of signal transducer and activator of transcription(STAT) signaling. Furthermore, 680C91 suppressed production of proinflammatory cytokines and STAT signaling in an animal model of inflammatory bowel disease. Specifically, 680C91 effectively attenuated acute phase colon cytokine responses in male mice subjected to dextran sulfate sodium (DSS)-induced colitis. Interestingly, this treatment also prevented the development of anxiodepressive-like neurobehaviors in DSS-treated mice during the recovery phase. The ability of 680C91 to prevent anxiodepressive-like behavior in response to chemically-induced colitis appeared to be due to rescue of attenuated dopamine responses in the nucleus accumbens. Thus, inhibition of STAT-mediated, but TDO-independent proinflammatory cytokines in macrophages can prevent inflammation-associated anxiety and depression. Identification of molecular mechanisms involved may facilitate the development of new treatments for gastrointestinal-neuropsychiatric comorbidity.

Laeverin/aminopeptidase Q induces indoleamine 2,3-dioxygenase-1 in human monocytes

Human extravillous trophoblast (EVT) invades the maternal endometrium and reconstructs uterine spiral arteries cooperatively with maternal immune cells. Although EVT has allogeneic paternal antigens, the maternal immune system does not reject it. Here, we found that laeverin (LVRN), an EVT-specific cell surface peptidase, interacts with monocytes to produce indoleamine 2,3-dioxygenase-1 (IDO1). LVRN-transfected Swan71 cells, a cytotrophoblast-derived cell line, and increased IDO1 expression in PBMC under cell-to-cell interacting conditions. Soluble recombinant LVRN (r-LVRN) interacted with CD14-positive monocytes and induced their IDO1 expression without the intervention of other immune cell populations. LVRN-induced IDO1 production was promoted in PMA-activated monocyte-like THP-1 cells. Furthermore, r-LVRN decreased the tryptophan level and increased the kynurenine/tryptophan ratio in the culture media of the PMA-treated THP-1 cells. These findings suggest that LVRN is one of the key molecules that mediate the interaction between EVT and monocytes/macrophages and creates an immunosuppressive environment at the maternal-fetal interface in the uterus.

The immunomodulatory role of IDO1-Kynurenine-NAD+ pathway in switching cold tumor microenvironment in PDAC

Pancreatic ductal adenocarcinoma (PDAC) is the most common exocrine tumor of the pancreas characterized by late diagnosis, adverse overall 5-year survival, a higher propensity for metastatic disease, and lack of efficacy of systemic therapy options. These adverse outcomes can be partly attributed to complex tumor microenvironment (TME). Over the past decade, immunotherapy has revolutionized the management of certain cancers; thus far, the immunologically 'non-inflamed' tumor microenvironment in PDACs has proven to be challenging. Indolamine 2,3-dioxygenase 1 (IDO1) is the rate-limiting enzyme in the catabolic pathway of L-Tryptophan, an essential amino acid, that gives rise to the immunosuppressive metabolite Kynurenine. IDO1, Indolamine 2,3-dioxygenase 2 (IDO2), and Tryptophan 2,3-dioxygenase (TDO) are the key enzymes in the tryptophan catabolic pathway but we focus on the role of the predominant enzyme form IDO1 in this review. Nicotinamide phosphoribosyl transferase (iNAMPT) regulates the intracellular concentration of NAD and is upregulated in the tumor. In light of the potential role of IDO1 as a driver of hostile TME in PDAC and NAD⁺ as a key coenzyme in anti-tumor immune response, this review urges focus on extensive research and initiation of clinical trials using IDO1 and NAMPT inhibitors in pancreatic cancer in the future.

Dietary Manipulation of Amino Acids for Cancer Therapy

Cancer cells cannot proliferate and survive unless they obtain sufficient levels of the 20 proteinogenic amino acids (AAs). Unlike normal cells, cancer cells have genetic and metabolic alterations that may limit their capacity to obtain adequate levels of the 20 AAs in challenging metabolic environments. However, since normal diets provide all AAs at relatively constant levels and ratios, these potentially lethal genetic and metabolic defects are eventually harmless to cancer cells. If we temporarily replace the normal diet of cancer patients with artificial diets in which the levels of specific AAs are manipulated, cancer cells may be unable to proliferate and survive. This article reviews in vivo studies that have evaluated the antitumor activity of diets restricted in or supplemented with the 20 proteinogenic AAs, individually and in combination. It also reviews our recent studies that show that manipulating the levels of several AAs simultaneously can lead to marked survival improvements in mice with metastatic cancers.

Modulation of immunity by tryptophan microbial metabolites

Tryptophan (Trp) is an essential amino acid that can be metabolized via endogenous and exogenous pathways, including the Kynurenine Pathway, the 5-Hydroxyindole Pathway (also the Serotonin pathway), and the Microbial pathway. Of these, the Microbial Trp metabolic pathways in the gut have recently been extensively studied for their production of bioactive molecules. The gut microbiota plays an important role in host metabolism and immunity, and microbial Trp metabolites can influence the development and progression of various diseases, including inflammatory, cardiovascular diseases, neurological diseases, metabolic diseases, and cancer, by mediating the body's immunity. This review briefly outlines the crosstalk between gut microorganisms and Trp metabolism in the body, starting from the three metabolic pathways of Trp. The mechanisms by which microbial Trp metabolites act on organism immunity are summarized, and the potential implications for disease prevention and treatment are highlighted.

Global analysis of the yeast knockout phenome

Genome-wide phenotypic screens in the budding yeast Saccharomyces cerevisiae, enabled by its knockout collection, have produced the largest, richest, and most systematic phenotypic description of any organism. However, integrative analyses of this rich data source have been virtually impossible because of the lack of a central data repository and consistent metadata annotations. Here, we describe the aggregation, harmonization, and analysis of ~14,500 yeast knockout screens, which we call Yeast Phenome. Using this unique dataset, we characterized two unknown genes (YHR045W and YGL117W) and showed that tryptophan starvation is a by-product of many chemical treatments. Furthermore, we uncovered an exponential relationship between phenotypic similarity and intergenic distance, which suggests that gene positions in both yeast and human genomes are optimized for function.

Identification of metabolic biomarkers for diagnosis of epithelial ovarian cancer using internal extraction electrospray ionization mass spectrometry (iEESI-MS)

BACKGROUND

Epithelial ovarian cancer (EOC) is the leading cause of death from gynecologic malignancies. The poor prognosis of EOC is mainly due to its asymptomatic early stage, lack of effective screening methods, and a late diagnosis in the advanced stages of the disease.

OBJECTIVE

This study investigated metabolomic abnormalities in epithelial ovarian cancers.

METHODS

Our study developed a novel strategy to rapidly identify the metabolic biomarkers in the plasma of the EOC patients using Internal Extraction Electrospray Ionization Mass Spectrometry (IEESI-MS) and Liquid Chromatography-mass Spectrometry (HPLC-MS), which could distinguish the differential metabolites in between plasma samples collected from 98 patients with epithelial ovarian cancer, including 78 cases with original (P), and 20 cases with self-configuration (ZP), as well as 60 healthy subjects, including 30 cases in the original sample (H), 30 cases in self-configuration (ZH), and 6 cases in a blind sample (B).

RESULTS

Our study detected 880 metabolites based on criteria variable importance in projection (VIP) > 1, among which 26 metabolites were selected for further identification. They are mainly metabolism-related lipids, amino acids, nucleic acids, and others. The metabolic pathways associated with the differential metabolites were explored by the KEGG analysis, a comprehensive database that integrates genome, chemistry, and system function information. The abnormal metabolites of EOC patients identified by IEESI-MS and HPLC-MS included Lysophosphatidylcholine (16:0) [Lyso PC (16:0)], L-Phenylalanine, L-Leucine, Phenylpyruvic acid, L-Tryptophan, and L-Histidine.

CONCLUSIONS

Identifying the abnormal metabolites of EOC patients through metabolomics analyses could provide a new strategy to identify valuable potential biomarkers for the screening and early diagnosis of EOC.

Metabolic Barriers to Glioblastoma Immunotherapy

Glioblastoma (GBM) is the most common primary brain tumor with a poor prognosis with the current standard of care treatment. To address the need for novel therapeutic options in GBM, immunotherapies which target cancer cells through stimulating an anti-tumoral immune response have been investigated in GBM. However, immunotherapies in GBM have not met with anywhere near the level of success they have encountered in other cancers. The immunosuppressive tumor microenvironment in GBM is thought to contribute significantly to resistance to immunotherapy. Metabolic alterations employed by cancer cells to promote their own growth and proliferation have been shown to impact the distribution and function of immune cells in the tumor microenvironment. More recently, the diminished function of anti-tumoral effector immune cells and promotion of immunosuppressive populations resulting from metabolic alterations have been investigated as contributory to therapeutic resistance. The GBM tumor cell metabolism of four nutrients (glucose, glutamine, tryptophan, and lipids) has recently been described as contributory to an immunosuppressive tumor microenvironment and immunotherapy resistance. Understanding metabolic mechanisms of resistance to immunotherapy in GBM can provide insight into future directions targeting the anti-tumor immune response in combination with tumor metabolism.

Kynureninase Upregulation Is a Prominent Feature of NFR2-Activated Cancers and Is Associated with Tumor Immunosuppression and Poor Prognosis

The nuclear factor erythroid 2-related factor 2 (NRF2) pathway is frequently activated in various cancer types. Aberrant activation of NRF2 in cancer is attributed to gain-of-function mutations in the NRF2-encoding gene NFE2L2 or a loss of function of its suppressor, Kelch-like ECH-associated protein 1 (KEAP1). NRF2 activation exerts pro-tumoral effects in part by altering cancer cell metabolism. Previously, we reported a novel mechanism of NRF2 tumoral immune suppression through the selective upregulation of the tryptophan-metabolizing enzyme kynureninase (KYNU) in lung adenocarcinoma. In the current study, we explored the relevance of NRF2-mediated KYNU upregulation across multiple cancer types. Specifically, using a gene expression dataset for 9801 tumors representing 32 cancer types from The Cancer Genome Atlas (TCGA), we demonstrated that elevated KYNU parallels increased gene-based signatures of NRF2-activation and that elevated tumoral KYNU mRNA expression is strongly associated with an immunosuppressive tumor microenvironment, marked by high expression of gene-based signatures of Tregs as well as the immune checkpoint blockade-related genes CD274 (PDL-1), PDCD1 (PD-1), and CTLA4, regardless of the cancer type. Cox proportional hazard models further revealed that increased tumoral KYNU gene expression was prognostic for poor overall survival in several cancer types, including thymoma, acute myeloid leukemia, low-grade glioma, kidney renal papillary cell carcinoma, stomach adenocarcinoma, and pancreatic ductal adenocarcinoma (PDAC). Using PDAC as a model system, we confirmed that siRNA-mediated knockdown of NRF2 reduced KYNU mRNA expression, whereas activation of NFE2L2 (the coding gene for NRF2) through either small-molecule agonists or siRNA-mediated knockdown of KEAP1 upregulated KYNU in PDAC cells. Metabolomic analyses of the conditioned medium from PDAC cell lines revealed elevated levels of KYNU-derived anthranilate, confirming that KYNU was enzymatically functional. Collectively, our study highlights the activation of the NRF2-KYNU axis as a multi-cancer phenomenon and supports the relevance of tumoral KYNU as a marker of tumor immunosuppression and as a prognostic marker for poor overall survival.

Identification and validation of a risk model and molecular subtypes based on tryptophan metabolism-related genes to predict the clinical prognosis and tumor immune microenvironment in lower-grade glioma

Background

Lower-grade glioma (LGG) is one of the most common malignant tumors in the central nervous system (CNS). Accumulating evidence have demonstrated that tryptophan metabolism is significant in tumor. Therefore, this study aims to comprehensively clarify the relationship between tryptophan metabolism-related genes (TRGs) and LGGs.

Methods

The expression level of TRGs in LGG and normal tissues was first analyzed. Next, the key TRGs with prognostic value and differential expression in LGGs were identified using the least absolute shrinkage and selection operator (LASSO) regression analysis. Subsequently, a risk model was constructed and Consensus clustering analysis was conducted based on the expression level of key TRGs. Then, the prognostic value, clinicopathological factors, and tumor immune microenvironment (TIME) characteristics between different risk groups and molecular subtypes were analyzed. Finally, the expression, prognosis, and TIME of each key TRGs were analyzed separately in LGG patients.

Results

A total of 510 patients with LGG from The Cancer Genome Atlas (TCGA) dataset and 1,152 normal tissues from the Genotype-Tissue Expression (GTEx) dataset were included to evaluate the expression level of TRGs. After LASSO regression analysis, we identified six key TRGs and constructed a TRGs risk model. The survival analysis revealed that the risk model was the independent predictor in LGG patients. And the nomogram containing risk scores and independent clinicopathological factors could accurately predict the prognosis of LGG patients. In addition, the results of the Consensus cluster analysis based on the expression of the six TRGs showed that it could classify the LGG patients into two distinct clusters, with significant differences in prognosis, clinicopathological factors and TIME between these two clusters. Finally, we validated the expression, prognosis and immune infiltration of six key TRGs in patients with LGG.

Conclusion

This study demonstrated that tryptophan metabolism plays an important role in the progression of LGG. In addition, the risk model and the molecular subtypes we constructed not only could be used as an indicator to predict the prognosis of LGG patients but also were closely related to the clinicopathological factors and TIME of LGG patients. Overall, our study provides theoretical support for the ultimate realization of precision treatment for patients with LGG.

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)

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.

Melatonin ameliorates disease severity in a mouse model of multiple sclerosis by modulating the kynurenine pathway

Melatonin (MT), a neurohormone with immunomodulatory properties, is one of the metabolites produced in the brain from tryptophan (TRP) that has already strong links with the neuropathogenesis of Multiple sclerosis (MS). However, the exact molecular mechanisms behind that are not fully understood. There is some evidence showing that MS and MT are interconnected via different pathways: Relapses of MS has a direct correlation with a low level of MT secretion and a growing body of evidence suggest that MT be therapeutic in Experimental Autoimmune Encephalomyelitis (EAE, a recognise animal model of MS) severity. Previous studies have demonstrated that the kynurenine pathway (KP), the main pathway of TRP catabolism, plays a key role in the pathogenesis of MS in humans and in EAE. The present study aimed to investigate whether MT can improve clinical signs in the EAE model by modulating the KP. C57BL/6 mice were induced with EAE and received different doses of MT. Then the onset and severity of EAE clinical symptoms were recorded. Two biological factors, aryl hydrocarbon receptor (AhR) and NAD+ which closely interact in the KP were also assessed. The results indicated that MT treatment at all tested doses significantly decrease the EAE clinical scores and the number of demyelinating plaques. Furthermore, MT treatment reduced the mRNA expression of the KP regulatory enzyme indoleamine 2,3-dioxygenase 1(IDO-1) and other KP enzymes. We also found that MT treatment reduces the mRNA expression of the AhR and inhibits the enzyme Nicotinamide N-Methyltransferase (Nnmt) overexpression leading to an increase in NAD+ levels. Collectively, this study suggests that MT treatment may significantly attenuates the severity of EAE by altering the KP, AhR and NAD+ metabolism.

The immunosuppressive role of indoleamine 2, 3-dioxygenase in glioblastoma: mechanism of action and immunotherapeutic strategies

Glioblastoma multiforme (GBM) is a fatal brain tumor in adults with a bleak diagnosis. Expansion of immunosuppressive and malignant CD4 + FoxP3 + GITR + regulatory T cells is one of the hallmarks of GBM. Importantly, most of the patients with GBM expresses the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase (IDO). While IDO1 is generally not expressed at appreciable levels in the adult central nervous system, it is rapidly stimulated and highly expressed in response to ongoing immune surveillance in cancer. Increased levels of immune surveillance in cancer are thus related to higher intratumoral IDO expression levels and, as a result, a worse OS in GBM patients. Conversion of the important amino acid tryptophan into downstream catabolite known as kynurenines is the major function of IDO. Decreasing tryptophan and increasing the concentration of immunomodulatory tryptophan metabolites has been shown to induce T-cell apoptosis, increase immunosuppressive programming, and death of tumor antigen-presenting dendritic cells. This observation supported the immunotherapeutic strategy, and the targeted molecular therapy that suppresses IDO1 activity. We review the current understanding of the role of IDO1 in tumor immunological escape in brain tumors, the immunomodulatory effects of its primary catabolites, preclinical research targeting this enzymatic pathway, and various issues that need to be overcome to increase the prospective immunotherapeutic relevance in the treatment of GBM malignancy.

Unbalanced IDO1/IDO2 Endothelial Expression and Skewed Keynurenine Pathway in the Pathogenesis of COVID-19 and Post-COVID-19 Pneumonia

Despite intense investigation, the pathogenesis of COVID-19 and the newly defined long COVID-19 syndrome are not fully understood. Increasing evidence has been provided of metabolic alterations characterizing this group of disorders, with particular relevance of an activated tryptophan/kynurenine pathway as described in this review. Recent histological studies have documented that, in COVID-19 patients, indoleamine 2,3-dioxygenase (IDO) enzymes are differentially expressed in the pulmonary blood vessels, i.e., IDO1 prevails in early/mild pneumonia and in lung tissues from patients suffering from long COVID-19, whereas IDO2 is predominant in severe/fatal cases. We hypothesize that IDO1 is necessary for a correct control of the vascular tone of pulmonary vessels, and its deficiency in COVID-19 might be related to the syndrome’s evolution toward vascular dysfunction. The complexity of this scenario is discussed in light of possible therapeutic manipulations of the tryptophan/kynurenine pathway in COVID-19 and post-acute COVID-19 syndromes.

The Kynurenine Pathway and Cancer: Why Keep It Simple When You Can Make It Complicated

Simple Summary

The kynurenine pathway has two main physiological roles: (i) it protects specific organs such as the eyes and placenta from strong immune reactions and (ii) it additionally generate in the liver and kidney a metabolite essential to all cells of human body. Abnormal activation of this pathway is recurrently observed in numerous cancer types. Its two functions are hijacked to promote tumor growth and cancer cell dissemination through multiple mechanisms. Clinical assays including administration of inhibitors of this pathway have not yet been successful. The complex regulation of this pathway is likely the reason behind this failure. In this review, we try to give an overview of the current knowledge about this pathway, to point out the next challenges, and to propose alternative therapeutic routes.

Abstract

The kynurenine pathway has been highlighted as a gatekeeper of immune-privileged sites through its ability to generate from tryptophan a set of immunosuppressive metabolic intermediates. It additionally constitutes an important source of cellular NAD⁺ for the organism. Hijacking of its immunosuppressive functions, as recurrently observed in multiple cancers, facilitates immune evasion and promotes tumor development. Based on these observations, researchers have focused on characterizing indoleamine 2,3-dioxygenase (IDO1), the main enzyme catalyzing the first and limiting step of the pathway, and on developing therapies targeting it. Unfortunately, clinical trials studying IDO1 inhibitors have thus far not met expectations, highlighting the need to unravel this complex signaling pathway further. Recent advances demonstrate that these metabolites additionally promote tumor growth, metastatic dissemination and chemoresistance by a combination of paracrine and autocrine effects. Production of NAD⁺ also contributes to cancer progression by providing cancer cells with enhanced plasticity, invasive properties and chemoresistance. A comprehensive survey of this complexity is challenging but necessary to achieve medical success.

Potential of Ferritin-Based Platforms for Tumor Immunotherapy

Ferritin is an iron storage protein that plays a key role in iron homeostasis and cellular antioxidant activity. Ferritin has many advantages as a tumor immunotherapy platform, including a small particle size that allows for penetration into tumor-draining lymph nodes or tumor tissue, a unique structure consisting of 24 self-assembled subunits, cavities that can encapsulate drugs, natural targeting functions, and a modifiable outer surface. In this review, we summarize related research applying ferritin as a tumor immune vaccine or a nanocarrier for immunomodulator drugs based on different targeting mechanisms (including dendritic cells, tumor-associated macrophages, tumor-associated fibroblasts, and tumor cells). In addition, a ferritin-based tumor vaccine expected to protect against a wide range of coronaviruses by targeting multiple variants of SARS-CoV-2 has entered phase I clinical trials, and its efficacy is described in this review. Although ferritin is already on the road to transformation, there are still many difficulties to overcome. Therefore, three barriers (drug loading, modification sites, and animal models) are also discussed in this paper. Notwithstanding, the ferritin-based nanoplatform has great potential for tumor immunotherapy, with greater possibility of clinical transformation.