Blockade of the AHR restricts a Treg-macrophage suppressive axis induced by L-Kynurenine

Immunometabolism of regulatory T cells in cancer

Regulatory T (Treg) cells play critical roles in maintaining immune tolerance and tissue homeostasis, but impede anti-tumor immunity. Recent work has established how Treg cells metabolically adapt within the tumor microenvironment (TME), and these adaptations frequently provide a functional advantage over effector T cells. Further, enhanced Treg cell function in the TME may contribute to the limited efficacy of current immunotherapies, especially immune checkpoint blockade (ICB). Here, we review recent progress in understanding mechanisms of Treg cell heterogeneity and function in tumors, with a particular focus on cellular metabolism as an underlying factor by which Treg cells are uniquely poised to thrive in the TME and contribute to tumorigenesis. We describe how cellular metabolism and nutrient or metabolic communication shape Treg cell lineage identity and function in the TME. We also discuss the interplay between ICB and Treg cell metabolism and function, and highlight current strategies targeting Treg cell metabolism specifically in the TME. Understanding metabolic control of intratumoral Treg cells provides excellent opportunities to uncover new or combination therapies for cancer.

Glutamate transporter SLC1A6 promotes resistance to immunotherapy in cancer

BACKGROUND

Resistance to immune checkpoint inhibitors remains a significant challenge in the treatment of cancer. Emerging evidence suggests that metabolic reprogramming plays a crucial role in tumor metabolism and progression. Our study strived to investigate the role and underlying mechanisms of the glutamate transporter SLC1A6 in resistance to immunotherapy of cancer.

METHODS

Single-cell RNA sequencing was performed on bladder cancer patients receiving neoadjuvant immunotherapy to identify the expression of SLC1A6 in treatment-resistant cases. The clinical prognostic value of SLC1A6 in cancer was validated using publicly available lung cancer single-cell datasets, as well as transcriptomic data from both bladder and lung cancer cohorts. Flow cytometry was employed to assess the impact of SLC1A6 knockdown on the effector function of CD8⁺ T cell. In vivo tumor models were used to evaluate the role of SLC1A6 in immunotherapy resistance, with immunofluorescence staining performed to examine GZMB⁺ CD8⁺ T cell infiltration.

RESULTS

SLC1A6 was highly expressed in bladder cancer patients resistant to neoadjuvant immunotherapy, and its expression was associated with disease progression, poor prognosis, and low immune infiltration. Knockdown of SLC1A6 in tumor cells enhanced CD8⁺ T cell effector function. SLC1A6 knockdown also improved the efficacy of immunotherapy and increased the infiltration of GZMB⁺ CD8⁺ T cells within the tumor microenvironment.

CONCLUSIONS

SLC1A6 plays a critical role in resistance to immunotherapy in cancer. Targeting SLC1A6 may provide a promising therapeutic strategy for improving responses to neoadjuvant immunotherapy and advancing combination treatment approaches.

Phase 1/2 Study of the Indoleamine 2,3-Dioxygenase 1 Inhibitor Linrodostat Mesylate Combined with Nivolumab or Nivolumab and Ipilimumab in Advanced Solid Tumors or Hematologic Malignancies

PURPOSE

To evaluate the safety, efficacy, pharmacokinetics, pharmacodynamics, and biomarkers of linrodostat mesylate, a selective, oral indoleamine 2,3-dioxygenase 1 inhibitor combined with nivolumab ± ipilimumab in advanced solid tumors and hematologic malignancies.

PATIENTS AND METHODS

In this phase 1/2 study, patients received once-daily linrodostat [part 1 (escalation), 25-400 mg; part 2 (expansion), 100 or 200 mg] plus nivolumab (480 mg every 4 weeks or 240 mg every 2 weeks) or triplet therapy (part 3, linrodostat 20-100 mg once daily; nivolumab 360 mg every 3 weeks or 480 mg every 4 weeks; ipilimumab 1 mg/kg every 6 weeks or every 8 weeks). Endpoints included safety and efficacy (coprimary; parts 2 and 3), pharmacokinetics, pharmacodynamics, biomarkers, and efficacy (part 1).

RESULTS

A total of 55, 494, and 41 patients were enrolled in parts 1, 2, and 3, respectively. Linrodostat exposures exceeded predicted therapeutic target concentrations starting at 50 mg. Rates of grade 3/4 adverse events were 50.1% to 63.4%. The maximum tolerated linrodostat dose was 200 mg; dose-limiting toxicities were primarily immune-related. Responses were observed across different cohorts, study parts, and tumor types, particularly in immunotherapy-naïve patients. Kynurenine decreased with linrodostat + nivolumab regardless of response. In contrast, IFN-γ gene expression signature was associated with response; in nonmelanoma patients, a composite of low tryptophan 2,3-dioxygenase gene expression plus high IFN-γ signature was associated with response.

CONCLUSIONS

Linrodostat + nivolumab ± ipilimumab demonstrated a manageable safety profile. Kynurenine changes supported indoleamine 2,3-dioxygenase 1 pathway inhibition but did not correlate with response. A composite biomarker of low tryptophan 2,3-dioxygenase expression plus high IFN-γ gene expression may predict response to linrodostat + nivolumab. See related commentary by Zang and Dorff, p. 2077.

Loss of aryl hydrocarbon receptor reduces pancreatic tumor growth by increasing immune cell infiltration

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease which remains poorly understood. Increasing evidence suggests that the aryl hydrocarbon receptor (AHR) plays a role in the pathogenesis of several cancers; however, its role in PDAC is unclear because AHR exhibits both pro- and anti-tumor activities. Here we evaluated the role of AHR in CR705 and K8484 murine PDAC cells in vitro and CR705 cells in vivo. Loss of Ahr did not affect cell proliferation compared with Cas9 control cells and no differences in tumor development between CR705Cas9 and CR705AhrKO cells were observed in immunocompromised mice. Conversely, tumors from CR705AhrKO cells grew more slowly than tumors from CR705Cas9 cells in immune competent mice. RNA sequencing identified 1279 genes upregulated and 586 genes downregulated in CR705AhrKO tumors compared with CR705Cas9 tumors. Pathway analysis identified immunoregulatory interactions, interferon signaling, and chemokine signaling among the top upregulated pathways. Increased infiltration of CD45+ cells and higher numbers of CD8+ T cells and F4/80+ cells were observed in CR705AhrKO tumors. Ahr deficiency in macrophages (LysMCre) or lymphocytes (RorcCre) did not alter tumor development of CR705Cas9 cells compared with Ahrfl/fl mice. CR705AhrKO tumors in RorcCre mice, but not in LysMCre mice had significantly lower tumor weights normalized to body weights compared with CR705AhrKO tumors in WT mice. These findings show that Ahr loss in CR705 pancreatic cancer cells is sufficient to induce proinflammatory gene responses that contribute to increased immune cell infiltration and reduced tumor growth.

Fusobacterium nucleatum-derived 3-indolepropionic acid promotes colorectal cancer progression via aryl hydrocarbon receptor activation in macrophages

An increasing body of research indicates that Fusobacterium nucleatum (F. nucleatum) significantly influences the onset and progression of colorectal cancer (CRC). Our previous study has shown that F. nucleatum exerts pro-tumorigenic effects through aryl hydrocarbon receptor (AhR) activation. However, the role of its microbial metabolites in regulating immune responses remains unclear. Here, we report for the first time that F. nucleatum-derived 3-Indolepropionic acid (IPA) activates AhR in macrophages, driving M2 polarization and tumor-promoting immunosuppression. We discovered that culture supernatant of F. nucleatum (CSF) robustly activates AhR in macrophages. In co-culture systems, CSF upregulated the expression of the M2 marker CD206 and elevated mRNA levels of CD163, TGF-β, IL-10, and VEGF. In a subcutaneous allograft model, CSF induced an elevated number of CD206+ macrophages and decreased presence of CD8+ T cells within the tumor microenvironment, thereby promoting tumor growth. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) revealed IPA as a novel major AhR-activating metabolite in CSF. Strikingly, IPA recapitulated CSF's effects in promoting tumor cell migration and immunosuppression, both in vitro and in vivo. Critically, the AhR inhibitor CH223191 abolished both IPA-mediated M2 polarization and tumor growth. Our study revealed a novel mechanism by which F. nucleatum-derived IPA reprograms macrophages through AhR activation to fuel CRC progression, providing potential therapeutic targets for CRC treatment and prognosis improvement.

Higher serum vitamin B6 is associated with lower all-cause mortality among cancer survivors in the National Health and Nutrition Examination Survey

Variations in serum concentrations of vitamin B6, vitamin B12, and folate may influence cancer development and progression. However, the association between these 3 serum B vitamins and all-cause mortality among cancer survivors remains unclear. We evaluated the potential associations between serum vitamins B6, B12, and folate and all-cause mortality among cancer survivors. Our hypothesis proposed that higher serum concentrations of vitamin B6, vitamin B12, and folate might be inversely associated with a lower risk of all-cause mortality in this population. Data from the National Health and Nutrition Examination Survey (NHANES) 1999-2018 were used. All-cause mortality was determined by linking participant data to National Death Index records till 31 December 2019. Serum vitamins B6, B12, and folate status were measured. Multivariable Cox regression analyses were applied to investigate the relationship between serum vitamins B6, B12, and folate concentrations and all-cause mortality among cancer survivors. Serum vitamin B6 was inversely associated with all-cause mortality, with a fully-adjusted HR of 0.54 (95%CI: 0.38, 0.78, Ptrend< .001). However, no statistically significant association was observed between serum vitamin B12 as well as serum folate concentration and all-cause mortality among cancer survivors (B12: fully-adjust HR = 0.90, 95%CI: 0.63, 1.27, Ptrend = .771; folate: fully-adjust HR = 0.82, 95%CI: 0.63, 1.08, Ptrend = .269). No statistically significant interaction for age, sex, and BMI was found in stratified analyses. No non-linear relationship was found except for serum folate. These results suggest that higher serum vitamin B6 may be associated with improved survival in cancer survivors.

The AhR regulates IFN-induced immune checkpoints in lung cancer cells through HNRNPH1, an RNA-binding protein, and INCR1, a novel long non-coding RNA

Although immune checkpoint inhibitors show great promise, not all patients respond and many do not achieve durable responses. Consequently, further investigations into potentially targetable molecules that regulate immune checkpoints are warranted. Previous studies in several cancers demonstrated that interferons produced by tumor-infiltrating leukocytes regulate immunosuppressive PD-L1, PD-L2 and IDO1 through JAK/STAT signaling. Here, we investigated a novel role for an immunosuppressive environmental chemical receptor, previously implicated in smoking-related cancers, in IFN signaling in human lung adenocarcinoma (LUAD) cells. Deletion of the aryl hydrocarbon receptor (AhR) from A549 LUAD cells significantly decreased baseline JAK2, STAT1, STAT3, IRF1 (a JAK/STAT target), PD-L1, PD-L2, and IDO1 expression. IFNγ and IFNα increased expression of JAK/STAT and immune checkpoint genes and proteins, but these increases were significantly diminished or absent in AhR-knockout cells. The AhR similarly controls IFN-induced, JAK/STAT-driven increases in multiple MHC class I- and class II-related genes. AhR control of type I and type II interferon signaling is mediated through up-regulation of a lncRNA, the IFN-stimulated non-coding RNA 1 (INCR1), and through repression of an RNA-binding protein, heterogeneous nuclear ribonucleoprotein H1 (HNRNPH1), which sequesters JAK/STAT-related and immune checkpoint gene transcripts. The data suggest that the AhR is a key mediator of tumor immunosuppression through regulation of IFN-induced INCR1 and JAK/STAT signaling and, thereby, expression of immune checkpoints. However, that immunosuppression may be tempered by AhR control of MHC expression. Given the multiple roles of JAK/STAT signaling in the immune system, the results also suggest multiple levels on which the AhR may affect tumor immunity.

Laquinimod treatment attenuates EAU by inhibiting both the inductive and effector phases in an APC-dependent manner

Purpose

To evaluate the immunomodulatory effects on experimental autoimmune uveitis (EAU) of the aryl hydrocarbon receptor (AhR) agonist Laquinimod (LAQ), and its active metabolite DELAQ, with a focus on dendritic cell- and T cell-mediated mechanisms.

Methods

EAU was induced in mice by active immunization or by adoptive transfer of activated T cells. Mice were treated with LAQ either from the time of immunization or from 7 days after. Effects of LAQ were examined in wild-type, global AhR-knockout, or dendritic cell-conditional AhR knockout mice. Direct vs. indirect effects of AhR agonism on dendritic cells and T cells were studied in vitro using DELAQ, a major active metabolite of LAQ.

Results

LAQ treatment from Day 0 fully suppressed EAU, while delayed treatment (Day 7) provided only partial protection. In the adoptive transfer model, LAQ-treated recipients showed reduced pathology. Global AhR-deficient mice developed severe EAU comparable to that of wild-type mice, with an elevated Th17 response. LAQ-treated mice displayed increased frequencies of cDC1 and FoxP3⁺ regulatory T cells. In vitro, DELAQ activated AhR signaling and induced Ido1 and Ido2 expression in dendritic cells. DELAQ inhibited the activation of naïve and memory mouse T cells in an APC-dependent manner, as the response to anti-CD3/CD28 stimulation was unaffected. Importantly, DELAQ suppressed recall responses of human PBMC to tetanus toxoid.

Conclusions

LAQ protects against EAU by acting on AhR-expressing antigen-presenting cells to impair both priming and reactivation of pathogenic T cells. Its active metabolite DELAQ does not suppress T cells directly, but re-programs dendritic cells toward a tolerogenic, IDO-expressing phenotype that promotes immune regulation.

Reversing the immunosuppressive tumor microenvironment via "Kynurenine starvation therapy" for postsurgical triple-negative breast cancer treatment

Immunotherapy is a potential strategy to suppress the postoperative recurrence and metastasis of triple-negative breast cancer (TNBC). However, the excessive accumulation of kynurenine (Kyn) leads to immunosuppressive tumor microenvironment (TME) and impedes immunotherapeutic efficacy. Herein, a two-pronged approach through "Kynurenine Starvation Therapy" is proposed based on the in-situ hydrogel implantation for postsurgical treatment of TNBC. The hydrogel is constructed via Schiff base reaction between oxidized dextran (ODEX) and 8-arm poly(ethylene glycol) amine (8-arm PEG-NH2), which exhibits excellent biocompatibility and gradual biodegradability. The indoleamine 2,3-dioxygenase 1 (IDO1) inhibitor NLG919 and kynureninase (KYNase) are noncovalently loaded into the hydrogel to prepare NLG919 + KYNase@Gel. The obtained hydrogel can sustainably release NLG919 and KYNase to synergistically deplete Kyn, thereby reversing immunosuppression to enhance the antitumor immunity within TME through "Kynurenine Starvation Therapy". Moreover, a single implantation of NLG919 + KYNase@Gel not only effectively inhibits the postoperative recurrence and metastasis in 4 T1 tumor-bearing mice, but also restrains the growth in an orthotopic TNBC mouse model. These findings highlight an innovative strategy to reinforce the antitumor immune response for the treatment of postsurgical TNBC.

Immunometabolism of tumor-associated macrophages: A therapeutic perspective

Tumor-associated macrophages (TAMs) play a pivotal role in the tumor microenvironment (TME), actively contributing to the formation of an immunosuppressive niche that fosters tumor progression. Consequently, there has been a growing interest in targeting TAMs as a promising avenue for cancer therapy. Recent advances in the field of immunometabolism have shed light on the influence of metabolic adaptations on macrophage physiology in the context of cancer. Here, we discuss the key metabolic pathways that shape the phenotypic diversity of macrophages. We place special emphasis on how metabolic reprogramming impacts the activation status of TAMs and their functions within the TME. Additionally, we explore alterations in TAM metabolism and their effects on phagocytosis, production of cytokines/chemokines and interaction with cytotoxic T and NK immune cells. Moreover, we examine the application of nanomedical approaches to target TAMs and assess the clinical significance of modulating the metabolism of TAMs as a strategy to develop new anti-cancer therapies. Taken together, in this comprehensive review article focusing on TAMs, we provide invaluable insights for the development of effective immunotherapeutic strategies and the enhancement of clinical outcomes for cancer patients.

Immunomodulatory mechanisms driving tumor escape in glioblastoma: The central role of IDO and tryptophan metabolism in local and systemic immunotolerance

BACKGROUND

Glioblastoma (GBM) is the most aggressive primary brain tumor exhibiting extensive immune evasion mechanisms that hinder effective therapeutic interventions. This narrative review explores the immunomodulatory pathways contributing to tumor escape in GBM, specifically focusing on the role of Tryptophan (TRP) metabolism and its downstream mediators Tryptophan metabolism through the kynurenine pathway (KP) is initiated by indoleamine 2,3-dioxygenase (IDO) and tryptophan-2,3-dioxygenase (TDO2) enzymes and serves as a crucial mechanism for promoting an immunosuppressive microenvironments and systemic immunotolerance. Emerging evidence also indicates a non-enzymatic role for IDO1 signaling in these processes. The downstream effectors interact with immune cells, inducing local immunosuppression within the tumor microenvironment and altering peripheral immune responses.

METHODS

We systematically reviewed databases (MEDLINE via PubMed, Science Direct, and Embase) through October 2024 to highlight the interplay between local immune escape mechanisms and circulating immunotolerance, emphasizing the role of TRP metabolic enzymes in supporting GBM progression.

RESULTS

The literature review identified 99 records. TRP-related mechanisms play a central role in fostering immunotolerance in GBM. These phenomena involve intricate interactions between the infiltrating and circulating myeloid and lymphoid compartments, ultimately shaping a tolerant, pro-tumoral environment and the peripheral immunophenotype.

CONCLUSIONS

The biological activity of IDO1 and TRP metabolites positions these compounds as potential markers of disease activity and promising molecular targets for future therapeutic approaches.

PRTN3 promotes IL33/Treg-mediated tumor immunosuppression by enhancing the M2 polarization of tumor-associated macrophages in lung adenocarcinoma

The immunosuppressive tumor microenvironment (TME) shaped by tumor-associated macrophages (TAMs) is essential for lung adenocarcinoma (LUAD) immune tolerance and tumor progression. Here, we first reported that proteinase 3 (PRTN3) promoted the alternative activation (M2) of TAMs and enhanced IL33/regulatory T cells (Tregs)-mediated tumor immunosuppression in LUAD. Firstly, clinical analysis revealed PRTN3 was highly expressed in TAMs and correlated with the tumor progression and poor prognosis in LUAD patients. Meanwhile, by using the myeloid cells-specific Prtn3-knockout mouse model, we demonstrated Prtn3 deficiency in macrophages remolded the immunosuppressive TME and suppressed tumor growth. The mechanism studies uncovered a novel signaling pathway that PRTN3 up-regulated IL33 expression in TAMs by suppressing AKT-mediated ubiquitinated degradation of FOXO1, which subsequently activated Il33 transcription. Furthermore, lack of PRTN3 or FOXO1 in macrophages greatly restrained IL33-induced Treg differentiation. Importantly, selective knockout of Prtn3 in macrophages significantly enhanced the antitumor effect of anti-PD1 therapy in the mouse model of LUAD. Thus, our work demonstrated that PRTN3 in macrophages, served as a key immunoregulator, contributed to impede the antitumor immune response through reinforcing the TAMs/Tregs crosstalk, which provided valuable insights to improve the immunotherapeutic effect by functional remodeling of TAMs to alleviate immunosuppression in LUAD.

New insights into tryptophan metabolism in cancer

Tryptophan (Trp) is an essential amino acid and key intermediate in a range of biological processes. Early studies identified altered Trp utilization in cancer cells favoring cancer survival and growth. Seminal findings linking Trp metabolism and suppression of immunity led to an explosion of interest ultimately culminating in clinical trials targeting these pathways in melanoma. The failure of these trials led to a clinical retreat in this approach; however, recent insights into the complex interplay of the various Trp circuits and between tumor cells, immune cells, and the microbiota have shown that reconsideration of Trp metabolism is needed. Here, we discuss recent developments in our understanding of Trp metabolism and apparent contradictions in the field. We also discuss adaptations that occur when Trp pathways are manipulated, which may impact therapy responses.

GPX4 knockdown suppresses M2 macrophage polarization in gastric cancer by modulating kynurenine metabolism

Background: Glutathione peroxidase 4 (GPX4), an important factor regulating redox homeostasis, plays an important role in tumor microenvironment and progression. However, the role of GPX4 in gastric cancer (GC) is unclear. Methods: Spectral flow cytometry and multiplex immunohistochemistry were employed to assess the correlation between GPX4 expression and immune cell infiltration. Metabolomics analysis of conditioned media from GPX4 knockdown NUGC3 cells identified metabolic alterations. Additionally, both in vitro and in vivo functional studies were conducted to elucidate the mechanistic role of GPX4 in regulating the tumor microenvironment and progression. Results: Knockdown of GPX4 in GC cells inhibited tumor growth, enhanced CD8+ T cell infiltration, and suppressed the polarization of tumor-associated macrophages (TAMs) toward the pro-tumor M2 phenotype. Multiplex immunohistochemistry revealed a positive correlation between GPX4 expression and M2 macrophage infiltration in clinical samples from patients with GC. Metabolomics revealed that GPX4 knockdown regulate kynurenine metabolism pathway. Furthermore, mechanistic studies reveal that GPX4 silencing elevates lipid peroxidation, triggering the conversion of KYNU ubiquitin chain modifications from K48 to K63. Such ubiquitination remodeling stabilizes KYNU expression (a key kynurenine-metabolizing enzyme), reduces kynurenine accumulation, and ultimately reprograms TAM polarization to enhance antitumor immunity. We also identified that the K96 and K163 sites are important for KYNU's modification by K48 and K63 ubiquitin chains. Conclusion: Our study not only affirm the role of GPx4 in GC progression but also highlight it as a promising target for reshaping the immune microenvironment.

Effects of Environmental Pollutants on Tryptophan Metabolism

Tryptophan (Trp) is an important essential amino acid that plays a variety of physiological functions in the human body, including being a precursor of neurotransmitter and participating in immune regulation. Currently, more and more studies show that some pollutants in the environment can affect the metabolism of Trp and consequently affect human health. The present paper offers a comprehensive overview of prior research investigating the impact of environmental pollutants, including inorganic and organic contaminants, microplastics, and nanoplastics on the nervous system, immune system, digestive system, and maternal-fetal pregnancy, revealing their detrimental effects on Trp metabolism and human well-being.

Decoding structural determinants of aryl hydrocarbon receptor antagonism by monoterpenoids

Monocyclic monoterpenoids carvones have been recently identified as atypical negative allosteric modulators of aryl hydrocarbon receptor (AhR). In the current work, we performed AhR antagonist activity screening of 100 natural and synthetic monoterpenoids, and their analogues. Using SAR approach, structural determinants of AhR antagonist activity were assigned, including CO presence/position, planarity, and C3/C5-alkylation. Applying pyramidal selection criteria, including absence of residual agonist activity, no cytotoxicity, strong antagonist potency, and pan-antagonism against diverse AhR agonists, we distilled four lead AhR antagonists (carvacrol, o-cresol, 3-methyl-S-carvone, EN-2). Whereas 3-methyl-S-carvone and EN-2 were non-competitive AhR pan-antagonists, carvacrol and o-cresol were ligand-selective AhR antagonists acting by unclear mechanism. We characterized in detail the effects of lead compounds at cellular functions of AhR, including AhR nuclear translocation, AhR dimerization with ARNT, and the expression of AhR-regulated genes. As a proof of concept, effects of monoterpenoids in the murine macrophages were investigated.

Perspectives on photodynamic therapy combined with immunotherapy in treatment of colorectal cancer: An overview based on experimental studies

Colorectal cancer (CRC) is one of the major cancers threatening human health, with high mortality, tumor drug resistance and metastasis. Due to its advantages of non-invasive, strongly targeted and limited side effects, Photodynamic therapy (PDT) has become a promising treatment for CRC. Remarkably, PDT has been shown to activate T cell-adaptive immune response and induce immunogenic cell death (ICD). Used in combination with other treatment techniques, PDT has considerable promise in the management of colorectal cancer. In particular, the combination of PDT and tumor immunotherapy, the systemic anti-tumor immune response was enhanced more significantly. This strategy is expected to achieve a synergistic anti-tumor effect by inducing tumor cell apoptosis, regulating tumor immune microenvironment and effectively activating anti-tumor immunity during treatment process. This review focuses on the research of PDT combined with immunotherapy to improve the treatment of CRC. In most studies, a positive effect was observed for combination therapy, experimentally indicating new therapeutic opportunities for CRC.

Taurine and proline promote lung tumour growth by co-regulating Azgp1/mTOR signalling pathway

Accurate metabolic biomarkers for lung cancer prognosis remain scarce but crucial. Taurine and proline, two metabolites, are consistently elevated across various cancer stages in previous studies, hinting at their potential role in disease progression. This study is the first to reveal how these metabolites contribute to poor prognosis. Transcriptomic analysis uncovered that taurine and proline downregulated Zinc-α2-glycoprotein (Azgp1), a gene linked to key metabolic pathways. Additionally, Azgp1 could also significantly affect downstream lipid metabolic pathways in lung cancer. Both taurine and proline influenced lipid metabolism via mammalian target of rapamycin (mTOR). When Azgp1 was overexpressed, lung cancer progression slowed significantly, alongside reduced mTOR activity. These findings underscore the pro-cancer role of taurine and proline, highlighting the Azgp1/mTOR axis as a vital, yet overlooked, pathway in lung cancer. This study not only advances our understanding but also identifies new therapeutic avenues.

AHR Agonist ITE Boosted PD1 Antibody's Effects by Inhibiting Myeloid-Derived Cells Suppressive Cells in an Orthotopic Mouse Glioma Model

Background: Glioblastoma is "cold". Consequently, immune checkpoint blockade therapy has failed to improve patients' survival, which is negatively correlated with patients' peripheral MDSC counts. AHR is known to mediate immune-suppressive functions of certain tryptophan metabolites such as kynurenine; yet, there lack of reports on how AHR agonists affect glioma immunity. Methods/Objectives: We hypothesized that ITE could synergize with PD1 antibody as AHR is one major node of immune-suppressive pathways, and tested it using an immune-competent mouse glioma model. Results: The combination of ITE+PD1 antibody glioma MDSC was significantly reduced, along with increased infiltration of the CD4-CD8+ and CD4+CD8+ T cells, leading to extended mouse survival. ITE treatment alone significantly reduces the infiltration of CD11b+Ly6G+Ly6Clo cells, namely PMN-MDSCs, and neutrophils, while the combination with PD1 antibody significantly reduces all MDSCs plus neutrophils. The presence of ITE inhibits the expression of IL11 and the in vitro induction of MDSCs from mouse PBMCs by IL11. The identification of the ITE-AHR-IL11-MDSC pathway provides more mechanistic insights into AHR's effects. The fact that ITE, which is otherwise immune-suppressive, can activate immunity in glioma indicates that searching for drugs targeting AHR should go beyond antagonists.

[Immune Checkpoints Mediate Tumor Immune Regulation through Metabolic Pathways]

Immune checkpoints include a series of receptor-ligand pairs that play a key role in the proliferation, activation, and immune regulatory responses of immune cells. Although immune checkpoint inhibitors (ICIs), such as programmed death protein 1 (PD-1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) have achieved good therapeutic effects in clinical practice, some patients still experience ineffective treatment and immune resistance. A large amount of evidence has shown that immune checkpoint proteins are related to cell metabolism during immune regulation. On the one hand, immune checkpoints connect to alter the metabolic reprogramming of tumor cells to compete for nutrients required by immune cells. On the other hand, immune checkpoints regulate the metabolic pathways of immune cells, such as phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) to affect the activation of immune cells. Based on a review of the literature, this article reviews the mechanisms by which PD-1, CTLA-4, T cell immunoreceptor with Ig and ITIM domains (TIGIT), T cell immunoglobulin and mucin domain-containing protein 3 (TIM-3), cluster of differentiation 47 (CD47), and indoleamine 2,3-dioxygenase 1 (IDO1) regulate cell metabolic reprogramming, and looks forward to whether targeting the ligand-receptor pairs of immune checkpoints in a "dual regulation" manner and inhibiting metabolic pathways can effectively solve the problem of tumor immune resistance.
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Microbial dysbiosis with tryptophan metabolites alteration in lower respiratory tract is associated with clinical responses to anti-PD-1 immunotherapy in advanced non-small cell lung cancer

Lower respiratory tract microbiome constitutes a unique immune microenvironment for advanced non-small cell lung cancer as one of dominant localized microbial components. However, there exists little knowledge on the associations between this regional microbiome and clinical responses to anti-PD-1 immunotherapy from clinical perspectives. Here, we equivalently collected bronchoalveolar lavage fluids from 56 advanced NSCLC participants treated with none (untreated, n = 28) or anti-PD-1 immunotherapy (treated, n = 28), which was further divided into responder (n = 17) and non-responder (n = 11) subgroups according to clinical responses, aiming to compare their microbial discrepancy by performing metagenomic sequencing and targeted metabolic alterations by tryptophan sequencing. Correspondingly, microbial diversities transformed significantly after receiving immunotherapeutic agents, where Gammaproteobacteria and Campylobacter enriched, but Escherichia, Streptococcus, Chlamydia, and Staphylococcus reduced at the genus level, differences of which failed to be achieved among subgroups with various clinical responses (responder or non-responder; LDA > 2, P < 0.05*). And the relative abundance of Staphylococcus and Streptomyces was escalated in response subgroup to anti-PD-1 immunotherapy by microbial compositional analysis (as relative abundance ≥ 3%, P < 0.05*), no significance of which was achieved among treated and untreated groups. In addition, relative abundances of bacterial tryptophan metabolites and its derivatives were also higher in the responder subgroup, distinctively being associated with divergent genera (VIP > 1, P < 0.05*). Our study revealed predictive performance of lower respiratory tract microbiome to antitumoral immunotherapy and further suggested that anti-PD-1 immunotherapy may alter lower respiratory tract microbiome composition and interact with its tryptophan metabolites to regulate therapeutic efficacy in advanced NSCLC, performing as potential biomarkers to prognosis and interventional strategies.

Bridging epigenomics and tumor immunometabolism: molecular mechanisms and therapeutic implications

Epigenomic modifications-such as DNA methylation, histone acetylation, and histone methylation-and their implications in tumorigenesis, progression, and treatment have emerged as a pivotal field in cancer research. Tumors undergo metabolic reprogramming to sustain proliferation and metastasis in nutrient-deficient conditions, while suppressing anti-tumor immunity in the tumor microenvironment (TME). Concurrently, immune cells within the immunosuppressive TME undergo metabolic adaptations, leading to alterations in their immune function. The complicated interplay between metabolites and epigenomic modulation has spotlighted the significance of epigenomic regulation in tumor immunometabolism. In this review, characteristics of the epigenomic modification associated with tumors are systematically summarized alongside with their regulatory roles in tumor metabolic reprogramming and immunometabolism. Classical and emerging approaches are delineated to broaden the boundaries of research on the crosstalk research on the crosstalk between tumor immunometabolism and epigenomics. Furthermore, we discuss potential therapeutic strategies that target tumor immunometabolism to modulate epigenomic modifications, highlighting the burgeoning synergy between metabolic therapies and immunotherapy as a promising avenue for cancer treatment.

Exploring effects of gut microbiota on tertiary lymphoid structure formation for tumor immunotherapy

Anti-tumor immunity, including innate and adaptive immunity is critical in inhibiting tumorigenesis and development of tumor. The adaptive immunity needs specific lymph organs such as tertiary lymphoid structures (TLSs), which are highly correlated with improved survival outcomes in many cancers. In recent years, with increasing attention on the TLS in tumor microenvironment, TLSs have emerged as a novel target for anti-tumor therapy. Excitingly, studies have shown the contribution of TLSs to the adaptive immune responses. However, it is unclear how TLSs to form and how to more effectively defense against tumor through TLS formation. Recent studies have shown that the inflammation plays a critical role in TLS formation. Interestingly, studies have also found that gut microbiota can regulate the occurrence and development of inflammation. Therefore, we here summarize the potential effects of gut microbiota- mediated inflammation or immunosuppression on the TLS formation in tumor environments. Meanwhile, this review also explores how to manipulate mature TLS formation through regulating gut microbiota/metabolites or gut microbiota associated signal pathways for anti-tumor immunity, which potentially lead to a next-generation cancer immunotherapy.

The aryl hydrocarbon receptor controls IFN-γ-induced immune checkpoints PD-L1 and IDO via the JAK/STAT pathway in lung adenocarcinoma

While immunotherapy has shown some efficacy in lung adenocarcinoma (LUAD) patients, many respond only partially or not at all. One limitation in improving outcomes is the lack of a complete understanding of immune checkpoint regulation. Here, we investigated a possible link between an environmental chemical receptor implicated in lung cancer and immune regulation, the AhR, a known but counterintuitive mediator of immunosuppression (interferon (IFN)-γ), and regulation of two immune checkpoints (PD-L1 and IDO). AhR gene-edited LUAD cell lines, a syngeneic LUAD mouse model, bulk and scRNA sequencing of LUADs and tumor-infiltrating T cells were used to map out a signaling pathway leading from IFN-γ through the AhR to JAK/STAT, PD-L1, IDO, and tumor-mediated immunosuppression. The data demonstrate that: (1) IFN-γ activation of the JAK/STAT pathway leading to PD-L1 and IDO1 up-regulation is mediated by the AhR in murine and human LUAD cells, (2) AhR-driven IDO1 induction results in the production of Kynurenine (Kyn), an AhR ligand, which likely mediates an AhR→IDO1→Kyn→AhR amplification loop, (3) transplantation of AhR-knockout LUAD cells results in long-term tumor immunity in most recipients. (4) The 23% of AhR-knockout tumors that do grow do so at a much slower pace than controls and exhibit higher densities of CD8+ T cells expressing markers of immunocompetence, increased activity, and increased cell-cell communication. The data definitively link the AhR to IFN-γ-induced JAK/STAT pathway and immune checkpoint-mediated immunosuppression and support the targeting of the AhR in the context of LUAD.

The Kynurenine Pathway and Indole Pathway in Tryptophan Metabolism Influence Tumor Progression

Tryptophan (Trp), an essential amino acid, is solely acquired through dietary intake. It is vital for protein biosynthesis and acts as a precursor for numerous key bioactive compounds. The Kynurenine Pathway and the Indole Pathway are the main metabolic routes and are extensively involved in the occurrence and progression of diseases in the digestive, nervous, and urinary systems. In the Kynurenine Pathway, enzymes crucial to tryptophan metabolism, indoleamine-2,3-dioxygenase 1 (IDO1), IDO2, and Trp-2,3-dioxygenase (TDO), trigger tumor immune resistance within the tumor microenvironment and nearby lymph nodes by depleting Trp or by activating the Aromatic Hydrocarbon Receptor (AhR) through its metabolites. Furthermore, IDO1 can influence immune responses via non-enzymatic pathways. The Kynurenine Pathway exerts its effects on tumor growth through various mechanisms, including NAD+ regulation, angiogenesis promotion, tumor metastasis enhancement, and the inhibition of tumor ferroptosis. In the Indole Pathway, indole and its related metabolites are involved in gastrointestinal homeostasis, tumor immunity, and drug resistance. The gut microbiota related to indole metabolism plays a critical role in determining the effectiveness of tumor treatment strategies and can influence the efficacy of immunochemotherapy. It is worth noting that there are conflicting effects of the Kynurenine Pathway and the Indole Pathway on the same tumor phenotype. For example, different tryptophan metabolites affect the cell cycle differently, and indole metabolism has inconsistent protective effects on tumors in different regions. These differences may hold potential for enhancing therapeutic efficacy.

Harnessing amino acid pathways to influence myeloid cell function in tumor immunity

Amino acids are pivotal regulators of immune cell metabolism, signaling pathways, and gene expression. In myeloid cells, these processes underlie their functional plasticity, enabling shifts between pro-inflammatory, anti-inflammatory, pro-tumor, and anti-tumor activities. Within the tumor microenvironment, amino acid metabolism plays a crucial role in mediating the immunosuppressive functions of myeloid cells, contributing to tumor progression. This review delves into the mechanisms by which specific amino acids-glutamine, serine, arginine, and tryptophan-regulate myeloid cell function and polarization. Furthermore, we explore the therapeutic potential of targeting amino acid metabolism to enhance anti-tumor immunity, offering insights into novel strategies for cancer treatment.

The Role of Aryl Hydrocarbon Receptor in Skin Homeostasis: Implications for Therapeutic Strategies in Skin Disorders

The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, is extensively expressed in diverse human organs and plays a pivotal role in mediating the onset, progression, and severity of numerous diseases. Recent research has explored the substantial impact of AhR on skin homeostasis and related pathologies. As a multi-layered organ, the skin comprises multiple cell populations that express AhR. In this review, we introduce the role of AhR in various skin cells and its impact on skin barrier function. Furthermore, we explore the involvement of AhR in the development of various skin diseases, highlighting its potential as a therapeutic target for skin disorders. By targeting AhR, we may open new avenues for the development of novel and efficient skin disease treatments.

Navigating the metabolic landscape of regulatory T cells: from autoimmune diseases to tumor microenvironments

Regulatory T cells (Tregs) are essential for maintaining immune homeostasis, playing crucial roles in modulating autoimmune conditions and contributing to the suppressive tumor microenvironment. Their cellular metabolism governs their generation, stability, proliferation, and suppressive function. Enhancing Treg metabolism to boost their suppressive function offers promising therapeutic potential for alleviating inflammatory symptoms in autoimmune diseases. Conversely, inhibiting Treg metabolism to reduce their suppressive function can enhance the efficacy of traditional immunotherapy in cancer patients. This review explores recent advances in targeting Treg metabolism in autoimmune diseases and the metabolic adaptations of Tregs within the tumor microenvironment that increase their immunosuppressive function.

Aromatic Amino Acid Metabolites: Molecular Messengers Bridging Immune-Microbiota Communication

Aromatic amino acid (AAA) metabolites, derived from tryptophan, phenylalanine, and tyrosine through coordinated host and microbial metabolism, have emerged as critical modulators of immune function. We examine the complex journey of AAAs from dietary intake through intestinal absorption and metabolic transformation, highlighting the crucial role of host-microbe metabolic networks in generating diverse immunomodulatory compounds. This review provides a unique integrative perspective by mapping the molecular mechanisms through which these metabolites orchestrate immune responses. Through detailed analysis of metabolite-receptor and metabolite-transporter interactions, we reveal how specific molecular recognition drives cell type-specific immune responses. Our comprehensive examination of signaling networks-from membrane receptor engagement to nuclear receptor activation to post-translational modifications- demonstrates how the same metabolite can elicit distinct functional outcomes in different immune cell populations. The context-dependent nature of these molecular interactions presents both challenges and opportunities for therapeutic development, particularly in inflammatory conditions where metabolite signaling pathways are dysregulated. Understanding the complexity of these regulatory networks and remaining knowledge gaps is fundamental for advancing metabolite-based therapeutic strategies in immune-mediated disorders.

Targeting Metabolic Vulnerabilities to Combat Drug Resistance in Cancer Therapy

Drug resistance remains a significant barrier to effective cancer therapy. Cancer cells evade treatment by reprogramming their metabolism, switching from glycolysis to oxidative phosphorylation (OXPHOS), and relying on alternative carbon sources such as glutamine. These adaptations not only enable tumor survival but also contribute to immune evasion through mechanisms such as reactive oxygen species (ROS) generation and the upregulation of immune checkpoint molecules like PD-L1. This review explores the potential of targeting metabolic weaknesses in drug-resistant cancers to enhance therapeutic efficacy. Key metabolic pathways involved in resistance, including glycolysis, glutamine metabolism, and the kynurenine pathway, are discussed. The combination of metabolic inhibitors with immune checkpoint inhibitors (ICIs), particularly anti-PD-1/PD-L1 therapies, represents a promising approach to overcoming both metabolic and immune evasion mechanisms. Clinical trials combining metabolic and immune therapies have shown early promise, but further research is needed to optimize treatment combinations and identify biomarkers for patient selection. In conclusion, targeting cancer metabolism in combination with immune checkpoint blockade offers a novel approach to overcoming drug resistance, providing a potential pathway to improved outcomes in cancer therapy. Future directions include personalized treatments based on tumor metabolic profiles and expanding research to other tumor types.

Global Trends in Research of Amino Acid Metabolism in T Lymphocytes in Recent 15 Years: A Bibliometric Analysis

Amino acid metabolism in T cells determines the therapeutic efficacy of T-cell-targeting drugs. To assess the direction of amino acid metabolism in T cells and construct related knowledge structure, we performed a bibliometric analysis aiming at amino acid metabolism in T cells utilizing studies publicized in recent 15 years. Three hundred thirty-seven related studies were downloaded from the Web of Science Core Collection (WoSCC), and the information on countries, institutes, and authors was collected and analyzed. In addition, the present research status and future trends were explored according to the results yielded from the analysis of cited references and keywords. This study revealed that publications regarding amino acid metabolism in T cells gradually increased each year. The USA is the top producer and most influential country in this field. Recent research has focused on the correlation between the metabolism of several amino acids and regulatory T cells (Tregs) and CD8+ T cells. Overall, this research offers a comprehensive exhibition on the field of amino acid metabolism in T cells, which will help researchers to study this domain more effectively and intuitively.

AXL: shapers of tumor progression and immunosuppressive microenvironments

As research progresses, our understanding of the tumor microenvironment (TME) has undergone profound changes. The TME evolves with the developmental stages of cancer and the implementation of therapeutic interventions, transitioning from an immune-promoting to an immunosuppressive microenvironment. Consequently, we focus intently on the significant role of the TME in tumor proliferation, metastasis, and the development of drug resistance. AXL is highly associated with tumor progression; however, previous studies on AXL have been limited to its impact on the biological behavior of cancer cells. An increasing body of research now demonstrates that AXL can influence the function and differentiation of immune cells, mediating immune suppression and thereby fostering tumor growth. A comprehensive analysis to identify and overcome the causes of immunosuppressive microenvironments represents a novel approach to conquering cancer. In this review, we focus on elucidating the role of AXL within the immunosuppressive microenvironments, discussing and analyzing the effects of AXL on tumor cells, T cells, macrophages, natural killer (NK) cells, fibroblasts, and other immune-stromal cells. We aim to clarify the contributions of AXL to the progression and drug resistance of cancer from its functional role in the immune microenvironment.

Targeting tumor-associated macrophages: Novel insights into immunotherapy of skin cancer

BACKGROUND

The incidence of skin cancer is currently increasing, and conventional treatment options inadequately address the demands of disease management. Fortunately, the recent rapid advancement of immunotherapy, particularly immune checkpoint inhibitors (ICIs), has ushered in a new era for numerous cancer patients. However, the efficacy of immunotherapy remains suboptimal due to the impact of the tumor microenvironment (TME). Tumor-associated macrophages (TAMs), a major component of the TME, play crucial roles in tumor invasion, metastasis, angiogenesis, and immune evasion, significantly impacting tumor development. Consequently, TAMs have gained considerable attention in recent years, and their roles have been extensively studied in various tumors. However, the specific roles of TAMs and their regulatory mechanisms in skin cancer remain unclear.

AIM OF REVIEW

This paper aims to elucidate the origin and classification of TAMs, investigate the interactions between TAMs and various immune cells, comprehensively understand the precise mechanisms by which TAMs contribute to the pathogenesis of different types of skin cancer, and finally discuss current strategies for targeting TAMs in the treatment of skin cancer.

KEY SCIENTIFIC CONCEPTS OF OVERVIEW

With a specific emphasis on the interrelationship between TAMs and skin cancer, this paper posits that therapeutic modalities centered on TAMs hold promise in augmenting and harmonizing with prevailing clinical interventions for skin cancer, thereby charting a novel trajectory for advancing the landscape of immunotherapeutic approaches for skin cancer.

Amitriptyline revitalizes ICB response via dually inhibiting Kyn/Indole and 5-HT pathways of tryptophan metabolism in ovarian cancer

Reprogramming tryptophan metabolism (TRP) may be able to overcome immunosuppression and restore the immune checkpoint blockade (ICB) response in patients with epithelial ovarian cancer (EOC) resistant to ICB therapy because TRP metabolism is involved in the kynurenine/indole and serotonin pathways of tryptophan metabolism. Herein, employing amitriptyline (AMI), an antagonist of TLR4 and serotonin transporter (SERT), we revealed that AMI remodels the immunological landscape of EOC. In particular, AMI lowered the expression of IDO1, IL-4I1, and PD-L1, the quantity of KYN and indoles, and the level of immunosuppressive immune cells MDSC, Tregs, and CD8+CD39+/PD-1+ T cell. AMI boosted the killing potential of anti-PD-1-directed CD8+T cells and worked in concert with PD-1 inhibitors to suppress tumor growth and to prolong the survival of EOC-bearing mice. This work highlights AMI as an effective regulator of ICB response by manipulating EOC cell TRP metabolism, indicating it could be a potential strategy for improving EOC ICB therapy.

Harnessing aryl hydrocarbon receptor dynamics: Unveiling therapeutic pathways in esophageal squamous cell carcinoma

This editorial discusses the insightful minireview by Rahmati et al. The minireview delves into the role of the aryl hydrocarbon receptor in the development and progression of esophageal squamous cell carcinoma, highlighting its potential as a promising therapeutic target. The authors concisely summarize the current understanding of how aryl hydrocarbon receptor modulation influences immune responses and the tumor microenvironment, offering fresh perspectives on therapeutic strategies. This editorial aimed to emphasize the significance of these findings and their potential impact on future research and clinical practices for the management of esophageal squamous cell carcinoma.

Metabolic targeting of regulatory T cells in oral squamous cell carcinoma: new horizons in immunotherapy

Oral squamous cell carcinoma (OSCC) is a prevalent oral malignancy, which poses significant health risks with a high mortality rate. Regulatory T cells (Tregs), characterized by their immunosuppressive capabilities, are intricately linked to OSCC progression and patient outcomes. The metabolic reprogramming of Tregs within the OSCC tumor microenvironment (TME) underpins their function, with key pathways such as the tryptophan-kynurenine-aryl hydrocarbon receptor, PI3K-Akt-mTOR and nucleotide metabolism significantly contributing to their suppressive activities. Targeting these metabolic pathways offers a novel therapeutic approach to reduce Treg-mediated immunosuppression and enhance anti-tumor responses. This review explores the metabolic dependencies and pathways that sustain Treg function in OSCC, highlighting key metabolic adaptations such as glycolysis, fatty acid oxidation, amino acid metabolism and PI3K-Akt-mTOR signaling pathway that enable Tregs to thrive in the challenging conditions of the TME. Additionally, the review discusses the influence of the oral microbiome on Treg metabolism and evaluates potential therapeutic strategies targeting these metabolic pathways. Despite the promising potential of these interventions, challenges such as selectivity, toxicity, tumor heterogeneity, and resistance mechanisms remain. The review concludes with perspectives on personalized medicine and integrative approaches, emphasizing the need for continued research to translate these findings into effective clinical applications for OSCC treatment.

Macrophages promote pre-metastatic niche formation of breast cancer through aryl hydrocarbon receptor activity

Macrophages that acquire an immunosuppressive phenotype play a crucial role in establishing the pre-metastatic niche (PMN), which is essential for facilitating breast cancer metastasis to distant organs. Our study showed that increased activity of the aryl hydrocarbon receptor (AHR) in lung macrophages plays a crucial role in establishing the immunosuppressive PMN in breast cancer. Specifically, AHR activation led to high expression of PD-L1 on macrophages by directly binding to the promoter of Pdl1. This upregulation of PD-L1 promoted the differentiation of regulatory T cells (Tregs) within the PMN, further enhancing immunosuppressive conditions. Mice with Ahr conditional deletion in macrophages had reduced lung metastasis of breast cancer. The elevated AHR levels in PMN macrophages were induced by GM-CSF, which was secreted by breast cancer cells. Mechanistically, the activated STAT5 signaling pathway induced by GM-CSF prevented AHR from being ubiquitinated, thereby sustaining its activity in macrophages. In breast cancer patients, the expression of AHR and PD-L1 was correlated with increased Treg cell infiltration, and higher levels of AHR were associated with a poor prognosis. These findings reveal that the crosstalk of breast cancer cells, lung macrophages, and Treg cells via the GM-CSF-STAT5-AHR-PD-L1 cascade modulates the lung pre-metastatic niche during breast cancer progression.

Stimulus Responsive Nanocarrier for Enhanced Antitumor Responses Against Hepatocellular Carcinoma

Background

Hepatocellular carcinoma (HCC) is a serious global health concern, accounting for about 90% of all liver cancer instances. Surgical treatment is a fundamental aspect of HCC management; however, the challenge of postoperative recurrence significantly impacts mortality rates.

Methods

We have developed a pH and reactive oxygen species (ROS) dual stimulus-responsive drug delivery system (PN@GPB-PEG NPs) loaded with chemotherapeutic paclitaxel (PTX) and indoleamine 2.3-dioxygenase (IDO) inhibitor NLG919, for HCC chemoimmunotherapy. The physiochemical properties, such as particle size, zeta potential, morphology, and encapsulation efficiency, were characterized. Furthermore, we investigated in vitro cytotoxicity, cellular uptake and immunogenic cell death in tumor cells treated with our nanoparticles. In vivo biodistribution, antitumor effects and immune responses were assessed in an HCC mice model.

Results

PN@GPB-PEG NPs display pH-responsive properties with improved targeting abilities toward tumors and improved uptake by HCC cells. Upon exposure to oxygen peroxide (H2O2), the sophisticated design allows for rapid release of therapeutic agents. In this process, PTX induces immunogenic cell death (ICD), which activates the immune system to generate an antitumor response. Simultaneously, NLG919 works to inhibit IDO, mitigating the immunosuppressive environment. This combination strategy leverages the advantages of both chemotherapy and immunotherapy, resulting in a powerful synergistic antitumor effect. In a mouse model of HCC, our nanoparticles effectively inhibited the growth of primary and recurrent tumors.

Conclusion

These encouraging results highlight the potential of our nanocarrier system as an innovative therapeutic approach to address HCC primary tumor and postsurgical recurrence, providing hope for enhanced patient outcomes.

Indoleamine 2,3-dioxygenase-1 involves in CD8+T cell exhaustion in glioblastoma via regulating tryptophan levels

Indoleamine 2,3-dioxygenase-1 (IDO-1) is an enzyme that catalyzes the metabolism of tryptophan (Trp). It is expressed in limited amounts in normal tissues but significantly upregulated during inflammation and infection. Various inflammatory factors, especially IFN-γ, can induce the expression of IDO-1. While extensive research has been conducted on the role of IDO-1 in tumors, its specific role in complex central nervous system tumors such as glioblastoma (GBM) remains unclear. This study aims to explore the role of IDO-1 in the development of GBM and analyze its association with tryptophan levels and CD8+T cell exhaustion in the tumor region. To achieve this, we constructed an orthotopic mouse glioblastoma tumor model to investigate the specific mechanisms between IDO-1, GBM, and CD8+T cell exhaustion. Our results showed that IDO-1 can promote CD8+T cell exhaustion by reducing tryptophan levels. When IDO-1 was knocked down in glioblastoma cells, other cells within the tumor microenvironment upregulated IDO-1 expression to compensate for the loss and enhance immunosuppressive effects. Therefore, the data suggest that the GBM microenvironment controls tryptophan levels by regulating IDO-1 expression, which plays a critical role in immune suppression. These findings support the use of immune therapy in combination with IDO-1 inhibitors or tryptophan supplementation as a potential treatment strategy.

Kynurenine-AhR reduces T-cell infiltration and induces a delayed T-cell immune response by suppressing the STAT1-CXCL9/CXCL10 axis in tuberculosis

Tuberculosis, caused by Mycobacterium tuberculosis (Mtb), is a critical global health issue that is complicated by the ability of the pathogen to delay the host's T-cell immune response. This delay in T-cell recruitment to the site of infection is a pivotal survival strategy for Mtb, allowing it to establish a persistent chronic infection. To investigate the underlying mechanisms, this study focused on Mtb's exploitation of host tryptophan metabolism. Mtb upregulates indoleamine 2,3-dioxygenase 1 (IDO1) in inflammatory macrophages, thereby increasing kynurenine (Kyn) production. Kyn then activates the aryl hydrocarbon receptor (AhR), leading to the upregulation of suppressor of cytokine signaling 3 and subsequent inhibition of the JAK-STAT1 signaling pathway. This results in reduced secretion of the chemokines CXCL9 and CXCL10, which are crucial for T-cell recruitment to the lungs. Supported by in vivo mouse models, our findings reveal that disrupting this pathway through AhR knockout significantly enhances T-cell infiltration and activity, thereby undermining Mtb-induced immunosuppression. In contrast, additional Kyn injection obviously inhibited T-cell infiltration and activity. These results highlight potential therapeutic targets of AhR and IDO1, offering new avenues for enhancing the host immune response against tuberculosis and guiding future vaccine development efforts.

Identification of VISTA regulators in macrophages mediating cancer cell survival

Numerous human cancers have exhibited the ability to elude immune checkpoint blockade (ICB) therapies. This type of resistance can be mediated by immune-suppressive macrophages that limit antitumor immunity in the tumor microenvironment (TME). Here, we elucidate a strategy to shift macrophages into a proinflammatory state that down-regulates V domain immunoglobulin suppressor of T cell activation (VISTA) via inhibiting AhR and IRAK1. We used a high-throughput microfluidic platform combined with a genome-wide CRISPR knockout screen to identify regulators of VISTA levels. Functional characterization showed that the knockdown of these hits diminished VISTA surface levels on macrophages and sustained an antitumor phenotype. Furthermore, targeting of both AhR and IRAK1 in mouse models overcame resistance to ICB treatment. Tumor immunophenotyping indicated that infiltration of cytotoxic CD8+ cells, natural killer cells, and antitumor macrophages was substantially increased in treated mice. Collectively, AhR and IRAK1 are implicated as regulators of VISTA that coordinate a multifaceted barrier to antitumor immune responses.

Metabolic checkpoints in glioblastomas: targets for new therapies and non-invasive detection

Glioblastoma (GBM) is a highly malignant tumor of the central nervous system that remains intractable despite advancements in current tumor treatment modalities, including immunotherapy. In recent years, metabolic checkpoints (aberrant metabolic pathways underlying the immunosuppressive tumor microenvironment) have gained attention as promising therapeutic targets and sensitive biomarkers across various cancers. Here, we briefly review the existing understanding of tumor metabolic checkpoints and their implications in the biology and management of GBM. Additionally, we discuss techniques that could evaluate metabolic checkpoints of GBM non-invasively, thereby potentially facilitating neo-adjuvant treatment and dynamic surveillance.

TDO2 inhibition counters Benzo[a]pyrene-induced immune evasion and suppresses tumorigenesis in lung adenocarcinoma

INTRODUCTION

Benzo[a]pyrene (BaP) is a toxic polycyclic aromatic hydrocarbon known as an exogenous AhR ligand. This study investigates the role of BaP in inducing immune checkpoint expression in lung adenocarcinoma (LUAD) and the underlying mechanisms involving the aryl hydrocarbon receptor (AhR) and tryptophan (Trp) metabolism.

METHODS

We assessed the expression of immune checkpoint molecules, including PD-L1 and ICOSL, in lung epithelial cell lines (BEAS-2B and H1975) exposed to BaP. The involvement of AhR in BaP-induced immune checkpoint expression was examined using AhR silencing (siAhR). Additionally, the role of Trp metabolism in BaP-mediated immune evasion was explored through culturing in Trp (-/+) condition media, treatments with the inhibitors of rate-limiting enzymes in Trp metabolism (TDO2 and IDO1) and analyses of Trp-catabolizing enzymes. The therapeutic potential of targeting Trp metabolism, specifically TDO2, was evaluated in vivo using C57BL/6 mice orthotopically inoculated with LUAD cells.

RESULTS

BaP exposure significantly upregulated the mRNA and surface expression of PD-L1 and ICOSL, with AhR playing a crucial role in this induction. Trp metabolism was found to enhance BaP-mediated immune evasion, as indicated by stronger induction of immune checkpoints in Trp (+) media and the upregulation of Trp-catabolizing enzymes. TDO2 inhibition markedly suppressed the surface expression of PD-L1 and ICOSL, demonstrating the importance of Trp metabolism in BaP-induced immune evasion. Further analysis confirmed the high TDO2 expression in lung adenocarcinoma and its association with poor patient survival. Using an orthotopic implantation mouse model, we demonstrated the inhibitory effect of two different TDO2 inhibitors on tumorigenesis, immune checkpoints, and tryptophan metabolism.

CONCLUSIONS

This study highlights the key mechanisms behind BaP-induced immune evasion in LUAD, particularly through the TDO2/AhR axis. It reveals how TDO2 inhibitors can counteract immune checkpoint activation and boost anti-tumor immunity, suggesting new paths for targeted lung cancer immunotherapy. The findings significantly improve our understanding of immune evasion in LUAD and underscore the therapeutic promise of TDO2 inhibition.

The tryptophan metabolic pathway of the microbiome and host cells in health and disease

The intricate and dynamic tryptophan (Trp) metabolic pathway in both the microbiome and host cells highlights its profound implications for health and disease. This pathway involves complex interactions between host cellular and bacteria processes, producing bioactive compounds such as 5-hydroxytryptamine (5-HT) and kynurenine derivatives. Immune responses to Trp metabolites through specific receptors have been explored, highlighting the role of the aryl hydrocarbon receptor in inflammation modulation. Dysregulation of this pathway is implicated in various diseases, such as Alzheimer's and Parkinson's diseases, mood disorders, neuronal diseases, autoimmune diseases such as multiple sclerosis (MS), and cancer. In this article, we describe the impact of the 5-HT, Trp, indole, and Trp metabolites on health and disease. Furthermore, we review the impact of microbiome-derived Trp metabolites that affect immune responses and contribute to maintaining homeostasis, especially in an experimental autoimmune encephalitis model of MS.

Unveiling the Immune effects of AHR in tumors: a decade of insights from bibliometric analysis (2010-2023)

BACKGROUND

The Aryl Hydrocarbon Receptor (AHR) is a transcription factor that regulates several biological processes. Its potential in anti-tumor immunotherapy is becoming clearer, yet no bibliometric studies on this topic exist. This study aims to understand the current research landscape and identify future directions through a bibliometric analysis of AHR's anti-tumor immunological effects.

METHODS

We conducted a comprehensive bibliometric analysis of AHR antitumor immunotherapy papers in the Web of Science Core Collection. Various aspects of the publications were analyzed, and research hotspots and future trends were identified using scientific bibliometric tools and statistical methods.

RESULTS

We collected 592 English papers published between 2010 and 2023, with an almost annual increase. Most publications were from the USA, followed by China, Germany, and Italy. The journal "Frontiers in Immunology" had the most papers, and the most cited paper was Christiane A. Opitz's "An endogenous tumour-promoting ligand of the human aryl hydrocarbon receptor." The research is centered around AHR gene expression, with a growing focus on intestinal disease and the development of Programmed cell death ligand 1 (PD-L1) drugs.

CONCLUSION

This bibliometric study highlights the significance of AHR in immunomodulatory research, outlining the research trends and key contributors. It suggests AHR's immune effects may mediate the process of colitis cancer transformation, providing valuable insights for future anti-tumor immunotherapy strategies based on AHR.

The interplay between microbiome and host factors in pathogenesis and therapy of head and neck cancer

Heterogeneous cancers that lack strong driver mutations with high penetrance, such as head and neck squamous cell carcinoma (HNSCC), present unique challenges to understanding their aetiology due to the complex interactions between genetics and environmental factors. The interplay between lifestyle factors (such as poor oral hygiene, smoking, or alcohol consumption), the oral and gut microbiome, and host genetics appears particularly important in the context of HNSCC. The complex interplay between the gut microbiota and cancer treatment outcomes has also received increasing attention in recent years. This review article describes the bidirectional communication between the host and the oral/gut microbiome, focusing on microbiome-derived metabolites and their impact on systemic immune responses and the modulation of the tumour microenvironment. In addition, we review the role of host lifestyle factors in shaping the composition of the oral/gut microbiota and its impact on cancer progression and therapy. Overall, this review highlights the rationality of considering the oral/gut microbiota as a critical determinant of cancer therapy outcomes and points to therapeutic opportunities offered by targeting the oral/gut microbiota in the management of HNSCC.

Collagen extracellular matrix promotes gastric cancer immune evasion by activating IL4I1-AHR signaling

BACKGROUND

Gastric cancer (GC) remains a significant global health challenge with poor prognosis, partly due to its ability to evade the immune system. The extracellular matrix (ECM), particularly collagen, plays a crucial role in tumor immune evasion, but the underlying mechanisms are not fully understood. This study investigates the role of collagen ECM in promoting immune evasion in gastric cancer by activating the IL4I1-AHR signaling pathway.

METHODS

We cultured gastric cancer cells in 3D collagen gels and assessed their immune evasion capabilities by co-culturing with HER2-specific CAR-T cells. The expression of IL4I1 and its metabolites was analyzed, and the role of integrin αvβ1 in mediating the effects of collagen was explored. Additionally, the impact of IL4I1-induced AHR activation on CAR-T cell exhaustion was evaluated, both in vitro and in vivo.

RESULTS

We found that gastric cancer cells cultured on collagen exhibited increased resistance to CAR-T cell cytotoxicity, which was associated with upregulated immune checkpoint molecules and downregulated effector cytokines on CAR-T cells. This was linked to increased IL4I1 expression, which was further induced by integrin αvβ1 signaling within the 3D collagen environment. IL4I1 metabolites, particularly KynA, promoted CAR-T cell exhaustion by activating the AHR pathway, leading to decreased cytotoxicity and tumor growth inhibition.

CONCLUSIONS

Our study reveals a novel mechanism by which the collagen ECM facilitates immune evasion in gastric cancer through the activation of IL4I1-AHR signaling, contributing to CAR-T cell exhaustion. Targeting this pathway could potentially enhance the efficacy of CAR-T cell therapy in gastric cancer.

Raman spectroscopy on dried blood plasma allows diagnosis and monitoring of colorectal cancer

Colorectal cancer (CRC) remains challenging to diagnose, necessitating the identification of a noninvasive biomarker that can differentiate it from other conditions such as inflammatory bowel diseases (IBD) and diverticular disease (DD). Raman spectroscopy (RS) stands out as a promising technique for monitoring blood biochemical profiles, with the potential to identify distinct signatures identifying CRC subjects. We performed RS analysis on dried plasma from 120 subjects: 32 CRC patients, 37 IBD patients, 20 DD patients, and 31 healthy controls. We also conducted longitudinal studies of CRC patient's postsurgery to monitor the spectral changes over time. We identified six spectral features that showed significant differences between CRC and non-CRC patients, corresponding to tryptophan, tyrosine, phenylalanine, lipids, carotenoids, and disulfide bridges. These features enabled the classification of CRC patients with an accuracy of 87.5%. Moreover, longitudinal analysis revealed that the spectral differences normalized over 6 months after surgery, indicating their association with the presence of the disease. Our study demonstrates the potential of RS to identify specific biomolecular signatures related to CRC. These results suggest that RS could be a novel screening and monitoring tool, providing valuable insights for the development of noninvasive and accurate diagnostic methods for CRC.

Pancreatic ductal adenocarcinoma cells reshape the immune microenvironment: Molecular mechanisms and therapeutic targets

Pancreatic ductal adenocarcinoma (PDAC) is a digestive system malignancy characterized by challenging early detection, limited treatment alternatives, and generally poor prognosis. Although there have been significant advancements in immunotherapy for hematological malignancies and various solid tumors in recent decades, with impressive outcomes in recent preclinical and clinical trials, the effectiveness of these therapies in treating PDAC continues to be modest. The unique immunological microenvironment of PDAC, especially the abnormal distribution, complex composition, and variable activation states of tumor-infiltrating immune cells, greatly restricts the effectiveness of immunotherapy. Undoubtedly, integrating data from both preclinical models and human studies helps accelerate the identification of reliable molecules and pathways responsive to targeted biological therapies and immunotherapies, thereby continuously optimizing therapeutic combinations. In this review, we delve deeply into how PDAC cells regulate the immune microenvironment through complex signaling networks, affecting the quantity and functional status of immune cells to promote immune escape and tumor progression. Furthermore, we explore the multi-modal immunotherapeutic strategies currently under development, emphasizing the transformation of the immunosuppressive environment into an anti-tumor milieu by targeting specific molecular and cellular pathways, providing insights for the development of novel treatment strategies.

Amino acid metabolic reprogramming in the tumor microenvironment and its implication for cancer therapy

Amino acids are essential building blocks for proteins, crucial energy sources for cell survival, and key signaling molecules supporting the resistant growth of tumor cells. In tumor cells, amino acid metabolic reprogramming is characterized by the enhanced uptake of amino acids as well as their aberrant synthesis, breakdown, and transport, leading to immune evasion and malignant progression of tumor cells. This article reviews the altered amino acid metabolism in tumor cells and its impact on tumor microenvironment, and also provides an overview of the current clinical applications of amino acid metabolism. Innovative drugs targeting amino acid metabolism hold great promise for precision and personalized cancer therapy.