Indoleamine 2,3-dioxygenase Research Articles

Tryptophan-Kynurenine Pathway Activation and Cognition in Virally Suppressed Women With HIV.

Immune and cognitive dysfunction persists even in virally suppressed women with HIV (VS-WWH). Since inflammation and HIV proteins induce the enzyme indoleamine 2,3-dioxygenase (IDO), converting tryptophan (T) to kynurenine (K) while producing downstream neurotoxic metabolites, we investigated IDO activation (KT ratio) in relation to cognition in VS-WWH and demographically similar women without HIV (WWoH). Ninety-nine VS-WWH on stable antiretroviral therapy and 102 WWoH (median age 52 vs 54 years; 73% vs 74% Black, respectively) from the New York and Chicago sites of the Women's Interagency HIV Study (WIHS) completed a neuropsychological test battery assessing motor function, processing speed, attention/working memory, verbal fluency, verbal learning and memory, and executive function and had plasma measured for tryptophan-kynurenine metabolites through liquid chromatography-tandem mass spectrometry and monocyte-derived [soluble cluster of differentiation-14 (sCD14), soluble cluster of differentiation-163 (sCD163), monocyte chemoattractant protein-1 (MCP-1)] plus general inflammatory markers [tumor necrosis factor alpha-2 receptor (TNF-R2), high-sensitivity C-reactive protein, high-sensitivity interleukin-6] through enzyme-linked immunosorbent assays between 2017 and 2020. VS-WWH had a higher KT ratio (P < 0.01) and higher sCD14 levels (P < 0.05) compared with WWoH. Higher sCD163 was associated with higher KT ratio (R = 0.29, P < 0.01) and worse fine motor function in VS-WWH; after adjusting for sCD163 and sCD14 in multivariable regressions, higher KT ratio remained significantly associated with impaired fine motor function in VS-WWH only (standardized β = -0.29, P < 0.05). IDO activation was not associated with cognition in WWoH. IDO activation (K:T) was associated with worse fine motor control in VS-WWH independent of measured systemic inflammation. Further studies investigating biological mechanisms linking IDO activation to fine motor function among VS-WWH are warranted.

Inhibition of Indoleamine 2,3-Dioxygenase Exerts Antidepressant-like Effects through Distinct Pathways in Prelimbic and Infralimbic Cortices in Rats under Intracerebroventricular Injection with Streptozotocin.

The application of intracerebroventricular injection of streptozotocin (ICV-STZ) is considered a useful animal model to mimic the onset and progression of sporadic Alzheimer's disease (sAD). In rodents, on day 7 of the experiment, the animals exhibit depression-like behaviors. Indoleamine 2,3-dioxygenase (IDO), a rate-limiting enzyme catalyzing the conversion of tryptophan (Trp) to kynurenine (Kyn), is closely related to depression and AD. The present study aimed to investigate the pathophysiological mechanisms of preliminary depression-like behaviors in ICV-STZ rats in two distinct cerebral regions of the medial prefrontal cortex, the prelimbic cortex (PrL) and infralimbic cortex (IL), both presumably involved in AD progression in this model, with a focus on IDO-related Kyn pathways. The results showed an increased Kyn/Trp ratio in both the PrL and IL of ICV-STZ rats, but, intriguingly, abnormalities in downstream metabolic pathways were different, being associated with distinct biological effects. In the PrL, the neuroprotective branch of the Kyn pathway was attenuated, as evidenced by a decrease in the kynurenic acid (KA) level and Kyn aminotransferase II (KAT II) expression, accompanied by astrocyte alterations, such as the decrease in glial fibrillary acidic protein (GFAP)-positive cells and increase in morphological damage. In the IL, the neurotoxicogenic branch of the Kyn pathway was enhanced, as evidenced by an increase in the 3-hydroxy-kynurenine (3-HK) level and kynurenine 3-monooxygenase (KMO) expression paralleled by the overactivation of microglia, reflected by an increase in ionized calcium-binding adaptor molecule 1 (Iba1)-positive cells and cytokines with morphological alterations. Synaptic plasticity was attenuated in both subregions. Additionally, microinjection of the selective IDO inhibitor 1-Methyl-DL-tryptophan (1-MT) in the PrL or IL alleviated depression-like behaviors by reversing these different abnormalities in the PrL and IL. These results suggest that the antidepressant-like effects linked to Trp metabolism changes induced by 1-MT in the PrL and IL occur through different pathways, specifically by enhancing the neuroprotective branch in the PrL and attenuating the neurotoxicogenic branch in the IL, involving distinct glial cells.

IDO+ Endothelial Cells in Glomeruli of Kidney Transplantation Patients With Glomerulitis.

Kidney transplantation is the preferred treatment option for patients with end-stage renal disease. However, long-term graft survival remains a challenge. The enzyme indoleamine 2,3 dioxygenase (IDO) has been reported to have immunomodulatory effects with IDO transcripts being elevated in both antibody-mediated rejection and T cell-mediated rejection. A metal-conjugated antibody panel for the staining of kidney biopsies was developed, allowing the visualization of 41 structural and immune markers on a single tissue slide to gain in-depth insight into the composition and localization of the immune cell compartment. Staining was applied to week 4 and 24 protocol biopsies of 49 patients as well as on 15 indication biopsies of the TRITON study and 4 additional transplantation biopsies with glomerulitis. A highly distinctive and specific glomerular IDO expression was observed in biopsies from 3 of 49 patients in imaging mass cytometry. Immunohistochemistry confirmed IDO expression in glomeruli of 10 of 10 cases with glomerulitis. IDO was found to be expressed by CD31+ glomerular endothelial cells, accompanied by the presence of granzyme-B+Tbet+CD7+CD45RA+ natural killer cells and CD68+ macrophages. Furthermore, a proportion of both the immune cells and endothelial cells expressed Ki-67, indicative of cell proliferation, which was not observed in control glomeruli. Our results show glomerular IDO expression in transplanted kidneys with glomerulitis, which is accompanied by increased numbers of natural killer cells and macrophages and likely reflects local immune activation.

Indoleamine-2,3-dioxygenase inhibition improves immunity and is safe for concurrent use with cART during Mtb/SIV coinfection.

Chronic immune activation promotes tuberculosis (TB) reactivation in the macaque Mycobacterium tuberculosis (M. tuberculosis)/SIV coinfection model. Initiating combinatorial antiretroviral therapy (cART) early lowers the risk of TB reactivation, but immune activation persists. Studies of host-directed therapeutics (HDTs) that mitigate immune activation are, therefore, required. Indoleamine 2,3, dioxygenase (IDO), a potent immunosuppressor, is one of the most abundantly induced proteins in NHP and human TB granulomas. Inhibition of IDO improves immune responses in the lung, leading to better control of TB, including adjunctive to TB chemotherapy. The IDO inhibitor D-1 methyl tryptophan (D1MT) is, therefore, a bona fide TB HDT candidate. Since HDTs against TB are likely to be deployed in an HIV coinfection setting, we studied the effect of IDO inhibition in M. tuberculosis/SIV coinfection, adjunctive to cART. D1MT is safe in this setting, does not interfere with viral suppression, and improves the quality of CD4+ and CD8+ T cell responses, including reconstitution, activation and M. tuberculosis-specific cytokine production, and access of CD8+ T cells to the lung granulomas; it reduces granuloma size and necrosis, type I IFN expression, and the recruitment of inflammatory IDO+ interstitial macrophages (IMs). Thus, trials evaluating the potential of IDO inhibition as HDT in the setting of cART in M. tuberculosis/HIV coinfected individuals are warranted.

Tryptophan and Its Derived Metabolites as Biomarkers for Tuberculosis Disease: A Systematic Review

Feasible diagnostic assays are required to detect new tuberculosis (TB) cases and monitor treatment. This study aimed to evaluate evidence on tryptophan (Trp) and its metabolites as proposed biomarkers for TB. Through specific keyword searches, we identified 170 relevant literature sources and included seven publications (from 2013 to 2023). The biomarker used in these studies were indoleamine 2, 3-dioxygenase (IDO) activity, IDO-1 gene expression, and plasma IDO protein, measured using ELISA, liquid chromatography-mass spectrometry, ultraperformance liquid chromatography mass spectrometry, and transcriptional profiling. The studies encompassed a pediatric case-control and six studies involving adults, pregnant women with TB-HIV, and individuals with multidrug-resistant tuberculosis, active TB, and latent TB. The assessment of IDO activity and IDO protein level demonstrated promising performance in distinguishing active TB from controls and in evaluating treatment failure and recurrent cases to controls. Trp and its metabolites fulfilled nearly all of target product profile criteria for detecting active TB. This study highlights the potential of utilizing host Trp and its metabolites as non-sputum-based biomarker for TB infection.

Prediction Model for Early-Stage CKD Using the Naples Prognostic Score and Plasma Indoleamine 2,3-dioxygenase Activity.

Changes in inflammation, immunity, and nutritional status can promote the development of chronic kidney disease (CKD), and the Naples prognostic score (NPS) reflects changes in these three general clinical parameters. Indoleamine 2.3-dioxygenase (IDO) can block the function of inflammatory cells and inhibit the production of inflammatory cytokines. We examined use of the NPS and IDO activity to predict early-stage CKD. Clinical and demographic parameters and the NPS were recorded for 47 CKD patients and 30 healthy controls. A one-way ANOVA or the rank sum test was used to compare variables in the different groups. Spearman or Pearson correlation coefficients were calculated, and logistic regression was used to identify significant factors. Receiver operating characteristic (ROC) analysis was also performed. The NPS had a positive correlation with plasma IDO activity and IDO activity was lowest in controls, and increased with CKD stage. ROC analysis indicated that NPS had an area under the curve (AUC) of 0.779 when comparing controls with all CKD patients. A prediction model for CKD (-4.847 + [1.234 × NPS] + [6.160 × plasma IDO activity]) demonstrated significant differences between controls and patients with early-stage CKD, and for patients with different stages of CKD. This model had AUC values of 0.885 (control vs CKD1-4), 0.876 (control vs CKD2), 0.818 (CKD2 vs CKD3), and 0.758 (CKD3 vs CKD4). A prediction model based on the NPS and IDO provided good to excellent predictions of early-stage CKD.

Synergistic action of gemcitabine and celecoxib in promoting the antitumor efficacy of anti-programmed death-1 monoclonal antibody by triggering immunogenic cell death.

Emerging evidence suggests that immunogenic chemotherapy not only kills tumor cells but also improves the immune-suppressive tumor microenvironment by inducing immunogenic cell death (ICD), leading to sustained anti-tumor effects. The lack of ICD inducers explored in lung cancer necessitates investigation into new inducers for this context, therefore, this study aims to explore whether the gemcitabine (GEM) and celecoxib can activate the immunogenic chemotherapy progress in lung cancer tissue. We assessed five chemotherapeutic agents for their ability to trigger ICD using ex vivo and in vivo experiments, including western blotting (WB), flow cytometry, and tumor preventive vaccine assays. Additionally, we evaluated the synergistic effects of GEM, celecoxib, and anti-programmed death 1 monoclonal antibody (aPD-1) in tumor-bearing mice to understand how GEM activates antitumor immunity and enhances immunochemotherapy. GEM was identified as an effective ICD inducer, showing high expression of calreticulin (CRT) and heat shock protein 90 (HSP90). Co-culture with GEM-treated cells [Lewis lung carcinoma (LLC) and CMT-64] enhanced dendritic cell (DC) activity, evidenced by maturation markers and increased phagocytic capacity. Moreover, celecoxib was found to enhance ICD by reducing indoleamine 2,3-dioxygenase 1 (IDO1) expression and increasing reactive oxygen species (ROS)-based endoplasmic reticulum (ER) stress. The combination therapy [GEM, celecoxib, and aPD-1 (GCP)] exhibited potent and sustained antitumor activity in immunocompetent mice, with enhanced recruitment of tumor-infiltrating lymphocytes. These findings support the potential use of GCP therapy as a treatment option for lung cancer patients.

Restoring hippocampal glucose metabolism rescues cognition across Alzheimer's disease pathologies.

Impaired cerebral glucose metabolism is a pathologic feature of Alzheimer Disease (AD), and recent proteomic studies highlight a disruption of glial carbohydrate metabolism with disease progression. Here, we report that inhibition of indoleamine-2,3-dioxygenase 1 (IDO1), which metabolizes tryptophan to kynurenine (KYN) in the first step of the kynurenine pathway, rescues hippocampal memory function and plasticity in preclinical models of amyloid and tau pathology by restoring astrocytic metabolic support of neurons. Activation of IDO1 in astrocytes by amyloid-beta 42 and tau oligomers, two major pathological effectors in AD, increases KYN and suppresses glycolysis in an AhR-dependent manner. Conversely, pharmacological IDO1 inhibition restores glycolysis and lactate production. In amyloid-producing APP Swe -PS1 ΔE9 and 5XFAD mice and in tau-producing P301S mice, IDO1 inhibition restores spatial memory and improves hippocampal glucose metabolism by metabolomic and MALDI-MS analyses. IDO1 blockade also rescues hippocampal long-term potentiation (LTP) in a monocarboxylate transporter (MCT)-dependent manner, suggesting that IDO1 activity disrupts astrocytic metabolic support of neurons. Indeed, in vitro mass-labeling of human astrocytes demonstrates that IDO1 regulates astrocyte generation of lactate that is then taken up by human neurons. In co-cultures of astrocytes and neurons derived from AD subjects, deficient astrocyte lactate transfer to neurons was corrected by IDO1 inhibition, resulting in improved neuronal glucose metabolism. Thus, IDO1 activity disrupts astrocytic metabolic support of neurons across both amyloid and tau pathologies and in a model of AD iPSC-derived neurons. These findings also suggest that IDO1 inhibitors developed for adjunctive therapy in cancer could be repurposed for treatment of amyloid- and tau-mediated neurodegenerative diseases.

IDO1 Inhibitor RY103 Suppresses Trp-GCN2-Mediated Angiogenesis and Counters Immunosuppression in Glioblastoma.

Glioma is characterized by strong immunosuppression and excessive angiogenesis. Based on existing reports, it can be speculated that the resistance to anti-angiogenic drug vascular endothelial growth factor A (VEGFA) antibody correlates to the induction of novel immune checkpoint indoleamine 2,3-dioxygenase 1 (IDO1), while IDO1 has also been suggested to be related to tumor angiogenesis. Herein, we aim to clarify the potential role of IDO1 in glioma angiogenesis and the mechanism behind it. Bioinformatic analyses showed that the expressions of IDO1 and angiogenesis markers VEGFA and CD34 were positively correlated and increased with pathological grade in glioma. IDO1-overexpression-derived-tryptophan depletion activated the general control nonderepressible 2 (GCN2) pathway and upregulated VEGFA in glioma cells. The tube formation ability of angiogenesis model cells could be inhibited by IDO1 inhibitors and influenced by the activity and expression of IDO1 in condition medium. A significant increase in serum VEGFA concentration and tumor CD34 expression was observed in IDO1-overexpressing GL261 subcutaneous glioma-bearing mice. IDO1 inhibitor RY103 showed positive anti-tumor efficacy, including the anti-angiogenesis effect and upregulation of natural killer cells in GL261 glioma-bearing mice. As expected, the combination of RY103 and anti-angiogenesis agent sunitinib was proved to be a better therapeutic strategy than either monotherapy.

Multi‐synergistic chemotherapeutic drug assemblies to activate colorectal cancer immunotherapy by modulating the multilevel immunosuppressive characteristics

AbstractThe life‐threatening colorectal cancer exhibits multilevel immunosuppressive characteristics, including low immunogenicity, abnormal cellular metabolism, and acidic immunosuppressive microenvironment. In this work, multi‐synergistic chemotherapeutic drug assemblies are fabricated to activate colorectal cancer immunotherapy by modulating the multilevel immunosuppressive characteristics. Without any drug excipients, the glycolysis inhibitor of lonidamine (LON), indoleamine 2,3‐dioxygenase 1 (IDO‐1) inhibitor of NLG919 (NLG), and the photosensitizer of chlorine e6 could self‐assemble into drug assemblies (LNC) with uniform nano‐size distribution and increased drug stability. Moreover, LNC could also promote cellular uptake and enhance drug penetration to enable efficient drug co‐delivery. Especially, the photodynamic therapy (PDT) of LNC could disrupt tumor cells to release tumor‐associated antigens, thus efficiently suppressing primary tumor growth and improving tumor immunogenicity. Meanwhile, LNC could also reduce the activity of IDO‐1 and attenuate the glycolysis metabolism, thereby reversing the multilevel immunosuppressive characteristics to promote T cell activation. Benefiting from the multi‐synergistic effects, LNC efficiently eradicates the primary tumor growth and also activates systemic antitumor immunity for metastatic tumor inhibition. Such a simple formulation but a multi‐synergistic strategy may accelerate the development of translational nanomedicine for colorectal cancer immunotherapy by using small molecular drug combinations.

Toll-Like Receptors Mediate Opposing Dendritic Cell Effects on Treg/Th17 Balance in Mice With Intracerebral Hemorrhage.

Dendritic cells (DCs) regulate the immune response associated with T lymphocytes, but their role in stroke remains unclear. In this study, we investigated the causal relationship between DCs and T-cell response in intracerebral hemorrhage (ICH) by focusing on TLRs (toll-like receptors) that may modulate the function of DCs. We studied the effects of TLR4, TLR2, and TLR9 on DC-mediated T-cell response and the outcomes of ICH using male C57BL/6 and CD11c-DTx (diphtheria toxin) receptor mice. We administered specific agents intraperitoneally or orally and evaluated the results using flow cytometry, real-time polymerase chain reaction, Western blotting, immunofluorescence staining, histopathology, and behavioral tests. TLR4 and TLR2 activation induces DC maturation and reduces the ratio of regulatory T to T-helper 17 cells in the brain and periphery after ICH. When either of these receptors is activated, it can worsen neuroinflammation and exacerbate ICH outcomes. TLR9 also promotes DC maturation, stabilizing the number of DCs, particularly conventional DCs. TLR9 has the opposite effects on regulatory T/T-helper 17 balance, neuroinflammation, and ICH outcomes compared with TLR4 and TLR2. Upon stimulation, TLR4 and TLR9 may achieve these effects through the p38-MAPK (p38-mitogen-activated protein kinase)/MyD88 (myeloid differentiation primary response gene 88) and indoleamine 2,3-dioxygenase 1 (IDO1)/GCN2 (general control nonderepressible 2) signaling pathways, respectively. DCs act as intermediaries for TLR-mediated T-cell response. TLR-mediated opposing effects of DCs on T-cell response may provide novel strategies to treat ICH.

BICC1 drives pancreatic cancer stemness and chemoresistance by facilitating tryptophan metabolism.

Pancreatic adenocarcinoma is the fourth leading cause of malignancy-related deaths, with rapid development of drug resistance driven by pancreatic cancer stem cells. However, the mechanisms sustaining stemness and chemotherapy resistance in pancreatic ductal adenocarcinoma (PDAC) remain unclear. Here, we demonstrate that Bicaudal C homolog 1 (BICC1), an RNA binding protein regulating numerous cytoplasmic mRNAs, facilitates chemoresistance and stemness in PDAC. Mechanistically, BICC1 activated tryptophan catabolism in PDAC by up-regulating indoleamine 2,3-dioxygenase-1 (IDO1) expression, a tryptophan-catabolizing enzyme. Increased levels of tryptophan metabolites contribute to NAD+ synthesis and oxidative phosphorylation, leading to a stem cell-like phenotype. Blocking BICC1/IDO1/tryptophan metabolism signaling greatly improves the gemcitabine (GEM) efficacy in several PDAC models with high BICC1 level. These findings indicate that BICC1 is a critical tryptophan metabolism regulator that drives the stemness and chemoresistance of PDAC and thus a potential target for combinatorial therapeutic strategy against chemoresistance.

Supramolecular artificial Nano-AUTACs enable tumor-specific metabolism protein degradation for synergistic immunotherapy.

Autophagy-targeting chimera (AUTAC) has emerged as a powerful modality that can selectively degrade tumor-related pathogenic proteins, but its low bioavailability and nonspecific distribution significantly restrict their therapeutic efficacy. Inspired by the guanine structure of AUTAC molecules, we here report supramolecular artificial Nano-AUTACs (GM NPs) engineered by AUTAC molecule GN [an indoleamine 2,3-dioxygenase (IDO) degrader] and nucleoside analog methotrexate (MTX) through supramolecular interactions for tumor-specific protein degradation. Their nanostructures allow for precise localization and delivery into cancer cells, where the intracellular acidic environment can disrupt the supramolecular interactions to release MTX for eradicating tumor cells, modulating tumor-associated macrophages, activating dendritic cells, and inducing autophagy. Specifically, the induced autophagy facilitates the released GN for degrading immunosuppressive IDO to further enhance effector T cell activity and inhibit tumor growth and metastasis. This study offers a unique strategy for building a nanoplatform to advance the field of AUTAC in tumor immunotherapy.

Association of Indoleamine 2,3-Dioxygenase (IDO) Activity with Outcome after Cardiac Surgery in Adult Patients.

Indoleamine 2,3-deoxygenase (IDO) plays an important role in the catabolism of the amino acid tryptophan. Tryptophan and its metabolites are key immune modulators. Increased IDO activity has been observed in various diseases and is associated with worse clinical outcomes. However, comprehensive research regarding its role in cardiac surgery remains limited. Therefore, we aimed to investigate perioperative changes in IDO activity and pathway metabolites, along with their impact on clinical outcomes in adult patients undergoing cardiac surgery. As an observational cohort study conducted at the Inselspital in Bern from January to December 2019, we retrospectively analyzed the data of prospectively collected biobank samples of patients undergoing cardiac surgery with the use of cardiopulmonary bypass. IDO pathway metabolite analysis was conducted by mass spectrometry. Perioperative dynamics were descriptively assessed and associated with pre-defined clinical outcome measures (30-day mortality, 1-year mortality, incidence of stroke and myocardial infarction, and length of hospital stay) through a multi-step exploratory regression analysis. A cohort of 192 adult patients undergoing cardiac surgery with the use of cardiopulmonary bypass were included (median age 67.0, IQR 60.0-73.0, 75.5% male). A significant perioperative decrease in the kynurenine/tryptophan (Kyn/Trp) ratio (-2.298, 95% CI -4.028 to -596, p = 0.009) and significant perioperative dynamics in the associated metabolites was observed. No association of perioperative changes in IDO activity and pathway metabolites with clinical outcomes was found. A significant decrease in the Kyn/Trp ratio among adult patients undergoing cardiac surgery indicates a perioperative downregulation of IDO, which stands in contrast to other pro-inflammatory conditions. Further studies are needed to investigate IDO in the setting of perioperative immunomodulation, which is a key driver of postoperative complications in cardiac surgery patients.

Chemo-immunotherapy by nanoliposomal epacadostat and docetaxel combination to IDO1 inhibition and tumor microenvironment suppression

The over-activation of tryptophan (Trp) metabolism to kynurenine (Kyn) catalyzed by Indoleamine 2,3-dioxygenase-1 (IDO1) enzyme, is one of the main metabolic pathways involved in tumor microenvironment (TME) immune escape and cancer treatment failure. The most efficient of IDO1 inhibitors is Epacadostat (EPA). Since monotherapy with single-agent IDO1 inhibitor regimen has led to an insufficient anti-tumor activity, we examined the efficacy of simultaneous treatment by Liposomal epacadostat (Lip-EPA) as a potent IDO inhibitor, in combination with docetaxel (DTX) as a complement immunogenic cell death (ICD) agent against B16F10 model. First, the in vitro combination index (CI) of epacadostat (EPA) and DTX was investigated by using the unified theory. Then, the in vivo efficacy of the combination therapy was assessed. Results indicated the synergestic cytotoxic effect of the combination on B16F10 compared to normal fibroblast cells (NIH). The immune profiling demonstrated a significant increase in the percentage of infiltrated T lymphocytes and IFN-γ release, a significant decrease in the percentage of regulatory T cells (Treg) population and the subsequent low levels of IL-10 generation in mice treated with Lip-EPA + DTX. Further, a significant tumor growth delay (TGD = 69.15 %) and an increased life span (ILS > 47.83 %) was observed with the combination strategy. Histopathology analysis revealed a remarkable increase in the Trp concentration following combination treatment, while Kyn levels significantly decreased. Results showed that the nano-liposomal form of IDO1 inhibitor in combination with chemotherapy could significantly improve the imunity response and dominate the tumor immuno-suppressive micro-environment, which merits further investigations.

The Toxoplasma oxygen-sensing protein, TgPhyA, is required for resistance to interferon gamma-mediated nutritional immunity in mice.

As Toxoplasma gondii disseminates through its host, the parasite must sense and adapt to its environment and scavenge nutrients. Oxygen (O2) is one such environmental factor and cytoplasmic prolyl 4-hydroxylases (PHDs) are evolutionarily conserved O2 cellular sensing proteins that regulate responses to changes in O2 availability. Toxoplasma expresses 2 PHDs. One of them, TgPHYa hydroxylates SKP1, a subunit of the SCF-E3 ubiquitin ligase complex. In vitro, TgPHYa is important for growth at low O2 levels. However, studies have yet to examine the role that TgPHYa or any other pathogen-encoded PHD plays in virulence and disease. Using a type II ME49 Toxoplasma TgPHYa knockout, we report that TgPHYa is important for Toxoplasma virulence and brain cyst formation in mice. We further find that while TgPHYa mutant parasites can establish an infection in the gut, they are unable to efficiently disseminate to peripheral tissues because the mutant parasites are unable to survive within recruited immune cells. Since this phenotype was abrogated in IFNγ knockout mice, we studied how TgPHYa mediates survival in IFNγ-treated cells. We find that TgPHYa is not required for release of parasite-encoded effectors into host cells that neutralize anti-parasitic processes induced by IFNγ. In contrast, we find that TgPHYa is required for the parasite to scavenge tryptophan, which is an amino acid whose levels are decreased after IFNγ up-regulates the tryptophan-catabolizing enzyme, indoleamine dioxygenase (IDO). We further find, relative to wild-type mice, that IDO knockout mice display increased morbidity when infected with TgPHYa knockout parasites. Together, these data identify the first parasite mechanism for evading IFNγ-induced nutritional immunity and highlight a novel role that oxygen-sensing proteins play in pathogen growth and virulence.

Reprogrammed IDO-Induced Immunosuppressive Microenvironment Synergizes with Immunogenic Magnetothermodynamics for Improved Cancer Therapy.

Indoleamine 2,3-dioxygenase (IDO), highly expressed in hepatocellular carcinoma (HCC), plays a pivotal role in creating an immune-suppressive tumor microenvironment. Inhibiting IDO activity has emerged as a promising immunotherapeutic strategy; however, the delivery of IDO inhibitors to the tumor site is constrained, limiting their therapeutic efficacy. In this study, we developed a magnetic vortex nanodelivery system for the targeted delivery of the IDO inhibitor NLG919, integrated with magnetic hyperthermia therapy to reverse the immune-suppressive microenvironment of liver cancer and inhibit tumor growth. This system comprises thermoresponsive polyethylenimine-coated ferrimagnetic vortex-domain iron oxide nanorings (PI-FVIOs) loaded with NLG919 (NLG919/PI-FVIOs). Under thermal effects, NLG919 can be precisely released from the delivery system, counteracting IDO-mediated immune suppression and synergizing with NLG919/PI-FVIOs-mediated magnetothermodynamic (MTD) therapy-induced immunogenic cell death (ICD), resulting in effective HCC suppression. In vivo studies demonstrate that this combination therapy significantly inhibits tumor growth and metastasis by enhancing the accumulation of cytotoxic T lymphocytes and suppressing regulatory T cells within the tumor. Overall, our findings reveal that NLG919/PI-FVIOs can induce a potent antitumor immune response by disrupting the IDO pathway and activating the ICD, offering a promising therapeutic avenue for HCC treatment.

Lycopene alleviates BCG-induced depressive phenotypes in mice by disrupting 5-HT3 receptor – IDO1 interplay in the brain

The 5-HT3 receptor and indoleamine 2,3-dioxygenase 1 (IDO1) enzyme play a crucial role in the pathogenesis of depression as their activation reduces serotonin contents in the brain. Since molecular docking analysis revealed lycopene as a potent 5-HT3 receptor antagonist and IDO1 inhibitor, we hypothesized that lycopene might disrupt the interplay between the 5-HT3 receptor and IDO1 to mitigate depression. In mice, the depression-like phenotypes were induced by inoculating Bacillus Calmette-Guerin (BCG). Lycopene (intraperitoneal; i.p.) was administered alone or in combination with 5-HT3 receptor antagonist ondansetron (i.p.) or IDO1 inhibitor minocycline (i.p.), and the behavioral screening was performed by the sucrose preference test, open field test, tail suspension test, and splash test which are based on the different principles. Further, the brains were subjected to the biochemical analysis of serotonin and its precursor tryptophan by the HPLC. The results showed depression-like behavior in BCG-inoculated mice, which was reversed by lycopene administration. Moreover, prior treatment with ondansetron or minocycline potentiated the antidepressant action of lycopene. Minocycline pretreatment also enhanced the antidepressant effect of ondansetron indicating the regulation of IDO1 activity by 5-HT3 receptor-triggered signaling. Biochemical analysis of brain samples revealed a drastic reduction in the levels of tryptophan and serotonin in depressed animals, which were restored following treatment with lycopene and its combination with ondansetron or minocycline. Taken together, the data from molecular docking, behavioral experiments, and biochemical estimation suggest that lycopene might block the 5-HT3 receptor and consequently inhibit the activity of IDO1 to ameliorate BCG-induced depression in mice.

Cyclometalated iridium(III) complex based on isoquinoline alkaloid synergistically elicits the ICD response and IDO inhibition via autophagy-dependent ferroptosis

The development of anticancer drugs to treat triple-negative breast cancer (TNBC) is an ongoing challenge. Immunogenic cell death (ICD) has garnered considerable interest worldwide as a promising synergistic modality for cancer chemoimmunotherapy. However, only few drugs or treatment modalities can trigger an ICD response and none of them exert a considerable clinical effect against TNBC. Therefore, new agents with potentially effective chemoimmunotherapeutic response are required. In this study, five new cyclometalated Ir(III) complexes containing isoquinoline alkaloid CˆN ligands were designed and synthesized. Among them, Ir-1 exhibited the highest in vitro cytotoxicity. Mechanistically, Ir-1 could trigger autophagy-dependent ferroptosis and a subsequent ferroptosis-dependent ICD response as well as indoleamine 2,3-dioxygenase (IDO) inhibition via reactive oxygen species (ROS)-mediated endoplasmic reticulum (ER) stress in MDA-MB-231 cells. When immunocompetent BALB/c mice were vaccinated with Ir-1-treated dying TNBC cells, antitumor CD8+ T-cell response and Foxp3+ T-cell depletion were induced, resulting in long-lasting antitumor immunity in TNBC cells. Moreover, combination therapy with Ir-1 and anti-PD1 could substantially augment in vivo therapeutic effects. Based on these results, Ir-1 is a promising candidate for chemoimmunotherapy against TNBC and its effects are mediated synergistically via ICD induction and IDO blockage.

Repurposing ibrutinib for chemo-immunotherapy in a phase 1b study of ibrutinib with indoximod plus metronomic cyclophosphamide and etoposide for patients with childhood brain cancer.

TPS2703 Background: In children, brain cancer is the leading cause of cancer related death. The indoleamine 2,3-dioxygenase (IDO) pathway is a metabolic checkpoint, expressed by host myeloid and dendritic cells, that suppresses anti-tumor immune responses following chemotherapy. We recently published results of a first-in-children phase 1 trial (NCT02502708) that showed the oral IDO-pathway inhibitor indoximod was well tolerated and provided meaningful clinical benefit for many patients with progressive childhood brain tumors, when given in combination with oral chemotherapy regimens (1). Using preclinical models, we have also reported the importance of the Bruton’s Tyrosine Kinase (BTK) pathway as a key upstream driver of IDO during chemotherapy (2). Thus, we hypothesize that adding the BTK-inhibitor ibrutinib to the previously studied regimen of investigational indoximod IDO-inhibitor plus oral metronomic cyclophosphamide and etoposide will synergistically enhance anti-tumor immune responses, leading to improvement in Objective Response Rate (ORR) with manageable overlapping toxicity. Methods: The current study (NCT05106296) is an Investigator-Sponsored, open label, single-arm phase 1b trial comprised of a Dose-escalation Cohort (n=18) using a 3+3 dose escalation design to establish safety and dosing of ibrutinib in the combined regimen; followed by an Expansion Cohort (n=19) at the MTD to evaluate efficacy. Patients are treated with the all-oral 4-drug chemo-immunotherapy regimen in 28-day cycles using: (i) ibrutinib [Study Dose once daily on days 1-21]; (ii) indoximod [38.4 mg/kg/day divided twice daily throughout the cycle]; (iii) cyclophosphamide [2.5 mg/kg/dose, maximum dose 100 mg, once daily on days 1-21]; and (iv) etoposide [50 mg/m2/dose once daily on days 1-21]. Eligible patients are age 12 to 25 years with relapsed or refractory brain cancer, MRI evidence of current active disease not recently treated with radiation/proton therapy, ECOG performance score 0-2, and meet standard organ function requirements. Patients with systemic infection, autoimmune disease, recent live-virus vaccination, comorbid conditions that may overlap with expected regimen toxicities, or chronic treatment with anticoagulants or strong CYP3A inhibitors are excluded. Primary Objectives are to: (i) determine the pediatric recommended phase 2 dose (RP2D) of ibrutinib for the combined regimen (Dose-escalation Cohort), and (ii) evaluate preliminary evidence of efficacy for the combined regimen in terms of ORR (Expansion Cohort). Exploratory analyses use single-cell RNA and TCR sequencing (scRNAseq/TCRseq) of cryopreserved serial peripheral blood samples to monitor for treatment-expanded TCR clonotypes and study their phenotype. 1. Neuro-Oncology 26:348-361, 2024. 2. Immunity54:2354-2371, 2021. Clinical trial information: NCT05106296 .