Indoleamine 2,3-dioxygenase 1

Overview

Indoleamine 2,3-dioxygenase 1 (IDO1) is a protein-coding gene that encodes an enzyme involved in tryptophan catabolism along the kynurenine pathway. In biomedical research, IDO1 is widely recognized as an immunoregulatory factor because its activity can contribute to local tryptophan depletion and the accumulation of immunosuppressive Metabolites, thereby shaping T-cell responses and broader tumor immune microenvironments. For this reason, IDO1 is often discussed as a non-classical immune checkpoint rather than a conventional receptor-ligand checkpoint.

In cancer and inflammatory disease contexts, IDO1 has been studied as a mechanism of immune escape and treatment resistance. It is frequently considered alongside pathways involving STAT1, dendritic cell activation, STING1 signaling, and PD-L1-mediated immune suppression. Recent work has also linked IDO1 to mitochondrion-associated signaling and to the immunosuppressive behavior of cancer-associated fibroblast-rich tumor stroma, underscoring its relevance in breast cancer and other solid tumors.

Focus of Latest Publications

Recent publications continue to position indoleamine 2,3-dioxygenase 1 (IDO1) as an important immunometabolic target in cancer and other disease contexts. In breast cancer, IDO1 was highlighted in a network pharmacology and machine learning study of Schisandrin A, where it emerged as one of four prognosis-related core targets in triple-negative breast cancer and was also implicated in tumor immune microenvironment regulation. The same study reported high binding affinity between Schisandrin A and IDO1 in molecular docking analyses, alongside in vitro antiproliferative effects in MDA-MB-231 cells. A separate review of breast cancer immune checkpoints also emphasized IDO1 as a non-classical immune checkpoint involved in immune escape through metabolic and signaling pathways distinct from the PD-1/PD-L1 axis.

Several studies focused on direct IDO1 inhibition as a therapeutic strategy. A hierarchical virtual screening framework combined scaffold-aware machine learning, ensemble docking, consensus scoring, and molecular dynamics to prioritize potential IDO1 inhibitors from FDA-approved drugs, with the workflow designed for reproducibility and robust candidate selection. In another medicinal chemistry study, triazole analogues were developed as selective IDO1 inhibitors; the lead compound 3b showed submicromolar enzymatic potency against IDO1, strong selectivity over IDO2 and TDO, and dose-dependent suppression of kynurenine production with restoration of IL-2 signaling. This compound also induced apoptosis in HepG2 cells, with evidence supporting activation of the intrinsic mitochondrial apoptotic pathway.

IDO1 blockade was also explored in combination immunotherapy. A nanomedicine study showed that co-delivery of a STING agonist and an IDO1 inhibitor enhanced dendritic cell activation, antigen cross-presentation, cytokine secretion, and cytotoxic T lymphocyte priming, producing stronger antitumor effects than monotherapy or simple physical combination. The therapeutic benefit depended on STING signaling in host cells and type I conventional dendritic cells. In a separate triple-negative breast cancer study, copper peroxide nanoparticles were used to amplify reactive oxygen species-based photochemotherapy and immunogenic cell death; the resulting antitumor response was further strengthened by relieving IDO1-mediated immunosuppression in combination with a checkpoint inhibitor.

Beyond oncology, IDO1 was linked to immunometabolic regulation in inflammatory and neurobehavioral settings. A study of a polysaccharide from Polygonatum sibiricum reported antidepressant-like effects in a chronic restraint stress mouse model, accompanied by restoration of tryptophan metabolism through suppression of the IDO1-mediated kynurenine pathway and promotion of serotonin synthesis. Another publication described a phenolic fraction from Elsholtzia penduliflora as ameliorating influenza A virus-induced acute lung injury by inhibiting the IDO-1–mitochondria–STAT1 signaling axis, underscoring the broader relevance of IDO1 in immune and metabolic stress responses.

Key Publications

Jun Integrated Network Pharmacology and Machine Learning to Reveal the Mechanisms of Schisandrin A Against Triple-Negative Breast Cancer. (Journal of cellular and molecular medicine, 2026, PMID 42220063): "Molecular docking studies demonstrated a high binding affinity of Schisandrin A with IDO1 and PKM."
May A Reproducible Hierarchical Virtual Screening Framework Integrating Scaffold-Aware Machine Learning, Ensemble Docking, and Molecular Dynamics: Application to IDO1. (Journal of chemical information and modeling, 2026, PMID 42210816): "Indoleamine 2,3-dioxygenase 1 (IDO1) is a heme-containing enzyme implicated in cancer immune escape and remains an attractive therapeutic target despite recent clinical setbacks."
Jun Polysaccharide PSLP-1 from Polygonatum sibiricum Stems and Leaves Alleviates Depressive-like Behaviors and Modulates Gut Microbiota and Tryptophan Metabolism along the Gut-Brain Axis. (Journal of agricultural and food chemistry, 2026, PMID 42212449): "PSLP-1 was also associated with restoration of tryptophan metabolism, characterized by suppression of the indoleamine 2,3-dioxygenase 1-mediated kynurenine pathway and promotion of tryptophan hydroxylase-related 5-hydroxytryptamine synthesis."
May Metabolic enzymes and immune receptors as emerging checkpoints in breast cancer: mechanisms, clinical trials, and therapeutic implications. (Naunyn-Schmiedeberg's archives of pharmacology, 2026, PMID 42059928): "...non-classical immune checkpoints such as IDO1, IL4I1, VISTA, and TIGIT, which mediate immune escape through metabolic and signaling pathways distinct from the PD-1/PD-L1 axis."
Jun Discovery of triazole analogues as selective IDO1 inhibitors: Dual mechanistic effects on kynurenine pathway suppression and apoptosis in cancer cells. (Bioorganic chemistry, 2026, PMID 41856068): "Indoleamine 2,3-dioxygenase 1 (IDO1) is a key immunoregulatory enzyme and a prospective target for cancer immunotherapy, while triggering cell death through apoptosis is a complementary anticancer strategy."
Apr Phenolic fraction of Elsholtzia penduliflora W.W.Sm. ameliorates influenza A virus-induced acute lung injury by inhibiting the IDO-1-mitochondria-STAT1 signaling axis. (Journal of ethnopharmacology, 2026, PMID 41794257): "Phenolic fraction of Elsholtzia penduliflora W.W.Sm. ameliorates influenza A virus-induced acute lung injury by inhibiting the IDO-1-mitochondria-STAT1 signaling axis."
Apr Co-delivery of a STING agonist and indoleamine 2,3-dioxygenase 1 blockade activates type I dendritic cells in cancer. (Journal of controlled release : official journal of the Controlled Release Society, 2026, PMID 41702511): "Indoleamine 2,3-dioxygenase 1 (IDO1) has been implicated as a key resistance mechanism that undermines the antitumor effects of STING activation."
Apr Bidirectionally H2O2-suppliable and antioxidant-consumable copper peroxide nanoparticles for photochemodynamic immunotherapy. (Biomaterials, 2026, PMID 41525757): "Moreover, the dully enhanced CDT/PDT damages of the nanoparticles provoke potent immunogenic cell death that further synergizes with immune checkpoint inhibitor via relieving indoleamine 2,3-dioxygenase 1-mediated immunosuppression, thus amplifying immunotherapeutic efficacy against primary, distant and metastatic TNBCs."