Indoleamine 2,3-dioxygenase 1
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.