Protein / target

Indoleamine 2,3-dioxygenase 1

Encoded byIDO1P14902Homo sapiensSwiss-Prot

UniProt: P14902 Ensembl: ENSG00000131203 HGNC: HGNC:6059 NCBI Gene: 3620

Clinically validated

Therapeutic maturity

Approved medicines

Open Targets target-level

Small-molecule tractable

Druggability

Advanced Clinical

Research papers

Protein at a glance

Biological role

L-tryptophan 2,3-dioxygenase

Strongest disease association

Neoplasms

Via encoding gene IDO1 · Literature evidence · score 0.42

Therapeutic position

Established drug target

Small molecules

Research activity

Emerging research

11 papers · latest 2025

Derived from structured UniProt, Open Targets and literature data on this page.

Protein profile

UniProt 2026_02

Canonical identity and biological annotation from UniProt.

Function overview

Catalyzes the first and rate limiting step of the catabolism of the essential amino acid tryptophan along the kynurenine pathway.

View complete UniProt function annotation

Catalyzes the first and rate limiting step of the catabolism of the essential amino acid tryptophan along the kynurenine pathway (PubMed:17671174, PubMed:18026683). Involved in the peripheral immune tolerance, contributing to maintain homeostasis by preventing autoimmunity or immunopathology that would result from uncontrolled and overreacting immune responses (PubMed:25691885). Tryptophan shortage inhibits T lymphocytes division and accumulation of tryptophan catabolites induces T-cell apoptosis and differentiation of regulatory T-cells (PubMed:25691885). Acts as a suppressor of anti-tumor immunity (PubMed:14502282, PubMed:23103127, PubMed:25157255, PubMed:25691885). Limits the growth of intracellular pathogens by depriving tryptophan (PubMed:25691885). Protects the fetus from maternal immune rejection (PubMed:25691885)

Subcellular location

Cytoplasm, cytosol

Domains and Gene Ontology detail (16)

Gene Ontology

Ccytoplasm
Ccytosol
Csmooth muscle contractile fiber
Cstereocilium bundle
Felectron transfer activity
Fheme binding
Findoleamine 2,3-dioxygenase activity
FL-tryptophan 2,3-dioxygenase activity
Fmetal ion binding
P'de novo' NAD+ biosynthetic process from L-tryptophan
Pfemale pregnancy
Pimmune system process

403 aa · 45 kDa

Biological roles

What this protein does, drawn together from its UniProt function, Gene Ontology terms and Reactome pathways.

Immune signallingUniProt · GO

View supporting evidence

Immune signalling

·Catalyzes the first and rate limiting step of the catabolism of the essential amino acid…
·positive regulation of T cell apoptotic process

Concepts derived from UniProt GO Reactome — each badge above shows which sources supported that role.

Translational evidence

Open Targets 26

Why this target matters therapeutically, strongest evidence first. Disease associations are gene-level (via the gene that encodes this protein) and open into the full confidence synthesis; the development universe, tractability and safety annotations are target-level, from Open Targets.

Strongest disease associations · via encoding gene IDO1

Gene-level evidence surfaced through the gene IDO1that encodes this protein — not a direct protein–disease relationship. Ranked by Forefront's causal-directness weighting, so genetically- and clinically-evidenced diseases lead over ones that merely share the literature.

Neoplasms

0.56Moderately supported

Clinical evidence dominant · Open Targets 0.42

Melanoma

0.53Moderately supported

Clinical evidence dominant · Open Targets 0.39

Squamous Cell Carcinoma of Head and Neck

0.52Moderately supported

Clinical evidence dominant · Open Targets 0.39

Carcinoma, Non-Small-Cell Lung

0.50Moderately supported

Clinical evidence dominant · Open Targets 0.37

Carcinoma, Renal Cell

0.41Limited support

Clinical evidence dominant · Open Targets 0.30

View evidence synthesis (5)

NeoplasmsModerately supported

0.56

agreement 0.40–0.71

Clinical76%Literature24%

Open Targets aggregate 0.42 · 2 independent evidence families

MelanomaModerately supported

0.53

agreement 0.37–0.68

Clinical76%Literature24%

Open Targets aggregate 0.39 · 2 independent evidence families

Squamous Cell Carcinoma of Head and NeckModerately supported

0.52

agreement 0.36–0.68

Clinical77%Literature23%

Open Targets aggregate 0.39 · 2 independent evidence families

Carcinoma, Non-Small-Cell LungModerately supported

0.50

agreement 0.35–0.66

Clinical76%Literature25%

Open Targets aggregate 0.37 · 2 independent evidence families

Carcinoma, Renal CellLimited support

0.41

agreement 0.26–0.57

Clinical75%Literature25%

Open Targets aggregate 0.30 · 2 independent evidence families

The evidence agreement range shows how closely the independent evidence families agree — it is not a statistical confidence interval, and nothing here is fitted to outcome data. Derived from Open Targets evidence types under Forefront weighting; the per-type scores above show the calculation.

Show all associations

Neoplasms0.42

Melanoma0.39

Squamous Cell Carcinoma of Head and Neck0.39

Carcinoma, Non-Small-Cell Lung0.37

Urothelial carcinoma0.33

Carcinoma, Renal Cell0.30

Glioblastoma0.14

Drug development

2 compounds recorded · 1 approved · 1 in clinical development

Open Targets' development universe — every compound recorded against the target at any stage, not all approved medicines.

View all recorded compounds (2)

LINRODOSTATPhase 3

EPACADOSTATApproval

Open Targets known-drugs universe. Drug name and highest clinical stage only — the disease relationship is NOT read from this slice (it carries trial-context noise); approved indications come from the canonical graph above.

Tractability

Small molecules — Strong

Advanced Clinical and Structure with Ligand support this modality.

Protein degraders — Emerging

Feasibility evidence (literature and small molecule binder) — no clinical-stage drug of this modality recorded.

View underlying tractability evidence (7)

SM · Advanced ClinicalSM · Structure with LigandSM · High-Quality LigandSM · High-Quality PocketSM · Druggable FamilyPR · LiteraturePR · Small Molecule Binder

Raw Open Targets tractability assessment buckets, by modality.

Safety-related annotations

moderate or severe depressionClinPGx

Terms indexed against this target in Open Targets' safety data, with their datasource. These are annotations, not causal claims: the direction of effect (whether activation or inhibition is implicated), species and evidence strength are not captured here, so an entry does not mean that modulating this target is known to cause that condition.