A Phase II Study to Determine the Safety and Efficacy of the Oral Inhibitor of Indoleamine 2,3-Dioxygenase (IDO) Enzyme INCB024360 in Patients with Myelodysplastic Syndromes

Clin Lymphoma Myeloma Leuk. 2019 Mar;19(3):157-161. doi: 10.1016/j.clml.2018.12.005. Epub 2018 Dec 20.


Background: INCB024360 is an oral inhibitor of the enzyme indoleamine 2,3-dioxygenase (IDO), which catalyzes the degradation of tryptophan to kynurenine. Preclinical data suggest that IDO1 inhibition by INCB024360 will increase T cell proliferation, and decrease T regulatory cells and myeloid derived suppressor cells suppressive activity. We conducted a phase II study to explore activity and pharmacodynamics of INCB024360 in patients with myelodysplastic syndromes.

Patients and methods: All patients were treated with INCB024360 600 mg orally twice a day for at least 16 weeks. Fifteen patients were enrolled. The median age was 72 years. The International Prognostic Scoring System risk was low in 27% (n = 4), intermediate-1 in 47% (n = 7), and intermediate-2 in 27% (n = 4). All patients had prior azacitidine.

Results: The best response was stable disease in 12 (80%) patients and progressive disease in 3 (20%) patients. The treatment was relatively well-tolerated. One patient developed hypothyroidism and adrenal insufficiency (grade 2), and 1 patient had low testosterone level. The mean IDO expression was 39% at baseline and 26% after treatment (n = 9; P = .4). The mean burst forming unit-erythroid changed from 72 to 191 colonies/106 (n = 5; P = .036), and the mean colony forming unit-granulocye, monocyte from 62 to 180 colonies/106 (n = 6; P = .5). The mean myeloid derived suppressor cell % (CD33Lin-HLA cells) was 29.5% at baseline compared with 27.6% after treatment (n = 9; P = .7). The mean T-regulatory effector memory cell % changed from 9.6% at screening to 7.4% at end of treatment (n = 14; P = .8). The mean kynurenine/tryptophan ratio decreased from 45 at baseline to 26 (42% reduction) at cycle 2, day 1 (P < .005).

Conclusion: Future directions may include testing INCB024360 early in the course of the disease.

Keywords: Hypomethyalting agents failure; Immune; Innate immunity; MDSC; T reg cells.

Publication types

  • Clinical Trial, Phase II
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Oral
  • Aged
  • Female
  • Humans
  • Indoleamine-Pyrrole 2,3,-Dioxygenase / pharmacology
  • Indoleamine-Pyrrole 2,3,-Dioxygenase / therapeutic use*
  • Male
  • Myelodysplastic Syndromes


  • Indoleamine-Pyrrole 2,3,-Dioxygenase