Epacadostat (INCB024360) is an orally available hydroxyamidine and inhibitor of indoleamine 2,3- dioxygenase (IDO1), with an IC₅₀ of 10 nM. It shows little activity against other related enzymes such as IDO2 or tryptophan 2,3-dioxygenase (TDO). Epacadostat displays potential immunomodulating and antineoplastic activities.