In vitro activity: Epacadostat (formerly known as INCB024360 or INCB24360) is an orally available, potent and selective IDO1 inhibitor with IC50 of 10 nM. Epacadostat has potential immunomodulating and antineoplastic activities. By inhibiting IDO1 and decreasing kynurenine in tumor cells, Epacadostat increases and restores the proliferation and activation of various immune cells, including dendritic cells, NK cells, T-cells, and a reduction in tumor-associated regulatory T cells. Epacadostat was under investigation in a phase 3 clinical trial. But according to the results presented at the 2018 ASCO Annual Meeting, in patients with unresectable or metastatic melanoma, adding epacadostat to pembrolizumab (Keytruda) did not result in greater clinical benefit over pembrolizumab alone, according to data from the phase III ECHO-301/KEYNOTE-252 study. In IFN-γ–treated human HeLa cells, INCB024360 potently inhibits kynurenine production. INCB024360 also promotes T and natural killer (NK)-cell growth, increases IFN-gamma production, and reduces conversion to regulatory T (T(reg))-like cells. [1]

Kinase Assay: Epacadostat (formerly known as INCB024360 or INCB24360) is an orally available, potent and selective IDO1 inhibitor with IC50 of 10 nM.

Cell Assay: In Hela cells, INCB024360 selectively inhibits the activity of human IDO1 with IC50 values of about 10nM. On the other hand INCB024360demonstrates little inhibition activity against human IDO1 or TDO (tryptophan 2, 3-dioxygenase). In coculture systems of human dendritic cells with allogeneic lymphocytes, INCB024360 inhibit T-cell proliferation and cytokine production and influence the viability of NK cells. INCB024360 also increase CD86 expression and promote activation T cells by DCs.

#1: INCB024360 (100 mg/kg, p.o.), via IDO1 inhibition, suppresses kyn generation and tumor growth in immunocompetent, but not immunodeficient, mice. In mice bearing CT26 colon carcinoma, INCB024360 (100 mg/kg, p.o.) also inhibits the growth of IDO-expressing tumors by reducing kynurenine. [2]

#2: For the WT C57BL/6J mice, treatment started at the same time when MLL/AF9 cells were transplanted. For the patient-derived AML cells (PDX) transplanted into NSG mice, treatment started eight weeks after transplant, at the same time as Ara-C and during three weeks. Mice were supplied with ad libitum epacadostat-supplemented diet (Research Diets Inc.) at 800 mg/kg (low dose) or 1.6 g/kg (high dose). For the PDX transplanted into NSGS mice, treatment started three weeks after transplant, by daily gavage at 300 mg/kg (InvivoChem, catalog no. V0942, dissolved in 10% DMSO, 40% PEG 300, and 50% NaCl 0.9%) for two weeks. [3]

#1: Dissolved in 3% N,N–Dimethylacetamide, 10% (2-Hydroxypropyl) β-Cyclodextrin; 100 mg/kg; p.o. administration;

#2: Dissolved in 10% DMSO, 40% PEG 300, and 50% NaCl 0.9% [3]