epacadostat epacadostat epacadostat (previously incb24360) is an investigational drug for cancer. epacadostat is an inhibitor of indoleamine 2,3-dioxygenase-1 (ido1). epacadostat inhibits ido1 by competitively blocking it, without interfering with ido2 or tryptophan 2,3-dioxygenase (tdo). it has antitumor activity in some models, though is most effective when combined with other immunotherapy agents. epacadostatclinical dataatc codel01xx58 (who) identifiers iupac name n-(3-bromo-4-fluorophenyl)-n′-hydroxy-4--1,2,5-oxadiazole-3-carboximidamide cas number1204669-58-8drugbankdb11717chemspider34448418unii71596a9r13keggd11049chemical and physical dataformulac11h13brfn7o4smolar mass438.23 g·mol−13d model (jsmol)interactive image smiles c1cc(c(cc1n/c(=n\o)/c2c(non2)nccns(=o)(=o)n)br)f inchi inchi=1s/c11h13brfn7o4s/c12-7-5-6(1-2-8(7)13)17-11(18-21)9-10(20-24-19-9)15-3-4-16-25(14,22)23/h1-2,5,16,21h,3-4h2,(h,15,20)(h,17,18)(h2,14,22,23)key:fbkmwojepmpvtq-uhfffaoysa-n history and clinical trials as of 2017, the combination of epacadostat with pembrolizumab (keytruda) was being investigated by incyte and merck & co. in several cancers, as was the combination of epacadostat with nivolumab (opdivo) by incyte and bristol myers squibb. in april 2018, incyte announced they were halting the phase iii echo-301/keynote-252 (nct02752074) trial of epacadostat with pembrolizumab for melanoma as the combination therapy missed the first primary endpoint of improving progression-free survival vs. pembrolizumab alone. the second primary endpoint of overall survival is not yet determined.