Indoximod (Indoximod (NLG-8189)) is a methylated tryptophan with immune checkpoint inhibitory activity. Indoximod inhibits the enzyme indoleamine 2, 3-dioxygenase (IDO), which degrades the essential amino acid tryptophan, and may increase or maintain tryptophan levels important to T cell function. Tryptophan depletion is associated with immunosuppression involving T cell arrest and anergy.

(S)-Indoximod (L-Abrine) exhibits inhibition of rabbit small intestine indoleamine 2, 3-dioxygenase, competitive inhibition of IDO, reduction of Foxp3 protein expression in tumor of C57BL/6 mouse allografted with mouse LLC cells at 200 mg/kg, induction of IDO1 protein expression in tumor of C57BL/6 mouse allografted with mouse LLC cells at 200 mg/kg, antitumor activity against mouse LLC cells allografted in C57BL/6 mouse, antiproliferative activity against mouse LLC cells at 50 uM.

(Rac)-Indoximod (1-Methyl-DL-tryptophan) is a potent inhibitor of indoleamine 2,3-dioxygenase (IDO). Combined treatment with IFN-γ and (Rac)-Indoximod significantly suppresses the activity of α-SMA-expressing human cardiac myofibroblasts (hCMs) and promotes apoptosis by up-regulating the genes IRF-1, Fas, and FasL. Moreover, this co-treatment effectively improves cardiac fibrosis[1].