Panoply™ Human IDO1 Over-expressing Stable Cell Line

Indoleamine 2,3-dioxygenase (IDO1) plays a crucial regulatory role in immunosuppression by catalyzing the oxidation of L-tryptophan. IDO1 expression is associated with poor prognosis in various cancers and resistance to immune checkpoint therapies. Here, researchers characterized a novel small-molecule IDO1 inhibitor, NTRC 3883-0, using a series of biochemical and cellular experiments and various cancer models. In a co-culture system of IDO1-overexpressing cells and healthy donor lymphocytes, NTRC 3883-0 deactivated the inhibitory effect of IDO1 on CD8-positive T cell proliferation, demonstrating its immunomodulatory activity. In a homologous mouse model constructed using IDO1-overexpressing B16F10 melanoma cells, NTRC 3883-0 effectively antagonized IDO1-induced changes in L-tryptophan and L-kynurenine levels, confirming its in vivo target-regulated effects. Furthermore, researchers investigated the expression and activity of IDO1 in primary cell cultures established from malignant ascites fluid from ovarian cancer patients. In these cultures, IFNγ stimulation induced IDO1 expression, and its activity was inhibited by NTRC 3883-0.

To determine whether NTRC 3883-0 could modulate immune cell activity in vitro, researchers conducted a co-culture experiment of human IDO1-overexpressing HEK293 cells (HEK-hIDO1) cells with healthy donor peripheral blood mononuclear cells (PBMCs) (Figure 1). Cytotoxic T cell proliferation was detected by labeling PBMCs with carboxyfluorescein succinimide (CFSE), a fluorescent dye that dilutes during cell proliferation, followed by flow cytometry analysis of CD8-positive T cells. When CD8-positive T cells were co-cultured with HEK-hIDO1 cells in a medium containing 7.5 µM Trp, their proliferation ceased (Figure 1A). When a high concentration of Trp (200 µM) was added to the medium co-cultured with HEK-hIDO1 cells, CD8-positive T cells continued to proliferate (Figure 1A). This indicates that the inhibitory effect of IDO1 is caused by Trp consumption, rather than by the production of immunosuppressive metabolites. Under low Trp conditions, the addition of 10 µM NTRC 3883-0 to the co-culture system of HEK-hIDO1 cells and PBMCs relieved the inhibitory effect of IDO1 expression on T cell proliferation (Figure 1B), and the effect was similar to that of treatment with 1 µM epacadostat (Figure 1C). This indicates that NTRC 3883-0 can regulate immune cell function.

Figure 1. Co-culture assays of HEK-hIDO1 cells with lymphocytes from a healthy donor. (Grobben Y, et al., 2021)