Figure 3. In vitro activities of IDO1-specific inhibitor (NLG919). (A) Molecular structural formula of NLG919, a highly selective inhibitor of IDO1. (B) NLG919 inhibited IDO1 enzyme activity in vitro. The 4T1 cells were treated with IFN-γ together with different concentrations of NLG919. Kyn level in supernatant was measured 2 days later using high performance liquid chromatography mass spectrometry. The 4T1 cells treated only with IFN-γ were set as blank control. (C) IDO1 inhibition reversed T-cell suppression mediated by IDO-expressing murine breast cancer cells (4T1). The 4T1 cells and splenocytes were co-cultured, and then, treated with IL-2, anti-CD3 antibody, and IFN-γ together with NLG919 for 3 days. The proliferation of CD8⁺ T cells was examined by fluorescence-activated cell sorting analysis.

Data represent means ± standard deviation.

IDO1 = indoleamine 2,3-dioxygenase 1; Kyn = kynurenine; IL = interleukin; IFN = interferon.

^*p < 0.05; ^†p < 0.01 (versus control).