Abstract: Indoleamine 2,3-dioxygenase 1 (IDO1) plays a key role in cancer immunity,the aim of this study was to discover new IDO1 inhibitors.The inhibitor screening model of indoleamine 2,3-dioxygenase 1 (IDO1) was established by using HeLa cell line,and two small molecule compounds inhibit IDO1 activity were screened out.Interferon-γ (IFN-γ) was added to induce the expression of IDO1 in HeLa cells seeded in 48-well plates,to reflect the enzymatic activity of IDO1 secreted by HeLa cells.Screening of the compound library revealed that daphnetin and an oxazole compound ZH-26 inhibited IDO1 activity,and the IC₅₀ values of daphnetin and ZH-26 were analyzed using GraphPad Prism software.The IC₅₀ of daphnetin was 16.50±0.33 μM,and the IC₅₀ of ZH-26 was 4.68±0.21 μM.In addition,the inhibitory effects on IDO1 activity which was overexpressed in HEK-293A cells were also observed after treatment with different concentrations of daphnetin and ZH-26.Western blot assay showed that daphnetin significantly down-regulated the expression of IDO1 induced by IFN-γ whereas ZH-26 had no such effect.Daphnetin and ZH-26 did not show obvious cytotoxic effect in HeLa cells.In conclusion,daphnetin and ZH-26 were firstly found to inhibit IDO1 activity in this study,which not only provided new insight into the understanding of anti-tumor effect of daphnetin,but also warranted further development of both compounds as new drug candidates for tumor immunotherapy by targeting IDO1.

Key words: indoleamine 2,3-dioxygenase 1, screen, daphnetin, oxazoles