Structure-activity Relationship of Indomethacin Derivatives as IDO1 Inhibitors.

Background/aim Indoleamine 2,3-dioxygenase (IDO) is regarded as an important molecular target for cancer immune therapy. This study aimed to examine the IDO1 inhibitory activity of newly synthesized indomethacin derivatives to develop an IDO1 inhibitor. Materials and methods The inhibitory effects of indole-containing compounds against recombinant human IDO1 (rhIDO1) were evaluated. Results While some drugs including those with an indole scaffold could inhibit rhIDO1, simple indole compounds were inactive. A total of 27 indomethacin derivatives, including 18 newly synthesized derivatives, were evaluated. Numerous derivatives showed enhanced IDO1 inhibitory activity. The functional group at the 3-position had a strong effect on IDO1 inhibitory activity. The IDO1 inhibitory activity was not directly correlated with tumor cell cytotoxicity. Conclusion We report the finding of novel IDO1 inhibitors and the structure-activity relationship based on indomethacin derivatives. Our findings will be beneficial for the development of IDO1 inhibitors for cancer immune therapy.