Design, Synthesis, and Biological Evaluation of Novel Hydroxyamidine Derivatives as Indoleamine 2,3-Dioxygenase 1 Inhibitors

Indoleamine 2,3-dioxygenase 1 (IDO1) is a rate-limiting enzyme that catalyzes the conversion of tryptophan into kynurenine and represents a potential target for tumor immunotherapy. In this study, we designed and synthesized a series of <i>N</i>'-hydroxyamidine analogues through pharmacophore fusion and bioisosterism principles. The results indicated that compounds I-1 and I-2 exhibited activity similar to that of Epacadostat in inhibiting recombinant hIDO1 and hIDO1 expression in HeLa cells. Moreover, the compounds not only effectively stimulated T cell proliferation but also inhibited the proliferation of Lewis Lung Carcinoma cells. RNA sequencing analysis indicated that these compounds primarily exert immunotherapeutic effects. Surface plasmon resonance and molecular docking confirmed the interactions between the compounds and IDO1. The physicochemical properties along with pharmacokinetic profiles of both compounds were also predicted, and they were found to possess favorable characteristics. The active compounds developed in this research may serve as valuable references for discovering highly effective IDO1 inhibitors.