Indoleamine-2,3-Dioxygenase 1 Enzyme Inhibition: A Useful Target to Screen Chemicals for their Therapeutic Potential

Indoleamine 2,3-dioxygenase 1 (IDO1) is a key immunoregulatory enzyme that catalyzes the oxidative cleavage of L-tryptophan to N-formyl kynurenine, playing a critical role in immune tolerance and various pathological conditions, including cancer, autoimmune diseases, cataractogenesis, and neurodegenerative disorders. In this study, molecular docking was performed using a phytochemical library to identify compounds with strong binding affinity and favorable interactions within the IDO1 active site. Based on these in silico findings, selected compounds were further evaluated using a newly developed and cost-effective optimized fluorescence-based assay employing lens homogenate enzyme preparations to quantitatively assess IDO1 activity. Dose–response experiments revealed that several phytochemicals exhibited significant concentration-dependent inhibition of IDO1, with promising IC₅₀ values. The consistency between docking results and experimental inhibition supports the potential of these compounds as IDO1 inhibitors. This integrated in silico–in vitro approach provides a reliable platform for screening IDO1 modulators and identifies promising natural inhibitors for further development as therapeutics for IDO1-associated diseases.