CHEMBL5733269

Enzymatic IDO Assay: The IC50 values for each compound were determined by testing the activity of IDO in a mixture containing 50 mM potassium phosphate buffer at pH 6.5; 70 nM purified human IDO protein, 200 μM L-tryptophan, 20 mM ascorbate, 20 μM methylene blue, 0.1% DMSO. The inhibitors were initially diluted in DMSO at 100 mM and were diluted in potassium phosphate 50 mM, added to the reaction mixture at final concentrations raging from 1 mM to 5 nM and preincubated with the enzyme for 5 min at 25° C. The reaction was started by addition of L-tryptophan to 200 μM and incubated 15 min at 37° C. The reaction was stopped by addition of 0.5 vol of 30% trichloroacetic acid and incubated 30 min at 60° C. to hydrolyze N-formylkynurenine to kynurenine. The reaction was centrifuged at 3400 g for 5 min to remove precipitated protein and the supernatant was reacted with 2% (w/v) of p-dimethylaminobenzaldehyde in acetic acid. The reaction was incubated 10 min at 25° C. and read at 480 nm in a spectrophotometer. Control samples with no IDO inhibitor, or with no IDO enzyme or with the reference inhibitors 1-methyl-tryptophan (200 μM) and menadione (1.2 μM) were used as controls to set the parameters for the non-linear regressions necessary for determination of the IC50 for each compound. Nonlinear regressions and determination of the IC50 values were performed using the GraphPad Prism 4 software. Compounds with an IC50 of less than 500 μM were considered as active inhibitors in this assay.