To study the cellular hIDO2 inhibition of candidate compounds, recombinant plasmid pcDNA3.1(+)-hIDO2 is constructed and transfected into human glioblastoma U87 MG cells which had no IDO1 expression (confirmed by RT-PCR and western blot) therefore eliminated the interference of IDO1. U87 MG cells are cultivated in DMEM containing 50 U/mL penicillin, 50 mg/mL streptomycin, 4500 mg/L glucose, and 10% inactivated FBS at 37°C with 5% CO₂ and 95% humidity. When a cell density of 80% confluent monolayer is reached, U87 MG cells are transfected with pcDNA3.1(+)-hIDO2 using the transfection reagent Lipofectamine 2000 according to the manufacturer's instructions. An empty pcDNA3.1(+) expression vector is served as control. After 18 h of incubation, the transfected cells are seeded in 96-well culture plates at a density of 2.5×10⁴ cells/well in a final volume of 200 μL supplemented with 200 μM L-Trp. A serial dilution of the tested compounds is added to the culture medium after an additional 6 h of incubation. The reaction is terminated by addition of 30% (w/v) trichloroacetic acid (10 μL for 140 μL of the reaction mixture) 24 h later. The plates are incubated at 65°C in water bath for 15 min to facilitate the transformation of N-formylkynurenine to L-kynurenine, followed by centrifugation at 13,000× g for 10 min to remove the sediments. 100 μL of the supernatant are then transferred to another 96-well plate and mixed with a same volume of 2% (w/v) 4-dimethylaminobenzaldehyde in acetic acid. The percentages of inhibition of tryptophan degradation or kynurenine production by the compounds are calculated by measuring the absorption at 492 nm using a microplate reader. Cellular IC₅₀s are determined via non-linear regression analysis using GraphPad Prism 5.0^[1].

MCE has not independently confirmed the accuracy of these methods. They are for reference only.

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