On-line screening of indoleamine 2,3-dioxygenase 1 inhibitors by partial filling capillary electrophoresis combined with rapid polarity switching

•Fast screening of indoleamine 2,3-dioxygenase 1 inhibitors in natural products.•On-line enzymatic incubation integrated with capillary electrophoresis.•Partial filling of the capillary combined with rapid polarity switching. Indoleamine 2,3-dioxygenase 1 (IDO1) has been shown to play an important role in the immune escape process of tumors, and therefore is considered as a promising target for tumor immunotherapy. In this study, off-line and on-line capillary electrophoresis methods were developed for IDO1 inhibitors screening from natural product extracts. The optimized separation conditions of CE were achieved with 32 mM sodium tetraborate (pH 9.22) as background electrolyte, using a separation voltage of 21 kV. The off-line CE method was verified by the determination of enzymatic kinetic parameters and inhibitory mechanisms of two known inhibitors. A partial filling on-line CE method combined with rapid polarity switching was used for rapid screening of IDO1 inhibitors. The whole reaction and separation process was completed within 5 min. The on-line CE screening results showed that six of 18 natural products had inhibitory effect on IDO1, namely Carthamus tinctorius, Schisandra chinensis, Raisin, Coffee, Hawthorn and Radix angelicae sinensis. The results of on-line CE experiments were consistent with the off-line results, which proved the practicability and effectiveness of the method for inhibitors screening.