Simulation Analysis of Occupancy Rates of Baicalein， Quercetin and Galangin on Target Sites of Xanthine Oxidase / 中国实验方剂学杂志

Objective:To simulate the occupancy rates of baicalein， quercetin and galangin on the target sites of xanthine oxidase <italic>in vivo</italic>. Method:In this experiment， the half inhibitory concentration （IC₅₀） of febuxostat， baicalein， quercetin and galangin against xanthine oxidase were determined by <italic>in vitro</italic> enzymatic reaction. Binding free energy was predicted by molecular docking technology and their association rate constant （k_on） and dissociation rate constant （k_off） were determined by surface plasmon resonance technology. Based on measured binding kinetic parameters （k_on and k_off） and extracted pharmacokinetic data， the target occupancy model <italic>in vivo</italic> was established. Result:The IC₅₀values of febuxostat， baicalein， quercetin and galangin were 0.002 7， 1.63， 0.38， 1.59 µmol·L^-1， respectively. The IC₅₀ of febuxostat was very close to that reported in the literature. The predicted curve of target occupancy rate <italic>in vivo</italic> of febuxostat was consistent with its duration of clinical efficacy. When single intragastric administration of long-circulating liposomes of quercetin with dose of 100 mg·kg^-1 in rats， the time of target occupancy rate >70% <italic>in vivo</italic> lasted for about 3.9 h. When rats were orally administered baicalein and galangin with dose of 200 mg·kg^-1， the time of target occupancy rate >50% <italic>in vivo </italic>lasted for about 10 h and 1.7 h， respectively. Conclusion:The prediction model of xanthine oxidase target occupancy constructed by drug target binding kinetics and <italic>in vivo</italic> pharmacokinetic curves can effectively evaluate the <italic>in vivo</italic> inhibitory activity of compounds against the target.