Prediction of the pharmacokinetics and pharmacodynamics of topiroxostat in humans by integrating the physiologically based pharmacokinetic model with the drug-target residence time model

Topiroxostat is a selective xanthine oxidoreductase (XOR) inhibitor for the management of hyperuricemia in patients with or without gout. In this work, we aim to employ the physiologically based pharmacokinetic (PBPK) model with the drug-target residence time model to predict and characterize both the pharmacokinetics (PK) and pharmacodynamics (PD) of topiroxostat in humans. The plasma concentration-time profile of topiroxostat was simulated based on drug properties and human physiology parameters. The predictive power of this PBPK model was then demonstrated by comparison of stimulated to observed pharmacokinetic parameters. The utility of the model was further demonstrated through predicting the oral absorption and disposition characteristics of topiroxostat in humans. Finally, by combining the PBPK model and the drug-target residence time model, we successfully predicted the target occupancy and built the relationship between PK and PD using in vitro, in vivo and in silico information. The results showed that topiroxostat exhibited significant in vivo pharmacological activity even after the complete clearance of this drug from the liver (target site), which may be due to the long residence time of the binary topiroxostat-XOR complex. This work may be helpful to guide future investigations of topiroxostat and also provides a novel strategy for PK/PD studies.