The ability to predict in vivo hepatic clearance accurately is important in understanding potential clinical exposure and half-life as well as establishing dosage regimens. It is a common goal of drug discovery projects to reduce the clearance in order to improve exposure and reduce dose. Progress in optimising DMPK properties together with the chemical space occupied by some new drug targets has resulted in an increase in the number of metabolically stable compounds being encountered in drug discovery.
Low clearance (or metabolically stable) compounds present a particular challenge as it can be difficult to predict accurately the in vivo half-life using standard in vitro suspension methods. This can lead to the under-prediction of half-life. In fact, there have been a few instances where a half-life has originally been predicted by in vitro assessment to be a few days whereas in reality, once in the clinic, the half-life has been found to be much longer.
The standard approach for determining in vitro clearance involves incubating hepatocytes in suspension with the compound and measuring parent compound disappearance with time. However, prolonged incubation times, required for the accurate determination of in vitro intrinsic clearance of metabolically stable compounds, are restricted in suspension incubations due to decreases in drug metabolising enzyme activity and cell viability. To address this issue, novel methods are being developed to allow extended incubation periods.
Cyprotex’s parent company, Evotec, have recently developed an in vitro method, which utilises plated primary human hepatocytes and matrix overlay, allowing the time course to be extended for up to 5 days. The data generated using this approach is comparable with other ‘low clearance’ methods reported in the literature. Furthermore, a strong correlation is observed with in vivo human intrinsic clearance demonstrating the clear benefits of this approach.
Find out more about our low clearance method