Utility of hepatocellular systems to measure drug transport and metabolism for prediction of in vivo drug clearance

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Abstract

Predictive pharmacokinetics now forms a critical part of the drug discovery process. However, metabolic data has been demonstrated to under-predict in vivo clearance, while no large scale analysis has been performed for hepatic uptake data. The primary aim of this thesis was therefore to investigate the utility of various clearance parameters generated in hepatocellular assays for the prediction of in vivo clearance. Large scale literature analyses were performed for uptake data in both rat and human hepatocytes. In the rat, it was highlighted that over-prediction was the predominant issue for suspension and media loss hepatocyte assays. Conversely, monolayer and SCH assays suffered from under-prediction. However, in human hepatocytes under-prediction was observed in all assay formats. Use of empirical scaling factors improved predictions in both species, and are recommended for future use. The media loss assay, a method described by Soars et al[1], was further developed in rat hepatocytes through inclusion of transporter and metabolic enzyme inhibitors. Using a two-compartment model, individual clearance parameters (CLmet, CLactive and CLpassive) were estimated, and were also used to estimate binding and partitioning terms (Kp, Kpu and fucell). IVIVE of data produced from this assay resulted in a lower bias than had been noted from literature data. However, it was hypothesised that additional clearance parameters could be used in a mechanistic approach to further improve predictions. SCH assays were performed to generate estimates of uptake rates, as well as efflux rates from both the sinusoidal and canalicular membranes. Combining clearance terms from both the media loss and SCH assays using the CLint,total term led to less bias when predicting in vivo clearance than observed using uptake or metabolism data alone. Additionally, the use of empirical scaling factors identified from the literature analysis led to further reduction in prediction bias. Future work must now focus on the application of this research to human hepatocytes. It is concluded that the work presented in this thesis provides evidence for the usefulness of both uptake and extended clearance terms, in conjunction with empirical scaling methods, for the prediction of in vivo clearance. Adaptation of the media loss assay allowed the estimation of several key pharmacokinetic parameters. Although some of these are not always useful in a quantitative fashion, they remain essential properties of a compound that must be considered when predicting behaviour within the body.

Keyword(s)

Hepatocytes; In vivo prediction; Pharmacokinetics

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