Prediction of hepatic clearance in human from in vitro data for successful drug development

Abstract

The in vivo metabolic clearance in human has been successfully predicted by using in vitro data of metabolic stability in cryopreserved preparations of human hepatocytes. In the predictions by human hepatocytes, the systematic underpredictions of in vivo clearance have been commonly observed among different datasets. The regression-based scaling factor for the in vitro-to-in vivo extrapolation has mitigated discrepancy between in vitro prediction and in vivo observation. In addition to the elimination by metabolic degradation, the important roles of transporter-mediated hepatic uptake and canalicular excretion have been increasingly recognized as a rate-determining step in the hepatic clearance. It has been, therefore, proposed that the in vitro assessment should allow the evaluation of clearances for both transporter(s)-mediated uptake/excretion and metabolic degradation. This review first outlines the limited ability of subcellular fractions such as liver microsomes to predict hepatic clearance in vivo. It highlights the advantages of cryopreserved human hepatocytes as one of the versatile in vitro systems for the prediction of in vivo metabolic clearance in human at the early development stage. The following section discusses the mechanisms underlying the systematic underprediction of in vivo intrinsic clearance by hepatocytes. It leads to the proposal for the assessment of hepatic uptake clearance as one of the kinetically important determinants for accurate predictions of hepatic clearance in human. The judicious combination of advanced technologies and understandings for the drug disposition allows us to rationally optimize new chemical entities to the drug candidate with higher probability of success during the clinical development.

Fig. 1

Interindividual variation of metabolic clearance among cryopreserved human hepatocytes and an empirical scaling factor for the quantitative prediction. Data are from (27)

Fig. 2

Correlation of metabolic clearance between in vitro and in vivo among cryopreserved hepatocytes from different donors

Fig. 3

Comparison between liver microsomes and hepatocytes for the metabolic stability screening at discovery stage

Fig. 4

Comparison of predicted and observed oral clearance in First-in-Human (FIH) studies. Numbers are corresponding to those compounds in Table I

Fig. 5

Correlation between in vivo intrinsic clearance and in vitro metabolic clearance for 25 drugs in human. Data are taken from (26)

Fig. 6

Accuracy of prediction for the hepatic clearance in human from in vitro metabolic clearance with or without incorporating unbound fractions. Data in the shaded area are considered to be successful (0.5 < fold error < 2). Data are taken from (19)

Fig. 7

Effects of intrinsic clearance (CL_int) on hepatic clearance (CL_H; a) and oral clearance (CL_oral; b) in various mathematical models. Simulations were carried out by “well-stirred” model (Eq. 10), “parallel-tube” model (Eq. 11) and “dispersion” model (Eq. 2). The values of Q _H, f _B, and D _N are 21 (mL/min/kg), 1.0, and 0.17, respectively. The value of CL_oral was calculated from CL_H and F_H (Eq. 3) based on the Eq. 5, assuming

Fig. 8

Ratio of intrinsic clearance for unbound drugs calculated from plasma clearance in rat (CL_{int, ub, in vivo}) to that determined in the incubation with isolated rat hepatocytes (CL_{int, ub, in vitro}). Calculations of in vitro intrinsic clearance (CL_{int, ub, in vitro}) were based on (1) the initial disappearance rate in whole suspension [conventional method] (filled circles, with average ratio = 57, dotted line), (2) the AUC in the medium (filled triangles, with average ratio = 16) and (3) the initial disappearance rate in the media (empty circles, with average ratio = 3, solid line) in the isolated rat hepatocytes. Data are taken from (135)

Fig. 9

Lead optimization for the successful development candidate by the predictions of hepatic and oral clearance in human. Future workflow for the incorporation of transporter-mediated hepatic uptake into the optimization strategy is shown by dotted lines