Using Quantitative Systems Toxicology to Investigate Observed Species Differences in CKA-Mediated Hepatotoxicity

Abstract

CKA, a chemokine receptor antagonist intended for treating inflammatory conditions, produced dose-dependent hepatotoxicity in rats but advanced into the clinic where single doses of CKA up to 600 mg appeared safe in humans. Because existing toxicological platforms used during drug development are not perfectly predictive, a quantitative systems toxicology model investigated the hepatotoxic potential of CKA in humans and rats through in vitro assessments of CKA on mitochondrial respiration, oxidative stress, and bile acid transporters. DILIsym predicted that single doses of CKA caused serum ALT >3xULN in a subset of the simulated rat population, while single doses in a simulated human population did not produce serum ALT elevations. Species differences were largely attributed to differences in liver exposure, but increased sensitivity to inhibition of mitochondrial respiration in the rat also contributed. We conclude that mechanistic modeling can elucidate species differences in the hepatotoxic potential of drug candidates.

Figure 1.

CKA chemical structure and physiologically based pharmacokinetic (PBPK) model diagram and results. A, Chemical structure of CKA. B, Schematic diagram representing the PBPK model consisting of blood, gut, liver, muscle, and other tissue compartments. PBPK results for (C) humans and (D) rats. Dark lines represent observed plasma concentrations of CKA. Light lines represent predicted plasma concentrations of CKA based on the PBPK model. Human simulations were run for 96 h, rat simulations for 72 h. The horizontal axis is cropped to provide greater detail during the initial increase in plasma concentration.

Figure 2.

Oxygen consumption rate (OCR) and oxidative stress measurements in response to CKA treatment. Observed and simulated percentage changes in (A) OCR and (B) oxidative stress in CKA-treated cells compared with vehicle control. In vitro respiration data were obtained from HepG2 cells incubated with CKA and measured using the Seahorse XF instrument. Simulated OCR responses were generated using MITOsym with the electron transport chain (ETC) inhibition parameter value optimized to the measured data. Oxidative stress data were obtained from HepG2 cells treated with CKA and measured using fluorescent imaging. Simulated oxidative stress responses were generated using DILIsym with the ROS production constant value optimized to the measured data.

Figure 3.

Simulated and observed peak alanine transaminase (ALT) levels in rats administered 50, 200, or 500 mg/kg CKA. Maximum ALT fold change from baseline for increasing doses of CKA. Dots represent data from preclinical studies and asterisks denote simulation results for rat SimPops (n = 294). Results are quantitatively summarized in Table 2.

Figure 4.

Qualitative sensitivity analysis based on toxicity mechanisms in rat SimPops. A single dose of 500 mg/kg CKA was simulated in rat SimPops with a single mechanism (top row) or combination of two DILI mechanisms (bottom row). (A) bile acid (BA) transporter inhibition only, (B) reactive oxygen species (ROS) generation only, (C) mitochondrial electron transport chain (ETC) inhibition only, (D) ETC inhibition + ROS generation, (E) ETC inhibition + BA transporter inhibition, (F) BA transporter inhibition + ROS generation. Simulations with a single DILI mechanism (top row) suggest that ETC inhibition is the main contributor to CKA-mediated rat hepatotoxicity. When two DILI mechanisms are combined, ETC inhibition and BA transporter inhibition together produce a greater peak plasma alanine transaminase (ALT), suggesting BA transporter inhibition as the secondary contributor to hepatotoxicity. Qualitative results are supported by multiple regression analysis results shown in Supplementary Table 2.