Hepatocellular exposure of troglitazone metabolites in rat sandwich-cultured hepatocytes lacking Bcrp and Mrp2: interplay between formation and excretion

Permeabilized cryopreserved human hepatocytes as an exogenous metabolic system in a novelmetabolism-dependent cytotoxicity assay (MDCA) for the evaluation of metabolic activation anddetoxification of drugs associated with drug induced liver injuries: Results with acetaminophen,amiodarone, cyclophosphamide, ketoconazole, nefazodone, and troglitazone

We report here a novel in vitro experimental system, the metabolism-dependent cytotoxicity assay (MDCA), for the definition of the roles of hepatic drug metabolism in toxicity. MDCA employs permeabilized cofactor-supplemented cryopreserved human hepatocytes (MetMax{trade mark, serif} human hepatocytes, MMHH), as an exogenous metabolic activating system, and HEK-293 cells, a cell line devoid of drug metabolizing enzyme activity, as target cells for the quantification of drug toxicity. The assay was performed in the presence and absence of cofactors for key drug metabolism pathways known to play key roles in drug toxicity: NADPH/NAD+ for phase 1 oxidation, UDPGA for UGT mediated glucuronidation, PAPS for SULT mediated sulfation, and GSH for GST mediated GSH conjugation. Six drugs with clinically significant hepatoxicity, resulting in liver failure or a need for liver transplantation: acetaminophen, amiodarone, cyclophosphamide, ketoconazole, nefazodone and troglitazone were evaluated. All six drugs exhibited cytotoxicity enhancement by NADPH, suggesting metabolic activation via phase 1 oxidation. Attenuation of cytotoxicity by UDPGA was observed for acetaminophen, ketoconazole and troglitazone, by PAPS for acetaminophen, ketoconazole and troglitazone, and by GSH for all six drugs. Our results suggest that MDCA can be applied towards the elucidation of metabolic activation and detoxification pathways, providing information that can be applied in drug development to guide structure optimization to reduce toxicity and to aid the assessment of metabolism-based risk factors for drug toxicity. GSH detoxification represents an endpoint for the identification of drugs forming cytotoxic reactive metabolites, a key property of drugs with idiosyncratic hepatotoxicity. Significance Statement Application of the metabolism-dependent cytotoxicity assay (MDCA) for the elucidation of the roles of metabolic activation and detoxification pathways in drug toxicity may provide information to guide structure optimization in drug development to reduce hepatotoxic potential, and to aid the assessment of metabolism-based risk factors. GSH detoxification represents an endpoint for the identification of drugs forming cytotoxic reactive metabolites may be applied towards the evaluation of idiosyncratic hepatotoxicity.

In vitro drug metabolism and pharmacokinetics of a novel thiazolidinedione derivative, a potential anticancer compound

Thiazolidinediones are known for their activity against Type 2 diabetes and are currently being repurposed for their potent anti-cancer activity. In the present study, we have assessed in vitro metabolic properties and in vivo pharmacokinetic parameters of a novel thiazolidinedione derivative, BIT-15-67, a potential anticancer compound. BIT-15-67 showed low solubility in aqueous buffers at different pH values. The permeability was determined across the Caco-2 monolayer and BIT-15-67 showed high permeability and an efflux ratio of less than 2 suggesting that it is not a substrate of the efflux transporters (P-gp & BCRP). The plasma protein binding was evaluated by equilibrium dialysis and the compound exhibited moderate binding to mouse and rat plasma proteins. BIT-15-67 was stable (half-life > 30 min.) in mouse, rat, dog and human liver microsomes and unstable (half-life <15 min.) in rat hepatocytes suggesting possible Phase II metabolism. Liquid chromatography-tandem mass spectrometry was used to identify Phase I and Phase II metabolites. One of each Phase I and Phase II metabolites have been identified in rat hepatocytes samples. The BIT-15-67 is not an inhibitor of CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4. The PK parameters were determined in both male and female Wistar rats after single intravenous dose administration of BIT-15-67. In rats, the mean plasma clearance of BIT-15-67 was higher in males than in females and the terminal plasma elimination half-life was shorter in males than in females. The compound was highly distributed in the tissues. Overall, the absolute oral bioavailability was 5-fold higher in females (38 %) than in males (7 %). In female nude mice with tumors, BIT-15-67 was well distributed among the collected tissues with the highest concentration in the liver. The ratio of the concentrations in tumor vs. the plasma was 0.5 which could be an important attribute in the development of the compound for anti-cancer research.

Sandwich-Cultured Hepatocytes for Mechanistic Understanding of Hepatic Disposition of Parent Drugs and Metabolites by Transporter-Enzyme Interplay

Functional interplay between transporters and drug-metabolizing enzymes is currently one of the hottest topics in the field of drug metabolism and pharmacokinetics. Uptake transporter-enzyme interplay is important to determine intrinsic hepatic clearance based on the extended clearance concept. Enzyme and efflux transporter interplay, which includes both sinusoidal (basolateral) and canalicular efflux transporters, determines the fate of metabolites formed in the liver. As sandwich-cultured hepatocytes (SCHs) maintain metabolic activities and form a canalicular network, the whole interplay between uptake and efflux transporters and drug-metabolizing enzymes can be investigated simultaneously. In this article, we review the utility and applicability of SCHs for mechanistic understanding of hepatic disposition of both parent drugs and metabolites. In addition, the utility of SCHs for mimicking species-specific disposition of parent drugs and metabolites in vivo is described. We also review application of SCHs for clinically relevant prediction of drug-drug interactions caused by drugs and metabolites. The usefulness of mathematical modeling of hepatic disposition of parent drugs and metabolites in SCHs is described to allow a quantitative understanding of an event in vitro and to develop a more advanced model to predict in vivo disposition.

Recent Progress in Hepatocyte Culture Models and Their Application to the Assessment of Drug Metabolism, Transport, and Toxicity in Drug Discovery: The Value of Tissue Engineering for the Successful Development of a Microphysiological System

Tissue engineering technology has provided many useful culture models. This article reviews the merits of this technology in a hepatocyte culture system and describes the applications of the sandwich-cultured hepatocyte model in drug discovery. In addition, we also review recent investigations of the utility of the 3-dimensional bioprinted human liver tissue model and spheroid model. Finally, we present the future direction and developmental challenges of a hepatocyte culture model for the successful establishment of a microphysiological system, represented as an organ-on-a-chip and even as a human-on-a-chip. A merit of advanced culture models is their potential use for detecting hepatotoxicity through repeated exposure to chemicals as they allow long-term culture while maintaining hepatocyte functionality. As a future direction, such advanced hepatocyte culture systems can be connected to other tissue models for evaluating tissue-to-tissue interaction beyond cell-to-cell interaction. This combination of culture models could represent parts of the human body in a microphysiological system.

Sandwich-Cultured Hepatocytes as a Tool to Study Drug Disposition and Drug-Induced Liver Injury

Sandwich-cultured hepatocytes (SCH) are metabolically competent and have proper localization of basolateral and canalicular transporters with functional bile networks. Therefore, this cellular model is a unique tool that can be used to estimate biliary excretion of compounds. SCH have been used widely to assess hepatobiliary disposition of endogenous and exogenous compounds and metabolites. Mechanistic modeling based on SCH data enables estimation of metabolic and transporter-mediated clearances, which can be used to construct physiologically based pharmacokinetic models for prediction of drug disposition and drug-drug interactions in humans. In addition to pharmacokinetic studies, SCH also have been used to study cytotoxicity and perturbation of biological processes by drugs and hepatically generated metabolites. Human SCH can provide mechanistic insights underlying clinical drug-induced liver injury (DILI). In addition, data generated in SCH can be integrated into systems pharmacology models to predict potential DILI in humans. In this review, applications of SCH in studying hepatobiliary drug disposition and bile acid-mediated DILI are discussed. An example is presented to show how data generated in the SCH model were used to establish a quantitative relationship between intracellular bile acids and cytotoxicity, and how this information was incorporated into a systems pharmacology model for DILI prediction.

Challenges and Opportunities with Predicting in Vivo Phase II Metabolism via Glucuronidation from in Vitro Data

Glucuronidation is the most important phase II metabolic pathway which is responsible for the clearance of many endogenous and exogenous compounds. To better understand the elimination process for compounds undergoing glucuronidation and identify compounds with desirable in vivo pharmacokinetic properties, many efforts have been made to predict in vivo glucuronidation using in vitro data. In this article, we reviewed typical approaches used in previous predictions. The problems and challenges in prediction of glucuronidation were discussed. Besides that different incubation conditions can affect the prediction accuracy, other factors including efflux / uptake transporters, enterohepatic recycling, and deglucuronidation reactions also contribute to the disposition of glucuronides and make the prediction more difficult. PBPK modeling, which can describe more complicated process in vivo, is a promising prediction strategy which may greatly improve the prediction of glucuronidation and potential DDIs involving glucuronidation. Based on previous studies, we proposed a transport-glucuronidation classification system, which was built based on the kinetics of both glucuronidation and transport of the glucuronide. This system could be a very useful tool to achieve better in vivo predictions.

Prediction of the Clinical Risk of Drug-Induced Cholestatic Liver Injury Using an In Vitro Sandwich Cultured Hepatocyte Assay

Drug-induced liver injury (DILI) is of concern to the pharmaceutical industry, and reliable preclinical screens are required. Previously, we established an in vitro bile acid-dependent hepatotoxicity assay that mimics cholestatic DILI in vivo. Here, we confirmed that this assay can predict cholestatic DILI in clinical situations by comparing in vitro cytotoxicity data with in vivo risk. For 38 drugs, the frequencies of abnormal increases in serum alkaline phosphatase (ALP), transaminases, gamma glutamyltranspeptidase (γGT), and bilirubin were collected from interview forms. Drugs with frequencies of serum marker increases higher than 1% were classified as high DILI risk compounds. In vitro cytotoxicity was assessed by monitoring lactate dehydrogenase release from rat and human sandwich-cultured hepatocytes (SCRHs and SCHHs) incubated with the test drugs (50 μM) for 24 hours in the absence or presence of a bile acids mixture. Receiver operating characteristic analyses gave optimal cutoff toxicity values of 19.5% and 9.2% for ALP and transaminases in SCRHs, respectively. Using this cutoff, high- and low-risk drugs were separated with 65.4-78.6% sensitivity and 66.7-79.2% specificity. Good separation was also achieved using SCHHs. In conclusion, cholestatic DILI risk can be successfully predicted using a sandwich-cultured hepatocyte-based assay.