Evaluation of multiple mechanism-based toxicity endpoints in primary cultured human hepatocytes for the identification of drugs with clinical hepatotoxicity: Results from 152 marketed drugs with known liver injury profiles

Control compounds for preclinical drug-induced liver injury assessment: Consensus-driven systematic review by the ProEuroDILI network

BACKGROUND & AIMS

Idiosyncratic drug-induced liver injury (DILI) is a complex and unpredictable event caused by drugs, and herbal or dietary supplements. Early identification of human hepatotoxicity at preclinical stages remains a major challenge, in which the selection of validated in vitro systems and test drugs has a significant impact. In this systematic review, we analyzed the compounds used in hepatotoxicity assays and established a list of DILI-positive and -negative control drugs for validation of in vitro models of DILI, supported by literature and clinical evidence and endorsed by an expert committee from the COST Action ProEuroDILI Network (CA17112).

METHODS

Following 2020 PRISMA guidelines, original research articles focusing on DILI which used in vitro human models and performed at least one hepatotoxicity assay with positive and negative control compounds, were included. Bias of the studies was assessed by a modified 'Toxicological Data Reliability Assessment Tool'.

RESULTS

A total of 51 studies (out of 2,936) met the inclusion criteria, with 30 categorized as reliable without restrictions. Although there was a broad consensus on positive compounds, the selection of negative compounds lacked clarity. 2D monoculture, short exposure times and cytotoxicity endpoints were the most tested, although there was no consensus on drug concentrations.

CONCLUSIONS

Extensive analysis highlighted the lack of agreement on control compounds for in vitro DILI assessment. Following comprehensive in vitro and clinical data analysis together with input from the expert committee, an evidence-based consensus-driven list of 10 positive and negative control drugs for validation of in vitro models of DILI is proposed.

IMPACT AND IMPLICATIONS

Prediction of human toxicity early in the drug development process remains a major challenge, necessitating the development of more physiologically relevant liver models and careful selection of drug-induced liver injury (DILI)-positive and -negative control drugs to better predict the risk of DILI associated with new drug candidates. Thus, this systematic study has crucial implications for standardizing the validation of new in vitro models of DILI. By establishing a consensus-driven list of positive and negative control drugs, the study provides a scientifically justified framework for enhancing the consistency of preclinical testing, thereby addressing a significant challenge in early hepatotoxicity identification. Practically, these findings can guide researchers in evaluating safety profiles of new drugs, refining in vitro models, and informing regulatory agencies on potential improvements to regulatory guidelines, ensuring a more systematic and efficient approach to drug safety assessment.

Safety, pharmacokinetics, and antiviral activity of the capsid inhibitor AB-506 from Phase 1 studies in healthy subjects and those with hepatitis B

AB-506 is a potent, pan-genotypic small molecule capsid inhibitor that inhibits hepatitis B virus (HBV) pregenomic RNA encapsidation. We assessed the safety, pharmacokinetics, and antiviral activity of AB-506 in two randomized, double-blinded Phase 1 studies in healthy subjects (HS) and subjects with chronic HBV infection (CHB). Single ascending and multiple doses of AB-506 or placebo (30-1000 mg or 400 mg daily for 10 days) were assessed in HS. AB-506 or placebo was assessed at either 160 mg or 400 mg daily for 28 days in subjects with CHB. A second follow-up study examined AB-506 or placebo at 400 mg daily for 28 days in 14 Caucasian and 14 East-Asian HS. Twenty-eight days of AB-506 at 160 mg and 400 mg produced mean HBV-DNA declines from baseline of 2.1 log₁₀ IU/ml and 2.8 log₁₀ IU/ml, respectively. Four subjects with CHB (all Asian) had Grade 4 alanine aminotransferase (ALT) elevations (2 at each dose) as HBV DNA was declining; three events led to treatment discontinuation. In the second follow-up study, 2 Asian HS had serious transaminitis events leading to treatment and study termination. No subjects had bilirubin elevations or signs of hepatic decompensation. Conclusion: AB-506 demonstrated mean HBV-DNA declines of >2 log₁₀ ; however, transient but severe ALT flares were observed in 4 Asian subjects with CHB. In the follow-up study in HS, 2 additional Asian HS had Grade 4 flares, suggesting that AB-506 hepatotoxicity contributed to the ALT elevations. The AB-506 development program was terminated because of these findings.

In vitro cell-based models of drug-induced hepatotoxicity screening: progress and limitation

Drug-induced liver injury (DILI) is one of the major causes of post-approval withdrawal of therapeutics. As a result, there is an increasing need for accurate predictive in vitro assays that reliably detect hepatotoxic drug candidates while reducing drug discovery time, costs, and the number of animal experiments. In vitro hepatocyte-based research has led to an improved comprehension of the underlying mechanisms of chemical toxicity and can assist the prioritization of therapeutic choices with low hepatotoxicity risk. Therefore, several in vitro systems have been generated over the last few decades. This review aims to comprehensively present the development and validation of 2D (two-dimensional) and 3D (three-dimensional) culture approaches on hepatotoxicity screening of compounds and highlight the main factors affecting predictive power of experiments. To this end, we first summarize some of the recognized hepatotoxicity mechanisms and related assays used to appraise DILI mechanisms and then discuss the challenges and limitations of in vitro models.

Relationships between the Structure and Severe Drug-Induced Liver Injury for Low, Medium, and High Doses of Drugs

Assessment of structure-activity relationships (SARs) for predicting severe drug-induced liver injury (DILI) is essential since in vivo and in vitro preclinical methods cannot detect many druglike compounds disrupting liver functions. To date, plenty of SAR models for the prediction of DILI have been developed; however, none of them considered the route of drug administration and daily dose, which may introduce significant bias into prediction results. We have created a dataset of 617 drugs with parenteral and oral administration routes and consistent information on DILI severity. We have found a clear relationship between route, dose, and DILI severity. According to SAR, nearly 40% of moderate- and non-DILI-causing drugs would cause severe DILI if they were administered at high oral doses. We have proposed the following approach to predict severe DILI. New compounds recommended to be used at low oral doses (<∼10 mg daily), or parenterally, can be considered not causing severe DILI. DILI for compounds administered at medium oral doses (∼10-100 mg daily; 22.2% of drugs under consideration) can be considered unpredictable because reasonable SAR models were not obtained due to the small size and heterogeneity of the corresponding dataset. The DILI potential of the compounds recommended to be used at high oral doses (more than ∼100 mg daily) can be estimated using SAR modeling. The balanced accuracy of the approach calculated by a 10-fold cross-validation procedure is 0.803. The developed approach can be used to estimate severe DILI for druglike compounds proposed to use at low and high oral doses or parenterally at the early stages of drug development.

Evaluation of a Three-Dimensional Primary Human Hepatocyte Spheroid Model: Adoption and Industrialization for the Enhanced Detection of Drug-Induced Liver Injury

Drug-induced liver injury is a leading cause of compound attrition during both preclinical and clinical drug development, and early strategies are in place to tackle this recurring problem. Human-relevant in vitro models that are more predictive of hepatotoxicity hazard identification, and that could be employed earlier in the drug discovery process, would improve the quality of drug candidate selection and help reduce attrition. We present an evaluation of four human hepatocyte in vitro models of increasing culture complexity (i.e., two-dimensional (2D) HepG2 monolayers, hepatocyte sandwich cultures, three-dimensional (3D) hepatocyte spheroids, and precision-cut liver slices), using the same tool compounds, viability end points, and culture time points. Having established the improved prediction potential of the 3D hepatocyte spheroid model, we describe implementing this model into an industrial screening setting, where the challenge was matching the complexity of the culture system with the scale and throughput required. Following further qualification and miniaturization into a 384-well, high-throughput screening format, data was generated on 199 compounds. This clearly demonstrated the ability to capture a greater number of severe hepatotoxins versus the current routine 2D HepG2 monolayer assay while continuing to flag no false-positive compounds. The industrialization and miniaturization of the 3D hepatocyte spheroid complex in vitro model demonstrates a significant step toward reducing drug attrition and improving the quality and safety of drugs, while retaining the flexibility for future improvements, and has replaced the routine use of the 2D HepG2 monolayer assay at GlaxoSmithKline.

Messenger RNA Expression of Albumin, Transferrin, Transthyretin, Asialoglycoprotein Receptor, Cytochrome P450 Isoform, Uptake Transporter, and Efflux Transporter Genes as a Function of Culture Duration in Prolonged Cultured Cryopreserved Human Hepatocytes as Collagen-Matrigel Sandwich Cultures: Evidence for Redifferentiation upon Prolonged Culturing

Hepatic gene expression as a function of culture duration was evaluated in prolonged cultured human hepatocytes. Human hepatocytes from seven donors were maintained as near-confluent collagen-Matrigelsandwich cultures, with messenger RNA expression for genes responsible for key hepatic functions quantified by real-time polymerase chain reaction at culture durations of 0 (day of plating), 2, 7, 9, 16, 23, 26, 29, 36, and 43 days. Key hepatocyte genes were evaluated, including the differentiation markers albumin, transferrin, and transthyretin; the hepatocyte-specific asialoglycoprotein receptor 1 cytochrome P450 isoforms CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4, and CYP3A7; uptake transporter isoforms SLC10A1, SLC22A1, SLC22A7, SLCO1B1, SLCO1B3, and SLCO2B1; efflux transporter isoforms ATP binding cassette (ABC)B1, ABCB11, ABCC2, ABCC3, ABCC4, and ABCG2; and the nonspecific housekeeping gene hypoxanthine ribosyl transferase 1 (HPRT1). The well established dedifferentiation phenomenon was observed on day 2, with substantial (>80%) decreases in gene expression in day 2 cultures observed for all genes evaluated except HPRT1 and efflux transporters ABCB1, ABCC2, ABCC3 (<50% decrease in expression), ABCC4 (>400% increase in expression), and ABCG2 (no decrease in expression). All genes with a >80% decrease in expression were found to have increased levels of expression on day 7, with peak expression observed on either day 7 or day 9, followed by a gradual decrease in expression up to the longest duration evaluated of 43 days. Our results provide evidence that cultured human hepatocytes undergo redifferentiation upon prolonged culturing. SIGNIFICANCE STATEMENT: This study reports that although human hepatocytes underwent dedifferentiation upon 2 days of culture, prolonged culturing resulted in redifferentiation based on gene expression of differentiation markers, uptake and efflux transporters, and cytochrome P450 isoforms. The observed redifferentiation suggests that prolonged (>7 days) culturing of human hepatocyte cultures may represent an experimental approach to overcome the initial dedifferentiation process, resulting in "stabilized" hepatocytes that can be applied toward the evaluation of drug properties requiring an extended period of treatment and evaluation.

Overview of drug induced liver injury in Brazil: What is the role of public health policy on the evidence?

BACKGROUND

Adverse drug reactions are responsible for increased costs and morbidity in the health system. Hepatotoxicity can be induced both by non-prescription drugs and by those used for chronic diseases. It is the main cause of safety-related drug marketing withdrawals and could be responsible for irreversible and fatal injuries.

AIM

To identify and to summarize Brazilian studies reporting the drug-induced liver injury.

METHODS

A systematic review of Brazilian studies was carried out until June 2020. It was found 32 studies, being 10 retrospective cohorts, 12 prospective cohorts, 5 cross-sectional, 3 case-control, one case series and one randomized clinical trial. In most studies were investigated tuberculosis patients followed by other infectious conditions like human immunodeficiency virus (HIV) and hepatitis C virus. The hepatotoxicity ranged from one to 57%, led by isoniazid, rifampicin, and pyrazinamide. Few studies reported algorithm to assess causality. In most studies, there were moderate outcomes and it was necessary drug interruption. However, few severe outcomes, such as chronic liver damage and liver transplantation were reported.

RESULTS

Twenty-two different criteria for hepatotoxicity were found. The great heterogeneity did not allow a meta-analysis. Standardization of parameter of drug-induced liver injury and greater effort in pharmacovigilance could contribute to learn more about drug-induced liver injury (DILI)'s epidemiology in Brazil.

CONCLUSION

The development of strategic public health policies seems to have an influence on the DILI scientific evidence in Brazil due to main studies are in HIV and tuberculosis line care, two strategic health policies in Brazil.

Oxidative Stress in Drug-Induced Liver Injury (DILI): From Mechanisms to Biomarkers for Use in Clinical Practice

Idiosyncratic drug-induced liver injury (DILI) is a type of hepatic injury caused by an uncommon drug adverse reaction that can develop to conditions spanning from asymptomatic liver laboratory abnormalities to acute liver failure (ALF) and death. The cellular and molecular mechanisms involved in DILI are poorly understood. Hepatocyte damage can be caused by the metabolic activation of chemically active intermediate metabolites that covalently bind to macromolecules (e.g., proteins, DNA), forming protein adducts-neoantigens-that lead to the generation of oxidative stress, mitochondrial dysfunction, and endoplasmic reticulum (ER) stress, which can eventually lead to cell death. In parallel, damage-associated molecular patterns (DAMPs) stimulate the immune response, whereby inflammasomes play a pivotal role, and neoantigen presentation on specific human leukocyte antigen (HLA) molecules trigger the adaptive immune response. A wide array of antioxidant mechanisms exists to counterbalance the effect of oxidants, including glutathione (GSH), superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPX), which are pivotal in detoxification. These get compromised during DILI, triggering an imbalance between oxidants and antioxidants defense systems, generating oxidative stress. As a result of exacerbated oxidative stress, several danger signals, including mitochondrial damage, cell death, and inflammatory markers, and microRNAs (miRNAs) related to extracellular vesicles (EVs) have already been reported as mechanistic biomarkers. Here, the status quo and the future directions in DILI are thoroughly discussed, with a special focus on the role of oxidative stress and the development of new biomarkers.

Functional Proliferating Human Hepatocytes: In Vitro Hepatocyte Model for Drug Metabolism, Excretion, and Toxicity

To develop a functional alternative hepatocyte model for primary human hepatocytes (PHHs) with proliferative property, essential drug metabolic, and transporter functions, proliferating human hepatocytes (ProliHHs) expanded from PHHs were fully characterized in vitro. Herein, ProliHHs generated from multiple PHHs donors could be expanded more than 200-fold within four passages and maintained their metabolic or transporter capacities partially. Furthermore, ProliHHs were able to regain the mature hepatic property after three-dimensional (3D) culture. Particularly, the downregulated mRNA expression and function of three major cytochrome P450 (P450) enzymes (CYP1A2, CYP2B6, and CYP3A4) in the proliferating process (ProliHHs-P) could be recovered by 3D culture. The metabolic variabilities across different PHHs donors could be inherited to their matured ProliHHs (ProliHHs-M). The intrinsic clearances of seven major P450 enzymes in ProliHHs-M correlated well (r = 0.87) with those in PHHs. Also, bile canaliculi structures could be observed in sandwich-cultured ProliHHs (SC-ProliHHs), and the biliary excretion index of four probe compounds [cholyl-lys-fluorescein, 5-(and-6)-carboxy-2', 7'-dichlorofluorescein diacetate (CDF), deuterium-labeled sodium taurocholate acid, and rosuvastatin] in SC-ProliHHs (>10%) were close to sandwich-cultured PHHs. More importantly, both ProliHHs-P and ProliHHs-M could be used to evaluate hepatotoxicity. Therefore, these findings demonstrated that the 3D and sandwich culture system could be used to recover the metabolic and transporter functions in ProliHHs for clearance prediction and cholestasis risk assessment, respectively. Together, ProliHHs could be a promising substitute for PHHs in drug metabolism, transport, and hepatotoxicity screening. SIGNIFICANCE STATEMENT: This report describes the study of drug metabolic capacities, efflux transporter functions, and toxicity assessments of proliferating human hepatocytes (ProliHHs). The metabolic variability in different primary human hepatocyte donors could be inherited by their matured ProliHHs derivatives. Also, ProliHHs could form canalicular networks in sandwich culture and display biliary excretion capacities. More importantly, both the proliferative and maturation statuses of ProliHHs could be used to evaluate hepatotoxicity. Together, ProliHHs were feasible to support drug candidate screening in hepatic metabolism, disposition, and toxicity.

Models of Idiosyncratic Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a leading cause of attrition during the early and late stages of drug development and after a drug is marketed. DILI is generally classified as either intrinsic or idiosyncratic. Intrinsic DILI is dose dependent and predictable (e.g., acetaminophen toxicity). However, predicting the occurrence of idiosyncratic DILI, which has a very low incidence and is associated with severe liver damage, is difficult because of its complex nature and the poor understanding of its mechanism. Considering drug metabolism and pharmacokinetics, we established experimental animal models of DILI for 14 clinical drugs that cause idiosyncratic DILI in humans, which is characterized by the formation of reactive metabolites and the involvement of both innate and adaptive immunity. On the basis of the biomarker data obtained from the animal models, we developed a cell-based assay system that predicts the potential risks of drugs for inducing DILI. These findings increase our understanding of the mechanisms of DILI and may help predict and prevent idiosyncratic DILI due to certain drugs.

The integrated use of in silico methods for the hepatotoxicity potential of Piper methysticum

Herbal products as supplements and therapeutic intervention have been used for centuries. However, their toxicities are not completely evaluated and the mechanisms are not clearly understood. Dried rhizome of the plant kava (Piper methysticum) is used for its anxiolytic, and sedative effects. The drug is also known for its hepatotoxicity potential. Major constituents of the plant were identified as kavalactones, alkaloids and chalcones in previous studies. Kava hepatotoxicity mechanism and the constituent that causes the toxicity have been debated for decades. In this paper, we illustrated the use of computational tools for the hepatotoxicity of kava constituents. The proposed mechanisms and major constituents that are most probably responsible for the toxicity have been scrutinized. According to the experimental and prediction results, the kava constituents play a substantial role in hepatotoxicity by some means or other via glutathione depletion, CYP inhibition, reactive metabolite formation, mitochondrial toxicity and cyclooxygenase activity. Some of the constituents, which have not been tested yet, were predicted to involve mitochondrial membrane potential, caspase-3 stimulation, and AhR activity. Since Nrf2 activation could be favorable for prevention of hepatotoxicity, we also suggest that these compounds should undergo testing given that they were predicted not to be activating Nrf2. Among the major constituents, alkaloids appear to be the least studied and the least toxic group in general. The outcomes of the study could help to appreciate the mechanisms and to prioritize the kava constituents for further testing.

Mechanism-based integrated assay systems for the prediction of drug-induced liver injury

Drug-induced liver injury (DILI) can cause hepatic failure and result in drug withdrawal from the market. It has host-related and compound-dependent mechanisms. Preclinical prediction of DILI risk is very challenging and safety assessments based on animals inadequately forecast human DILI risk. In contrast, human-derived in vitro cell culture-based models could improve DILI risk prediction accuracy. Here, we developed and validated an innovative method to assess DILI risk associated with various compounds. Fifty-four marketed and withdrawn drugs classified as DILI risks of "most concern", "less concern", and "no concern" were tested using a combination of four assays addressing mitochondrial injury, intrahepatic lipid accumulation, inhibition of bile canalicular network formation, and bile acid accumulation. Using the inhibitory potencies of the drugs evaluated in these in vitro tests, an algorithm with the highest available DILI risk prediction power was built by artificial neural network (ANN) analysis. It had an overall forecasting accuracy of 73%. We excluded the intrahepatic lipid accumulation assay to avoid overfitting. The accuracy of the algorithm in terms of predicting DILI risks was 62% when it was constructed by ANN but only 49% when it was built by the point-added scoring method. The final algorithm based on three assays made no DILI risk prediction errors such as "most concern " instead of "no concern" and vice-versa. Our mechanistic approach may accurately predict DILI risks associated with numerous candidate drugs.

Hepatotoxicity Modeling Using Counter-Propagation Artificial Neural Networks: Handling an Imbalanced Classification Problem

Drug-induced liver injury is a major concern in the drug development process. Expensive and time-consuming in vitro and in vivo studies do not reflect the complexity of the phenomenon. Complementary to wet lab methods are in silico approaches, which present a cost-efficient method for toxicity prediction. The aim of our study was to explore the capabilities of counter-propagation artificial neural networks (CPANNs) for the classification of an imbalanced dataset related to idiosyncratic drug-induced liver injury and to develop a model for prediction of the hepatotoxic potential of drugs. Genetic algorithm optimization of CPANN models was used to build models for the classification of drugs into hepatotoxic and non-hepatotoxic class using molecular descriptors. For the classification of an imbalanced dataset, we modified the classical CPANN training algorithm by integrating random subsampling into the training procedure of CPANN to improve the classification ability of CPANN. According to the number of models accepted by internal validation and according to the prediction statistics on the external set, we concluded that using an imbalanced set with balanced subsampling in each learning epoch is a better approach compared to using a fixed balanced set in the case of the counter-propagation artificial neural network learning methodology.

Models of Drug Induced Liver Injury (DILI) - Current Issues and Future Perspectives

Background:

Drug-induced Liver Injury (DILI) is an important cause of acute liver failure cases in the United States, and remains a common cause of withdrawal of drugs in both preclinical and clinical phases.

Methods:

A structured search of bibliographic databases – Web of Science Core Collection, Scopus and Medline for peer-reviewed articles on models of DILI was performed. The reference lists of relevant studies was prepared and a citation search for the included studies was carried out. In addition, the characteristics of screened studies were described.

Results:

One hundred and six articles about the existing knowledge of appropriate models to study DILI in vitro and in vivo with special focus on hepatic cell models, variations of 3D co-cultures, animal models, databases and predictive modeling and translational biomarkers developed to understand the mechanisms and pathophysiology of DILI are described.

Conclusion:

Besides descriptions of current applications of existing modeling systems, associated advantages and limitations of each modeling system and future directions for research development are discussed as well.

Advancing Predictive Hepatotoxicity at the Intersection of Experimental, in Silico, and Artificial Intelligence Technologies

Adverse drug reactions, particularly those that result in drug-induced liver injury (DILI), are a major cause of drug failure in clinical trials and drug withdrawals. Hepatotoxicity-mediated drug attrition occurs despite substantial investments of time and money in developing cellular assays, animal models, and computational models to predict its occurrence in humans. Underperformance in predicting hepatotoxicity associated with drugs and drug candidates has been attributed to existing gaps in our understanding of the mechanisms involved in driving hepatic injury after these compounds perfuse and are metabolized by the liver. Herein we assess in vitro, in vivo (animal), and in silico strategies used to develop predictive DILI models. We address the effectiveness of several two- and three-dimensional in vitro cellular methods that are frequently employed in hepatotoxicity screens and how they can be used to predict DILI in humans. We also explore how humanized animal models can recapitulate human drug metabolic profiles and associated liver injury. Finally, we highlight the maturation of computational methods for predicting hepatotoxicity, the untapped potential of artificial intelligence for improving in silico DILI screens, and how knowledge acquired from these predictions can shape the refinement of experimental methods.

N-acetylcysteine and prednisolone treatment improved serum biochemistries in suspected flupirtine cases of severe idiosyncratic liver injury

BACKGROUND & AIMS

The analgesic flupirtine has been linked to cases of severe idiosyncratic drug-induced liver injury (sFILI). We therefore examined whether N-acetylcysteine (NAC) and glucocorticoid therapy is effective in the management of sFILI.

METHODS

In a retrospective cohort study efficacy of NAC-infusion and oral prednisolone treatments on liver-function-tests (LFTs) and clinical outcome of 21 sFILI cases was evaluated by comparing it to an external cohort of 30 sFILI cases not receiving the antidote. LFTs were also assayed in human hepatocyte cultures treated with flupirtine for 96 hours. Additionally, modulation of glutathione stores in cultures of human hepatocytes treated with 80 drugs was investigated.

RESULTS

Upon admission, patients presented Alanine aminotransferase (ALT), aspartate aminotransferase (AST) and bilirubin elevations of up to 90-, 35- and 30-fold of upper limits of normal (ULN) respectively. The average INR was 2.2, and 50% of patients had a high Model for end-stage liver disease (MELD) score of ≥25 and included 5 cases of 28-32. The combined NAC/prednisolone treatment was well tolerated and led to significant ALT, AST and INR improvements within 2 weeks. However, the hyperbilirubinaemia resolved slowly. Two patients with late start of NAC/prednisolone treatment developed hepatic encephalopathy and required liver transplantation; the remaining patients recovered without long-term sequela. Based on serum biochemistries sFILI cases resolved more rapidly (P < .01) when compared to untreated sFILI patients and included a case with fatal outcome. Additionally, in vitro studies revealed glutathione depletion as a common culprit for drugs with liver liabilities.

CONCLUSIONS

Based on these initial findings a prospective randomized clinical trial (RCT) is needed to confirm safety and efficacy of NAC/prednisolone treatment in sFILI.

A Novel In Vitro Experimental System for the Evaluation of Drug Metabolism: Cofactor-Supplemented Permeabilized Cryopreserved Human Hepatocytes (MetMax Cryopreserved Human Hepatocytes)

We report here a novel experimental system, cryopreserved MetMax human hepatocytes (MMHHs), for in vitro drug metabolism studies. MMHHs consist of cofactor-supplemented permeabilized cryopreserved human hepatocytes. The use procedures for MMHHs are significantly simplified from that for conventional cryopreserved human hepatocytes (CCHHs): 1) storage at -80°C instead of in liquid nitrogen and 2) usage directly after thawing without centrifugation and microscopic evaluation of cell density and viability and cell density adjustment. In this study, we compared MMHHs and CCHHs in CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2D6, CYP2E1, CYP3A4, CYP2J2, monoamine oxidase A, aldehyde oxidase, flavin-containing monooxygenase, UDP-glucuronyl transferase, SULT, N-acetyltransferase 1, and acetaminophen glutathione (GSH) conjugation activities based on liquid chromatography-tandem mass spectrometry quantification of substrate metabolism. MMHHs were prepared from CCHHs consisting of hepatocytes pooled from 10 individual donors. The drug metabolizing enzyme activities of both CCHHs and MMHHs were cell concentration and time dependent, with specific activities of MMHHs ranging from 27.2% (carboxylesterase 2) to 234.2% (acetaminophen GSH conjugation) of that for CCHHs. As observed in CCHHs, sequential oxidation and conjugation was observed in MMHHs for coumarin, 7-ethoxycoumarin, and acetaminophen. 7-Hydroxycoumarin conjugation results showed that metabolic pathways in MMHHs could be selected via the choice of cofactors, with glucuronidation but not sulfation observed in the presence of UDP-glucuronic acid and not 3-phosphoadenosine-5-phosphosulfate, and vice versa. Results with noncytotoxic and cytotoxic concentrations of acetaminophen showed that drug metabolism was compromised in CCHHs but not in MMHHs. Our results suggest that the MMHHs system represents a convenient and robust in vitro experimental system for the evaluation of drug metabolism.

Chemical and cellular oxidant production induced by naphthalene secondary organic aerosol (SOA): effect of redox-active metals and photochemical aging

Exposure to air pollution is a leading global health risk. Secondary organic aerosol (SOA) constitute a large portion of ambient particulate matter (PM). In this study, the water-soluble oxidative potential (OP) determined by dithiothreitol (DTT) consumption and intracellular reactive oxygen and nitrogen species (ROS/RNS) production was measured for SOA generated from the photooxidation of naphthalene in the presence of iron sulfate and ammonium sulfate seed particles. The measured intrinsic OP varied for aerosol formed using different initial naphthalene concentrations, however, no trends were observed between OP and bulk aerosol composition or seed type. For all experiments, aerosol generated in the presence of iron-containing seed induced higher ROS/RNS production compared to that formed in the presence of inorganic seed. This effect was primarily attributed to differences in aerosol carbon oxidation state \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\boldsymbol{(}}{\bar{{\bf{O}}{\bf{S}}}}_{{\bf{c}}}{\boldsymbol{)}}$$\end{document}(OS¯c). In the presence of iron, radical concentrations are elevated via iron redox cycling, resulting in more oxidized species. An exponential trend was also observed between ROS/RNS and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\boldsymbol{(}}{\bar{{\bf{O}}{\bf{S}}}}_{{\bf{c}}}{\boldsymbol{)}}$$\end{document}(OS¯c) for all naphthalene SOA, regardless of seed type or aerosol formation condition. This may have important implications as aerosol have an atmospheric lifetime of a week, over which \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\boldsymbol{(}}{\bar{{\bf{O}}{\bf{S}}}}_{{\bf{c}}}{\boldsymbol{)}}$$\end{document}(OS¯c) increases due to continued photochemical aging, potentially resulting in more toxic aerosol.

Drug rechallenge following drug-induced liver injury

Drug-induced hepatocellular injury is identified internationally by alanine aminotransferase (ALT) levels equal to or exceeding 5× the upper limit of normal (ULN) appearing within 3 months of drug initiation, after alternative causes are excluded. Upon withdrawing the suspect drug, ALT generally decrease by 50% or more. With drug readministration, a positive rechallenge has recently been defined by an ALT level of 3-5× ULN or greater. Nearly 50 drugs are associated with positive rechallenge after drug-induced liver injury (DILI): antimicrobials; and central nervous system, cardiovascular and oncology therapeutics. Drugs associated with high rates of positive rechallenge exhibit multiple risk factors: daily dose >50 mg, an increased incidence of ALT elevations in clinical trials, immunoallergic clinical injury, and mitochondrial impairment in vitro. These drug factors interact with personal genetic, immune, and metabolic factors to influence positive rechallenge rates and outcomes. Drug rechallenge following drug-induced liver injury is associated with up to 13% mortality in prospective series of all prescribed drugs. In recent oncology trials, standardized systems have enabled safer drug rechallenge with weekly liver chemistry monitoring during the high-risk period and exclusion of patients with hypersensitivity. However, high positive rechallenge rates with other innovative therapeutics suggest that caution should be taken with rechallenge of high-risk drugs.

CONCLUSION

For critical medicines, drug rechallenge may be appropriate when 1) no safer alternatives are available, 2) the objective benefit exceeds the risk, and 3) patients are fully informed and consent, can adhere to follow-up, and alert providers to hepatitis symptoms. To better understand rechallenge outcomes and identify key risk factors for positive rechallenge, additional data are needed from controlled clinical trials, prospective registries, and large health care databases. (Hepatology 2017;66:646-654).

Synergistic Cytotoxicity from Drugs and Cytokines In Vitro as an Approach to Classify Drugs According to Their Potential to Cause Idiosyncratic Hepatotoxicity: A Proof-of-Concept Study

Idiosyncratic drug-induced liver injury (IDILI) typically occurs in a small fraction of patients and has resulted in removal of otherwise efficacious drugs from the market. Current preclinical testing methods are ineffective in predicting which drug candidates have IDILI liability. Recent results suggest that immune mediators such as tumor necrosis factor-α (TNF) and interferon-γ (IFN) interact with drugs that cause IDILI to kill hepatocytes. This proof-of-concept study was designed to test the hypothesis that drugs can be classified according to their ability to cause IDILI in humans using classification modeling with covariates derived from concentration-response relationships that describe cytotoxic interaction with cytokines. Human hepatoma (HepG2) cells were treated with drugs associated with IDILI or with drugs lacking IDILI liability and cotreated with TNF and/or IFN. Detailed concentration-response relationships were determined for calculation of parameters such as the maximal cytotoxic effect, slope, and EC₅₀ for use as covariates for classification modeling using logistic regression. These parameters were incorporated into multiple classification models to identify combinations of covariates that most accurately classified the drugs according to their association with human IDILI. Of 14 drugs associated with IDILI, almost all synergized with TNF to kill HepG2 cells and were successfully classified by statistical modeling. IFN enhanced the toxicity mediated by some IDILI-associated drugs in the presence of TNF. In contrast, of 10 drugs with little or no IDILI liability, none synergized with inflammatory cytokines to kill HepG2 cells and were classified accordingly. The resulting optimal model classified the drugs with extraordinary selectivity and specificity.

Integrating Drug's Mode of Action into Quantitative Structure-Activity Relationships for Improved Prediction of Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is complex in mechanism. Different drugs could undergo different mechanisms but result in the same DILI type, while the same drug could lead to different DILI types via different mechanisms. Therefore, predicting a drug's potential for DILI should take its underlying mechanisms into consideration. To achieve that, we constructed a novel approach by incorporating the drug's Mode of Action (MOA) into Quantitative Structure-Activity Relationship (QSAR) modeling. This MOA-DILI approach was examined using a data set of 333 drugs. The drugs were first grouped according to their MOA profiles (positive or negative in each MOA) based on the Tox21 qHTS assays. QSAR models for individual MOA assays were developed and subsequently combined to obtain the MOA-DILI model. A hold-out testing strategy (222 drugs for training and 111 drugs as a test set) was employed, which yielded a predictive accuracy of 0.711. The MOA-DILI model was directly compared with the standard QSAR approach using the same hold-out strategy, and the QSAR model yielded an accuracy of 0.662. To minimize the random chance in splitting training/test sets, the hold-out testing process was repeated 1000 times, and the observed difference in prediction accuracy between MOA-DILI and QSARs was statistically significant (P value <0.0001). Out of 17 MOAs used, four assays (i.e., antioxidant response elements, PPAR-gamma, estrogen receptor, and thyroid receptor assays) contributed most to the improved prediction of the MOA-DILI model over QSARs. In conclusion, the MOA-DILI approach has the potential to significantly improve predictive outcomes and to reveal complex relationships between MOAs and DILI, all of which would be helpful in developing DILI predictive models in drug screening and for risk assessment of industrial chemicals.

An Automated Multiplexed Hepatotoxicity and CYP Induction Assay Using HepaRG Cells in 2D and 3D

Drug-induced liver injury (DILI) and drug-drug interactions (DDIs) are concerns when developing safe and efficacious compounds. We have developed an automated multiplex assay to detect hepatotoxicity (i.e., ATP depletion) and metabolism (i.e., cytochrome P450 1A [CYP1A] and cytochrome P450 3A4 [CYP3A4] enzyme activity) in two-dimensional (2D) and three-dimensional (3D) cell cultures. HepaRG cells were cultured in our proprietary micromold plates and produced spheroids. HepaRG cells, in 2D or 3D, expressed liver-specific proteins throughout the culture period, although 3D cultures consistently exhibited higher albumin secretion and CYP1A/CYP3A4 enzyme activity than 2D cultures. Once the spheroid hepatic quality was assessed, 2D and 3D HepaRGs were challenged to a panel of DILI- and CYP-inducing compounds for 7 days. The 3D HepaRG model had a 70% sensitivity to liver toxins at 7 days, while the 2D model had a 60% sensitivity. In both the 2D and 3D HepaRG models, 83% of compounds were predicted to be CYP inducers after 7 days of compound exposure. Combined, our results demonstrate that an automated multiplexed liver spheroid system is a promising cell-based method to evaluate DILI and DDI for early-stage drug discovery.

Evaluation of DILI Predictive Hypotheses in Early Drug Development

Drug-induced liver injury (DILI) is a leading cause of drug failure in clinical trials and a major reason for drug withdrawals. DILI has been shown to be dependent on both daily dose and extent of hepatic metabolism. Yet, early in drug development daily dose is unknown. Here, we perform a comprehensive analysis of the published hypotheses that attempt to predict DILI, including a new analysis of the Biopharmaceutics Drug Disposition Classification System (BDDCS) in evaluating the severity of DILI warnings in drug labels approved by the FDA and the withdrawal status due to adverse drug reactions (ADRs). Our analysis confirms that higher doses ≥50 mg/day lead to increased DILI potential, but this property alone is not sufficient to predict the DILI potential. We evaluate prior attempts to categorize DILI such as Rule of 2, BSEP inhibition, and measures of key mechanisms of toxicity compared to BDDCS classification. Our results show that BDDCS Class 2 drugs exhibit the highest DILI severity and that all of the published methodologies evaluated here, except when daily dose is known, do not yield markedly better predictions than BDDCS. The assertion that extensive metabolized compounds are at higher risk of developing DILI is confirmed but can be enhanced by differentiating BDDCS Class 2 from Class 1 drugs. We do not propose that the BDDCS classification, which does not require knowledge of the clinical dose, is sufficiently predictive/accurate of DILI potential for new molecular entities but suggest that comparison of proposed DILI prediction methodologies with BDDCS classification is a useful tool to evaluate the potential reliability of newly proposed algorithms.

CONCLUSION

The most successful approaches to predict DILI potential all include a measure of dose, yet there is a quantifiable uncertainty associated with the predicted dose early in drug development. Here, we compare the possibility of predicting DILI potential using the BDDCS classification versus previously published methods and note that many hypothesized predictive DILI metrics do no better than just avoiding BDDCS Class 2 drugs.

Endoplasmic Reticulum Stress Induction and ERK1/2 Activation Contribute to Nefazodone-Induced Toxicity in Hepatic Cells

Nefazodone, an antagonist for the 5-hydroxytryptanine receptor, has been used for the treatment of depression. Acute liver injury has been documented to be associated with the use of nefazodone; however, the mechanisms of nefazodone-induced liver toxicity are not well defined. In this report, using biochemical and molecular analyses, we characterized the molecular mechanisms underlying the hepatotoxicity of nefazodone. We found that nefazodone induced endoplasmic reticulum (ER) stress in HepG2 cells, as the expression of typical ER stress markers, including CHOP, ATF-4, and p-eIF2α, was significantly increased, and splicing of XBP1 was observed. Nefazodone-suppressed protein secretion was evaluated using a Gaussia luciferase reporter assay that measures ER stress. The ER stress inhibitors (4-phenylbutyrate and salubrinal) and knockdown of ATF-4 gene attenuated nefazodone-induced ER stress and cytotoxicity. Nefazodone activated the MAPK signaling pathway, as indicated by increased phosphorylation of JNK, ERK1/2, and p38. Inhibition of ERK1/2 reduced ER stress caused by nefazodone. Taken together, our findings suggest that ER stress contributes to nefazodone-induced toxicity in HepG2 cells and that the MAPK signaling pathway plays an important role in ER stress.

Key Challenges and Opportunities Associated with the Use of In Vitro Models to Detect Human DILI: Integrated Risk Assessment and Mitigation Plans

Drug-induced liver injury (DILI) is a major cause of late-stage clinical drug attrition, market withdrawal, black-box warnings, and acute liver failure. Consequently, it has been an area of focus for toxicologists and clinicians for several decades. In spite of considerable efforts, limited improvements in DILI prediction have been made and efforts to improve existing preclinical models or develop new test systems remain a high priority. While prediction of intrinsic DILI has improved, identifying compounds with a risk for idiosyncratic DILI (iDILI) remains extremely challenging because of the lack of a clear mechanistic understanding and the multifactorial pathogenesis of idiosyncratic drug reactions. Well-defined clinical diagnostic criteria and risk factors are also missing. This paper summarizes key data interpretation challenges, practical considerations, model limitations, and the need for an integrated risk assessment. As demonstrated through selected initiatives to address other types of toxicities, opportunities exist however for improvement, especially through better concerted efforts at harmonization of current, emerging and novel in vitro systems or through the establishment of strategies for implementation of preclinical DILI models across the pharmaceutical industry. Perspectives on the incorporation of newer technologies and the value of precompetitive consortia to identify useful practices are also discussed.

Inhibition of bile salt transport by drugs associated with liver injury in primary hepatocytes from human, monkey, dog, rat, and mouse

Interference of bile salt transport is one of the underlying mechanisms for drug-induced liver injury (DILI). We developed a novel bile salt transport activity assay involving in situ biosynthesis of bile salts from their precursors in primary human, monkey, dog, rat, and mouse hepatocytes in suspension as well as LC-MS/MS determination of extracellular bile salts transported out of hepatocytes. Glycine- and taurine-conjugated bile acids were rapidly formed in hepatocytes and effectively transported into the extracellular medium. The bile salt formation and transport activities were time‒ and bile-acid-concentration‒dependent in primary human hepatocytes. The transport activity was inhibited by the bile salt export pump (BSEP) inhibitors ketoconazole, saquinavir, cyclosporine, and troglitazone. The assay was used to test 86 drugs for their potential to inhibit bile salt transport activity in human hepatocytes, which included 35 drugs associated with severe DILI (sDILI) and 51 with non-severe DILI (non-sDILI). Approximately 60% of the sDILI drugs showed potent inhibition (with IC50 values <50 μM), but only about 20% of the non-sDILI drugs showed this strength of inhibition in primary human hepatocytes and these drugs are associated only with cholestatic and mixed hepatocellular cholestatic (mixed) injuries. The sDILI drugs, which did not show substantial inhibition of bile salt transport activity, are likely to be associated with immune-mediated liver injury. Twenty-four drugs were also tested in monkey, dog, rat and mouse hepatocytes. Species differences in potency were observed with mouse being less sensitive than other species to inhibition of bile salt transport. In summary, a novel assay has been developed using hepatocytes in suspension from human and animal species that can be used to assess the potential for drugs and/or drug-derived metabolites to inhibit bile salt transport and/or formation activity. Drugs causing sDILI, except those by immune-mediated mechanism, are highly associated with potent inhibition of bile salt transport.