Chimeric mice with humanized liver: Application in drug metabolism and pharmacokinetics studies for drug discovery

Quantitative prediction of CYP3A-mediated drug-drug interactions by correctly estimating fraction metabolized using human liver chimeric mice

BACKGROUND AND PURPOSE

Fraction metabolized (fm ) and fraction transported (ft ) are important for understanding drug-drug interactions (DDIs) in drug discovery and development. However, current in vitro systems cannot accurately estimate in vivo fm due to inability to reflect the ft by efflux transporters (ft,efflux ). This study demonstrates how CYP3A-mediated DDI for CYP3A/P-gp substrates can be predicted using Hu-PXB mice as human liver chimeric mice.

EXPERIMENTAL APPROACH

For estimating human in vitro fm by CYP3A enzyme (fm,CYP3A,in vitro ), six drugs, including CYP3A/P-gp substrates (alprazolam, cyclosporine, docetaxel, midazolam, prednisolone, and theophylline) and human hepatocytes were incubated with or without ketoconazole as a CYP3A inhibitor. We calculated fm,CYP3A,in vitro based on hepatic intrinsic clearance. To estimate human in vivo fm,CYP3A (fm,CYP3A,in vivo ), we collected information on clinical DDI caused by ketoconazole for these six drugs. We calculated fm,CYP3A,in vivo using the change of total clearance (CLtotal ). For evaluating the human DDI predictability, the six drugs were administered intravenously to Hu-PXB and SCID mice with or without ketoconazole. We calculated the change of CLtotal caused by ketoconazole. We compared the CLtotal change in humans with that in Hu-PXB and SCID mice.

KEY RESULTS

The fm,CYP3A,in vitro was overestimated compared to the fm,CYP3A,in vivo . Hu-PXB mice showed much better correlation in the change of CLtotal with humans (R2  = 0.95) compared to SCID mice (R2  = 0.0058).

CONCLUSIONS AND IMPLICATIONS

CYP3A-mediated DDI can be predicted by correctly estimating human fm,CYP3A,in vivo using Hu-PXB mice. These mice could be useful predicting hepatic fm and ft,efflux .

Novel Screening System for Biliary Excretion of Drugs Using Human Cholangiocyte Organoid Monolayers with Directional Drug Transport

It has recently been reported that cholangiocyte organoids can be established from primary human hepatocytes. The purpose of this study was to culture the organoids in monolayers on inserts to investigate the biliary excretory capacity of drugs. Cholangiocyte organoids prepared from hepatocytes had significantly higher mRNA expression of CK19, a bile duct epithelial marker, compared to hepatocytes. The organoids also expressed mRNA for efflux transporters involved in biliary excretion of drugs, P-glycoprotein (P-gp), multidrug resistance-associated protein 2 (MRP2), and breast cancer resistance protein (BCRP). The subcellular localization of each protein was observed. These results suggest that the membrane-cultured cholangiocyte organoids are oriented with the upper side being the apical membrane side (A side, bile duct lumen side) and the lower side being the basolateral membrane side (B side, hepatocyte side), and that each efflux transporter is localized to the apical membrane side. Transport studies showed that the permeation rate from the B side to the A side was faster than from the A side to the B side for the substrates of each efflux transporter, but this directionality disappeared in the presence of inhibitor of each transporter. In conclusion, the cholangiocyte organoid monolayer system has the potential to quantitatively evaluate the biliary excretion of drugs. The results of the present study represent an unprecedented system using human cholangiocyte organoids, which may be useful as a screening model to directly quantify the contribution of biliary excretion to the clearance of drugs.

Quantitative Prediction of OATP-Mediated Disposition and Biliary Clearance Using Human Liver Chimeric Mice

Drug biliary clearance (CLbile) in vivo is among the most difficult pharmacokinetic parameters to predict accurately and quantitatively because biliary excretion is influenced by metabolic enzymes, transporters, and passive diffusion across hepatocyte membranes. The purpose of this study is to demonstrate the use of Hu-FRG mice [Fah-/-/Rag2-/-/Il2rg-/- (FRG) mice transplanted with human-derived hepatocytes] to quantitatively predict human organic anion transporting polypeptide (OATP)-mediated drug disposition and CLbile To predict OATP-mediated disposition, six OATP substrates (atorvastatin, fexofenadine, glibenclamide, pitavastatin, pravastatin, and rosuvastatin) were administered intravenously to Hu-FRG and Mu-FRG mice (FRG mice transplanted with mouse hepatocytes) with or without rifampicin as an OATP inhibitor. We calculated the hepatic intrinsic clearance (CLh,int) and the change of hepatic clearance (CLh) caused by rifampicin (CLh ratio). We compared the CLh,int of humans with that of Hu-FRG mice and the CLh ratio of humans with that of Hu-FRG and Mu-FRG mice. For predicting CLbile, 20 compounds (two cassette doses of 10 compounds) were administered intravenously to gallbladder-cannulated Hu-FRG and Mu-FRG mice. We evaluated the CLbile and investigated the correlation of human CLbile with that of Hu-FRG and Mu-FRG mice. We found good correlations between humans and Hu-FRG mice in CLh,int (100% within threefold) and CLh ratio (R2 = 0.94). Moreover, we observed a much better relationship between humans and Hu-FRG mice in CLbile (75% within threefold). Our results suggest that OATP-mediated disposition and CLbile can be predicted using Hu-FRG mice, making them a useful in vivo drug discovery tool for quantitatively predicting human liver disposition. SIGNIFICANCE STATEMENT: OATP-mediated disposition and biliary clearance of drugs are likely quantitatively predictable using Hu-FRG mice. The findings can enable the selection of better drug candidates and the development of more effective strategies for managing OATP-mediated DDIs in clinical studies.

Analysis of the Bile Acid Composition in a Fibroblast Growth Factor 19-Expressing Liver-Humanized Mouse Model and Its Use for CYP3A4-Mediated Drug-Drug Interaction Studies

Numerous biomedical applications have been described for liver-humanized mouse models, such as in drug metabolism or drug-drug interaction (DDI) studies. However, the strong enlargement of the bile acid (BA) pool due to lack of recognition of murine intestine-derived fibroblast growth factor-15 by human hepatocytes and a resulting upregulation in the rate-controlling enzyme for BA synthesis, cytochrome P450 (CYP) 7A1, may pose a challenge in interpreting the results obtained from such mice. To address this challenge, the human fibroblast growth factor-19 (FGF19) gene was inserted into the Fah-/- , Rag2-/- , Il2rg-/- NOD (FRGN) mouse model, allowing repopulation with human hepatocytes capable of responding to FGF19. While a decrease in CYP7A1 expression in human hepatocytes from humanized FRGN19 mice (huFRGN19) and a concomitant reduction in BA production was previously shown, a detailed analysis of the BA pool in these animals has not been elucidated. Furthermore, there are sparse data on the use of this model to assess potential clinical DDI. In the present work, the change in BA composition in huFRGN19 compared with huFRGN control animals was systematically evaluated, and the ability of the model to recapitulate a clinically described CYP3A4-mediated DDI was assessed. In addition to a massive reduction in the total amount of BA, FGF19 expression in huFRGN19 mice resulted in significant changes in the profile of various primary, secondary, and sulfated BAs in serum and feces. Moreover, as observed clinically, administration of the pregnane X receptor agonist rifampicin reduced the oral exposure of the CYP3A4 substrate triazolam. SIGNIFICANCE STATEMENT: Transgenic expression of FGF19 normalizes the unphysiologically high level of bile acids in a chimeric liver-humanized mouse model and leads to massive changes in bile acid composition. These adaptations could overcome one of the potential impediments in the use of these mouse models for drug-drug interaction studies.

Novel approach for verification of a human PBPK modeling strategy using chimeric mice in the health risk assessment of epyrifenacil

In the human risk assessment by physiologically based pharmacokinetic modeling (PBPK), verification of the modeling strategy and confirmation of the reliability of the output data are important when the clinical data are not available. A new herbicide, epyrifenacil, is metabolized to S-3100-CA in mammals and causes hepatotoxicity in mice. S-3100-CA is transferred to the liver by transporters and eliminated by biliary excretion and metabolism. In the previous human PBPK research, we succeeded in predicting S-3100-CA pharmacokinetics by obtaining human hepatic parameters from chimeric mice with humanized liver after we checked the model's quantitative performance using mouse experimental data. To further enhance the reliability of human PBPK data, verification of the following two points was considered effective: 1) verification of model applicability to pharmacokinetics prediction in multiple animal species, and 2) verification of the parameter acquisition methods. In this study, we applied the same modeling strategy to rats, i.e., we obtained rat hepatic parameters for PBPK from chimeric mice with rat hepatocytes, not from rats. As the simulation results, rat internal dosimetry was precisely reproduced, although it tended to be slightly overestimated by approximately two times. From the results of the sensitivity analysis, this overestimation was mainly due to hepatic parameters from chimeric mice. Therefore, it is suggested that a similar slight prediction error may occur also in human PBPK using chimeric mice, but considering the degree of error, it can be said that our modeling strategy is robust and the predicted human internal dosimetry in the previous research is reliable.

In vitro and in vivo metabolic profiling of PD105, a PI3Kδ inhibitor, using UHPLC-Q-Exactive plus-MS

PD105, a PI3Kδ inhibitor, is a candidate for the treatment of rheumatoid arthritis. This study aims to identify the metabolic profiling in vitro and in vivo by UHPLC-Q-Exactive Plus-MS.The in vitro metabolism of PD105 was studied by mouse liver microsomes and hepatocytes, while the in vivo metabolic profiling was obtained from mouse plasma, urine, and faeces. A total of 20 metabolites were tentatively identified based on accurate mass, fragment pathways, and characteristic fragment ions, including 4 in vitro and 20 in vivo.The proposed metabolic pathways of PD105 showed that there were 18 phase I metabolites and 2 phase II metabolites. The phase I metabolic pathways included oxidation, hydration, desaturation and oxidative dechlorination, while the phase II metabolic reactions were mainly methylation and arginine conjugation. Among them, oxidation was the main metabolic pathway of PD105.The comprehensive metabolic profiling contributed to further elucidation of pharmacological action and mechanism of PD105.

Applications of In Silico Models to Predict Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a major cause of the withdrawal of pre-marketed drugs, typically attributed to oxidative stress, mitochondrial damage, disrupted bile acid homeostasis, and innate immune-related inflammation. DILI can be divided into intrinsic and idiosyncratic DILI with cholestatic liver injury as an important manifestation. The diagnosis of DILI remains a challenge today and relies on clinical judgment and knowledge of the insulting agent. Early prediction of hepatotoxicity is an important but still unfulfilled component of drug development. In response, in silico modeling has shown good potential to fill the missing puzzle. Computer algorithms, with machine learning and artificial intelligence as a representative, can be established to initiate a reaction on the given condition to predict DILI. DILIsym is a mechanistic approach that integrates physiologically based pharmacokinetic modeling with the mechanisms of hepatoxicity and has gained increasing popularity for DILI prediction. This article reviews existing in silico approaches utilized to predict DILI risks in clinical medication and provides an overview of the underlying principles and related practical applications.

Influence of Zhuanggu Guanjie Pill on Seven Cytochrome P450 Enzymes Based on Probe Cocktail and Pharmacokinetics Approaches

BACKGROUND

The use of herbal medicines has tremendously increased over the past few decades. Case reports and controlled clinical investigations of herbal-drug interactions have been reported. Since Cytochrome P450 (CYP) enzymes play an important role in drug interactions. The evaluation of the influence of herbal medicines on the activities of CYPs is beneficial to promote scientific and rational clinical use of herbal medicines.

OBJECTIVE

Herein, we aimed to develop and validate a method to simultaneously quantify seven CYP cocktail probe drugs consisting of phenacetin (PNC), bupropion (BPP), losartan potassium (LK), omeprazole (OMP), dextromethorphan (DM), chlorzoxazone (CZZ) and midazolam (MDZ) and their respective metabolites in a single acquisition run and use this method to evaluate the influence of Zhuanggu Guanjie Pill (ZGGJP) on seven CYPs.

METHODS

A cost-effective and simple UHPLC-(±)ESI-MS/MS method for simultaneous determination of seven probe drugs and metabolites in rat plasma was developed and validated. Male and female rats were randomly divided into three groups and treated with 1.2 g/kg/d ZGGJP, 5 g/kg/d ZGGJP and 0.5% CMC-Na for 14 consecutive days. After 24 h of the last administration, all rats were administrated orally with probe drugs. The influence of ZGGJP on the CYPs was carried out by comparing the metabolic ratio (Cmax, AUC0-t) of metabolites/probe drugs in rats.

RESULTS

The calibration curves were linear, with correlation coefficient > 0.99 for seven probe drugs and their corresponding metabolites. Intra- and inter-day precisions were not greater than 15% RSD and the accuracies were within ±15% of nominal concentrations. The ZGGJP showed significant inductive effect on CYP1A2, CYP2B6, CYP2C9 and CYP3A in male and female rats.

CONCLUSION

ZGGJP had inductive effects on CYP1A2, CYP2B6, CYP2C9 and CYP3A in male and female rats.

Prediction of the human pharmacokinetics of epyrifenacil and its major metabolite, S-3100-CA, by a physiologically based pharmacokinetic modeling using chimeric mice with humanized liver

Human internal dosimetry of pesticides is essential in the risk assessment when toxicity has been confirmed in laboratory animals. While human toxicokinetics data of pesticides are hardly obtained intendedly, the use of physiologically based pharmacokinetic (PBPK) modeling has become important for predicting human internal dosimetry. Especially, when the compound exhibits complicated pharmacokinetics via active uptake, metabolism, and biliary excretion in liver, it is difficult to obtain these hepatic parameters only by the in vitro experiments. Epyrifenacil, a new herbicide, is rapidly metabolized to S-3100-CA (CA) in mammals and causes hepatotoxicity in mice. CA is eliminated from the systemic circulation by biliary excretion and metabolism in liver. Although uptake of CA by transporters is observed in mouse primary hepatocytes, significantly less of it is observed in human primary hepatocytes. In order to evaluate human internal dosimetry of CA, a precise PBPK model was developed. To obtain human hepatic parameters, i.e., hepatic elimination intrinsic clearance via biliary excretion and metabolism, we used chimeric mice with humanized liver as a model to reproduce the complicated pharmacokinetics of CA in humans. After we developed a mouse PBPK model, by replacing mouse parameters with those of humans, we calculated CA concentration in human liver. Comparing the predicted CA exposure in human liver with the measured values in mice, we demonstrated a clear interspecies difference of approximately 4 times lower C_max and AUC in humans. This result suggested that the risk of hepatotoxicity is less in humans than in mice.

Liver-humanized mice: A translational strategy to study metabolic disorders

The liver is the metabolic core of the whole body. Tools commonly used to study the human liver metabolism include hepatocyte cell lines, primary human hepatocytes, and pluripotent stem cells-derived hepatocytes in vitro, and liver genetically humanized mouse model in vivo. However, none of these systems can mimic the human liver in physiological and pathological states satisfactorily. Liver-humanized mice, which are established by reconstituting mouse liver with human hepatocytes, have emerged as an attractive animal model to study drug metabolism and evaluate the therapeutic effect in "human liver" in vivo because the humanized livers greatly replicate enzymatic features of human hepatocytes. The application of liver-humanized mice in studying metabolic disorders is relatively less common due to the largely uncertain replication of metabolic profiles compared to humans. Here, we summarize the metabolic characteristics and current application of liver-humanized mouse models in metabolic disorders that have been reported in the literature, trying to evaluate the pros and cons of using liver-humanized mice as novel mouse models to study metabolic disorders.

Survival-Assured Liver Injury Preconditioning (SALIC) Enables Robust Expansion of Human Hepatocytes in Fah-/- Rag2-/- IL2rg-/- Rats

Although liver-humanized animals are desirable tools for drug development and expansion of human hepatocytes in large quantities, their development is restricted to mice. In animals larger than mice, a precondition for efficient liver humanization remains preliminary because of different xeno-repopulation kinetics in livers of larger sizes. Since rats are ten times larger than mice and widely used in pharmacological studies, liver-humanized rats are more preferable. Here, Fah-/- Rag2-/- IL2rg-/- (FRG) rats are generated by CRISPR/Cas9, showing accelerated liver failure and lagged liver xeno-repopulation compared to FRG mice. A survival-assured liver injury preconditioning (SALIC) protocol, which consists of retrorsine pretreatment and cycling 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) administration by defined concentrations and time intervals, is developed to reduce the mortality of FRG rats and induce a regenerative microenvironment for xeno-repopulation. Human hepatocyte repopulation is boosted to 31 ± 4% in rat livers at 7 months after transplantation, equivalent to approximately a 1200-fold expansion. Human liver features of transcriptome and zonation are reproduced in humanized rats. Remarkably, they provide sufficient samples for the pharmacokinetic profiling of human-specific metabolites. This model is thus preferred for pharmacological studies and human hepatocyte production. SALIC may also be informative to hepatocyte transplantation in other large-sized species.

Advanced preclinical models for evaluation of drug-induced liver injury - consensus statement by the European Drug-Induced Liver Injury Network [PRO-EURO-DILI-NET]

Drug-induced liver injury (DILI) is a major cause of acute liver failure (ALF) and one of the leading indications for liver transplantation in Western societies. Given the wide use of both prescribed and over the counter drugs, DILI has become a major health issue for which there is a pressing need to find novel and effective therapies. Although significant progress has been made in understanding the molecular mechanisms underlying DILI, our incomplete knowledge of its pathogenesis and inability to predict DILI is largely due to both discordance between human and animal DILI in preclinical drug development and a lack of models that faithfully recapitulate complex pathophysiological features of human DILI. This is exemplified by the hepatotoxicity of acetaminophen (APAP) overdose, a major cause of ALF because of its extensive worldwide use as an analgesic. Despite intensive efforts utilising current animal and in vitro models, the mechanisms involved in the hepatotoxicity of APAP are still not fully understood. In this expert Consensus Statement, which is endorsed by the European Drug-Induced Liver Injury Network, we aim to facilitate and outline clinically impactful discoveries by detailing the requirements for more realistic human-based systems to assess hepatotoxicity and guide future drug safety testing. We present novel insights and discuss major players in APAP pathophysiology, and describe emerging in vitro and in vivo pre-clinical models, as well as advanced imaging and in silico technologies, which may improve prediction of clinical outcomes of DILI.

Anthocyanins from purple sweet potato alleviate doxorubicin-induced cardiotoxicity in vitro and in vivo

In this study, anthocyanins were extracted and purified from purple sweet potato anthocyanins (PSPA) and the alleviative effect of PSPA on doxorubicin (DOX)-induced cardiotoxicity was investigated. High Performance Liquid Chromatography-Mass Spectrometry (HPLC-MS) results showed that 10 kinds of substances were identified in PSPA and the PSPA was mainly composed of cyanidin (62.9%) and peonidin (21.46%). In in vitro experiments, PSPA reduced the excessive release of inflammatory factors (NO and TNF-α) induced by DOX and decreased the secretion of trimethylamine oxide (TMAO), lactic dehydrogenase (LDH), and creatine kinase (CK) caused by myocardial injury. In in vivo experiments, PSPA inhibited the release of NO and MDA levels in heart tissue. Meanwhile, mice treated with PSPA decreased the levels of LDH, CK, TNF-α, and TMAO in serum and heart tissue when compared with the DOX group. In addition, the histopathological results of the heart tissue also showed a protective effect of PSPA on the pathological changes in heart. These results provide a reference for the application of PSPA as a functional food to intervene in DOX-induced cardiotoxicity. PRACTICAL APPLICATIONS: The effects of anthocyanins from purple sweet potato anthocyanins (PSPA) on doxorubicin (DOX)-induced cardiotoxicity were investigated in vitro and in vivo. The results indicated that PSPA could significantly ameliorate DOX-induced heart failure. The obtained results could provide the potential application of PSPA as an alternative therapy for cardiotoxicity caused by DOX in the functional food industry.

Empirical and theoretical approaches for the prediction of human hepatic clearance using chimeric mice with humanised liver: the use of physiologically based scaling, a novel solution for potential overprediction due to coexisting mouse metabolism

Chimeric mice are immunodeficient mice in which the majority of the hepatic parenchymal cells are replaced with human hepatocytes.Following intravenous administration of 24 model compounds to control and chimeric mice, human hepatic clearance (CL_h) was predicted using the single-species allometric scaling (SSS) method. Predictability of the chimeric mice was better than that of the control mice.Human CL_h was predicted by the physiologically based scaling (PBS) method, wherein observed CL_h in chimeric mice was first converted to intrinsic CL_h (CL_h,int). As the liver of chimeric mice contains remaining mouse hepatocytes, CL_h,int was corrected by in vitro CL_h ratios of the mouse to human hepatocytes according to their hepatocyte replacement index. Further, predicted human CL_h was calculated based on an assumption that CL_h,int in chimeric mice normalised for their liver weight was equal to CL_h,int per liver weight in humans. Consequently, better prediction performance was observed with the use of the PBS method than the SSS method.SSS method is an empirical method, and the effects of coexisting mouse metabolism cannot be avoided. However, the PBS method with in vitro CL_h correction might be a potential solution and may expand the application of chimeric mice in new drug development.

UPLC-MS/MS method for the simultaneous quantification of pravastatin, fexofenadine, rosuvastatin, and methotrexate in a hepatic uptake model and its application to the possible drug-drug interaction study of triptolide

A rapid and specific UPLC-MS/MS method with a total run time of 3.5 min was developed for the determination of pravastatin, fexofenadine, rosuvastatin, and methotrexate in rat primary hepatocytes. After protein precipitation with 70% acetonitrile (containing 30% H2 O), these four analytes were separated under gradient conditions with a mobile phase consisting of 0.03% acetic acid (v/v) and methanol at a flow rate of 0.50 mL/min. The linearity, recovery, matrix effect, accuracy, precision, and stability of the method were well validated. We evaluated drug-drug interactions based on these four compounds in freshly suspended hepatocytes. The hepatic uptake of pravastatin, fexofenadine, rosuvastatin, and methotrexate at 4°C was significantly lower than that at 37°C, and the hepatocytes were saturable with increased substrate concentration and culture time, suggesting that the rat primary hepatocyte model was successfully established. Triptolide showed a significant inhibitory effect on the hepatic uptake of these four compounds. In conclusion, this method was successfully employed for the quantification of pravastatin, fexofenadine, rosuvastatin, and methotrexate and was used to verify the rat primary hepatocyte model for Oatp1, Oatp2, Oatp4, and Oat2 transporter studies. Then, we applied this model to explore the effect of triptolide on these four transporters.

In vivo evaluation of intestinal human CYP3A inhibition by macrolide antibiotics in CYP3A-humanised mice

It is important to predict drug-drug interactions via inhibition of intestinal cytochrome P450 3A (CYP3A) which is a determinant of bioavailability of orally administered CYP3A substrates. However, inhibitory effects of macrolide antibiotics on CYP3A-mediated metabolism are not entirely identical between humans and rodents.We investigated the effects of macrolide antibiotics, clarithromycin and erythromycin, on in vitro and in vivo metabolism of triazolam, a CYP3A substrate, in CYP3A-humanised mice generated by using a mouse artificial chromosome vector carrying a human CYP3A gene.Metabolic activities of triazolam were inhibited by macrolide antibiotics in liver and intestine microsomes of CYP3A-humanised mice.The area under the plasma concentration-time curve ratios of 4-hydroxytriazolam to triazolam after oral dosing of triazolam were significantly decreased by multiple administration of macrolide antibiotics. The plasma concentrations ratios of α-hydroxytriazolam and 4-hydroxytriazolam to triazolam in portal blood were significantly decreased by multiple administration of clarithromycin in CYP3A-humanised mice.These results suggest that intestinal CYP3A activity was inhibited by macrolide antibiotics in CYP3A-humanised mice in vitro and in vivo. The plasma concentrations of triazolam and its metabolites in the portal blood of CYP3A-humanised mice would be useful for direct evaluation of intestinal CYP3A-mediated drug-drug interactions.

Recent trends in drugs of abuse metabolism studies for mass spectrometry-based analytical screening procedures

The still increasing number of drugs of abuse, particularly the so-called new psychoactive substances (NPS), poses an analytical challenge for clinical and forensic toxicologists but also for doping control. NPS usually belong to various classes such as synthetic cannabinoids, phenethylamines, opioids, or benzodiazepines. Like other xenobiotics, NPS undergo absorption, distribution, metabolism, and excretion processes after consumption, but only very limited data concerning their toxicokinetics and safety properties is available once they appear on the market. The inclusion of metabolites in mass spectral libraries is often crucial for the detection of NPS especially in urine screening approaches. Authentic human samples may represent the gold standard for identification of metabolites but are often not available and clinical studies cannot be performed due to ethical concerns. However, numerous alternative in vitro and in vivo models are available. This trends article will give an overview on selected models, discuss current studies, and highlight recent developments.

Advancements in stem cell-derived hepatocyte-like cell models for hepatotoxicity testing

Drug-induced liver injury (DILI) is one of the leading causes of clinical trial failures and high drug attrition rates. Currently, the commonly used hepatocyte models include primary human hepatocytes (PHHs), animal models, and hepatic cell lines. However, these models have disadvantages that include species-specific differences or inconvenient cell extraction methods. Therefore, a novel, inexpensive, efficient, and accurate model that can be applied to drug screening is urgently needed. Owing to their self-renewable ability, source abundance, and multipotent competence, stem cells are stable sources of drug hepatotoxicity screening models. Because 3D culture can mimic the in vivo microenvironment more accurately than can 2D culture, the former is commonly used for hepatocyte culture and drug screening. In this review, we introduce the different sources of stem cells used to generate hepatocyte-like cells and the models for hepatotoxicity testing that use stem cell-derived hepatocyte-like cells.

Prediction of Drug Clearance from Enzyme and Transporter Kinetics

Accurate estimation of in vivo clearance in human is pivotal to determine the dose and dosing regimen for drug development. In vitro-in vivo extrapolation (IVIVE) has been performed to predict drug clearance using empirical and physiological scalars. Multiple in vitro systems and mathematical modeling techniques have been employed to estimate in vivo clearance. The models for predicting clearance have significantly improved and have evolved to become more complex by integrating multiple processes such as drug metabolism and transport as well as passive diffusion. This chapter covers the use of conventional as well as recently developed methods to predict metabolic and transporter-mediated clearance along with the advantages and disadvantages of using these methods and the associated experimental considerations. The general approaches to improve IVIVE by use of appropriate scalars, incorporation of extrahepatic metabolism and transport and application of physiologically based pharmacokinetic (PBPK) models with proteomics data are also discussed. The chapter also provides an overview of the advantages of using such dynamic mechanistic models over static models for clearance predictions to improve IVIVE.

Regenerative medicine for the hepatobiliary system: A review

Liver transplantation, the only proven treatment for end-stage liver disease and acute liver failure, is hampered by the scarcity of donors. Regenerative medicine provides an alternative therapeutic approach. Tremendous efforts dedicated to liver regenerative medicine include the delivery of transplantable cells, microtissues, and bioengineered whole livers via tissue engineering and the maintenance of partial liver function via extracorporeal support. This brief review summarizes the current status of regenerative medicine for the hepatobiliary system. For liver regenerative medicine, the focus is on strategies for expansion of transplantable hepatocytes, generation of hepatocyte-like cells, and therapeutic potential of engineered tissues in liver disease models. For biliary regenerative medicine, the discussion concentrates on the methods for generation of cholangiocyte-like cells and strategies in the treatment of biliary disease. Significant advances have been made in large-scale and long-term expansion of liver cells. The development of tissue engineering and stem cell induction technology holds great promise for the future treatment of hepatobiliary diseases. The application of regenerative medicine in liver still lacks extensive animal experiments. Therefore, a large number of preclinical studies are necessary to provide sufficient evidence for their therapeutic effectiveness. Much remains to be done for the treatment of hepatobiliary diseases with regenerative medicine.

Characterization of plasma protein binding in two mouse models of humanized liver, PXB mouse and humanized TK-NOG mouse

The unbound fractions in plasma (f _up) in two mouse models of humanized liver mice, PXB and humanized TK-NOG mice, were compared with human f _up values using equilibrium dialysis method. A good relationship between f _up values obtained from PXB mice and humans was observed; the f _up of 34/39 compounds (87.2%) in PXB mice were within 3-fold of human f _up. In contrast, a weak correlation was observed between human and humanized TK-NOG mouse f _up values; the f _up of 15/24 compounds (62.5%) in humanized TK-NOG mice were within 3-fold of human f _up. As different profiles of plasma protein binding (PPB) profiles were observed between PXB and humanized TK-NOG mice, f _up evaluation is necessary in each mouse model to utilize these humanized liver mice for pharmacological, drug-drug interaction (DDI), and toxicity studies. The unbound fraction in the mixed plasma of human and SCID mouse plasma (85:15) was well correlated with f _up in PXB mice (38/39 compounds within a 3-fold). Thus, this artificial PXB mouse plasma could be used to evaluate PPB.

Prediction of Human Disproportionate and Biliary Excreted Metabolites Using Chimeric Mice with Humanized Liver

The PXB-mouse is potentially a useful in vivo model to predict human hepatic metabolism and clearance. Four model compounds, [¹⁴C]desloratadine, [³H]mianserin, cyproheptadine, and [³H]carbazeran, all reported with disproportionate human metabolites, were orally administered to PXB- or control SCID mice to elucidate the biotransformation of each of them. For [¹⁴C]desloratadine in PXB-mice, O-glucuronide of 3-hydroxydesloratadine was observed as the predominant metabolite in both the plasma and urine. Both 3-hydroxydesloratadine and its O-glucuronide were detected as major drug-related materials in the bile, whereas only 3-hydroxydesloratadine was detected in the feces, suggesting that a fraction of 3-hydroxydesloratadine in feces was derived from deconjugation of its O-glucuronide by gut microflora. This information can help understand the biliary clearance mechanism of a drug and may fill the gap in a human absorption, distribution, metabolism, and excretion study, in which the bile samples are typically not available. The metabolic profiles in PXB-mice were qualitatively similar to those reported in humans in a clinical study in which 3-hydroxydesloratadine and its O-glucuronide were major and disproportionate metabolites compared with rat, mouse, and monkey. In the control SCID mice, neither of the metabolites was detected in any matrix. Similarly, for the other three compounds, all human specific or disproportionate metabolites were detected at a high level in PXB-mice, but they were either minimally observed or not observed in the control mice. Data from these four compounds indicate that studies in PXB-mice can help predict the potential for the presence of human disproportionate metabolites (relative to preclinical species) prior to conducting clinical studies and understand the biliary clearance mechanism of a drug. SIGNIFICANCE STATEMENT: Studies in PXB-mice have successfully predicted the human major and disproportionate metabolites compared with preclinical safety species for desloratadine, mianserin, cyproheptadine, and carbazeran. In addition, biliary excretion data from PXB-mice can help illustrate the human biliary clearance mechanism of a drug.

Predictability of human pharmacokinetics of drugs that undergo hepatic organic anion transporting polypeptide (OATP)-mediated transport using single-species allometric scaling in chimeric mice with humanized liver: integration with hepatic drug metabolism

We previously reported a prediction method for human pharmacokinetics (PK) using single species allometric scaling (SSS) and the complex Dedrick plot in chimeric mice with humanized liver to predict the total clearance (CL_t), distribution volumes in steady state (Vd_ss) and plasma concentration-time profiles of several drugs metabolized by cytochrome P450 (P450) and non-P450 enzymes. In the present study, we examined eight compounds (bosentan, cerivastatin, fluvastatin, pitavastatin, pravastatin, repaglinide, rosuvastatin, valsartan) as typical organic anion transporting polypeptide (OATP) substrates and six compounds metabolized by P450 and non-P450 enzymes to evaluate the predictability of CL_t, Vd_ss and plasma concentration-time profiles after intravenous administration to chimeric mice. The predicted CL_t and Vd_ss of drugs that undergo OATP-mediated uptake and P450/non-P450-mediated metabolism reflected the observed data from humans within a threefold error range. We also examined the possibility of predicting plasma concentration-time profiles of drugs that undergo OATP-mediated uptake using the complex Dedrick plot in chimeric mice. Most profiles could be superimposed with observed profiles from humans within a two- to threefold error range. PK prediction using SSS and the complex Dedrick plot in chimeric mice can be useful for evaluating drugs that undergo both OATP-mediated uptake and P450/non-P450-mediated metabolism.

A novel Css-MRTpo approach to simulate oral plasma concentration-time profiles of the partial glucokinase activator PF-04937319 and its disproportionate N-demethylated metabolite in humans using chimeric mice with humanized livers

A Css-MRTpo superposition method was devised to predict (retrospectively) oral plasma concentration-time profiles of PF-04937319 and its MIST-related metabolite, M1, in humans using chimeric mice with humanized liver.Original PK data were taken from a published report in which PF-04937319 and M1 were given to chimeric mice orally and/or intravenously. Human CL and Vss were predicted by single-species allometry and MRTiv,pred were calculated as Vss,pred/CL,pred. MRTpo,human were assumed to be MRTiv,pred plus MAT or mean metabolite formation time (MFT). Human Css was calculated by dividing the corrected oral dose by Vss,pred.Chronological sampling time and measured plasma concentrations were corrected by MRTpo,human and Css,human, respectively, and transformed to the corresponding values in humans.The obtained concentration-time profile of PF-04937319 was superimposed well with the observed data after single and repeated oral administration to humans. The transformed plasma concentration of M1 was somewhat lower than the observed value, but a slow increase of the simulated metabolite reflected gradual increase of observed M1 on Day 1. Transformed M1 gave an almost-flat concentration-time profile on Day 14, which was consistent with the curve observed in humans. Application of this novel method to other MIST-related compounds is discussed.

Effect of Rifampicin on the Plasma Concentrations of Bile Acid-O-Sulfates in Monkeys and Human Liver-Transplanted Chimeric Mice With or Without Bile Flow Diversion

The present study examined the significance of enterohepatic circulation and the effect of rifampicin [an inhibitor of organic anion-transporting polypeptide 1B (OATP1B)] on the plasma concentrations of bile acid-O-sulfates (glycochenodeoxycholate-O-sulfate, lithocholate-O-sulfate, glycolithocholate-O-sulfate, and taurolithocholate-O-sulfate) in monkeys and human liver-transplanted chimeric mice (PXB mouse). Rifampicin significantly increased the area under the curve of bile acid-O-sulfates in monkeys (13-69 times) and PXB mice (13-25 times) without bile flow diversion. Bile flow diversion reduced the concentration of plasma bile acid-O-sulfates under control conditions in monkeys and the concentration of plasma glycochenodeoxycholate-O-sulfate in PXB mice. It also diminished diurnal variation of plasma lithocholate-O-sulfate, glycolithocholate-O-sulfate, and taurolithocholate-O-sulfate in PXB mice under control conditions. Bile flow diversion did not affect the plasma concentration of bile acid-O-sulfates in monkeys and PXB mice treated with rifampicin. Plasma coproporphyrin I and III levels were constant in monkeys throughout the study, even with bile flow diversion. This study demonstrated that bile acid-O-sulfates are endogenous OATP1B biomarkers in monkeys and PXB mice. Enterohepatic circulation can affect the baseline levels of plasma bile acid-O-sulfates and modify the effect of OATP1B inhibition.

Predicting drug-induced cholestasis: preclinical models

INTRODUCTION

In almost 50% of patients with drug-induced liver injury (DILI), the bile flow from the liver to the duodenum is impaired, a condition known as cholestasis. However, this toxic response only appears in a small percentage of the treated patients (idiosyncrasy). Prediction of drug-induced cholestasis (DIC) is challenging and emerges as a safety issue that requires attention by professionals in clinical practice, regulatory authorities, pharmaceutical companies, and research institutions. Area covered: The current synopsis focuses on the state-of-the-art in preclinical models for cholestatic DILI prediction. These models differ in their goal, complexity, availability, and applicability, and can widely be classified in experimental animals and in vitro models. Expert opinion: Drugs are a growing cause of cholestasis, but the progress made in explaining mechanisms and differences in susceptibility is not growing at the same rate. We need reliable models able to recapitulate the features of DIC, particularly its idiosyncrasy. The homogeneity and the species-specific differences move animal models away from a fair predictability. However, in vitro human models are improving and getting closer to the real hepatocyte phenotype, and they will likely be the choice in the near future. Progress in this area will not only need reliable predictive models but also mechanistic insights.

[Contribution of chimeric mice with a humanized liver to the evaluation of pharmacology, toxicity, and pharmacokinetics in drug discovery and development]

To develop new drugs with high efficacy and safety, it is important to predict the pharmacological, toxicological, and pharmacokinetic profiles of drug candidates in humans. Chimeric mice with a humanized liver are mice in which human hepatocytes have been transplanted, such that mouse liver cells are replaced with human hepatocytes; these mice have been used as prediction models. Studies performed thus far indicate that chimeric mice with a humanized liver can be used for the prediction of human-specific metabolite formation and plasma concentration-time curves for several drugs. Furthermore, studies advocate the utility of chimeric mice with a humanized liver for modelling drug-induced hepatotoxicity and disease such as hepatitis virus infection in safety and pharmacological evaluations respectively. Taken together, these findings indicate that chimeric mice with a humanized liver can be used to evaluate the relationship between pharmacokinetics, toxicity, and efficacy; the contribution by active metabolites may also be assessed. In recent years, new and improved animal models have been developed to overcome the disadvantages of chimeric mice with a humanized liver. It is expected that their usefulness for optimization of drug candidates and translational research in drug discovery and development will further increase.

Human-Derived Organ-on-a-Chip for Personalized Drug Development

To reduce the required capital and time investment in the development of new pharmaceutical agents, there is an urgent need for preclinical drug testing models that are predictive of drug response in human tissues or organs. Despite tremendous advancements and rigorous multistage screening of drug candidates involving computational models, traditional cell culture platforms, animal models and most recently humanized animals, there is still a large deficit in our ability to predict drug response in patient groups and overall attrition rates from phase 1 through phase 4 of clinical studies remain well above 90%. Organ-on-a-chip (OOC) platforms have proven potential in providing tremendous flexibility and robustness in drug screening and development by employing engineering techniques and materials. More importantly, in recent years, there is a clear upward trend in studies that utilize human-induced pluripotent stem cell (hiPSC) to develop personalized tissue or organ models. Additionally, integrated multiple organs on the single chip with increasingly more sophisticated representation of absorption, distribution, metabolism, excretion and toxicity (ADMET) process are being utilized to better understand drug interaction mechanisms in the human body and thus showing great potential to better predict drug efficacy and safety. In this review, we summarize these advances, highlighting studies that took the next step to clinical trials and research areas with the utmost potential and discuss the role of the OOCs in the overall drug discovery process at a preclinical and clinical stage, as well as outline remaining challenges.