Comparison of predictability for human pharmacokinetics parameters among monkeys, rats, and chimeric mice with humanised liver

Empirical scaling factor for predicting human pharmacokinetic profiles of disproportionate metabolites using the Css-MRTpo method and chimeric mice with humanised livers

Predicting plasma concentration-time profiles of disproportionate metabolites in humans is crucial for evaluating metabolites according to the Safety Testing guidelines. We evaluated Css-MRTpo, an empirical method, using chimeric mice with humanised livers capable of generating human-disproportionate metabolites. Azilsartan and AZ-M2 were administered to humanised chimeric mice, and pharmacokinetic parameters were obtained. Pharmacokinetic data for DS-1971a and DS-M1 in humanised chimeric mice were obtained from the literature. The human plasma concentration-time profiles of these compounds were simulated using the Css-MRTpo method. Azilsartan, DS-1971a, and PF-04937319 produced human disproportionate metabolites, AZ-M2, DS-M1, and PF-M1, respectively. The predicted human pharmacokinetic profiles of PF-04937319 and PF-M1 were obtained from a previous study, and their outcomes were re-evaluated. Our findings revealed that the plasma concentrations of the three metabolites were unexpectedly underpredicted, whereas the three unchanged drugs were reasonably predicted. Further, the introduction of the empirical scaling factor of 3, obtained from six model compounds, improved the predictability of metabolites, suggesting the potential usefulness of the Css-MRTpo method in combination with humanised chimeric mice for predicting the pharmacokinetic profiles of disproportionate metabolites at the early stage of new drug development.

Challenges and Opportunities for In Vitro-In Vivo Extrapolation of Aldehyde Oxidase-Mediated Clearance: Toward a Roadmap for Quantitative Translation

Underestimation of aldehyde oxidase (AO)-mediated clearance by current in vitro assays leads to uncertainty in human dose projections, thereby reducing the likelihood of success in drug development. In the present study we first evaluated the current drug development practices for AO substrates. Next, the overall predictive performance of in vitro-in vivo extrapolation of unbound hepatic intrinsic clearance (CLint,u) and unbound hepatic intrinsic clearance by AO (CLint,u,AO) was assessed using a comprehensive literature database of in vitro (human cytosol/S9/hepatocytes) and in vivo (intravenous/oral) data collated for 22 AO substrates (total of 100 datapoints from multiple studies). Correction for unbound fraction in the incubation was done by experimental data or in silico predictions. The fraction metabolized by AO (fmAO) determined via in vitro/in vivo approaches was found to be highly variable. The geometric mean fold errors (gmfe) for scaled CLint,u (mL/min/kg) were 10.4 for human hepatocytes, 5.6 for human liver cytosols, and 5.0 for human liver S9, respectively. Application of these gmfe's as empirical scaling factors improved predictions (45%-57% within twofold of observed) compared with no correction (11%-27% within twofold), with the scaling factors qualified by leave-one-out cross-validation. A road map for quantitative translation was then proposed following a critical evaluation on the in vitro and clinical methodology to estimate in vivo fmAO In conclusion, the study provides the most robust system-specific empirical scaling factors to date as a pragmatic approach for the prediction of in vivo CLint,u,AO in the early stages of drug development. SIGNIFICANCE STATEMENT: Confidence remains low when predicting in vivo clearance of AO substrates using in vitro systems, leading to de-prioritization of AO substrates from the drug development pipeline to mitigate risk of unexpected and costly in vivo impact. The current study establishes a set of empirical scaling factors as a pragmatic tool to improve predictability of in vivo AO clearance. Developing clinical pharmacology strategies for AO substrates by utilizing mass balance/clinical drug-drug interaction data will help build confidence in fmAO.

Dissecting Parameters Contributing to the Underprediction of Aldehyde Oxidase-Mediated Metabolic Clearance of Drugs

We investigated the effect of variability and instability in aldehyde oxidase (AO) content and activity on the scaling of in vitro metabolism data. AO content and activity in human liver cytosol (HLC) and five recombinant human AO preparations (rAO) were determined using targeted proteomics and carbazeran oxidation assay, respectively. AO content was highly variable as indicated by the relative expression factor (REF; i.e., HLC to rAO content) ranging from 0.001 to 1.7 across different in vitro systems. The activity of AO in HLC degrades at a 10-fold higher rate in the presence of the substrate as compared with the activity performed after preincubation without substrate. To scale the metabolic activity from rAO to HLC, a protein-normalized activity factor (pnAF) was proposed wherein the activity was corrected by AO content, which revealed up to sixfold higher AO activity in HLC versus rAO systems. A similar value of pnAF was observed for another substrate, ripasudil. Physiologically based pharmacokinetic (PBPK) modeling revealed a significant additional clearance (CL; 66%), which allowed for the successful prediction of in vivo CL of four other substrates, i.e., O-benzyl guanine, BIBX1382, zaleplon, and zoniporide. For carbazeran, the metabolite identification study showed that the direct glucuronidation may be contributing to around 12% elimination. Taken together, this study identified differential protein content, instability of in vitro activity, role of additional AO clearance, and unaccounted metabolic pathways as plausible reasons for the underprediction of AO-mediated drug metabolism. Consideration of these factors and integration of REF and pnAF in PBPK models will allow better prediction of AO metabolism. SIGNIFICANCE STATEMENT: This study elucidated the plausible reasons for the underprediction of aldehyde oxidase (AO)-mediated drug metabolism and provided recommendations to address them. It demonstrated that integrating protein content and activity differences and accounting for the loss of AO activity, as well as consideration of extrahepatic clearance and additional pathways, would improve the in vitro to in vivo extrapolation of AO-mediated drug metabolism using physiologically based pharmacokinetic modeling.

Predicting Total Drug Clearance and Volumes of Distribution Using the Machine Learning-Mediated Multimodal Method through the Imputation of Various Nonclinical Data

Pharmacokinetic research plays an important role in the development of new drugs. Accurate predictions of human pharmacokinetic parameters are essential for the success of clinical trials. Clearance (CL) and volume of distribution (Vd) are important factors for evaluating pharmacokinetic properties, and many previous studies have attempted to use computational methods to extrapolate these values from nonclinical laboratory animal models to human subjects. However, it is difficult to obtain sufficient, comprehensive experimental data from these animal models, and many studies are missing critical values. This means that studies using nonclinical data as explanatory variables can only apply a small number of compounds to their model training. In this study, we perform missing-value imputation and feature selection on nonclinical data to increase the number of training compounds and nonclinical datasets available for these kinds of studies. We could obtain novel models for total body clearance (CL_tot) and steady-state Vd (Vd_ss) (CL_tot: geometric mean fold error [GMFE], 1.92; percentage within 2-fold error, 66.5%; Vd_ss: GMFE, 1.64; percentage within 2-fold error, 71.1%). These accuracies were comparable to the conventional animal scale-up models. Then, this method differs from animal scale-up methods because it does not require animal experiments, which continue to become more strictly regulated as time passes.

Current Therapeutic Landscape and Safety Roadmap for Targeting the Aryl Hydrocarbon Receptor in Inflammatory Gastrointestinal Indications

Target modulation of the AhR for inflammatory gastrointestinal (GI) conditions holds great promise but also the potential for safety liabilities both within and beyond the GI tract. The ubiquitous expression of the AhR across mammalian tissues coupled with its role in diverse signaling pathways makes development of a “clean” AhR therapeutically challenging. Ligand promiscuity and diversity in context-specific AhR activation further complicates targeting the AhR for drug development due to limitations surrounding clinical translatability. Despite these concerns, several approaches to target the AhR have been explored such as small molecules, microbials, PROTACs, and oligonucleotide-based approaches. These various chemical modalities are not without safety liabilities and require unique de-risking strategies to parse out toxicities. Collectively, these programs can benefit from in silico and in vitro methodologies that investigate specific AhR pathway activation and have the potential to implement thresholding parameters to categorize AhR ligands as “high” or “low” risk for sustained AhR activation. Exploration into transcriptomic signatures for AhR safety assessment, incorporation of physiologically-relevant in vitro model systems, and investigation into chronic activation of the AhR by structurally diverse ligands will help address gaps in our understanding regarding AhR-dependent toxicities. Here, we review the role of the AhR within the GI tract, novel therapeutic modality approaches to target the AhR, key AhR-dependent safety liabilities, and relevant strategies that can be implemented to address drug safety concerns. Together, this review discusses the emerging therapeutic landscape of modalities targeting the AhR for inflammatory GI indications and offers a safety roadmap for AhR drug development.

Elucidation of the species differences of epyrifenacil-induced hepatotoxicity between mice and humans by mass spectrometry imaging analysis in chimeric mice with humanized liver

Epyrifenacil, one of the protoporphyrinogen oxidase (PPO)-inhibiting herbicides, is hepatotoxic in rodents. Previous in vitro assays detected species differences in both kinetics (active hepatic uptake) and dynamics (PPO inhibitory activity) of S-3100-CA, which is a causal metabolite of the hepatotoxicity, suggesting that humans are less sensitive to the epyrifenacil-induced hepatotoxicity than are rats and mice. To elucidate the species differences in the epyrifenacil-induced hepatotoxicity between mice and humans simultaneously, this study fed epyrifenacil to chimeric mice with humanized liver with low replacement index of human hepatocytes. The distribution of S-3100-CA in the liver and subsequent protoporphyrin IX (PPIX) accumulation, an index of PPO inhibition, were compared between human and host mouse hepatocytes using mass spectrometry imaging (MSI) analysis of chimeric liver. The results showed that S-3100-CA and PPIX were significantly colocalized in regions of the liver slice containing host mouse hepatocytes, and thus it was suggested that epyrifenacil had significantly less effect on human livers than mouse livers because of the species differences in both kinetics and dynamics of S-3100-CA. Moreover, the hepatic uptake assay using cryopreserved primary hepatocytes of rats, mice and humans with inhibitors revealed that S-3100-CA is a substrate of organic anion transporting polypeptides (OATPs). These data corroborate the contribution of OATPs to hepatocellular uptake of S-3100-CA, especially in mice, and subsequent PPIX accumulation by more potent S-3100-CA-induced PPO inhibition in mice. MSI analysis of chimeric mice with humanized liver is a useful technique for elucidating species differences in pharmacokinetics and subsequent changes in toxicological biomarkers.

Utility of Göttingen minipigs for the prediction of human pharmacokinetic profiles after intravenous drug administration

Göttingen minipigs are increasingly used to evaluate the pharmacokinetic (PK) profiles of drug candidates. However, their accuracy in predicting human PK parameters is unclear. In this study, we investigated the utility of Göttingen minipigs for predicting human PK profiles. We evaluated the PK parameters of 30 compounds with diverse metabolic pathways after intravenous administration in minipigs. Human total clearance (CLtotal) was corrected using the blood to plasma ratio, and the volume of distribution at steady state (Vd(ss)) was corrected with plasma unbound fraction (fup). CLtotal and Vd(ss) were predicted using single-species allometric scaling using data from minipigs and other reported animal models (monkeys, human liver chimeric mice, and rats). The predicted values were compared with actual values reported in humans. Göttingen minipig were superior to rats because of their better predictability of Vd(ss) and CLtotal, as represented by lower absolute average fold error values. However, their predictability for Vd(ss) was inferior to monkey and human liver chimeric mice. Prediction of CLtotal from blood-based minipig data showed excellent correlation with human data, and comparable predictability with monkey and human liver chimeric mice. Thus, Göttingen minipigs can be used as an optional model for preclinical pharmaceutical research for predicting human CLtotal.

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.

Prediction of human pharmacokinetics for low-clearance compounds using pharmacokinetic data from chimeric mice with humanized livers

Development of low-clearance (CL) compounds that can be slowly metabolized is a major goal in the pharmaceutical industry. However, the pursuit of low intrinsic CL (CL_int ) often leads to significant challenges in evaluating the pharmacokinetics of such compounds. Although in vitro-in vivo extrapolation is widely used to predict human CL, its application has been limited for low-CL_int compounds because of the low turnover of parent compounds in metabolic stability assays. To address this issue, we focused on chimeric mice with humanized livers (PXB-mice), which have been increasingly reported to accurately predict human CL in recent years. The predictive accuracy for nine low-CL_int compounds with no significant turnover in a human hepatocyte assay was investigated using PXB-mouse methods such as single-species allometric scaling (PXB-SSS) approach and a novel physiologically based scaling (PXB-PBS) approach that assumes that the CL_int per hepatocyte is equal between humans and PXB-mice. The percentages of compounds with predicted CL within 2- and 3-fold ranges of the observed CL for low-CL_int compounds were 89% and 100%, respectively, for both PXB-SSS and PXB-PBS approaches. Moreover, the predicted CL was mostly consistent among the methods. Conversely, percentages of compounds with predicted CL within 2- and 3-fold ranges of the observed CL for low-CL_int compounds were 50% and 63%, respectively for multispecies allometric scaling (MA). Overall, these PXB-mouse methods were much more accurate than conventional MA approaches, suggesting that PXB-mice are useful tool for predicting the human CL of low-CL_int compounds that are slowly metabolized.

Human total clearance values and volumes of distribution of typical human cytochrome P450 2C9/19 substrates predicted by single-species allometric scaling using pharmacokinetic data sets from common marmosets genotyped for P450 2C19

Common marmosets (Callithrix jacchus) are small non-human primates that genetically lack cytochrome P450 2C9 (CYP2C9). Polymorphic marmoset CYP2C19 compensates by mediating oxidations of typical human CYP2C9/19 substrates.Twenty-four probe substrates were intravenously administered in combinations to marmosets assigned to extensive or poor metaboliser (PM) groups by CYP2C19 genotyping. Eliminations from plasma of cilomilast, phenytoin, repaglinide, tolbutamide, and S-warfarin in the CYP2C19 PM group were significantly slow; these drugs are known substrates of human CYP2C8/9/19.Human total clearance values and volumes of distribution of the 24 test compounds were extrapolated using single-species allometric scaling with experimental data from marmosets and found to be mostly comparable with the reported values.Human total clearance values and volumes of distribution of 15 of the 24 test compounds similarly extrapolated using reported data sets from cynomolgus or rhesus monkeys were comparable to the present predicted results, especially to those based on data from PM marmosets.These results suggest that single-species allometric scaling using marmosets, being small, has advantages over multiple-species-based allometry and could be applicable for pharmacokinetic predictions at the discovery stage of drug development.

Evaluation of the Utility of PXB Chimeric Mice for Predicting Human Liver Partitioning of Hepatic Organic Anion-Transporting Polypeptide Transporter Substrates

The ability to predict human liver-to-plasma unbound partition coefficient (K_puu) is important to estimate unbound liver concentration for drugs that are substrates of hepatic organic anion-transporting peptide (OATP) transporters with asymmetric distribution into the liver relative to plasma. Herein, we explored the utility of PXB chimeric mice with humanized liver that are highly repopulated with human hepatocytes to predict human hepatic disposition of OATP substrates, including rosuvastatin, pravastatin, pitavastatin, valsartan, and repaglinide. In vitro total uptake clearance and transporter-mediated active uptake clearance in C57 mouse hepatocytes were greater than in PXB chimeric mouse hepatocytes for rosuvastatin, pravastatin, pitavastatin, and valsartan. Consistent with in vitro uptake data, enhanced hepatic uptake and resulting total systemic clearance were observed with the above four compounds in severely compromised immune-deficient (SCID) control mice compared with the PXB chimeric mice, which suggest that mouse has a stronger transporter-mediated hepatic uptake than human. In vivo liver-to-plasma K_puu from PXB chimeric and SCID control mice were also compared, and rosuvastatin and pravastatin K_puu in SCID mice were more than 10-fold higher than that in PXB chimeric mice, whereas pitavastatin, valsartan, and repaglinide K_puu in SCID mice were comparable with K_puu in PXB chimeric mice. Finally, PXB chimeric mouse liver-to-plasma K_puu values were compared with the reported human K_puu, and a good correlation was observed as the PXB K_puu vales were within 3-fold of human K_puu Our results indicate that PXB mice could be a useful tool to delineate hepatic uptake and enable prediction of human liver-to-plasma K_puu of hepatic uptake transporter substrates. SIGNIFICANCE STATEMENT: We evaluated PXB mouse with humanized liver for its ability to predict human liver disposition of five organic anion-transporting polypeptide transporter substrates. Both in vitro and in vivo data suggest that mouse liver has a stronger transporter-mediated hepatic uptake than the humanized liver in PXB mouse. More importantly, PXB liver-to-plasma unbound partition coefficient (K_puu) values were compared with the reported human K_puu, and a good correlation was observed. PXB mice could be a useful tool to project human liver-to-plasma K_puu of hepatic uptake transporter substrates.

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.

Characterization and applications of chimeric mice with humanized livers for preclinical drug development

We have succeeded in stable mass production of chimeric PXB-mice, whose liver is repopulated by human hepatocytes at a ratio of more than 70%, and we are providing these mice to academia and pharmaceutical companies to support the development of new drugs or studies of liver function. Furthermore, we isolated human hepatocytes, called PXB-cells, from the chimeric mice, and provide them for clients weekly for in vitro studies. In this review, we summarize the existing characterizations of PXB-mice and PXB-cells and their present and future applications.

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.

Aldehyde oxidase and its role as a drug metabolizing enzyme

Aldehyde oxidase (AO) is a cytosolic enzyme that belongs to the family of structurally related molybdoflavoproteins like xanthine oxidase (XO). The enzyme is characterized by broad substrate specificity and marked species differences. It catalyzes the oxidation of aromatic and aliphatic aldehydes and various heteroaromatic rings as well as reduction of several functional groups. The references to AO and its role in metabolism date back to the 1950s, but the importance of this enzyme in the metabolism of drugs has emerged in the past fifteen years. Several reviews on the role of AO in drug metabolism have been published in the past decade indicative of the growing interest in the enzyme and its influence in drug metabolism. Here, we present a comprehensive monograph of AO as a drug metabolizing enzyme with emphasis on marketed drugs as well as other xenobiotics, as substrates and inhibitors. Although the number of drugs that are primarily metabolized by AO are few, the impact of AO on drug development has been extensive. We also discuss the effect of AO on the systemic exposure and clearance these clinical candidates. The review provides a comprehensive analysis of drug discovery compounds involving AO with the focus on developmental candidates that were reported in the past five years with regards to pharmacokinetics and toxicity. While there is only one known report of AO-mediated clinically relevant drug-drug interaction (DDI), a detailed description of inhibitors and inducers of AO known to date has been presented here and the potential risks associated with DDI. The increasing recognition of the importance of AO has led to significant progress in predicting the site of AO-mediated metabolism using computational methods. Additionally, marked species difference in expression of AO makes it is difficult to predict human clearance with high confidence. The progress made towards developing in vivo, in vitro and in silico approaches for predicting AO metabolism and estimating human clearance of compounds that are metabolized by AO have also been discussed.

Prediction of Human Hepatic Clearance for Cytochrome P450 Substrates via a New Culture Method Using the Collagen Vitrigel Membrane Chamber and Fresh Hepatocytes Isolated from Liver Humanized Mice

In drug discovery, hepatocytes have been widely utilized as in vitro tools for predicting the in vivo hepatic clearance (CL) of drug candidates. However, conventional hepatocyte models do not always reproduce in vivo physiological function, and CYP activities in particular decrease quite rapidly during culture. Furthermore, conventional in vitro assays have limitations in their ability to predict hepatic CL of metabolically stable drug candidates. In order to accurately predict hepatic CL of candidate drugs, a new method of culturing hepatocytes that activates their functional properties, including CYP activities, is in high demand. In the previous study, we established a novel long-term culture method for PXB-cells^® using a collagen vitrigel membrane (CVM) chamber, which can maintain CYP activity and liver specific functions at high levels for several weeks. In this study, the vitrigel culture method was applied to predictions of hepatic CL for 22 CYP typical substrates with low to middle CL, and the prediction accuracy by this method was assessed by comparing CL data between predicted (in vitro intrinsic CL using the dispersion model) and observed (in vivo clinical data) values. The results of this study showed that in vitro CL values for approximately 60% (13/22) and 80% (18/22) of the compounds were predicted within a 2- and 3-fold difference with in vivo CL, respectively. These results suggest that the new culture method using the CVM chamber and PXB-cells is a promising in vitro system for predicting human hepatic CL with high accuracy for CYP substrates, including metabolically stable drug candidates.

Nanostructured liquid crystalline formulation as a remarkable new drug delivery system of anti-epileptic drugs for treating children patients

PURPOSE

Development of a new dosage-form of antiepileptic-drugs appropriated for children.

METHODS

Clonazepam (Cl) was formulated as cubosomal-gel (cub-gel) to be used as a patch reservoir through transdermal-route. Cubosomes prepared using glycerol-mono-oleate(GMO)/Pluronic-F127(PF127) mixture. An actual-statistical design was used to investigate the effect of different stabilizing agents (Ethanol and PVA) and surfactant concentration on cubosomes' particle size and entrapping-efficiency. The selected formulae were evaluated by testing particle-morphology, in vitro drug release and stability. Cub-gel was prepared using selected cubosome formulae. The optimal cub-gel subjected to in vitro dissolution, ex-vivo permeation and skin deposition studies followed by studying its pharmacological effect.

RESULTS

Using PVA or Et as stabilizers with PF127 significantly decreases the average cubosomes'PS (352 ±  2.8 and 264 ± 2.16 nm) and increases EE (58.97 ± 4.57% and 54.21 ± 3.89%). Cubosomes increase the initial release rate of Cl to ensure rapid therapeutic effect (37.39% and 46.04% in the first hour) followed by a prolonged release till 4 h. Cub-gel containing PVA showed significantly higher Cl-transdermal permeation when compared to Cl-suspension. Moreover, increases the retention-time (89.57% at 48 h) and skin-deposition up to 6-times. It also reduces the epileptic seizures and alters the behavioral parameters induced by pilocarpine.

CONCLUSIONS

Cubosomal-gel could be considered an innovative dosage-form for Cl through the transdermal route.

Human relevance of rodent liver tumour formation by constitutive androstane receptor (CAR) activators

A large number of nongenotoxic chemicals have been shown to increase the incidence of liver tumours in rats and/or mice by a mode of action (MOA) involving activation of the constitutive androstane receptor (CAR). Studies with the model CAR activator phenobarbital (PB) and its sodium salt (sodium phenobarbital; NaPB) have demonstrated that the key and associative events for rat and mouse liver tumour formation include CAR activation, increased hepatocyte replicative DNA synthesis (RDS), induction of cytochrome P450 CYP2B subfamily enzymes, liver hypertrophy, increased altered hepatic foci and hepatocellular adenomas/carcinomas. The key species difference between the rat and mouse compared to humans, is that human hepatocytes are refractory to the mitogenic effects of PB/NaPB and other CAR activators. While PB/NaPB and other CAR activators stimulate RDS in rat and mouse hepatocytes in both in vitro and in vivo studies, such compounds do not stimulate RDS in cultured human hepatocytes and in in vivo studies performed in chimeric mice with humanised livers. In terms of species differences in RDS, unlike the rat and mouse, humans are similar to other species such as the Syrian hamster and guinea pig in being nonresponsive to the mitogenic effects of CAR activators. Overall, the MOA for rat and mouse liver tumour formation by PB/NaPB and other CAR activators is considered qualitatively not plausible for humans. This conclusion is supported by data from a number of epidemiological studies, which demonstrate that chronic treatment with PB does not increase the incidence of liver cancer in humans.

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.

[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.