An evaluation of the latestin vitrotools for drug metabolism studies

Insights into Inhalation Drug Disposition: The Roles of Pulmonary Drug-Metabolizing Enzymes and Transporters

The past five decades have witnessed remarkable advancements in the field of inhaled medicines targeting the lungs for respiratory disease treatment. As a non-invasive drug delivery route, inhalation therapy offers numerous benefits to respiratory patients, including rapid and targeted exposure at specific sites, quick onset of action, bypassing first-pass metabolism, and beyond. Understanding the characteristics of pulmonary drug transporters and metabolizing enzymes is crucial for comprehending efficient drug exposure and clearance processes within the lungs. These processes are intricately linked to both local and systemic pharmacokinetics and pharmacodynamics of drugs. This review aims to provide a comprehensive overview of the literature on lung transporters and metabolizing enzymes while exploring their roles in exogenous and endogenous substance disposition. Additionally, we identify and discuss the principal challenges in this area of research, providing a foundation for future investigations aimed at optimizing inhaled drug administration. Moving forward, it is imperative that future research endeavors to focus on refining and validating in vitro and ex vivo models to more accurately mimic the human respiratory system. Such advancements will enhance our understanding of drug processing in different pathological states and facilitate the discovery of novel approaches for investigating lung-specific drug transporters and metabolizing enzymes. This deeper insight will be crucial in developing more effective and targeted therapies for respiratory diseases, ultimately leading to improved patient outcomes.

Artemisia extracts differ from artemisinin effects on human hepatic CYP450s 2B6 and 3A4 in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

The Chinese medicinal herb, Artemisia annua L., has been used for >2,000 yr as traditional tea infusions to treat a variety of infectious diseases including malaria, and its use is spreading globally (along with A. afra Jacq. ex Willd.) mainly through grassroots efforts.

AIM OF THE STUDY

Artemisinin is more bioavailable delivered from the plant, Artemisia annua L. than the pure drug, but little is known about how delivery via a hot water infusion (tea) alters induction of hepatic CYP2B6 and CYP3A4 that metabolize artemisinin.

MATERIALS AND METHODS

HepaRG cells were treated with 10 μM artemisinin or rifampicin (positive control), and teas (10 g/L) of A. annua SAM, and A. afra SEN and MAL with 1.6, 0.05 and 0 mg/g DW artemisinin in the leaves, respectively; qPCR and Western blots were used to measure CYP2B6 and CYP3A4 responses. Enzymatic activity of these P450s was measured using human liver microsomes and P450-Glo assays.

RESULTS

All teas inhibited activity of CYP2B6 and CYP3A4. Artemisinin and the high artemisinin-containing tea infusion (SAM) induced CYP2B6 and CYP3A4 transcription, but artemisinin-deficient teas, MAL and SEN, did not. Artemisinin increased CYP2B6 and CYP3A4 protein levels, but none of the three teas did, indicating a post-transcription inhibition by all three teas.

CONCLUSIONS

This study showed that Artemisia teas inhibit activity and artemisinin autoinduction of CYP2B6 and CYP3A4 post transcription, a response likely the effect of other phytochemicals in these teas. Results are important for understanding Artemisia tea posology.

Hepatic Models in Precision Medicine: An African Perspective on Pharmacovigilance

Pharmaceuticals are indispensable to healthcare as the burgeoning global population is challenged by diseases. The African continent harbors unparalleled genetic diversity, yet remains largely underrepresented in pharmaceutical research and development, which has serious implications for pharmaceuticals approved for use within the African population. Adverse drug reactions (ADRs) are often underpinned by unique variations in genes encoding the enzymes responsible for their uptake, metabolism, and clearance. As an example, individuals of African descent (14-34%) harbor an exclusive genetic variant in the gene encoding a liver metabolizing enzyme (CYP2D6) which reduces the efficacy of the breast cancer chemotherapeutic Tamoxifen. However, CYP2D6 genotyping is not required prior to dispensing Tamoxifen in sub-Saharan Africa. Pharmacogenomics is fundamental to precision medicine and the absence of its implementation suggests that Africa has, to date, been largely excluded from the global narrative around stratified healthcare. Models which could address this need, include primary human hepatocytes, immortalized hepatic cell lines, and induced pluripotent stem cell (iPSC) derived hepatocyte-like cells. Of these, iPSCs, are promising as a functional in vitro model for the empirical evaluation of drug metabolism. The scale with which pharmaceutically relevant African genetic variants can be stratified, the expediency with which these platforms can be established, and their subsequent sustainability suggest that they will have an important role to play in the democratization of stratified healthcare in Africa. Here we discuss the requirement for African hepatic models, and their implications for the future of pharmacovigilance on the African continent.

Alpinetin: A Review of Its Pharmacology and Pharmacokinetics

Flavonoids isolated from medicinal herbs have been utilized as valuable health-care agents due to their virous biological applications. Alpinetin is a natural flavonoid that emerges in many widely used medicinal plants, and has been frequently applied in Chinese patent drugs. Accumulated evidence has demonstrated that alpinetin possesses a broad range of pharmacological activities such as antitumor, antiinflammation, hepatoprotective, cardiovascular protective, lung protective, antibacterial, antiviral, neuroprotective, and other properties through regulating multiple signaling pathways with low systemic toxicity. However, pharmacokinetic studies have documented that alpinetin may have poor oral bioavailability correlated to its extensive glucuronidation. Currently, the reported pharmacological properties and pharmacokinetics profiles of alpinetin are rare to be scientifically reviewed. In this article, we aimed to highlight the mechanisms of action of alpinetin in various diseases to strongly support its curative potentials for prospective clinical applications. We also summarized the pharmacokinetics properties and proposed some viable strategies to convey an appreciable reference for future advances of alpinetin in drug development.

In vitro evaluation of nanoplastics using human lung epithelial cells, microarray analysis and co-culture model

Nanoplastics, including polystyrene nanoplastics (PS-NPs), are widely existed in the atmosphere, which can be directly and continuously inhaled into the human body, posing a serious threat to the respiratory system. Therefore, it is urgent to estimate the potential pulmonary toxicity of airborne NPs and understand its underlying mechanism. In this research, we used two types of human lung epithelial cells (bronchial epithelium transformed with Ad12-SV40 2B, BEAS-2B) and (human pulmonary alveolar epithelial cells, HPAEpiC) to investigate the association between lung injury and PS-NPs. We found PS-NPs could significantly reduce cell viability in a dose-dependent manner and selected 7.5, 15 and 30 μg/cm² PS-NPs as the exposure dosage levels. Microarray detection revealed that 770 genes in the 7.5 μg/cm² group and 1951 genes in the 30 μg/cm² group were distinctly altered compared to the control group. Function analysis suggested that redox imbalance might play central roles in PS-NPs induced lung injury. Further experiments verified that PS-NPs could break redox equilibrium, induce inflammatory effects, and triggered apoptotic pathways to cause cell death. Importantly, we found that PS-NPs could decrease transepithelial electrical resistance by depleting tight junctional proteins. Result also demonstrated that PS-NPs-treated cells increased matrix metallopeptidase 9 and Surfactant protein A levels, suggesting the exposure of PS-NPs might reduce the repair ability of the lung and cause tissue damage. In conclusion, nanoplastics could induce oxidative stress and inflammatory responses, followed by cell death and epithelial barrier destruction, which might result in tissue damage and lung disease after prolonged exposure.

Arsenic: Various species with different effects on cytochrome P450 regulation in humans

Arsenic is well-recognized as one of the most hazardous elements which is characterized by its omnipresence throughout the environment in various chemical forms. From the simple inorganic arsenite (iAsIII) and arsenate (iAsV) molecules, a multitude of more complex organic species are biologically produced through a process of metabolic transformation with biomethylation being the core of this process. Because of their differential toxicity, speciation of arsenic-based compounds is necessary for assessing health risks posed by exposure to individual species or co-exposure to several species. In this regard, exposure assessment is another pivotal factor that includes identification of the potential sources as well as routes of exposure. Identification of arsenic impact on different physiological organ systems, through understanding its behavior in the human body that leads to homeostatic derangements, is the key for developing strategies to mitigate its toxicity. Metabolic machinery is one of the sophisticated body systems targeted by arsenic. The prominent role of cytochrome P450 enzymes (CYPs) in the metabolism of both endobiotics and xenobiotics necessitates paying a great deal of attention to the possible effects of arsenic compounds on this superfamily of enzymes. Here we highlight the toxicologically relevant arsenic species with a detailed description of the different environmental sources as well as the possible routes of human exposure to these species. We also summarize the reported findings of experimental investigations evaluating the influence of various arsenicals on different members of CYP superfamily using human-based models.

Advancements in practical and scientific bioanalytical approaches to metabolism studies in drug development

Advancement in metabolism profiling approaches and bioanalytical techniques has been revolutionized over the last two decades. Different in vitro and in vivo approaches along with advanced bioanalytical techniques are enabling the accurate qualitative and quantitative analysis of metabolites. This review summarizes various modern in vitro and in vivo approaches for executing metabolism studies with special emphasis on the recent advancement in the field. Advanced bioanalytical techniques, which can be employed in metabolism studies, have been discussed suggesting their particular application based on specific study objectives. This article can efficiently guide the researchers to scientifically plan metabolism studies and their bioanalysis during drug development programs taking advantage of a detailed understanding of instances of failure in the past.

Building three-dimensional lung models for studying pharmacokinetics of inhaled drugs

Drug development is a critical step in the development pipeline of pharmaceutical industry, commonly performed in traditional cell culture and animal models. Though, those models hold critical gapsin the prediction and the translation of human pharmacokinetic (PK) and pharmacodynamics (PD) parameters. The advances in tissue engineering have allowed the combination of cell biology with microengineering techniques, offering alternatives to conventional preclinical models. Organ-on-a-chips and three-dimensional (3D) bioprinting models present the potentialityof simulating the physiological and pathological microenvironment of living organs and tissues, constituting this way,more realistic models for the assessment of absorption, distribution, metabolism and excretion (ADME) of drugs. Therefore, this review will focus on lung-on-a-chip and 3D bioprinting techniques for developing lung models that can be usedfor predicting PK/PD parameters.

Electrochemical simulation of metabolic reduction and conjugation reactions of unsymmetrical bisacridine antitumor agents, C-2028 and C-2053

Electrochemistry (EC) coupled with analysis techniques such as liquid chromatography (LC) and mass spectrometry (MS) has been developed as a powerful tool for drug metabolism simulation. The application of EC in metabolic studies is particularly favourable due to the low matrix contribution compared to in vitro or in vivo biological models. In this paper, the EC(/LC)/MS system was applied to simulate phase I metabolism of the representative two unsymmetrical bisacridines (UAs), named C-2028 and C-2053, which contain nitroaromatic group susceptible to reductive transformations. UAs are a novel potent class of antitumor agents of extraordinary structures that may be useful in the treatment of difficult for therapy human solid tumors such as breast, colon, prostate, and pancreatic tumors. It is considered that the biological action of these compounds may be due to the redox properties of the nitroaromatic group. At first, the relevant conditions for the electrochemical conversion and product identification process, including the electrode potential range, electrolyte composition, and working electrode material, were optimized with the application of 1-nitroacridine as a model compound. Electrochemical simulation of C-2028 and C-2053 reductive metabolism resulted in the generation of six and five products, respectively. The formation of hydroxylamine m/z [M+H-14]⁺, amine m/z [M+H-30]⁺, and novel N-oxide m/z [M+H-18]⁺ species from UAs was demonstrated. Furthermore, both studied compounds were shown to be stable, retaining their dimeric forms, during electrochemical experiments. The electrochemical method also indicated the susceptibility of C-2028 to phase II metabolic reactions. The respective glutathione and dithiothreitol adducts of C-2028 were identified as ions at m/z 873 and m/z 720. In conclusion, the electrochemical reductive transformations of antitumor UAs allowed for the synthesis of new reactive intermediate forms permitting the study of their interactions with biologically crucial molecules.

In Vitro Hepatic Metabolism of Curcumin Diethyl Disuccinate by Liver S9 from Different Animal Species

Liver S9 (LS9) is a nearly complete collection of all hepatic drug-metabolizing enzymes. It is a low-cost model for predicting drug metabolic activity. This study aimed to identify the suitability of using LS9 of different animal sources in drug metabolism profiling with respect to the possible translation of the in vitro outcomes to clinical studies. The in vitro hepatic metabolism of curcumin diethyl disuccinate (CDD) in LS9 of rats, dogs, monkeys, and humans was evaluated. The identity of CDD metabolites and the metabolism kinetic parameters, including degradation rate constant, in vitro/in vivo intrinsic clearance, and half-life, were determined. CDD was rapidly metabolized into monoethylsuccinyl curcumin and curcumin in LS9 of all tested species mainly by carboxylesterases (CESs), including CES1 and CES2, and butyrylcholinesterase. The in vitro intrinsic clearance of CDD was in the order of human > dog > monkey > rat, whereas that of monoethylsuccinyl curcumin in the order of dog > monkey > human > rat; this parameter was not correlated with their respective in vivo clearance, which followed the order of dog > monkey > rat > human. Therefore, in vitro drug metabolism data inferred from LS9 of nonhuman origin, especially from monkeys and dogs, cannot be used as preclinical data for human trials, as humans have a smaller liver-to-body weight ratio than monkeys, dogs, and rats. The in vivo drug metabolism is dictated by the anatomical factors of the test subject.

Characterization of Differential Tissue Abundance of Major Non-CYP Enzymes in Human

The availability of assays that predict the contribution of cytochrome P450 (CYP) metabolism allows for the design of new chemical entities (NCEs) with minimal oxidative metabolism. These NCEs are often substrates of non-CYP drug-metabolizing enzymes (DMEs), such as UDP-glucuronosyltransferases (UGTs), sulfotransferases (SULTs), carboxylesterases (CESs), and aldehyde oxidase (AO). Nearly 30% of clinically approved drugs are metabolized by non-CYP enzymes. However, knowledge about the differential hepatic versus extrahepatic abundance of non-CYP DMEs is limited. In this study, we detected and quantified the protein abundance of eighteen non-CYP DMEs (AO, CES1 and 2, ten UGTs, and five SULTs) across five different human tissues. AO was most abundantly expressed in the liver and to a lesser extent in the kidney; however, it was not detected in the intestine, heart, or lung. CESs were ubiquitously expressed with CES1 being predominant in the liver, while CES2 was enriched in the small intestine. Consistent with the literature, UGT1A4, UGT2B4, and UGT2B15 demonstrated liver-specific expression, whereas UGT1A10 expression was specific to the intestine. UGT1A1 and UGT1A3 were expressed in both the liver and intestine; UGT1A9 was expressed in the liver and kidney; and UGT2B17 levels were significantly higher in the intestine than in the liver. All five SULTs were detected in the liver and intestine, and SULT1A1 and 1A3 were detected in the lung. Kidney abundance was the most variable among the studied tissues, and overall, high interindividual variability (>15-fold) was observed for UGT2B17, CES2 (intestine), SULT1A1 (liver), UGT1A9, UGT2B7, and CES1 (kidney). These differential tissue abundance data can be integrated into physiologically based pharmacokinetic (PBPK) models for the prediction of non-CYP drug metabolism and toxicity in hepatic and extrahepatic tissues.

Integrated Array Chip for High-Throughput Screening of Species Differences in Metabolism

Species differences in metabolism may produce failure prediction of drug efficacy/toxicity in humans. Integration of metabolic competence and cellular effect assays in vitro can provide insight into the species differences in metabolism; however, a co-culture platform with features of high throughput, operational simplicity, low sample consumption, and independent layouts is required for potential usage in industrial test settings. Herein, we developed an integrated array chip (IAC) to evaluate the species differences in metabolism through metabolism-induced anticancer bioactivity as a case. The IAC consisted of two functional parts: a micropillar chip for immobilization of liver microsomes and a microwell chip for three-dimensional (3D) tumor cell culture. First, optimized parameters of the micropillar chip for microsomal encapsulation were obtained by cross-shaped protrusions and a 2.5 μL volume of 3D agarose spots. Next, we examined factors influencing metabolism-induced anticancer bioactivity. Feasibility of the IAC was validated by four model prodrugs using image-based bioactivity detection and mass spectrometry (MS)-based metabolite analysis. Finally, a species-specific IAC was used for selection of animal species that best resembles metabolism-induced drug response to humans at throughputs. Overall, the IAC provides a promising co-culture platform for identifying species differences in metabolism and selection of animal models to accelerate drug discovery.

Characterization of lacosamide metabolites by UHPLC–ESI–HRMS method

In this study, the in vitro phase I metabolism of lacosamide was characterized with the use of ultra-high-performance liquid chromatography combined with high-resolution mass spectrometry (quadrupole time-of-flight). The use of two metabolism simulation techniques (photocatalysis and human liver microsomes) allowed the characterization of a polar metabolite of parent compound, not yet described. The experiment with the participation of HLM gave the ability to describe the full liver metabolic pathway of lacosamide. It has been proven that this molecule undergoes deacetylation, demethylation, and during liver tissue metabolism. Photocatalysis with the use of a TiO2 catalyst was proved to be a complementary technique in mimicking in vitro drug metabolism.

Validation of in vitro methods for human cytochrome P450 enzyme induction: Outcome of a multi-laboratory study

CYP enzyme induction is a sensitive biomarker for phenotypic metabolic competence of in vitro test systems; it is a key event associated with thyroid disruption, and a biomarker for toxicologically relevant nuclear receptor-mediated pathways. This paper summarises the results of a multi-laboratory validation study of two in vitro methods that assess the potential of chemicals to induce cytochrome P450 (CYP) enzyme activity, in particular CYP1A2, CYP2B6, and CYP3A4. The methods are based on the use of cryopreserved primary human hepatocytes (PHH) and human HepaRG cells. The validation study was coordinated by the European Union Reference Laboratory for Alternatives to Animal Testing of the European Commission's Joint Research Centre and involved a ring trial among six laboratories. The reproducibility was assessed within and between laboratories using a validation set of 13 selected chemicals (known human inducers and non-inducers) tested under blind conditions. The ability of the two methods to predict human CYP induction potential was assessed. Chemical space analysis confirmed that the selected chemicals are broadly representative of a diverse range of chemicals. The two methods were found to be reliable and relevant in vitro tools for the assessment of human CYP induction, with the HepaRG method being better suited for routine testing. Recommendations for the practical application of the two methods are proposed.

Triple co-culture of human alveolar epithelium, endothelium and macrophages for studying the interaction of nanocarriers with the air-blood barrier

Predictive in vitro models are valuable alternatives to animal experiments for evaluating the transport of molecules and (nano)particles across biological barriers. In this work, an improved triple co-culture of air-blood barrier was set-up, being exclusively constituted by human cell lines that allowed to perform experiments at air-liquid interface. Epithelial NCI-H441 cells and endothelial HPMEC-ST1.6R cells were seeded at the apical and basolateral sides of a Transwell® membrane, respectively. Differentiated THP-1 cells were also added on the top of the epithelial layer to mimetize alveolar macrophages. Translocation and permeability studies were also performed. It was observed that around 14-18% of 50-nm Fluorospheres®, but less than 1% of 1.0 µm-Fluorospheres® could pass through the triple co-culture as well as the epithelial monoculture and bi-cultures, leading to the conclusion that both in vitro models represented a significant biological barrier and could differentiate the translocation of different sized systems. The permeability of isoniazid was similar between the epithelial monoculture and bi-cultures when compared with the triple co-culture. However, when in vitro models were challenged with lipopolysaccharide, the release of interleukin-8 increased in the bi-cultures and triple co-culture, whereas the NCI-H441 monoculture did not show any proinflammatory response. Overall, this new in vitro model is a potential tool to assess the translocation of nanoparticles across the air-blood barrier both in healthy state and proinflammatory state. STATEMENT OF SIGNIFICANCE: The use of in vitro models for drug screening as an alternative to animal experiments is increasing over the last years, in particular, models to assess the permeation through biological membranes. Cell culture models are mainly constituted by one type of cells forming a confluent monolayer, but due to its oversimplicity they are being replaced by three-dimensional (3D) in vitro models, that present a higher complexity and reflect more the in vivo-like conditions. Being the pulmonary route one of the most studied approaches for drug administration, several in vitro models of alveolar epithelium have been used to assess the drug permeability and translocation and toxicity of nanocarriers. Nevertheless, there is still a lack of 3D in vitro models that mimic the morphology and the physiological behavior of the alveolar-capillary membrane. In this study, a 3D in vitro model of the air-blood barrier constituted by three different relevant cell lines was established and morphologically characterized. Different permeability/translocation studies were performed to achieve differences/similarities comparatively to each monoculture (epithelium, endothelium, and macrophages) and bi-cultures (epithelial cells either cultured with endothelial cells or macrophages). The release of pro-inflammatory cytokines (namely interleukin-8) after incubation of lipopolysaccharide, a pro-inflammatory inductor, was also evaluated in this work.

New Synthetic Cannabinoids Metabolism and Strategies to Best Identify Optimal Marker Metabolites

Synthetic cannabinoids (SCs) were initially developed as pharmacological tools to probe the endocannabinoid system and as novel pharmacotherapies, but are now highly abused. This is a serious public health and social problem throughout the world and it is highly challenging to identify which SC was consumed by the drug abusers, a necessary step to tie adverse health effects to the new drug's toxicity. Two intrinsic properties complicate SC identification, their often rapid and extensive metabolism, and their generally high potency relative to the natural psychoactive Δ9-tetrahydrocannabinol in cannabis. Additional challenges are the lack of reference standards for the major urinary metabolites needed for forensic verification, and the sometimes differing illicit and licit status and, in some cases, identical metabolites produced by closely related SC pairs, i.e., JWH-018/AM-2201, THJ-018/THJ-2201, and BB-22/MDMB-CHMICA/ADB-CHMICA. We review current SC prevalence, establish the necessity for SC metabolism investigation and contrast the advantages and disadvantages of multiple metabolic approaches. The human hepatocyte incubation model for determining a new SC's metabolism is highly recommended after comparison to human liver microsomes incubation, in silico prediction, rat in vivo, zebrafish, and fungus Cunninghamella elegans models. We evaluate SC metabolic patterns, and devise a practical strategy to select optimal urinary marker metabolites for SCs. New SCs are incubated first with human hepatocytes and major metabolites are then identified by high-resolution mass spectrometry. Although initially difficult to obtain, authentic human urine samples following the specified SC exposure are hydrolyzed and analyzed by high-resolution mass spectrometry to verify identified major metabolites. Since some SCs produce the same major urinary metabolites, documentation of the specific SC consumed may require identification of the SC parent itself in either blood or oral fluid. An encouraging trend is the recent reduction in the number of new SC introduced per year. With global collaboration and communication, we can improve education of the public about the toxicity of new SC and our response to their introduction.

A proteomic time course through the differentiation of human induced pluripotent stem cells into hepatocyte-like cells

Numerous in vitro models endeavour to mimic the characteristics of primary human hepatocytes for applications in regenerative medicine and pharmaceutical science. Mature hepatocyte-like cells (HLCs) derived from human induced pluripotent stem cells (hiPSCs) are one such in vitro model. Due to insufficiencies in transcriptome to proteome correlation, characterising the proteome of HLCs is essential to provide a suitable framework for their continual optimization. Here we interrogated the proteome during stepwise differentiation of hiPSCs into HLCs over 40 days. Whole cell protein lysates were collected and analysed using stabled isotope labelled mass spectrometry based proteomics. Quantitative proteomics identified over 6,000 proteins in duplicate multiplexed labelling experiments across two different time course series. Inductive cues in differentiation promoted sequential acquisition of hepatocyte specific markers. Analysis of proteins classically assigned as hepatic markers demonstrated trends towards maximum relative abundance between differentiation day 30 and 32. Characterisation of abundant proteins in whole cells provided evidence of the time dependent transition towards proteins corresponding with the functional repertoire of the liver. This data highlights how far the proteome of undifferentiated precursors have progressed to acquire a hepatic phenotype and constructs a platform for optimisation and improved maturation of HLC differentiation.

Characterization and reproducibility of HepG2 hanging drop spheroids toxicology in vitro

Hepatotoxicity remains a major challenge in drug development despite preclinical toxicity screening using hepatocytes of human origin. To overcome some limitations of reproducing the hepatic phenotype, more structurally and functionally authentic cultures in vitro can be introduced by growing cells in 3D spheroid cultures. Characterisation and reproducibility of HepG2 spheroid cultures using a high-throughput hanging drop technique was performed and features contributing to potential phenotypic variation highlighted. Cultured HepG2 cells were seeded into Perfecta 3D® 96-well hanging drop plates and assessed over time for morphology, viability, cell cycle distribution, protein content and protein-mass profiles. Divergent aspects which were assessed included cell stocks, seeding density, volume of culture medium and use of extracellular matrix additives. Hanging drops are advantageous due to no complex culture matrix being present, enabling background free extractions for downstream experimentation. Varying characteristics were observed across cell stocks and batches, seeding density, culture medium volume and extracellular matrix when using immortalized HepG2 cells. These factors contribute to wide-ranging cellular responses and highlights concerns with respect to generating a reproducible phenotype in HepG2 hanging drop spheroids.

Assessment of drug-drug interaction potential and PBPK modeling of CC-223, a potent inhibitor of the mammalian target of rapamycin kinase

1. CC-223 was studied in vitro for metabolism and drug-drug interactions (DDI), and in clinic for interaction with ketoconazole. 2. In vitro, human metabolites of CC-223 included O-desmethyl CC-223 (M1), keto (M2), N-oxide (M3) and imine (M13), with M1 being the most prominent metabolite. 3. CC-223 was metabolized by CYP2C9 and CYP3A, while metabolism of M1 was mediated by CYP2C8 and CYP3A. Ketoconazole increased CC-223 and M1 exposure by 60-70% in healthy volunteers. 4. CC-223 (IC₅₀ ≥ 27 µM) and M1 (IC₅₀ ≥ 46 µM) were inhibitors of CYP2C9 and CYP2C19 in human liver microsomes. CC-223 and M1 were moderate inducers of CYP3A in human hepatocytes. 5. CC-223 was a substrate of BCRP, and M1 was a substrate of P-gp and BCRP. CC-223 was an inhibitor of P-gp (IC₅₀ = 3.67 µM) and BCRP (IC₅₀ = 11.7 µM), but at a clinically relevant concentration showed no inhibition of other transporters examined. M1 is a weak inhibitor of P-gp and BCRP. 6. PBPK model of CC-223 and M1 was developed and verified using clinical results. Model based predictions of DDI with ketoconazole were in agreement with observed results enabling prospective predictions of DDIs between CC-223 and CYP3A4 inhibitors.

Chemical inhibition and stable knock-down of efflux transporters leads to reduced glucuronidation of wushanicaritin in UGT1A1-overexpressing HeLa cells: the role of breast cancer resistance protein (BCRP) and multidrug resistance-associated proteins (MRPs) in the excretion of glucuronides

We determine the contributions of BCRP and MRP transporters in HeLa cells.

Drug Metabolism in Preclinical Drug Development: A Survey of the Discovery Process, Toxicology, and Computational Tools

BACKGROUND

While establishing efficacy in translational models and humans through clinically-relevant endpoints for disease is of great interest, assessing the potential toxicity of a putative therapeutic drug is critical. Toxicological assessments in the pre-clinical discovery phase help to avoid future failure in the clinical phases of drug development. Many in vitro assays exist to aid in modular toxicological assessment, such as hepatotoxicity and genotoxicity. While these methods have provided tremendous insight into human toxicity by investigational new drugs, they are expensive, require substantial resources, and do not account for pharmacogenomics as well as critical ADME properties. Computational tools can fill this niche in toxicology if in silico models are accurate in relating drug molecular properties to toxicological endpoints as well as reliable in predicting important drug-target interactions that mediate known adverse events or adverse outcome pathways (AOPs).

METHODS

We undertook an unstructured search of multiple bibliographic databases for peer-reviewed literature regarding computational methods in predictive toxicology for in silico drug discovery. As this review paper is meant to serve as a survey of available methods for the interested reader, no focused criteria were applied. Literature chosen was based on the writers' expertise and intent in communicating important aspects of in silico toxicology to the interested reader.

CONCLUSION

This review provides a purview of computational methods of pre-clinical toxicologic assessments for novel small molecule drugs that may be of use for novice and experienced investigators as well as academic and commercial drug discovery entities.

Microfabricated Physiological Models for In Vitro Drug Screening Applications

Microfluidics and microfabrication have recently been established as promising tools for developing a new generation of in vitro cell culture microdevices. The reduced amounts of reagents employed within cell culture microdevices make them particularly appealing to drug screening processes. In addition, latest advancements in recreating physiologically relevant cell culture conditions within microfabricated devices encourage the idea of using such advanced biological models in improving the screening of drug candidates prior to in vivo testing. In this review, we discuss microfluidics-based models employed for chemical/drug screening and the strategies to mimic various physiological conditions: fine control of 3D extra-cellular matrix environment, physical and chemical cues provided to cells and organization of co-cultures. We also envision future directions for achieving multi-organ microfluidic devices.

TAMH: A Useful In Vitro Model for Assessing Hepatotoxic Mechanisms

In vitro models for hepatotoxicity can be useful tools to predict in vivo responses. In this review, we discuss the use of the transforming growth factor-α transgenic mouse hepatocyte (TAMH) cell line, which is an attractive model to study drug-induced liver injury due to its ability to retain a stable phenotype and express drug-metabolizing enzymes. Hepatotoxicity involves damage to the liver and is often associated with chemical exposure. Since the liver is a major site for drug metabolism, drug-induced liver injury is a serious health concern for certain agents. At the molecular level, various mechanisms may protect or harm the liver during drug-induced hepatocellular injury including signaling pathways and endogenous factors (e.g., Bcl-2, GSH, Nrf2, or MAPK). The interplay between these and other pathways in the hepatocyte can change upon drug or drug metabolite exposure leading to intracellular stress and eventually cell death and liver injury. This review focuses on mechanistic studies investigating drug-induced toxicity in the TAMH line and how alterations to hepatotoxic mechanisms in this model relate to the in vivo situation. The agents discussed herein include acetaminophen (APAP), tetrafluoroethylcysteine (TFEC), flutamide, PD0325901, lapatinib, and flupirtine.

Decreased Expression of Multidrug Resistance-Associated Protein 4 (MRP4/ABCC4) Leads to Reduced Glucuronidation of Flavonoids in UGT1A1-Overexpressing HeLa Cells: The Role of Futile Recycling

In this study, the role of futile recycling (or deglucuronidation) in the disposition of two flavonoids (i.e., genistein and apigenin) was explored using UGT1A1-overexpressing HeLa cells (or HeLa1A1 cells). Glucuronidation of the flavonoids by HeLa1A1 cell lysate followed the substrate inhibition kinetics (Vmax = 0.10 nmol/min/mg, Km = 0.54 μM, and Ksi = 2.0 μM for genistein; Vmax = 0.19 nmol/min/mg, Km = 0.56 μM, and Ksi = 3.7 μM for apigenin). Glucuronide was efficiently generated and excreted after incubation of the cells with the aglycone (at doses of 1.25-20 nmol). The excretion rates were 0.40-0.69 and 0.84-1.1 nmol/min/mg protein for genistein glucuronide (GG) and apigenin glucuronide (AG), respectively. Furthermore, glucuronide excretion and total glucuronidation were significantly reduced in MRP4 knocked-down as compared to control cells. The alterations were well characterized by a two-compartment pharmacokinetic model incorporating the process of futile recycling (defined by a first-order rate constant, Kde). The derived Kde values were 15 and 25 h(-1) for GG and AG, respectively. This was well consistent with the in vitro observation that AG was subjected to more efficient futile recycling compared to GG. In conclusion, futile recycling was involved in cellular glucuronidation, accounting for transporter-dependent glucuronidation of flavonoids.

Stable knock-down of efflux transporters leads to reduced glucuronidation in UGT1A1-overexpressing HeLa cells: the evidence for glucuronidation-transport interplay

Efflux of glucuronide is facilitated by the membrane transporters including BCRP and MRPs. In this study, we aimed to determine the effects of transporter expression on glucuronide efflux and cellular glucuronidation. Single efflux transporter (i.e., BCRP, MRP1, MRP3, or MRP4) was stably knocked-down in UGT1A1-overexpressing HeLa cells. Knock-down of transporters was performed by stable transfection of short-hairpin RNA (shRNA) using lentiviral vectors. Glucuronidation and glucuronide transport in the cells were characterized using three different aglycones (i.e., genistein, apigenin, and emodin) with distinct metabolic activities. BCRP knock-down resulted in significant reductions in excretion of glucuronides (42.9% for genistein glucuronide (GG), 21.1% for apigenin glucuronide (AG) , and 33.7% for emodin glucuronide (EG); p < 0.01) and in cellular glucuronidation (38.3% for genistein, 38.6% for apigenin, and 34.7% for emodin; p < 0.01). Knock-down of a MRP transporter led to substantial decreases in excretion of GG (32.3% for MRP1, 36.7% for MRP3, and 36.6% for MRP4; p < 0.01) and AG (59.3% for MRP1, 24.7% for MRP3, and 34.1% for MRP4; p < 0.01). Also, cellular glucuronidation of genistein (38.3% for MRP1, 32.3% for MRP3, and 31.1% for MRP4; p < 0.01) and apigenin (40.6% for MRP1, 32.4% for MRP3, and 34.6% for MRP4; p < 0.001) was markedly suppressed. By contrast, silencing of MRPs did not cause any changes in either excretion of EG or cellular glucuronidation of emodin. In conclusion, cellular glucuronidation was significantly altered by decreasing expression of efflux transporters, revealing a strong interplay of glucuronidation with efflux transport.