The future of drug safety testing: expanding the view and narrowing the focus

Drug-induced liver injury in older adults

Drug-induced liver injury (DILI) is an important cause of hospitalisation and of medication deregistration. In old age, susceptibility to DILI is affected by changes in physiology and increased interindividual variability, compounded by an increased prevalence of disease and the frailty syndrome. While dose-related or predictable DILI reactions are often detected in preclinical trials, the occurrence of rare hypersensitivity or idiosyncratic reactions cannot be reliably predicted from preclinical studies or even by clinical trials. The limited participation of older adults in clinical trials means that the susceptibility of this population to DILI is largely unknown. Vigilance during clinical trials and postmarketing surveillance must be universally practised. A systematic approach should be taken to determine not only which medicines are hepatotoxic and should be removed from the market, but also the hepatotoxicity risks from marketed drugs to consumers with different characteristics, many of whom are older people.

Development and regulatory application of microRNA biomarkers

MicroRNAs, a class of regulatory small non-coding RNAs, are emerging as promising biomarkers for different health outcomes. Due to their tissue specificity, stability in extracellular space and high conservation between preclinical test species, applications of novel miRNA-based biomarkers for drug safety testing regarding hepatotoxicity and cardiotoxicity are investigated. Furthermore, miRNA expression is altered by environmental exposure such as cigarette smoke or polychlorinated biphenyls. As a consequence, miRNAs potentially influence tumor suppressor genes and oncogenes and may influence carcinogenesis. This has raised the interest in the use of miRNA profiles for health risk assessment. This review summarizes the recent developments in miRNA research with focus on biomarkers for drug safety testing and biomarkers for health outcomes related to environmental exposures.

Industry perspectives on biomarker qualification

Biomarkers have the potential to expedite drug development, increase patient safety, and optimize clinical response. Yet few have achieved regulatory qualification. A survey was conducted to clarify industry's perspective on biomarker qualification and identify the most promising biomarkers for drug development. The results across toxicities/clinical areas highlight challenges in regulatory qualification, although early prioritization and alignment on an evidentiary standard framework are key factors in facilitating biomarker development and qualification.

Excitation-contraction coupling of human induced pluripotent stem cell-derived cardiomyocytes

Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) hold enormous potential in many fields of cardiovascular research. Overcoming many of the limitations of their embryonic counterparts, the application of iPSC-CMs ranges from facilitating investigation of familial cardiac disease and pharmacological toxicity screening to personalized medicine and autologous cardiac cell therapies. The main factor preventing the full realization of this potential is the limited maturity of iPSC-CMs, which display a number of substantial differences in comparison to adult cardiomyocytes. Excitation–contraction (EC) coupling, a fundamental property of cardiomyocytes, is often described in iPSC-CMs as being more analogous to neonatal than adult cardiomyocytes. With Ca²⁺ handling linked, directly or indirectly, to almost all other properties of cardiomyocytes, a solid understanding of this process will be crucial to fully realizing the potential of this technology. Here, we discuss the implications of differences in EC coupling when considering the potential applications of human iPSC-CMs in a number of areas as well as detailing the current understanding of this fundamental process in these cells.

A critical assessment of the scientific basis, and implementation, of regulations for the safety assessment and marketing of innovative tobacco-related products

Our scientific, logistical, ethical and animal welfare-related concerns about the latest US Food and Drug Administration (FDA) regulations for existing and so-called 'new' tobacco products, aimed at reducing harmful exposures, are explained. Such claims for sales in the USA now have to be based on a wide range of information, a key part of which will increasingly be data on safety and risk. One of the pathways to achieve marketing authorisation is to demonstrate substantial equivalence (SE) with benchmark products, called predicates. However, the regulations are insufficiently transparent with regard to: a) a rationale for the cut-off date for 'old' and 'new' products, and for exempting the former from regulation; b) the scientific validity and operation of SE; c) options for product labelling to circumvent SE; d) the experimental data required to support, and criteria to judge, a claim; and e) a strategy for risk assessment/management. Scientific problems related to the traditional animal methods used in respiratory disease and inhalation toxicology, and the use of quantitative comparators of toxicity, such as the No Observed Adverse Effect Level, are discussed. We review the advantages of relevant in vitro, mechanism-based, target tissue-oriented technologies, which an advisory report of the Institute of Medicine of the US National Academy of Sciences largely overlooked. These benefits include: a) the availability, for every major site in the respiratory tract, of organotypic human cell-based tissue culture systems, many of which are already being used by the industry; b) the accurate determination of concentrations of test materials received by target cells; c) methods for exposure to particulate and vapour phases of smoke, separately or combined; d) the ability to study tissue-specific biotransformation; and e) the use of modern, human-focused methodologies, unaffected by species differences. How data extrapolation, for risk assessment, from tissue culture to the whole animal, could be addressed, is also discussed. A cost (to animal welfare)-benefit (to society, including industry and consumers) analysis was conducted, taking into account the above information; the potential for animal suffering; the extensive data already available; the existence of other, less hazardous forms of nicotine delivery; the fact that much data will be generated solely for benchmarking; and that many smokers (especially nicotine-dependents) ignore health warnings. It is concluded that, in common with policies of several tobacco companies and countries, the use of laboratory animals for tobacco testing is very difficult, if not impossible, to justify. Instead, we propose and argue for an integrated testing scheme, starting with extensive chemical analysis of the ingredients and by-products associated with the use of tobacco products and their toxicity, followed by use of in vitro systems and early clinical studies (involving specific biomarkers) with weight-of-evidence assessments at each stage. Appropriate adjustment factors could be developed to enable concentration-response data obtained in vitro, with the other information generated by the strategy, to enable the FDA to meet its objectives. It is hoped that our intentionally provocative ideas will stimulate further debate on this contentious area of regulatory testing and public safety.

In vitro study on the safety of near infrared laser therapy in its potential application as postmastectomy lymphedema treatment

Clinical studies demonstrated the effectiveness of laser therapy in the management of postmastectomy lymphedema, a discomforting disease that can arise after surgery/radiotherapy and gets progressively worse and chronic. However, safety issues restrict the possibility to treat cancer patients with laser therapy, since the effects of laser radiation on cancer cell behavior are not completely known and the possibility of activating postmastectomy residual cancer cells must be considered. This paper reports the results of an in vitro study aimed to investigate the effect of a class IV, dual-wavelength (808 nm and 905 nm), NIR laser system on the behavior of two human breast adenocarcinoma cell lines (namely, MCF7 and MDA-MB361 cell lines), using human dermal fibroblasts as normal control. Cell viability, proliferation, apoptosis, cell cycle and ability to form colonies were analyzed in order to perform a cell-based safety testing of the laser treatment in view of its potential application in the management of postmastectomy lymphedema. The results showed that, limited to the laser source, treatment conditions and experimental models used, laser radiation did not significantly affect the behavior of human breast adenocarcinoma cells, including their clonogenic efficiency. Although these results do not show any significant laser-induced modification of cancer cell behavior, further studies are needed to assess the possibility of safely applying NIR laser therapy for the management of postmastectomy lymphedema.

Life in 3D is never flat: 3D models to optimise drug delivery

The development of safe, effective and patient-acceptable drug products is an expensive and lengthy process and the risk of failure at different stages of the development life-cycle is high. Improved biopharmaceutical tools which are robust, easy to use and accurately predict the in vivo response are urgently required to help address these issues. In this review the advantages and challenges of in vitro 3D versus 2D cell culture models will be discussed in terms of evaluating new drug products at the pre-clinical development stage. Examples of models with a 3D architecture including scaffolds, cell-derived matrices, multicellular spheroids and biochips will be described. The ability to simulate the microenvironment of tumours and vital organs including the liver, kidney, heart and intestine which have major impact on drug absorption, distribution, metabolism and toxicity will be evaluated. Examples of the application of 3D models including a role in formulation development, pharmacokinetic profiling and toxicity testing will be critically assessed. Although utilisation of 3D cell culture models in the field of drug delivery is still in its infancy, the area is attracting high levels of interest and is likely to become a significant in vitro tool to assist in drug product development thus reducing the requirement for unnecessary animal studies.

[Investigation of Predisposition Biomarkers to Identify Risk Factors for Drug-induced Liver Injury in Humans: Analyses of Endogenous Metabolites in an Animal Model Mimicking Human Responders to APAP-induced Hepatotoxicity]

Drug-induced liver injury is a main reason of regulatory action pertaining to drugs, including restrictions to clinical indications and withdrawal from the marketplace. Acetaminophen (APAP) is a commonly used and effective analgesic/antipyretic agent and relatively safe drug even in long-term treatment. However, it is known that APAP at therapeutic doses may cause hepatotoxicity in some individuals. Hence great efforts have been made to identify risk factors for APAP-induced chronic hepatotoxicity. We investigated the contribution of undernourishment to susceptibility to APAP-induced chronic hepatotoxicity using an animal model. We employed daytime restricted fed (RF) rats as a modified-nutritional state model for human APAP-induced hepatotoxicity. RF and ad libitum fed (ALF) rats were given APAP at 0, 300, and 500 mg/kg for 3 months. Plasma and urinary glutathione-related metabolomes and liver function parameters were measured during the dosing period. Endogenous metabolites forming at different levels between the RF and ALF rats could be potential predisposition biomarkers for APAP-induced hepatotoxicity. In addition, RF rats were considered a useful model to estimate the contribution of nutritional state of patients to APAP-induced chronic hepatotoxicity. In this article we report our current research focusing on nutritional state as risk factor for APAP-induced chronic hepatotoxicity and our findings of hepatotoxicity biomarkers.

The role for microRNAs in drug toxicity and in safety assessment

INTRODUCTION

Adverse drug reactions present significant challenges that impact pharmaceutical development and are major burdens to public health services worldwide. In response to this need, the field of toxicology is rapidly expanding to identify key pathways involved in drug toxicity.

AREAS COVERED

MicroRNAs (miRNAs) are a class of small evolutionary conserved endogenous non-coding RNAs that regulate the translation of protein-coding genes. A wide range of toxicants alter miRNA levels in target organs and these altered miRNAs can also be detected in easily accessible biological fluids. This, combined with an early miRNA response to toxic insults and miRNA stability, substantiates the potential for these small molecules to be useful biomarkers for drug safety assessment.

EXPERT OPINION

miRNAs are early indicators and useful tools to detect drug-induced toxicity. Incorporation of miRNA profiling into the drug safety testing process will complement currently used techniques and may substantially enhance drug safety. With the increasing interests in translational research, the field of miRNA biomarker research will continue to expand and become an important part of the investigation of human drug toxicity.

Renal Safety Pharmacology in Drug Discovery and Development

The kidney is a complex excretory organ playing a crucial role in various physiological processes such as fluid and electrolyte balance, control of blood pressure, removal of waste products, and drug disposition. Drug-induced kidney injury (DIKI) remains a significant cause of candidate drug attrition during drug development. However, the incidence of renal toxicities in preclinical studies is low, and the mechanisms by which drugs induce kidney injury are still poorly understood. Although some in vitro investigational tools have been developed, the in vivo assessment of renal function remains the most widely used methodology to identify DIKI. Stand-alone safety pharmacology studies usually include assessment of glomerular and hemodynamic function, coupled with urine and plasma analyses. However, as renal function is not part of the ICH S7A core battery, such studies are not routinely conducted by pharmaceutical companies. The most common approach consists in integrating renal/urinary measurements in repeat-dose toxicity studies. In addition to the standard analyses and histopathological examination of kidneys, novel promising urinary biomarkers have emerged over the last decade, offering greater sensitivity and specificity than traditional renal parameters. Seven of these biomarkers have been qualified by regulatory agencies for use in rat toxicity studies.

Anticancer efficacy and absorption, distribution, metabolism, and toxicity studies of aspergiolide A in early drug development

Since the first anthracycline was discovered, many other related compounds have been studied in order to overcome its defects and improve efficacy. In the present paper, we investigated the anticancer effects of a new anthracycline, aspergiolide A (ASP-A), from a marine-derived fungus in vitro and in vivo, and we evaluated the absorption, distribution, metabolism, and toxicity drug properties in early drug development. We found that ASP-A had activity against topoisomerase II that was comparable to adriamycin. ASP-A decreased the growth of various human cancer cells in vitro and induced apoptosis in BEL-7402 cells via a caspase-dependent pathway. The anticancer efficacy of ASP-A on the growth of hepatocellular carcinoma xenografts was further assessed in vivo. Results showed that, compared with the vehicle group, ASP-A exhibited significant anticancer activity with less loss of body weight. A pharmacokinetics and tissue distribution study revealed that ASP-A was rapidly cleared in a first order reaction kinetics manner, and was enriched in cancer tissue. The maximal tolerable dose (MTD) of ASP-A was more than 400 mg/kg, and ASP-A was not considered to be potentially genotoxic or cardiotoxic, as no significant increase of micronucleus rates or inhibition of the hERG channel was seen. Finally, an uptake and transport assay of ASP-A was performed in monolayers of Caco-2 cells, and ASP-A was shown to be absorbed through the active transport pathway. Altogether, these results indicate that ASP-A has anticancer activity targeting topoisomerase II, with a similar structure and mechanism to adriamycin, but with much lower toxicity. Nonetheless, further molecular structure optimization is necessary.

An impedance-based cellular assay using human iPSC-derived cardiomyocytes to quantify modulators of cardiac contractility

Cardiovascular toxicity, a prominent reason for late-stage failures in drug development, has resulted in a demand for in vitro assays that can predict this liability in early drug discovery. Current in vitro cardiovascular safety testing primarily focuses on ion channel modulation and low throughput cardiomyocyte (CM) contractility measurements. We evaluated both human induced pluripotent stem cell-derived CMs (hiPSC-CMs) and rat neonatal CMs (rat CMs) on the xCELLigence Cardio system which uses impedance technology to quantify CM beating properties in a 96-well format. Forty-nine compounds were tested in concentration-response mode to determine potency for modulation of CM beating, a surrogate biomarker for contractility. These compounds had previously been tested in vivo and in a low throughput in vitro optical-based contractility assay that measures sarcomere shortening in electrically paced dog CMs. In comparison with in vivo contractility effects, hiPSC-CM impedance had assay sensitivity, specificity, and accuracy values of 90%, 74%, and 82%, respectively. These values compared favorably to values reported for the dog CM optical assay (83%, 84%, and 82%) and were slightly better than impedance using rat CMs (77%, 74%, and 74%). The potency values from the hiPSC-CM and rat CM assays spanned four orders of magnitude and correlated with values from the dog CM optical assay (r(2 )= 0.76 and 0.70, respectively). The Cardio system assay has >5× higher throughput than the optical assay. Thus, hiPSC-CM impedance testing can help detect the human cardiotoxic potential of novel therapeutics early in drug discovery, and if a hazard is identified, has sufficient throughput to support the design-make-test-analyze cycle to mitigate this liability.

Comparative gene and protein expression analyses of a panel of cytokines in acute and chronic drug-induced liver injury in rats

Drug-induced liver injury (DILI) is a significant safety issue associated with medication use, and is the major cause of failures in drug development and withdrawal in post marketing. Cytokines are signaling molecules produced and secreted by immune cells and play crucial roles in the progression of DILI. Although there are numerous reports of cytokine changes in several DILI models, a comprehensive analysis of cytokine expression changes in rat liver injury induced by various compounds has, to the best of our knowledge, not been performed. In the past several years, we have built a public, free, large-scale toxicogenomics database, called Open TG-GATEs, containing microarray data and toxicity data of the liver of rats treated with various hepatotoxic compounds. In this study, we measured the protein expression levels of a panel of 24 cytokines in frozen liver of rats treated with a total of 20 compounds, obtained in the original study that formed the basis of the Open TG-GATEs database and analyzed protein expression profiles combined with mRNA expression profiles to investigate the correlation between mRNA and protein expression levels. As a result, we demonstrated significant correlations between mRNA and protein expression changes for interleukin (IL)-1β, IL-1α, monocyte chemo-attractant protein (MCP)-1/CC-chemokine ligand (Ccl)2, vascular endothelial growth factor A (VEGF-A), and regulated upon activation normal T cell expressed and secreted (RANTES)/Ccl5 in several different types of DILI. We also demonstrated that IL-1β protein and MCP-1/Ccl2 mRNA were commonly up-regulated in the liver of rats treated with different classes of hepatotoxicants and exhibited the highest accuracy in the detection of hepatotoxicity. The results also demonstrate that hepatic mRNA changes do not always correlate with protein changes of cytokines in the liver. This is the first study to provide a comprehensive analysis of mRNA-protein correlations of factors involved in various types of DILI, as well as additional insights into the importance of understanding complex cytokine expression changes in assessing DILI.

Applicability Domain ANalysis (ADAN): a robust method for assessing the reliability of drug property predictions

We report a novel method called ADAN (Applicability Domain ANalysis) for assessing the reliability of drug property predictions obtained by in silico methods. The assessment provided by ADAN is based on the comparison of the query compound with the training set, using six diverse similarity criteria. For every criterion, the query compound is considered out of range when the similarity value obtained is larger than the 95th percentile of the values obtained for the training set. The final outcome is a number in the range of 0-6 that expresses the number of unmet similarity criteria and allows classifying the query compound within seven reliability categories. Such categories can be further exploited to assign simpler reliability classes using a traffic light schema, to assign approximate confidence intervals or to mark the predictions as unreliable. The entire methodology has been validated simulating realistic conditions, where query compounds are structurally diverse from those in the training set. The validation exercise involved the construction of more than 1000 models. These models were built using a combination of training set, molecular descriptors, and modeling methods representative of the real predictive tasks performed in the eTOX project (a project whose objective is to predict in vivo toxicological end points in drug development). Validation results confirm the robustness of the proposed assessment methodology, which compares favorably with other classical methods based solely on the structural similarity of the compounds. ADAN characteristics make the method well-suited for estimate the quality of drug predictions obtained in extremely unfavorable conditions, like the prediction of drug toxicity end points.

Micromolded gelatin hydrogels for extended culture of engineered cardiac tissues

Defining the chronic cardiotoxic effects of drugs during preclinical screening is hindered by the relatively short lifetime of functional cardiac tissues in vitro, which are traditionally cultured on synthetic materials that do not recapitulate the cardiac microenvironment. Because collagen is the primary extracellular matrix protein in the heart, we hypothesized that micromolded gelatin hydrogel substrates tuned to mimic the elastic modulus of the heart would extend the lifetime of engineered cardiac tissues by better matching the native chemical and mechanical microenvironment. To measure tissue stress, we used tape casting, micromolding, and laser engraving to fabricate gelatin hydrogel muscular thin film cantilevers. Neonatal rat cardiac myocytes adhered to gelatin hydrogels and formed aligned tissues as defined by the microgrooves. Cardiac tissues could be cultured for over three weeks without declines in contractile stress. Myocytes on gelatin had higher spare respiratory capacity compared to those on fibronectin-coated PDMS, suggesting that improved metabolic function could be contributing to extended culture lifetime. Lastly, human induced pluripotent stem cell-derived cardiac myocytes adhered to micromolded gelatin surfaces and formed aligned tissues that remained functional for four weeks, highlighting their potential for human-relevant chronic studies.

The application of 3D cell models to support drug safety assessment: opportunities & challenges

The selection of drug candidates early in development has become increasingly important to minimize the use of animals and to avoid costly failures of drugs later in development. In vitro systems to predict and assess organ toxicity have so far been of limited value due to difficulties in demonstrating in vivo-relevant toxicity at a cell culture level. To overcome the limitations of single-cell type monolayer cultures and short-lived primary cell preparations, researchers have created novel 3-dimensional culture systems which appear to more closely resemble in vivo biology. These could become a key for the pharmaceutical industry in the evaluation of drug candidates. However, the value and acceptance of those new models in standard drug safety applications have yet to be demonstrated. This review aims to provide an overview of the different approaches undertaken in the field of pre-clinical safety assessment, organ toxicity, in particular, with an emphasis on examples and technical challenges.

Exploratory toxicology as an integrated part of drug discovery. Part I: Why and how

Toxicity and clinical safety have major impact on drug development success. Moving toxicological studies into earlier phases of the R&D chain prevents drug candidates with a safety risk from entering clinical development. However, to identify candidates without such risk, safety has to be designed actively. Therefore, we argue that toxicology should be fully integrated into the discovery process. We describe our strategy, including safety assessment of novel targets, selection of chemical series without inherent liabilities, designing out risk factors and profiling of candidates, and we discuss considerations regarding what to screen for. We aim to provide timely go/no-go decisions (fail early) and direction to the discovery teams, by steering away from safety risk (showing what will not fail).

In vitro-in vivo extrapolation of drug-induced proarrhythmia predictions at the population level

Drug cardiotoxicity is a serious issue for patients, regulators, pharmaceutical companies and health service payers because they are all affected by its consequences. Despite the wide range of data they generate, existing approaches for cardiac safety testing might not be adequate and sufficiently cost-effective, probably as a result of the complexity of the problem. For this reason, translational tools (based on biophysically detailed, mathematical models) allowing for in vitro-in vivo extrapolation are gaining increasing interest. This current review describes approaches that can be used for cardiac safety assessment at the population level, by accounting for various sources of variability including kinetics of the compound of interest.

A multi-endpoint in vivo larval zebrafish (Danio rerio) model for the assessment of integrated cardiovascular function

INTRODUCTION

Despite effective in vitro preclinical strategies to identify cardiovascular (CV) liabilities, there remains a need for early functional assessment prior to complex in vivo mammalian models. The larval zebrafish (Danio rerio, Zf) has been suggested for this role: previous data suggest that cardiac electrophysiology and vascular ultrastructure are comparable with mammals, and also indicate responsiveness of individual Zf CV system endpoints to some functional modulators. Little information is, however, available regarding integrated functional CV responses to drug treatment. Consequently, we developed a novel larval Zf model capable of simultaneous quantification of chronotropic, inotropic and arrhythmic effects, alongside measures of blood flow and vessel diameter.

METHODS

Non-invasive video analysis of the heart and dorsal aorta of anaesthetized and agarose-embedded larval ZF was used to measure multiple cardiovascular endpoints, simultaneously, following treatment with a range of functional modulators of CV physiology.

RESULTS

Changes in atrial and ventricular beat frequencies were detected in response to acute treatment with cardio-stimulants (adrenaline and theophylline), and negative chrono/inotropes (cisapride, haloperidol, terfenadine and verapamil). Arrhythmias were also observed including terfenadine-induced 2:1 atrial-ventricular (A-V) block, a previously proposed hERG surrogate measure. Significant increases in blood flow were detected in response to adrenaline and theophylline exposure; and decreases after cisapride, haloperidol, terfenadine, and verapamil treatment. Using dorsal aorta (DA) blood flow and ventricular beat rate, surrogate stoke volumes were also calculated for all compounds.

DISCUSSION

These data support the use of this approach for CV function studies. Moreover the throughput and compound requirements (approximately 3 compounds/person effort/week and <10 mg) make our approach potentially suitable for higher throughput drug safety and efficacy applications, pending further assessment of ZF-mammalian pharmacological comparability.

Monitoring drug self-aggregation and potential for promiscuity in off-target in vitro pharmacology screens by a practical NMR strategy

A simple NMR assay was applied to monitor the tendency of compounds to self-aggregate in aqueous media. The observation of unusual spectral trends as a function of compound concentration appears to be signatory of the formation of self-assemblies. (1)H NMR resonances of aggregating compounds were sensitive to the presence of a range of molecular assemblies in solution including large molecular-size entities, smaller multimers, and mixtures of assembled species. The direct observation of aggregates via unusual NMR spectra also correlated with promiscuous behavior of molecules in off-target in vitro pharmacology assays. This empirical assay can have utility for predicting compound promiscuity and should complement predictive methods that principally rely on the computing of descriptors such as lipophilicity (cLogP) and topological surface area (TPSA). This assay should serve as a practical tool for medicinal chemists to monitor compound attributes in aqueous solution and various pharmacologically relevant media, as demonstrated herein.

Animal models of human disease: challenges in enabling translation

Animal models have historically played a critical role in the exploration and characterization of disease pathophysiology, target identification, and in the in vivo evaluation of novel therapeutic agents and treatments. In the wake of numerous clinical trial failures of new chemical entities (NCEs) with promising preclinical profiles, animal models in all therapeutic areas have been increasingly criticized for their limited ability to predict NCE efficacy, safety and toxicity in humans. The present review discusses some of the challenges associated with the evaluation and predictive validation of animal models, as well as methodological flaws in both preclinical and clinical study designs that may contribute to the current translational failure rate. The testing of disease hypotheses and NCEs in multiple disease models necessitates evaluation of pharmacokinetic/pharmacodynamic (PK/PD) relationships and the earlier development of validated disease-associated biomarkers to assess target engagement and NCE efficacy. Additionally, the transparent integration of efficacy and safety data derived from animal models into the hierarchical data sets generated preclinically is essential in order to derive a level of predictive utility consistent with the degree of validation and inherent limitations of current animal models. The predictive value of an animal model is thus only as useful as the context in which it is interpreted. Finally, rather than dismissing animal models as not very useful in the drug discovery process, additional resources, like those successfully used in the preclinical PK assessment used for the selection of lead NCEs, must be focused on improving existing and developing new animal models.

Cellular impedance assays for predictive preclinical drug screening of kinase inhibitor cardiovascular toxicity

Cardiovascular (CV) toxicity is a leading contributor to drug attrition. Implementing earlier testing has successfully reduced human Ether-à-go-go-Related Gene-related arrhythmias. How- ever, analogous assays targeting functional CV effects remain elusive. Demand to address this gap is particularly acute for kinase inhibitors (KIs) that suffer frequent CV toxicity. The drug class also presents some particularly challenging requirements for assessing functional CV toxicity. Specifically, an assay must sense a downstream response that integrates diverse kinase signaling pathways. In addition, sufficient throughput is essential for handling inherent KI nonselectivity. A new opportunity has emerged with cellular impedance technology, which detects spontaneous beating cardiomyocytes. Impedance assays sense morphology changes downstream of cardiomyocyte contraction. To evaluate cardiomyocyte impedance assays for KI screening, we investigated two distinct KI classes where CV toxicity was discovered late and target risks remain unresolved. Microtubule-associated protein/microtubule affinity regulating kinase (MARK) inhibitors decrease blood pressure in dogs, whereas checkpoint kinase (Chk) inhibitors (AZD7762, SCH900776) exhibit dose-limiting CV toxicities in clinical trials. These in vivo effects manifested in vitro as cardiomyocyte beat cessation. MARK effects were deemed mechanism associated because beat inhibition potencies correlated with kinase inhibition, and gene knockdown and microtubule-targeting agents suppressed beating. MARK inhibitor impedance and kinase potencies aligned with rat blood pressure effects. Chk inhibitor effects were judged off-target because Chk and beat inhibition potencies did not correlate and knockdowns did not alter beating. Taken together, the data demonstrate that cardiomyocyte impedance assays can address three unmet needs-detecting KI functional cardiotoxicity in vitro, determining mechanism of action, and supporting safety structure-activity relationships.

Hybrid in silico models for drug-induced liver injury using chemical descriptors and in vitro cell-imaging information

Drug-induced liver injury (DILI) is a major adverse drug reaction that accounts for one-third of post-marketing drug withdrawals. Several classifiers for human hepatotoxicity using chemical descriptors with limited prediction accuracies have been published. In this study, we developed predictive in silico models based on a set of 156 DILI positive and 136 DILI negative compounds for DILI prediction. First, models based on a chemical descriptor (CDK, Dragon and MOE) and in vitro cell-imaging endpoints [human hepatocyte imaging assay technology (HIAT) descriptors] were built using random forest (RF) and five-fold cross-validation procedure. Then three hybrid models were built using HIAT and a single type of chemical descriptors. Generally, the models based only on chemical descriptors were poor, with a correct classification rate (CCR) around 0.60 when the default threshold value (i.e. threshold = 0.50) was used. The hybrid models afforded a CCR of 0.73 with a specificity of 0.74 and a better true positive rate (sensitivity of 0.71), which is crucial in drug toxicity screening for the purpose of patient safety. The benefit of hybrid models was even more drastic when stricter classification thresholds were employed (e.g. CCR would be 0.83 when double thresholds (non-toxic < 0.40 and toxic > 0.60) were used for the hybrid model). We have developed rigorously validated hybrid models which can be used in virtual screening of lead compounds with potential hepatotoxicity. Our study also showed a chemical structure and in vitro biological data can be complementary in enhancing the prediction accuracy of human hepatotoxicity and can afford rational mechanistic interpretation.

Predicting the Drug Safety for Traditional Chinese Medicine through a Comparative Analysis of Withdrawn Drugs Using Pharmacological Network

As the major issue to limit the use of drugs, drug safety leads to the attrition or failure in clinical trials of drugs. Therefore, it would be more efficient to minimize therapeutic risks if it could be predicted before large-scale clinical trials. Here, we integrated a network topology analysis with cheminformatics measurements on drug information from the DrugBank database to detect the discrepancies between approved drugs and withdrawn drugs and give drug safety indications. Thus, 47 approved drugs were unfolded with higher similarity measurements to withdrawn ones by the same target and confirmed to be already withdrawn or discontinued in certain countries or regions in subsequent investigations. Accordingly, with the 2D chemical fingerprint similarity calculation as a medium, the method was applied to predict pharmacovigilance for natural products from an in-house traditional Chinese medicine (TCM) database. Among them, Silibinin was highlighted for the high similarity to the withdrawn drug Plicamycin although it was regarded as a promising drug candidate with a lower toxicity in existing reports. In summary, the network approach integrated with cheminformatics could provide drug safety indications effectively, especially for compounds with unknown targets or mechanisms like natural products. It would be helpful for drug safety surveillance in all phases of drug development.

A public-private consortium advances cardiac safety evaluation: achievements of the HESI Cardiac Safety Technical Committee

INTRODUCTION

The evaluation of cardiovascular side-effects is a critical element in the development of all new drugs and chemicals. Cardiac safety issues are a major cause of attrition and withdrawal due to adverse drug reactions (ADRs) in pharmaceutical drug development.

METHODS

The evolution of the HESI Technical Committee on Cardiac Safety from 2000-2013 is presented as an example of an effective international consortium of academic, government, and industry scientists working to improve cardiac safety.

RESULTS AND DISCUSSION

The HESI Technical Committee Working Groups facilitated the development of a variety of platforms for resource sharing and communication among experts that led to innovative strategies for improved drug safety. The positive impacts arising from these Working Groups are described in this article.

Drug attrition during pre-clinical and clinical development: understanding and managing drug-induced cardiotoxicity

Cardiovascular toxicity remains a major cause of concern during preclinical and clinical development as well as contributing to post-approval withdrawal of medicines. This issue is particularly relevant for anticancer drugs where, the significant improvement in the life expectancies of patients has dramatically extended the use and duration of drug therapies. Nevertheless, cardiotoxicity is also observed with other classes of drugs, including antibiotics, antidepressants, and antipsychotics. This article summarizes the clinical manifestations of drug-induced cardiotoxicity by various cancer chemotherapies and novel drugs for the treatment of other diseases. Furthermore, it presents on overview of biomarker and imaging techniques for the detection of drug-induced cardiotoxicity. Guidelines for the management of patients exposed to drugs with cardiotoxic potential are presented as well as a checklist for collecting information when a safety signal is observed in clinical trials to more effectively assess the risk of cardiotoxicity and manage patient safety.

Identification of novel translational urinary biomarkers for acetaminophen-induced acute liver injury using proteomic profiling in mice

Drug-induced liver injury (DILI) is the leading cause of acute liver failure. Currently, no adequate predictive biomarkers for DILI are available. This study describes a translational approach using proteomic profiling for the identification of urinary proteins related to acute liver injury induced by acetaminophen (APAP). Mice were given a single intraperitoneal dose of APAP (0–350 mg/kg bw) followed by 24 h urine collection. Doses of ≥275 mg/kg bw APAP resulted in hepatic centrilobular necrosis and significantly elevated plasma alanine aminotransferase (ALT) values (p<0.0001). Proteomic profiling resulted in the identification of 12 differentially excreted proteins in urine of mice with acute liver injury (p<0.001), including superoxide dismutase 1 (SOD1), carbonic anhydrase 3 (CA3) and calmodulin (CaM), as novel biomarkers for APAP-induced liver injury. Urinary levels of SOD1 and CA3 increased with rising plasma ALT levels, but urinary CaM was already present in mice treated with high dose of APAP without elevated plasma ALT levels. Importantly, we showed in human urine after APAP intoxication the presence of SOD1 and CA3, whereas both proteins were absent in control urine samples. Urinary concentrations of CaM were significantly increased and correlated well with plasma APAP concentrations (r = 0.97; p<0.0001) in human APAP intoxicants, who did not present with elevated plasma ALT levels. In conclusion, using this urinary proteomics approach we demonstrate CA3, SOD1 and, most importantly, CaM as potential human biomarkers for APAP-induced liver injury.

Profiling of toxicity and identification of distinct apoptosis profiles using a 384-well high-throughput flow cytometry screening platform

Methods and techniques used to detect apoptosis have benefited from advances in technologies such as flow cytometry. With a large arsenal of lasers, fluorescent labels, and readily accessible biological targets, it is possible to detect multiple targets with unique combinations of fluorescent spectral signatures from a single sample. Traditional flow cytometry has been limited as a screening tool as the sample throughput has been low, whereas the data analysis and generation of screening relevant results have been complex. The HTFC Screening System running ForeCyt software is an instrument platform designed to perform high-throughput, multiplexed screening with seamless transformation of flow cytometry data into screening hits. We report the results of a screen that simultaneously quantified caspase 3/7 activation, annexin V binding, cell viability, and mitochondrial integrity. Assay performance over 5 days demonstrated robustness, reliability, and performance of the assay. This system is high throughput in that a 384-well plate can be read and fully analyzed within 30 min and is sensitive with an assay window of at least 10-fold for all parameters and a Z' factor of ≥0.75 for all endpoints and time points. From a screen of 231 compounds, 11 representative toxicity profiles highlighting differential activation of apoptotic pathways were identified.