Immunogenicity Risk Assessment of Process-Related Impurities in An Engineered T Cell Receptor Cellular Product.

Cell therapies such as genetically modified T cells have emerged as a promising and viable treatment for hematologic cancers and are being aggressively pursued for a wide range of diseases and conditions that were previously difficult to treat or had no cure. The process development requires genetic modifications to T cells to express a receptor (engineered T cell receptor (eTCR)) of specific binding qualities to the desired target. Protein reagents utilized during the cell therapy manufacturing process, to facilitate these genetic modifications, are often present as process-related impurities at residual levels in the final drug product and can represent a potential immunogenicity risk upon infusion. This manuscript presents a framework for the qualification of an assay for assessing the immunogenicity risk of AA6 and Cas9 residuals. The same framework applies for other residuals; however, AAV6 and Cas9 were selected as they were residuals from the manufacturing of an engineered T cell receptor cellular product in development. The manuscript: 1) elucidates theoretical risks, 2) summarizes analytical data collected during process development, 3) describes the qualification of an in vitro human PBMC cytokine release assay to assess immunogenicity risk from cellular product associated process residuals; 4) identifies a multiplexed inflammatory innate and adaptive cytokine panel with pre-defined criteria using relevant positive controls; and 5) discusses qualification challenges and potential solutions for establishing meaningful thresholds. The assessment is not only relevant to establishing safe exposure levels of these residuals but also in guiding risk assessment and CMC strategy during the conduct of clinical trials.

Investigation Into the Role of ERK in Tyrosine Kinase Inhibitor-Induced Neuropathy.

Chemotherapy-induced peripheral neuropathy (CIPN) is a common and debilitating adverse event that can alter patient treatment options and halt candidate drug development. A case study is presented here describing the preclinical and clinical development of CC-90003, a small molecule extracellular signal-regulated kinase (ERK)1/2 inhibitor investigated as an oncology therapy. In a Phase Ia clinical trial, CC-90003 elicited adverse drug-related neuropathy and neurotoxicity that contributed to discontinued development of CC-90003 for oncology therapy. Preclinical evaluation of CC-90003 in dogs revealed clinical signs and electrophysiological changes consistent with peripheral neuropathy that was reversible. Mice did not exhibit signs of neuropathy upon daily dosing with CC-90003, supporting that rodents generally poorly predict CIPN. We sought to investigate the mechanism of CC-90003-induced peripheral neuropathy using a phenotypic in vitro assay. Translating preclinical neuropathy findings to humans proves challenging as no robust in vitro models of CIPN exist. An approach was taken to examine the influence of CIPN-associated drugs on human-induced pluripotent stem cell-derived peripheral neuron (hiPSC-PN) electrophysiology on multielectrode arrays (MEAs). The MEA assay with hiPSC-PNs was sensitive to CIPN-associated drugs cisplatin, sunitinib, colchicine, and importantly, to CC-90003 in concordance with clinical neuropathy incidence. Biochemical data together with in vitro MEA data for CC-90003 and 12 of its structural analogs, all having similar ERK inhibitory activity, revealed that CC-90003 disrupted in vitro neuronal electrophysiology likely via on-target ERK inhibition combined with off-target kinase inhibition and translocator protein inhibition. This approach could prove useful for assessing CIPN risk and interrogating mechanisms of drug-induced neuropathy.

Cardiovascular microphysiological systems (CVMPS) for safety studies - a pharma perspective.

The integrative responses of the cardiovascular (CV) system are essential for maintaining blood flow to provide oxygenation, nutrients, and waste removal for the entire body. Progress has been made in independently developing simple in vitro models of two primary components of the CV system, namely the heart (using induced pluripotent stem-cell derived cardiomyocytes) and the vasculature (using endothelial cells and smooth muscle cells). These two in vitro biomimics are often described as immature and simplistic, and typically lack the structural complexity of native tissues. Despite these limitations, they have proven useful for specific "fit for purpose" applications, including early safety screening. More complex in vitro models offer the tantalizing prospect of greater refinement in risk assessments. To this end, efforts to physically link cardiac and vascular components to mimic a true CV microphysiological system (CVMPS) are ongoing, with the goal of providing a more holistic and integrated CV response model. The challenges of building and implementing CVMPS in future pharmacological safety studies are many, and include a) the need for more complex (and hence mature) cell types and tissues, b) the need for more realistic vasculature (within and across co-modeled tissues), and c) the need to meaningfully couple these two components to allow for integrated CV responses. Initial success will likely come with simple, bioengineered tissue models coupled with fluidics intended to mirror a vascular component. While the development of more complex integrated CVMPS models that are capable of differentiating safe compounds and providing mechanistic evaluations of CV liabilities may be feasible, adoption by pharma will ultimately hinge on model efficiency, experimental reproducibility, and added value above current strategies.

Human ileal organoid model recapitulates clinical incidence of diarrhea associated with small molecule drugs.

Drug-induced gastrointestinal toxicity (GIT) is a common treatment-emergent adverse event that can negatively impact dosing, thereby limiting efficacy and treatment options for patients. An in vitro assay of GIT is needed to address patient variability, mimic the microphysiology of the gut, and accurately predict drug-induced GIT. Primary human ileal organoids (termed 'enteroids') have proven useful for stimulating intestinal stem cell proliferation and differentiation to multiple cell types present in the gut epithelium. Enteroids have enabled characterization of gut biology and the signaling involved in the pathogenesis of disease. Here, enteroids were differentiated from four healthy human donors and assessed for culture duration-dependent differentiation status by immunostaining for gut epithelial markers lysozyme, chromogranin A, mucin, and sucrase isomaltase. Differentiated enteroids were evaluated with a reference set of 31 drugs exhibiting varying degrees of clinical incidence of diarrhea, a common manifestation of GIT that can be caused by drug-induced thinning of the gut epithelium. An assay examining enteroid viability in response to drug treatment demonstrated 90% accuracy for recapitulating the incidence of drug-induced diarrhea. The human enteroid viability assay developed here presents a promising in vitro model for evaluating drug-induced diarrhea.

Developing in vitro assays to transform gastrointestinal safety assessment: potential for microphysiological systems.

Drug-induced gastrointestinal toxicities (DI-GITs) are among the most common adverse events in clinical trials. High prevalence of DI-GIT has persisted among new drugs due in part to the lack of robust experimental tools to allow early detection or to guide optimization of safer molecules. Developing in vitro assays for the leading GI toxicities (nausea, vomiting, diarrhoea, constipation, and abdominal pain) will likely involve recapitulating complex physiological properties that require contributions from diverse cell/tissue types including epithelial, immune, microbiome, nerve, and muscle. While this stipulation may be beyond traditional 2D monocultures of intestinal cell lines, emerging 3D GI microtissues capture interactions between diverse cell and tissue types. These interactions give rise to microphysiologies fundamental to gut biology. For GI microtissues, organoid technology was the breakthrough that introduced intestinal stem cells with the capability of differentiating into each of the epithelial cell types and that self-organize into a multi-cellular tissue proxy with villus- and crypt-like domains. Recently, GI microtissues generated using miniaturized devices with microfluidic flow and cyclic peristaltic strain were shown to induce Caco2 cells to spontaneously differentiate into each of the principle intestinal epithelial cell types. Second generation models comprised of epithelial organoids or microtissues co-cultured with non-epithelial cell types can successfully reproduce cross-'tissue' functional interactions broadening the potential of these models to accurately study drug-induced toxicities. A new paradigm in which in vitro assays become an early part of GI safety assessment could be realized if microphysiological systems (MPS) are developed in alignment with drug-discovery needs. Herein, approaches for assessing GI toxicity of pharmaceuticals are reviewed and gaps are compared with capabilities of emerging GI microtissues (e.g., organoids, organ-on-a-chip, transwell systems) in order to provide perspective on the assay features needed for MPS models to be adopted for DI-GIT assessment.

Thalidomide Inhibits Human iPSC Mesendoderm Differentiation by Modulating CRBN-dependent Degradation of SALL4.

Exposure to thalidomide during a critical window of development results in limb defects in humans and non-human primates while mice and rats are refractory to these effects. Thalidomide-induced teratogenicity is dependent on its binding to cereblon (CRBN), the substrate receptor of the Cul4A-DDB1-CRBN-RBX1 E3 ubiquitin ligase complex. Thalidomide binding to CRBN elicits subsequent ubiquitination and proteasomal degradation of CRBN neosubstrates including SALL4, a transcription factor of which polymorphisms phenocopy thalidomide-induced limb defects in humans. Herein, thalidomide-induced degradation of SALL4 was examined in human induced pluripotent stem cells (hiPSCs) that were differentiated either to lateral plate mesoderm (LPM)-like cells, the developmental ontology of the limb bud, or definitive endoderm. Thalidomide and its immunomodulatory drug (IMiD) analogs, lenalidomide, and pomalidomide, dose-dependently inhibited hiPSC mesendoderm differentiation. Thalidomide- and IMiD-induced SALL4 degradation can be abrogated by CRBN V388I mutation or SALL4 G416A mutation in hiPSCs. Genetically modified hiPSCs expressing CRBN E377V/V388I mutant or SALL4 G416A mutant were insensitive to the inhibitory effects of thalidomide, lenalidomide, and pomalidomide on LPM differentiation while retaining sensitivity to another known limb teratogen, all-trans retinoic acid (atRA). Finally, disruption of LPM differentiation by atRA or thalidomide perturbed subsequent chondrogenic differentiation in vitro. The data here show that thalidomide, lenalidomide, and pomalidomide affect stem cell mesendoderm differentiation through CRBN-mediated degradation of SALL4 and highlight the utility of the LPM differentiation model for studying the teratogenicity of new CRBN modulating agents.

Cardiovascular Toxicity Induced by Kinase Inhibitors: Mechanisms and Preclinical Approaches.

Kinase inhibitors have transformed the treatment of many cancers and are showing the same promise for other indications including inflammatory diseases. This class of drugs is one of the most predominant in the pharmaceutical industry, but development and clinical utility is often limited by a broad spectrum of cardiovascular (CV) toxicities including QT prolongation and arrhythmia, left ventricular dysfunction, congestive heart failure, ischemia and myocardial infarction, and hypertension. In this review article, we provide a broad overview of the spectrum of CV events detected in clinical trials of kinase inhibitors and the known and proposed on- and off-target links between kinase inhibitor targets and these specific cardiotoxicities. We also examine the unique features of kinase inhibitors that have impeded complete mechanistic understanding of kinase inhibitor-associated cardiotoxicities and contributed to the disconnect between preclinical predictions and clinical findings. We then discuss various in vitro models currently in use that are amenable for high-throughput screening as well as lower throughput models that are valuable for mechanistic insight. These physiologically relevant models, together with newer "omic"-wide approaches will help to increase our understanding of the mechanisms underlying kinase inhibitor-associated cardiotoxicity and enable rational design of kinase inhibitors in the future.

Human stem cell-derived cardiomyocytes in cellular impedance assays: bringing cardiotoxicity screening to the front line.

Cardiovascular (CV) toxicity is a leading cause of drug attrition and withdrawal. Introducing in vitro assays with higher throughput should permit earlier CV hazard identification and enable medicinal chemists to design-out liabilities. Heretofore, development of in vitro CV assays has been limited by the challenge of replicating integrated cardiovascular physiology while achieving the throughput and consistency required for screening. These challenges appear to be met with a combination of human stem cell-derived cardiomyocytes (CM) which beat spontaneously and monitoring the response with technology that can assess drug-induced changes in voltage dependent contraction such as cellular impedance which has been validated with excellent predictivity for drug-induced arrhythmia and contractility. Here, we review advances in cardiomyocyte impedance with emphasis on stem cell-derived cardiomyocyte models for toxicity screening. Key perspectives include: the electrical principles of impedance technology, impedance detection of cardiomyocyte beating, beat parameter selection/analysis, validation in toxicity and drug discovery, and future directions. As a conclusion, an in vitro screening cascade is proffered using the downstream, inclusive detection of CM impedance assays as a primary screen followed by complementary CM assays chosen to enable mechanism-appropriate follow-up. The combined approach will enhance testing for CV liabilities prior to traditional in vivo models.

Refining the human iPSC-cardiomyocyte arrhythmic risk assessment model.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs) are capable of detecting drug-induced clinical arrhythmia, Torsade de Pointes (TdP), and QT prolongation. Efforts herein employ a broad set of structurally diverse drugs to optimize the predictive algorithm for applications in discovery toxicology and cardiac safety screening. The changes in the beat rhythm and rate of a confluent monolayer of hiPS-CMs by 88 marketed and 30 internal discovery compounds were detected with real-time cellular impedance measurement and quantified by measures of arrhythmic beating (IB20, lowest concentration inducing ≥ 20% arrhythmic [irregular, atypical] beats in 3 consecutive 20-s sweeps, and predicted proarrhythmic score [PPS]-IB20) or changes in beat rate (BR20, the lowest concentration inducing a reduction in beat rate of ≥ 20% at 3 consecutive sweeps compared with the time-matched vehicle control group, and PPS-BR20). Drug-induced arrhythmic beats and reductions in beat rates are predictive of clinical arrhythmia and QT prolongation, respectively. A threshold of ≤ 10 µM for class determination results in 82% in vitro-in vivo concordance for TdP prediction and 91% sensitivity for non-TdP arrhythmia detection, or 83% and 91% if clinically efficacious plasma (effective serum therapeutic concentration [C eff]) values are incorporated. This human cardiomyocyte arrhythmic risk (hCAR) model provides greater predictivity for torsadogenicity in humans compared with either human ether-a-go-go-related gene (hERG) inhibition (75%) or QT prolongation (81%). The concordance of beat rate reductions to predict clinical QT prolongation is 86%, or 87% when C eff is considered, which is greater than a hERG signal (80%). Further, arrhythmic beats resulting from cytotoxicity were identified by a distinct arrhythmic beating pattern, which occurred after the onset of cytolethality. This hCAR assay showed increased performance over existing preclinical tools in predicting clinical QT prolongation, arrhythmia, and TdP. Thus, hiPS-CMs are a relevant cell system to improve evaluating cardiac safety liabilities of drug candidates.

Cancer genetics and the cardiotoxicity of the therapeutics.

Cancer genomics has focused on the discovery of mutations and chromosomal structural rearrangements that either increase susceptibility to cancer or support the cancer phenotype. Protein kinases are the most frequently mutated genes in the cancer genome, making them attractive therapeutic targets for drug design. However, the use of some of the kinase inhibitors (KIs) has been associated with toxicities to the heart and vasculature, including acute coronary syndromes and heart failure. Herein we discuss the genetic basis of cancer, focusing on mutations in the kinase genome (kinome) that lead to tumorigenesis. This will allow an understanding of the real and potential power of modern cancer therapeutics. The underlying mechanisms that drive the cardiotoxicity of the KIs are also examined. The preclinical models for predicting cardiotoxicity, including induced pluripotent stem cells and zebrafish, are reviewed, with the hope of eventually being able to identify problematic agents before their use in patients. Finally, the use of biomarkers in the clinic is discussed, and newer strategies (i.e., metabolomics and enhanced imaging strategies) that may allow earlier and more accurate detection of cardiotoxicity are reviewed.

The effects of jaspamide on human cardiomyocyte function and cardiac ion channel activity.

Jaspamide (jasplakinolide; NSC-613009) is a cyclodepsipeptide that has antitumor activity. A narrow margin of safety was observed between doses required for efficacy in mouse tumor models and doses that caused severe acute toxicity in rats and dogs. We explored the hypothesis that the observed toxicity was due to cardiotoxicity. Jaspamide was tested in a patch clamp assay to determine its effect on selected cardiac ion channels. Jaspamide (10 µM) inhibited Kv1.5 activity by 98.5%. Jaspamide also inhibited other channels including Cav1.2, Cav3.2, and HCN2; however, the Kv11.1 (hERG) channel was minimally affected. Using spontaneously contracting human cardiomyocytes derived from induced pluripotent stem cells, effects on cardiomyocyte contraction and viability were also examined. Jaspamide (30 nM to 30 µM) decreased cardiomyocyte cell indices and beat amplitude, putative measurements of cell viability and cardiac contractility, respectively. Concentration-dependent increases in rhythmic beating rate were noted at ≤ 6 h of treatment, followed by dose-dependent decreases after 6 and 72 h exposure. The toxic effects of jaspamide were compared with that of the known cardiotoxicant mitoxantrone, and confirmed by multiparameter fluorescence imaging analysis. These results support the hypothesis that the toxicity observed in rats and dogs is due to toxic effects of jaspamide on cardiomyocytes.

Determination of the human cardiomyocyte mRNA and miRNA differentiation network by fine-scale profiling.

To gain insight into the molecular regulation of human heart development, a detailed comparison of the mRNA and miRNA transcriptomes across differentiating human-induced pluripotent stem cell (hiPSC)-derived cardiomyocytes and biopsies from fetal, adult, and hypertensive human hearts was performed. Gene ontology analysis of the mRNA expression levels of the hiPSCs differentiating into cardiomyocytes revealed 3 distinct groups of genes: pluripotent specific, transitional cardiac specification, and mature cardiomyocyte specific. Hierarchical clustering of the mRNA data revealed that the transcriptome of hiPSC cardiomyocytes largely stabilizes 20 days after initiation of differentiation. Nevertheless, analysis of cells continuously cultured for 120 days indicated that the cardiomyocytes continued to mature toward a more adult-like gene expression pattern. Analysis of cardiomyocyte-specific miRNAs (miR-1, miR-133a/b, and miR-208a/b) revealed an miRNA pattern indicative of stem cell to cardiomyocyte specification. A biostatistitical approach integrated the miRNA and mRNA expression profiles revealing a cardiomyocyte differentiation miRNA network and identified putative mRNAs targeted by multiple miRNAs. Together, these data reveal the miRNA network in human heart development and support the notion that overlapping miRNA networks re-enforce transcriptional control during developmental specification.

High purity human-induced pluripotent stem cell-derived cardiomyocytes: electrophysiological properties of action potentials and ionic currents.

Human-induced pluripotent stem cells (hiPSCs) can differentiate into functional cardiomyocytes; however, the electrophysiological properties of hiPSC-derived cardiomyocytes have yet to be fully characterized. We performed detailed electrophysiological characterization of highly pure hiPSC-derived cardiomyocytes. Action potentials (APs) were recorded from spontaneously beating cardiomyocytes using a perforated patch method and had atrial-, nodal-, and ventricular-like properties. Ventricular-like APs were more common and had maximum diastolic potentials close to those of human cardiac myocytes, AP durations were within the range of the normal human electrocardiographic QT interval, and APs showed expected sensitivity to multiple drugs (tetrodotoxin, nifedipine, and E4031). Early afterdepolarizations (EADs) were induced with E4031 and were bradycardia dependent, and EAD peak voltage varied inversely with the EAD take-off potential. Gating properties of seven ionic currents were studied including sodium (I(Na)), L-type calcium (I(Ca)), hyperpolarization-activated pacemaker (I(f)), transient outward potassium (I(to)), inward rectifier potassium (I(K1)), and the rapidly and slowly activating components of delayed rectifier potassium (I(Kr) and I(Ks), respectively) current. The high purity and large cell numbers also enabled automated patch-clamp analysis. We conclude that these hiPSC-derived cardiomyocytes have ionic currents and channel gating properties underlying their APs and EADs that are quantitatively similar to those reported for human cardiac myocytes. These hiPSC-derived cardiomyocytes have the added advantage that they can be used in high-throughput assays, and they have the potential to impact multiple areas of cardiovascular research and therapeutic applications.

HPLC-MS/MS methods for the quantitative analysis of 5-oxoproline (pyroglutamate) in rat plasma and hepatic cell line culture medium.

5-Oxoproline (5-OP; pyroglutamate) is an intermediate in the biosynthesis of the endogenous tripeptide glutathione and has been seen to be elevated in the biofluids and tissues of rats following the administration of glutathione-depleting hepatotoxic xenobiotics such as acetaminophen (paracetamol), bromobenzene and ethionine. As 5-OP is a potential biomarker for hepatotoxicity HPLC-MS/MS methods have been developed for its quantification in in vitro cell culture media and rat plasma. For the cell culture media the lower limit of quantification (LLOQ), defined as the lowest concentration on the calibration curve, was 10 ng/ml. Minimal carry over was observed for cell culture media between injections (less than 5% at all concentrations examined), precision and accuracy were generally better than 20% for within and between day analyses. For rat plasma a LLOQ of 50 ng/ml was obtained. Carry over for plasma was less than 5% for all concentrations, within and between batch accuracy and precision were generally better than 20%. The methods were linear for both sample types from the LLOQ up to 1 µg/ml. For samples obtained from rats subjected to chronic administration of the hepatotoxin methapyrilene, concentrations of 5-OP were not observed to increase significantly at any time point compared to controls. 5-OP was also determined in the culture media of human liver epithelial (THLE) cells transfected with cytochrome P450 2E1 (THLE-2E1). Following exposure of THLE-2E1 cells to acetaminophen, large increases in the concentrations of 5-OP were observed, which correlated with reduced cellular glutathione content and with cell toxicity. These results show that LC-MS/MS can be used to perform rapid, sensitive, and quantitative determination of 5-OP in vivo and in vitro and will enable additional investigations into the utility of 5-OP as a biomarker of liver drug-induced liver injury.

Estimating the risk of drug-induced proarrhythmia using human induced pluripotent stem cell-derived cardiomyocytes.

Improved in vitro systems for predicting drug-induced toxicity are needed in the pharmaceutical and biotechnology industries to decrease late-stage drug attrition. One unmet need is an early screen for cardiotoxicity, which accounts for about one third of safety-based withdrawn pharmaceuticals. Herein, the first published report of a high-throughput functional assay employing a monolayer of beating human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) is described, detailing a model that accurately detects drug-induced cardiac abnormalities. Using 96-well plates with interdigitated electrode arrays that assess impedance, the rhythmic, synchronous contractions of the iPSC-CMs were detected. Treatment of the iPSC-CMs with 28 different compounds with known cardiac effects resulted in compound-specific changes in the beat rate and/or the amplitude of the impedance measurement. Changes in impedance for the compounds tested were comparable with the results from a related technology, electric field potential assessment obtained from microelectrode arrays. Using the results from the set of compounds, an index of drug-induced arrhythmias was calculated, enabling the determination of a drug's proarrhythmic potential. This system of interrogating human cardiac function in vitro opens new opportunities for predicting cardiac toxicity and studying cardiac biology.

The electrophysiological effects of cardiac glycosides in human iPSC-derived cardiomyocytes and in guinea pig isolated hearts.

BACKGROUND/AIMS: Monitoring changes in the field potential (FP) of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) following compound administration has been proposed as a novel screening tool to evaluate cardiac ion channel interactions and QT liability. Here we extended the use of FP to evaluate the pharmacological and toxicological properties of cardiac glycosides. METHODS: FPs were recorded using microelectrode arrays (MEAs) in spontaneously beating hiPSC-CMs. The in vitro effects of ouabain and digoxin on FPs were compared with data generated on hemodynamic and ECG parameters in guinea pig Langendorff hearts. RESULTS: In hiPSC-CMs, ouabain and digoxin reduced Na(+)-spike amplitude, shortened FP duration (FPD), increased Ca(2+)-wave amplitude, and dose-dependently induced arrhythmic beats. The ouabain-induced changes observed in hiPSC-CMs correlated well with the effects seen in isolated hearts which revealed QT shortening, enhancement of contractility, and arrhythmogenesis. Nifedipine, an L-type Ca(2+) channel blocker, reduced Ca(2+)-wave amplitude and FPD in hiPSC-CMs, and led to parallel effects of decreased ventricular contractility and shortened QT interval in isolated hearts. Further, nifedipine attenuated the Ca(2+)-peak amplitude and proarrhythmic effect of both glycosides. These results suggested that FPD and Ca(2+)-wave amplitude are comparable surrogates of QT interval and contractility of intact hearts, respectively. CONCLUSION: hiPSC-CMs reflect similar cardiac pharmacology as seen in isolated cardiac preparations and thus are a suitable model in study of the pharmacology and toxicology of cardioactive ion channel and transporter modulators.

Characterization of xenobiotic-induced hepatocellular enzyme induction in rats: anticipated thyroid effects and unique pituitary gland findings.

During routine safety evaluation of RO2910, a non-nucleoside reverse transcriptase inhibitor for HIV infection, histopathology findings concurrent with robust hepatocellular induction occurred in multiple organs, including a unique, albeit related, finding in the pituitary gland. For fourteen days, male and female rats were administered, by oral gavage vehicle, 100, 300, or 1000 mg/kg/day of RO2910. Treated groups had elevated serum thyroid-stimulating hormone and decreased total thyroxine, and hypertrophy in the liver, thyroid gland, and pituitary pars distalis. These were considered consequences of hepatocellular induction and often were dose dependent and more pronounced in males than in females. Hepatocellular centrilobular hypertrophy corresponded with increased expression of cytochrome P450s 2B1/2, 3A1, and 3A2 and UGT 2B1. Bilateral thyroid follicular cell hypertrophy occurred concurrent to increased mitotic activity and sometimes colloid depletion, which were attributed to changes in thyroid hormone levels. Males had hypertrophy of thyroid-stimulating hormone-producing cells (thyrotrophs) in the pituitary pars distalis. All findings were consistent with the well-established adaptive physiologic response of rodents to xenobiotic-induced hepatocellular microsomal enzyme induction. Although the effects on the pituitary gland following hepatic enzyme induction-mediated hypothyroidism have not been reported previously, other models of stress and thyroid depletion leading to pituitary stimulation support such a shared pathogenesis.

Cardiotoxicity of kinase inhibitors: the prediction and translation of preclinical models to clinical outcomes.

Targeted therapeutics, particularly those that inhibit the activity of protein kinases that are mutated and/or overexpressed in cancer, have revolutionized the treatment of some cancers and improved survival rates in many others. Although these agents dominate drug development in cancer, significant toxicities, including cardiotoxicity, have emerged. In this Review, we examine the underlying mechanisms that result in on-target or off-target cardiotoxicities of small molecule kinase inhibitors. We also discuss how well the various preclinical safety models and strategies might predict clinical cardiotoxicity. It is hoped that a thorough understanding of the mechanisms underlying cardiotoxicity will lead to the development of safe, effective drugs and consequently, fewer costly surprises as agents progress through clinical trials.

HPLC-MS/MS methods for the quantitative analysis of ophthalmic acid in rodent plasma and hepatic cell line culture medium.

Ophthalmic acid (OA), an endogenous tripeptide analogue of glutathione, has been suggested as a potential biomarker for paracetamol/acetaminophen hepatotoxicity. Here HPLC-MS/MS methods have been developed for the precise, sensitive and specific detection and quantification of OA in in vitro cell culture medium and plasma. For the cell culture medium the LLOQ was found to be 1 ng/ml, with less than 1% between sample carry over at all concentrations and precision below 15% for within day and below 9% for between day analyses. For rat plasma the presence of endogenous OA resulted in the LLOQ being 25 ng/ml (defined as the lowest concentration on the calibration curve where the base peak was less than 20% of the LLOQ). For the plasma assay the percentage carry over was less than 1% for all concentrations and within and between batch precision was below 21%. The methods were linear for both sample types from the LLOQ up to 5 µg/ml. The method was successfully applied to the determination of OA in samples obtained following the chronic administration of the rat hepatotoxin methapyrilene, where plasma OA concentrations were observed to show a weak negative correlation with those of established liver injury biomarkers such as aspartate aminotransferase (AST).

Mechanism of subendocardial cell proliferation in the rat and relevance for understanding drug-induced valvular heart disease in humans.

A number of drugs and drug candidates, including fenfluramine and ergot derivatives, are associated with valvulopathy in humans; however, these responses are poorly predicted from animal studies. In vitro and in vivo evidence suggests that these compounds exert their pathological effect through activation of serotonin 2B receptor (5HT2BR) signaling. However, the variable effect of fenfluramine and other 5HT2BR agonists in rodents has cast doubt on the relevance of animal findings to predicting human risk. Herein, a candidate compound, RO3013, induced subendocardial cell proliferation in the mitral and tricuspid valves in rats after only 3 days of daily dosing. Additionally, there was a treatment-related increase in immunostaining of the proliferation marker Ki67, and phosphorylated Smad3 in the heart indicative of TGFß signaling co-localized with 5HT2BR expression. To substantiate the hypothesis that RO3013-induced valvular proliferation is secondary to 5HT2BR activation, the compound was evaluated in vitro and found to bind to the human 5HT2BR with a K(i) of 3.8µM; however, it was virtually devoid of agonist activity in a functional assay in human cells. By contrast, RO3013 bound to the rat 5HT2BR with a K(i) of 1.2µM and activated the receptor with an EC50 of 0.5µM. This agonist potency estimate is in good agreement with the free plasma concentrations of RO3013 at which valvular proliferation was observed. These results suggest that the rat may be susceptible to 5HT2BR-mediated valvular proliferation similar to humans; yet, the significant differences between binding and functional activities can be a possible explanation for the observed species-selective receptor responses.