Workshop Report: FDA Workshop on Improving Cardiotoxicity Assessment With Human-Relevant Platforms.

Given that cardiovascular safety concerns remain the leading cause of drug attrition at the preclinical drug development stage, the National Center for Toxicological Research of the US Food and Drug Administration hosted a workshop to discuss current gaps and challenges in translating preclinical cardiovascular safety data to humans. This white paper summarizes the topics presented by speakers from academia, industry, and government intended to address the theme of improving cardiotoxicity assessment in drug development. The main conclusion is that to reduce cardiovascular safety liabilities of new therapeutic agents, there is an urgent need to integrate human-relevant platforms/approaches into drug development. Potential regulatory applications of human-derived cardiomyocytes and future directions in employing human-relevant platforms to fill the gaps and overcome barriers and challenges in preclinical cardiovascular safety assessment were discussed. This paper is intended to serve as an initial step in a public-private collaborative development program for human-relevant cardiotoxicity tools, particularly for cardiotoxicities characterized by contractile dysfunction or structural injury.

Combining an in silico proarrhythmic risk assay with a tPKPD model to predict QTc interval prolongation in the anesthetized guinea pig assay.

Human-based in silico models are emerging as important tools to study the effects of integrating inward and outward ion channel currents to predict clinical proarrhythmic risk. The aims of this study were 2-fold: 1) Evaluate the capacity of an in silico model to predict QTc interval prolongation in the in vivo anesthetized cardiovascular guinea pig (CVGP) assay for new chemical entities (NCEs) and; 2) Determine if a translational pharmacokinetic/pharmacodynamic (tPKPD) model can improve the predictive capacity. In silico simulations for NCEs were performed using a population of human ventricular action potential (AP) models. PatchXpress® (PX) or high throughput screening (HTS) ion channel data from respectively n = 73 and n = 51 NCEs were used as inputs for the in silico population. These NCEs were also tested in the CVGP (n = 73). An M5 pruned decision tree-based regression tPKPD model was used to evaluate the concentration at which an NCE is liable to prolong the QTc interval in the CVGP. In silico results successfully predicted the QTc interval prolongation outcome observed in the CVGP with an accuracy/specificity of 85%/73% and 75%/77%, when using PX and HTS ion channel data, respectively. Considering the tPKPD predicted concentration resulting in QTc prolongation (EC5%) increased accuracy/specificity to 97%/95% using PX and 88%/97% when using HTS. Our results support that human-based in silico simulations in combination with tPKPD modeling can provide correlative results with a commonly used early in vivo safety assay, suggesting a path toward more rapid NCE assessment with reduced resources, cycle time, and animal use.

Assessment of the clinical cardiac drug-drug interaction associated with the combination of hepatitis C virus nucleotide inhibitors and amiodarone in guinea pigs and rhesus monkeys.

In 2015, European and U.S. health agencies issued warning letters in response to 9 reported clinical cases of severe bradycardia/bradyarrhythmia in hepatitis C virus (HCV)-infected patients treated with sofosbuvir (SOF) in combination with other direct acting antivirals (DAAs) and the antiarrhythmic drug, amiodarone (AMIO). We utilized preclinical in vivo models to better understand this cardiac effect, the potential pharmacological mechanism(s), and to identify a clinically translatable model to assess the drug-drug interaction (DDI) cardiac risk of current and future HCV inhibitors. An anesthetized guinea pig model was used to elicit a SOF+AMIO-dependent bradycardia. Detailed cardiac electrophysiological studies in this species revealed SOF+AMIO-dependent selective nodal dysfunction, with initial, larger effects on the sinoatrial node. Further studies in conscious, rhesus monkeys revealed an emergent bradycardia and bradyarrhythmia in 3 of 4 monkeys administered SOF+AMIO, effects not observed with either agent alone. Morever, bradycardia and bradyarrhythmia were not observed in rhesus monkeys when intravenous infusion of MK-3682 was completed after AMIO pretreatment. CONCLUSIONS: These are the first preclinical in vivo experiments reported to replicate the severe clinical SOF+AMIO cardiac DDI and provide potential in vivo mechanism of action. As such, these data provide a preclinical risk assessment paradigm, including a clinically relevant nonhuman primate model, with which to better understand cardiovascular DDI risk for this therapeutic class. Furthermore, these studies suggest that not all HCV DAAs and, in particular, not all HCV nonstructural protein 5B inhibitors may exhibit this cardiac DDI with amiodarone. Given the selective in vivo cardiac electrophysiological effect, these data enable targeted cellular/molecular mechanistic studies to more precisely identify cell types, receptors, and/or ion channels responsible for the clinical DDI. (Hepatology 2016;64:1430-1441).

Interaction between amiodarone and hepatitis-C virus nucleotide inhibitors in human induced pluripotent stem cell-derived cardiomyocytes and HEK-293 Cav1.2 over-expressing cells.

Several clinical cases of severe bradyarrhythmias have been reported upon co-administration of the Hepatitis-C NS5B Nucleotide Polymerase Inhibitor (HCV-NI) direct-acting antiviral agent, sofosbuvir (SOF), and the Class-III anti-arrhythmic amiodarone (AMIO). We model the cardiac drug-drug interaction (DDI) between AMIO and SOF, and between AMIO and a closely-related SOF analog, MNI-1 (Merck Nucleotide Inhibitor #1), in functional assays of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), to provide mechanistic insights into recently reported clinical cases. AMIO co-applied with SOF or MNI-1 increased beating rate or field potential (FP) rate and decreased impedance (IMP) and Ca(2+) transient amplitudes in hiPSC-CM syncytia. This action resembled that of Ca(2+) channel blockers (CCBs) in the model, but CCBs did not substitute for AMIO in the DDI. AMIO analog dronedarone (DRON) did not substitute for, but competed with AMIO in the DDI. Ryanodine and thapsigargin, decreasing intracellular Ca(2+) stores, and SEA-0400, a Na(+)/Ca(2+) exchanger-1 (NCX1) inhibitor, partially antagonized or suppressed DDI effects. Other agents affecting FP rate only exerted additive or subtractive effects, commensurate with their individual effects. We also describe an interaction between AMIO and MNI-1 on Cav1.2 ion channels in an over-expressing HEK-293 cell line. MNI-1 enhanced Cav1.2 channel inhibition by AMIO, but did not affect inhibition of Cav1.2 by DRON, verapamil, nifedipine, or diltiazem. Our data in hiPSC-CMs indicate that HCV-NI agents such as SOF and MNI-1 interact with key intracellular Ca(2+)-handling mechanisms. Additional study in a Cav1.2 HEK-293 cell-line suggests that HCV-NIs potentiate the inhibitory action of AMIO on L-type Ca(2+) channels.

Resolving the Reversed Rate Effect of Calcium Channel Blockers on Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes and the Impact on In Vitro Cardiac Safety Evaluation.

Calcium channel blockers (CCBs), such as diltiazem, nifedipine, and verapamil, cause tachycardia effects on several commercially available human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), when tested in culture media provided by suppliers, rather than bradycardia effects, as seen in vivo. We found that in test conditions where Na+ current of hiPSC-CMs was reduced to certain threshold by either specific Na+ channel blocker tetrodotoxin (TTX), or by voltage-dependent inactivation using elevated extracellular potassium concentrations, CCBs produced bradycardia effects on hiPSC-CMs. However, elevated extracellular potassium concentrations or the presence of TTX did not change other pharmacological responses of hiPSC-CMs, including CCBs' effects on contraction intensity and duration; beating rate change by calcium channel opener FPL64176, HCN blocker ivabradine, and ß-adrenergic agonist isoproterenol; and action potential duration prolongation by hERG channel blocker dofetilide. We concluded that action potentials of hiPSC-CMs, with regards to the CCB phenotype, were Na+ current driven. When Na+ channel availability was reduced to a critical level, their action potentials became Ca2+ current driven, and their responses to CCBs correlated well to those seen in vivo. Importantly, the corrected bradycardia effect of calcium channel block with our defined conditions will provide more reliable results in cardiac safety readouts of test compounds that integrate multiple effects including calcium channel inhibition.

Human-induced pluripotent stem cell-derived cardiomyocytes have limited IKs for repolarization reserve as revealed by specific KCNQ1/KCNE1 blocker.

OBJECTIVE: We investigated if there is IKs, and if there is repolarization reserve by IKs in human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). DESIGN: We used a specific KCNQ1/KCNE1 channel blocker, L-000768673, with an IC50 of 9 nM, and four hERG-specific blockers, astemizole, cisapride, dofetilide, and E-4031 to investigate the issue. RESULTS: L-000768673 concentration-dependently prolonged feature point duration (FPD)-a surrogate signal of action potential duration-from 1 to 30 nM without pacing or paced at 1.2 Hz, resulting from IKs blockade in hiPSC-CMs. At higher concentrations, the effect of L-000768673 on IKs was mitigated by its effect on ICa-L, resulting in shortened FPD, reduced impedance amplitude, and increased beating rate at 1 µM and above, recapitulating the self-limiting properties of L-000768673 on action potentials. All four hERG-specific blockers prolonged FPD as expected. Co-application of L-000768673 at sub-threshold (0.1 and 0.3 nM) and threshold (1 nM) concentrations failed to synergistically enhance the effects of hERG blockers on FPD prolongation, rather it showed additive effects, inconsistent with the repolarization reserve role of IKs in mature human myocytes that enhanced IKr response, implying a difference between hiPSC-CMs used in this study and mature human cardiomyocytes. CONCLUSION: There was IKs current in hiPSC-CMs, and blockade of IKs current caused prolongation of action potential of hiPSC-CMs. However, we could not demonstrate any synergistic effects on action potential duration prolongation of hiPSC-CMs by blocking hERG current and IKs current simultaneously, implying little or no repolarization reserve by IKs current in hiPSC-CMs used in this study.

HiPSC-CMs from different sex and ethnic origin donors exhibit qualitatively different responses to several classes of pharmacological challenges.

We investigated whether human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) created from diverse origins could have qualitatively (not just quantitatively) different responses to pharmacological reagents. Specifically, we challenged six hiPSC-CM syncytia made from a female Caucasian, a female black non-Hispanic, a female white non-Hispanic, a male Caucasian non-Hispanic, a male Asian Indian, and a male-Asian, respectively, with eight different classes of pharmacological reagents (hERG channel blocker cisapride and dofetilide, calcium channel opener FPL64176, ß-adrenergic agonist Isoproterenol, HCN channel blocker Ivabradine, IKs current blocker L-000768673, sodium channel blocker tetrodotoxin, and calcium channel blocker verapamil). We focused our analysis and comparison on qualitative differences (e.g., yes or no), and, found the following: hiPSC-CMs from female donors were uniformly more sensitive to dofetilide or cisapride, whereas those from male donors of all races were less sensitive to the two typical hERG blockers; isoproterenol had no chronotropic effect at all in one line; and two lines reacted to tetrodotoxin at very low concentrations and were more sensitive to external stimulation. We conclude that not all hiPSC-CMs are suitable for drug testing in terms of cardiac safety assessment, and pre-set acceptance criteria need to be established before any hiPSC-CMs can be used in CiPA-style study to evaluate cardiac liabilities of drug candidates.

Drug-induced shortening of the electromechanical window is an effective biomarker for in silico prediction of clinical risk of arrhythmias.

BACKGROUND AND PURPOSE: Early identification of drug-induced cardiac adverse events is key in drug development. Human-based computer models are emerging as an effective approach, complementary to in vitro and animal models. Drug-induced shortening of the electromechanical window has been associated with increased risk of arrhythmias. This study investigates the potential of a cellular surrogate for the electromechanical window (EMw) for prediction of pro-arrhythmic cardiotoxicity, and its underlying ionic mechanisms, using human-based computer models. EXPERIMENTAL APPROACH: In silico drug trials for 40 reference compounds were performed, testing up to 100-fold the therapeutic concentrations (EFTPCmax ) and using a control population of human ventricular action potential (AP) models, optimised to capture pro-arrhythmic ionic profiles. EMw was calculated for each model in the population as the difference between AP and Ca2+ transient durations at 90%. Drug-induced changes in the EMw and occurrence of repolarisation abnormalities (RA) were quantified. KEY RESULTS: Drugs with clinical risk of Torsade de Pointes arrhythmias induced a concentration-dependent EMw shortening, while safe drugs lead to increase or small change in EMw. Risk predictions based on EMw shortening achieved 90% accuracy at 10× EFTPCmax , whereas RA-based predictions required 100× EFTPCmax to reach the same accuracy. As it is dependent on Ca2+ transient, the EMw was also more sensitive than AP prolongation in distinguishing between pure hERG blockers and multichannel compounds also blocking the calcium current. CONCLUSION AND IMPLICATIONS: The EMw is an effective biomarker for in silico predictions of drug-induced clinical pro-arrhythmic risk, particularly for compounds with multichannel blocking action.

Response of safety pharmacologists to challenges arising from the rapidly evolving changes in the pharmaceutical industry.

This commentary highlights and expands upon the thoughts conveyed in the lecture by Dr. Alan S. Bass, recipient of the 2017 Distinguished Service Award from the Safety Pharmacology Society, given on 27 September 2017 in Berlin, Germany. The lecture discussed the societal, scientific, technological, regulatory and economic events that dramatically impacted the pharmaceutical industry and ultimately led to significant changes in the strategic operations and practices of safety pharmacology. It focused on the emerging challenges and opportunities, and considered the lessons learned from drug failures and the influences of world events, including the financial crisis that ultimately led to a collapse of the world economies from which we are now recovering. Events such as these, which continue to today, challenge the assumptions that form the foundation of our discipline and dramatically affect the way that safety pharmacology is practiced. These include the latest scientific and technological developments contributing to the design and advancement of safe medicines. More broadly, they reflect the philosophical mission of safety pharmacology and the roles and responsibilities served by safety pharmacologists. As the discipline of Safety Pharmacology continues to evolve, develop and mature, the reader is invited to reflect on past experiences as a framework towards a vision of the future of the field.

Cell culture conditions affect the ability of high content imaging assay to detect drug-induced changes in cellular parameters in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs).

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are widely used for drug safety and efficacy testing with various techniques, including high content imaging (HCI). Upon drug treatment, a significant number of hiPSC-CMs grown in regular 96-well plates coated with fibronectin detached from the bottom of the plate, complicating data acquisition. Several cell culture configurations were tested to improve cell adherence, and the effects of these configurations on total cell number, separation of feature values between the negative (DMSO 0.1%) and positive (antimycin, staurosporine) controls, scale of feature value differences, and data variability were statistically calculated. hiPSC-CMs were plated on fibronectin- (in "blanket" configuration) or MaxGel- (in "sandwich" configuration) coated plates and covered with a layer of either HydroMatrix or MaxGel 2, 7, or 11d after plating. After a total of 14d in culture, cells were treated with compounds, labeled with four fluorescent dyes (Hoechst, TMRM, NucView, and RedDot), and imaged with GE INCell2000. Based on the statistical parameters calculated, the MaxGel 25% 7d "sandwich" was superior to all other tested conditions when the cells were treated with 0.3 µM antimycin for 2 h and test compounds 10 µM crizotinib and 30 µM amiodarone for 48 h. For staurosporine treatment, the best culturing condition varied between MaxGel "sandwich" systems, depending on which parameters were under consideration. Thus, cell culturing conditions can significantly affect the ability of high content imaging to detect changes in cellular features during compound treatment and should be thoroughly evaluated before committing to compound testing.

Assessing Drug-Induced Long QT and Proarrhythmic Risk Using Human Stem-Cell-Derived Cardiomyocytes in a Ca2+ Imaging Assay: Evaluation of 28 CiPA Compounds at Three Test Sites.

The goal of this research consortium including Janssen, MSD, Ncardia, FNCR/LBR, and Health and Environmental Sciences Institute (HESI) was to evaluate the utility of an additional in vitro assay technology to detect potential drug-induced long QT and torsade de pointes (TdP) risk by monitoring cytosolic free Ca2+ transients in human stem-cell-derived cardiomyocytes (hSC-CMs). The potential proarrhythmic risks of the 28 comprehensive in vitro proarrhythmia assay (CiPA) drugs linked to low, intermediate, and high clinical TdP risk were evaluated in a blinded manner using Ca2+-sensitive fluorescent dye assay recorded from a kinetic plate reader system (Hamamatsu FDSS/µCell and FDSS7000) in 2D cultures of 2 commercially available hSC-CM lines (Cor.4U and CDI iCell Cardiomyocytes) at 3 different test sites. The Ca2+ transient assay, performed at the 3 sites using the 2 different hSC-CMs lines, correctly detected potential drug-induced QT prolongation among the 28 CiPA drugs and detected cellular arrhythmias-like/early afterdepolarization in 7 of 8 high TdP-risk drugs (87.5%), 6 of 11 intermediate TdP-risk drugs (54.5%), and 0 of 9 low/no TdP-risk drugs (0%). The results were comparable among the 3 sites and from 2 hSC-CM cell lines. The Ca2+ transient assay can serve as a user-friendly and higher throughput alternative to complement the microelectrode array and voltage-sensing optical action potential recording assays used in the HESI-CiPA study for in vitro assessment of drug-induced long QT and TdP risk.

Response of human induced pluripotent stem cell-derived cardiomyocytes to several pharmacological agents when intrinsic syncytial pacing is overcome by acute external stimulation.

We challenged human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) syncytia, mainly, CDI iCells with several classes of well-characterized pharmacological agents (including hERG blocker, Nav1.5 blocker, Cav1.2 blocker and opener, ß-adrenergic agonist, and If blocker) under pacing conditions, utilizing the Cardio-ECR instrument, a non-invasive platform featuring simultaneous and continuous measurement of synchronized beating rate and contractility (both signals were acquired simultaneously and well aligned). We found that: 1) with increasing acute stimulation rates (no pacing; 1, 1.5, and 2Hz), beat interval was gradually shortened mainly in the relaxation phase of each beat cycle; 2) typical responses of iCells hiPSC-CMs to all tested pharmacological agents were either attenuated or even eliminated by pacing, in a concentration- and stimulation rate-dependent manner; and 3) when iCells were influenced by pharmacological agents and cannot follow pacing rates, they still beat regularly at exactly 1/2 or 1/3 of pacing rates. We concluded that when intrinsic syncytial pacing was overcome by faster, external stimulations, beat intervals of hiPSC-CMs were mainly shortened in the relaxation phase, instead of proportionally in each beat cycle, with increasing pacing rates. In addition, in response to pharmacological agents upon pacing, hiPSC-CMs exhibited distinct patterns of refractoriness, manifested by skipped beats in pacing-rate dependent manner, and attenuation (or even abolition) of the typical response evoked under spontaneous beating.

Cardiac drug-drug interaction between HCV-NS5B pronucleotide inhibitors and amiodarone is determined by their specific diastereochemistry.

Severe bradycardia/bradyarrhythmia following coadministration of the HCV-NS5B prodrug sofosbuvir with amiodarone was recently reported. Our previous preclinical in vivo experiments demonstrated that only certain HCV-NS5B prodrugs elicit bradycardia when combined with amiodarone. In this study, we evaluate the impact of HCV-NS5B prodrug phosphoramidate diastereochemistry (D-/L-alanine, R-/S-phosphoryl) in vitro and in vivo. Co-applied with amiodarone, L-ala,SP prodrugs increased beating rate and decreased beat amplitude in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), but D-ala,RP produgs, including MK-3682, did not. Stereochemical selectivity on emerging bradycardia was confirmed in vivo. Diastereomer pairs entered cells equally well, and there was no difference in intracellular accumulation of L-ala,SP metabolites ± amiodarone, but no D-ala,RP metabolites were detected. Cathepsin A (CatA) inhibitors attenuated L-ala,SP prodrug metabolite formation, yet exacerbated L-ala,SP + amiodarone effects, implicating the prodrugs in these effects. Experiments indicate that pharmacological effects and metabolic conversion to UTP analog are L-ala,SP prodrug-dependent in cardiomyocytes.

Use of FDSS/µCell imaging platform for preclinical cardiac electrophysiology safety screening of compounds in human induced pluripotent stem cell-derived cardiomyocytes.

FDSS/µCell is a high-speed acquisition imaging platform (Hamamatsu Ltd., Hamamatsu, Japan) that allows for simultaneous high-throughput reading under controlled conditions. We evaluated the Ca(2+) transients or optical membrane potential changes of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) (iCells) in the presence or absence of 44 pharmacological agents known to interfere with cardiac ion channels (e.g., hERG, IKs, NaV1.5, CaV1.2). We tested two Ca(2+)-sensitive fluorescence dyes (Codex ACTOne® and EarlyTox®) and a membrane potential dye (FLIPR® membrane potential dye). We were able to quantify and report drug-induced early-after depolarizations (EAD)-like waveforms, cardiomyocyte ectopic beats and changes in beating rate from a subgroup of pharmacological agents acting acutely (within a 1-hour period). Cardiovascular drugs, such as dofetilide and d,l-sotalol, exhibited EAD-like signals at 3nM and 10µM, respectively. CNS drugs, such as haloperidol and sertindole, exhibited EAD-like signals and ectopic beats at 30nM and 1µM, respectively. Other drugs, such as astemizole, solifenacin, and moxifloxacin, exhibited similar arrhythmias at 30nM, 3µM and 300µM, respectively. Our data suggest that the membrane potential and intracellular Ca(2+) signal are tightly coupled, supporting the idea that the EAD-like signals reported are the accurate representation of an EAD signal of the cardiac action potential. Finally, the EAD-like Ca(2+) signal was well correlated to clinically-relevant concentrations where Torsade de Pointes (TdPs) arrhythmias were noted in healthy volunteers treated orally with some of the compounds we tested, as reported in PharmaPendium®.

Application of a systems pharmacology model for translational prediction of hERG-mediated QTc prolongation.

Drug-induced QTc interval prolongation (Δ QTc) is a main surrogate for proarrhythmic risk assessment. A higher in vivo than in vitro potency for hERG-mediated QTc prolongation has been suggested. Also, in vivo between-species and patient populations' sensitivity to drug-induced QTc prolongation seems to differ. Here, a systems pharmacology model integrating preclinical in vitro (hERG binding) and in vivo (conscious dog Δ QTc) data of three hERG blockers (dofetilide, sotalol, moxifloxacin) was applied (1) to compare the operational efficacy of the three drugs in vivo and (2) to quantify dog-human differences in sensitivity to drug-induced QTc prolongation (for dofetilide only). Scaling parameters for translational in vivo extrapolation of drug effects were derived based on the assumption of system-specific myocardial ion channel densities and transduction of ion channel block: the operational efficacy (transduction of hERG block) in dogs was drug specific (1-19% hERG block corresponded to ≥10 msec Δ QTc). System-specific maximal achievable Δ QTc was estimated to 28% from baseline in both dog and human, while %hERG block leading to half-maximal effects was 58% lower in human, suggesting a higher contribution of hERG-mediated potassium current to cardiac repolarization. These results suggest that differences in sensitivity to drug-induced QTc prolongation may be well explained by drug- and system-specific differences in operational efficacy (transduction of hERG block), consistent with experimental reports. The proposed scaling approach may thus assist the translational risk assessment of QTc prolongation in different species and patient populations, if mediated by the hERG channel.

Characterization of an investigative safety pharmacology model to assess comprehensive cardiac function and structure in chronically instrumented conscious beagle dogs.

INTRODUCTION: There has been an increasing need to conduct investigative safety pharmacology studies to complement regulatory-required studies, particularly as it applies to a comprehensive assessment of cardiovascular (CV) risk. METHODS: We describe refined methodology using a combination of telemetry and direct signal acquisition to record concomitant peripheral hemodynamics, ECG, and left ventricular (LV) structure (LV chamber size and LV wall thickness) and function, including LV pressure-volume (PV) loops to determine load independent measures of contractility (end systolic elastance, Ees, and preload recruitable stroke work, PRSW) in conscious beagle dogs. Following baseline characterization, 28days of chronic rapid ventricular pacing (RVP) was performed and cardiac function monitored: both as a way to compare measures during development of dysfunction and to characterize feasibility of a model to assess CV safety in animals with underlying cardiac dysfunction. RESULTS: While ±dP/dT decreased within a few days of RVP and remained stable, more comprehensive cardiac function measurements, including Ees and PRSW, provided a more sensitive assessment confirming the value of such endpoints for a more clear functional assessment. After 28days of RVP, the inodilator pimobendan was administered to further demonstrate the ability to detect changes in cardiac function. Expectedly pimobendan caused a leftward shift in the PV loop, improved ejection fraction (EF) and significantly improved Ees and PRSW. DISCUSSION: In summary, the data show the feasibility and importance in measuring enhanced cardiac functional parameters in conscious normal beagle dogs and further describe a relatively stable cardiac dysfunction model that could be used as an investigative safety pharmacology risk assessment tool.

Multi-parametric assessment of cardiomyocyte excitation-contraction coupling using impedance and field potential recording: A tool for cardiac safety assessment.

INTRODUCTION: The ICH S7B guidelines recommend that all new chemical entities should be subjected to hERG repolarization screening due to its association with life-threatening "Torsades de Pointes" (TdP) arrhythmia. However, it has become evident that not all hERG channel inhibitors result in TdP and not all compounds that induce QT prolongation and TdP necessarily inhibit hERG. In order to address the limitations of the S7B/E14 guidelines, the FDA through a public/private partnership initiated the Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative to examine the possible modification and refinement of the ICH E14/S7B guidelines. One of the main components of the CiPA initiative is to utilize a predictive assay system together with human cardiomyocytes for risk assessment of arrhythmia. METHOD: In this manuscript we utilize the xCELLigence® CardioECR system which simultaneously measures excitation-contraction coupling together with human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) to assess the effect of 8 reference compounds across 3 different independent sites. These 8 compounds were part of Phase I CiPA validation study. RESULTS: Our data demonstrate that hERG channel blockers, such as E4031 and moxifloxacin, prolonged field potential duration (FPD) at low concentration and induced arrhythmic beating activity as measured by field potential (FP) recording and impedance (IMP) recordings at higher concentrations. On the contrary, nifedipine, an inhibitor of calcium channel, didn't disrupt the periodicity of cell beating and weakened cell contractile activity and shortened FPD. Multichannel inhibitors, such as flecainide, quinidine and mexiletine, not only increased FPD and induced arrhythmia but also significantly reduced the amplitude of FP spike. JNJ303, an IKs inhibitor, only affected FPD. Comparison of the compound effect on FPD across the 3 different sites is consistent in terms of trend of the effect with observed 3-10 fold differences in minimal effective concentration at which a minimum of 10% response is detected. In addition, pentamidine, a hERG trafficking inhibitor which induced irregular beating activity over a more prolonged duration of time was readily flagged in this assay system. Taken together, this multi-parameter assay using hiPSC-CMs in conjunction with simultaneous measurement of ion channel activity and contractility can be a reliable approach for risk assessment of proarrhythmic compounds.

Sensitivity of pharmacokinetic-pharmacodynamic analysis for detecting small magnitudes of QTc prolongation in preclinical safety testing.

INTRODUCTION: Preclinical concentration-effect (pharmacokinetic-pharmacodynamic, PKPD) modeling has successfully quantified QT effects of several drugs known for significant QT prolongation. This study investigated its sensitivity for detecting small magnitudes of QT-prolongation in a typical preclinical cardiovascular (CV) safety study in the conscious telemetered dog (crossover study in 4-8 animals receiving a vehicle and three dose levels). Results were compared with conventional statistical analysis (analysis of covariance, ANCOVA). METHODS: A PKPD model predicting individual QTc was first developed from vehicle arms of 28 typical CV studies and one positive control study (sotalol). The model quantified between-animal, inter-occasion and within-animal variability and described QTc over 24h as a function of circadian variation and drug concentration. This "true" model was used to repeatedly (n = 500) simulate studies with typical drug-induced QTc prolongation (∆QTc) of 1 to 12 ms at high-dose peak concentrations. Simulated studies were re-analyzed by both PKPD analysis (with varying complexity) and ANCOVA. Sensitivity (power) was calculated as the percentage of studies in which a significant (α = 0.05) drug effect was found. One simulation scenario did not include a concentration-effect relationship and served to investigate false-positive rates. Exposure-effect relationships were derived from both PKPD analysis (linear concentration-effect) and ANCOVA (linear trend test for dose) and compared. RESULTS: PKPD analysis/ANCOVA had a sensitivity of 80% to detect the effects of 7/13 ms (n = 4), 5/10 ms (n = 6) and 4.5/8 ms (n = 8), respectively. The false-positive rate was much higher using ANCOVA (40%) compared to PKPD analysis (1%). Typical drug effects were more precisely predicted using estimated concentration-effect slopes (± 1.5-2.8 ms) than dose-effect slopes (± 3.3-3.7 ms). DISCUSSION: Preclinical PKPD analysis can increase the confidence in the quantification of small QTc effects and potentially allow reducing the number of animals while maintaining the required study sensitivity. This underscores the value of PKPD modeling in preclinical safety testing.

QT interval correction assessment in the anesthetized guinea pig.

INTRODUCTION: The anesthetized guinea pig (ANES GP) has proven to be an effective small animal model to evaluate cardiac electrophysiologic effects of drug-candidate molecules during lead optimization. While heart rate (HR) corrected QT interval (QTc) is a key variable to determine test article-dependent repolarization effects, ideal correction methods are an area of constant debate given the potential influence of anesthesia, autonomic tone, species, strain and gender on the QT/HR relationship. The aim of this study was to characterize the ability of common correction formulas to normalize rate-dependent effects on the QT interval in the ketamine/xylazine ANES GP. METHODS: Atrial pacing (n=10), ivabradine or ephedrine (n=6/group) infusions were used, respectively to evaluate the effects of a wide range of HRs on the QT/HR relationship. Correction formulas (Bazett [QTcb], Fridericia [QTcf] and Van de Water [QTcVdW]) were applied and the best fit formula was determined with the aid of the slope of their QT-HR linear relationship. RESULTS: From 100 to 220bpm, QTcb underestimated the change in QT interval duration (QT/HR slope=0.35 to 0.67). However, QTcVdW was more appropriate in this HR range (QT/HR slope=-0.07 and 0.09). At higher HRs (>220bpm), QTcb performed better (QT/HR slope=-0.02 and 0.07) as compared to QTcf (QT/HR slope=-0.18 to -0.1) and QTcVdW (QT/HR slope=-0.2 to -0.17) (p<0.01). All the correction formulas identified dofetilide- and sotalol-dependent repolarization delay (n=6/group) but QTcb and QTcf demonstrated reduced sensitivity as compared to fixed cardiac pacing (p<0.01). In contrast, QTcVdW resulted in an apparent underestimation of the QT interval duration at HR levels above the basal ketamine/xylazine ANES GP HRs (>220bpm) with ephedrine (n=6). DISCUSSION: The best fit correction formula in the ANES GP was highly dependent on the HR range. In the ketamine/xylazine model, QTcVdW performed best with HR <220bpm and QTcb performed best with HR >220bpm. The QTcVdW correction formula was thus selected in the ketamine/xylazine ANES GP since HRs in this model are generally within the optimal range for this correction formula.

Renal studies in safety pharmacology and toxicology: A survey conducted in the top 15 pharmaceutical companies.

INTRODUCTION: With the recent development of more sensitive biomarkers to assess kidney injury preclinically, a survey was designed i) to investigate what strategies are used to investigate renal toxicity in both ICH S7A compliant Safety Pharmacology (SP) studies after a single dose of a compound and within repeat-dose toxicity studies by large pharmaceutical companies today; ii) to understand whether renal SP studies have impact or utility in drug development and/or if it may be more appropriate to assess renal effects after multiple doses of compounds; iii) to ascertain how much mechanistic work is performed by the top 15 largest pharmaceutical companies (as determined by R&D revenue size); iv) to gain an insight into the impact of the validation of DIKI biomarkers and their introduction in the safety evaluation paradigm; and v) to understand the impact of renal/urinary safety study data on progression of projects. METHODS: Two short anonymous surveys were submitted to SP leaders of the top 15 pharmaceutical companies, as defined by 2012 R&D portfolio size. Fourteen multiple choice questions were designed to explore the strategies used to investigate renal effects in both ICH S7A compliant SP studies and within toxicology studies. RESULTS: A 67% and 60% response rate was obtained in the first and second surveys, respectively. Nine out of ten respondent companies conduct renal excretory measurements (eg. urine analysis) in toxicology studies whereas only five out of ten conduct specific renal SP studies; and all of those 5 also conduct the renal excretory measurements in toxicology studies. These companies measure and/or calculate a variety of parameters as part of these studies, and also on a case by case basis include regulatory qualified and non-qualified DIKI biomarkers. Finally, only one company has used renal/urinary functional data alone to stop a project, whereas the majority of respondents combine renal data with other target organ assessments to form an integrated decision-making set. CONCLUSION: These short surveys highlighted areas of similarity: a) urinary measurements are most commonly taken on repeat-dose toxicity studies, and b) renal SP studies are less often utilised. The two major differences are a) lack of consistent use of DIKI biomarkers in urinary safety studies and b) the way large pharmaceutical companies assess renal function. Finally, suggestions were made to improve the safety assessment methods for determining the safety of compounds with potential renal liability.