Repolarization studies using human stem cell-derived cardiomyocytes: Validation studies and best practice recommendations.

Human stem cell-derived cardiomyocytes (hSC-CMs) hold great promise as in vitro models to study the electrophysiological effects of novel drug candidates on human ventricular repolarization. Two recent large validation studies have demonstrated the ability of hSC-CMs to detect drug-induced delayed repolarization and "cellrhythmias" (interrupted repolarization or irregular spontaneous beating of myocytes) linked to Torsade-de-Pointes proarrhythmic risk. These (and other) studies have also revealed variability of electrophysiological responses attributable to differences in experimental approaches and experimenter, protocols, technology platforms used, and pharmacologic sensitivity of different human-derived models. Thus, when evaluating drug-induced repolarization effects, there is a need to consider 1) the advantages and disadvantages of different approaches, 2) the need for robust functional characterization of hSC-CM preparations to define "fit for purpose" applications, and 3) adopting standardized best practices to guide future studies with evolving hSC-CM preparations. Examples provided and suggested best practices are instructional in defining consistent, reproducible, and interpretable "fit for purpose" hSC-CM-based applications. Implementation of best practices should enhance the clinical translation of hSC-CM-based cell and tissue preparations in drug safety evaluations and support their growing role in regulatory filings.

Publisher Correction: Cross-site and cross-platform variability of automated patch clamp assessments of drug effects on human cardiac currents in recombinant cells.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Cross-site and cross-platform variability of automated patch clamp assessments of drug effects on human cardiac currents in recombinant cells.

Automated patch clamp (APC) instruments enable efficient evaluation of electrophysiologic effects of drugs on human cardiac currents in heterologous expression systems. Differences in experimental protocols, instruments, and dissimilar site procedures affect the variability of IC50 values characterizing drug block potency. This impacts the utility of APC platforms for assessing a drug's cardiac safety margin. We determined variability of APC data from multiple sites that measured blocking potency of 12 blinded drugs (with different levels of proarrhythmic risk) against four human cardiac currents (hERG [IKr], hCav1.2 [L-Type ICa], peak hNav1.5, [Peak INa], late hNav1.5 [Late INa]) with recommended protocols (to minimize variance) using five APC platforms across 17 sites. IC50 variability (25/75 percentiles) differed for drugs and currents (e.g., 10.4-fold for dofetilide block of hERG current and 4-fold for mexiletine block of hNav1.5 current). Within-platform variance predominated for 4 of 12 hERG blocking drugs and 4 of 6 hNav1.5 blocking drugs. hERG and hNav1.5 block. Bland-Altman plots depicted varying agreement across APC platforms. A follow-up survey suggested multiple sources of experimental variability that could be further minimized by stricter adherence to standard protocols. Adoption of best practices would ensure less variable APC datasets and improved safety margins and proarrhythmic risk assessments.

Cardiac contractility: Correction strategies applied to telemetry data from a HESI-sponsored consortium.

INTRODUCTION: QT has a long history of heart rate (HR) correction but limited investigations have been undertaken to assess the impact of cardiovascular parameters on left ventricular (LV) contractility in drug safety testing. Cardiac contractility is affected by preload (Cyon-Frank-Starling law), afterload (Anrep effect) and HR (Bowditch effect). We evaluated multi-parameter correction methods to help with dP/dtmax interpretation. METHODOLOGY: Modeling was undertaken using data from dogs in single or double 4×4 Latin square studies. Correction models (16 fitting formulas×2 modeling approaches (universal and individualized)×2 correction approaches (linear or proportional)) were evaluated. 3D/2D cloud analysis of the beat-to-beat data for the control, pimobendan, and either itraconazole or atenolol groups were used to evaluate correlations between parameters and derive an optimal correction method. RESULTS: Cardiac contractility (i.e., dP/dtmax) was best correlated to HR and systolic LV pressure with a correlation coefficient of 0.8. In decreasing order, dP/dtmin, mean arterial blood pressure (BP), systolic BP, diastolic BP, arterial pulse pressure and LV end diastolic pressure (LVEDP) showed a reduced correlation to dP/dtmax. Subject-specific models improved the correction by up to 14% when compared to universal correction models. The non-linear correction model was superior to the linear model. DISCUSSION: Results suggest that the optimal correction formula for dP/dtmax would be subject-specific, non-linear and would include HR and LV systolic pressure. Correcting contractility for HR and systolic LV pressure may enhance data interpretation in non-clinical drug safety assessments. Similar correction methods could be evaluated for other species used in safety pharmacology.

An evaluation of the utility of LVdP/dt40, QA interval, LVdP/dtmin and Tau as indicators of drug-induced changes in contractility and lusitropy in dogs.

INTRODUCTION: The importance of drug-induced effects on the inotropic state of the heart is well known. Unlike hemodynamic and cardiac electrophysiological methods, which have been routinely used in drug safety testing for years, the non-clinical assessment of drug effects on myocardial contractility is used less frequently with no established translation to humans. The goal of these studies was to determine whether assessment of alternate measures of cardiac inotropy could detect drug-induced changes in the contractile state of the heart using drugs known to have clinically relevant positive and negative effects on myocardial contractility. This study also evaluated drug-induced effects on lusitropy (relaxation) parameters of the heart. METHODS: A double 4×4 Latin square study design using Beagle dogs (n=8) was conducted. Drugs were administrated orally. Arterial blood pressure (BP), left ventricular pressure (LVP) and the electrocardiogram (ECG) were assessed across different laboratories using the same protocol. Each of the six laboratories studied at least 2 drugs (one positive inotrope (pimobendan or amrinone) and one negative inotrope (itraconazole or atenolol) at 3 doses selected to match clinical exposure data and a vehicle control). Animals were instrumented with an ITS telemetry system or DSI's D70-PCTP or PhysioTel™ Digital system. The data acquisition and analysis systems used were Ponemah, Notocord or EMKA. RESULTS: The derived inotropic and lusitropic parameters evaluated included peak systolic and end diastolic LVP, LVdP/dtmax, LVdP/dt40, QA interval, LVdP/dtmin and Tau. This study showed that LVdP/dt40 provided essentially identical results to LVdP/dtmax qualifying it as an index to assess drug effects on cardiac contractility. LVdP/dt40 provided an essentially identical assessment to that of LVdP/dtmax. The QA interval did not react sensitively to the drugs tested in this study; however, it did detect large effects and could be useful in early cardiovascular safety studies. The lusitropic parameter, LVdP/dtmin, was modestly decreased, and Tau was increased, by atenolol and itraconazole. At the doses tested, amrinone and pimobendan produced no changes in LVdP/dtmin while Tau was modestly increased. The drugs did not produce effects on BP, HR or the ECG at the doses tested. Blood samples were drawn to confirm drug exposures predicted from independent pharmacokinetic studies. DISCUSSION: These findings indicate that this experimental model can accurately and consistently detect changes in cardiac contractility, across multiple sites and instrumentation systems. While LVdP/dt40 produced responses similar to LVdP/dtmax, the QA interval and lusitropic parameters LVdP/dtmin and Tau were not markedly changed at the dose of drugs tested. Further studies with drugs that affect early diastolic relaxation through calcium handling are needed to better evaluate drug-induced changes on lusitropic properties of the heart.

The evaluation of drug-induced changes in cardiac inotropy in dogs: Results from a HESI-sponsored consortium.

INTRODUCTION: Drug-induced effects on the cardiovascular system remain a major cause of drug attrition. While hemodynamic (blood pressure (BP) and heart rate (HR)) and electrophysiological methods have been used in testing drug safety for years, animal models for assessing myocardial contractility are used less frequently and their translation to humans has not been established. The goal of these studies was to determine whether assessment of contractility and hemodynamics, when measured across different laboratories using the same protocol, could consistently detect drug-induced changes in the inotropic state of the heart using drugs known to have clinically relevant positive and negative effects on myocardial contractility. METHODS: A 4×4 double Latin square design (n=8) design using Beagle dogs was developed. Drugs were administrated orally. Arterial blood pressure, left ventricular pressure (LVP) and the electrocardiogram were assessed. Each of the six laboratories studied at least 2 drugs (one positive inotrope (pimobendan or amrinone) and one negative inotrope) (itraconazole or atenolol) at 3 doses selected to match clinical exposure data and a vehicle control. Animals were instrumented with an ITS telemetry system, DSI's D70-PCTP system or DSI's Physiotel Digital system. Data acquisition and analysis systems were Ponemah, Notocord or EMKA. RESULTS: Derived parameters included: diastolic, systolic and mean arterial BP, peak systolic LVP, HR, end-diastolic LVP, and LVdP/dtmax as the primary contractility index. Blood samples were drawn to confirm drug exposures predicted from independent pharmacokinetic studies. Across the laboratories, a consistent change in LVdP/dtmax was captured despite some differences in the absolute values of some of the hemodynamic parameters prior to treatment. DISCUSSION: These findings indicate that this experimental model, using the chronically instrumented conscious dog, can accurately and consistently detect changes in cardiac contractility, across multiple sites and instrumentation systems, and that data obtained in this model may also translate to clinical outcomes.

Public health laboratories and radiological readiness.

OBJECTIVE: To document the ability of public health laboratories to respond to radiological emergencies. METHODS: The Association of Public Health Laboratories developed, distributed, and analyzed two separate surveys of public health laboratories representing the 50 US states and major nonstate jurisdictions. The 2009 All-Hazards Laboratory Preparedness Survey examined overall laboratory capability and capacity, with a subset of questions on radiation preparedness. A 2011 survey focused exclusively on radiation readiness. RESULTS: The 50 state and District of Columbia public health laboratories responded to the 2009 All-Hazards Laboratory Preparedness Survey, representing a 98% response rate. In addition to the above laboratories, environmental and agricultural laboratories responded to the 2011 Radiation Capabilities Survey, representing a 76% response rate. Twenty-seven percent of the All-Hazards Survey respondents reported the ability to measure radionuclides in clinical specimens; 6% reported that another state agency or department accepted and analyzed these samples via a radioanalytical method. Of the Radiation Capabilities Survey respondents, 60% reported the ability to test environmental samples, such as air, soil, or surface water, for radiation; 48% reported the ability to test nonmilk food samples; 47% reported the ability to test milk; and 56% reported sending data for drinking water to the Environmental Protection Agency. CONCLUSIONS: Survey data reveal serious gaps in US radiological preparedness. In 2007, federal experts estimated it would take more than 4 years to screen 100 000 individuals for radiation exposure and 6 years to test environmental samples from a large-scale radiological emergency, relying on existing laboratory assets. Although some progress has been made since 2007, public health laboratory radiological test capabilities and capacities remain insufficient to respond to a major event. Adequate preparation requires significant new investment to build and enhance laboratory emergency response networks, as well as investments in the broader public health system in which public health laboratories function.