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Evaluation of stem cell-derived cardiomyocytes (SC-CM) using multi-electrode array (MEA) has attracted attention as a novel model to detect drug-induced arrhythmia. An experiment was conducted to determine if MEA recording from human induced pluripotent SC-CM (hiPSC-CM) could assess proarrhythmic risk. Ten hERG blockers, 4 Naþ blockers, and 1 IKs blocker were evaluated blindly. Eight drugs are associated with Torsades de Pointes (TdP) and 4 are not. Multiple parameters, including field potential duration (FPD), Naþ slope, Naþ amplitude, beat rate (BR), and early after-depolarization (EAD) were recorded. Minimum effective concentrations (MEC) that elicited a significant change were calculated. Our results determined that FPD and EAD were unable to distinguish torsadogenic from benign compounds, Naþ slope and amplitude could not differentiate Naþ channel blockade from hERG blockade, BR had an inconsistent response to pharmacological treatment, and that hiPSC-CM were, in general, insensitive to IKs inhibition. A ratio was calculated that relates MEC for evoking FPD prolongation, or triggering EAD, to the human therapeutic unbound Cmax(MEC/Cmax). The key finding was that the ratio was sensitive, but specificity was low. Consistently, the ratio had high positive predictive value and low negative predictive value. In conclusion, MEA recordings of hiPSC-CM were sensitive for FPD and EAD detection, but unable to distinguish agents with low- and high-risk for TdPs. Although some published reports suggested great potential for MEA recordings in hSC-CM to assess preclinical cardiac toxicity, the current evaluation implies that this model would have a high false-positive rate in regard to proarrhythmic risk. [ABSTRACT FROM AUTHOR]

Oxytocin, a nine amino acid peptide, is highly conserved in placental mammals, including humans. Oxytocin has a physiological role in parturition and parenteral administration of the synthetic peptide is used to induce labor and control postpartum hemorrhage. Endogenous levels of oxytocin before labor are ~20 pg/mL, but pharmacological administration of the peptide can achieve levels of 110 pg/mL (0.1 nmol/L) following intravenous administration. Cardiac arrhythmia and premature ventricular contractions have been associated with oxytocin administration in addition to QTc interval prolongation. In the conscious rabbit model, intravenous oxytocin produced QT and QTc prolongation. The mechanism of oxytocin-induced QTc prolongation is uncertain but could be the result of indirect changes in autonomic nervous tone, or a direct effect on the duration of cardiomyocyte repolarization. The purpose of this study was to examine the ability of oxytocin to alter cardiac repolarization directly. Two conventional models were used: QTc interval evaluation in the isolated rabbit heart (IRH) and assessment of action potential duration (APD) in human ventricular myocytes (HVM). Oxytocin did not prolong QTc intervals in IRH or APD in HVM when tested at suprapharmacological concentrations, for example, up to 1 μmol/L. The results indicate that oxytocin has very low risk for eliciting QTc and APD prolongation directly, and infer that the QTc changes observed in vivo may be attributed to an indirect mechanism. [ABSTRACT FROM AUTHOR]

The ICH S7B guideline describes the requirement to conduct an in vitro I Kr (hERG) and in vivo QTc assay for human risk assessment of new drug products, but the guidance is devoid of recommendations on study execution or quality. In the absence of standard practice, multiple study designs and experimental approaches have been utilized, especially with the nonclinical QTc assay. Since 2009, our approach to the in vivo QTc assay has been consistent for small molecules and yields reproducible and sensitive levels for QTc signal detection. Our database and experience indicate that nonrodent telemetry studies can achieve high sensitivity and a calculated metric of study power can be used to indicate study quality. Using a retrospective statistical power analysis of multiple studies (n = 14 dog; n = 6 NHP), the detection sensitivity for a specific study design (N = 8; double Latin square cross-over) was determined. The output of the power analysis is the minimal detectable effect at 80% power and a 95% probability level. The design provided an average sensitivity to detect a 4.7 (2.0%) and 6.5 (1.9%) msec QTcI change in dog and NHP, respectively. These findings suggest that this experimental approach has a consistent and reproducible sensitivity to enable a robust QTcI risk evaluation and can be used confidently to support an integrated nonclinical-clinical pro-arrhythmia risk assessment. The inclusion of power analysis (i.e., QTc sensitivity) data in a regulatory submission provides key information to critical stakeholders about the quality of the in vivo QTc assessment and its value for human safety testing. [ABSTRACT FROM AUTHOR]

The ICH E14/S7B Questions and Answers (Q&As) guideline introduces the concept of a "double negative" nonclinical scenario (negative hERG assay and negative in vivo QTc study) to demonstrate that a drug does not produce a clinically relevant QT prolongation (i.e., no QT liability). This nonclinical "double negative" data package, along with negative Phase 1 clinical QTc data, may be sufficient to substitute for a clinical Thorough QT (TQT) study in some specific cases. While standalone GLP in vivo cardiovascular studies in non-rodent species are standard practice during nonclinical drug development for small molecule programs, a variety of approaches to the design, conduct, analysis and interpretation are utilized across pharmaceutical companies and contract research organizations (CROs) that may, in some cases, negatively impact the stringent sensitivity needed to fulfill the new Q&As. Subject matter experts from both Pharma and CROs have collaborated to recommend best practices for more robust nonclinical cardiovascular telemetry studies in non-rodent species, with input from clinical and regulatory experts. The aim was to increase consistency and harmonization across the industry and to ensure delivery of high quality nonclinical QTc data to meet the proposed sensitivities defined within the revised ICH E14/S7B Q&As guideline (Q&As 5.1 and 6.1). The detailed best practice recommendations presented here cover the design and execution of the safety pharmacology cardiovascular study, including optimal methods for acquiring, analyzing, reporting, and interpreting the resulting QTc and pharmacokinetic data to allow for direct comparison to clinical exposures and assessment of safety margin for QTc prolongation. [ABSTRACT FROM AUTHOR]

In prior clinical studies, levocetirizine (LEVO) has demonstrated no effect on ventricular repolarization (QTc intervals), therefore it is a relevant negative control to assess in nonclinical assays to define low proarrhythmic risk. LEVO was tested in beagle dog and cynomolgus monkey (nonhuman primate [NHP]) telemetry models to understand the nonclinical‐clinical translation of this negative control. One oral dose of vehicle, LEVO (10 mg/kg/species) or moxifloxacin (MOXI; 30 mg/kg/dog; 80 mg/kg/NHP) was administered to instrumented animals (N = 8/species) using a cross‐over dosing design; MOXI was the in‐study positive control. Corrected QT interval values (QTcI) were calculated using an individual animal correction factor. Blood samples were taken for drug exposure during telemetry and for pharmacokinetic (PK) analysis (same animals; different day) for exposure‐response (C‐QTc) modeling. Statistical analysis of QTc‐by‐timepoint data showed that LEVO treatment was consistent with vehicle, thus no effect on ventricular repolarization was observed over 24 h in both species. PK analysis indicated that LEVO‐maximum concentration levels in dogs (range: 12,300–20,100 ng/ml) and NHPs (range: 4090–12,700 ng/ml) were ≥4‐fold higher than supratherapeutic drug levels in clinical QTc studies. Slope analysis values in dogs (0.00019 ms/ng/ml) and NHPs (0.00016 ms/ng/ml) were similar to the human C‐QTc relationship and indicated no relationship between QTc intervals and plasma levels of LEVO. MOXI treatment caused QTc interval prolongation (dog: 18 ms; NHP: 29 ms). The characterization of LEVO in these non‐rodent telemetry studies further demonstrates the value and impact of the in vivo QTc assay to define a "no QTc effect" profile and support clinical safety assessment. [ABSTRACT FROM AUTHOR]

The potential for unintended drug induced changes in cardiac contractility is a major concern in medicines development. Whilst direct left ventricular pressure (LVP) measurement is the gold standard for measuring cardiac contractility in vivo, it is resource intensive and poses a welfare burden on research animals. In contrast, arterial blood pressure (BP) measurement has fewer challenges. Symmetric Projection Attractor Reconstruction (SPAR) is a signal processing technique which transforms physiological time-series signals into a corresponding visual image ('attractor'), amplifying morphology changes within physiological waveforms. It was hypothesized that SPAR analysis of BP signals would provide a surrogate measure of cardiac contractility by specifically amplifying the maximum slope of the systolic upstroke. BP (abdominal aorta) signals obtained from beagle dogs, treated with positive and negative inotropes, were retrospectively analysed to identify signal features that correlated with the maximum upslope of the LVP signal from simultaneously acquired LVP recordings. SPAR transformation of BP signals quantified drug induced changes in the maximum slope of the systolic upstroke. We identified key SPAR metrics that provided >0.8 correlation with the LVP maximum upslope, outperforming the BP systolic upstroke alone. This was observed for all 4 different drugs, doses and time points evaluated across studies. Thus, we conclude that the SPAR measures derived from the BP signal could be used as a first pass in vivo screen to flag any risk of drug induced changes in cardiac contractility during the conduct of non-clinical medicines development, potentially reducing or replacing the need to perform direct left ventricular measurements. [ABSTRACT FROM AUTHOR]

BACKGROUND: The concept of chemical agents having properties that confer potential hazard called key characteristics (KCs) was first developed to identify carcinogenic hazards. Identification of KCs of cardiovascular (CV) toxicants could facilitate the systematic assessment of CV hazards and understanding of assay and data gaps associated with current approaches. OBJECTIVES: We sought to develop a consensus-based synthesis of scientific evidence on the KCs of chemical and nonchemical agents known to cause CV toxicity along with methods to measure them. METHODS: An expert working group was convened to discuss mechanisms associated with CV toxicity. RESULTS: The group identified 12 KCs of CV toxicants, defined as exogenous agents that adversely interfere with function of the CV system. The KCs were organized into those primarily affecting cardiac tissue (numbers 1–4 below), the vascular system (5–7), or both (8–12), as follows: 1) impairs regulation of cardiac excitability, 2) impairs cardiac contractility and relaxation, 3) induces cardiomyocyte injury and death, 4) induces proliferation of valve stroma, 5) impacts endothelial and vascular function, 6) alters hemostasis, 7) causes dyslipidemia, 8) impairs mitochondrial function, 9) modifies autonomic nervous system activity, 10) induces oxidative stress, 11) causes inflammation, and 12) alters hormone signaling. DISCUSSION: These 12 KCs can be used to help identify pharmaceuticals and environmental pollutants as CV toxicants, as well as to better understand the mechanistic underpinnings of their toxicity. For example, evidence exists that fine particulate matter [PM = 2.5 µm in aerodynamic diameter (PM2.5)] air pollution, arsenic, anthracycline drugs, and other exogenous chemicals possess one or more of the described KCs. In conclusion, the KCs could be used to identify potential CV toxicants and to define a set of test methods to evaluate CV toxicity in a more comprehensive and standardized manner than current approaches. [ABSTRACT FROM AUTHOR]

Contractility measurements using primary isolated cardiac myocytes (CM) have commonly been used in understanding the physiology and pharmacology of cellular mechanics. In the majority of studies, CM from healthy animals were used, and fewer studies were performed with CM from diseased hearts. To better understand the translational value of contractility on the cellular level of a diseased animal model, myocytes were isolated from left ventricles of a tachypacing-induced heart failure (HF) canine model, and their contractility was measured by recording sarcomere shortening using an image-based IonOptix video system. A side-by-side comparison study was performed in myocytes isolated from 13 normal and 5 tachypacing-induced HF canines by evaluating both basal contractility and pharmacological responses to inotropic agents with different mechanisms, including dobutamine, isoproterenol, milrinone, levosimendan, pimobendan, diltiazem, and flecainide. Myocytes isolated from HF canines exhibited compromised contractility at the sarcomere level in comparison to normal myocytes, specifically, HF myocytes have smaller sarcomere contraction amplitude, longer resting sarcomere length, slower velocity of contraction and relaxation. In addition, they have altered pharmacological responses compared to that of normal canines, with much less potent effects observed in the application of classic inotropic agents, such as isoproterenol, dobutamine, and milrinone. These results indicate that myocytes isolated from tachy-paced HF canines have altered physiological and pharmacological properties, which could be utilized for understanding pathophysiology and developing pharmacological interventions for HF. [ABSTRACT FROM AUTHOR]