Frank Cools

A translational assessment of preclinical versus clinical tools for the measurement of cardiac contractility: Comparison of LV dP/dtmax with echocardiography in telemetry implanted beagle dogs

INTRODUCTION Regarding evaluation of drug-induced changes in left ventricular contractility in safety pharmacology there is still a gap in knowledge between preclinically and clinically used measurements. METHODS As a step towards translation of preclinical to clinical outcomes, this study in telemetered dogs was initiated to compare indexes of contractility, such as LV dP/dt(max) (contractility measured as the maximum raise of pressure in the left ventricle) and LV dP/dt(max)/P (contractility measured as the maximum raise of pressure in the left ventricle, corrected for pressure) (telemetry; both commonly preclinically used) and EF (ejection fraction) and FS (fractional shortening) (echocardiography; both commonly clinically used). Different inotropic states were induced by minoxidil, milrinone, isoprenaline, clonidine, atenolol and verapamil. RESULTS Both techniques demonstrated reproducible changes in contractility which showed a clear linear association. A change in LV dP/dt(max) of 1000 mmHg/s (in the range of 2500 to 7500 mmHg/s; in healthy dogs) corresponded with a change in ejection fraction of approximately 7% and a fractional shortening of approximately 6%. A change of 10/s LV dP/dt(max)/P (in the range of 35 to 85/s; in healthy dogs) corresponded with a change in ejection fraction of approximately 7% and a fractional shortening of 7%. DISCUSSION The correlation found in this study could potentially enable a better--translational--assessment of the clinical relevance of changes in contractility indices measured with telemetry devices in preclinical safety studies.

Direct effects of arsenic trioxide on action potentials in isolated cardiac tissues: Importance of the choice of species, type of cardiac tissue and perfusion time

INTRODUCTION The aim of the present study was to evaluate direct/acute effects of arsenic trioxide on action potentials (APs) in isolated cardiac tissues, and to investigate if the choice of species and tissue and the duration of the perfusion play a role in arsenic-induced acute/direct prolongation of AP/QT. METHODS AND RESULTS Direct electrophysiological effects of arsenic trioxide were measured in cardiac tissues isolated from four different species using micro-electrode recording. Arsenic (after 30 to 95 min perfusion at 10 μM) significantly prolonged APD(90), increased triangulation of the AP and elicited early afterdepolarizations (EADs) only in isolated guinea-pig and dog Purkinje fibers but not in rabbit and porcine (minipig) Purkinje fibers. Arsenic induced a prolongation of the APD(90) and increases in triangulation and the occurrence of EADs was not observed in papillary muscles of guinea-pigs and rabbits. Arsenic at 4 increasing concentrations from 0.1 μM to 10 μM at the standard perfusion-time of 15 min per concentration, and after a continuous 90-min perfusion at 1 μM and 1 Hz did not induce these direct effects on APD(90), triangulation and EADs in isolated guinea-pig Purkinje fibers, but it at 1 µM elicited EADs in 2 out of 7 preparations after 90 min at 0.2 Hz. DISCUSSION The present study demonstrates that the choice of species and cardiac tissue as well as perfusion-time play important roles in arsenic-induced direct/acute effects on APD(90) and induction of EADs in vitro.

Inter-study variability of preclinical in vivo safety studies and translational exposure-QTc relationships--a PKPD meta-analysis.

Preclinical cardiovascular safety studies (CVS) have been compared between facilities with respect to their sensitivity to detect drug‐induced QTc prolongation (ΔQTc). Little is known about the consistency of quantitative ΔQTc predictions that are relevant for translation to humans.

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

Drug‐induced QTc interval prolongation (ΔQTc) 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 ΔQTc) 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 ΔQTc). System‐specific maximal achievable ΔQTc 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.

Models for zero-inflated, correlated count data with extra heterogeneity: when is it too complex?

Statistical analysis of count data typically starts with a Poisson regression. However, in many real-life applications, it is observed that the variation in the counts is larger than the mean, and one needs to deal with the problem of overdispersion in the counts. Several factors may contribute to overdispersion: (1) unobserved heterogeneity due to missing covariates, (2) correlation between observations (such as in longitudinal studies), and (3) the occurrence of many zeros (more than expected from the Poisson distribution). In this paper, we discuss a model that allows one to explicitly take each of these factors into consideration. The aim of this paper is twofold: (1) investigate whether we can identify the cause of overdispersion via model selection, and (2) investigate the impact of a misspecification of the model on the power of a covariate. The paper is motivated by a study of the occurrence of drug-induced arrhythmia in beagle dogs based on electrocardiogram recordings, with the objective to evaluate the effect of potential drugs on the heartbeat irregularities. Copyright

15 Prevalence of ECG arrhythmias in non-implanted, drug-naive, freely moving beagle dogs

The purpose of this study was to assess the normal prevalence rate of spontaneous arrhythmias in 51 drug-naive, non-implanted, freely moving Beagle dogs (10 M+41 F, CEDS, France). Non-implanted ECG assessment was done in jacketed dogs with six external leads and a T47G-encoder (PhysioJacket, ITS). Trained lab personnel visually scrutinised the full 22-h (day and night) ECG recordings and scored the incidence of different types of arrhythmias.Abstract 15 Table 1 Arrhythmia % of the dogs Day Night Incidence/period 1st degree AV-block 5.9% 15.7% Up to 23 2nd degree AV-block 39.2% 39.2% Up to 310 Atrial premature complex 35.3% 45.1% Up to 1006 Junctional complex 19.6% 33.3% Up to 625 Junctional escape complex 41.2% 58.8% Up to 30 Run of junctional complexes 17.6% 21.6% Up to 165 Run of junctional escape complexes 13.7% 33.3% Up to 23 Junctional tachycardia 13.7% 13.7% Up to 12 Ventricular complex 17.6% 13.7% Up to 10 Ventricular escape complex 7.8% 13.7% Up to 1007 Ventricular premature complex 15.7% 11.8% Up to 134 Run of ventricular complexes 3.9% 2.0% Up to 18 Run of ventricular escape complexes 3.9% 2.0% Up to 13 Only one of these 51 animals showed no arrhythmias during the 22-h observation period. Based on this assessment of spontaneous ventricular arrhythmias, we judged 12 (23.5%) of these animals to be unsuitable for telemetry implantation for use in safety pharmacology studies. In conclusion, thorough evaluation of ECG morphology of naïve Beagle dogs before implantation of telemetry instruments will improve conscious telemetered-dog arrhythmia studies.

05 The electro-mechanical window as Torsade de Pointes risk marker in conscious and anaesthetised dogs after IKS blockade

The electro-mechanical window (EMw) is a recently proposed biomarker describing the temporal difference between electrical and mechanical events in beating hearts and is a precursor to identify Torsade de Pointes (TdP) risk in the anaesthetised dog.1 In follow-up studies, conscious dogs (n=6; telemetered) showed comparable baseline values to anaesthetised dogs (n=20): QT=250 vs 252 ms, QLVPend=347 vs 339 ms and EMw=+96 vs +87 ms, respectively. To compare the EMw in conscious and anaesthetised dogs after IKs blockade.2 Six conscious dogs were orally treated with JNJ303 (20 mg/kg) and four anaesthetised dogs received infusions of JNJ303 (cumulative 2.5 mg/kg). In both conditions JNJ303 induced QT prolongation, a large negative EMw and TdP appeared in 50% of the dogs in each condition (pause-dependent and adrenergic-dependent). In the conscious dogs significant differences in maximum plasma levels (PL), QT and EMw were observed between dogs that induced TdP and those without TdP: PL (4950 vs 1473 ng/ml), QT (427 vs 351 ms) and EMw (−150 vs −68 ms), without differences in RR (642 vs 654 ms) and QLVPend (273 vs 287 ms), respectively. Also in anaesthetised dogs long QT (766 ms) and large negative EMw (−445 ms) at similar PL (5743 ng/ml) were observed. In conclusion a potent IKs blocker (JNJ303) can cause TdP in conscious and anaesthetised dogs, coupled with a large negative EMw.