Berengere Dumotier

Cisapride‐induced prolongation of cardiac action potential and early afterdepolarizations in rabbit Purkinje fibres

Cisapride, a gastrointestinal prokinetic agent, has been associated with cases of Torsades de Pointes but its effects on the cardiac action potential have not been described. We investigated its electrophysiological effects on rabbit isolated Purkinje fibres. The results demonstrated that cisapride (0.01 ×10 μm) lengthened concentration‐dependently the action potential duration without modifying other parameters and induced early after depolarizations and subsequent triggered activity. This typical class III antiarrhythmic effect, that showed ‘reverse’ rate‐dependence and was reduced by increasing external K concentration, can account for clinical arrhythmogenesis.

Report and recommendations of the workshop of the European Centre for the Validation of Alternative Methods for Drug-Induced Cardiotoxicity.

Cardiotoxicity is among the leading reasons for drug attrition and is therefore a core subject in non-clinical and clinical safety testing of new drugs. European Centre for the Validation of Alternative Methods held in March 2008 a workshop on “Alternative Methods for Drug-induced Cardiotoxicity” in order to promote acceptance of alternative methods reducing, refining or replacing the use of laboratory animals in this field. This review reports the outcome of the workshop. The participants identified the major clinical manifestations, which are sensitive to conventional drugs, to be arrhythmias, contractility toxicity, ischaemia toxicity, secondary cardiotoxicity and valve toxicity. They gave an overview of the current use of alternative tests in cardiac safety assessments. Moreover, they elaborated on new cardiotoxicological endpoints for which alternative tests can have an impact and provided recommendations on how to cover them.

Relevance of in vitro SCREENIT results for drug-induced QT interval prolongation in vivo: a database review and analysis.

INTRODUCTION The use of an isolated rabbit heart model (SCREENIT) to predict drug-induced QTc prolongation in animals was assessed using hERG and telemetry data. PURPOSE We compiled data from (i) hERG assay (IC50s), (ii) SCREENIT assay (APD60) and (iii) in vivo non-rodent telemetry studies (QTc interval) and evaluated the reliability of APD60 to fit with IC50s and QTc prolongation using the ratio to free plasma level (FPL). Eighty-two compounds were separated into three classes based on hERG IC50s (class I: IC50s< or =1 microM, n=7; class II: IC50s>1 microM to < or =10 microM, n=15; class III: IC50s>10 microM, n=60). RESULTS Three class I compounds did not prolong QTc at the FPL equivalent to their IC50s (43% hERG false positives). There were no false positives in SCREENIT. Six class II compounds prolonged the QTc interval. Results showed 40% hERG false negatives and no SCREENIT false negatives. Nine compounds had no effect on QTc, and two prolonged APD60 at an equivalent concentration/FPL (13% false positives). Three class III compounds prolonged QTc at an FPL lower than maximum SCREENIT concentrations (5% false negatives). Four other compounds generated SCREENIT false positive results (7%). CONCLUSION SCREENIT increased the predictability of preclinical results for QTc prolongation without generating any false positive results in class I (13% in class II). Making decisions without isolated heart data increases the risk for eliminating efficient drugs displaying hERG inhibition.

Conformational Refinement of Hydroxamate-Based Histone Deacetylase Inhibitors and Exploration of 3-Piperidin-3-ylindole Analogues of Dacinostat (LAQ824)

Inspired by natural product HDAC inhibitors, we prepared a series of conformationally restrained HDAC inhibitors based on the hydroxamic acid dacinostat (LAQ824, 7). Several scaffolds with improved biochemical and cellular potency, as well as attenuated hERG inhibition, were identified, suggesting that the introduction of molecular rigidity is a viable strategy to enhance HDAC binding and mitigate hERG liability. Further SAR studies around a 3-piperidin-3-ylindole moiety resulted in the discovery of compound 30, for which a unique conformation was speculated to contribute to overcoming increased lipophilicity and attenuating hERG binding. Separation of racemate 30 afforded 32, the R enantiomer, which demonstrated improved potency in both enzyme and cellular assays compared to dacinostat.

Repercussions of pharmacologic reduction in ionic currents on action potential configuration in rabbit Purkinje fibers: Are they indicative of proarrhythmic potential?

The evaluation of the cardiac safety of newly developed drugs by electrophysiological studies are today mandatory in several countries. A number of experimental models performed either on multicellular preparations or on native or cloned ionic channels have been used but the predictivity of the results remains a matter of debate, particularly if a drug exerts mixed ionic channel‐blocking effects. The present study was designed to scrutinize the repercussions of selectively decreasing the main ionic currents which play a role in the repolarization process. Using conventional microelectrodes, action potentials were recorded from rabbit Purkinje fibers stimulated at 1 Hz and 0.2 Hz and exposed to a broad range of cumulative and increasing concentrations. The compounds used were 1) potassium channel blockers (4‐aminopyridine, dofetilide, terikalant, and indapamide), 2) chloride current blocker (4,4′‐diisothiocyanatostilbene‐2,2′‐disulfonic acid), and 3) calcium channel antagonists (nifedipine, verapamil, and cadmium). It appears from our results that the modifications observed in the repolarization phase and in the spike‐and‐dome aspect showed that the antagonists evaluated were not as specific as one would expected and that they affected action potential profiles as a result of additional nonspecific effects which may influence the incidence of proarrhythmic events. In conclusion, we propose the use of rabbit Purkinje fibers as an in vitro model adequate for the evaluation of the cardiac safety of newly developed drugs. Drug Dev. Res. 47:63–76, 1999.

Antimalarial drugs: QT prolongation and cardiac arrhythmias

Most available antimalarial drugs induce cardiac side effects. These side effects include various mild heart rate changes (amodiaquine) to excessive prolongation of the QT interval (halofantrine) which may lead to lethal arrhythmias such as Torsade de Pointes (TdP). The cellular mechanism of such events during antimalarial therapy is principally related to ion channel inhibition (e.g., human ether-a-go-go related gene channel) which may slow the repolarisation process and create a good substrate for arrhythmia (when dispersion of repolarisation is present). However, other antimalarial drugs do not show as potent cardiac side effects, like co-arthemeter and sulfadoxine-pyrimethamine. Considering that TdP are favoured by a complex combination of electrophysiological changes, a predictive cardiosafety strategy for new antimalarial drugs should comprise assays with an increasing level of information from ion channel level, cellular and organ level, to the whole organism. In this review, the actual knowledge on underlying mechanisms of QT prolongation and TdP is described, followed by the cardiac safety profiles of present antimalarial drugs.

Secondary pharmacology: screening and interpretation of off-target activities – focus on translation

Secondary pharmacology is an essential component of drug discovery and is used extensively in the pharmaceutical industry for achieving optimal specificity of new drugs via early hazard identification and off-target mitigation. The importance of this discipline has been achieved by increasing its translational value, based on the recognition of biological target-drug molecule-adverse drug reaction (ADR) associations and integration of secondary pharmacology data with pharmacokinetic parameters. Information obtained from clinical ADRs, from recognition of specific phenotypes of animal models and from hereditary diseases provides increasing regulatory confidence in the target-based approach to ADR prediction and mitigation. Here, we review the progress of secondary pharmacology during the past decade and highlight and demonstrate its applications and impact in drug discovery.

“Use-dependent” effects of cisapride on postrest action potentials in rabbit ventricular myocardium

Repercussions of cisapride-induced blocking effects on repolarisation of K(+) channels in open and inactivated states investigated in rabbit ventricular myocardium during rest and under stimulation were compared with effects of K(+)-blocking drugs (4-aminopyridine, dofetilide, terikalant). Major lengthening in the first postrest action potential indicates affinity for closed channels. Gradual lengthening during stimulation implies affinity for open channels. Four (control, add-in, steady-state, washout) 20-min rest periods were alternated with regular stimulation (0.5 Hz). Each drug was added during add-in and steady-state periods. Similarly to dofetilide (10 nM) and terikalant (0.3 microM), cisapride (1 microM) increasingly lengthened action potentials during stimulation, whereas 4-aminopyridine (1 mM) prolonged mostly the first postrest action potential. Our results indicate that cisapride induced use-dependent lengthening of repolarisation, compatible with an affinity for open K(+) channels. We also found that in isolated rabbit ventricular myocytes, cisapride (1-10 microM) decreased the inward rectifier K(+) current, an effect contributing to the proarrhythmic potential.

Xenobiotic CAR Activators Induce Dlk1-Dio3 Locus Noncoding RNA Expression in Mouse Liver

Derisking xenobiotic-induced nongenotoxic carcinogenesis (NGC) represents a significant challenge during the safety assessment of chemicals and therapeutic drugs. The identification of robust mechanism-based NGC biomarkers has the potential to enhance cancer hazard identification. We previously demonstrated Constitutive Androstane Receptor (CAR) and WNT signaling-dependent up-regulation of the pluripotency associated Dlk1-Dio3 imprinted gene cluster noncoding RNAs (ncRNAs) in the liver of mice treated with tumor-promoting doses of phenobarbital (PB). Here, we have compared phenotypic, transcriptional ,and proteomic data from wild-type, CAR/PXR double knock-out and CAR/PXR double humanized mice treated with either PB or chlordane, and show that hepatic Dlk1-Dio3 locus long ncRNAs are upregulated in a CAR/PXR-dependent manner by two structurally distinct CAR activators. We further explored the specificity of Dlk1-Dio3 locus ncRNAs as hepatic NGC biomarkers in mice treated with additional compounds working through distinct NGC modes of action. We propose that up-regulation of Dlk1-Dio3 cluster ncRNAs can serve as an early biomarker for CAR activator-induced nongenotoxic hepatocarcinogenesis and thus may contribute to mechanism-based assessments of carcinogenicity risk for chemicals and novel therapeutics.

Blinded Contractility Analysis in hiPSC-Cardiomyocytes in Engineered Heart Tissue Format: Comparison With Human Atrial Trabeculae

Abstract Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) may serve as a new assay for drug testing in a human context, but their validity particularly for the evaluation of inotropic drug effects remains unclear. In this blinded analysis, we compared the effects of 10 indicator compounds with known inotropic effects in electrically stimulated (1.5 Hz) hiPSC-CM-derived 3-dimensional engineered heart tissue (EHT) and human atrial trabeculae (hAT). Human EHTs were prepared from iCell hiPSC-CM, hAT obtained at routine heart surgery. Mean intra-batch variation coefficient in baseline force measurement was 17% for EHT and 49% for hAT. The PDE-inhibitor milrinone did not affect EHT contraction force, but increased force in hAT. Citalopram (selective serotonin reuptake inhibitor), nifedipine (LTCC-blocker) and lidocaine (Na+ channel-blocker) had negative inotropic effects on EHT and hAT. Formoterol (beta-2 agonist) had positive lusitropic but no inotropic effect in EHT, and positive clinotropic, lusitropic, and inotropic effects in hAT. Tacrolimus (calcineurin-inhibitor) had a negative inotropic effect in EHTs, but no effect in hAT. Digoxin (Na+-K+-ATPase-inhibitor) showed a positive inotropic effect only in EHTs, but no effect in hAT probably due to short incubation time. Ryanodine (ryanodine receptor-inhibitor) reduced contraction force in both models. Rolipram and acetylsalicylic acid showed noninterpretable results in hAT. Contraction amplitude and kinetics were more stable over time and less variable in hiPSC-EHTs than hAT. HiPSC-EHT faithfully detected cAMP-dependent and -independent positive and negative inotropic effects, but limited beta-2 adrenergic or PDE3 effects, compatible with an immature CM phenotype.