Drug-induced hypertension or hypotension can have significant clinical consequences, yet BP regulation involves complex, multi-level mechanisms, making translational assessment of pressor effects more challenging than for endpoints such as cardiac repolarization (hERG/QT). Current nonclinical BP studies primarily use telemetry in conscious, freely moving non-rodents, enabling continuous high-fidelity hemodynamic monitoring. These models show reasonable concordance with human data, but some translational challenges exist.The Health and Environmental Sciences Institute (HESI) Global Integrative Strategies Working Group (WG) was established to improve nonclinical cardiovascular (CV) safety assessment through more informative, translational preclinical models. After earlier success characterizing drug-induced effects on cardiac contractility, the WG focused on drug-associated blood pressure (BP) changes. Provided here is the importance of nonclinical models in predicting BP changes and associated challenges. A HESI Global multi-site study focused on addressing these gaps is also introduced. The study aimed to evaluate the reproducibility and translatability of the standard telemetered dog model using compounds with well-characterized mechanisms (midodrine, nifedipine, hydralazine, prazosin, milrinone). Early results show consistent hemodynamic profiles across laboratories, with final results published separately, showing utility of this model for BP liability assessment.

Increases in arterial blood pressure (BP) contribute to adverse cardiovascular (CV) outcomes in patients; preclinical effects of a drug on BP are routinely evaluated during the safety pharmacology assessments as outlined in the ICH S7A guidance. A Health and Environmental Sciences Institute (HESI) Consortium initiated a multi-site study with the objective to assess the ability of the standard conscious telemetry instrumented CV dog model to detect drug-induced changes in BP and evaluate translation to human data. The goal of these studies is also to determine the reproducibility and consistency of BP assessment when measured across different laboratories using the same study protocol and recording methodology to detect drug-induced changes in hemodynamics using drugs known to clinically elevate and reduce BP. Animals were chronically instrumented with a BP catheter and ECG electrodes for telemetric collection of hemodynamic and ECG endpoints, respectively. Study endpoints include systolic, diastolic, and mean BP, heart rate, electrocardiogram (ECG), body temperature, and locomotor activity. Drugs evaluated include midodrine (alpha-1 agonist), nifedipine (calcium channel blocker), hydralazine (direct-acting smooth muscle relaxant), prazosin (alpha-1 blocker) and milrinone (phosphodiesterase-3 inhibitor). Drugs were selected based on known pharmacological mechanisms of action, primary cardiovascular effects as well as availability of clinical effect and exposure data. Drugs were evaluated in beagle dogs using a double (8 × 4) Latin square design and administered orally at 3 doses selected to match clinical exposure data with a vehicle control. A full pharmacokinetic profile for each drug was conducted in dogs at doses selected using automated blood sampling (ABS). Initial analysis shows that all 5 positive control drugs show consistent hemodynamic profiles (e.g., BP elevation or reduction) in the dog as seen in humans. These data sets with additional testing at multiple sites will be amenable to further statistical analysis, super-interval analysis and follow-up study endpoint evaluation such as pressure waveform analysis. The results from this chronically instrumented conscious dog model will provide essential information about accuracy and consistency in blood pressure measurement across multiple sites and translation of preclinical BP data to clinical outcomes.

Elevated arterial blood pressure (BP) is highly correlated with adverse cardiovascular (CV) outcomes in patients. The effects of a drug on arterial pressure are routinely evaluated during preclinical safety assessment as outlined in the ICH S7A guidance document. A Health and Environmental Sciences Institute (HESI) Consortium initiated a multi-site study with the objective to assess the ability of the standard conscious telemetered CV beagle dog model to detect drug-induced changes in BP and evaluate translation to human data. Animals will be chronically instrumented with a BP catheter and ECG electrodes for telemetric collection of hemodynamic endpoints. Study endpoints include systolic, diastolic, and mean BP, heart rate, electrocardiogram (ECG), body temperature, and locomotor activity. Drugs evaluated include midodrine (alpha-1 agonist), nifedipine (calcium channel blocker), hydralazine (direct-acting smooth muscle relaxant), prazosin (alpha-1 blocker) and milrinone (phosphodiesterase-3 inhibitor) were selected based on known mechanisms of action as well as availability of clinical exposure data. Drugs will be evaluated in beagle dogs using a single (4 × 4) or double (8 × 4) Latin square design. Drugs will be administered orally at 3 doses selected to match clinical exposure data and a vehicle control. A full pharmacokinetic profile for each drug will be conducted at the doses selected at a single site (Abbvie). Blood samples at participating sites will be drawn to confirm drug exposures predicted from independent pharmacokinetic studies. The goal of these studies is to determine whether the assessment of BP, when measured across different laboratories using the same protocol, can consistently detect drug-induced changes in hemodynamics using drugs known to clinically increase and decrease BP.

Cardiovascular adverse drug reactions remain a leading cause of drug attrition. They may emerge during non-clinical or clinical development and often remain undetected until post-marketing, prompting increased regulatory focus. Historically, non-clinical cardiovascular safety testing has centered on assessing QT interval prolongation and torsades de pointes risk, primarily via inhibition of the delayed rectifier potassium current IKr. Such focus may overlook broader cardiovascular liabilities affecting other parameters of the cardiovascular system. This review explores the status and limitations of current non-clinical cardiovascular safety assessments, in particular the over-reliance on the core battery studies defined in ICH S7A and S7B and the insufficient use of mechanistic follow-up assessments. We highlight the gaps between the results of non-clinical cardiovascular safety testing and the emergence of cardiovascular adverse drug reactions in later clinical phases or real-world use. We conclude that to narrow the gaps, there is a need to advance non-clinical methods to detect and adequately measure adverse effects on cardiac rhythm, myocardial contraction, blood pressure, and thrombogenicity. The review further discusses emerging trends and challenges for improving translational relevance, including advanced in vitro and in vivo models, and proposes a re-evaluation of outdated regulatory frameworks to better address diverse cardiovascular risks. Emphasis is placed on functional and mechanistic endpoints over structural pathology, aligning non-clinical safety methodologies with clinical outcomes.

AbstractThe human voltage‐gated sodium channel Nav1.5 (hNav1.5/SCN5A) plays a critical role in the initiation and propagation of action potentials in cardiac myocytes, and its modulation by various drugs has significant implications for cardiac safety. Drug‐dependent block of Nav1.5 current (INa) can lead to significant alterations in cardiac electrophysiology, potentially resulting in conduction slowing and an increased risk of proarrhythmic events. This review aims to provide a comprehensive overview of the mechanisms by which various pharmacological agents interact with Nav1.5, focusing on the molecular determinants of drug binding and the resultant electrophysiological effects. We discuss the structural features of Nav1.5 that influence drug affinity and specificity. Special attention is given to the concept of state‐dependent block, where drug binding is influenced by the conformational state of the channel, and its relevance to therapeutic efficacy and safety. The review also examines the clinical implications of INa block, highlighting case studies of drugs that have been associated with adverse cardiac events, and how the Vaughan‐Williams Classification system has been employed to qualify “unsafe” sodium channel block. Furthermore, we explore the methodologies currently used to assess INa block in nonclinical and clinical settings, with the hope of providing a weight of evidence approach including in silico modeling, in vitro electrophysiological assays and in vivo cardiac safety studies for mitigating proarrhythmic risk early in drug discovery. This review underscores the importance of understanding Nav1.5 pharmacology in the context of drug development and cardiac risk assessment.

Introduction: Characterization of the incidence of spontaneous arrhythmias to identify possible drug-related ef-fects is often an important part of the analysis in safety pharmacology studies using telemetry.Methods: A retrospective analysis in non-clinical species with and without telemetry transmitters was conducted. Electrocardiograms (24 h) from male and female beagle dogs (n = 131), Go center dot ttingen minipigs (n = 108) and cynomolgus non-human primates (NHP; n = 78) were analyzed.Results: Ventricular tachycardia (VT) was observed in 3% of the dogs but was absent in minipigs and NHPs. Ventricular fibrillation (VF) was not observed in the 3 species. Ventricular premature beats (VPBs) were more frequent during daytime and atrioventricular blocks (AVBs) were more frequent at night in all species. A limited number of animals exhibited a high arrhythmia frequency and there was no correlation between animals with higher frequency of an arrhythmia type and the frequency of other arrythmias in the same animals. Clinical chemistry or hematology parameters were not different with or without telemetry devices. NHP with a trans-mural left ventricular pressure (LVP) catheter exhibited a greater incidence of VPBs and PJCs compared to telemetry animals without LVP. Discussion: All species were similar with regards to the frequency of ventricular ectopic beats (26-46%) while the dog seemed to have more frequent junctional complexes and AVB compared to NHP and minipigs. Arrhythmia screening may be considered during pre-study evaluations, to exclude animals with abnormally high arrhythmia incidence.

The content of this article derives from a Health and Environmental Sciences Institute (HESI) consortium with a focus to improve cardiac safety during drug development. A detailed literature review was conducted to evaluate the concordance between nonclinical repolarization assays and the clinical thorough QT (TQT) study. Food and Drug Administration and HESI developed a joint database of nonclinical and clinical data, and a retrospective analysis of 150 anonymized drug candidates was reviewed to compare the performance of 3 standard nonclinical assays with clinical TQT study findings as well as investigate mechanism(s) potentially responsible for apparent discrepancies identified. The nonclinical assays were functional (IKr) current block (Human ether-a-go-go related gene), action potential duration, and corrected QT interval in animals (in vivo corrected QT). Although these nonclinical assays demonstrated good specificity for predicting negative clinical QT prolongation, they had relatively poor sensitivity for predicting positive clinical QT prolongation. After review, 28 discordant TQT-positive drugs were identified. This article provides an overview of direct and indirect mechanisms responsible for QT prolongation and theoretical reasons for lack of concordance between clinical TQT studies and nonclinical assays. We examine 6 specific and discordant TQT-positive drugs as case examples. These were derived from the unique HESI/Food and Drug Administration database. We would like to emphasize some reasons for discordant data including, insufficient or inadequate nonclinical data, effects of the drug on other cardiac ion channels, and indirect and/or nonelectrophysiological effects of drugs, including altered heart rate. We also outline best practices that were developed based upon our evaluation.

This article describes acute toxicity data in cynomolgus monkeys following oral treatment with vildagliptin, a dipeptidyl peptidase-4 inhibitor. Acute toxicity symptoms in cynomolgus monkeys include edema formation of the extremities, tails, and face associated with skeletal muscle necrosis, and elevations of lactate dehydrogenase, creatine kinase, alanine transaminase, and aspartate aminotransferase activities in the serum; hypothermia; hypotension; tachycardia; moribundity; and death in a few isolated instances. In surviving animals, symptoms were reversible even if treatment was continued. Cynomolgus monkeys from Mauritius appear more sensitive than monkeys of Asian origin. The underlying mechanism(s) of these symptoms in cynomolgus monkeys is currently not well understood, although a vascular mechanism including initial vasoconstriction and subsequent vascular leakage in distal extremities may play a role. The monkey data are reviewed and discussed in the context of other preclinical and clinical data, and it is concluded that acute toxicity following vildagliptin treatment is a monkey-specific phenomenon without relevance for humans.

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 x 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/dt(max) 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/dt(max) 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. (C) 2015 The Authors. Published by Elsevier Inc.

The purpose of this article is to characterize skin lesions in cynomolgus monkeys following vildagliptin (dipeptidyl peptidase-4 inhibitor) treatment. Oral vildagliptin administration caused dose-dependent and reversible blister formation, peeling and flaking skin, erosions, ulcerations, scabs, and sores involving the extremities at ≥5 mg/kg/day and necrosis of the tail and the pinnae at ≥80 mg/kg/day after 3 weeks of treatment. At the affected sites, the media and the endothelium of dermal arterioles showed hypertrophy/hyperplasia. Skin lesion formation was prevented by elevating ambient temperature. Vildagliptin treatment also produced an increase in blood pressure and heart rate likely via increased sympathetic tone. Following treatment with vildagliptin at 80 mg/kg/day, the recovery time after lowering the temperature in the feet of monkeys and inducing cold stress was prolonged. Ex vivo investigations showed that small digital arteries from skin biopsies of vildagliptin-treated monkeys exhibited an increase in neuropeptide Y-induced vasoconstriction. This finding correlated with a specific increase in NPY and in NPY1 receptors observed in the skin of vildagliptin-treated monkeys. Present data provide evidence that skin effects in monkeys are of vascular origin and that the effects on the NPY system in combination with increased peripheral sympathetic tone play an important pathomechanistic role in the pathogenesis of cutaneous toxicity.

Juvenile rat toxicity studies with the direct renin inhibitor aliskiren were initiated to support treatment in the pediatric population. In Study 1, aliskiren was administered orally to juvenile rats at doses of 0, 30, 100 or 300 mg/kg/day with repeated dosing from postpartum day (PPD) 8 to PPD 35/36. In-life, clinical pathology, anatomic pathology, and toxicokinetics evaluations were performed. In Study 2, single oral doses of aliskiren (0, 100 or 300 mg/kg) were given to 14-, 21-, 24-, 28-, 31- or 36-day-old rats; in-life data and toxicokinetics were evaluated. Study 3 was a single dose (3 mg/kg i.v.) pharmacokinetic study in juvenile rats on PPD 8, 14, 21 and 28. In Study 4, naïve rats were used to investigate ontogenic changes of the multidrug-resistant protein 1 (MDR1) and the organic anion transporting polypeptide (OATP) mRNA in several organs. Oral administration of aliskiren at 100 and 300 mg/kg caused unexpected mortality and severe morbidity in 8-day-old rats. Aliskiren plasma and tissue concentrations were increased in rats aged 21days and younger. Expression of MDR1 and OATP mRNA in the intestine, liver and brain was significantly lower in very young rats. In conclusion, severe toxicity and increased exposure in very young rats after oral administration of aliskiren are considered to be the result of immature drug transporter systems. Immaturity of MDR1 in enterocytes appears to be the most important mechanism responsible for the high exposure.

BACKGROUNDAliskiren is the first orally bioavailable direct renin inhibitor approved for the treatment of hypertension in adults. Juvenile toxicity studies in rats were initiated to support treatment in the pediatric population.METHODSIn Study 1, aliskiren oral administration was initiated on postpartum day (PPD) 14, after nephrogenesis was completed, and continued through PPD 70 at doses of 0, 30, 100, and 300 mg/kg/day. In-life, clinical pathology, anatomic pathology, developmental, behavioral, reproductive, and toxicokinetics evaluations were performed. In Study 2, oral administration was initiated on PPD 8, before completion of nephrogenesis, and continued through PPD 35/36. In-life, clinical pathology, anatomic pathology, developmental, and toxicokinetics evaluations were performed.RESULTSWith dosing initiated on PPD 8, mortality at 100 and 300 mg/kg/day and slightly increased kidney weight at 100 mg/kg/day occurred. Decreased absolute lymphocyte count at 300 mg/kg/day at the end of dosing occurred with dosing initiated on PPD 14. There were clinical signs and transient effects on body weight gains in both studies. There were no changes in other parameters. Systemic exposure was much higher on PPD 8 and 14 compared with adult rats on PPD 64.CONCLUSIONSAll effects produced by aliskiren, including kidney effects, were reversible. Increased exposure in very young animals is considered to be the result of immature drug transporter systems.

BACKGROUND The ventricular components (QRS and QT) on the electrocardiogram (ECG) depend on the properties of ventricular action potentials that can be modulated by drugs via specific ion channels. However, the correlation of ECG ventricular waveforms with underlying ion actions is not well established and has been extensively debated.OBJECTIVE To conduct a blinded in vitro assessment of the ionic mechanisms for drug-induced ECG changes.METHODS AND RESULTS Fourteen cardiac and noncardiac drugs with known effects on cardiac ion channels were selected by the study sponsor, and were tested in the rabbit left ventricular wedge preparation with recording of the ECG and contractility. The investigators who performed the experiments and analyzed the data were blinded to names, concentrations, and molecular weights of the drugs. The compounds were prepared by the sponsor and sent to the investigators as 56 stock solutions. The effects of I-Kr, I-Ks, I-Ca,(L), I-Na blocker, and I-KATP opener on QRS, QT, and Tp-e, were evaluated. Disclosure of the names and concentrations after completion of the study revealed that there were highly correlated ECG changes with underlying ionic mechanisms and proarrhythmic potential of drugs that, respectively, target I-Kr, I-Ks, I-Ca,I-L, I-Na, and I-KATP. Among ECG parameters, Tp-e was more useful in differentiating drugs' actions.CONCLUSIONS Specific electrophysiological action and the consequent proarrhythmic potential of a drug can be accurately determined by analysis of drug-induced changes in ECG in the rabbit left ventricular wedge preparation. Change in Tp-e provides the most relevant information.

BACKGROUND:Terfenadine's proarrhythmia prompted market withdrawal; therapeutic antihistaminic concentration is less than 1 nM, whereas IC50 of IKr and INa exceed 200 nM.METHODS AND RESULTS:Rabbit hearts were perfused with terfenadine (1-10,000 nM; 10-450 minutes). A dosage of 1 nM tended to shorten action potential duration (APD60) (-30 ± 30.5 ms; n = 6); 10 nM (450 minutes) significantly prolonged APD60 (46 ± 11 ms; n = 6), but after 1 hour washout, APD60 further prolonged. Above 30 nM, APD60 shortening was followed by prolongation; net effect depended on exposure time (n = 33). In the μM range, cardiac wavelength (λ) shortened (APD60 shortened, conduction slowed; P < 0.05). Terfenadine induced triangulation, reverse use dependence, instability and dispersion of repolarization (TRIaD) at 1 to 1000 nM, increasing with concentration (450 minutes: 1 nM yielded 50% of hearts, 10 nM 100%) and exposure (100 nM: 10 minutes yielded 16%, 30 minutes 33%, 150 minutes 66%, 450 minutes 100%). TRIaD with APD prolongation preceded two Torsade de Pointes, with shortening seven ventricular tachycardia and five ventricular fibrillation. Terfenadine causes normally little QTc prolongation in patients and Food and Drug Administration records suggest that incidence of ventricular tachycardia/ventricular fibrillation exceeds Torsade de Pointes.CONCLUSION:For terfenadine, TRIaD predicts drug-induced proarrhythmia: with λ prolongation, Torsade de Pointes is preferred, otherwise ventricular tachycardia/ventricular fibrillation. APD/QTc alone is clearly inadequate for proarrhythmia evaluation.

Biological therapeutic agents (biologicals), such as monoclonal antibodies (mAbs), are increasingly important in the treatment of human disease, and many types of biologicals are in clinical development. During preclinical drug development, cardiovascular safety pharmacology studies are performed to assess cardiac safety in accord with the ICH S7A and S7B regulations that guide these studies. The question arises, however, whether or not it is appropriate to apply these guidelines, which were devised primarily to standardize small molecule drug testing, to the cardiovascular evaluation of biologicals. We examined the scientific literature and formed a consensus of scientific opinion to determine if there is a rational basis for conducting an in vitro hERG assay as part of routine preclinical cardiovascular safety testing for biologicals. We conclude that mAb therapeutics have very low potential to interact with the extracellular or intracellular (pore) domains on hERG channel and, therefore, are highly unlikely to inhibit hERG channel activity based on their targeted, specific binding properties. Furthermore, mAb are large molecules (>140,000 Da) that cannot cross plasma membranes and therefore would be unable to access and block the promiscuous inner pore of the hERG channel, in contrast with typical small molecule drugs. Consequently, we recommend that it is not appropriate to conduct an in vitro hERG assay as part of a preclinical strategy for assessing the heart rate corrected QT interval (QTc) prolongation risk of mAbs and other types of biologicals. It is more appropriate to assess QTc risk by integrating cardiovascular endpoints into repeat-dose general toxicology studies performed in an appropriate non-rodent species. These recommendations should help shape future regulatory strategy and discussions for the cardiovascular safety pharmacology testing of mAbs as well as other biologicals and provide guidance for the preclinical cardiovascular evaluation of such agents.

Contemporary preclinical in vitro and in vivo methods have been imperfect in predicting drug-induced Torsades de Pointes (TdP) in humans. A better understanding of additional relevant factors in the genesis of drug-induced TdP is necessary. New sophisticated in vitro techniques, such as arterially perfused ventricular wedge preparations or isolated perfused hearts, potentially offer a better understanding of torsadogenic mechanisms and a refinement of drug testing. Of particular interest are the dispersion of repolarization and the refractoriness of different cell types across the ventricular wall, triangulation of the action potential, reverse use dependence and instability of the action potential duration. In vivo models are currently refined by establishing parameters such as beat-to-beat variability and T-wave morphology as derived from the in vitro proarrhythmia indices. Animal models of proarrhythmia are to date not recommended for routine evaluation. A pharmacodynamic interaction with combinations of torsadogenic compounds is another area to be considered. Little is known about channel/receptor cross talk, although considerable evidence exists that cardiac G protein-coupled receptors can modulate hERG channel function. More investigations are necessary to further evaluate the role of altered gene expression, mutations, and polymorphisms in drug-induced TdP. A novel mechanism of drug-induced torsadogenesis is the reduced expression of hERG channel protein on the plasma membrane due to a trafficking defect. Pharmacokinetic and metabolism data are crucial for calculating the risk of a torsadogenic potential in man. Consideration of intracardiac accumulation can help in delineating pharmacokinetic–pharmacodyamic relationships. In silico virtual screening procedures with new chemical entities to predict hERG block may develop as a promising tool. The role of in silico modeling of TdP arrhythmia is likely to become increasingly important for organizing and integrating the vast amount of generated data. At present, however, in silico methods cannot replace existing preclinical in vitro and in vivo models.

Prolongation of the QTc interval of the electrocardiogram (ECG) is used as a surrogate marker for a rare, but life threatening, ventricular arrhythmia known as torsades de pointes (TdP). However, the clear link between QTc prolongation and the arrhythmogenic risk has not been demonstrated unequivocally. In the present review article, we examine (a) the current understanding of electrophysiological and pharmacological mechanisms linking changes in action potential (AP) properties with proarrhythmia and (b) the value of the isolated, paced Langendorff-perfused female rabbit heart model (Screenit system) in predicting the torsadogenic potential of drugs in man. The Screenit system records monophasic action potentials (MAPs) from which the following parameters are evaluated: action potential duration (APD), conduction, instability (indicative of beat to beat APD variability), triangulation (indicative of changes of Phase 3 repolarization), and reverse-use dependency (indicating that the APD is more prolonged at slow heart rates). So far, over 16,000 experiments have been conducted, including approximately 300 dedicated tests to evaluate, in a blinded manner, approximately 70 clinically used drugs. The drugs tested covered a wide range of compounds from various pharmacological and chemical classes with clinical torsadogenic propensity, as well as drugs without the latter effect in clinical settings. Overall, the Screenit system and its associated analysis classified the drugs based on their effects on AP morphology and conduction and additionally identified, in a qualitative manner, drugs clinically associated with TdP. Such an identification is based on the triangulation, reverse-use dependency, and instability of the AP, as well as on the direct indexes of proarrhythmia such as early afterdepolarization (EADs), ventricular tachycardia (VT), and ventricular fibrillation (VF). Overall, drugs that readily induce arrhythmia and/or EADs and/or causes triangulation, reverse-use dependency, and/or instability and/or a chaotic Poincaré plot in a range of concentrations likely to be achieved in man is likely to cause TdP in man, eventually. Only if none of these elements is present, at concentrations well exceeding the free therapeutic plasma concentration, can one expect that the drug will probably be devoid of torsadonenicity. Therefore, this in vitro model provides detailed information on the overall profile of drug-induced electrophysiological effects. In combination with other in vitro and in vivo repolarization assays and with pharmacokinetic data in man, it is a valuable tool to establish an integrated cardiovascular risk assessment of pharmaceutical compounds.

Several antimalarial drugs are known to produce a QT interval prolongation via a blockade of the rapidly activating delayed rectifier K+ current (I-Kr), encoded by the human-ether-a-go-go-related gene (hERG). We investigated the influence of lumefantrine and its major metabolite desbutyl-lumefantrine, as well as halofantrine, chloroquine, and mefloquine, on wild type hERG K+ channels in stably transfected human embryonic kidney cells (HEK293) using the whole cell patch-clamp technique. All of the tested antimalarial drugs inhibited the hERG K+ channels in a concentration- and time-dependent manner. Only halofantrine blocked hERG tail currents voltage-dependently. The ranking of the half-maximal inhibitory concentrations (IC50) of the antimalarials was: halofantrine (0.04 muM) < chloroquine (2.5 muM) < mefloquine (2.6 muM) < desbutyl-lumefantrine (5.5 muM) < lumefantrine (8.1 muM). Lumefantrine and desbutyl-lumefantrine showed a slower inhibition of IKr than the other tested antimalarials. In conclusion, lumefantrine and desbutyl-lumefantrine inhibited significantly the hERG tail current with a higher IC50-value than mefloquine, chloroquine and halofantrine. This, together with the calculated cardiac safety indices, suggests that lumefantrine and desbutyl-lumefantrine have a weaker proarrhythmic potential than their comparator compounds. (C) 2003 Elsevier B.V. All rights reserved.