Inefficacy of a highly selective T-type calcium channel blocker in preventing atrial fibrillation related remodeling.

BACKGROUND: The T-type Ca(2+) channel (I(CaT)) blocker mibefradil prevents AF-promoting remodeling occurring with atrial tachycardia, an action that has been attributed to I(CaT) inhibition. However, mibefradil has other effects, including ability to inhibit L-type Ca(2+) channels, Na(+) channels and cytochromes. Thus, the relationship between I(CaT) inhibition and remodeling protection in AF is still unknown. OBJECTIVE: To assess the effects of a novel highly selective Cav3 (I(CaT)) blocker, AZ9112, on atrial remodeling induced by 1-week atrial tachypacing (AT-P) in dogs. METHODS: Mongrel dogs were subjected to AT-P at 400 bpm for 7 days, with atrioventricular-node ablation and right-ventricular demand pacing (80 bpm) to control ventricular rate. Four groups of dogs were studied in investigator-blinded fashion: (1) a sham group, instrumented but without tachypacing or drug therapy (n = 5); (2) a placebo group, tachypaced but receiving placebo (n = 6); (3) a positive control tachypacing group receiving mibefradil (n = 6); and (4) a test drug group, subjected to tachypacing during oral treatment with AZ9112 (n = 8). RESULTS: One-week AT-P decreased atrial effective refractory period (ERP) at 6 of 8 sites and diminished rate-dependent atrial ERP abbreviation. Mibefradil eliminated AT-P-induced ERP-abbreviation at 4 of these 6 sites, while AZ9112 failed to affect ERP at any. Neither drug significantly affected AF vulnerability or AF duration. CONCLUSIONS: I(CaT) blockade with the highly selective compound AZ9112 failed to prevent rate-related atrial remodeling. Thus, prevention of atrial electrophysiological remodeling by mibefradil cannot be attributed exclusively to I(CaT) blockade. These results indicate that I(CaT) inhibition is not likely to be a useful approach for AF therapy.

Discovery of N-[[1-[2-(tert-butylcarbamoylamino)ethyl]-4-(hydroxymethyl)-4-piperidyl]methyl]-3,5-dichloro-benzamide as a selective T-type calcium channel (Cav3.2) inhibitor.

The T-type calcium channel inhibitor Mibefradil was reported to protect the heart from atrial remodeling, a key process involved in the development of atrial fibrillation and arrhythmias. Mibefradil is not a selective T-type calcium channel inhibitor and also affects the function of different ion channels. Our aim was to develop a selective T-type calcium channel inhibitor to validate the importance of T-type-related pharmacology in atrial fibrillation. Structural optimisation of a previously disclosed hit series focussed on minimising exposure to the central nervous system and improving pharmacokinetic properties, while maintain adequate potency and selectivity. This resulted in the design of N-[[1-[2-(tert-butylcarbamoylamino)ethyl]-4-(hydroxymethyl)-4-piperidyl]methyl]-3,5-dichloro-benzamide, a novel, selective, peripherally restricted chemical probe to verify the role of T-type calcium channel inhibition on atrial fibrillation protection.

Assessment of ventricular repolarization variability with the DeltaT50 method improves identification of patients with congenital long QT syndromes.

BACKGROUND: We analyzed ventricular repolarization variability in genotyped long QT syndrome (LQTS) patients and in healthy volunteers (HV). METHOD: The deltaT50, that is, the temporal variability of ventricular repolarization at 50% of the T-wave downslope, was analyzed every 15th minute on 175 and 390 Holter electrocardiogram (ECG) recordings from HV and genotyped LQTS patients, respectively. The average deltaT50 and QTcF were calculated in each subject. RESULTS: DeltaT50 was 2.26 ± 0.71 ms (mean ± SD) in the HV and 5.74 ± 2.30 ms in the LQTS population (P < 0.0001). The sensitivity and specificity of QTcF (cutoff value 450 ms) to discriminate between the LQTS patients and the HV were 51.5% and 98.9%, and for deltaT50 (cutoff value 3 ms) 93.9% and 88.6%, respectively. The combination of both variables improved the diagnosis of the LQTS patients even further. Subgroups of LQTS patients at higher risk of cardiac events (with LQTS3, JLN, QTc > 500 ms or symptoms) had higher deltaT50 than subgroups at lower risk (with LQTS1, QTc < 450 ms or without symptoms). The variation in deltaT50 between day and night was concordant with the risk of symptoms; patients with LQTS1 had higher deltaT50 in the daytime and patients with LQTS3 had higher deltaT50 during the night. CONCLUSION: DeltaT50 more accurately distinguished between LQTS patients and HV than QTcF and was higher in LQTS patients with a higher risk of cardiac events. DeltaT50 can be used together with QTcF to improve the diagnosis in patients with the LQTS phenotype and tentatively also be of value for risk assessment in such patients.

Application of human stem cell-derived cardiomyocytes in safety pharmacology requires caution beyond hERG.

Human embryonic stem cell-derived cardiomyocytes (hESC-CM) have been proposed as a new model for safety pharmacology. So far, a thorough description of their basic electrophysiology and extensive testing, and mechanistic explanations, of their overall pro-arrhythmic ability is lacking. Under standardized conditions, we have evaluated the sensitivity of hESC-CM to proarrhythmic provocations by blockade of hERG and other channels. Using voltage patch clamp, some ion current densities (pA/pF) in hESC-CM were comparable to adult CM: I(Kr) (-12.5 ± 6.9), I(Ks) (0.65 ± 0.12), I(Na,peak) (-72 ± 21), I(Na,late) (-1.10 ± 0.36), and I(Ca,L) (-4.3 ± 0.6). I(f) density was larger (-10 ± 1.1) and I(K1) not existent or very small (-2.67 ± 0.3). The low I(K1) density was corroborated by low KCNJ2 mRNA levels. Effects of pro-arrhythmic compounds on action potential (AP) parameters and provocation of early afterdepolarizations (EADs) revealed that Chromanol293B (100 µmol/l) and Bay K8644 (1 µmol/l) both significantly prolonged APD(90). ATX-II (<1 µmol/l ) and BaCl(2) (10 µmol/l ) had no effect on APD. The only compound that triggered EADs was hERG blocker Cisapride. Computer simulations and AP clamp showed that the immature AP of hESC-CM prevents proper functioning of I(Na)-channels, and result in lower peak/maximal currents of several other channels, compared to the adult situation. Lack of functional I(K1) channels and shifted I(Na) channel activation cause a rather immature electrophysiological phenotype in hESC-CM, and thereby limits the potential of this model to respond accurately to pro-arrhythmic triggers other than hERG block. Maturation of the electrical phenotype is a prerequiste for future implementation of the model in arrhythmogenic safety testing.

Discovery of N-(1-adamantyl)-2-(4-alkylpiperazin-1-yl)acetamide derivatives as T-type calcium channel (Cav3.2) inhibitors.

Chemical evolution of a HTS-based fragment hit resulted in the identification of N-(1-adamantyl)-2-[4-(2-tetrahydropyran-4-ylethyl)piperazin-1-yl]acetamide, a novel, selective T-type calcium channel (Ca(v)3.2) inhibitor with in vivo antihypertensive effect in rats.

DeltaT50--a new method to assess temporal ventricular repolarization variability.

BACKGROUND: Increased beat-to-beat variability in cardiac repolarization time is a tentative risk marker of drug-induced torsades de pointes. We developed a new, automatic method based on the temporal variability of the T-wave down slope to assess this variability. METHOD AND RESULTS: Leads V(1) to V(6) of resting electrocardiograms were recorded in 42 healthy subjects (18-68 years, 22 men). The temporal variability at 50% of the T-wave down slope, deltaT50 (1.5 ± 0.41 milliseconds; range, 0.86-2.66 milliseconds), was measured with an accuracy of 1 millisecond on at least 9 pairs of electrocardiogram complexes with a signal-to-noise ratio more than 10 and changes in the R-R interval less than 150 milliseconds. The correlation between repeated measurements of deltaT50 was high. DeltaT50 was measured without corrections for age, sex, heart rate, T-wave amplitude, signal-to-noise ratio, R-R variability, and QTcF because none of these factors explained more than 4% of the within-subject deltaT50 variability. CONCLUSION: The beat-to-beat repolarization variability was measured with high fidelity with the deltaT50 method and was a robust measure in healthy volunteers.

Model systems for the discovery and development of antiarrhythmic drugs.

Cardiovascular diseases are the leading cause of mortality worldwide and about 25% of cardiovascular deaths are due to disturbances in cardiac rhythm or "arrhythmias". Arrhythmias were traditionally treated with antiarrhythmic drugs, but increasing awareness of the risks of presently available antiarrhythmic agents has greatly limited their usefulness. Most common treatment algorithms still involve small molecule drugs, and antiarrhythmic agents with improved efficacy and safety are sorely needed. This paper reviews the model systems that are available for discovery and development of new antiarrhythmic drugs. We begin with a presentation of screening methods used to identify specific channel-interacting agents, with a particular emphasis on high-throughput screens. Traditional manual electrophysiological methods, automated electrophysiology, fluorescent dye methods, flux assays and radioligand binding assays are reviewed. We then discuss a variety of relevant arrhythmia models. Two models are widely used in testing for arrhythmogenic actions related to excess action potential prolongation, an important potential adverse effect of chemical entities affecting cardiac rhythm: the methoxamine-sensitized rabbit and the dog with chronic atrioventricular block. We then go on to review models used to assess potential antiarrhythmic actions. For ventricular arrhythmias, chemical induction methods, cardiac or neural electrical stimulation, ischaemic heart models and models of cardiac channelopathies can be used to identify effective antiarrhythmic agents. For atrial arrhythmias, potentially useful models include vagally-maintained atrial fibrillation, acute asphyxia with atrial burst-pacing, sterile pericarditis, Y-shaped atria surgical incisions, chronic atrial dilation models, atrial electrical remodelling due to sustained atrial tachycardia, heart failure-related atrial remodelling, and acute atrial ischaemia. It is hoped that the new technologies now available and the recently-developed models for arrhythmia-response assessment will permit the introduction of newer and more effective antiarrhythmic therapies in the near future.

Functional effects of the late sodium current inhibition by AZD7009 and lidocaine in rabbit isolated atrial and ventricular tissue and Purkinje fibre.

AZD7009 (tert-Butyl-2-(7-[(2S)-3-(4-cyanophenoxy)-2-hydroxypropyl]-9-oxa-3,7-diazabicyclo[3.3.1]non-3-yl)ethylcarbamate) is an antiarrhythmic agent that increases atrial refractoriness, shows high antiarrhythmic efficacy and has low proarrhythmic potential. This study was primarily undertaken to determine the effects of AZD7009 on the late sodium current and to examine the impact of late sodium current inhibition on action potential duration in various myocardial cells. AZD7009 inhibited the late sodium current in Chinese Hamster Ovary K1 (CHO K1) cells expressing hNa(v)1.5 with an IC(50) of 11+/-2 microM. The late sodium current in isolated rabbit atrial and ventricular myocytes was also concentration dependently inhibited by AZD7009. Action potentials were recorded during exposure to 5 microM E-4031 (1-[2-(6-methyl-2pyridyl)ethyl]-4-(4-methylsulfonyl aminobenzoyl)piperidine), a compound that selectively inhibits the rapid delayed rectifier potassium current (I(Kr)), and to E-4031 in combination with AZD7009 or lidocaine in rabbit atrial and ventricular tissue and Purkinje fibres. In Purkinje fibres, but not in ventricular tissue, AZD7009 and lidocaine attenuated the E-4031-induced action potential duration prolongation. In atrial cells, AZD7009, but not lidocaine, further prolonged the E-4031-induced action potential duration. E-4031 induced early afterdepolarisations (EADs) in Purkinje fibres, EADs that were totally suppressed by AZD7009 or lidocaine. In conclusion, excessive action potential duration prolongation induced by E-4031 was attenuated by AZD7009 and lidocaine in rabbit Purkinje fibre, but not in atrial or ventricular tissue, most likely by inhibiting the late sodium current. Furthermore, the opposite effect by AZD7009 on action potential duration in atrial tissue suggests that AZD7009, in addition to inhibiting I(Kr), also inhibits other repolarising currents in the atria.

Comparison of the QT interval response during sinus and paced rhythm in conscious and anesthetized beagle dogs.

INTRODUCTION: The aim of the present study was to compare sensitivity in detecting the drug-induced QT interval prolongation in three dog models: conscious telemetered at sinus rhythm and conscious and anesthetized dogs during atrial pacing. The test substances used represent different chemical classes with different pharmacological and pharmacokinetic profiles. METHOD: Dofetilide and moxifloxacin were tested in all models, whereas cisapride and terfenadine were tested in the conscious telemetered and paced models. All substances were given as two consecutive 1.5-h intravenous infusions (infusions 1 and 2). The individual concentration-time courses of dofetilide, moxifloxacin, and cisapride were linked to the drug-induced effects on the QT interval and described with a pharmacokinetic-pharmacodynamic model to obtain an estimate of the unbound plasma concentrations at steady state that give a 10- and 20-ms drug-induced QT interval prolongation (CE10ms and CE20ms). RESULTS: In the conscious telemetered, conscious paced, and anesthetized dog models, the mean CE10ms values were 1.4, 4.0, and 2.5 nM for dofetilide and 1300, 1800, and 12,200 nM for moxifloxacin. For cisapride, the CE10ms values were 8.0 and 4.4 nM in the conscious telemetered and conscious paced dog models. The drug-induced QT interval prolongation during the last 30 min of infusions 1 and 2 was comparable in the conscious models, but smaller in the anesthetized dog model. Terfenadine displayed a marked delay in onset of response, which could only be detected by the extended ECG recording. DISCUSSION: All dog models investigated detected QT interval prolongation after administration of the investigated test substances with similar sensitivity, except for a lower sensitivity in the anesthetized dogs following moxifloxacin administration. The conscious telemetered dog model was favorable, mainly due to the extended continuous ECG recording, which facilitated detection and quantification of delayed temporal differences between systemic exposure and drug-induced QT interval prolongation.

A novel approach to data processing of the QT interval response in the conscious telemetered beagle dog.

INTRODUCTION: Drug-induced QT interval prolongation may lead to ventricular arrhythmias. The aim of the study was to optimize QT interval data processing to quantify drug-induced QT interval prolongation in the telemetry instrumented conscious dog model. METHODS: The test substances cisapride, dofetilide, haloperidol, and terfenadine and corresponding vehicles were given to male and female beagle dogs during two consecutive 90-min intravenous infusions. Cardiovascular parameters were recorded for 24 h and exposure to the drugs was measured. The delayed response in the QT interval after an abrupt change in heart rate was investigated. Eight mathematical models to describe the QT interval-heart rate relationship were compared and different sets of covariates were used to quantify the drug-induced effect on the QT interval. RESULTS: After an abrupt decrease in heart rate, a 75% adaptation of the QT interval was reached after 54+/-9 s. A linear model was preferred to correct the drug-induced effect on the QT interval for heart rate, vehicle effect, serial correlation, plasma concentration and time of day. All test substances significantly prolonged the QT interval. DISCUSSION: To optimize the processing of QT interval data, the delay in QT interval response after an abrupt change in heart rate should be considered. The QT interval-heart rate relationship and vehicle response were individual-specific and corrections were therefore made individually. When estimating the drug-induced effect on the QT interval it is considered advantageous to use plasma concentration as a covariate, as well as adjusting for vehicle effect and serial correlation in measurements. The conscious dog model detected significant increases in the QT interval for all test substances investigated.

Pharmacokinetic-pharmacodynamic modeling of drug-induced effect on the QT interval in conscious telemetered dogs.

INTRODUCTION: To assure drug safety, the investigation of the relationship between plasma concentration and drug-induced prolongation of the QT interval of the ECG is a challenge in drug discovery. For this purpose, dofetilide was utilized to demonstrate the benefits of characterizing the complete time course of concentrations and effect in conscious beagle dogs in the assessment of drug safety. METHOD: On two separate occasions, four male and two female beagle dogs were given vehicle or the test substance, dofetilide (0.25 mumol/kg), over a 3-h intravenous infusion. Cardiovascular parameters, including QT intervals, were recorded for 24-h using radiotelemetry. The QT interval was corrected individually for heart rate, vehicle treatment, and serial correlation (QT(c)). Exposure (plasma concentration) to dofetilide was measured and described by a two-compartment model. The individual concentration-time course of dofetilide was linked to the QT(c) interval via an effect compartment and a pharmacodynamic E(max) model, to account for the observed hysteresis. RESULTS: Dofetilide induced a concentration-dependent increase in the QT(c) interval, with an EC(50) of 9 nM (3-30 nM, 95% C.I.) and an E(max) of 59+/-9 ms. A hysteresis loop was observed by plotting plasma concentrations vs. QT interval in time order, indicating a delay in onset of effect. It was found to have an equilibrium half-life of 11+/-8 min. Based on the parameters potency and E(max), a representation was made of the drug-induced changes to the QT interval. DISCUSSION: An effect compartment model was found to accurately mimic the QT interval prolongation following administration of the test substance, dofetilide. The assessment of the individual concentration-effect relationship and confounding factors such as hysteresis might provide a better prediction of the safety profiles of new drug candidates.

Electrophysiological characterization and antiarrhythmic efficacy of the mixed potassium channel-blocking antiarrhythmic agent AZ13395438 in vitro and in vivo.

OBJECTIVE: To examine the electrophysiological, hemodynamic, and antiarrhythmic effects of the novel antiarrhythmic agent AZ13395438. METHODS: The ion channel-blocking potency of AZ13395438 was assessed in Chinese hamster ovary cells stably expressing various human cardiac ion channels and in human atrial myocytes. The in vivo electrophysiological, hemodynamic, and antiarrhythmic effects of intravenously administered AZ13395438 were examined in anesthetized rabbits, in anesthetized naive dogs, and in dogs subjected to rapid atrial pacing (RAP) for 8 weeks. Pharmacokinetic/pharmacodynamic (PKPD) modeling was applied to predict the potency of AZ13395438 in increasing atrial and ventricular refractoriness. RESULTS: AZ13395438 potently and predominantly blocked the atrial repolarizing potassium currents I(Kur), I(Ach), and I(to) in vitro. In vivo, AZ13395438 caused a concentration-dependent and selective increase in atrial refractoriness with no or small effects on ventricular refractoriness and repolarization and on hemodynamics in both rabbits and dogs. The PKPD modeling predicted unbound plasma concentrations of AZ13395438 of 0.20 ± 0.039, 0.38 ± 0.084, and 0.34 ± 0.057 µmol/L to increase the right atrial effective refractory period by 20 milliseconds in the rabbit and in the naive and the RAP dogs, respectively. In the RAP dog with atrial fibrillation (AF), AZ13395438 significantly increased AF cycle length and successfully converted AF to sinus rhythm in 12 of the 12 occasions at an unbound plasma concentration of 0.48 ± 0.076 µmol/L. During saline infusion, conversion was seen only in 4 of the 10 occasions (P = .003 vs AZ13395438). Furthermore, AZ13395438 reduced AF inducibility by burst pacing from 100% to 25% (P < .001). CONCLUSION: AZ13395438 can be characterized as a mixed potassium ion channel-blocking agent that selectively prolongs atrial versus ventricular refractoriness and shows promising antiarrhythmic efficacy in a clinically relevant animal model of AF.

Beat-by-beat QT interval variability, but not QT prolongation per se, predicts drug-induced torsades de pointes in the anaesthetised methoxamine-sensitized rabbit.

INTRODUCTION: Accumulating evidence suggest that drug-induced QT prolongation per se poorly predicts repolarisation-related proarrhythmia liability. We examined whether beat-by-beat variability of the QT interval may be a complementary proarrhythmia marker to QT prolongation. METHODS: Anaesthetised rabbits sensitized towards developing torsades de pointes (TdP) were infused for 30 min maximum with explorative antiarrhythmic compounds characterised as mixed ion channel blockers. Based on the outcome in this model the compounds were classified as having a low (TdPlow; n=5), intermediate (TdPintermediate; n=7) or high (TdPhigh; n=10) proarrhythmic potential. Dofetilide (n=4) was included as a representative of a selective IKr-blocking antiarrhythmic with known high proarrhythmic potential. QT interval prolongation and beat-by-beat QT variability (quantified as the short-term variability, STV) were continuously assessed during the infusion or up to the point where ventricular proarrhythmias were induced. RESULTS: All compounds significantly prolonged the QT interval. For TdPlow and TdPhigh compounds the QT interval maximally increased from 169 ± 14 to 225 ± 28 ms (p<0.05) and from 186 ± 21 to 268 ± 42 ms (p<0.01), respectively. Likewise, in the dofetilide-infused rabbits the QT interval maximally increased from 177 ± 11 to 243 ± 25 ms (p<0.01). In contrast, whereas the STV in rabbits administered the TdPhigh compounds or dofetilide significantly increased prior to proarrhythmia induction (from 1.6 ± 0.4 to 10.5 ± 5.6 ms and from 1.6 ± 0.5 to 5.9 ± 1.8 ms, p<0.01) it remained unaltered in the TdPlow group (1.3 ± 0.6 to 2.2 ± 0.9 ms). In the TdPintermediate group, rabbits experiencing TdP had a similar maximal QT prolongation as the non-susceptible rabbits whereas the change in the STV was significantly different (from 0.9 ± 0.5 to 8.7 ± 7.3 ms vs 0.8 ± 0.3 to 2.5 ± 1.1 ms). DISCUSSION: It is concluded from the present series of experiments in a sensitive rabbit model of TdP that increased beat-by-beat QT interval variability precedes drug-induced TdP. In addition, assessment of this potential proarrhythmia marker may be useful in discriminating highly proarrhythmic compounds from compounds with a low proarrhythmic potential.

New pharmacological targets and treatments for atrial fibrillation.

Atrial fibrillation (AF) is an arrhythmia of growing clinical concern that is increasing in prevalence and is associated with significant morbidity and mortality. Pharmacological agents remain the first-line therapy for the AF patient, and the potential advantages of sinus rhythm maintenance motivate continued efforts to identify novel pharmacological means to restore and maintain sinus rhythm. Traditional antiarrhythmic agents only moderately suppress AF and present problematic concerns of proarrhythmia and extracardiac toxicity. Current investigational or recently approved strategies for improving efficacy and safety of anti-AF agents include (i) specific or predominant blockade of atrial ion channels; (ii) "upstream therapies" affecting non-ion channel targets that influence electrical and structural remodeling, inflammation and oxidative stress; (iii) amiodarone derivatives with an improved safety profile; (iv) intracellular calcium handling; and (v) therapies aiming at alleviating conduction disturbances (gap junction coupling enhancers). This review provides a succinct overview of some of these strategies.

Quantified proarrhythmic potential of selected human embryonic stem cell-derived cardiomyocytes.

To improve proarrhythmic predictability of preclinical models, we assessed whether human ventricular-like embryonic stem cell-derived cardiomyocytes (hESC-CMs) can be selected following a standardized protocol. Also, we quantified their arrhythmogenic response and compared this to a contemporary used rabbit Purkinje fiber (PF) model. Multiple transmembrane action potentials (AP) were recorded from 164 hESC-CM clusters (9 different batches), and 12 isolated PFs from New Zealand White rabbits. AP duration (APD), early afterdepolarizations (EADs), triangulation (T), and short-term variability of repolarization (STV) were determined on application of the I(Kr) blocker E-4031 (0.03/0.1/0.3/1 muM). Isoproterenol (0.1 muM) was used to assess adrenergic response. To validate the phenotype, RNA isolated from atrial- and ventricular-like clusters (n=8) was analyzed using low-density Taqman arrays. Based on initial experiments, slow beating rate (<50 bpm) and long APD (>200 ms) were used to select 31 ventricular-like clusters. E-4031 (1 muM) prolonged APD (31/31) and induced EADs only in clusters with APD90>300 ms (11/16). EADs were associated with increased T (1.6+/-0.2 vs 2.0+/-0.3) and STV (2.7+/-1.5 vs 6.9+/-1.9). Rabbit PF reacted in a similar way with regards to EADs (5/12), increased T (1.3+/-0.1 vs 1.9+/-0.4), and STV (1.2+/-0.9 vs 7.1+/-5.6). According to ROC values, hESC-CMs (STV 0.91) could predict EADs at least equivalent to PF (STV 0.69). Isoproterenol shortened APD and completely suppressed EADs. Gene expression analysis revealed that HCN1/2, KCNA5, and GJA5 were higher in atrial/nodal-like cells, whereas KCNJ2 and SCN1B were higher in ventricular-like cells (P<0.05). Selection of hESC-CM clusters with a ventricular-like phenotype can be standardized. The proarrhythmic results are qualitatively and quantitatively comparable between hESC-CMs and rabbit PF. Our results indicate that additional validation of this new safety pharmacology model is warranted.

Early integration of pharmacokinetic and dynamic reasoning is essential for optimal development of lead compounds: strategic considerations.

The aims of this report are firstly to raise awareness among kineticists and pharmacologists as to why pharmacokinetic-pharmacodynamic (PKPD) integration is essential for target validation (TV), optimizing development of lead compounds (lead generation [LG] and lead optimization [LO]) and scaling these to human. A related aim is to demonstrate strategic examples of PKPD collaborations that have improved the planning, execution and evaluation of experiments in primary and safety pharmacology. Examples include design of TV studies, design and data 'pruning' of PKPD studies in LO, analysis of data with marginal and substantial temporal (time) differences between exposure and response, design of safety pharmacology studies, assessment of safety margin and assessment of uncertainties in predictions of first dose in human.

Improvement of cardiac efficacy and safety models in drug discovery by the use of stem cell-derived cardiomyocytes.

BACKGROUND: The pharmaceutical industry suffers from high attrition rates during late phases of drug development. Improved models for early evaluation of drug efficacy and safety are needed to address this problem. Recent developments have illustrated that human stem cell-derived cardiomyocytes are attractive for using as a model system for different cardiac diseases and as a model for screening, safety pharmacology and toxicology. OBJECTIVE: In this review, we discuss contemporary drug discovery models and their characteristics for cardiac efficacy testing and safety assessment. Additionally, we evaluate various sources of stem cells and how these cells could potentially improve early screening and safety models. CONCLUSION: We conclude that human stem cells offer a source of physiologically relevant cells that show great potential as a future tool in cardiac drug discovery. However, some technical challenges related to cell differentiation and production and also to validation of improved platforms remain and must be overcome before successful application can become a reality.

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.

Blocking characteristics of hERG, hNav1.5, and hKvLQT1/hminK after administration of the novel anti-arrhythmic compound AZD7009.

INTRODUCTION: AZD7009 is a novel anti-arrhythmic compound under development for short- and long-term management of atrial fibrillation and flutter. Electrophysiological studies in animals have shown high anti-arrhythmic efficacy, predominant action on atrial electrophysiology, and low proarrhythmic activity. The main aim of this study was to characterize the blocking effects of AZD7009 on the human ether-a-go-go-related gene (hERG), the hNav1.5, and the hKvLQT1/hminK currents. METHODS AND RESULTS: hERG, hKvLQT1/hminK, and hNav1.5 were expressed in CHO K1 cells. Currents were measured using the whole-cell configuration of the voltage-clamp technique. AZD7009 inhibited the hERG current with an IC50 of 0.6 +/- 0.07 microM (n = 6). AZD7009 1 microM hyperpolarized the potential for half-maximal activation from -8.2 +/- 0.1 mV to -18.0 +/- 0.6 mV (P < 0.001, n = 14) and induced pre-pulse potentiation at potentials near the activation threshold. The hNav1.5 current was blocked with an IC50 of 4.3 +/- 1.20 microM at 10 Hz (n = 6) and block developed use-dependently. Recovery from use-dependent block was slow, tau= 131 seconds. AZD7009 inhibited the hKvLQT1/hminK current only at high concentrations (IC50= 193 +/- 20 microM, n = 6). CONCLUSION: AZD7009 inhibits both the hERG and the hNav1.5 current, and it is most likely this combined current block that underlies the prolongation of the refractoriness and the low proarrhythmic activity demonstrated in animals in vivo.

Blocking characteristics of hKv1.5 and hKv4.3/hKChIP2.2 after administration of the novel antiarrhythmic compound AZD7009.

AZD7009 is a novel antiarrhythmic compound in early clinical development for management of atrial fibrillation. Electrophysiological studies in animals have shown high antiarrhythmic efficacy, predominant action on atrial electrophysiology, and low proarrhythmic activity. AZD7009 has previously been shown to inhibit hERG and hNav1.5 currents. The main objective of the present study was to characterize the effects of AZD7009 on hKv1.5 and hKv4.3/hKChIP2.2 currents to get a deeper understanding of the ion channel-blocking properties of the compound. hKv1.5 and hKv4.3/hKChIP2.2 currents were expressed in CHO cells. Currents were measured using the whole-cell configuration of the voltage-clamp technique. AZD7009 inhibited hKv1.5 and hKv4.3/hKChIP2.2 currents with equal potency: the IC50 for hKv1.5 block was 27.0 +/- 1.6 muM (n = 6), and the IC50 for hKv4.3/hKChIP2.2 block was 23.7 +/- 4.4 muM (n = 5). Block of the hKv4.3/hKChIP2.2 current was frequency dependent with larger block at higher frequency, whereas block of the hKv1.5 current was slightly decreased at higher frequency. In conclusion, AZD7009 inhibits both the hKv1.5 and the hKv4.3/hKChIP2.2 currents. These effects likely contribute to the effects described in animals in vivo.