QT interval correction assessment in the anesthetized guinea pig

Research Progress on the Cardiotoxicity of EGFR-TKIs in Non-Small Cell Lung Cancer

OPINION STATEMENT

With the development of molecular biology and histology techniques, targeted therapy for non-small cell lung cancer (NSCLC) has emerged, which is highly effective and has marginal side effects. Epidermal growth factor receptor (EGFR) was the first driver gene discovered, whose three generations of therapeutic use have its characteristics and benefits in clinical practice. However, cardiovascular complications by EGFR-tyrosine kinase inhibitors (EGFR-TKIs) in preclinical studies have been increasingly reported, including heart failure, cardiomyopathy, and QT prolongation, among others. Cardiotoxicity of targeted drugs significantly affects the therapeutic effect of NSCLC and has become the second leading cause of death in NSCLC. The aim of the present review was to recognize the potential cardiotoxicity of third-generation targeted drugs in the treatment of NSCLC and their associated mechanisms to help clinicians identify and prevent it early in the treatment, minimize the cardiotoxicity of targeted drugs, and improve the therapeutic effect of patients.

Acute osimertinib exposure induces electrocardiac changes by synchronously inhibiting the currents of cardiac ion channels

Introduction: As the third generation of epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI), osimertinib has demonstrated more significant cardiotoxicity than previous generations of EGFR-TKIs. Investigating the mechanism of osimertinib cardiotoxicity can provide a reference for a comprehensive understanding of osimertinib-induced cardiotoxicity and the safety of the usage of this drug in clinical practice. Methods: Multichannel electrical mapping with synchronous ECG recording was used to investigate the effects of varying osimertinib concentrations on electrophysiological indicators in isolated Langendorff-perfused hearts of guinea pigs. Additionally, a whole-cell patch clamp was used to detect the impact of osimertinib on the currents of hERG channels transfected into HEK293 cells and the Nav1.5 channel transfected into Chinese hamster ovary cells and acute isolated ventricular myocytes from SD rats. Results: Acute exposure to varying osimertinib concentrations produced prolongation in the PR interval, QT interval, and QRS complex in isolated hearts of guinea pigs. Meanwhile, this exposure could concentration-dependently increase the conduction time in the left atrium, left ventricle, and atrioventricular without affecting the left ventricle conduction velocity. Osimertinib inhibited the hERG channel in a concentration-dependent manner, with an IC50 of 2.21 ± 1.29 μM. Osimertinib also inhibited the Nav1.5 channel in a concentration-dependent manner, with IC50 values in the absence of inactivation, 20% inactivation, and 50% inactivation of 15.58 ± 0.83 μM, 3.24 ± 0.09 μM, and 2.03 ± 0.57 μM, respectively. Osimertinib slightly inhibited the currents of L-type Ca2+ channels in a concentration-dependent manner in acutely isolated rat ventricular myocytes. Discussion: Osimertinib could prolong the QT interval; PR interval; QRS complex; left atrium, left ventricle, and atrioventricular conduction time in isolated guinea pig hearts. Furthermore, osimertinib could block the hERG, Nav1.5, and L-type Ca2+ channels in concentration-dependent manners. Therefore, these findings might be the leading cause of the cardiotoxicity effects, such as QT prolongation and decreased left ventricular ejection fraction.

Enzastaurin cardiotoxicity: QT interval prolongation, negative inotropic responses and negative chronotropic action

Several clinical trials observed that enzastaurin prolonged QT interval in cancer patients. However, the mechanism of enzastaurin-induced QT interval prolongation is unclear. Therefore, this study aimed to assess the effect and mechanism of enzastaurin on QT interval and cardiac function. The Langendorff and Ion-Optix MyoCam systems were used to assess the effects of enzastaurin on QT interval, cardiac systolic function and intracellular Ca²⁺ transient in guinea pig hearts and ventricular myocytes. The effects of enzastaurin on the rapid delayed rectifier (I_Kr), the slow delayed rectifier K⁺ current (I_Ks), transient outward potassium current (I_to), action potentials, Ryanodine Receptor 2 (RyR2) and the sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2a (SERCA2a) expression and activity in HEK 293 cell system and primary cardiomyocytes were investigated using whole-cell recording technique and western blotting. We found that enzastaurin significantly prolonged QT interval in guinea pig hearts and increased the action potential duration (APD) in guinea pig cardiomyocytes in a dose-dependent manner. Enzastaurin potently inhibited I_Kr by binding to the human Ether-à-go-go-Related gene (hERG) channel in both open and closed states, and hERG mutant channels, including S636A, S631A, and F656V attenuated the inhibitory effect of enzastaurin. Enzastaurin also moderately decreased I_Ks. Additionally, enzastaurin also induced negative chronotropic action. Moreover, enzastaurin impaired cardiac systolic function and reduced intracellular Ca²⁺ transient via inhibition of RyR2 phosphorylation. Taken together, we found that enzastaurin prolongs QT, reduces heart rate and impairs cardiac systolic function. Therefore, we recommend that electrocardiogram (ECG) and cardiac function should be continuously monitored when enzastaurin is administered to cancer patients.

Angiotensin II type 1 receptor blockade attenuates gefitinib-induced cardiac hypertrophy via adjusting angiotensin II-mediated oxidative stress and JNK/P38 MAPK pathway in a rat model

Gefitinib is a tyrosine kinase inhibitor (TKI) of the epidermal growth factor receptor (EGFR), used for the treatment of advanced or metastatic non-small cell lung cancer. Recently, studies proved that Gefitinib-induced cardiotoxicity through induction of oxidative stress leads to cardiac hypertrophy. The current study was conducted to understand the mechanisms underlying gefitinib-induced cardiac hypertrophy through studying the roles of angiotensin II (AngII), oxidative stress, and mitogen-activated protein kinase (MAPK) pathway. Male Wistar albino rats were treated with valsartan, gefitinib, or both for four weeks. Blood samples were collected for AngII and cardiac markers measurement, and hearts were harvested for histological study and biochemical analysis. Gefitinib caused histological changes in the cardiac tissues and increased levels of cardiac hypertrophy markers, AngII and its receptors. Blocking of AngII type 1 receptor (AT1R) via valsartan protected hearts and normalized cardiac markers, AngII levels, and the expression of its receptors during gefitinib treatment. valsartan attenuated gefitinib-induced NADPH oxidase and oxidative stress leading to down-regulation of JNK/p38-MAPK pathway. Collectively, AT1R blockade adjusted AngII-induced NADPH oxidase and JNK/p38-MAPK leading to attenuation of gefitinib-induced cardiac hypertrophy. This study found a pivotal role of AngII/AT1R signaling in gefitinib-induced cardiac hypertrophy, which may provide novel approaches in the management of EGFRIs-induced cardiotoxicity.

Mechanisms of gefitinib-induced QT prolongation

Gefitinib, a tyrosine kinase inhibitor, was the first targeted therapy for non-small cell lung cancer (NSCLC). Gefitinib could block human Ether-à-go-go-Related Gene (hERG) channel, an important target in drug-induced long QT syndrome. However, it is unclear whether gefitinib could induce QT interval prolongation. Here, whole-cell patch-clamp technique was used for evaluating the effect of gefitinib on rapidly-activating delayed rectifier K⁺ current (I_Kr), slowly-activating delayed rectifier K⁺ current (I_Ks), transient outward potassium current (I_to), inward rectifier K⁺ current (I_K1) and on action potentials in guinea pig ventricular myocytes. The Langendorff heart perfusion technique was used to determine drug effect on the ECG. Gefitinib depressed I_Kr by binding to open and closed hERG channels in a concentration-dependent way (IC_50: 1.91 μM). The inhibitory effect of gefitinib on wildtype hERG channels was reduced at the hERG mutants Y652A, S636A, F656V and S631A (IC_50: 8.51, 13.97, 18.86, 32.99 μM), indicating that gefitinib is a pore inhibitor of hERG channels. In addition, gefitinib accelerated hERG channel inactivation and decreased channel steady-state inactivation. Gefitinib also decreased I_Ks with IC₅₀ of 23.8 μM. Moreover, gefitinib increased action potential duration (APD) in guinea pig ventricular myocytes and the corrected QT interval (QTc) in isolated perfused guinea pig hearts in a concentration-dependent way (1-30 μM). These findings indicate that gefitinib could prolong QTc interval by potently blocking hERG channel, modulating kinetic properties of hERG channel. Partial block of KCNQ1/KCNE1 could also contribute to delayed repolarization and prolonged QT interval. Thus, caution should be taken when gefitinib is used for NSCLC treatment.

Differentiating multichannel block on the guinea pig ECG: Use of Tpeak-Tend and J-Tpeak

INTRODUCTION

The anaesthetised guinea pig is a well characterised assay for early assessment of drug effects on ventricular repolarisation and risk of Torsade de Pointes (TdP). We assessed whether a selective hERG blocker with known TdP risk could be differentiated from lower risk, balanced ion channel blockers in the guinea pig, using corrected QT (QTc) interval alongside novel electrocardiogram (ECG) biomarkers J-T_peakc and T_peak-T_end. Effects were compared with previous clinical investigations at similar plasma concentrations and with another index of TdP risk, the electromechanical window (EMW).

METHODS

Twenty-two Dunkin Hartley guinea pigs anaesthetised with sodium pentobarbitone were instrumented for haemodynamic measurement and ECG recording. Three ascending doses of vehicle (n = 6), dofetilide (2, 6 or 20 μg/kg; n = 7), ranolazine (2, 6 or 20 mg/kg; n = 5) or verapamil (0.1, 0.3 or 1.0 mg/kg; n = 4) were administered intravenously.

RESULTS

As reported in previous clinical studies, dofetilide induced dose-dependent increases in QTc interval, with increases in both J-T_peakC or T_peak-T_end, while verapamil caused no significant increase in QTc interval, J-T_peakC or T_peak-T_end. Ranolazine caused dose-dependent increases in QTc interval and corrected J-T_peakc, but had no effect on T_peak-T_end, which is in contrast to the effects reported in humans at similar concentrations. Only dofetilide caused a clear, dose-related decrease in the EMW.

DISCUSSION

These findings suggest that measurements of J-T_peakc and T_peak-T_end in addition to QT interval, may help differentiate pure hERG channel blockers with high risk of TdP from lower risk, multichannel blockers.

Drug-induced QT prolongation: Concordance of preclinical anesthetized canine model in relation to published clinical observations for ten CiPA drugs

INTRODUCTION

The Comprehensive In Vitro Proarrhythmia Assay (CiPA) initiative differentiates torsadogenic risk of 28 drugs affecting ventricular repolarization based on multiple in vitro human derived ionic currents. However, a standardized prospective assessment of the electrophysiologic effects of these drugs in an integrated in vivo preclinical cardiovascular model is lacking. This study questioned whether QTc interval prolongation in a preclinical in vivo model could detect clinically reported QTc prolongation and assign torsadogenic risk for ten CiPA drugs.

METHODS

An acute intravenous administered ascending dose anesthetized dog cardiovascular model was used to assess QTc prolongation along with other electrocardiographic (PR, QRS intervals) and hemodynamic (heart rate, blood pressures, left ventricular contractility) parameters at plasma concentrations spanning and exceeding clinical exposures. hERG current block potency was characterized using IC₅₀ values from automated patch clamp.

RESULTS

All eight drugs eliciting clinical QTc prolongation also delayed repolarization in anesthetized dogs at plasma concentrations within four-fold clinical exposures. In vitro QTc safety margins (defined based on clinical C_max values/plasma concentrations eliciting statistically significant QTc prolongation in dogs) were lower for high vs intermediate torsadogenic risk drugs. In comparison, hERG IC₁₀ values represented as total drug concentrations were better predictors of preclinical QTc prolongation than hERG IC₅₀ values.

CONCLUSION

There was good concordance for QTc prolongation in the anesthetized dog model and clinical torsadogenic risk assignment. QTc assessment in the anesthetized dog remains a valuable part of a more comprehensive preclinical integrated risk assessment for delayed repolarization and torsadogenic risk as part of a global cardiovascular evaluation.

Unanesthetized Rodents Demonstrate Insensitivity of QT Interval and Ventricular Refractory Period to Pacing Cycle Length

Aim: The cardiac electrophysiology of mice and rats has been analyzed extensively, often in the context of pathological manipulations. However, the effects of beating rate on the basic electrical properties of the rodent heart remain unclear. Due to technical challenges, reported electrophysiological studies in rodents are mainly from ex vivo preparations or under deep anesthesia, conditions that might be quite far from the normal physiological state. The aim of the current study was to characterize the ventricular rate-adaptation properties of unanesthetized rats and mice.

Methods: An implanted device was chronically implanted in rodents for atrial or ventricular pacing studies. Following recovery from surgery, QT interval was evaluated in rodents exposed to atrial pacing at various frequencies. In addition, the frequency dependence of ventricular refractoriness was tested by conventional ventricular programmed stimulation protocols.

Results: Our findings indicate total absence of conventional rate-adaptation properties for both QT interval and ventricular refractoriness. Using monophasic action potential recordings in isolated mice hearts we could confirm the previously reported shortening of the action potential duration at fast pacing rates. However, we found that this mild shortening did not result in similar decrease of ventricular refractory period.

Conclusion: Our findings indicate that unanesthetized rodents exhibit flat QT interval and ventricular refractory period rate-dependence. This data argue against empirical use of QT interval correction methods in rodent studies. Our new methodology allowing atrial and ventricular pacing of unanesthetized freely moving rodents may facilitate more appropriate utility of these important animal models in the context of cardiac electrophysiology studies.

Cardiac drug-drug interaction between HCV-NS5B pronucleotide inhibitors and amiodarone is determined by their specific diastereochemistry

Severe bradycardia/bradyarrhythmia following coadministration of the HCV-NS5B prodrug sofosbuvir with amiodarone was recently reported. Our previous preclinical in vivo experiments demonstrated that only certain HCV-NS5B prodrugs elicit bradycardia when combined with amiodarone. In this study, we evaluate the impact of HCV-NS5B prodrug phosphoramidate diastereochemistry (D-/L-alanine, R-/S-phosphoryl) in vitro and in vivo. Co-applied with amiodarone, L-ala,S_P prodrugs increased beating rate and decreased beat amplitude in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), but D-ala,R_P produgs, including MK-3682, did not. Stereochemical selectivity on emerging bradycardia was confirmed in vivo. Diastereomer pairs entered cells equally well, and there was no difference in intracellular accumulation of L-ala,S_P metabolites ± amiodarone, but no D-ala,R_P metabolites were detected. Cathepsin A (CatA) inhibitors attenuated L-ala,S_P prodrug metabolite formation, yet exacerbated L-ala,S_P + amiodarone effects, implicating the prodrugs in these effects. Experiments indicate that pharmacological effects and metabolic conversion to UTP analog are L-ala,S_P prodrug-dependent in cardiomyocytes.

A Novel Positron Emission Tomography (PET) Approach to Monitor Cardiac Metabolic Pathway Remodeling in Response to Sunitinib Malate

Sunitinib is a tyrosine kinase inhibitor approved for the treatment of multiple solid tumors. However, cardiotoxicity is of increasing concern, with a need to develop rational mechanism driven approaches for the early detection of cardiac dysfunction. We sought to interrogate changes in cardiac energy substrate usage during sunitinib treatment, hypothesising that these changes could represent a strategy for the early detection of cardiotoxicity. Balb/CJ mice or Sprague-Dawley rats were treated orally for 4 weeks with 40 or 20 mg/kg/day sunitinib. Cardiac positron emission tomography (PET) was implemented to investigate alterations in myocardial glucose and oxidative metabolism. Following treatment, blood pressure increased, and left ventricular ejection fraction decreased. Cardiac [¹⁸F]-fluorodeoxyglucose (FDG)-PET revealed increased glucose uptake after 48 hours. [¹¹C]Acetate-PET showed decreased myocardial perfusion following treatment. Electron microscopy revealed significant lipid accumulation in the myocardium. Proteomic analyses indicated that oxidative metabolism, fatty acid β-oxidation and mitochondrial dysfunction were among the top myocardial signalling pathways perturbed. Sunitinib treatment results in an increased reliance on glycolysis, increased myocardial lipid deposition and perturbed mitochondrial function, indicative of a fundamental energy crisis resulting in compromised myocardial energy metabolism and function. Our findings suggest that a cardiac PET strategy may represent a rational approach to non-invasively monitor metabolic pathway remodeling following sunitinib treatment.

Clemizole hydrochloride blocks cardiac potassium currents stably expressed in HEK 293 cells

BACKGROUND AND PURPOSE

Clemizole, a histamine H₁ receptor antagonist has a potential therapeutic effect on hepatitis C infection and also potently inhibits TRPC5 ion channels. The aim of the present study was to investigate whether clemizole blocks cardiac K⁺ currents and thus affects cardiac repolarization.

EXPERIMENTAL APPROACH

Whole-cell patch techniques was used to examine the effects of clemizole on hERG channel current, I_Ks and K_v 1.5 channel current in HEK 293 cell expression systems as well as on ventricular action potentials of guinea pig hearts. Isolated hearts from guinea pigs were used to determine the effect on the ECG.

KEY RESULTS

Clemizole decreased hERG current by blocking both open and closed states of the channel in a concentration-dependent manner (IC₅₀ : 0.07 μM). The S631A, S636A, Y652A and F656V hERG mutant channels reduced the inhibitory effect of clemizole (IC₅₀ : 0.82, 0.89, 1.49 and 2.98 μM, respectively), suggesting that clemizole is a pore blocker of hERG channels. Clemizole also moderately decreased I_Ks and human K_v 1.5 channel current. Moreover, clemizole increased the duration of the ventricular action potential in guinea pig hearts and the QTc interval in isolated perfused hearts from guinea pigs, in a concentration-dependent manner (0.1-1.0 μM).

CONCLUSION AND IMPLICATIONS

Our results provide the first evidence that clemizole potently blocks hERG channels, moderately inhibits cardiac I_Ks , delays cardiac repolarization and thereby prolongs QT interval. Thus, caution should be taken when clemizole is used as a TRPC5 channel blocker or for treating hepatitis C infection.

Assessment of the clinical cardiac drug-drug interaction associated with the combination of hepatitis C virus nucleotide inhibitors and amiodarone in guinea pigs and rhesus monkeys

In 2015, European and U.S. health agencies issued warning letters in response to 9 reported clinical cases of severe bradycardia/bradyarrhythmia in hepatitis C virus (HCV)-infected patients treated with sofosbuvir (SOF) in combination with other direct acting antivirals (DAAs) and the antiarrhythmic drug, amiodarone (AMIO). We utilized preclinical in vivo models to better understand this cardiac effect, the potential pharmacological mechanism(s), and to identify a clinically translatable model to assess the drug-drug interaction (DDI) cardiac risk of current and future HCV inhibitors. An anesthetized guinea pig model was used to elicit a SOF+AMIO-dependent bradycardia. Detailed cardiac electrophysiological studies in this species revealed SOF+AMIO-dependent selective nodal dysfunction, with initial, larger effects on the sinoatrial node. Further studies in conscious, rhesus monkeys revealed an emergent bradycardia and bradyarrhythmia in 3 of 4 monkeys administered SOF+AMIO, effects not observed with either agent alone. Morever, bradycardia and bradyarrhythmia were not observed in rhesus monkeys when intravenous infusion of MK-3682 was completed after AMIO pretreatment.

CONCLUSIONS

These are the first preclinical in vivo experiments reported to replicate the severe clinical SOF+AMIO cardiac DDI and provide potential in vivo mechanism of action. As such, these data provide a preclinical risk assessment paradigm, including a clinically relevant nonhuman primate model, with which to better understand cardiovascular DDI risk for this therapeutic class. Furthermore, these studies suggest that not all HCV DAAs and, in particular, not all HCV nonstructural protein 5B inhibitors may exhibit this cardiac DDI with amiodarone. Given the selective in vivo cardiac electrophysiological effect, these data enable targeted cellular/molecular mechanistic studies to more precisely identify cell types, receptors, and/or ion channels responsible for the clinical DDI. (Hepatology 2016;64:1430-1441).

Recalibration of nonclinical safety pharmacology assessment to anticipate evolving regulatory expectations

Safety pharmacology (SP) has evolved in terms of architecture and content since the inception of the SP Society (SPS). SP was initially focused on the issue of drug-induced QT prolongation, but has now become a broad spectrum discipline with expanding expectations for evaluation of drug adverse effect liability in all organ systems, not merely the narrow consideration of torsades de pointes (TdP) liability testing. An important part of the evolution of SP has been the elaboration of architecture for interrogation of non-clinical models in terms of model development, model validation and model implementation. While SP has been defined by mandatory cardiovascular, central nervous system (CNS) and respiratory system studies ever since the core battery was elaborated, it also involves evaluation of drug effects on other physiological systems. The current state of SP evolution is the incorporation of emerging new technologies in a wide range of non-clinical drug safety testing models. This will refine the SP process, while potentially expanding the core battery. The continued refinement of automated technologies (e.g., automated patch clamp systems) is enhancing the scope for detection of adverse effect liability (i.e., for more than just IKr blockade), while introducing a potential for speed and accuracy in cardiovascular and CNS SP by providing rapid, high throughput ion channel screening methods for implementation in early drug development. A variety of CNS liability assays, which exploit isolated brain tissue, and in vitro electrophysiological techniques, have provided an additional level of complimentary preclinical safety screens aimed at establishing the seizurogenic potential and risk for memory dysfunction of new chemical entities (NCEs). As with previous editorials that preface the annual themed issue on SP methods published in the Journal of Pharmacological and Toxicological Methods (JPTM), we highlight here the content derived from the most recent (2015) SPS meeting held in Prague, Czech Republic. This issue of JPTM continues the tradition of providing a publication summary of articles primarily presented at the SPS meeting with direct bearing on the discipline of SP. Novel method development and refinement in all areas of the discipline are reflected in the content.

The shifting landscape of safety pharmacology in 2015

The relative importance of the discipline of safety pharmacology (which integrates physiology, pharmacologyand toxicology) has evolved since the incorporation of the Safety Pharmacology Society (SPS) as an entity on August 10, 2000. Safety pharmacology (SP), as a synthesis of these other fields of knowledge, is concerned with characterizing the safety profile (or potential undesirable pharmacodynamic effects) of new chemical entities (NCEs) and biologicals. Initially focused on the issue of drug-induced QT prolongation it has developed into an important discipline over the past 15years with expertise beyond its initial focus on torsades de pointes (TdP). It has become a repository for interrogation of models for drug safety studies and innovative non-clinical model development, validation and implementation. Thus, while safety pharmacology consists of the triumvirate obligatory cardiovascular, central nervous system (CNS) and respiratory system core battery studies it also involves assessing drug effects on numerous other physiological systems (e.g., ocular, auditory, renal, gastrointestinal, blood, immune) leveraging emerging new technologies in a wide range of non-clinical drug safety testing models. As with previous editorials that preface the themed issue on safety pharmacology methods published in the Journal of Pharmacological and Toxicological Methods (JPTM), we highlight here the content derived from the most recent (2014) SPS meeting held in Washington, DC. The dynamics of the discipline remain fervent and method development, extension and refinement are reflected in the content. This issue of the JPTM continues the tradition of providing a publication summary of articles (reviews, commentaries and methods) with impact on the discipline of safety pharmacology.