Charge is an important determinant of hemodynamic and adverse cardiovascular effects of cationic drugs.

Cationic compounds are diverse and atypical therapeutic substances. In the present study we examined whether a prototypical class effect of cationic drugs in the cardiovascular system exists and whether this might be predictable on the basis of chemistry. The dose-dependent effects of cationic compounds of varying molecular weights and charge were examined on the blood pressure (BP), heart rate (HR) and the ECG in anesthetized rats. The compounds examined were protamine, hexadimethrine, tetraethylammonium (TEA), low molecular weight poly-L-lysine (LMW-PLL) and high molecular weight PLL (HMW-PLL). All of the compounds examined except TEA produced a dose-dependent reduction in BP. No changes occurred in HR even when high doses were administered. The ECG effects of these cationic compounds included a dose-dependent prolongation of the QT interval, especially at higher doses. All compounds transiently decreased the size of the P-wave after i.v. bolus administration whereas only protamine and hexadimethrine prolonged the PR and QRS intervals and only at the highest dose (32 mg/kg) administered. All cationic compounds, except TEA and saline, evoked ventricular premature beats (VPB), and protamine and HMW-PLL also evoked brief episodes of ventricular tachycardia (VT). The incidence and frequency of arrhythmias was not dose-dependent and no animals experienced protracted episodes of arrhythmia incidence. These dose dependent effects of the polycationic compounds tested suggest a collective mechanism of action that relates the effect of charge of the compound to the onset and persistence of observed cardiovascular toxicity, and adverse cardiovascular effect risk appears to be predictable on this basis.

Biophysics and Molecular Biology of Cardiac Ion Channels for the Safety Pharmacologist.

Cardiac safety pharmacology is a continuously evolving discipline that uses the basic principles of pharmacology in a regulatory-driven process to generate data to inform risk/benefit assessment of a new chemical entity (NCE). The aim of cardiac safety pharmacology is to characterise the pharmacodynamic/pharmacokinetic (PK/PD) relationship of a drug's adverse effects on the heart using continuously evolving methodology. Unlike Toxicology, safety pharmacology includes within its remit a regulatory requirement to predict the risk of rare cardiotoxic (potentially lethal) events such as torsades de pointes (TdP), which is statistically associated with drug-induced changes in the QT interval of the ECG due to blockade of I Kr or K v11.1 current encoded by hERG. This gives safety pharmacology its unique character. The key issues for the safety pharmacology assessment of a drug on the heart are detection of an adverse effect liability, projection of the data into safety margin calculation and clinical safety monitoring. This chapter will briefly review the current cardiac safety pharmacology paradigm outlined in the ICH S7A and ICH S7B guidance documents and the non-clinical models and methods used in the evaluation of new chemical entities in order to define the integrated risk assessment for submission to regulatory authorities. An overview of how the present cardiac paradigm was developed will be discussed, explaining how it was based upon marketing authorisation withdrawal of many non-cardiovascular compounds due to unanticipated proarrhythmic effects. The role of related biomarkers (of cardiac repolarisation, e.g. prolongation of the QT interval of the ECG) will be considered. We will also provide an overview of the 'non-hERG-centric' concepts utilised in the evolving comprehensive in vitro proarrhythmia assay (CIPA) that details conduct of the proposed ion channel battery test, use of human stem cells and application of in silico models to early cardiac safety assessment. The summary of our current understanding of the triggers of TdP will include the interplay between action potential (AP) prolongation, early and delayed afterdepolarisation and substrates for re-entry arrhythmias.

Haemodynamic Assessment in Safety Pharmacology.

Evaluation of the effects of a drug on arterial blood pressure is important in nonclinical safety pharmacology assessment. Detecting large and obvious changes in blood pressure is an unchallenging task. Detecting small changes is more difficult, and interpretation of findings requires careful risk/benefit evaluation. Detecting subtle and small changes in blood pressure is important in particular with respect to increases, since blood pressure above the normal range is associated with increased risk of stroke and sudden cardiac death. Cardiovascular safety pharmacology has been preoccupied with drug-induced changes in the electrocardiogram, and by comparison, there has been little in the way of contemporaneous improvements in the level of complexity and sophistication involved in blood pressure assessment. Thus, it is important to understand the nature of drug-induced changes in blood pressure, appreciate the plethora of agents currently used clinically (and over the counter) that alter blood pressure and understand safety pharmacology study design in order to optimize assessment of a new chemical entity (NCE) or biologic agent in this context.

Innovative approaches to cardiovascular safety pharmacology assessment.

This editorial prefaces the annual themed issue on safety pharmacology (SP) methods which has been published since 2004 in the Journal of Pharmacological and Toxicological Methods (JPTM). Here we highlight content derived from the 2023 Safety Pharmacology Society (SPS) meeting held in Brussels, Belgium. The meeting generated 138 abstracts, reproduced in the current volume of JPTM. As in prior years, the manuscripts reflect various areas of innovation in SP including in silico modeling of stroke volume, cardiac output and systemic vascular resistance, computational approaches that compare drug-induced proarrhythmic sensitivity of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), an evaluation of the utility of the corrected J-Tpeak and Tpeak-to-Tend parameters from the ECG as potential proarrhythmia biomarkers, and the applicability of nonclinical concentration-QTc (C-QTc) modeling of data derived from the conduct of the in vivo QTc study as a component of the core battery of safety pharmacology studies.

Safety pharmacology 2023 and implementation of the ICH E14/S7B Q&A guidance document.

This editorial prefaces the annual themed issue on safety pharmacology (SP) methods published since 2004 in the Journal of Pharmacological and Toxicological Methods (JPTM). We highlight here the content derived from the recent 2022 Safety Pharmacology Society (SPS) and Canadian Society of Pharmacology and Therapeutics (CSPT) joint meeting held in Montreal, Quebec, Canada. The meeting also generated 179 abstracts (reproduced in the current volume of JPTM). As in previous years the manuscripts reflect various areas of innovation in SP including a comparison of the sensitivity of cross-over and parallel study designs for QTc assessment, use of human-induced pluripotent stem cell (hi-PSC) neuronal cell preparations for use in neuropharmacological safety screening, and hiPSC derived cardiac myocytes in assessing inotropic adversity. With respect to the latter, we anticipate the emergence of a large data set of positive and negative controls that will test whether the imperative to miniaturize, humanize and create a high throughput process is offset by any loss of precision and accuracy.

The effect of combined ß-lactoglobulin supplementation and resistance exercise training prior to limb immobilisation on muscle protein synthesis rates in healthy young adults: study protocol for a randomised controlled trial.

BACKGROUND: The decline in skeletal muscle mass experienced following a short-term period (days to weeks) of muscle disuse is mediated by impaired rates of muscle protein synthesis (MPS). Previous RCTs of exercise or nutrition prehabilitation interventions designed to mitigate disuse-induced muscle atrophy have reported limited efficacy. Hence, the aim of this study is to investigate the impact of a complex prehabilitation intervention that combines ß-lactoglobulin (a novel milk protein with a high leucine content) supplementation with resistance exercise training on disuse-induced changes in free-living integrated rates of MPS in healthy, young adults. METHODS/DESIGN: To address this aim, we will recruit 24 healthy young (18-45 years) males and females to conduct a parallel, double-blind, 2-arm, randomised placebo-controlled trial. The intervention group will combine a 7-day structured resistance exercise training programme with thrice daily dietary supplementation with 23 g of ß-lactoglobulin. The placebo group will combine the same training programme with an energy-matched carbohydrate (dextrose) control. The study protocol will last 16 days for each participant. Day 1 will be a familiarisation session and days 2-4 will be the baseline period. Days 5-11 represent the 'prehabilitation period' whereby participants will combine resistance training with their assigned dietary supplementation regimen. Days 12-16 represent the muscle disuse-induced 'immobilisation period' whereby participants will have a single leg immobilised in a brace and continue their assigned dietary supplementation regimen only (i.e. no resistance training). The primary endpoint of this study is the measurement of free-living integrated rates of MPS using deuterium oxide tracer methodology. Measurements of MPS will be calculated at baseline, over the 7-day prehabilitation period and over the 5-day immobilisation period separately. Secondary endpoints include measurements of muscle mass and strength that will be collected on days 4 (baseline), 11 (end of prehabilitation) and 16 (end of immobilisation). DISCUSSION: This novel study will establish the impact of a bimodal prehabilitation strategy that combines ß-lactoglobulin supplementation and resistance exercise training in modulating MPS following a short-term period of muscle disuse. If successful, this complex intervention may be translated to clinical practice with application to patients scheduled to undergo, for example, hip or knee replacement surgery. TRIAL REGISTRATION: NCT05496452. Registered on August 10, 2022. PROTOCOL VERSION: 16-12-2022/1.

Similarity Maps for Ventricular Arrhythmia Classification.

Ventricular arrhythmias are the primary arrhythmias that cause sudden cardiac death. In current clinical and preclinical research, the discovery of new therapies and their translation is hampered by the lack of consistency in diagnostic criteria for distinguishing between ventricular tachycardia (VT) and ventricular fibrillation (VF). This study develops a new set of features, similarity maps, for discrimination between VT and VF using deep neural network architectures. The similarity maps are designed to capture the similarity and the regularity within an ECG trace. Our experiments show that the similarity maps lead to a substantial improvement in distinguishing VT and VF.

Safety pharmacology in 2022: Taking one small step for cardiovascular safety assay development but one giant leap for regulatory drug safety assessment.

The 2021 Annual Safety Pharmacology (SP) Society (SPS) meeting was held virtually October 4-8, 2021 due to the continuing COVID-19 global pandemic. This themed issue of J Pharmacol Toxicol Methods comprises articles arising from the meeting. As in previous years the manuscripts reflect various areas of innovation in SP including a perspective on aging and its impact on drug attrition during safety assessments, an integrated assessment of respiratory, cardiovascular and animal activity of in vivo nonclinical studies, development of a dynamic QT-rate correction method in primates, evaluation of the "comprehensive in vitro proarrhythmia assay" (CiPA) ion channel protocol to the automated patch clamp, and best practices regarding the conduct of hERG electrophysiology studies and an analysis of secondary pharmacology assays by the FDA. The meeting also generated 85 abstracts (reproduced in the current volume of J Pharmacol Toxicol Methods). It appears that the validation of methods remains a challenge in SP. Nevertheless, the continued efforts to mine approaches to detection of proarrhythmia liability remains a baffling obsession given the ability of Industry to completely prevent drugs entering into clinical study only to be found to have proarrhythmic properties, with no reports of such for at least ten years. Perhaps it is time to move on from CiPA and find genuine problems to solve?

OCT2013, an ischaemia-activated antiarrhythmic prodrug, devoid of the systemic side effects of lidocaine.

BACKGROUND AND PURPOSE: Sudden cardiac death (SCD) caused by acute myocardial ischaemia and ventricular fibrillation (VF) is an unmet therapeutic need. Lidocaine suppresses ischaemia-induced VF, but its utility is limited by side effects and a narrow therapeutic index. Here, we characterise OCT2013, a putative ischaemia-activated prodrug of lidocaine. EXPERIMENTAL APPROACH: The rat Langendorff-perfused isolated heart, anaesthetised rat and rat ventricular myocyte preparations were utilised in a series of blinded and randomised studies to investigate the antiarrhythmic effectiveness, adverse effects and mechanism of action of OCT2013, compared with lidocaine. KEY RESULTS: In isolated hearts, OCT2013 and lidocaine prevented ischaemia-induced VF equi-effectively, but OCT2013 did not share lidocaine's adverse effects (PR widening, bradycardia and negative inotropy). In anaesthetised rats, i.v. OCT2013 and lidocaine suppressed VF and increased survival equi-effectively; OCT2013 had no effect on cardiac output even at 64 mg·kg-1 i.v., whereas lidocaine reduced it even at 1 mg·kg-1 . In adult rat ventricular myocytes, OCT2013 had no effect on Ca2+ handling, whereas lidocaine impaired it. In paced isolated hearts, lidocaine caused rate-dependent conduction slowing and block, whereas OCT2013 was inactive. However, during regional ischaemia, OCT2013 and lidocaine equi-effectively hastened conduction block. Chromatography and MS analysis revealed that OCT2013, detectable in normoxic OCT2013-perfused hearts, became undetectable during global ischaemia, with lidocaine becoming detectable. CONCLUSIONS AND IMPLICATIONS: OCT2013 is inactive but is bio-reduced locally in ischaemic myocardium to lidocaine, acting as an ischaemia-activated and ischaemia-selective antiarrhythmic prodrug with a large therapeutic index, mimicking lidocaine's benefit without adversity.

Planning experiments: Updated guidance on experimental design and analysis and their reporting III.

Scientists who plan to publish in British Journal of Pharmacology (BJP) must read this article before undertaking a study. This editorial provides guidance for the design of experiments. We have published previously two guidance documents on experimental design and analysis (Curtis et al., 2015; Curtis et al., 2018). This update clarifies and simplifies the requirements on design and analysis for BJP manuscripts. This editorial also details updated requirements following an audit and discussion on best practice by the BJP editorial board. Explanations for the requirements are provided in the previous articles. Here, we address new issues that have arisen in the course of handling manuscripts and emphasise three aspects of design that continue to present the greatest challenge to authors: randomisation, blinded analysis and balance of group sizes.

Safety pharmacology during the COVID pandemic.

This editorial summarizes the content of the current themed issue of J Pharmacol Toxicol Methods derived from the 2020 Annual Safety Pharmacology Society (SPS) meeting that was held virtually September 14-17, 2020 due to the ongoing COVID-19 global pandemic. A selection of articles arising from the virtual meeting is summarized. Like previous years they continue to reflect current areas of innovation in SP including new methodologies to predict human safety, best practices for IKr current measurement, and best practice considerations for the conduct of in vivo nonclinical QT studies. The meeting included scientific content from 94 abstracts (reproduced in the current volume of J Pharmacol Toxicol Methods). This continued innovation reflects a rubric in SP that identifies problems, seeks solutions and, importantly, validates the solutions.

GEORGE®: A Pilot Study of a Smartphone Application for Huntington's Disease.

BACKGROUND: Current Huntington's disease (HD) measures are limited to subjective, episodic assessments conducted in clinic. Smartphones can enable the collection of objective, real-world data but their use has not been extensively evaluated in HD. OBJECTIVE: Develop and evaluate a smartphone application to assess feasibility of use and key features of HD in clinic and at home. METHODS: We developed GEORGE®, an Android smartphone application for HD which assesses voice, chorea, balance, gait, and finger tapping speed. We then conducted an observational pilot study of individuals with manifest HD, prodromal HD, and without a movement disorder. In clinic, participants performed standard clinical assessments and a battery of active tasks in GEORGE. At home, participants were instructed to complete the activities thrice daily for one month. Sensor data were used to measure chorea, tap rate, and step count. Audio data was not analyzed. RESULTS: Twenty-three participants (8 manifest HD, 5 prodromal HD, 10 controls) enrolled, and all but one completed the study. On average, participants used the application 2.1 times daily. We observed a significant difference in chorea score (HD: 19.5; prodromal HD: 4.5, p = 0.007; controls: 4.3, p = 0.001) and tap rate (HD: 2.5 taps/s; prodromal HD: 8.9 taps/s, p = 0.001; controls: 8.1 taps/s, p = 0.001) between individuals with and without manifest HD. Tap rate correlated strongly with the traditional UHDRS finger tapping score (left hand: r = -0.82, p = 0.022; right hand: r = -0.79, p = 0.03). CONCLUSION: GEORGE is an acceptable and effective tool to differentiate individuals with and without manifest HD and measure key disease features. Refinement of the application's interface and activities will improve its usability and sensitivity and, ideally, make it useful for clinical care and research.

The COVID-19 Pandemic and Coronary Angiography for ST-Elevation Myocardial Infarction, Use of Mechanical Support, and Mechanical Complications in Canada: A Canadian Association of Interventional Cardiology National Survey.

BACKGROUND: As a result of the COVID-19 pandemic first wave, reductions in ST-elevation myocardial infarction (STEMI) invasive care, ranging from 23% to 76%, have been reported from various countries. Whether this change had any impact on coronary angiography (CA) volume or on mechanical support device use for STEMI and post-STEMI mechanical complications in Canada is unknown. METHODS: We administered a Canada-wide survey to all cardiac catheterization laboratory directors, seeking the volume of CA use for STEMI performed during the period from March 1 2020 to May 31, 2020 (pandemic period), and during 2 control periods (March 1, 2019 to May 31, 2019 and March 1, 2018 to May 31, 2018). The number of left ventricular support devices used, as well as the number of ventricular septal defects and papillary muscle rupture cases diagnosed, was also recorded. We also assessed whether the number of COVID-19 cases recorded in each province was associated with STEMI-related CA volume. RESULTS: A total of 41 of 42 Canadian catheterization laboratories (98%) provided data. There was a modest but statistically significant 16% reduction (incidence rate ratio [IRR] 0.84; 95% confidence interval 0.80-0.87) in CA for STEMI during the first wave of the pandemic, compared to control periods. IRR was not associated with provincial COVID-19 caseload. We observed a 26% reduction (IRR 0.74; 95% confidence interval 0.61-0.89) in the use of intra-aortic balloon pump use for STEMI. Use of an Impella pump and mechanical complications from STEMI were exceedingly rare. CONCLUSIONS: We observed a modest 16% decrease in use of CA for STEMI during the pandemic first wave in Canada, lower than the level reported in other countries. Provincial COVID-19 caseload did not influence this reduction.

INTRODUCTION: Après la première vague de la pandémie de COVID-19, de nombreux pays ont déclaré une réduction de 23 % à 76 % des soins invasifs de l'infarctus du myocarde avec élévation du segment ST (STEMI). On ignore si ce changement a entraîné des répercussions sur le volume d'angiographies coronariennes (AC) ou sur l'utilisation des dispositifs d'assistance mécanique lors de STEMI et des complications mécaniques post-STEMI au Canada. MÉTHODES: Nous avons réalisé un sondage pancanadien auprès de tous les directeurs de laboratoire de cathétérisme cardiaque pour obtenir le volume d'utilisation des AC lors des STEMI réalisées durant la période du 1er mars 2020 au 31 mai 2020 (période de pandémie) et durant 2 périodes témoins (1er mars 2019 au 31 mai 2019 et 1er mars 2018 au 31 mai 2018). Le nombre de dispositifs d'assistance ventriculaire gauche utilisés et le nombre de cas de communications interventriculaires et de ruptures du muscle papillaire diagnostiqués ont également été enregistrés. Nous avons aussi évalué si le nombre de cas de COVID-19 enregistrés dans chaque province était associé au volume d'AC liées aux STEMI. RÉSULTATS: Au total, 41 des 42 laboratoires canadiens de cathétérisme (98 %) ont fourni des données. Lors de la comparaison de la première vague de la pandémie aux périodes témoins, nous avons noté une réduction modeste, mais significative, sur le plan statistique de 16 % (ratio du taux d'incidence [RTI] 0,84; intervalle de confiance à 95 % 0,80-0,87) des AC lors de STEMI. Le RTI n'était pas associé au nombre provincial de cas de COVID-19. Nous avons observé une réduction de 26 % (RTI 0,74; intervalle de confiance à 95 % 0,61-0,89) de l'utilisation de pompes à ballonnet intra-aortique lors de STEMI. L'utilisation d'une pompe Impella et les complications mécaniques après les STEMI étaient extrêmement rares. CONCLUSIONS: Nous avons observé une diminution modeste de 16 % de l'utilisation des AC lors de STEMI durant la première vague de la pandémie au Canada, soit une diminution plus faible que ce que les autres pays ont signalé. Le nombre provincial de cas de COVID-19 n'a pas influencé cette réduction.

The continuing evolution of torsades de pointes liability testing methods: is there an end in sight?

Drug-induced torsades de pointes (TdP) is a syndrome that includes a potentially lethal cardiac arrhythmia. It has been identified as a possible adverse drug reaction (ADR) for drugs which affect the repolarization processes of the heart. In order to predict the potential for TdP liability, regulatory guidelines have been developed which require that new drugs be safety screened. Unfortunately, however, despite this requirement there are no validated preclinical models with TdP incidence as a hard endpoint. Therefore, surrogate biomarkers are used. The most common and eliciting the most discussion/controversy among cardiovascular scientists is the duration of the QT interval of the ECG. Since no single model is available to wholly assess drug-induced TdP liability, safety pharmacologists employ a battery of complementary preclinical models in order to develop an integrated risk assessment (IRA). Ideally, the IRA should be comprised of the results from the effects of the new chemical entity (NCE) on the human ether-a-go-go related (hERG) gene assay (actually a screen for block of the hERG gene product, the inward rectifying K current, IKr) and ECG effects in the conscious canine. However, since neither model is ideal the findings are generally supplemented by conduct of several additional experimental in vitro assays, namely the rabbit left ventricular wedge preparation, Langendorff isolated rabbit heart or isolated canine Purkinje fibre; nevertheless, as with many preclinical models, there is only limited validation and a resultant lack of general acceptance. Institution of regulatory guidance documents such as ICH S7A and S7B in conjunction with heightened awareness of the electrophysiological mechanisms that may be responsible for the development of TdP has led to a sharp fall in proarrhythmic compounds securing licensing, but at what costs? Supplementary experimental assays have furthered our understanding of drug-induced torsadogenesis, and it is now recognized that TdP is a multicausal event. This means that a perceived "positive" torsadogenic risk using one of the aforementioned models does not necessarily guarantee proarrhythmia. There has been an overall fall in the total number of NCEs pursued through development due to strict regulatory guidelines. Here we suggest that regulatory barriers can be alleviated by improving the integrated risk approach. But this requires better validation and deployment of existing preclinical models together with the invention of more precise and accurate models.

Druggable targets for sudden cardiac death prevention: lessons from the past and strategies for the future.

Sudden cardiac death (SCD) is most commonly caused by ventricular fibrillation (VF). The single largest cohort of victims is the population with little or no prior overt heart disease. Effective prevention will require long-term prophylaxis by drugs in large numbers of people identified by risk factors. This means that safe as well as effective drugs are required. Drugs with overt effects on cardiac electrophysiology have failed in the clinic owing to poor effectiveness and/or adverse effects. This article examines possible new drug targets. We have focused on acute myocardial ischaemia as it is the most strikingly proarrhythmic pathology, and the most common cause of coronary artery disease-related VF and SCD according to inferences from epidemiology, drug trials and decades of animal research. To set the scene we have briefly explored drugs that have failed in the clinic in order to identify possible targets that have been overlooked or underexploited. We conclude that the best strategy is identification of pathology-specific targets that render drugs active only where and when their action is required.

Twenty years of safety pharmacology model validation and the wider implications of this to drug discovery.

This editorial summarizes the content of the current themed issue of J Pharm Tox Methods derived from the 2019 Annual Safety Pharmacology Society (SPS) meeting held in Barcelona, Spain, and reflects on 20 years of innovation in the elaboration of methods for evaluating adversity, particularly during the nonclinical research phase. Given the success of safety pharmacology (SP) in the last 20 years, we propose that the rubric for SP method invention and validation be examined in more detail to explore whether it may have wider relevance to the drug discovery process. Articles arising from the Barcelona meeting are summarized here. They reflect current areas of controversy and innovation in SP. Not for the first time in recent years, the suitability of the No Observable Adverse Effect Level (NOAEL) as a variable in SP was considered in an article derived from a survey of SPS members. It was found from the survey and concluded from the analysis that the NOAEL is not necessary for assessing the safety of a New Chemical Entity (NCE). The meeting included scientific content from more than 190 abstracts (reproduced in the current volume of J Pharm Tox Methods). The impact of the INSPIRE program on the educational endeavor of SP, cardiovascular SP with regard to hERG and advances in CiPA and stem cells assays, the use of the echocardiogram in SP, the applicability of deep learning methods in SP and toxicology studies, the role of biomarkers in renal SP studies, and advances in CNS SP are highlighted in this issue of the Journal. This continued innovation reflects a rubric in SP that identifies problems, seeks solutions and, importantly, validates the solutions. If there is a lesson to be learned from the 20 years of annual SP methods themed issues it is that drug discovery efforts may benefit from a more rigorous validation process for discovery methods, using positive and negative controls for validation, as is done in SP method validation.

The application of electrophysiological methods to characterize AMPA receptors in dissociated adult rat and non-human primate cerebellar neurons for use in neuronal safety pharmacology assessments of the central nervous system.

INTRODUCTION: Pre-clinically, safety risk assessment of a drug is primarily tested in vivo using functional evaluation of adult animals while the mechanistic etiology of drug-induced CNS adverse effects is often uncharacterized. In vitro electrophysiology may provide a better understanding of drug effects without additional animal use. However, in vitro protocols are typically designed for using embryonic or juvenile animals. METHODS: We examined whether brain tissue isolated from adult rats (3-5 months old) and adult non-human primates (NHPs) (2-8 years old) can generate qualitatively equivalent readouts for electrophysiology to characterize AMPAR synaptic and single channel currents. We used a known positive AMPAR allosteric modulator (LY451395) to template a response profile and provide proof-of-concept data to assess responses of these native AMPARs in a drug context. RESULTS: Brain slices from adult animals provided a support to measure AMPAR-driven excitatory post-synaptic currents (EPSCs), and can be dissociated into primary neuronal cultures for AMPAR single channel characterization. Additionally, similarities and differences in AMPAR basal kinetics and responses to LY451395 were seen between the two animal species. DISCUSSION: Glutamatergic synaptic activity and AMPAR biophysical properties in adult animals may be used to characterize test-article-mediated alterations in CNS responses. The use of older animals opens the possibility for in vivo test-article administration, either acutely or repeatedly, before in vitro electrophysiological assessment in order to reveal cumulative or delayed-onset effects, adding versatility to safety pharmacology assessment of the CNS.

Characterisation of mexiletine's translational therapeutic index for suppression of ischaemia-induced ventricular fibrillation in the rat isolated heart.

The 'translational therapeutic index' (TTI) is a drug's ratio of nonclinical threshold dose (or concentration) for significant benefit versus threshold for adversity. In early nonclinical research, discovery and safety studies are normally undertaken separately. Our aim was to evaluate a novel integrated approach for generating a TTI for drugs intended for prevention of ischaemia-induced ventricular fibrillation (VF). We templated the current best available class 1b antiarrhythmic, mexiletine, using the rat Langendorff preparation. Mexiletine's beneficial effects on the incidence of VF caused by 120 min regional ischaemia were contrasted with its concurrent adverse effects (on several variables) in the same hearts, to generate a TTI. Mexiletine 0.1 and 0.5 µM had no adverse effects, but did not reduce VF incidence. Mexiletine 1 µM reduced VF incidence to 0% but had adverse effects on atrioventricular conduction and ventricular repolarization. Separate studies undertaken using an intraventricular balloon revealed no detrimental effects of mexiletine (1 and 5 µM) on mechanical function, or any benefit against reperfusion-related dysfunction. Mexiletine's TTI was found to be less than two, which accords with its clinical therapeutic index. Although non-cardiac adversity, identifiable from additional in vivo studies, may reduce the TTI further, it cannot increase it. Our experimental approach represents a useful early-stage integrated risk/benefit method that, when TTI is found to be low, would eliminate unsuitable class 1b drugs prior to next stage in vivo work, with mexiletine's TTI defining the gold standard that would need to be bettered.

Is there a role for the no observed adverse effect level in safety pharmacology?

In nonclinical toxicology the highest dose or exposure without test article-related adverse effects, known as the No Observed Adverse Effect Level (NOAEL), is a variable that may be determined. In safety pharmacology the vast majority of the endpoints measured are quantitative numeric functional endpoints such as changes in heart rate, blood pressure or respiratory frequency, endpoints that are usually not assessed using a defined framework of adversity. Therefore, we asked the question: is there a role for the NOAEL in safety pharmacology? To help answer this question, we conducted a survey via the Safety Pharmacology Society. We found that within safety pharmacology there is no formal definition of adversity and no guidance on defining NOAEL. We also found, perhaps unsurprisingly, there is no agreed rubric for using a NOAEL in safety pharmacology and we learned that the NOAEL is not a requirement in order to progress a new investigational drug through the regulatory process. Thus, a summary label such as NOAEL lacks nuance and disregards context in relation to the nature and the severity of the safety pharmacology findings. Consequently, defining 'adversity' and determining a NOAEL in safety pharmacology studies are not recommended since the range of functional endpoints investigated do not conform to a binary 'toxic/non-toxic' rubric. Focusing on describing test article-related effects on safety pharmacology endpoints, using reasoned arguments as part of an integrated risk assessment, will ensure that the clinical pharmacologists and regulatory bodies see a clear description of relevant findings at each dose or exposure level.

Perception of validity of clinical and preclinical methods for assessment of torsades de pointes liability.

In 2007 a meeting on drug-induced torsades de pointes (TdP) was held in London, UK, under the auspices of the British Society for Cardiovascular Research (BSCR). One of the objectives was to explore the validity of available biomarkers, risk factors and preclinical investigational methods for the detection of drug-induced TdP liability - preclinical methods and clinical 'thorough QT' testing. The first symposium was entitled "How validated are current models and biomarkers for testing drug-induced torsades de pointes liability?" Validation, as far as the symposium was concerned, meant that the endpoints measured in the method predict TdP liability specifically, selectively and quantitatively. Topics (and the publications derived from the presentations) were: human volunteer phase 1 studies [Vik, T., Pollard, C., & Sager, P. (2008-this issue), the anaesthetized rabbit TDP model [Carlsson, L. (2008-this issue), the AV blocked canine preparation [Oros, A., Beekman, J. D. M., & Vos, M. A. (2008-this issue), QT interval and its corrections in the in vivo conscious canine [Fossa, A. A. (2008-this issue), the rabbit heart failure model [Hamlin, R. L., & Kijtawornrat, A. (2008-this issue), the rabbit Langendorff preparation and the Screenit approach [Dumotier, B. M., Deurinck, M., Yang, Y., Traebert, M., & Suter, W. (2008-this issue), the wedge preparation [Yan G.-X. (2008-this issue)] and hERG screens [Hancox, J. C., McPate, M. J., El Harchi, A., & Zhang, Y. h. (2008-this issue). Unbeknownst to the speakers before the start of the sessions, the audience were invited, during the session, to rate each approach on a 0 to 10 scale in terms of the extent to which each approach appeared to be validated. The outcome of this exercise forms the basis of this article. We invite you to evaluate for yourselves the accompanying reviews in this edition of Pharmacology and Therapeutics.