Nick McMahon

Simulation of multiple ion channel block provides improved early prediction of compounds' clinical torsadogenic risk

Aims The level of inhibition of the human Ether-à-go-go-related gene (hERG) channel is one of the earliest preclinical markers used to predict the risk of a compound causing Torsade-de-Pointes (TdP) arrhythmias. While avoiding the use of drugs with maximum therapeutic concentrations within 30-fold of their hERG inhibitory concentration 50% (IC50) values has been suggested, there are drugs that are exceptions to this rule: hERG inhibitors that do not cause TdP, and drugs that can cause TdP but are not strong hERG inhibitors. In this study, we investigate whether a simulated evaluation of multi-channel effects could be used to improve this early prediction of TdP risk. Methods and results We collected multiple ion channel data (hERG, Na, l-type Ca) on 31 drugs associated with varied risks of TdP. To integrate the information on multi-channel block, we have performed simulations with a variety of mathematical models of cardiac cells (for rabbit, dog, and human ventricular myocyte models). Drug action is modelled using IC50 values, and therapeutic drug concentrations to calculate the proportion of blocked channels and the channel conductances are modified accordingly. Various pacing protocols are simulated, and classification analysis is performed to evaluate the predictive power of the models for TdP risk. We find that simulation of action potential duration prolongation, at therapeutic concentrations, provides improved prediction of the TdP risk associated with a compound, above that provided by existing markers. Conclusion The suggested calculations improve the reliability of early cardiac safety assessments, beyond those based solely on a hERG block effect.

Scientific review and recommendations on preclinical cardiovascular safety evaluation of biologics.

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

Translation of flecainide- and mexiletine-induced cardiac sodium channel inhibition and ventricular conduction slowing from nonclinical models to clinical

INTRODUCTION Nonclinical in vivo models used for cardiovascular safety testing have not previously been studied for their sensitivity for detection of conduction slowing resulting from cardiac sodium channel block. The goal of this study was to examine the sensitivity of in vivo models to cardiac sodium channel block, and translation of the effect from in vitro to in vivo models using sodium channel inhibitors flecainide and mexiletine; flecainide, but not mexiletine is commonly associated with QRS complex prolongation in humans. METHODS Inhibition of cloned cardiac sodium channels (hNav1.5) was studied using the IonWorks platform. Conduction slowing was measured in vitro in the rabbit isolated ventricular wedge (RVW) and in vivo in the conscious telemetered rat and dog, and anaesthetised dog. RESULTS Flecainide and mexiletine inhibited hNav1.5 channels with IC50 values of 10.7 and 67.2 μM respectively. In the RVW, QRS was increased by flecainide at 60 bpm, and at 120bpm, there was an increased effect of both drugs. In conscious rats, flecainide significantly increased QRS complex duration; mexiletine had no significant effect, but there was an increase at the highest dose in 4/6 animals. QRS complex was increased by flecainide and mexiletine in anaesthetised dogs but this was not statistically significant; in conscious dog, only flecainide produced a significant increase in QRS complex. DISCUSSION When compared to clinical data, effects of flecainide and mexiletine in RVW and conscious dog compared well with effects in patients and healthy volunteers in terms of sensitivity. The anaesthetised dog was least sensitive for detection of changes in QRS. All assays showed some differentiation between the expected conduction slowing activity of flecainide and mexiletine. Based on these data, RVW and conscious dog were most predictive for effects of compounds on QRS complex and cardiac conduction.

How do the top 12 pharmaceutical companies operate safety pharmacology

INTRODUCTION How does safety pharmacology operate in large pharmaceutical companies today? By understanding our current position, can we prepare safety pharmacology to successfully navigate the complex process of drug discovery and development? METHODS A short anonymous survey was conducted, by invitation, to safety pharmacology representatives of the top 12 pharmaceutical companies, as defined by 2009 revenue figures. A series of multiple choice questions was designed to explore group size, accountabilities, roles and responsibilities of group members, outsourcing policy and publication record. RESULTS A 92% response rate was obtained. Six out of 11 companies have 10 to 30 full time equivalents in safety pharmacology, who hold similar roles and responsibilities; although the majority of members are not qualified at PhD level or equivalent. Accountabilities were similar across companies and all groups have accountability for core battery in vivo studies and problem solving activities but differences do exist for example with in vitro safety screening and pharmacodynamic/pharmokinetic modeling (PK/PD). The majority of companies outsource less than 25% of studies, with in vitro profiling being the most commonly outsourced activity. Finally, safety pharmacology groups are publishing 1 to 4 articles each year. CONCLUSION This short survey has highlighted areas of similarity and differences in the way large pharmaceutical companies operate safety pharmacology.

Comparison of non-invasive and implanted telemetric measurement of blood pressure and electrocardiogram in conscious beagle dogs.

INTRODUCTION The objective of this study was to evaluate the ability of a non-invasive telemetry monitoring system to detect and quantify changes in blood pressure and electrocardiogram (ECG) parameters in response to vehicle, L-NAME or minoxidil administration to freely moving beagle dogs. Data from a non-invasive telemetry monitoring system were compared to data captured from an invasive telemetry implant in the same animals. METHODS Blood pressure and ECG data were simultaneously acquired from male dogs using a non-invasive and an invasive implanted telemetry system for 2 hours predose and 24 hours post dosing with vehicle (n=5), minoxidil at 1 mg/kg (n=4) and L-NAME at 10 mg/kg (n=5) on separate test days. Values for mean blood pressure, systolic blood pressure, diastolic blood pressure, pulse pressure, heart rate, RR, PR, QRS, QT and QTcL (heart rate corrected QT interval) interval were reported for both methods. RESULTS Statistically significant reductions in blood pressure and pulse pressure and increases in heart rate, with associated ECG interval changes were apparent following dosing with minoxidil using both methods. Statistically significant increases in blood pressure and pulse pressure were apparent following dosing with L-NAME when using the invasive telemetry system, changes were apparent when using the non-invasive telemetry system, however, no change was apparent for pulse pressure, they were of shorter duration and not statistically significant. Statistically significant decreases in heart rate, with associated changes in ECG intervals, were apparent following treatment with L-NAME for both invasive and non-invasive methods. DISCUSSION This study shows that the non-invasive system can be successfully used to acquire both ECG and blood pressure data in freely moving jacketed dogs for at least 26 hours, yet requires further technique refinement to improve system sensitivity to detect smaller changes in blood pressure.

WITHDRAWN: Scientific review and recommendations on preclinical cardiovascular safety evaluation of biologics

Amgen, Inc, Department of Investigative Toxicology, Thousand Oaks, CA, 91320, USA Schering-Plough Research Institute, Kenilworth, NJ, 07033, USA F. Hoffmann-La Roche Ltd., Non-Clinical Safety, Basel, Switzerland Wyeth Research, Chazy, New York, 12921, USA Abbott Laboratories, Department of Integrative Pharmacology, Abbott Park, IL 60064, USA AstraZeneca, Mereside, Alderley Park, Macclesfield, Cheshire, SK10-4TG, U.K. GlaxoSmithKline, Safety Assessment, The Frythe, Welwyn, Herts, AL6 9AR, U.K. Novartis Pharmaceutic Corp., One Health Plaza, East Hanover, NJ, 07936, USA Merck Research Laboratories, Safety Assessment, West Point, PA, 19486, USA Lilly Research Laboratories, Global Safety Pharmacology, Greenfield, IN 46140, USA Johnson & Johnson PR&D, Global Preclinical Toxicology/Pathology, Raritan, NJ, 00869, USA