Jacketed external telemetry can incorporate cardiovascular safety assessment into toxicology studies, accelerating drug development timelines.

Recent technological advances have dramatically broadened the scope of safety pharmacology studies as originally envisioned in the International Conference on Harmonization (ICH) S7A and S7B guidances, where “the use of new technologies and methodologies in accordance with sound scientific principles” was encouraged. Recent revisions to the ICH S6(R1) guidance state that safety pharmacology “may be investigated in separate studies or incorporated in the design of toxicity studies” for biotechnology-derived products. 
In the context of these guidelines, jacketed telemetry has emerged as a technology capable of integrating high-quality cardiovascular safety studies with repeat-dose toxicology studies, thus accelerating drug development timelines. Jacketed telemetry is closely aligned with the “3Rs” of animal use: a humane approach to animal research focused on replacing the use of animals when possible, reducing the number of animals needed in a study to the minimal number necessary to achieve scientifically valid results, and refining procedures to minimize the potential for pain and distress. 
The incorporation of electrocardiogram (ECG) and blood pressure measurements in a repeat-dose toxicology study has typically involved the use of snapshot data collections performed on conscious, restrained animals, generally yielding 30 to 120 sec of ECG and/or external cuff blood pressure data. While these data may technically fulfill minimal safety assessment requirements, they are subject to high variability and are of limited probative value due to the confounding effects of sympathetic stimulation of the animals during the data acquisition process. While ECGs may be useful for the detection of overt cardiovascular abnormalities, such as irregular heart rate or rhythm, it would be difficult—if not impossible—to accurately evaluate possible drug-mediated ECG effects in the presence of restraint-induced increases in sympathetic tone.
The contract research organization (CRO) infrastructure is broadly focused on those portions of the drug development process that are inefficient for sponsors to maintain in-house. As such, CROs continuously revise their experimental procedures, incorporating the latest validated advances in technology to assist sponsors in accelerating the drug development process. 
In 2011, Charles River completed the GLP validation of jacketed external telemetry (JET), enabling sponsors to acquire continuous recordings of key ECG intervals such as P-wave duration and PR, QRS, QT, and rate-corrected QT intervals, all fully integrated within a typical repeat-dose toxicology study. The incorporation of JET within a toxicology study offers several distinct advantages compared to the conventional snapshot approach for obtaining cardiovascular safety data. 
JET data are better able to detect low-frequency abnormalities because more ECG waveforms are being sampled—for 24 hours instead of two minutes. As JET data are continuously acquired from conscious, unrestrained animals, the absence of restraint-induced increases in sympathetic tone provides a stable and unperturbed hemodynamic background. This system dramatically enhances sensitivity to detect subtle cardiovascular effects that may be treatment related. 
Since the ECG and blood pressure data are collected during the day and night photoperiods, species with significant diurnal changes, for example, reduced heart rate during sleep, may offer even more information about possible drug effects. For example, minor changes in heart rate may be more easily identified during the sleep cycle when snapshot ECG collections, by definition, are not feasible.
Charles River has also validated the JET blood pressure component, which can be used to simultaneously collect ECGs and blood pressures from unrestrained animals in a typical repeat-dose toxicology study. This provides all of the advantages previously described for ECGs with the addition of high-fidelity peripheral blood pressures. This is an exceedingly valuable drug development tool, particularly when employed in conjunction with extremely sensitive in vitro assays, which enable the robust detection of possible cardiac ion channel interactions (hERG, sodium, and calcium). For example, the in vitro assay for hERG activity has drastically reduced the potential for an unexpected in vivo QT prolonging effect, indicative of a delay in cardiac repolarization that may place the subject—human or animal—at risk for adverse cardiac events, including sudden cardiac death.
While “QT surprises” during clinical development have diminished, recently, unexpected small increases in blood pressure—which were only detected after chronic administration in man—have been responsible for a number of highly publicized drug failures, such as with the CETP inhibitor, torcetrapib. The integrated use of JET (with blood pressure) in conjunction with an adequately designed repeat-dose toxicology study can be used to detect a 5 to 10 mmHg change in blood pressure during chronic dosing. This test system has the potential to reduce, or possibly eliminate, expensive late-stage clinical failures due to previously undetectable changes in blood pressure that are present only during repeat dosing. Importantly, such studies are currently not within the scope or intent of the definitive single-dose cardiovascular safety pharmacology study, and thus represent a clear gap in current integrated cardiovascular risk assessments. 
Clinical thorough QT (TQT) studies typically involve the extraction of multiple ECG “triplicates” (three ECG waveforms obtained during defined periods of stable resting heart rate) from a continuous ECG collection. The methodological dissimilarity to preclinical snapshot ECGs makes translation problematic. The replacement of restrained snapshots with JET improves the translational power between preclinical and clinical observations, enabling more appropriate comparisons to support development decisions. 
Although jacketed ECG and blood pressure technology will not replace the fully implantable standalone telemetry model, it does provide researchers with a sensitive tool to detect subtle cardiovascular effects in repeat-dose toxicology studies. This may obviate the need for standalone safety pharmacology studies for many drug development programs—biotechnology-derived products, oncology test articles, etc.—and reduce animal use. In the event of a cardiovascular finding with JET, it is advisable to implement a definitive cardiovascular safety study, employing fully implanted telemetry devices with epicardial ECG lead placements. However, by integrating these assessments into the obligate repeat-dose toxicology study designs, drug developers can reduce animal use by reducing the number of studies and generate acute and chronic safety data to assess the effects of both primary exposure and any possible effects of drug accumulation following multiple exposures. In addition, they can evaluate other mechanisms of toxicity that may involve delayed effects—parent accumulation, metabolites, etc.—or delayed effects on transcription and translation of target and off-target proteins and ensure that exposures are directly comparable between the safety and toxicology data as they are simultaneously generated in the same animals. 
The benefit of integrating cardiovascular safety assessments into a repeat-dose design reduces the potential for unforeseen and uncontrolled variables to affect subsequent interpretations. Refinements and new technologies, such as JET, also allow CROs to use fewer animals to collect the same information and promote the 3Rs of animal use. Ultimately, use of such integrative technologies as JET will result in more comprehensive and predictive studies where the results accurately portend human safety, enabling the earlier detection and resolution of possible safety issues.
About the author
Robert Kaiser received his PhD in biochemistry from the University of Nevada and joined Charles River Laboratories in 2005 as a research scientist in toxicology. Mr. Holzgrefe has extensive drug discovery and drug development experience with more than 30 years in the pharmaceutical industry.