Combining an in silico proarrhythmic risk assay with a tPKPD model to predict QTc interval prolongation in the anesthetized guinea pig assay.

Human-based in silico models are emerging as important tools to study the effects of integrating inward and outward ion channel currents to predict clinical proarrhythmic risk. The aims of this study were 2-fold: 1) Evaluate the capacity of an in silico model to predict QTc interval prolongation in the in vivo anesthetized cardiovascular guinea pig (CVGP) assay for new chemical entities (NCEs) and; 2) Determine if a translational pharmacokinetic/pharmacodynamic (tPKPD) model can improve the predictive capacity. In silico simulations for NCEs were performed using a population of human ventricular action potential (AP) models. PatchXpress® (PX) or high throughput screening (HTS) ion channel data from respectively n = 73 and n = 51 NCEs were used as inputs for the in silico population. These NCEs were also tested in the CVGP (n = 73). An M5 pruned decision tree-based regression tPKPD model was used to evaluate the concentration at which an NCE is liable to prolong the QTc interval in the CVGP. In silico results successfully predicted the QTc interval prolongation outcome observed in the CVGP with an accuracy/specificity of 85%/73% and 75%/77%, when using PX and HTS ion channel data, respectively. Considering the tPKPD predicted concentration resulting in QTc prolongation (EC5%) increased accuracy/specificity to 97%/95% using PX and 88%/97% when using HTS. Our results support that human-based in silico simulations in combination with tPKPD modeling can provide correlative results with a commonly used early in vivo safety assay, suggesting a path toward more rapid NCE assessment with reduced resources, cycle time, and animal use.

QT interval correction assessment in the anesthetized guinea pig.

INTRODUCTION: The anesthetized guinea pig (ANES GP) has proven to be an effective small animal model to evaluate cardiac electrophysiologic effects of drug-candidate molecules during lead optimization. While heart rate (HR) corrected QT interval (QTc) is a key variable to determine test article-dependent repolarization effects, ideal correction methods are an area of constant debate given the potential influence of anesthesia, autonomic tone, species, strain and gender on the QT/HR relationship. The aim of this study was to characterize the ability of common correction formulas to normalize rate-dependent effects on the QT interval in the ketamine/xylazine ANES GP. METHODS: Atrial pacing (n=10), ivabradine or ephedrine (n=6/group) infusions were used, respectively to evaluate the effects of a wide range of HRs on the QT/HR relationship. Correction formulas (Bazett [QTcb], Fridericia [QTcf] and Van de Water [QTcVdW]) were applied and the best fit formula was determined with the aid of the slope of their QT-HR linear relationship. RESULTS: From 100 to 220bpm, QTcb underestimated the change in QT interval duration (QT/HR slope=0.35 to 0.67). However, QTcVdW was more appropriate in this HR range (QT/HR slope=-0.07 and 0.09). At higher HRs (>220bpm), QTcb performed better (QT/HR slope=-0.02 and 0.07) as compared to QTcf (QT/HR slope=-0.18 to -0.1) and QTcVdW (QT/HR slope=-0.2 to -0.17) (p<0.01). All the correction formulas identified dofetilide- and sotalol-dependent repolarization delay (n=6/group) but QTcb and QTcf demonstrated reduced sensitivity as compared to fixed cardiac pacing (p<0.01). In contrast, QTcVdW resulted in an apparent underestimation of the QT interval duration at HR levels above the basal ketamine/xylazine ANES GP HRs (>220bpm) with ephedrine (n=6). DISCUSSION: The best fit correction formula in the ANES GP was highly dependent on the HR range. In the ketamine/xylazine model, QTcVdW performed best with HR <220bpm and QTcb performed best with HR >220bpm. The QTcVdW correction formula was thus selected in the ketamine/xylazine ANES GP since HRs in this model are generally within the optimal range for this correction formula.

Rats recovering from unilateral barrel-cortex ischemia are capable of completing a whisker-dependent task using only their affected whiskers.

Rats use their vibrissae for a variety of exploratory tasks including location of objects and discrimination of texture. This study examines recovery in vibrissal function following a unilateral ischemic injury to the somatosensory cortex. Vibrissal function was examined in adult food-restricted rats performing on a two-texture discrimination device. Animals were trained and tested until the criteria of >80% correct choices was demonstrated on three consecutive days. Ischemic rats were constrained to use the affected whiskers by clipping the ipsilateral vibrissae. One group was tested after ischemia, a second group was trained before ischemia and then tested, and a third group was pre-trained and received whisker stimulation and tested post-ischemia. Nai;ve animals recovering from ischemia took longer to reach criteria than intact or unilateral trimmed control animals. Pre-trained animals with compression ischemia receiving whisker stimulation with sucrose water completed the task to criteria in the fewest number of trials. The results indicate that recovery of vibrissal function occurs following a unilateral ischemic injury. Histological analysis in animals without whisker stimulation indicates that the number of normal appearing cortical barrels following ischemia was inversely correlated to the number of trials needed to complete the behavioral task. This suggests that the natural recovery of the ability to discriminate textures is related to the degree of damage to the barrel cortex. The relationship between cortical barrels and behavioral recovery did not hold for the ischemic animals receiving whisker stimulation. This latter group demonstrated recovery despite marked anatomical lesions suggesting that the intervention influenced reorganization.