Cardiac sodium channel antagonism - Translation of preclinical in vitro assays to clinical QRS prolongation

Results from a Joined Prospective Study to Evaluate the Sensitivity of the In Vivo Dog QT Assay in Line with the ICH E14/S7B Q&A Best Practices

The ICH E14/S7B Q&As highlighted the need for best practices concerning the design, execution, analysis, interpretation, and reporting of the in vivo non-rodent QT assay as a component of the integrated risk assessment to potentially support a TQT waiver or substitute. We conducted a dog telemetry study to assess the effects on QTc of six reference compounds (five positive and one negative) previously evaluated by Darpo et al. (2015) in humans. The sensitivity of the assay to detect QTc increases was determined, and exposure-response analysis was performed, as done in clinical practice. By-timepoint analysis showed QTc prolongation induced by moxifloxacin, dofetilide, dolasetron, ondansetron, and quinine within human relevant plasma exposures ranges. Moreover, a hysteresis was observed for quinine. As expected, levocetirizine showed no statistically significant effect on QTc across a range of exposure, well exceeding the therapeutic Cmax. Power analyses confirmed the study ability to detect statistically significant QTc changes of less than 10 milliseconds with 80% probability, even with a sample size as low as n = 4 animals. Finally, concentration-QTc modeling enabled to predict the minimal plasma concentration needed to detect a 10 milliseconds QTc prolongation, including for quinine. The comparison with clinical available data supported the relevance of dogs under these experimental conditions as a robust translational predictor of drug-induced QTc prolongation in humans as a key pillar of the integrated risk assessment.

Simultaneous assessment of compound activity on cardiac Nav1.5 peak and late currents in an automated patch clamp platform

INTRODUCTION

High throughput in vitro profiling of the cardiac Nav1.5 peak sodium current (I_Na) is widely used in cardiac safety screening. However, there is no standardized high throughput method to measure late I_Na. This study assessed the pharmacological and biophysical properties of veratridine and ATX-II, as well as the channel mutation (Nav1.5-∆KPQ) on the late I_Na. We describe a method for simultaneous measurement of both peak and late I_Na.

METHODS

The planar patch clamp technique (QPatch) was applied to record the peak and late I_Na.

RESULTS

The Nav1.5-∆KPQ mutant produced a small late I_Na (41.9 ± 5.4 pA) not large enough to enable compound profiling. In contrast in wild type Nav1.5 expressing cells veratridine (100 μM) and ATX-II (100 nM) enhanced concentration-dependent increases in the late I_Na (maximum responses of 1162.2 ± 258.5 pA and 392.4 ± 71.3 pA, respectively). Veratridine inhibited, whereas, ATX-II had a minimal effect, on the peak I_Na and preserved the current-voltage curve. Peak and late I_Na inhibition was characterized for 25 clinical I_Na blockers in the presence of ATX-II. Compound IC₅₀ values for peak I_Na generated in the absence or presence of ATX-II correlated. The potency of the late I_Na block was found to be dependent on whether it was measured at the end of the depolarizing pulse or during the ramp.

DISCUSSION

In the presence of ATX-II, both peak and late I_Na could be assessed simultaneously. Late I_Na may be best assessed using the maximum response obtained during the ramp of the voltage protocol.