G018 Evaluation of IKr blocking properties of different molecules with or without torsadogenic properties

Abstract

Currently, industrials and regulatory authorities are worried by Torsades de Pointes (TdP), a type of ventricular tachycardia, which can lead to sudden death. The most recent guidelines from the International Committee of Harmonization, recommend to assess properly the risk of TdP, by different approaches, among others an in vitro method. This method consists on studying the blockade of a voltage-dependant potassium channel, called hERG. Indeed, hERG channel, responsible for the IKr current, seems to be blocked by the majority of the torsadogenic molecules and, is thus considered as an important marker of pro arrhythmic risk. CERB developed a bio-computerized database named TdPScreen® to predict the risk of TdP. Known molecules are classified according to their pro arrhythmic potential, from group A to C. The group A corresponds to drugs with numerous or several reports of TdP, the group B to compounds causing QT prolongation with TdP at very low frequency; and in group C to drugs with no report of TdP or QT prolongation. This database suggests that other factors than a single blockade of IKr could be involved in the genesis of druginduced TdP. We performed experiments in patch-clamp using HEK cells expressing stably the hERG channel. Different compounds from the different groups, above mentioned, were evaluated for their IKr blocking potency and compared to the TdPScreen® database. Results show some torsadogenic drugs might exhibit very low IKr blocking properties (e.g. D-sotalol), whereas other non-torsadogenic drugs are potent IKr inhibitors (e.g. verapamil, diltiazem…). These results, and others, indicate that drugs can block hERG current without any influence on TdP appearance. We conclude that assessing pro arrhythmic potential of compounds, only on the blocking effects of IKr, in vitro, can lead to the eviction of interesting molecules.