A pharmacological synopsis of small molecules, toxins and CiPA compounds targeting human cardiac Kv4.3 channels

Kv4.3 α-subunits associate with ancillary β-subunits of the KChIP2 family in heart muscular tissue to channel transient outward (Ito) currents. Decreased expression or dysfunction of Kv4.3 channels following myocardial infarction or during heart failure can contribute to abnormal repolarization, which may result in ventricular arrhythmias. Therefore, drug-induced inhibition of Kv4.3/KChIP2-mediated Ito exposes to potential cardio safety liabilities which are important to document early during the drug discovery process. In this study, we have characterized basic electrophysiological properties pertaining to Ito currents in CHO cells expressing recombinant Kv4.3 and KChIP2.2 subunits. The currents obtained were validated pharmacologically by assessing the efficacy of small molecule and peptide toxin inhibitors known from manual patch-clamp studies to block Ito. We then examined the inhibitory activities of 28 drugs with clinically documented high, medium or low pro-arrhythmic risk encompassing the test- and validation-sets of the Comprehensive in vitro Pro-Arrhythmia (CiPA) panel. While none of the CiPA drugs inhibited Kv4.3 at submicromolar concentrations (IC50 < 1 µM), two drugs (loratadine and nitrendipine) displayed intermediate potency (1 µM < IC50 < 10 µM), and four drugs (bepridil, quinidine, chlorpromazine and astemizole) revealed weak, but significant (10 µM < IC50 < 30 µM) inhibitors.