RT Journal Article SR Electronic T1 Comparative Evaluation of HERG Currents and QT Intervals following Challenge with Suspected Torsadogenic and Nontorsadogenic Drugs JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 1098 OP 1106 DO 10.1124/jpet.105.093393 VO 316 IS 3 A1 Alexander N. Katchman A1 John Koerner A1 Toshimasa Tosaka A1 Raymond L. Woosley A1 Steven N. Ebert YR 2006 UL http://jpet.aspetjournals.org/content/316/3/1098.abstract AB The purpose of the present study was to comparatively evaluate human HERG currents and QT intervals following challenge with suspected torsadogenic and nontorsadogenic drugs. Various concentrations of 14 different drugs were initially evaluated in terms of their relative potency to block IHERG in stably transfected human embryonic kidney cells. Four general categories of drugs were identified: high-potency blockers (IC50 < 0.1 μM) included lidoflazine, terfenadine, and haloperidol; moderate-potency blockers (0.1 μM < IC50 < 1 μM) included sertindole, thioridazine, and prenylamine; low-potency blockers (IC50 > 1 μM) included propafenone, loratadine, pyrilamine, lovastatin, and chlorpheniramine; and ineffective blockers (IC50 > 300 μM) included cimetidine, pentamidine, and arsenic trioxide. All measurements were performed using similar conditions and tested acute drug effects only (<30 min of drug exposure per measurement). Since two of the drugs that were ineffective IHERG blockers, arsenic trioxide and pentamidine, have been associated with cardiac repolarization delays (QT interval lengthening) and torsades de pointes ventricular arrhythmias in patients, we chose to evaluate them further using the isolated perfused rabbit heart model. Neither arsenic trioxide nor pentamidine had any significant effect on QT intervals in this model, even at relatively high (micromolar) concentrations. Similar results were obtained for loratadine in this model. When the hearts were challenged with a known torsadogenic drug such as cisapride, significant QT lengthening was rapidly induced. These results demonstrate that arsenic trioxide and pentamidine are essentially devoid of direct acute effects on cardiac repolarization or inhibition of IHERG.