Abstract. In safety pharmacology studies, the effects on the QT interval of electrocardiograms are routinely assessed using a telemetry system in cynomolgus monkeys. However, there is a lack of integrated databases concerning in vivo QT assays in conscious monkeys. As part of QT Interval Prolongation: Project for Database Construction (QT PRODACT), the present study examined 10 positive compounds with the potential to prolong the QT interval and 6 negative compounds considered to have no such effect on humans. The experiments were conducted at 7 facilities in accordance with a standard protocol established by QT PRODACT. The vehicle or 3 doses of each test compound were administered orally to male cynomolgus monkeys (n = 3 -4), and telemetry signals were recorded for 24 h. None of the negative compounds prolonged the corrected QT using Bazett's formula (QTcB) interval. On the other hand, almost all of the positive compounds prolonged the QTcB interval, but haloperidol, terfenadine, and thioridazine did not. The failure to detect the QTcB interval prolongation appeared to be attributable for the differences in metabolism between species and / or disagreement with Bazett's formula for tachycardia. In the cynomolgus monkeys, astemizole induced Torsade de Pointes and cisapride caused tachyarrhythmia at lower plasma concentrations than those observed in humans and dogs. These results suggest that in vivo QT assays in conscious monkeys represent a useful model for assessing the risks of drug-induced QT interval prolongation. Supplementary material (Appendix): available only at http://dx

Abstract. To construct a non-clinical database for drug-induced QT interval prolongation, the electrophysiological effects of 11 positive and 10 negative compounds on action potentials (AP) in guinea-pig papillary muscles were investigated in a multi-site study according to a standard protocol. Compounds with a selective inhibitory effect on the rapidly activated delayed rectifier potassium current (I Kr ) prolonged action potential duration at 90% repolarization (APD 90 ) in a concentration-dependent manner, those showing Ca 2+ current (I Ca ) inhibition shortened APD 30 , and those showing Na + current (I Na ) inhibition decreased action potential amplitude (APA) and V max . Some of the mixed ion-channel blockers showed a bell-shaped concentration-response curve for APD 90 , probably due to their blockade of I Na and / or I Ca , sometimes leading to a falsenegative result in the assay. In contrast, all positive compounds except for terfenadine and all negative compounds with I Kr -blocking activity prolonged APD 30-90 regardless of their I Na -and / or I Ca -blocking activities, suggesting that APD 30-90 is a useful parameter for evaluating the I Krblocking activity of test compounds. Furthermore, the assay is highly informative regarding the modulation of cardiac ion channels by test compounds. Therefore, when APD 90 and APD 30-90 are both measured, the action potential assay can be considered a useful method for assessing the risk of QT interval prolongation in humans in non-clinical safety pharmacology studies. Supplementary material (Appendix): available only at http://dx

Abstract. Drug concentrations that would prolong repolarization parameters by 10%, including action potential duration (APD 90 , APD 30 -90 ), in in vitro assays using guinea-pig papillary muscle and QTc intervals in in vivo assays using conscious dogs, conscious monkeys, and anesthetized dogs were compared. Although, both the in vitro and in vivo assays showed concentrationdependent responses for compounds that have been classified as torsadogenic in humans, only a weak correlation in EC 10 values was observed between the in vitro and in vivo assays. Among the in vivo QT assays, the EC 10 values obtained from conscious dogs, conscious monkeys, and anesthetized dogs correlated well with each other, but the EC 10 values in monkeys were somewhat lower in comparison to those in dogs. When in vivo QT assay EC 10 values were compared to the respective human effective therapeutic plasma concentration (ETPC), the ratios of EC 10 values to ETPCs were less than 20 for most torsadogenic compounds. In conclusion, the relationships between the extent of QTc interval prolongation and the concentration of drugs was highly consistent among the three in vivo models, suggesting that the ratios of EC 10 values in in vivo QT assays are useful for estimating the safety margin of drugs that prolong the QTc interval.