Abstract 14372: The Acquired Long QT-Causing Drugs Haloperidol and Terfenadine Cause Defects in HERG Trafficking

Abstract

Background: Mutations in K v 11.1 (HERG) cause inherited long QT syndrome (LQTS) type 2 by disrupting channel function or membrane trafficking. Acquired LQTS is caused by drug binding to HERG and directly blocking the channel pore, reducing I Kr and prolonging QTc in persons with decreased repolarization reserve. Alternatively, these drugs could bind to HERG and interfere with trafficking, reducing the number of HERG channels at the membrane. Objective: We sought to understand the effects of known acquired LQTS-causing drugs from various classes (terfenadine, haloperidol, ondansetron, fluconazole, azithromycin) on HERG trafficking. Methods: HEK293 cells stably expressing HERG (HERG-HEK293) were cultured in varying concentrations of selected drugs for 24 hours. Differences in trafficking were identified by immunoblot using the terminally-glycosylated HERG at 155 kD and the immature core-glycosylated HERG at 135 kD. Both the mutant HERG-G601S and HERG-HEK293 cells treated for 24 hours with arsenic trioxide (As 2 O 3 ) served as trafficking-deficient controls. Results: HERG-HEK293 cells treated with haloperidol ( > 50 μM) demonstrated a decrease in the size of the terminally glycosylated band, appearing at 140-145 kD in comparison to the fully glycosylated 155 kD (Fig. 1A). HERG-HEK293 cells treated with terfenadine ( > 15 μM) demonstrated a deficiency in terminal glycosylation (Fig. 1B). Ondansetron, fluconazole, and azithromycin treatments at 1, 10, and 100 μM demonstrated no effect on the fully glycosylated band. Conclusions: These data suggest terfenadine and haloperidol interfere with HERG trafficking, resulting in less mature HERG at the membrane. Together, these data provide insight into a non-pore blocking mechanism that may underlie some cases of acquired LQTS.