Coexistence of hERG current block and disruption of protein trafficking in ketoconazole-induced long QT syndrome

Background and purpose: Many drugs associated with acquired long QT syndrome (LQTS) directly block human ether-a-go-go-related gene (hERG) K+ channels. Recently, disrupted trafficking of the hERG channel protein was proposed as a new mechanism underlying LQTS, but whether this defect coexists with the hERG current block remains unclear. This study investigated how ketoconazole, a direct hERG current inhibitor, affects the trafficking of hERG channel protein. Experimental approach: Wild-type hERG and SCN5A/hNav 1.5 Na+ channels or the Y652A and F656C mutated forms of the hERG were stably expressed in HEK293 cells. The K+ and Na+ currents were recorded in these cells by using the whole-cell patch-clamp technique (23°C). Protein trafficking of the hERG was evaluated by Western blot analysis and flow cytometry. Key results: Ketoconazole directly blocked the hERG channel current and reduced the amount of hERG channel protein trafficked to the cell surface in a concentration-dependent manner. Current density of the hERG channels but not of the hNav 1.5 channels was reduced after 48 h of incubation with ketoconazole, with preservation of the acute direct effect on hERG current. Mutations in drug-binding sites (F656C or Y652A) of the hERG channel significantly attenuated the hERG current blockade by ketoconazole, but did not affect the disruption of trafficking. Conclusions and implications: Our findings indicate that ketoconazole might cause acquired LQTS via a direct inhibition of current through the hERG channel and by disrupting hERG protein trafficking within therapeutic concentrations. These findings should be considered when evaluating new drugs. British Journal of Pharmacology (2008) 153, 439–447; doi:10.1038/sj.bjp.0707537; published online 29 October 2007