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/hNa(v) 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 degrees 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 hNa(v) 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.