The protease inhibitor atazanavir blocks hERG K(+) channels expressed in HEK293 cells and obstructs hERG protein transport to cell membrane.

Abstract

Atazanavir (ATV) is a HIV-1 protease inhibitor for the treatment of AIDS patients, which is recently reported to provoke excessive prolongation of the QT interval and torsades de pointes (TdP). In order to elucidate its arrhythmogenic mechanisms, we investigated the effects of ATV on the hERG K(+) channels expressed in HEK293 cells. hERG K(+) currents were detected using whole-cell patch clamp recording in HEK293 cells transfected with EGFP-hERG plasmids. The expression of hERG protein was measured with Western blotting. Two mutants (Y652A and F656C) were constructed in the S6 domain within the inner helices of hERG K(+) channels that were responsible for binding of various drugs. The trafficking of hERG protein was studied with confocal microscopy. Application of ATV (0.01-30 μmol/L) concentration-dependently decreased hERG K(+) currents with an IC50 of 5.7±1.8 μmol/L. ATV (10 μmol/L) did not affect the activation and steady-state inactivation of hERG K(+) currents. Compared with the wild type hERG K(+) channels, both Y652A and F656C mutants significantly reduced the inhibition of ATV on hERG K(+) currents. Overnight treatment with ATV (0.1-30 μmol/L) concentration-dependently reduced the amount of fully glycosylated 155 kDa hERG protein without significantly affecting the core-glycosylated 135 kDa hERG protein in the cells expressing the WT-hERG protein. Confocal microscopy studies confirmed that overnight treatment with ATV obstructed the trafficking of hERG protein to the cell membrane. ATV directly blocks hERG K(+) channels via binding to the residues Y652 and F656 in the S6 domain, and indirectly obstructs the transport of the hERG protein to the cell membrane.