The hERG PAS domain: A major regulator of IKr and a promising anti-arrhythmic drug target.

Abstract

The hERG1 potassium channel conducts the critical cardiac repolarizing current IKr. Given its role in mediating electrical excitability, several groups have investigated the antiarrhythmic capacity of hERG1 activators in cardiac diseases marked by prolonged action potential duration (APD), such as long QT Syndrome. hERG1 activators have had limited success due to their off-target effects. We recently generated a single chain variable fragment (scFv) antibody, scFv2.10, that selectively binds the hERG1 Per-Arnt-Sim (PAS) domain. The PAS domain binds to the C-terminal cyclic nucleotide binding homology domain (CNBHD) and slows channel activation and promotes inactivation. scFv2.10 disrupts the PAS-CNBHD interaction, which in turn causes a two-fold increase in the time course of hERG1 activation and inactivation recovery, thereby increasing hERG1 current in HEK293 cells. In human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), disrupting the PAS-CNBHD interaction with scFv2.10 increases IKr and shortens APD. We hypothesized that the hERG1 PAS domain could represent a novel therapeutic target for diseases of impaired cardiac repolarization. To test this, we measured the antiarrhythmic capacity of scFv2.10 on a novel hiPSC-CM line derived from a patient with Jervell and Lange Nielsen syndrome (JLN). JLN syndrome is a severe form of long QT Syndrome Type 1 characterized by increased APD and incidence of sudden cardiac death. Compared to hiPSC-CMs derived from a healthy genetic background, JLN hiPSC-CMs display hallmarks of pro-arrhythmia including prolonged APD, increased action potential variability, and early afterdepolarizations. scFv2.10 reduced APD, action potential variability, and the incidence of early afterdepolarizations in JLN hiPSC-CMs, compared to GFP controls. These data demonstrate that the hERG1 PAS domain is a potential therapeutic target to treat disorders of electrical excitability.