Long QT syndrome (LQTS) increases the risk of torsades de pointes, a ventricular arrhythmia that can degenerate into ventricular fibrillation and sudden death. LQTS patients are currently treated with -adrenergic blockers;however, failure of -blocker therapy is significant in young children and women. ICD therapy has been recommended for this subset of high-risk LQTS patients;however, devices are expensive and not available to all patients in need. Thus, there remains a need for the discovery and development of additional treatment options for LQTS. Mechanism-based pharmacotherapy (e.g., mexilitine for LQT3) has been explored in the past, but little is known about the mechanisms of action or therapeutic utility of the recently discovered hERG1 channel activators. hERG1 activators shorten cardiac action potentials by altering channel gating, either by suppression of P-type inactivation, slowing deactivation, increasing channel open probability or a combination of these effects. We have mapped the putative binding site for several known hERG1 activators and correlated their binding site to primary mechanism of action. Here we propose to define the structural basis of altered channel gating induced by these drugs. We will also determine if hERG1 agonists can rescue the function of trafficking-deficient LQTS-associated mutant channels. A molecular-based understanding of the mechanisms of action of known hERG1 activators will enable rational drug design of additional compounds, and facilitate the design of preclinical tests for efficacy and safety. We will utilize biophysical (whole cell voltage clamp, cut-open Vaseline gap voltage clamp), biochemical (Western blot) and modeling techniques to characterize wild-type and mutant hERG1 channels heterologously expressed in Xenopus oocytes and HEK293 cells to characterize the mechanisms of action of four hERG1 channel activators: RPR260263, PD- 118057, NS1643 and ICA-105574.
The Aims of the project are to 1) determine binding stoichiometry of hERG1 channel activators, 2) define the mechanism of suppressed channel inactivation by hERG1 channel activators, 3) characterize electromechanical uncoupling induced by hERG1 channel activators, and 4) screen hERG1 activators for ability to rescue trafficking of LQTS-associated mutant channels. It is anticipated that a molecular-based understanding of the mechanisms of action of known hERG1 activators will enable rational drug design of additional compounds, and facilitate the design of preclinical tests for efficacy and safety.

Public Health Relevance

Outward current conducted by hERG1 potassium channels is an important determinant of normal cardiac electrical activity. Loss of function mutations in these channels or block of the channels by a wide spectrum of commonly used medications can cause induce dysrhythmia of the heart and lead to heart attacks and sudden death. The goals of this project are to understand the molecular mechanisms of a new class of drugs called hERG1 channel activators that counteract the functional effects of inherited mutations in hERG1 gene or blockers.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL055236-17
Application #
8521339
Study Section
Electrical Signaling, Ion Transport, and Arrhythmias Study Section (ESTA)
Program Officer
Lathrop, David A
Project Start
1996-07-01
Project End
2016-07-31
Budget Start
2013-08-01
Budget End
2014-07-31
Support Year
17
Fiscal Year
2013
Total Cost
$354,620
Indirect Cost
$116,620
Name
University of Utah
Department
Physiology
Type
Schools of Medicine
DUNS #
009095365
City
Salt Lake City
State
UT
Country
United States
Zip Code
84112
Wu, Wei; Sachse, Frank B; Gardner, Alison et al. (2014) Stoichiometry of altered hERG1 channel gating by small molecule activators. J Gen Physiol 143:499-512
Thomson, Steven J; Hansen, Angela; Sanguinetti, Michael C (2014) Concerted all-or-none subunit interactions mediate slow deactivation of human ether-à-go-go-related gene K+ channels. J Biol Chem 289:23428-36
Wu, Wei; Gardner, Alison; Sanguinetti, Michael C (2014) Cooperative subunit interactions mediate fast C-type inactivation of hERG1 K+ channels. J Physiol 592:4465-80
Sanguinetti, Michael C (2014) HERG1 channel agonists and cardiac arrhythmia. Curr Opin Pharmacol 15:22-7
Marzian, Stefanie; Stansfeld, Phillip J; Rapedius, Markus et al. (2013) Side pockets provide the basis for a new mechanism of Kv channel-specific inhibition. Nat Chem Biol 9:507-13
Garg, Vivek; Stary-Weinzinger, Anna; Sanguinetti, Michael C (2013) ICA-105574 interacts with a common binding site to elicit opposite effects on inactivation gating of EAG and ERG potassium channels. Mol Pharmacol 83:805-13
Garg, Vivek; Stary-Weinzinger, Anna; Sachse, Frank et al. (2011) Molecular determinants for activation of human ether-a-go-go-related gene 1 potassium channels by 3-nitro-n-(4-phenoxyphenyl) benzamide. Mol Pharmacol 80:630-7
Grunnet, Morten; Abbruzzese, Jennifer; Sachse, Frank B et al. (2011) Molecular determinants of human ether-a-go-go-related gene 1 (hERG1) K+ channel activation by NS1643. Mol Pharmacol 79:1-9
Abbruzzese, Jennifer; Sachse, Frank B; Tristani-Firouzi, Martin et al. (2010) Modification of hERG1 channel gating by Cd2+. J Gen Physiol 136:203-24
Sanguinetti, Michael C (2010) HERG1 channelopathies. Pflugers Arch 460:265-76

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