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Egly CL, Blackwell DJ, Schmeckpeper J, Delisle BP, Weaver CD, Knollmann BC. A High-Throughput Screening Assay to Identify Drugs that Can Treat Long QT Syndrome Caused by Trafficking-Deficient K V11.1 (hERG) Variants. Mol Pharmacol 2022; 101:236-245. [PMID: 35125346 PMCID: PMC9638947 DOI: 10.1124/molpharm.121.000421] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2021] [Accepted: 01/01/2022] [Indexed: 11/22/2022] Open
Abstract
Loss-of-function (LOF) variants in the KV11.1 potassium channel cause long QT syndrome (LQTS). Most variants disrupt intracellular channel transport (trafficking) to the cell membrane. Since some channel inhibitors improve trafficking of KV11.1 variants, a high-throughput screening (HTS) assay to detect trafficking enhancement would be valuable to the identification of drug candidates. The thallium (Tl+) flux assay technique, widely used for drug screening, was optimized using human embryonic kidney (HEK-293) cells expressing a trafficking-deficient KV11.1 variant in 384-well plates. Assay quality was assessed using Z prime (Z') scores comparing vehicle to E-4031, a drug that increases KV11.1 membrane trafficking. The optimized assay was validated by immunoblot, electrophysiology experiments, and a pilot drug screen. The combination of: 1) truncating the trafficking-deficient variant KV11.1-G601S (KV11.1-G601S-G965*X) with the addition of 2) KV11.1 channel activator (VU0405601) and 3) cesium (Cs+) to the Tl+ flux assay buffer resulted in an outstanding Z' of 0.83. To validate the optimized trafficking assay, we carried out a pilot screen that identified three drugs (ibutilide, azaperone, and azelastine) that increase KV11.1 trafficking. The new assay exhibited 100% sensitivity and specificity. Immunoblot and voltage-clamp experiments confirmed that all three drugs identified by the new assay improved membrane trafficking of two additional LQTS KV11.1 variants. We report two new ways to increase target-specific activity in trafficking assays-genetic modification and channel activation-that yielded a novel HTS assay for identifying drugs that improve membrane expression of pathogenic KV11.1 variants. SIGNIFICANCE STATEMENT: This manuscript reports the development of a high-throughput assay (thallium flux) to identify drugs that can increase function in KV11.1 variants that are trafficking-deficient. Two key aspects that improved the resolving power of the assay and could be transferable to other ion channel trafficking-related assays include genetic modification and channel activation.
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Affiliation(s)
- Christian L Egly
- Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee (C.L.E., D.J.B., J.S., B.C.K.); Department of Physiology, University of Kentucky, Lexington, Kentucky (B.P.D.); and Department of Pharmacology, Vanderbilt University, Nashville, Tennessee (C.D.W.)
| | - Daniel J Blackwell
- Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee (C.L.E., D.J.B., J.S., B.C.K.); Department of Physiology, University of Kentucky, Lexington, Kentucky (B.P.D.); and Department of Pharmacology, Vanderbilt University, Nashville, Tennessee (C.D.W.)
| | - Jeffrey Schmeckpeper
- Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee (C.L.E., D.J.B., J.S., B.C.K.); Department of Physiology, University of Kentucky, Lexington, Kentucky (B.P.D.); and Department of Pharmacology, Vanderbilt University, Nashville, Tennessee (C.D.W.)
| | - Brian P Delisle
- Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee (C.L.E., D.J.B., J.S., B.C.K.); Department of Physiology, University of Kentucky, Lexington, Kentucky (B.P.D.); and Department of Pharmacology, Vanderbilt University, Nashville, Tennessee (C.D.W.)
| | - C David Weaver
- Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee (C.L.E., D.J.B., J.S., B.C.K.); Department of Physiology, University of Kentucky, Lexington, Kentucky (B.P.D.); and Department of Pharmacology, Vanderbilt University, Nashville, Tennessee (C.D.W.)
| | - Björn C Knollmann
- Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee (C.L.E., D.J.B., J.S., B.C.K.); Department of Physiology, University of Kentucky, Lexington, Kentucky (B.P.D.); and Department of Pharmacology, Vanderbilt University, Nashville, Tennessee (C.D.W.)
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Abstract
RATIONALE The class Ic antiarrhythmic drug flecainide prevents ventricular tachyarrhythmia in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT), a disease caused by hyperactive RyR2 (cardiac ryanodine receptor) mediated calcium (Ca) release. Although flecainide inhibits single RyR2 channels in vitro, reports have claimed that RyR2 inhibition by flecainide is not relevant for its mechanism of antiarrhythmic action and concluded that sodium channel block alone is responsible for flecainide's efficacy in CPVT. OBJECTIVE To determine whether RyR2 block independently contributes to flecainide's efficacy for suppressing spontaneous sarcoplasmic reticulum Ca release and for preventing ventricular tachycardia in vivo. METHODS AND RESULTS We synthesized N-methylated flecainide analogues (QX-flecainide and N-methyl flecainide) and showed that N-methylation reduces flecainide's inhibitory potency on RyR2 channels incorporated into artificial lipid bilayers. N-methylation did not alter flecainide's inhibitory activity on human cardiac sodium channels expressed in HEK293T cells. Antiarrhythmic efficacy was tested utilizing a Casq2 (cardiac calsequestrin) knockout (Casq2-/-) CPVT mouse model. In membrane-permeabilized Casq2-/- cardiomyocytes-lacking intact sarcolemma and devoid of sodium channel contribution-flecainide, but not its analogues, suppressed RyR2-mediated Ca release at clinically relevant concentrations. In voltage-clamped, intact Casq2-/- cardiomyocytes pretreated with tetrodotoxin to inhibit sodium channels and isolate the effect of flecainide on RyR2, flecainide significantly reduced the frequency of spontaneous sarcoplasmic reticulum Ca release, while QX-flecainide and N-methyl flecainide did not. In vivo, flecainide effectively suppressed catecholamine-induced ventricular tachyarrhythmias in Casq2-/- mice, whereas N-methyl flecainide had no significant effect on arrhythmia burden, despite comparable sodium channel block. CONCLUSIONS Flecainide remains an effective inhibitor of RyR2-mediated arrhythmogenic Ca release even when cardiac sodium channels are blocked. In mice with CPVT, sodium channel block alone did not prevent ventricular tachycardia. Hence, RyR2 channel inhibition likely constitutes the principal mechanism of antiarrhythmic action of flecainide in CPVT.
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Affiliation(s)
- Dmytro O Kryshtal
- Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Vanderbilt University Medical Center, Nashville, TN (D.O.K., D.J.B., C.L.E., B.C.K.)
| | - Daniel J Blackwell
- Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Vanderbilt University Medical Center, Nashville, TN (D.O.K., D.J.B., C.L.E., B.C.K.)
| | - Christian L Egly
- Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Vanderbilt University Medical Center, Nashville, TN (D.O.K., D.J.B., C.L.E., B.C.K.)
| | - Abigail N Smith
- Department of Chemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, TN (A.N.S., S.M.B., J.N.J.)
| | - Suzanne M Batiste
- Department of Chemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, TN (A.N.S., S.M.B., J.N.J.)
| | - Jeffrey N Johnston
- Department of Chemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, TN (A.N.S., S.M.B., J.N.J.)
| | - Derek R Laver
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, NSW, Australia (D.R.L.)
| | - Bjorn C Knollmann
- Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Vanderbilt University Medical Center, Nashville, TN (D.O.K., D.J.B., C.L.E., B.C.K.)
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Kozek KA, Glazer AM, Ng CA, Blackwell D, Egly CL, Vanags LR, Blair M, Mitchell D, Matreyek KA, Fowler DM, Knollmann BC, Vandenberg JI, Roden DM, Kroncke BM. High-throughput discovery of trafficking-deficient variants in the cardiac potassium channel K V11.1. Heart Rhythm 2020; 17:2180-2189. [PMID: 32522694 DOI: 10.1016/j.hrthm.2020.05.041] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/15/2020] [Revised: 05/27/2020] [Accepted: 05/31/2020] [Indexed: 01/09/2023]
Abstract
BACKGROUND KCHN2 encodes the KV11.1 potassium channel responsible for IKr, a major repolarization current during the cardiomyocyte action potential. Variants in KCNH2 that lead to decreased IKr have been associated with long QT syndrome type 2 (LQT2). The mechanism of LQT2 is most often induced loss of KV11.1 trafficking to the cell surface. Accurately discriminating between variants with normal and abnormal trafficking would aid in understanding the deleterious nature of these variants; however, the volume of reported nonsynonymous KCNH2 variants precludes the use of conventional methods for functional study. OBJECTIVE The purpose of this study was to report a high-throughput, multiplexed screening method for KCNH2 genetic variants capable of measuring the cell surface abundance of hundreds of missense variants in the resulting KV11.1 channel. METHODS We developed a method to quantitate KV11.1 variant trafficking on a pilot region of 11 residues in the S5 helix. RESULTS We generated trafficking scores for 220 of 231 missense variants in the pilot region. For 5 of 5 variants, high-throughput trafficking scores validated when tested in single variant flow cytometry and confocal microscopy experiments. We further explored these results with planar patch electrophysiology and found that loss-of-trafficking variants do not produce IKr. Conversely, but expectedly, some variants that traffic normally were still functionally compromised. CONCLUSION We describe a new method for detecting KV11.1 trafficking-deficient variants in a multiplexed assay. This new method accurately generated trafficking data for variants in KV11.1 and is extendable both to all residues in KV11.1 and to other cell surface proteins.
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Affiliation(s)
- Krystian A Kozek
- Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Andrew M Glazer
- Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Chai-Ann Ng
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia; St Vincent's Clinical School, UNSW Sydney, Darlinghurst, New South Wales, Australia
| | - Daniel Blackwell
- Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Christian L Egly
- Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Loren R Vanags
- Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Marcia Blair
- Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Devyn Mitchell
- Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Kenneth A Matreyek
- Department of Genome Sciences, University of Washington, Seattle, Washington
| | - Douglas M Fowler
- Department of Genome Sciences, University of Washington, Seattle, Washington; Department of Bioengineering, University of Washington, Seattle, Washington
| | - Bjorn C Knollmann
- Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Jamie I Vandenberg
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia; St Vincent's Clinical School, UNSW Sydney, Darlinghurst, New South Wales, Australia
| | - Dan M Roden
- Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Brett M Kroncke
- Vanderbilt Center for Arrhythmia Research and Therapeutics, Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee.
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