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BioAssay: AID 651746

Specificity screen against KCNQ2 for identification of compounds that inhibit KCNQ1 potassium channels

Assay Implementation: Zhihong Lin Ph.D., Kaiping Xu M.S., Alison Neal B.S., Owen McManus Ph.D., Meng Wu Ph.D. ..more
 Tested Compounds
 Tested Compounds
 Tested Substances
 Tested Substances
AID: 651746
Data Source: Johns Hopkins Ion Channel Center (JHICC_KCNQ1_Inh_CounterQ2)
BioAssay Type: Primary, Primary Screening, Single Concentration Activity Observed
Depositor Category: NIH Molecular Libraries Probe Production Network
Deposit Date: 2012-11-02

Data Table ( Complete ):           View Active Data    View All Data
Sequence: potassium voltage-gated channel subfamily KQT member 2 [Rattus norvegicus]
Description ..   
Protein Family: KCNQ voltage-gated potassium channel

Gene:KCNQ2     Related Protein 3D Structures     More BioActivity Data..
BioActive Compounds: 1095
Related Experiments
2642Primary cell-based high-throughput screening assay for identification of compounds that inhibit KCNQ1 potassium channelsScreeningdepositor-specified cross reference
2697Summary of assays for compounds that inhibit KCNQ1 potassium channelsSummarydepositor-specified cross reference
588353Validation (re-confirmation) assay for identification of compounds that inhibit KCNQ1 potassium channelsScreeningdepositor-specified cross reference
588366Counter screen assay of the parental CHO cells for identification of compounds that inhibit KCNQ1 potassium channelsOtherdepositor-specified cross reference
624120Validation for compounds that inhibit KCNQ1 potassium channels on automated electrophysiology assayOtherdepositor-specified cross reference
652147Specificity screen against KCNQ1/KCNE1 for identification of compounds that inhibit KCNQ1 potassium channelsScreeningdepositor-specified cross reference
Data Source: Johns Hopkins Ion Channel Center (JHICC_KCNQ1_Inh_CounterQ2)
BioAssay Type: Primary, Primary Screening, Single Concentration Activity Observed, Duplicate

Source (MLPCN Center Name): Johns Hopkins Ion Channel Center (JHICC)
Center Affiliation: Johns Hopkins University, School of Medicine
Screening Center PI: Min Li, Ph.D.
Assay Provider: Meng Wu, Ph.D.
Network: Molecular Libraries Probe Production Centers Network (MLPCN)
Grant Proposal Number: 1 R03 MH090837-01
Grant Proposal PI: Meng Wu, Ph.D., Johns Hopkins University School of Medicine
Assay Implementation: Zhihong Lin Ph.D., Kaiping Xu M.S., Alison Neal B.S., Owen McManus Ph.D., Meng Wu Ph.D.

Name: Specificity screen against KCNQ2 for identification of compounds that inhibit KCNQ1 potassium channels


Voltage-gated potassium channels [1,2] are tetrameric membrane proteins that selectively conduct K+ across cellular membranes, thus open, close, and inactivate in response to changes in transmembrane voltage [3]. Individual subtypes of these potassium channels often have a unique expression patterns allowing cells to "fine-tune" membrane potentials and excitability according to their respective physiological functions [4]. Dysfunctions of these electrical excitability controlling proteins, either congenital or acquired, are attributed to a variety of diseases [5,6], such as cardiac arrhythmias, diabetes, hypertension, and epilepsy. Specific modulation of individual potassium channel types therefore represent an enormous potential for the development of physiological tool compounds and new drugs [7-9].

KCNQ1 (Kv7.1, KvLQT) [10,11] is an alpha-subunit subtype of the voltage-gated KCNQ potassium channel family, which is composed of five members of KCNQ1-KCNQ5. They share between 30% and 65% amino acid identity. A classical KCNQ alpha-subunit is composed of six transmembrane segments, including a voltage-sensor segment and a pore domain [12-15]. Unique from other members of KCNQ family [16], KCNQ1 has been generally absent from neuronal tissues, mainly expressed in heart, kidney, small intestine, pancreas, prostate and other non-excitable epithelial tissues. Also contrast to other members of KCNQ family which form both alpha-subunit homo- and heterotetrameric channels, KCNQ1 channels only form alpha-subunit homotetramers [10]. They commonly co-assemble with beta-subunit KCNE proteins to give rise to functional variations in different tissues.

These molecular assemblies have afforded KCNQ1 with two important physiological functions: 1) repolarization of the cardiac tissue following an action potential and 2) water and salt transport in epithelial tissues. Mutations in this gene are associated with hereditary long QT syndrome, diabetics [18], Romano-Ward syndrome, Jervell and Lange-Nielsen syndrome [19] and familial atrial fibrillation [20], as well as impairment of cyclic AMP-stimulated intestinal secretion of chloride ions related to cystic fibrosis [21,22] and pathological forms of secretary diarrhea [23-25]. Furthermore, drug-induced acquired KCNQ1 and KCNQ1/KCNE dysfunctions also raise concerns of KCNQ1/KCNE as potential hERG-like drug safety issue in pharmaceutical development [17].

Recently, evaluation of KCNQ1 channel activators or potentiators has generated interest as possible agents to counteract the loss of delayed rectifier function in LQT syndromes, as well as a counter screen target for activators of other KCNQ family members. KCNQ2 channels are widely expressed in neuronal tissues and selectivity against this channel was evaluated for KCNQ1 inhibitor compounds to aid in defining the pharmacological profile of select compounds identified in a high throughput screen of KCNQ1 using the MLSMR library of >300,000-500,000 compounds. Active compounds were evaluated for effects on KCNQ1 and KCNQ2 using a thallium influx assay.

Principle of the assay

The Tl+ ion, which is permeable through potassium channels, serves as a surrogate for K+ flux [26]. The thallium-sensitive dye is loaded into cells, and, in the absence of Tl+, exhibits very low basal fluorescence. Upon the addition of Tl+ to depolarized cells expressing KCNQ2 potassium channels, extracellular Tl+ enters cells through open KCNQ2 channels, and when bound to the dye, produces an increase in fluorescent signal that is monitored in real-time by a fluorescence imaging plate reader [27, 28]. If the activity of KCNQ2 is inhibited by a test compound, the fluorescent signal increase will decrease relative to control.

Assay overview:

A specificity screen against KCNQ2 was developed to evaluate compounds that inhibit KCNQ1 potassium channels in a primary screen (AID: 2642). A CHO-K1 cell line stably expressing KCNQ2 potassium channels is employed. The cells are treated with test compounds, followed by measurement of intracellular thallium, as monitored by a commercially available thallium-sensitive fluorescent dye, FluxOR. Compound effect was evaluated by the calculated FluxOR fluorescence ratio, normalized with negative controls, from duplicates. Compounds that show deviation in the FluxOR fluorescence in KCNQ2 cells that differ from buffer controls are considered non-specific hits.


KCNQ1, KCNQ2, HTS assay, counter, CHO-K1, 384, antagonist, inhibitor, FDSS, Thallium, fluorescence, Kinetic, FluxOR, JHICC, Johns Hopkins, MLSMR, Molecular Libraries Probe Production Centers Network, MLPCN

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4. Pischalnikova, A., and Sokolova, O. The Domain and Conformational Organization in Potassium Voltage-Gated Ion Channels. Journal of Neuroimmune Pharmacology 4(1), 71-82 (2009) PMID: 18836841
5. Peroz, D., Rodriguez, N., Choveau, F., et al. Kv7.1 (KCNQ1) properties and channelopathies. The Journal of Physiology 586(7), 1785-1789 (2008) PMID: 18174212
6. Cannon, S. C. Physiologic Principles Underlying Ion Channelopathies. Neurotherapeutics 4(2), 174-183 (2007) PMID: 17395127
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10. Jespersen, T., Grunnet, M., and Olesen, S.-P. The KCNQ1 Potassium Channel: From Gene to Physiological Function. Physiology 20(6), 408-416 (2005) PMID: 16287990
11. Mackie, A. R., and Byron, K. L. Cardiovascular KCNQ (Kv7) Potassium Channels: Physiological Regulators and New Targets for Therapeutic Intervention. Mol Pharmacol 74(5), 1171-1179 (2008) PMID: 18684841
12. Maljevic, S., Wuttke, T. V., and Lerche, H. Nervous system KV7 disorders: breakdown of a subthreshold brake. The Journal of Physiology 586(7), 1791-1801 (2008) PMID: 18238816
13. Robbins, J. KCNQ potassium channels: physiology, pathophysiology, and pharmacology. Pharmacology & Therapeutics 90(1), 1-19 (2001) PMID: 11448722
14. Hernandez, C. C., Zaika, O., Tolstykh, G. P., et al. Regulation of neural KCNQ channels: signalling pathways, structural motifs and functional implications. The Journal of Physiology 586(7), 1811-1821 (2008) PMID: 18238808
15. Delmas, P., and Brown, D. A. Pathways modulating neural KCNQ/M (Kv7) potassium channels. Nat Rev Neurosci 6(11), 850-862 (2005) PMID: 16261179
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17. Towart, R., Linders, J. T. M., Hermans, A. N., et al. Blockade of the IKs potassium channel: An overlooked cardiovascular liability in drug safety screening? Journal of Pharmacological and Toxicological Methods 60(1), 1-10 (2009) PMID: 19439185
18. Jonsson, A., Isomaa, B., Tuomi, T., et al. A variant in the KCNQ1 gene predicts future type 2 diabetes and mediates impaired insulin secretion. Diabetes, 58(10) 2409-13 (2009) PMID: 19584308
19. Schmitt, N., Schwarz, M., Peretz, A., et al. A recessive C-terminal Jervell and Lange-Nielsen mutation of the KCNQ1 channel impairs subunit assembly. EMBO J 19(3), 332-340 (2000) PMID: 10654932
20. OMIM. (2009)
21. Namkung, W., Song, Y., Mills, A. D., et al. In Situ Measurement of Airway Surface Liquid [K+] Using a Ratioable K+-sensitive Fluorescent Dye. J. Biol. Chem. 284(23), 15916-15926 (2009) PMID: 19364771
22. Moser, S., Harron, S., Crack, J., et al. Multiple KCNQ Potassium Channel Subtypes Mediate Basal Anion Secretion from the Human Airway Epithelial Cell Line Calu-3. Journal of Membrane Biology 221(3), 153-163 (2008) PMID: 18264812
23. Schroeder, B. C., Waldegger, S., Fehr, S., et al. A constitutively open potassium channel formed by KCNQ1 and KCNE3. Nature 403(6766), 196-199 (2000) PMID: 10646604
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25. Matos, J. E., Sausbier, M., Beranek, G., et al. Role of cholinergic-activated K Ca 1.1 (BK), K Ca 3.1 (SK4) and K V 7.1 (KCNQ1) channels in mouse colonic Cl - secretion. Acta Physiologica 189(3), 251-258 (2007) PMID: 17305705
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Protocol for the KCNQ2 thallium assay

1. Cell culture: Cells are routinely cultured in DMEM/F12 medium, supplemented with 10% Fetal Bovine Serum (FBS), 50 IU/ml penicillin, 50 ug/ml streptomycin, and 500 ug/ml G418
2. Cell plating: Add 50 ul/well of 120,000 cells/ml KCNQ2 cells re-suspended in DMEM/F12 medium with 10% FBS
3. Incubate overnight at 37C and 5% CO2
4. Remove medium and add 25 ul /well of 1x FluxOR solution to cells
5. Incubate 90 minutes at room temperature (RT) in the dark
6. Prepare 7.5X compound plates and control plates on Cybi-Well system: test compounds are prepared using assay buffer; controls are assay buffer (IC0), and inhibitor control XE991 (all with DMSO concentrations matched to that of test compounds)
7. Remove FluxOR dye solution and add 20 ul /well of assay buffer to cells
8. Add 4 ul of 7.5x compound stock into the cell plates via Cybi-Well system
9. Incubate all cell plates for 20 minutes at RT in the dark
10. Prepare 5x stimulus buffer containing 12.5 mM K2SO4 and 12.5 mM Tl2SO4
11. Load cell plates to Hamamatsu FDSS 6000 kinetic imaging plate reader
12. Measure fluorescence for 10 seconds at 1Hz to establish baseline
13. Depolarize cells with 6 ul/well of stimulus buffer and continue measuring fluorescence for 150 seconds
14. Calculate ratio readout (RatioKCNQ2) as F(max-min)/F0
15. Calculate the average and standard deviation for negative and positive controls in each plate, as well as Z and Z' factors [29].
16. Calculate the percentage of tested compounds with the following formula: Percentage (%)=100* (Ratio(cmpd)- AvgRatio(Buffer))/(AvgRatio(XE-991)-AvgRatio(Buffer)); Percentage(%): percentage change of compound readout over those of negative controls (Buffer), Ratio(cmpd): Ratio of the test compound. AvgRatio(Buffer): Ratio average of the negative controls with Buffer, Ratio(XE-991): Ratio of XE-991.
17. Outcome assignment: If the compound (the average of the duplicates of the Percentage (%, RatioPercentage) as readout) causes more than those of negative controls (Buffer) plus 5SD of negative controls (Buffer), the compound is considered to be active (Value=2). Otherwise, it is designated as inactive (Value=1).
18. Score assignment: An active test compound is assigned a score between 5 and 100 by calculation of Integer((log10([RatioPercentKCNQ2])-1.77)/0.0047+5), RatioPercentKCNQ2, as in the result definition. The inactive test compounds are assigned a score of 0.

List of reagents

1. KCNQ2-CHO cell lines (provided by JHICC)
2. PBS: pH7.4 (Gibco, Cat #10010)
3. Medium: DMEM/F12 50/50 (Mediatech, Cat #15-090-CV)
4. Fetal Bovine Serum (Gemini, Cat #100106)
5. 200 mM L-Glutamine (Gibco, Cat #25030)
6. 100x Penicillin-Streptomycin (Mediatech, Cat #30-001-CI)
7. 0.05% Trypsin-EDTA (Gibco, Cat #25300)
8. Geneticin: (Gibco, Cat #11811-031)
9. HEPES (Sigma, Cat #H4034)
10. XE-991 (Tocris Bioscience)
11. FluxOR detection kit (Invitrogen, Cat #F10017): FluxOR, assay buffer and stimulus buffer.
12. Triple-layer flask (VWR, Cat #62407-082)
13. BD Biocoat 384-well plates (BD, Cat #354663 and Lot #7346273)
Possible artifacts of this assay can include, but are not limited to: non-intended chemicals or dust in or on wells of the microtiter plate, compounds that non-specifically modulate the cell host or the targeted activity, and compounds that quench or emit light or fluorescence within the well. All test compound concentrations reported are nominal; the specific concentration for a particular test compound may vary based upon the actual sample provided by the MLSMR.
Categorized Comment - additional comments and annotations
From PubChem:
Assay Cell Type: CHO-K1
Result Definitions
OutcomeThe BioAssay activity outcomeOutcome
ScoreThe BioAssay activity ranking scoreInteger
1RatioPercentKCNQ2 (10μM**)Average percent inhibition of triplicate tests of each test compound readout (Percentage (%)) at a concentration of 10 microMFloat

** Test Concentration.
Additional Information
Grant Number: 1 R03 MH090837-01

Data Table (Concise)
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