Abstract
Small-conductance (KCa2.1-2.3) and intermediate-conductance (KCa3.1) calcium-activated K+ channels are critically involved in modulating calcium-signaling cascades and membrane potential in both excitable and nonexcitable cells. Activators of these channels constitute useful pharmacological tools and potential new drugs for the treatment of ataxia, epilepsy, and hypertension. Here, we used the neuroprotectant riluzole as a template for the design of KCa2/3 channel activators that are potent enough for in vivo studies. Of a library of 41 benzothiazoles, we identified 2 compounds, anthra[2,1-d]thiazol-2-ylamine (SKA-20) and naphtho[1,2-d]thiazol-2-ylamine (SKA-31), which are 10 to 20 times more potent than riluzole and activate KCa2.1 with EC50 values of 430 nM and 2.9 μM, KCa2.2 with an EC50 value of 1.9 μM, KCa2.3 with EC50 values of 1.2 and 2.9 μM, and KCa3.1 with EC50 values of 115 and 260 nM. Likewise, SKA-20 and SKA-31 activated native KCa2.3 and KCa3.1 channels in murine endothelial cells, and the more “drug-like” SKA-31 (half-life of 12 h) potentiated endothelium-derived hyperpolarizing factor-mediated dilations of carotid arteries from KCa3.1(+/+) mice but not from KCa3.1(-/-) mice. Administration of 10 and 30 mg/kg SKA-31 lowered mean arterial blood pressure by 4 and 6 mm Hg in normotensive mice and by 12 mm Hg in angiotensin-II-induced hypertension. These effects were absent in KCa3.1-deficient mice. In conclusion, with SKA-31, we have designed a new pharmacological tool to define the functional role of the KCa2/3 channel activation in vivo. The blood pressure-lowering effect of SKA-31 suggests KCa3.1 channel activation as a new therapeutic principle for the treatment of hypertension.
Footnotes
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This work was supported by the National Institutes of Health National Institute of Neurological Disorders and Stroke [Grant R21-NS052165] and the Deutsche Forschungsgemeinschaft [Grants from project A11 of SFB 593 and KO1899/10-1].
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H.W. and R.K. contributed equally to this work.
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ABBREVIATIONS: KCa, Ca2+-activated K+ channel; EDHF, endothelium-derived hyperpolarizing factor; ACh, acetylcholine; CA, carotid artery; CAEC, carotid artery endothelial cell; HPLC, high-performance liquid chromatography; RT, room temperature; MS, mass spectrometry; NMDA, N-methyl-d-aspartate; DMSO, dimethyl sulfoxide; HERG, human ether-a-go-go-related gene; HEK, human embryonic kidney; PBS, phosphate-buffered saline; MOPS, 3-(N-morpholino)propanesulfonic acid; TLC, thin-layer chromatography; WT, wild type; EBIO, 1-ethylbenzimidazolin-2-one; Kv, voltage-gated K+ channel; MAP, mean arterial pressure; NS8593, N-[(1R)-1,2,3,4-tetrahydro-1-naphthalenyl]-1H-benzimidazol-2-amine hydrochloride; riluzole, 2-amino-6-[trifluoromethoxy]benzothiazole; SKA-1, 2-aminobenzothiazole; SKA-2, 2-amino-6-methoxybenzothiazole; SKA-3, 2-amino-6-chlorobenzothiazole; SKA-4, 2-amino-6-nitrobenzothiazole; SKA-5, 2-mercapto-5-methoxybenzothiazole; SKA-6, 2-amino-6-nitrobenzothiazole; SKA-7, 2-amino-6-benzylbenzothiazole; SKA-8, 2-amino-5-trifluoromethoxybenzothiazole; SKA-11, 2-amino-6-[chlorodifluoromethoxy]benzothiazole; SKA-12, 5-trifluoromethoxy-1H-benzimidazol-2-amine; SKA-13, 5-chloro-6-methoxy-benzothiazol-2-amine; SKA-16, 2-amino-6-[methylsulfonyl]benzothiazole; SKA-17, 5,6-dimethoxy-1,3-benzothiazol-2-amine; SKA-18, 2-amino-6-fluorobenzothiazole; SKA-19, 2-amino-6-trifluoromethylthio-benzothiazole; SKA-20, anthra[2,1-d]thiazol-2-ylamine; SKA-21, 2-amino-6,11-dihydro-6,11-dioxoanthra[2,1-d]-thiazole; SKA-22, 2-amino-6-benzoylbenzothiazole; SKA-24, 6-acetyl-2-aminobenzothiazole; SKA-25, 2-aminobenzo[1,2-d:4,3-d′]bisthiazole; SKA-26, 2-amino-7H-pyrano[2,3-g]benzothiazol-7-one; SKA-29, 6,7-dihydro-5H-indeno[5,6-d]thiazol-2-amine; SKA-30, 6,7-dihydro[1,4]dioxino[2,3-f]-[1,3]benzothiazol-2-amine; SKA-31, naphtho[1,2-a]thiazol-2-ylamine; SKA-32, 2-amino-6-phenoxybenzothiazole; SKA-34, 2-amino-5-trifluoromethyl)-benzothiazole; SKA-35, 2-amino-6-(trifluoromethoxy)benzothiazole; SKA-36, 2,6-diaminobenzothiazole; SKA-41, 4-(4-trifluoromethoxyphenyl)thiazol-2-amine; SKA-42, 2-amino-5,6-difluorobenzothiazole; SKA-44, 2-amino-6,7,8,9-tetrahydronaphtho[2,1-d]thiazole; SKA-45, naphtho[2,1-d]thiazol-2-amine; SKA-46, 5-trifluoromethoxy-1,3-dihydro-2H-benzimidazol-2-thione; SKA-47, 5-[difluoromethoxy]-2-mercapto-1H-benzimidazole; SKA-48, 2-amino-5,6-dimethoxybenzothiazole; SKA-49, 6,7,8,9-tetrahydronaphtho[1,2-d]thiazol-2-amine; SKA-50, 2,6-diaminobenzo[1,2-d:4,5-d′]bisthiazole; SKA-51, 2-amino-6-[trifluoromethyl]benzothiazole; SKA-53, 2-amino-6-methyl-benzo[1,2-d. 5,4-d′]bisthiazole; SKA-56, thiazolo[4,5-c]quinolin-2-ylamine; UCL1684, 6,10-diaza-3(1,3),8(1,4)-dibenzena-1,5(1,4)-diquinolinacyclodecaphane; UCL1848, 8,14-diaza-1,7(1,4)-diquinolinacyclotetradecaphane; MDL105519, (E)-3-(2-phenyl-2-carboxyethenyl)-4,6-dichloro-1H-indole-2-carboxylic acid; TRAM-34, 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole; NS309, 6,7-dichloro-1H-indole-2,3-dione 3-oxime; CGP-39653, (E)-2-amino-4-propyl-5-phosphono-3-pentenoic acid; ICA-17043, bis(4-fluorophenyl)phenylacetamide.
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The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material. - Received August 15, 2008.
- Accepted October 27, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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Naphtho[1,2-d]thiazol-2-ylamine (SKA-31), a New Activator of KCa2 and KCa3.1 Potassium Channels, Potentiates the Endothelium-Derived Hyperpolarizing Factor Response and Lowers Blood Pressure
