Characterization of [(125)I]-SB-258585 binding to human recombinant and native 5-HT(6) receptors in rat, pig and human brain tissue.
SB-258585 (4-Iodo-N-[4-methoxy-3-(4-methyl-piperazin-1-yl)-phenyl]-benzen esulphonamide) is a high affinity ligand at 5-HT(6) receptors. It displays over 100 fold selectivity for the 5-HT(6) receptor over all other 5-HT receptors tested so far. SB-258585 has been radiolabelled, to high specific activity, for its characterization as a 5-HT(6) receptor selective radioligand. [(125)I]-SB-258585 bound, with high affinity, to a single population of receptors in a cell line expressing human recombinant 5-HT(6) receptors. Kinetic and saturation binding experiments gave pK(D) values of 9.01+/-0.09 and 9.09+/-0.02, respectively. In membranes derived from rat or pig striatum and human caudate putamen, [(125)I]-SB-258585 labelled a single site with high levels (>60%) of specific binding. Saturation analysis revealed pK(D) values of 8.56+/-0.07 for rat, 8.60+/-0.10 for pig and 8.90+/-0.02 for human. B(max) values for the tissues ranged from 173+/-23 and 181+/-25 fmol mg(-1) protein in rat and pig striatum, respectively, to 215+/-41 fmol mg(-1) protein in human caudate putamen. The pK(i) rank order of potency for a number of compounds, determined in competition binding assays with [(125)I]-SB-258585, at human caudate putamen membranes was: SB-271046>SB-258585>SB-214111>methiothepin>clozapine>5-Me-OT>5-HT>Ro 04-6790>mianserin>ritanserin=amitriptyline>5-CT>mesulergine. Similar profiles were obtained from pig and rat striatal membranes and recombinant 5-HT(6) receptors; data from the latter correlated well with [(3)H]-LSD binding. Thus, [(125)I]-SB-258585 is a high affinity, selective radioligand which can be used to label both recombinant and native 5-HT(6) receptors and will facilitate further characterization of this receptor subtype in animal and human tissues.
Department of Neuroscience Research, SmithKline Beecham Pharmaceuticals, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW.
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Hirst
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Minton
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Bromidge
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Moss
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Latter
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Riley
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Routledge
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Middlemiss
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Price
D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D002421:Caudate Nucleus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007457:Iodine Radioisotopes; D008238:Lysergic Acid Diethylamide / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology*; D011699:Putamen / Q000187:drug effects / Q000378:metabolism; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000187:drug effects / Q000378:metabolism*; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D012702:Serotonin Antagonists / Q000494:pharmacology*; D013449:Sulfonamides / Q000494:pharmacology*; D013552:Swine; D014316:Tritium
D007457:Iodine Radioisotopes; D010879:Piperazines; D011985:Receptors, Serotonin; D011994:Recombinant Proteins; C418570:SB 258585; D012702:Serotonin Antagonists; D013449:Sulfonamides; C097216:serotonin 6 receptor; D014316:Tritium; D008238:Lysergic Acid Diethylamide