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.
Hirst
W D
WD
Department of Neuroscience Research, SmithKline Beecham Pharmaceuticals, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW.
Minton
J A
JA
Bromidge
S M
SM
Moss
S F
SF
Latter
A J
AJ
Riley
G
G
Routledge
C
C
Middlemiss
D N
DN
Price
G W
GW
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