[3H]A-585539 [(1S,4S)-2,2-dimethyl-5-(6-phenylpyridazin-3-yl)-5-aza-2-azoniabicyclo[2.2.1]heptane], a novel high-affinity alpha7 neuronal nicotinic receptor agonist: radioligand binding characterization to rat and human brain.
Receptor binding was characterized for [(3)H](1S,4S)-2,2-dimethyl-5-(6-phenylpyridazin-3-yl)-5-aza-2-azoniabicyclo[2.2.1]heptane ([(3)H]A-585539), a selective high-affinity alpha7 nicotinic acetylcholine receptor (nAChR) agonist with rapid kinetics, low nonspecific binding, and high specific activity. At 4 degrees C, the association was monophasic and rapid (t((1/2)) = 8.0 min); dissociation was slower (t((1/2)) = 64.2 min). The K(d) in rat brain at 4 degrees C was 0.063 nM, whereas at 22 and 37 degrees C, the K(d) values were 0.188 and 0.95 nM, respectively. In contrast, the B(max) (34 fmol/mg protein) was unaffected by temperature. In human cortex, [(3)H]A-585539 bound with a K(d) of 0.066 nM and a B(max) of 5.8 fmol/mg protein at 4 degrees C, whereas under similar conditions, specific [(3)H]methyllycaconitine ([(3)H]MLA) binding was not measurable. A number of agonist and antagonist nAChR ligands displaced binding to rat brain membranes with rank order of affinity similar to that for [(3)H]MLA, and in general, a 5 to 10-fold higher affinity was observed for [(3)H]A-585539 binding. There was also a good correlation of K(i) values between [(3)H]A-585539 binding to rat brain and human cortex. The use of a alpha7/5-hydroxytryptamine type-3 chimera revealed that the N-terminal domain of alpha7 nAChR was sufficient to faithfully reproduce the pharmacology of [(3)H]A-585539 binding. Autoradiographic studies comparing [(3)H]A-585539 and [(125)I]alpha-bungarotoxin revealed a similar pattern of labeling in the rat. In summary, [(3)H]A-585539 was shown to have excellent binding characteristics in rat and human brain and represents the first high-affinity alpha7 agonist radioligand with utility in the characterization of this important nAChR subtype that is targeted toward ameliorating cognitive deficits underlying neuropsychiatric and neurodegenerative disorders.
Anderson
David J
DJ
Neuroscience Research, Global Pharmaceutical Research & Development, Abbott Laboratories, Abbott Park, IL 60064-6125, USA. david.j.anderson@abbott.com
Bunnelle
William
W
Surber
Bruce
B
Du
Jia
J
Surowy
Carol
C
Tribollet
Eliane
E
Marguerat
Anouk
A
Bertrand
Daniel
D
Gopalakrishnan
Murali
M
D000157:Aconitine / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D001549:Benzamides / Q000378:metabolism; D001921:Brain / Q000378:metabolism*; D001643:Bridged Bicyclo Compounds / Q000378:metabolism; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000378:metabolism*; D001952:Bridged-Ring Compounds / Q000378:metabolism; D002038:Bungarotoxins / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D009538:Nicotine / Q000378:metabolism; D018722:Nicotinic Agonists / Q000378:metabolism*; D018733:Nicotinic Antagonists / Q000378:metabolism; D011724:Pyridazines / Q000378:metabolism*; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000378:metabolism*; D013141:Spiro Compounds / Q000378:metabolism; D064569:alpha7 Nicotinic Acetylcholine Receptor
C525870:2,2-dimethyl-5-(6-phenylpyridazin-3-yl)-5-aza-2-azoniabicyclo(2.2.1)heptane; C408128:AR-R 17779; D001549:Benzamides; D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D001952:Bridged-Ring Compounds; D002038:Bungarotoxins; C579167:Chrna7 protein, human; C579165:Chrna7 protein, rat; D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; C498513:PNU-282987; D011724:Pyridazines; D011978:Receptors, Nicotinic; D013141:Spiro Compounds; D064569:alpha7 Nicotinic Acetylcholine Receptor; C054634:methyllycaconitine; D009538:Nicotine; D000157:Aconitine