RT Journal Article
SR Electronic
T1 [<sup>3</sup>H]A-585539 [(1<em>S</em>,4<em>S</em>)-2,2-Dimethyl-5-(6-phenylpyridazin-3-yl)-5-aza-2-azoniabicyclo[2.2.1]heptane], a Novel High-Affinity α7 Neuronal Nicotinic Receptor Agonist: Radioligand Binding Characterization to Rat and Human Brain
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 179
OP 187
DO 10.1124/jpet.107.130062
VO 324
IS 1
A1 David J. Anderson
A1 William Bunnelle
A1 Bruce Surber
A1 Jia Du
A1 Carol Surowy
A1 Eliane Tribollet
A1 Anouk Marguerat
A1 Daniel Bertrand
A1 Murali Gopalakrishnan
YR 2008
UL http://jpet.aspetjournals.org/content/324/1/179.abstract
AB Receptor binding was characterized for [3H](1S,4S)-2,2-dimethyl-5-(6-phenylpyridazin-3-yl)-5-aza-2-azoniabicyclo[2.2.1]heptane ([3H]A-585539), a selective high-affinity α7 nicotinic acetylcholine receptor (nAChR) agonist with rapid kinetics, low nonspecific binding, and high specific activity. At 4°C, the association was monophasic and rapid (t½ = 8.0 min); dissociation was slower (t½ = 64.2 min). The Kd in rat brain at 4°C was 0.063 nM, whereas at 22 and 37°C, the Kd values were 0.188 and 0.95 nM, respectively. In contrast, the Bmax (34 fmol/mg protein) was unaffected by temperature. In human cortex, [3H]A-585539 bound with a Kd of 0.066 nM and a Bmax of 5.8 fmol/mg protein at 4°C, whereas under similar conditions, specific [3H]methyllycaconitine ([3H]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 [3H]MLA, and in general, a 5 to 10-fold higher affinity was observed for [3H]A-585539 binding. There was also a good correlation of Ki values between [3H]A-585539 binding to rat brain and human cortex. The use of a α7/5-hydroxytryptamine type-3 chimera revealed that the N-terminal domain of α7 nAChR was sufficient to faithfully reproduce the pharmacology of [3H]A-585539 binding. Autoradiographic studies comparing [3H]A-585539 and [125I]α-bungarotoxin revealed a similar pattern of labeling in the rat. In summary, [3H]A-585539 was shown to have excellent binding characteristics in rat and human brain and represents the first high-affinity α7 agonist radioligand with utility in the characterization of this important nAChR subtype that is targeted toward ameliorating cognitive deficits underlying neuropsychiatric and neurodegenerative disorders. The American Society for Pharmacology and Experimental Therapeutics