Molecular imaging of alpha7 nicotinic acetylcholine receptors: design and evaluation of the potent radioligand [18F]NS10743.
OBJECTIVE
The outstanding diversity of cellular properties mediated by neuronal and nonneuronal alpha7 nicotinic acetylcholine receptors (alpha7 nAChR) points to the diagnostic potential of quantitative nuclear molecular imaging of alpha7 nAChR in neurology and oncology. It was our goal to radiolabel the alpha7 nAChR agonist 4-[5-(4-fluoro-phenyl)-[1,3,4]oxadiazol-2-yl]-1,4-diaza-bicyclo[3.2.2]nonane (NS10743) and to assess the selectivity of [(18)F]NS10743 binding site occupancy in animal experiments.


METHODS
[(18)F]NS10743 was synthesized by nucleophilic substitution of the nitro precursor. In vitro receptor affinity and selectivity were assessed by radioligand competition and autoradiography. The radiotracer properties were evaluated in female CD-1 mice by brain autoradiography and organ distribution. Target specificity was validated after treatment with SSR180711 (10 mg/kg, intraperitoneal), and metabolic stability was investigated using radio-HPLC.


RESULTS
The specific activity of [(18)F]NS10743 exceeded 150 GBq/micromol at a radiochemical purity >99%. In vitro, NS10743 and [(18)F]NS10743 showed high affinity and specificity towards alpha7 nAChR. The brain permeation of [(18)F]NS10743 was fast and sufficient with values of 4.83 and 1.60% injected dose per gram and brain to plasma ratios of 3.83 and 2.05 at 5 and 60 min after radiotracer administration. Brain autoradiography and organ distribution showed target-specific accumulation of [(18)F]NS10743 in brain substructures and various alpha7 nAChR-expressing organs. The radiotracer showed a high metabolic stability in vivo with a single polar radiometabolite, which did not cross the blood-brain barrier.


CONCLUSIONS
The good in vitro and in vivo features of [(18)F]NS10743 make this radioligand a promising candidate for quantitative in vivo imaging of alpha7 nAChR expression and encourage further investigations.
Deuther-Conrad
Winnie
W
Institute of Interdisciplinary Isotope Research, Leipzig, Germany. conrad@iif-leipzig.de
Fischer
Steffen
S
Hiller
Achim
A
Nielsen
Elsebet Østergaard
EØ
Timmermann
Daniel Brunicardi
DB
Steinbach
Jörg
J
Sabri
Osama
O
Peters
Dan
D
Brust
Peter
P
D000818:Animals; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D015195:Drug Design; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000378:metabolism*; D006801:Humans; D008495:Medical Oncology / Q000379:methods; D051379:Mice; D009462:Neurology / Q000379:methods; D019275:Radiopharmaceuticals / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000235:genetics* / Q000378:metabolism; D015203:Reproducibility of Results; D064569:alpha7 Nicotinic Acetylcholine Receptor
D019086:Bridged Bicyclo Compounds, Heterocyclic; C579167:Chrna7 protein, human; C579166:Chrna7 protein, mouse; D019275:Radiopharmaceuticals; D011978:Receptors, Nicotinic; C516833:SSR180711; D064569:alpha7 Nicotinic Acetylcholine Receptor; C403530:nicotinic receptor alpha3beta4; C403531:nicotinic receptor alpha4beta2; D019788:Fluorodeoxyglucose F18