Discovery of (-)-7-methyl-2-exo-[3'-(6-[18F]fluoropyridin-2-yl)-5'-pyridinyl]-7-azabicyclo[2.2.1]heptane, a radiolabeled antagonist for cerebral nicotinic acetylcholine receptor (alpha4beta2-nAChR) with optimal positron emission tomography imaging properties.
Gao Y,
Kuwabara H,
Spivak CE,
Xiao Y,
Kellar K,
Ravert HT,
Kumar A,
Alexander M,
Hilton J,
Wong DF,
Dannals RF,
Horti AG.
Department of Radiology, Division of Nuclear Medicine, The Johns Hopkins UniVersity School of Medicine, 600 North Wolfe Street, Baltimore, Maryland 21287-0816, USA.
Several isomers of 7-methyl-2-exo-([(18)F]fluoropyridinyl-5'-pyridinyl)-7-azabicyclo[2.2.1]heptane have been developed as radioligands with optimized brain kinetics for PET imaging of nAChR. The binding assay demonstrated that all isomers are beta-nAChR selective ligands with Ki = 0.02-0.3 nM. The experimental lipophilicity values of all isomers were in the optimal range for the cerebral radioligands (log D7.4= 0.67-0.99). The isomers with higher binding affinity manifested slow baboon brain kinetics, whereas the isomer with the lowest binding affinity (Ki = 0.3 nM) ((-)-7-methyl-2- exo-[3'-(6-[(18)F]fluoropyridin-2-yl)-5'-pyridinyl]-7-azabicyclo[2.2.1]heptane, [(18)F](-)-6c) and greatest lipophilicity (log D 7.4 = 0.99) exhibited optimal brain kinetics. [(18)F](-)-6c manifests a unique combination of the optimally rapid brain kinetics, high BP and brain uptake, and favorable metabolic profile. Pharmacological studies showed that (-)-6c is an alpha4beta2-nAChR antagonist with low side effects in mice. This combination of imaging properties suggests that [(18)F]-(-)- 6c is a potentially superior replacement for 2-[(18)F]fluoro-A-85380 and 6-[(18)F]fluoro-A-85380, the only available nAChR PET radioligands for humans.
PMID: 18605717 [PubMed - indexed for MEDLINE]