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

J Med Chem. 2008 Aug 14;51(15):4751-64. doi: 10.1021/jm800323d. Epub 2008 Jul 8.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 2,2'-Dipyridyl / analogs & derivatives*
  • 2,2'-Dipyridyl / chemical synthesis
  • 2,2'-Dipyridyl / chemistry
  • 2,2'-Dipyridyl / pharmacology
  • Animals
  • Brain / drug effects*
  • Brain / metabolism*
  • Cell Line
  • Heptanes / chemical synthesis*
  • Heptanes / chemistry
  • Heptanes / pharmacology*
  • Humans
  • Hydrophobic and Hydrophilic Interactions
  • Lipids / chemistry
  • Male
  • Mice
  • Molecular Structure
  • Nicotinic Antagonists / chemical synthesis*
  • Nicotinic Antagonists / chemistry
  • Nicotinic Antagonists / pharmacology*
  • Papio
  • Positron-Emission Tomography
  • Radioligand Assay
  • Rats
  • Receptors, Nicotinic / genetics
  • Receptors, Nicotinic / metabolism*
  • Stereoisomerism
  • Structure-Activity Relationship
  • Time Factors
  • Tropanes / chemical synthesis*
  • Tropanes / chemistry
  • Tropanes / pharmacology*

Substances

  • Heptanes
  • Lipids
  • Nicotinic Antagonists
  • Receptors, Nicotinic
  • Tropanes
  • nicotinic receptor alpha4beta2
  • 2,2'-Dipyridyl