Synthesis and in vivo studies of the stereoisomers of N-[11C]methyl-homoepibatidine

Nucl Med Biol. 2001 Aug;28(6):645-55. doi: 10.1016/s0969-8051(01)00225-6.

Abstract

The carbon-11 labeled enantiomers of nicotinic acetylcholine receptor (nAChR) ligand N-[11C]methyl-homoepibatidine have been synthesized to study the neuronal nicotinic acetylcholine receptors (nAChRs). In vivo evaluations were performed in mice and pig using positron emission tomography (PET). The radioligands displayed a strong enantioselectivity. The (-)-enantiomer showed high uptake in the brain while the (+)-enantiomer was rapidly washed out. In metabolite studies in mice >65% unchanged ligand was found in the blood after 60 minutes. No metabolites were found in the brain. After intravenous application of N-[11C]methyl-(-)-homoepibatidine in the pig specific accumulation in the thalamus was seen. Blocking experiments with cytisine showed specific binding consistent with labeling of the alpha4beta2-nAChR-subtype in the brain. Quantitative kinetic modeling of radiotracers in the pig brain was performed using the arterial input function. The brain uptake of the (-)-isomer was best fitted by a three-compartment model. High distribution volumes were found in the thalamus (DV(TOT) = 66.617, DV(S) = 59.910) versus a low uptake in the cerebellum (DV(TOT) = 8.605m, DV(S) = 1.898). The binding characteristics suggest N-[11C]methyl-(-)-homoepibatidine to be suited for PET imaging studies, but high toxicity prevents routine use in humans.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Brain / diagnostic imaging*
  • Brain / drug effects
  • Brain / metabolism
  • Bridged Bicyclo Compounds, Heterocyclic / chemical synthesis
  • Bridged Bicyclo Compounds, Heterocyclic / chemistry
  • Bridged Bicyclo Compounds, Heterocyclic / metabolism*
  • Bridged Bicyclo Compounds, Heterocyclic / toxicity
  • Female
  • Lethal Dose 50
  • Male
  • Mice
  • Mice, Inbred ICR
  • Nicotinic Agonists / chemical synthesis
  • Nicotinic Agonists / chemistry
  • Nicotinic Agonists / metabolism*
  • Nicotinic Agonists / toxicity
  • Pyridines / chemical synthesis
  • Pyridines / chemistry
  • Pyridines / metabolism*
  • Pyridines / toxicity
  • Rats
  • Species Specificity
  • Stereoisomerism
  • Swine
  • Tomography, Emission-Computed

Substances

  • Bridged Bicyclo Compounds, Heterocyclic
  • N-methylhomoepibatidine
  • Nicotinic Agonists
  • Pyridines
  • epibatidine