名称:
Synthesis and Evaluation of N-Methyl and S-Methyl 11C-Labeled 6-Methylthio-2-(4′-N,N-dimethylamino)phenylimidazo[1,2-a]pyridines as Radioligands for Imaging β-Amyloid Plaques in Alzheimer’s Disease
摘要:
6-Thiolato-substituted 2-(4'-N,N-dimethylamino)phenylimidazo[1,2-a]pyridines (RS-IMPYs; 1-4) were synthesized as candidates for labeling with carbon-11 (t(1/2) = 20.4 min) and imaging of A(beta) plaques in living human brain using positron emission tomography (PET). K-i values for binding of these ligands to Alzheimer's disease brain homogenates were measured in vitro,against tritium-labeled 6 (Pittsburgh compound B). MeS-IMPY (3, K-i = 7.93 nM) was labeled with carbon-11 at its S- or N-methyl position to give [C-11]7 or [C-11]8, respectively. After injection into rats, [C-11]7 or [C-11]8 gave moderately high brain uptakes of radioactivity followed by rapid washout to low levels. The ratio of radioactivity at maximal uptake to that at 60 min reached 18.7 for [C-11]7. [C-11]7 behaved similarly in mouse and monkey. [C-11]7 also bound selectively to A(beta) plaques in post mortem human Alzheimer's disease brain. Although rapidly metabolized in rat by N-demethylation, [C-11]7 was stable in rat brain homogenates. The ex vivo brain radiometabolites observed in rats have a peripheral origin. Overall, [C-11]7 merits further evaluation in human subjects.