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 beta-amyloid plaques in Alzheimer's disease.
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 [ (11)C] 7 or [ (11)C] 8, respectively. After injection into rats, [ (11)C] 7 or [ (11)C] 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 [ (11)C] 7. [ (11)C] 7 behaved similarly in mouse and monkey. [ (11)C] 7 also bound selectively to A beta plaques in post mortem human Alzheimer's disease brain. Although rapidly metabolized in rat by N-demethylation, [ (11)C] 7 was stable in rat brain homogenates. The ex vivo brain radiometabolites observed in rats have a peripheral origin. Overall, [ (11)C] 7 merits further evaluation in human subjects.
Cai
Lisheng
L
Molecular Imaging Branch and Clinical Brain Disorders Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland 20892, USA. cail@intra.nimh.nih.gov
Liow
Jeih-San
JS
Zoghbi
Sami S
SS
Cuevas
Jessica
J
Baetas
Cesar
C
Hong
Jinsoo
J
Shetty
H Umesha
HU
Seneca
Nicholas M
NM
Brown
Amira K
AK
Gladding
Robert
R
Temme
Sebastian S
SS
Herman
Mary M
MM
Innis
Robert B
RB
Pike
Victor W
VW
D000544:Alzheimer Disease / Q000000981:diagnostic imaging / Q000378:metabolism*; D016229:Amyloid beta-Peptides / Q000378:metabolism*; D000818:Animals; D001345:Autoradiography; D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism*; D002250:Carbon Radioisotopes; D006801:Humans; D007093:Imidazoles / Q000138:chemical synthesis* / Q000737:chemistry / Q000493:pharmacokinetics; D008253:Macaca mulatta; D008297:Male; D051379:Mice; D049268:Positron-Emission Tomography; D011725:Pyridines / Q000138:chemical synthesis* / Q000737:chemistry / Q000493:pharmacokinetics; D019275:Radiopharmaceuticals / Q000138:chemical synthesis* / Q000737:chemistry / Q000493:pharmacokinetics; D051381:Rats; D014018:Tissue Distribution
D016229:Amyloid beta-Peptides; D002250:Carbon Radioisotopes; D007093:Imidazoles; D011725:Pyridines; D019275:Radiopharmaceuticals