Synthesis and evaluation of 11C-labeled 6-substituted 2-arylbenzothiazoles as amyloid imaging agents.
The synthesis and evaluation of a series of neutral analogues of thioflavin-T (termed BTA's) with high affinities for aggregated amyloid and a wide range of lipophilicities are reported. Radiolabeling with high specific activity [(11)C]methyl iodide provided derivatives for in vivo evaluation. Brain entry in control mice and baboons was high for nearly all of the analogues at early times after injection, but the clearance rate of radioactivity from brain tissue varied by more than 1 order of magnitude. Upon the basis of its rapid clearance from normal mouse and baboon brain tissues, [N-methyl-(11)C]2-(4'-methylaminophenyl)-6-hydroxybenzothiazole (or [(11)C]6-OH-BTA-1) was selected as the lead compound for further evaluation. The radiolabeled metabolites of [(11)C]6-OH-BTA-1 were polar and did not enter brain. The binding affinities of [N-methyl-(3)H]6-OH-BTA-1 for homogenates of postmortem AD frontal cortex and synthetic Abeta(1-40) fibrils were similar (K(d) = 1.4 nM and 4.7 nM, respectively), but the ligand-to-Abeta peptide binding stoichiometry was approximately 400-fold higher for AD brain than Abeta(1-40) fibrils. Staining of AD frontal cortex tissue sections with 6-OH-BTA-1 indicated the selective binding of the compound to amyloid plaques and cerebrovascular amyloid. The encouraging in vitro and in vivo properties of [(11)C]6-OH-BTA-1 support the choice of this derivative for further evaluation in human subject studies of brain Abeta deposition.
Mathis
Chester A
CA
Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15213, USA. mathisca@msx.upmc.edu
Wang
Yanming
Y
Holt
Daniel P
DP
Huang
Guo-Feng
GF
Debnath
Manik L
ML
Klunk
William E
WE
D016229:Amyloid beta-Peptides / Q000737:chemistry / Q000378:metabolism*; D000814:Aniline Compounds / Q000138:chemical synthesis* / Q000737:chemistry / Q000493:pharmacokinetics; D000818:Animals; D001921:Brain / Q000378:metabolism / Q000473:pathology; D002250:Carbon Radioisotopes; D005260:Female; D066298:In Vitro Techniques; D007553:Isotope Labeling; D008297:Male; D051379:Mice; D010215:Papio; D010446:Peptide Fragments / Q000737:chemistry; D019275:Radiopharmaceuticals / Q000138:chemical synthesis* / Q000737:chemistry / Q000493:pharmacokinetics; D013844:Thiazoles / Q000138:chemical synthesis* / Q000737:chemistry / Q000493:pharmacokinetics; D014055:Tomography, Emission-Computed
C475519:2-(4'-(methylamino)phenyl)-6-hydroxybenzothiazole; D016229:Amyloid beta-Peptides; D000814:Aniline Compounds; D002250:Carbon Radioisotopes; D010446:Peptide Fragments; D019275:Radiopharmaceuticals; D013844:Thiazoles; C078592:amyloid beta-protein (1-40)