The Binding of 2-(4′-Methylaminophenyl)Benzothiazole to Postmortem Brain Homogenates Is Dominated by the Amyloid Component

Abstract

2-(4'-methylaminophenyl)benzothiazole (BTA-1) is an uncharged derivative of thioflavin-T that has high affinity for Abeta fibrils and shows very good brain entry and clearance. In this study, we asked whether BTA-1, at concentrations typical of those achieved during positron emission tomography (PET) studies, could specifically bind to amyloid deposits in the complex milieu of human brain or whether amyloid binding was overshadowed by nonspecific binding, found even in brains that did not contain amyloid deposits. We quantitatively assessed [3H]BTA-1 binding to crude homogenates of postmortem brain obtained from nine Alzheimer's disease (AD) subjects, eight controls, and six subjects with non-AD dementia. BTA-1 binding was >10-fold higher in AD brain, and the majority (94%) of the binding was specific (displaceable). High-affinity [3H]BTA-1 was observed only in AD brain gray matter and was not present in control brain gray matter, AD brain white matter, or cerebellum. The K(d) of [3H]BTA-1 for binding to AD brain (5.8 +/- 0.90 nm) was very similar to the K(d) for binding to synthetic Abeta fibrils. In addition, the K(i) of various BTA analogs for inhibition of [3H]BTA-1 binding to AD brain homogenates was very similar to their K(i) for inhibition of [3H]BTA-1 binding to synthetic Abeta fibrils. Nanomolar concentrations of [3H]BTA-1 did not appear to bind to neurofibrillary tangles. Finally, BTA-1 did not appear to bind significantly to common neuroreceptors or transporter sites. These data suggest that the binding of BTA-1 to AD brain is dominated by a specific interaction with Abeta amyloid deposits.

Characterizing regional correlation, laterality and symmetry of amyloid deposition in mild cognitive impairment and Alzheimer's disease with Pittsburgh Compound B

“…PiB has been shown in prior work to have a high binding affinity (K d = 1.4 nM) and specificity to amyloid in AD brains (Mathis et al, 2003) (Ikonomovic et al 2008), (Klunk et al 2003), . PET scans were acquired using an ECAT HR+ PET scanner (Siemens Medical Solutions, Erlangen, Germany) in three-dimensional mode (63 transaxial planes, 2.4-mm thickness; in-plane resolution = 4.1 mm full-width at half-maximum over a 15.2-cm field-ofview).…”

Quantum dots and prion proteins

“…Several research groups have launched programs to successfully identify the biomarkers for imaging Aβ plaques in the brain. [67][68][69] Even though computer tomography (CT) is not sensitive or specific in the evaluation of the disease, it may show atrophy at the advanced stage of the disease. Magnetic resonance imaging (MRI) is far more sensitive, especially with the addition of fluid attenuation inversion recovery (FLAIR) and diffusion weighted imaging (DWI).…”

Impact of amyloid imaging on drug development in Alzheimer's disease

“…Thus, while limbic areas have early and severe NFT pathology, the mesial temporal lobe has relatively little neuritic plaque pathology early in the course of AD. The cerebellum is notably free of neuritic plaques in AD (Fig 3), although diffuse Aβ deposits which do not label with fibrillar dyes, such as Congo red and PiB, are commonly observed [10,20,21]. Thus from an AD diagnostic perspective, one would look for the presence of Aβ deposits or the binding of an Aβ imaging agent in specific brain regions, and the absence of binding in other regions.…”

“…This presents more binding sites (higher B max ) for aggregated Aβ binding relative to NFT binding sites for ligands with high binding affinities for these protein deposits. It is interesting and important that some thioflavin-T derivatives, such as Pittsburgh Compound B (PiB) (2-(4′-methylaminophenyl)-6-hydroxybenzothiazole) (Fig 2), bind fibrillar Aβ deposits, with no detectable binding to soluble Aβ forms nor to NFTs or Lewy bodies [10] under conditions relevant to positron emission tomography (PET) studies (at ligand concentrations ~1 nM).…”