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The Journal of Neuroscience, 2001, 21:RC189:1-5
RAPID COMMUNICATION
Binding Characteristics of Radiofluorinated
6-Dialkylamino-2-Naphthylethylidene Derivatives as Positron Emission
Tomography Imaging Probes for -Amyloid Plaques in Alzheimer's
Disease
Eric D.
Agdeppa1,
Vladimir
Kepe1,
Jie
Liu1,
Samuel
Flores-Torres3,
Nagichettiar
Satyamurthy1,
Andrej
Petric4,
Greg M.
Cole5,
Gary W.
Small2,
Sung-Cheng
Huang1, and
Jorge R.
Barrio1
1 Division of Nuclear Medicine, Department of Molecular
and Medical Pharmacology, Laboratory of Structural Biology and
Molecular Medicine, and 2 Department of Psychiatry and
Biobehavioral Sciences, University of California Los Angeles School of
Medicine, Los Angeles, California 90095, 3 University of
Puerto Rico, Cayey, Puerto Rico 00736, 4 Faculty of
Chemistry and Chemical Technology, University of Ljubljana, SI-1000
Ljubljana, Slovenia, and 5 Veterans Administration
Hospital, Sepulveda, California 91343
Senile plaques (SPs) and neurofibrillary tangles (NFTs)
are hallmark pathologies accompanying the neurodegeneration involved in
Alzheimer's disease (AD), for which -amyloid (A ) peptide is a
major constituent of SPs. Our laboratories previously developed the
hydrophobic, fluorescent molecular-imaging probe
2-(1-{6-[(2-[18F]fluoroethyl)(methyl)amino]-2-naphthyl}ethylidene)malononitrile ([18F]FDDNP), which crosses the blood-brain
barrier and determines the localization and load of SPs and NFTs
in vivo in AD patients. In this report, we used
fluorimetric and radioactive binding assays to determine the binding
affinities of FDDNP and its analog,
1-{6-[(2-[18F]fluoroethyl)(methyl)amino]naphthalen-2-yl}ethanone
([18F]FENE), to synthetic fibrils of A (1-40).
FDDNP and FENE both appeared to bind to two kinetically distinguishable
binding sites on A (1-40) fibrils. Fluorescence
titrations yielded apparent Kd values of
0.12 and 0.16 nM for high-affinity binding sites for FDDNP
and FENE, respectively, and apparent Kd
values of 1.86 and 71.2 nM for the low-affinity binding
sites. The traditional radioactive binding assays also produced
apparent Kd values in the low nanomolar
range. The presence of two kinetically distinguishable binding sites
for FDDNP and FENE suggests multiple binding sites for SPs and
identifies the parameters that allow for the structural optimization of
this family of probes for in vivo use. The high-affinity binding of the probes to multiple binding sites on fibrils are consistent with results obtained with digital autoradiography, immunohistochemistry, and confocal fluorescence microscopy using human
brain specimens of AD patients.
Key words:
-amyloid fibrils; molecular-imaging probes; Alzheimer's disease; fluorescence titration; confocal fluorescence
microscopy; digital autoradiography
Copyright © Society for Neuroscience 0270-6474//$05.00/0
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