Validation of an (18)F-labeled biphenylalkyne as a positron emission tomography imaging agent for beta-amyloid plaques.
OBJECTIVE
Recently, the feasibility of detecting amyloid plaques in the living brain by positron emission tomography (PET) imaging has been successfully demonstrated. As such, imaging beta-amyloid (A beta) plaques in the brain may further advance the differential diagnosis of the disease and allow clinicians to measure the effectiveness of therapeutic drugs aimed at lowering plaques in the brain. We report herein the preclinical validation of a potential (18)F-labeled biphenylalkyne, AV-138, as a preliminary step toward developing the imaging agent for patients suspected of having Alzheimer's disease.


METHODS
In vitro binding was carried out in the homogenates prepared from postmortem AD brains with [(125)I]IMPY as the radioligand. [(18)F]AV-138 was successfully prepared using a tosylate precursor and Sumitomo modules for radiosynthesis. Similarly, specific binding of [(18)F]AV-138 (0.02-0.05 nM) to homogenates, prepared from gray and white matters of pooled AD patients and control subjects, was performed. Specific binding to A beta plaques was measured by autoradiography in AD brain sections (n=11), and the same brain sections were fluorescently stained with thioflavin-S (TF-S). Images of both radiolabeling and fluorescent staining of plaques obtained by a phosphor imager were used for correlation image analysis.


RESULTS
As expected, AV-138 displayed a high binding affinity (K(i)=2.4+/-0.7 nM) in AD gray matter homogenates (due to its high level of A beta plaque accumulation). Specific binding can be clearly measured in the AD gray matter homogenates, but not in the AD white matters. Control brain homogenates, due to a lack of A beta plaques, also showed no specific binding. Furthermore, in vitro autoradiography of postmortem AD brain sections showed that the high binding signal of [(18)F]AV-138 was specifically due to A beta plaques. Fluorescent staining of plaques with TF-S correlated well with the radiolabeling of [(18)F]AV-138 in AD brain sections (r>0.90).


CONCLUSIONS
Taken together, these preliminary results strongly suggest that [(18)F]AV-138 is potentially useful for imaging A beta plaques in the living human brain.
Wey
Shiaw-Pyng
SP
Department of Medical Imaging and Radiological Sciences, Graduate Institute of Medical Physics and Imaging Science, Chang Gung University, Taoyuan, 333 Taiwan.
Weng
Chi-Chang
CC
Lin
Kun-Ju
KJ
Yao
Cheng-Hsiang
CH
Yen
Tzu-Chen
TC
Kung
Hank F
HF
Skovronsky
Daniel
D
Kung
Mei-Ping
MP
D000480:Alkynes / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D000544:Alzheimer Disease / Q000473:pathology; D000814:Aniline Compounds / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D001345:Autoradiography; D001667:Binding, Competitive; D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D002851:Chromatography, High Pressure Liquid; D005026:Ethylene Glycols / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D005462:Fluorine Radioisotopes / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D008024:Ligands; D058225:Plaque, Amyloid / Q000000981:diagnostic imaging* / Q000378:metabolism; D049268:Positron-Emission Tomography / Q000379:methods*; D011720:Pyrazoles / Q000378:metabolism; D013194:Staining and Labeling
C542156:AV 138; D000480:Alkynes; D000814:Aniline Compounds; D005026:Ethylene Glycols; D005462:Fluorine Radioisotopes; D008024:Ligands; D011720:Pyrazoles; C000971:2,3-dihydro-1H-imidazo(1,2-b)pyrazole