Nicotinic α4β2 receptor imaging agents

Autor: Tanjore K. Narayanan, Steven G. Potkin, Bradley T. Christian, Rama Pichika, Jogeshwar Mukherjee, Balasubramaniam Easwaramoorthy, Bingzhi Shi, Daphne Collins
Rok vydání: 2006
Předmět:
Zdroj: Nuclear Medicine and Biology. 33:295-304
ISSN: 0969-8051
DOI: 10.1016/j.nucmedbio.2005.12.017
Popis: The α4β2 nicotinic acetylcholine receptor (nAChR) has been implicated in various neurodegenerative diseases. Optimal positron emission tomography (PET) imaging agents are therefore highly desired for this receptor. We report here the development and initial evaluation of 2-fluoro-3-[2-(( S )-3-pyrrolinyl)methoxy]pyridine (nifene). In vitro binding affinity of nifene in rat brain homogenate using 3 H-cytisine exhibited a K i =0.50 nM for the α4β2 sites. The radiosynthesis of 2- 18 F-fluoro-3-[2-(( S )-3-pyrrolinyl)methoxy]pyridine ( 18 F-nifene) was accomplished in 2.5 h with an overall radiochemical yield of 40–50%, decay corrected. The specific activity was estimated to be approx. 37–185 GBq/μmol. In vitro autoradiography in rat brain slices indicated selective binding of 18 F-nifene to anteroventral thalamic (AVT) nucleus, thalamus, subiculum, striata, cortex and other regions consistent with α4β2 receptor distribution. Rat cerebellum showed some binding, whereas regions in the hippocampus had the lowest binding. The highest ratio of >13 between AVT and cerebellum was measured for 18 F-nifene in rat brain slices. The specific binding was reduced (>95%) by 300 μM nicotine in these brain regions. Positron emission tomography imaging study of 18 F-nifene (130 MBq) in anesthetized rhesus monkey was carried out using an ECAT EXACT HR+ scanner. PET study showed selective maximal uptake in the regions of the anterior medial thalamus, ventro-lateral thalamus, lateral geniculate, cingulate gyrus, temporal cortex including the subiculum. The cerebellum in the monkeys showed lower binding than the other regions. Thalamus-to-cerebellum ratio peaked at 30–35 min postinjection to a value of 2.2 and subsequently reduced. The faster binding profile of 18 F-nifene indicates promise as a PET imaging agent and thus needs further evaluation.
Databáze: OpenAIRE
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