We report [18F]nifene binding to α4β2* nicotinic acetylcholinergic receptors (nAChRs) in Parkinson’s disease (PD). The study used transgenic Hualpha-Syn(A53T) PD mouse model of α-synucleinopathy for PET/CT studies in vivo and autoradiography in vitro. Additionally, postmortem human PD brain sections comprising of anterior cingulate were used in vitro to assess translation to human studies. Because the small size of mice brain poses challenges for PET imaging, improved methods for radiosynthesis of [18F]nifene and simplified PET/CT procedures in mice were developed by comparing intravenous (IV) and intraperitoneal (IP) administered [18F]nifene. An optimal PET/CT imaging time of 30–60 min post injection of [18F]nifene was established to provide thalamus to cerebellum ratio of 2.5 (with IV) and 2 (with IP). Transgenic Hualpha-Syn(A53T) mice brain slices exhibited 20–35% decrease while in vivo a 20–30% decrease of [18F]nifene was observed. Lewy bodies and α-synuclein aggregates were confirmed in human PD brain sections which lowered the [18F]nifene binding by more than 50% in anterior cingulate. Thus [18F]nifene offers a valuable tool for PET imaging studies of PD.

Objective:Imaging animal models of Alzheimer disease (AD) is useful for the development of therapeutic drugs and understanding AD. Transgenic Swedish hAPPswe Tg2576 mice are a good model of β-amyloid plaques. We report 18F-fluoro-2-deoxyglucose (18F-FDG) positron emission tomography (PET) imaging of brain and intrascapular brown adipose tissue (IBAT) in transgenic mice 2576 (Tg2576) and wild-type (WT) mice.Methods:Transgenic Tg2576 mice and WT mice, >18 months were injected intraperitonally with ≈ 25 to 30 MBq 18F-FDG while awake. After 60 minutes, they were anesthetized with isoflurane (2.5%) and imaged with Inveon MicroPET. Select mice were killed, imaged ex vivo, and 20 µm sections cut for autoradiography. 18F-FDG uptake in brain and IBAT PET and brain autoradiographs were analyzed.Results:Fasting blood glucose levels averaged 120 mg/dL for WT and 100 mg/dL for Tg2576. Compared to WT, Tg2576 mice exhibited a decrease in SUVglc in the various brain regions. Average reductions in the cerebrum regions were as high as −20%, while changes in cerebellum were −3%. Uptake of 18F-FDG in IBAT decreased by −60% in Tg2576 mice and was found to be significant. Intrascapular brown adipose tissue findings in Tg2576 mice are new and not previously reported. Use of blood glucose for PET data analysis and corpus callosum as reference region for autoradiographic analysis were important to detect change in Tg2576 mice.Conclusion:Our results suggest that 18F-FDG uptake in the Tg2576 mice brain show 18F-FDG deficits only when blood glucose is taken into consideration.

Several fluorine-18-labeled PET β-amyloid (Aβ) plaque radiotracers for Alzheimer’s disease (AD) are in clinical use. However, no radioiodinated imaging agent for Aβ plaques has been successfully moved forward for either single-photon emission computed tomography (SPECT) or positron emission tomography (PET) imaging. Radioiodinated pyridyl benzofuran derivatives for the SPECT imaging of Aβ plaques using iodine-123 and iodine-125 are being pursued. In this study, we assess the iodine-124 radioiodinated pyridyl benzofuran derivative 5-(5-[124I]iodobenzofuran-2-yl)-N,N-dimethylpyridin-2-amine ([124I]IBETA) (Ki = 2.36 nM) for utilization in PET imaging for Aβ plaques. We report our findings on the radioiododestannylation reaction used to prepare [124/125I]IBETA and evaluate its binding to Aβ plaques in a 5 × FAD mouse model and postmortem human AD brain. Both [125I]IBETA and [124I]IBETA are produced in >25% radiochemical yield and >85% radiochemical purity. The in vitro binding of [125I]IBETA and [124I]IBETA in transgenic 5 × FAD mouse model for Aβ plaques was high in the frontal cortex, anterior cingulate, thalamus, and hippocampus, which are regions of high Aβ accumulation, with very little binding in the cerebellum (ratio of brain regions to cerebellum was >5). The in vitro binding of [125I]IBETA and [124I]IBETA in postmortem human AD brains was higher in gray matter containing Aβ plaques compared to white matter (ratio of gray to white matter was >5). Anti-Aβ immunostaining strongly correlated with [124/125I]IBETA regional binding in both the 5 × FAD mouse and postmortem AD human brains. The binding of [124/125I]IBETA in 5 × FAD mouse and postmortem human AD brains was displaced by the known Aβ plaque imaging agent, Flotaza. Preliminary PET/CT studies of [124I]IBETA in the 5 × FAD mouse model suggested [124I]IBETA was relatively stable in vivo with a greater localization of [124I]IBETA in the brain regions with a high concentration of Aβ plaques. Some deiodination was observed at later time points. Therefore, [124I]IBETA may potentially be a useful PET radioligand for Aβ plaques in brain studies.

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Objective: Alzheimer's disease (AD) is a neurodegenerative disease characterized by aggregation of Tau protein into paired helical filaments causing neurofibrillary tangles (NFT) in the brain. The aim of this study was to develop and evaluate the effectiveness of a novel radioiodinated tracer, 6‐[125I]iodo‐3‐(1H‐pyrrolo[2,3‐c]pyridine‐1‐yl)isoquinoline ([125I]IPPI), for binding to Tau protein (Ki = 0.75 nM) in postmortem human brain (AD and cognitively normal (CN). Methods: Radiosynthesis of [125I]IPPI was carried out by radioiododestannylation and purified chromatographically. Computational modeling studies of IPPI and MK‐6240 binding on Tau fibril were evaluated. In vitro autoradiography studies were carried out with [3H]PIB for Aβ plaques and [125I]IPPI for Tau in AD and CN brains and evaluate drug effects. Results: [125I]IPPI was produced in >95% purity. Molecular modeling of IPPI revealed binding energies of IPPI (−7.8, −8.1, −8.2, −7.5 Kcal/mol) at the four sites were comparable to MK‐6240 (−8.7, −8.5, −8.3, −7.5 Kcal/mol). Ratio of average grey matter (GM) [125I]IPPI in AD versus CN was found to be 7.31 (p = .07) and AD GM/ white matter (WM) = 4.35 (p = .09). Ratio of average GM/WM [125I]IPPI in CN was 1.21. Binding of [125I]IPPI correlated with the presence of Tau, confirmed by anti‐Tau Dako A0024. Specifically bound [125I]IPPI to Tau in AD brains was displaced by MK‐6240 and IPPI (>90%). Monoamine oxidase inhibitors (MAO) inhibitors deprenyl and clorgyline effected [125I]IPPI binding at >1 µM concentrations. Conclusion: [125I]IPPI exhibited high binding in human AD frontal cortex and anterior cingulate and is a suitable radioiodinated ligand for Tau imaging.

Nicotinic acetylcholinergic receptors (nAChR's) have been implicated in several brain disorders, including addiction, Parkinson's disease, Alzheimer's disease and schizophrenia. Here we report in vitro selectivity and functional properties, toxicity in rats, in vivo evaluation in humans, and comparison across species of [ 18 F]Nifene, a fast acting PET imaging agent for a4b2* nAChRs. Nifene had subnanomolar affinities for ha2b2 (0.34 nM), ha3b2 (0.80 nM) and ha4b2 (0.83 nM) nAChR but weaker (27-219 nM) for hb4 nAChR subtypes and 169 nM for ha7 nAChR. In functional assays, Nifene (100 lM) exhibited 14% agonist and >50% antagonist characteristics. In 14-day acute toxicity in rats, the maximum tolerated dose (MTD) and the no observed adverse effect level

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Serotonin 5-HT3 receptors are involved in various brain functions including as an emesis target during cancer chemotherapy. We report here the development of (S)-2,3-dimethoxy-5-(3′-[18F]fluoropropyl)-N-(1-azabicyclo[2.2.2]oct-3-yl)benzamide ([18F]fesetron) as a potential PET imaging agent for serotonin 5-HT3 receptors. By radiolabeling((S)-2,3-dimethoxy-5-(3′-tosyloxypropyl)-N-(1-azabicyclo[2.2.2]oct-3-yl)benzamide) with fluorine-18, (S)-[18F]fesetron was obtained in 5 to 10% decay-corrected yields and with specific activities >74 GBq/μmol at the end of radiosynthesis. PET imaging in rats showed low uptake of [18F]fesetron in the brain with retention of binding in the striatal and cerebellar regions. Using colliculi as a reference region, ratios were 3.4 for striata and 2.5 for cerebellum. Ex vivo brain PET analysis displayed binding of [18F]fesetron in the hippocampus, striatum and cerebellar regions. Cerebellar regions corresponded to area postrema and nucleus tract solitaris known to contain 5-HT3 receptors. Dorsal hippocampus showed the highest uptake with ratio of >17 with respect to colliculi, while area postrema and striata had ratios of >10. Thus, [18F]fesetron exhibited a unique binding profile to rat brain regions known to contain significant amounts of serotonin 5-HT3 receptors. However, the very low brain uptake limits its usefulness as a PET radiotracer in this animal model.