Andreas Schildan

Decreased cerebral α4β2* nicotinic acetylcholine receptor availability in patients with mild cognitive impairment and Alzheimer's disease assessed with positron emission tomography.

PurposePostmortem studies indicate a loss of nicotinic acetylcholine receptor (nAChRs) in Alzheimer’s disease (AD). In order to establish whether these changes in the cholinergic system occur at an early stage of AD, we carried out positron emission tomography (PET) with a specific radioligand for the α4β2* nicotinic acetylcholine receptor (α4β2* nAChR) in patients with mild to moderate AD and in patients with amnestic mild cognitive impairment (MCI), who have a high risk to progress to AD.MethodsNine patients with moderate AD, eight patients with MCI and seven age-matched healthy controls underwent 2-[18F]fluoro-3-(2(S)-azetidinylmethoxy)pyridine (2-[18F]FA-85380) PET. After coregistration with individual magnetic resonance imaging the binding potential (BPND) of 2-[18F]FA-85380 was calculated using either the corpus callosum or the cerebellum as reference regions. PET data were analysed by region of interest analysis and by voxel-based analysis.ResultsBoth patients with AD and MCI showed a significant reduction in 2-[18F]FA-85380 BPND in typical AD-affected brain regions. Thereby, the corpus callosum was identified as the most suitable reference region. The 2-[18F]FA-85380 BPND correlated with the severity of cognitive impairment. Only MCI patients that converted to AD in the later course (n = 5) had a reduction in 2-[18F]FA-85380 BPND.Conclusion2-[18F]FA-85380 PET appears to be a sensitive and feasible tool for the detection of a reduction in α4β2* nAChRs which seems to be an early event in AD. In addition, 2-[18F]FA-85380 PET might give prognostic information about a conversion from MCI to AD.

Norchloro-fluoro-homoepibatidine (NCFHEB) — A promising radioligand for neuroimaging nicotinic acetylcholine receptors with PET☆

Cholinergic neurotransmission depends on the integrity of nicotinic acetylcholine receptors (nAChRs), and impairment of both is characteristic for various neurodegenerative diseases. Visualization of specific receptor subtypes by positron emission tomography (PET) has potential to assist with diagnosis of such neurodegenerative diseases and with design of suitable therapeutic approaches. The goal of our study was to evaluate in vivo the potential of (18)F-labelled (+)- and (-)-norchloro-fluoro-homoepibatidine ([(18)F]NCFHEB) in comparison to 2-[(18)F]F-A-85380 as PET tracers. In the brains of NMRI mice, highest levels of radioactivity were detected at 20 min post-injection of (+)-[(18)F]NCFHEB, (-)-[(18)F]NCFHEB, and 2-F-[(18)F]-A-85380 (7.45, 5.60, and 3.2% ID/g tissue, respectively). No marked pharmacological adverse effects were observed at 25 mug NCFHEB/kg. Uptake studies in RBE4 cells and in situ perfusion studies suggest an interaction of epibatidine and NCFHEB with the carrier-mediated choline transport at the blood-brain barrier. The data indicate that (+)- and (-)-[(18)F]NCFHEB have potential for further development as PET tracers.

Fully automated radiosynthesis of both enantiomers of [18F]Flubatine under GMP conditions for human application

A fully automatized radiosynthesis of (+)- and (-)-[(18)F]Flubatine ((+)- and (-)NCFHEB) by means of a commercially available synthesis module (TRACERlab FX FN) under GMP conditions is reported. Radiochemical yields of 30% within an overall synthesis time of 40 min were achieved in more than 70 individual syntheses. Specific activities were approximately 3000 GBq/μmol and radiochemical purity was determined to be at least 97%.

Evaluation of early-phase [(18)F]-florbetaben PET acquisition in clinical routine cases.

Objectives In recent years several [18F]-labelled amyloid PET tracers have been developed and have obtained clinical approval. There is accumulating evidence that early (post injection) acquisitions with these tracers are equally informative as conventional blood flow and metabolism studies for diagnosis of Alzheimers disease, but there have been few side-by-side studies. Therefore, we investigated the performance of early acquisitions of [18F]-florbetaben (FBB) PET compared to [18F]-fluorodeoxyglucose (FDG) PET in a clinical setting. Methods All subjects were recruited with clinical suspicion of dementia due to neurodegenerative disease. FDG PET was undertaken by conventional methods, and amyloid PET was performed with FBB, with early recordings for the initial 10 min (early-phase FBB), and late recordings at 90–110 min p.i. (late-phase FBB). Regional SUVR with cerebellar and global mean normalization were calculated for early-phase FBB and FDG PET. Pearson correlation coefficients between FDG and early-phase FBB were calculated for predefined cortical brain regions. Furthermore, a visual interpretation of disease pattern using 3-dimensional stereotactic surface projections (3D-SSP) was performed, with assessment of intra-reader agreement. Results Among a total of 33 patients (mean age 67.5 ± 11.0 years) included in the study, 18 were visually rated amyloid-positive, and 15 amyloid-negative based on late-phase FBB scans. Correlation coefficients for early-phase FBB vs. FDG scans displayed excellent agreement in all target brain regions for global mean normalization. Cerebellar normalization gave strong, but significantly lower correlations. 3D representations of early-phase FBB visually resembled the corresponding FDG PET images, irrespective of the amyloid-status of the late FBB scans. Conclusions Early-phase FBB acquisitions correlate on a relative quantitative and visual level with FDG PET scans, irrespective of the amyloid plaque density assessed in late FBB imaging. Thus, early-phase FBB uptake depicts a metabolism-like image, suggesting it as a valid surrogate marker for synaptic dysfunction, which could ultimately circumvent the need for additional FDG PET investigation in diagnosis of dementia.

Evaluation of metabolism, plasma protein binding and other biological parameters after administration of (−)-( 18 F)Flubatine in humans

INTRODUCTION (-)-[(18)F]Flubatine is a PET tracer with high affinity and selectivity for the nicotinic acetylcholine α4β2 receptor subtype. A clinical trial assessing the availability of this subtype of nAChRs was performed. From a total participant number of 21 Alzheimers disease (AD) patients and 20 healthy controls (HCs), the following parameters were determined: plasma protein binding, metabolism and activity distribution between plasma and whole blood. METHODS Plasma protein binding and fraction of unchanged parent compound were assessed by ultracentrifugation and HPLC, respectively. The distribution of radioactivity (parent compound+metabolites) between plasma and whole blood was determined ex vivo at different time-points after injection by gamma counting after separation of whole blood by centrifugation into the cellular and non-cellular components. In additional experiments in vitro, tracer distribution between these blood components was assessed for up to 90min. RESULTS A fraction of 15%±2% of (-)-[(18)F]Flubatine was found to be bound to plasma proteins. Metabolic degradation of (-)-[(18)F]Flubatine was very low, resulting in almost 90% unchanged parent compound at 90min p.i. with no significant difference between AD and HC. The radioactivity distribution between plasma and whole blood changed in vivo only slightly over time from 0.82±0.03 at 3min p.i. to 0.87±0.03 at 270min p.i. indicating the contribution of only a small amount of metabolites. In vitro studies revealed that (-)-[(18)F]Flubatine was instantaneously distributed between cellular and non-cellular blood parts. DISCUSSION (-)-[(18)F]Flubatine exhibits very favourable characteristics for a PET radiotracer such as slow metabolic degradation and moderate plasma protein binding. Equilibrium of radioactivity distribution between plasma and whole blood is reached instantaneously and remains almost constant over time allowing both convenient sample handling and facilitated fractional blood volume contribution assessment.

Internal Dose Assessment of (–)-18F-Flubatine, Comparing Animal Model Datasets of Mice and Piglets with First-in-Human Results

(−)-18F-flubatine is a promising tracer for neuroimaging of nicotinic acetylcholine receptors (nAChRs), subtype α4β2, using PET. Radiation doses after intravenous administration of the tracer in mice and piglets were assessed to determine the organ doses (ODs) and the effective dose (ED) to humans. The results were compared with subsequent clinical investigations in human volunteers. Methods: Twenty-seven female CD1 mice (weight ± SD, 28.2 ± 2.1 g) received intravenous injection of 0.75 ± 0.33 MBq of (−)-18F-flubatine. Up to 240 min after injection, 3 animals per time point were sacrificed and the organs harvested, weighed, and counted in a γ counter to determine mass and activity, respectively. Furthermore, whole-body PET scans of 5 female piglets (age ± SD, 44 ± 3 d; weight ± SD, 13.7 ± 1.7 kg) and 3 humans (2 men and 1 woman; age ± SD, 59.6 ± 3.9 y; weight ± SD, 74.3 ± 3.1 kg) were obtained up to 236 min (piglets) and 355 min (humans) after injection of 186.6 ± 7.4 and 353.7 ± 10.2 MBq of (−)-18F-flubatine, respectively, using a PET/CT scanner. The CT was used for delineation of the organs. Exponential curves were fitted to the time–activity-data, and time and mass scales were adapted to the human anatomy. The ODs were calculated using OLINDA/EXM (version 1.0); EDs were calculated with the tissue-weighting factors of ICRP103. Results: After the injection of (−)-18F-flubatine, there were no adverse or clinically detectable pharmacologic effects in any of the subjects. The highest activities after injection were found in the kidneys, urinary bladder, and liver. The urinary bladder receives the highest OD in all investigated species, followed by the kidneys and the liver for animals and humans, respectively. On the basis of mouse, piglet, and human kinetic data, the projected human ED of (−)-18F-flubatine was estimated to be 12.5 μSv/MBq in mice, 14.7 ± 0.7 μSv/MBq in piglets, and 23.4 ± 0.4 μSv/MBq in humans. Conclusion: As has been demonstrated for other PET radiotracers, preclinical (i.e., animal-derived) dosimetry underestimates the ED to humans, in the current case of (−)-18F-flubatine by 34%–44%.

Influence of additives to the formulation of n.c.a. [11C]PiB on sterile filter performance

The influence of different additives (PEG 300, PEG 400, PG) to the product solution of [(11)C]PiB was investigated with regard to tracer retention for a number of commonly used sterile filters for aseptic manufacturing of PET-tracers. The effect of the amount of additive with regard to tracer retention and the resulting viscosity of the filtration solution was determined. Recommendations for the individual combinations of filters and amounts of additives suitable for the different filtration methods that are implemented in commercially available synthesis modules are given as well.

Lower cortical Alpha4Beta2 nicotinic acetylcholine receptor binding and its relationship to cognitive dysfunction in early stage multiple sclerosis: A 2-[18F]F-A-85380 PET study

Purpose: Multiple sclerosis (MS) is considered as neuroinflammatory and neurodegenerative disorder in which cognitive dysfunction is a common feature even in early stage MS (Tsutsui and Stys, 2009). The α4β2 nicotinic acetylcholine receptors (α4β2-nAChR) are widely abundant in the human brain and play a role for cognition by modulating release of different neurotransmitters (1). To investigate alterations of α4β2-nAChR availability in MS and its relationship to cognitive symptoms, patients with early stage MS with negligible MRIbased cortical or global atrophy were studied using α4β2-nAChR specific 2-[18F]F-A-85380 (2FA) and PET (2FA-PET) and multiple cognitive tests.

[18F]BAY 94-9172 PET - Towards in vivo quantification of brain β-amyloid plaque load in Alzheimer disease

Background: Positron emission tomography (PET) permits quantitative measurement of biochemical and physiological processes in vivo. Linear simplification is usually used for quantitatively deriving functional parameters from kinetic data measured by PET. Particularly, the graphical linear method developed by Logan has became a routine tool for dynamic PET quantification. But linear methods may lead to bias in the estimated parameters, particularly for reversible kinetics. Under-estimation of linear methods is frequently reported and is commonly attributed to noise in the data. The source of the bias is commonly attributed to noise in the data. Methods: Assuming a two-tissue compartmental model for neuroreceptor studies and using fibrillar amyloid beta radioligand [11C] benzothiazole-aniline (Pittsburgh Compound-B [PIB]) as an example, we investigate the bias that originates from model error associated with model simplification. We find that the bias due to model error may be more significant than that due to noise. Conditions are derived under which Logan’s graphical method either overor under-estimates the distribution volume in the noise-free case. The bias caused by model error is quantified analytically. Our analysis shows that the bias of graphical methods is proportional to the variation of the ratio of specifically bound radioactivity to the total radioactivity in a region during the assumed equilibrium time window. Furthermore, visual examination of the linearity of the Logan plot is not sufficient for guaranteeing that equilibrium has been reached. A new model which retains the elegant properties of graphical analysis methods is presented, along with a numerical algorithm for its solution. Results: We perform simulations with the PIB using published clinical data. The results show that the proposed method significantly reduces the bias due to model error. The worst bias associated with Logan’s plot, -33.97%, is corrected to -12.71%. Moreover, the results for data acquired over a 70 minutes scan duration are at least as good as those obtained using existing methods for data acquired over a 90 minutes scan duration. Conclusions: This approach will have considerable impact on practical clinical situations, where the reduction of scan time will reduce cost and increase patient comfort. Additional information can be found at http://math.asu.edu/whongbin/GAmodelerror.php.

P1-285: First results toward in vivo quantification of cerebral β-amyloid plaque load in Alzheimer's disease by means of BAY 94-9172-PET

patients had significantly higher DVR reflecting greater AV-45 binding estimates in the following brain regions: frontal, temporal, fusiform gyrus, cingulate, insula, putamen, globus pallidus, as well as a summary measure of whole-cortex DVR. MMSE, WMS, and category fluency were not correlated with DVR in any brain region after controlling for diagnosis. However, regional DVR in frontal, temporal, occipital, fusiform gyrus, cingulate, parahippocampus, insula, putamen, and cortex correlated significantly with ADAS-Cog Word Recall after controlling for diagnosis (r .84-.92 for model). Similarly, regional DVR in thalamus and caudate nucleus correlated significantly with ADAS-Cog Constructional Praxis after controlling for diagnosis (r .61-.77 for model). Conclusions: DVR of [F] AV-45, a novel ligand for PET imaging of amyloid plaques, was significantly higher in AD in many cortical regions implicated in early AD. This suggests the utility of this ligand for AD diagnosis. Interestingly enough, DVR in hippocampus was not elevated reflecting the observation that neurofibrillary tangles are a more sensitive marker than plaques for early hippocampal involvement in AD. In two cognitive domains there was further evidence for correlation of cognitive performance with DVR after controlling for diagnosis, suggesting that [F] AV-45 may also be useful as a marker of AD severity.