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Introduction: The A2A adenosine receptor (A2AAR) is expressed in brain, vasculature and immune cells. According to the alterations of the A2AAR expression in multiple diseases, it is a highly attractive diagnostic and therapeutic target. We developed the A2AAR-specific PET radiotracer [18F]FLUDA and investigated it in healthy mice and piglets, in a rotenone-based mouse model of Parkinson’s disease (RMMPD) and in transgenic mice overexpressing the human A2AAR in heart (TG) [1 3]. Methods: On the basis of a one-pot two-step radiofluorination procedure, a remotely controlled automated radiosynthesis of [18F]FLUDA using the TRACERlab FX2N synthesis module was developed. In vitro autoradiography was performed with cryosections of tissue from animal models. In vivo stability was investigated in mouse by radio-HPLC analyses of blood plasma and brain homogenates. The biodistribution was investigated by dynamic PET/MR studies in healthy mice and piglets under control and blocking conditions (vehicle vs. blocking with 2.5 mg/kg tozadenant and/or 1.0 mg/kg istradefylline) and in both mouse models. The binding potential (BPND) in vivo was calculated using the simplified reference tissue modelling with the cerebellum as reference region. A single dose acute toxicity study was performed in Wistar rats according to the ICH guideline M3(R2). PET-derived radiation dosimetry was estimated in piglets. Results: A reliable and reproducible procedure for the automated production of [18F]FLUDA was successfully established (Fig. 1A) [4]. In vitro autoradiography revealed highly selective binding and high affinity of [18F]FLUDA towards the A2AAR of the three species (KD values 0.7-5.9 nM, Fig. 1B). At 15 min after i.v. injection of [18F]FLUDA in mice, the parent fraction accounted for about 100% in brain and 71% in plasma. PET studies confirmed the specific binding of [18F]FLUDA in vivo to the striatal A2AAR in mice and piglets (BPND=3.9 and 1.3, Fig. 1C). The availability of A2AAR in the Parkinson’s disease model was not significantly different from the control. The cardiac overexpression of human A2AAR resulted in a significantly higher accumulation of activity compared to control (1.4-fold higher ratio of the area-under-the curves obtained for myocard and blood, 1-10 min p.i., p=0.001). Toxicity studies revealed no adverse effects up to a dose of 30 µg/kg of FLUDA (approx. 4,000-fold of expected human dose). The estimated effective dose of [18F]FLUDA in humans is 16.4 µSv/MBq, which is in the range of other 18F-labeled radiotracers [5]. Conclusion: We have demonstrated that [18F]FLUDA is suitable for the determination of the availability of A2AAR in the brain in vitro and in vivo. No safety concerns are expected upon administration of [18F]FLUDA according to toxicity and dosimetry data. These results encourage the clinical translation of [18F]FLUDA. Acknowledgement: This work (project no. 100226753) was funded by the European-Regional-Development-Fund (ERDF) and Sächsische-Aufbaubank (SAB). References: [1] T.H. Lai and M. Toussaint et al., EJNNMI 2021, 48:2727–2736; [2] D. Gündel and M. Toussaint, Pharmaceuticals 2022, 15; [3] D. Gündel et al., Int. J. Mol. Sci. 2022, 23, 1025; [4] T.H. Lai et al., J. Label. Compd. Radiopharm. 2022, 65:162–166; [5] B. Sattler et al., J. Nucl. Med. 2020, 61:1014.

The reproducibility of findings is a compelling methodological problem that the neuroimaging community is facing these days. The lack of standardized pipelines for image processing, quantification and statistics plays a major role in the variability and interpretation of results, even when the same data are analysed. This problem is well-known in MRI studies, where the indisputable value of the method has been complicated by a number of studies that produce discrepant results. However, any research domain with complex data and flexible analytical procedures can experience a similar lack of reproducibility. In this paper we investigate this issue for brain PET imaging. During the 2018 NeuroReceptor Mapping conference, the brain PET community was challenged with a computational contest involving a simulated neurotransmitter release experiment. Fourteen international teams analysed the same imaging dataset, for which the ground-truth was known. Despite a plurality of methods, the solutions were consistent across participants, although not identical. These results should create awareness that the increased sharing of PET data alone will only be one component of enhancing confidence in neuroimaging results and that it will be important to complement this with full details of the analysis pipelines and procedures that have been used to quantify data.

The cerebral cholinergic system is involved in several cognitive processes and neuropsychiatric 2 diseases. For research purposes and later on in routine clinical settings new PET radioligands with more favorable characteristics than the established 3-pyridylether derivatives with their slow kinetics are necessary. Here we present the first in-human brain PET imaging data of the new α4β2 nicotinic acetylcholine receptor (nAChR)-targeting radioligand (+)-[18F]Flubatine. Primary aim of this study was to develop a kinetic modeling-based approach to quantify the α4β2 nAChR availability in the human brain and to compare respective data of healthy controls (HCs) with those of patients with Alzheimer’s disease (AD). Secondary aims were to investigate whether (+)-[18F]Flubatine binding was correlated to cognitive test data or β-amyloid radiotracer accumulation. Furthermore, the partial volume effect (PVE) on regional (+)-[18F]Flubatine binding was investigated. We examined 11 non-smoking HCs and 9 non-smoking patients with mild AD without anti-dementive drugs. Prior to (+)-[18F]Flubatine PET, all subjects underwent an extensive neuropsychological testing and a β-amyloid [11C]PiB PET/MRI examination. To evaluate the (+)-[18F]Flubatine PET data, we used full kinetic modeling (one and two tissue compartment 16 modeling (1TCM and 2TCM)) and regional as well as voxel-based analyses. 270 min p.i., the unchanged parent compound in arterial blood amounted to 97±2%. As revealed by regional analysis, (+)-[18F]Flubatine distribution volume (binding) was significantly reduced in the bilateral mesial temporal cortex in AD patients compared to HCs (right: AD: 10.6±1.1 vs HC: 11.6±1.4, p=0.049; left: AD: 11.0±1.1 vs HCs:12.2±1.8, p=0.046). Voxel-based analysis detected further clusters of reduced (+)-[18F]Flubatine in left precuneus/posterior cingulate cortex, right superior temporal and left middle temporal cortex (k>30, p0.5, p

Ziel: Vor erstmaliger Anwendung neuartiger Radiopharmaka im Menschen muss präklinisch eine Abschätzung der inneren Strahlenexposition des Menschen am Tiermodell erfolgen. Hierfür stehen computergenerierte VOXEL Phantome (VP) unterschiedlicher Tiermodelle zur Verfügung. Die Verschiedenen, teils regulatorisch für die klinische Anwendung zugelassenen Softwaretools für die Inkorporationsdosimetrie nutzen Implementationen dieser VP für die präklinische und klinische Dosimetrie. Basierend auf den anatomischen und geometrischen Verhältnissen enthalten die VP die in Zielorganen und Organsystemen absorbierte spezifische Fraktion der von Quellorganen ausgehenden/emittierten Strahlenenergie (specific absorbed fraction, SAF). Diese sind grundlegend für die in Organen und Organsystemen absorbierten Dosis (OD) nach dem MIRD Schema und werden durch Monte-Carlo-Simulation (MC) berechnet. Eigene Arbeiten haben gezeigt, dass im Vergleich zur Verwendung von Kleintieren mit Ferkeln eine den Verhältnissen am Menschen vergleichbarere Abschätzung der Strahlenexposition möglich ist. Daher wurde ein VP für Ferkel erstellt und dessen SAFs durch MC berechnet. Methodik: Ein 12 kg Ferkel (8 Wochen) wurde nach i.v. Injektion von [18F]Flubatine (185.4 MBq) bis zu 4,5 h p.i. in einem PET/CT (SIEMENS Biograph 16) gemessen und die List-Mode Daten nach Standardkorrekturen rekonstruiert. Unter Nutzung der PET bzw. CT Daten und der Software ROVER (ABX, Radeberg) wurden 18 Organe vorwiegend manuell segmentiert und als DICOM Structure Set exportiert. Mit der Software OEDIPE [1] erfolgte die Zuordnung der Gewebeeigenschaften der segmentierten Organe nach ICRU [2]. Anschließend erfolgt die Simulation in MCNPX (v.2.6.0) mit 20 Millionen Events als Abbruchkriterium. Ergebnisse: Mit OEDIPE gelingt unter Verwendung des Ergebnisses der MC-Simulation die Erzeugung der SAFs für ein VP des Ferkels. Für 28 Radionuklide wurden SAFs (mGy/MBq*s) für Gehirn, Leber, Gallenblase, Nieren, Dünn- und Dickdarm, Lunge, Herz, Pankreas, rotes Knochenmark, Milz, Magen, Schilddrüse, Thymus, Blase, Skelett, Wirbelsäule und Restkörper berechnet. Schlussfolgerung: Unter Nutzung von OEDIPE wurde erstmals ein VP des Ferkels erzeugt und durch MC-Simulation die SAFs berechnet. Dieses VP steht der Implementation in verschiedenen am Markt verfügbare Softwaretools zur Verfügung. Seine Anwendbarkeit für die präklinische Inkorporationsdosimetrie wird nunmehr durch den Vergleich mit anderen, bereits implementierten VP weiter untersucht.

α4β2* nicotinic receptors (α4β2* nAChRs) could provide a biomarker in neuropsychiatric disorders (e.g., Alzheimer's and Parkinson's diseases, depressive disorders, and nicotine addiction). However, there is a lack of α4β2* nAChR specific PET radioligands with kinetics fast enough to enable quantification of nAChR within a reasonable time frame. Following on from promising preclinical results, the aim of the present study was to evaluate for the first time in humans the novel PET radioligand (−)-[18F]Flubatine, formerly known as (−)-[18F]NCFHEB, as a tool for α4β2* nAChR imaging and in vivo quantification. Dynamic PET emission recordings lasting 270 min were acquired on an ECAT EXACT HR+ scanner in 12 healthy male non-smoking subjects (71.0 ± 5.0 years) following the intravenous injection of 353.7 ± 9.4 MBq of (−)-[18F]Flubatine. Individual magnetic resonance imaging (MRI) was performed for co-registration. PET frames were motion-corrected, before the kinetics in 29 brain regions were characterized using 1- and 2-tissue compartment models (1TCM, 2TCM). Given the low amounts of metabolite present in plasma, we tested arterial input functions with and without metabolite corrections. In addition, pixel-based graphical analysis (Logan plot) was used. The model's goodness of fit, with and without metabolite correction was assessed by Akaike's information criterion. Model parameters of interest were the total distribution volume VT (mL/cm3), and the binding potential BPND relative to the corpus callosum, which served as a reference region. The tracer proved to have high stability in vivo,with 90% of the plasma radioactivity remaining as untransformed parent compound at 90 min, fast brain kinetics with rapid uptake and equilibration between free and receptor bound tracer. Adequate fits of brain TACs were obtained with the 1TCM. VT could be reliably estimated within 90 min for all regions investigated, and within 30 min for low-binding regions such as the cerebral cortex. The rank order of VT by region corresponded well with the known distribution of α4β2* receptors (VT [thalamus] 27.4±3.8, VT [putamen] 12.7±0.9, VT [frontal cortex] 10.0±0.8, and VT [corpus callosum] 6.3±0.8). The BPND, which is a parameter of α4β2* nAChR availability, was 3.41±0.79 for the thalamus, 1.04±0.25 for the putamen and 0.61 ± 0.23 for the frontal cortex, indicating high specific tracer binding. Use of the arterial input function without metabolite correction resulted in a 10% underestimation in VT, and was without important biasing effects on BPND.