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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 cerebral expression of the A2A adenosine receptor (A2AAR) is altered in neurodegenerative disorders diseases such as Parkinson's (PD) or Huntington’s (HD) diseases, making these recep-tors an attractive diagnostic and therapeutic target. We aimed to further investigate the pharma-cokinetic properties in the brain of our recently developed A2AAR specific antagonist radioligand [18F]FLUDA. For this purpose, we retrospectively analysed dynamic PET studies of healthy mice and rotenone-treated mice, and undertook dynamic PET studies with healthy pigs. We performed analysis of mouse brain time-activity curves to calculate the mean residence time (MRT) by non-compartmental analysis and the binding potential (BPND) of [18F]FLUDA using the simplified reference tissue model (SRTM). For the pig studies, we performed a Logan graphical analysis to calculate the radiotracer distribution volume (VT) at baseline and under blocking conditions with tozadenant. The MRT of [18F]FLUDA in the striatum of mice was decreased by 30 % after treatment with the A2AAR antagonist, istradefylline. Mouse results showed the highest BPND (3.9 to 5.9) in the striatum. SRTM analysis showed a 20% lower A2AAR availability in the rotenone-treated mice compared to the control-aged group. Tozadenant treatment significantly decreased the VT (14.6 vs. 8.5 mL · g-1) and BPND values (1.3 vs. 0.3) in pig striatum. This study confirms the target specificity and a high BPND of [18F]FLUDA in the striatum. We conclude that [18F]FLUDA is a suitable tool for the non-invasive quantitation by PET of altered A2AAR expression in neurodegenerative diseases such as PD and HD.

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.

Introduction: Selective A₂AR antagonists have emerged as potential therapeutics for multiple diseases. With regard to Parkinson’s disease, adjunctive treatment of A₂AR antagonists potentially reduces adverse effects of long-term L-DOPA treatment. Therefore, imaging of receptor availability during the A2AR-tailored therapy is of utmost importance. We recently developed [¹⁸F]FLUDA as an novel A₂AR-specific PET radiotracer [1]. Methods: [¹⁸F]FLUDA was synthesized by an automated procedure Biological evaluation was performed in healthy mice and piglets. In vitro autoradiography was performed with brain cryosections. In vivo metabolism was analysed by radio-HPLC of plasma and brain homogenate. Pharamcokinetics and biodistribution was assessed by dynamic PET imaging under control and blocking conditions (2.5 mg/kg tozadenant and/or 1.0 mg/kg istradefylline). SUV ratio (SUVr) of striatum-over-cerebellum was used as a metric for specific uptake. A single dose acute toxicity study was performed in Wistar rats according to the ICH guideline M3(R2). Radiation dosimetry was investigated in piglets. Results: In vitro autoradiography revealed an A₂AR affinity (KD;) of 4.3 and 0.7 nM and an A₂AR density (Bmax) of 556 and 218 fmol/mg in the striatum of mice and piglets. No radiometabolites were detected in the mouse brain at 15 min p.i., whereas radiometabolites were found in piglet plasma but are assumed to not cross the blood-brain barrier. PET demonstrated high specific binding of [¹⁸F]FLUDA in both species (Fig.1). Toxicity studies revealed no adverse effects up to a dose of 30 µg/kg (~4000-fold of expected human dose). The ED to humans is 16.4 µSv/MBq, which is in the range of other ¹⁸F-labeled radiotracers [2]. Conclusion: We have demonstrated that [¹⁸F]FLUDA is suitable for determination of the A₂AR availability in the striatum. 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) has been funded by the European Regional Development Fund (ERDF) and Sächsische Aufbaubank (SAB). References: [1] Lai, T.H., Toussaint, M., Teodoro, R., Dukić-Stefanović, S., Gündel, D., Ludwig, F.-A., Wenzel, B., Schröder, S., Sattler, B., Moldovan, R.-P., Falkenburger, B.H., Sabri, O., Winnie Deuther-Conrad, W., Peter Brust, P. Improved in vivo PET imaging of the adenosine A₂A receptor in the brain using [¹⁸F]FLUDA, a deuterated radiotracer with high metabolic stability. Eur J Nucl Med Mol Imaging 2021, 48, 2727–2736. [2] Sattler, B., Kranz, M., Lai, T.H., Gündel, D., Toussaint, M., Schröder, S., Moldovan, R.-P., Winnie Deuther-Conrad, W., Teodoro, R., Sabri, O., Peter Brust, P. Preclincal incorporation dosimetry of [¹⁸F]FLUDA - a novel ¹⁸F-labeled tracer for PET imaging of the expression of the adenosine A₂A receptor (A₂AR). J Nucl Med 2020, 61:1014.

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

Purpose: Pridopidine is an investigational drug for Huntington disease (HD). Pridopidine was originally thought to act as a dopamine stabilizer. However, pridopidine shows highest affinity to the sigma-1 receptor (S1R) and enhances neuroprotection via the S1R in preclinical studies. Using [18F] fluspidine and [18F] fallypride PET, the purpose of this study was to assess in vivo target engagement/receptor occupancy of pridopidine to the S1R and dopamine D2/D3 receptor (D2/D3R) at clinical relevant doses in healthy volunteers (HVs) and as proof-of-concept in a small number of patients with HD. Methods: Using [18F] fluspidine PET (300 MBq, 0–90 min), 11 male HVs (pridopidine 0.5 to 90 mg; six dose groups) and three male patients with HD (pridopidine 90 mg) were investigated twice, without and 2 h after single dose of pridopidine. Using [18F] fallypride PET (200 MBq, 0–210 min), four male HVs were studied without and 2 h following pridopidine administration (90 mg). Receptor occupancy was analyzed by the Lassen plot. Results: S1R occupancy as function of pridopidine dose (or plasma concentration) in HVs could be described by a three-parameter Hill equation with a Hill coefficient larger than one. A high degree of S1R occupancy (87% to 91%) was found throughout the brain at pridopidine doses ranging from 22.5 to 90 mg. S1R occupancy was 43% at 1 mg pridopidine. In contrast, at 90 mg pridopidine, the D2/D3R occupancy was only minimal (~ 3%). Conclusions: Our PET findings indicate that at clinically relevant single dose of 90 mg, pridopidine acts as a selective S1R ligand showing near to complete S1R occupancy with negligible occupancy of the D2/D3R. The dose S1R occupancy relationship suggests cooperative binding of pridopidine to the S1R. Our findings provide significant clarification about pridopidine’s mechanism of action and support further use of the 45-mg twice-daily dose to achieve full and selective targeting of the S1R in future clinical trials of neurodegenerative disorders. Clinical Trials.gov Identifier: NCT03019289 January 12, 2017; EUDRA-CT-Nr. 2016-001757-41. © 2020, The Author(s).

Introduction Electrical gastric vagus nerve stimulation (VNS) shifts the sympathetic-vagal balance toward a parasympathetic predominance (1). We aim to assess central changes in α7 nAChR-mediated transmission and hypothesize that VNS changes the parasympathetic tone by changing the α7 nAChR availability in the nucleus tractus solitarii (NTS) and distinct cortical and subcortical regions (2). Material and Methods Following a standard 35-frames, 120-min protocol for dynamic brain PET imaging, data from eight piglets (15.6 ± 3.2 kg, ~6 weeks) were acquired post injection of 194.8 ± 9.4 MBq of [18F]DBT-10 (3) followed by T1-MPRAGE MRI: three baseline, two with infusion of the acetylcholine esterase inhibitor physostigmine (0.04 mg/kg, 1 ml/min, at 10 min prior to tracer injection; 0.24 mg/kg, 1 ml/min, at tracer injection/scan start over 120 min) and three with VNS in repeated sequences of 0.5 Hz over 5 min, 5 min pause started at scan start. TACs were analyzed using a 2-tissue compartment model involving a metabolite-corrected arterial input function to generate individual total distribution volumes (VT) as receptor parameter. Results Compared to baseline, we observed an increase of the mean VT after physostigmine infusion (61 %) as well as after VNS (28 %) without major alterations of K1 in the NTS (Figure 1 and 2). Conclusion These initial data indicate blood-flow-independent changes under VNS as compared with baseline suggesting an increase in α7 nAChR availability although the changes appear more heterogeneous in VNS as compared with physostigmine. The finding is in contrast to our hypothesis expecting lower α7 nAChR-availability as a result of increased acetylcholine release following VNS. We speculate that higher VT under VNS may reflect an increase in affinity of the α7 nAChR or result in an upregulation of the α7 nAChR. Increase of VT following physostigmine administration could be related to a positive allosteric effect on the α7 nAChR. Furthermore, the results of this study allow sample size estimations for further preclinical and clinical studies.

We present the amplification of a narrow-bandwidth signal at a wavelength of 1018 nm to a power exceeding 600 W with a stable output polarization state. The beam showed an excellent, nearly diffraction-limited beam quality. The high-power output could be realized using an in-house designed and fabricated fiber with a core-cladding diameter ratio of 32/260, ultra-low NA of 0.041, and ring-up doping. A seed source with high amplified spontaneous emission (ASE) suppression was also required, which was realized by a double-pass pre-amplifier with 13 W output power.

Aim/Introduction: The question of whether the presence of the APOE ε4 allele impacts α4β2 nicotinic acetylcholine receptor (α4β2-nAChR) availability in Alzheimer’s dementia (AD) was so far mainly studied post-mortem, and is subject of a controversial debate. We aimed to answering this question in vivo using the recently developed α4β2-nAChR-specific radioligand (-)-[18F] Flubatine and PET. Materials and Methods: Non-smoking, drug-naïve AD-APOE ε4+ (n=7; 76±6ys; 6 females; MMSE 24±3) and AD-APOE ε4- (n=9; 75±7ys; 7 females; MMSE 24±2, n. sign. vs. AD-APOE ε4+) were investigated using (-)-[18F]Flubatine (370 MBq, ECAT Exact HR+, 0-90min p.i.) and compared with non-smoking healthy controls (HC; n=13; 72±4ys; 7 females). For quantification of the α4β2-nAChR availability, kinetic modeling (1TCM, Logan) was performed and the distribution volume (VT) was calculated. VOI analyses of a-priori selected brain regions and exploratory SPM analyses were carried out (ANCOVA, significance at P3.0; P

© 2018 Elsevier B.V. Through litter decomposition enormous amounts of carbon is emitted to the atmosphere. Numerous large-scale decomposition experiments have been conducted focusing on this fundamental soil process in order to understand the controls on the terrestrial carbon transfer to the atmosphere. However, previous studies were mostly based on site-specific litter and methodologies, adding major uncertainty to syntheses, comparisons and meta-analyses across different experiments and sites. In the TeaComposition initiative, the potential litter decomposition is investigated by using standardized substrates (Rooibos and Green tea) for comparison of litter mass loss at 336 sites (ranging from −9 to +26 °C MAT and from 60 to 3113 mm MAP) across different ecosystems. In this study we tested the effect of climate (temperature and moisture), litter type and land-use on early stage decomposition (3 months) across nine biomes. We show that litter quality was the predominant controlling factor in early stage litter decomposition, which explained about 65% of the variability in litter decomposition at a global scale. The effect of climate, on the other hand, was not litter specific and explained

wird nachgereicht

Ziel: Bei der Translation neuartiger Radiotracer in die klinische Phase ist eine Abschätzung der Strahlenexposition vor Erstanwendung am Menschen notwendig. Hierbei werden die Organdosen (OD) sowie die effektive Dosis (ED) am Tiermodell abgeschätzt, welche nach i.v. Injektion eines Radiotracers entstehen. Erstmalig wurde Kleintier-PET/MRT zur rein bildgebungsbasierten Inkorporationsdosimetrie mit CD-1 Mäusen eingesetzt. Um den Einfluss von Speziesunterschieden zu untersuchen wurden PET/CT-Studien an Ferkeln durchgeführt und die Ergebnisse mit am Menschen erhobenen Ergebnissen (PET/CT) verglichen. Methodik: Nach i.v. Injektion von (-)- oder (+)-[18F]Flubatine (a, b) bzw. (S)- oder (R)-[18F]Fluspidine (c,d) wurden (i) In-vivo-PET/MRT- (MEDISO nanoScan, Budapest) und PET/CT-Scans (SIEMENS Biograph 16) bis zu 7 h p.i. durchgeführt, die List-Mode Daten unter Nutzung der Standardkorrekturen rekonstruiert und die Organaktivitäten (OA) mit ROVER (ABX, Radeberg) bestimmt; (ii) (a, c, d) Ex-vivo-Organentnahme an Mäusen und Messung der OA in einem Gammacounter durchgeführt (Goldstandard). Nach Extrapolation der Tierdaten auf menschliche Verhältnisse, wurden die OD und die ED mit OLINDA für 3 Spezies berechnet. Ergebnisse: Die Dosimetrie für a/b ergab eine ED (µSv/MBq) von 12,5/12,1 (30 Mäuse), 13,4/14,3 (8 Ferkel), 22,3/23,0 (n=6 Menschen) und für (c/d) 12,9/14,0 (6 Mäuse), 21,0/n.a. (4 Menschen). Während a und b eine vergleichbare Biokinetik sowie ED zeigen, ist die ED von c und d signifikant (p=0,025) verschieden basierend auf Enantiomeren Unterschieden. Weiterhin zeigt sich eine Unterschätzung der ED erhoben mit Tierdaten im Vergleich zum Menschen von 38% (Ferkel) bis 47% (Mäuse). Schlussfolgerung: Die Strahlenexposition nach i.v. Applikation von a,b,c,d liegt im Bereich der durch andere F-18-markierter Radiotracer. Die Abschätzung der ED unter Nutzung von Tiermodellen mit Hilfe eines Kleintier-PET/MRT ist unter Berücksichtigung der genannten Limitationen möglich und liefert mit dem Ex-vivo-Goldstandard vergleichbare Ergebnisse.

The 6th annual meeting to address key issues in positron emission tomography (PET)/magnetic resonance imaging (MRI) was held again in Tübingen, Germany, from March 27 to 29, 2017. Over three days of invited plenary lectures, round table discussions and dialogue board deliberations, participants critically assessed the current state of PET/MRI, both clinically and as a research tool, and attempted to chart future directions. The meeting addressed the use of PET/MRI and workflows in oncology, neurosciences, infection, inflammation and chronic pain syndromes, as well as deeper discussions about how best to characterise the tumour microenvironment, optimise the complementary information available from PET and MRI, and how advanced data mining and bioinformatics, as well as information from liquid biomarkers (circulating tumour cells and nucleic acids) and pathology, can be integrated to give a more complete characterisation of disease phenotype. Some issues that have dominated previous meetings, such as the accuracy of MR-based attenuation correction (AC) of the PET scan, were finally put to rest as having been adequately addressed for the majority of clinical situations. Likewise, the ability to standardise PET systems for use in multicentre trials was confirmed, thus removing a perceived barrier to larger clinical imaging trials. The meeting openly questioned whether PET/MRI should, in all cases, be used as a whole-body imaging modality or whether in many circumstances it would best be employed to give an in-depth study of previously identified disease in a single organ or region. The meeting concluded that there is still much work to be done in the integration of data from different fields and in developing a common language for all stakeholders involved. In addition, the participants advocated joint training and education for individuals who engage in routine PET/MRI. It was agreed that PET/MRI can enhance our understanding of normal and disrupted biology, and we are in a position to describe the in vivo nature of disease processes, metabolism, evolution of cancer and the monitoring of response to pharmacological interventions and therapies. As such, PET/MRI is a key to advancing medicine and patient care.

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.

Der Abstract wird nachgereicht.