Torild Wickstrøm

Radiolabeled Fucoidan as a P-Selectin Targeting Agent for In Vivo Imaging of Platelet-Rich Thrombus and Endothelial Activation

P-selectin expression is involved in the pathophysiology of biologically active arterial thrombus and endothelial activation after a transient ischemic event. Fucoidan is a polysaccharidic ligand of P-selectin, with a nanomolar affinity. In the present study, we propose a new approach of P-selectin molecular imaging based on radiolabeled fucoidan. Methods: Two kinds of experimental models were selected to evaluate the ability of radiolabeled fucoidan to detect P-selectin expression: platelet-rich arterial thrombi (vegetations of infective endocarditis and arterial mural thrombus) and myocardial ischemia–reperfusion. These 2 settings were chosen because they were clinically relevant, and both were associated with an important overexpression of platelet and endothelial P-selectin, respectively. Results: 99mTc-fucoidan SPECT was able to detect the presence of platelet-rich arterial thrombi in all animals, with a median target-to-background ratio of 5.2 in vegetations of endocarditis and 3.6 in mural aneurysmal thrombus, and to detect a persistent endothelial activation at 2 h after reperfusion. In this latter model, the magnitude of the signal was correlated with the extent of myocardium that underwent transient ischemia. The sensitivity of selectivity of the uptake and retention of 99mTc-fucoidan in both settings was excellent. Conclusion: This study supports 99mTc-fucoidan as a relevant imaging agent for in vivo detection of biologic activities associated with P-selectin overexpression, such as arterial thrombus and ischemic memory. Given the reported wide availability at a low cost, and its low toxicity, fucoidan seems to overcome some of the limitations of previous P-selectin–targeted imaging agents.

The development of an automated and GMP compliant FASTlab™ Synthesis of [18F]GE‐180; a radiotracer for imaging translocator protein (TSPO)

The level of the translocator protein (TSPO) increases dramatically in microglial cells when the cells are activated in response to neuronal injury and insult. The radiotracer [(18) F]GE-180 binds selectively and with high affinity to TSPO and can therefore be used to measure neuroinflammation in a variety of disease states. An optimized, automated synthesis of [(18) F]GE-180 has been developed for the GE FASTlab™ synthesizer. The entire process takes place on the single-use cassette. The radiolabelling is performed by nucleophilic fluorination of the S- enantiomer mesylate precursor. The crude product is purified post-radiolabelling using two solid-phase extraction cartridges integrated on the cassette. Experimental design and multivariate data analysis were used to assess the robustness, and critical steps were optimized with respect to efficacy and quality. The average radiochemical yield is 48% (RSD 6%, non-decay corrected), and the synthesis time including purification is approximately 43 min. The radiochemical purity is ≥95% for radioactive concentration ≤1100 MBq/mL. The total amount of precursor-related chemical impurities is 1-2 µg/mL. The use of solid-phase extraction purification results in a robust GMP compliant process with a product of high chemical and radiochemical purity and consistent performance across positron emission tomography (PET) centers.

Dynamic TSPO-PET for assessing early effects of cerebral hypoxia and resuscitation in new born pigs

INTRODUCTION Inflammation associated with microglial activation may be an early prognostic indicator of perinatal hypoxic ischemic injury, where translocator protein (TSPO) is a known inflammatory biomarker. This piglet study used dynamic TSPO-PET with [18F]GE180 to evaluate if microglial activation after global perinatal hypoxic injury could be detected. METHODS New born anesthetized pigs (n = 14) underwent hypoxia with fraction of inspired oxygen (FiO2)0.08 until base excess -20 mmol/L and/or a mean arterial blood pressure decrease to 20 mm Hg, followed by resuscitation with FiO2 0.21 or 1.0. Three piglets served as controls and one had intracranial injection of lipopolysaccharide (LPS). Whole body [18F]GE180 Positron emission tomography-computed tomography (PET-CT) was performed repeatedly up to 32 h after hypoxia and resuscitation. Volumes of interest were traced in the basal ganglia, cerebellum and liver using MRI as anatomic correlation. Standardized uptake values (SUVs) were measured at baseline and four time-points, quantifying microglial activity over time. Statistical analysis used Mann Whitney- and Wilcoxon rank test with significance value set to p < 0.05. RESULTS At baseline (n = 5), mean SUVs ±1 standard deviation were 0.43 ± 0.10 and 1.71 ± 0.62 in brain and liver respectively without significant increase after hypoxia at the four time-points (n = 5-13/time point). Succeeding LPS injection, SUV increased 80% from baseline values. CONCLUSIONS Cerebral inflammatory response caused by severe asphyxia was not possible to detect with [18F]GE180 PET CT the first 32 h after hypoxia and only sparse hepatic uptake was revealed. ADVANCES IN KNOWLEDGE Early microglial activation as indicator of perinatal hypoxic ischemic injury was not detectable by TSPO-PET with [18F]GE180. IMPLICATIONS FOR PATIENT CARE TSPO-PET with [18F]GE180 might not be suitable for early detection of perinatal hypoxic ischemic brain injury.