1. Fluorine-18-Labeled Antibody Ligands for PET Imaging of Amyloid-β in Brain
- Author
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Stina Syvänen, Johanna Rokka, Xiaotian T. Fang, Dag Erlend Olberg, Lars Lannfelt, Jonas Eriksson, Dag Sehlin, and Rebecca Faresjö
- Subjects
Genetically modified mouse ,Fluorine Radioisotopes ,Physiology ,Cognitive Neuroscience ,Transferrin receptor ,Ligands ,trans-cyclooctene (TCO) ,Biochemistry ,Mice ,03 medical and health sciences ,Tetrazine ,chemistry.chemical_compound ,0302 clinical medicine ,inverse electron demand Diels−Alder reaction ,Animals ,Distribution (pharmacology) ,positron emission tomography (PET) ,030304 developmental biology ,0303 health sciences ,biology ,Chemistry ,Brain ,inverse electron demand Diels-Alder reaction ,Cell Biology ,General Medicine ,Receptor-mediated endocytosis ,Fluorine-18 ,In vitro ,Positron-Emission Tomography ,antibody radioligand ,biology.protein ,Biophysics ,tetrazine ,Radiologi och bildbehandling ,Antibody ,030217 neurology & neurosurgery ,Research Article ,Radiology, Nuclear Medicine and Medical Imaging ,Conjugate - Abstract
Antibodies are attractive as radioligands due to their outstanding specificity and high affinity, but their inability to cross the blood–brain barrier (BBB) limits their use for CNS targets. To enhance brain distribution, amyloid-β (Aβ) antibodies were fused to a transferrin receptor (TfR) antibody fragment, enabling receptor mediated transport across the BBB. The aim of this study was to label these bispecific antibodies with fluorine-18 and use them for Aβ PET imaging. Bispecific antibody ligands RmAb158-scFv8D3 and Tribody A2, both targeting Aβ and TfR, were functionalized with trans-cyclooctene (TCO) groups and conjugated with 18F-labeled tetrazines through an inverse electron demand Diels–Alder reaction performed at ambient temperature. 18F-labeling did not affect antibody binding in vitro, and initial brain uptake was high. Conjugates with the first tetrazine variant ([18F]T1) displayed high uptake in bone, indicating extensive defluorination, a problem that was resolved with the second and third tetrazine variants ([18F]T2 and [18F]T3). Although the antibody ligands’ half-life in blood was too long to optimally match the physical half-life of fluorine-18 (t1/2 = 110 min), [18F]T3-Tribody A2 PET seemed to discriminate transgenic mice (tg-ArcSwe) with Aβ deposits from wild-type mice 12 h after injection. This study demonstrates that 18F-labeling of bispecific, brain penetrating antibodies is feasible and, with further optimization, could be used for CNS PET imaging.
- Published
- 2020
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