Abstract
Positron emission tomography (PET) is a quickly expanding, non-invasive molecular imaging technology, and there is high demand for new specific imaging probes. Herein, we present a generic protocol for direct radiolabeling of heat-sensitive biomolecules with the positron-emitting radioisotope fluorine-18 (18F) using the aluminum fluoride restrained complexing agent (Al18F-RESCA) method. The Al18F-RESCA method combines the chemical advantages of a chelator-based radiolabeling method with the unique physical properties of the radionuclide of choice, fluorine-18. Proteins of interest can be conjugated to RESCA via amine coupling using (±)-H3RESCA-TFP, followed by purification using size-exclusion chromatography (SEC). Next, RESCA-derivatized biomolecules can be labeled in one step, at room temperature (~20 °C) in an aqueous medium with aluminum fluoride (Al18F). Al18F-labeled proteins can be obtained with moderate (12–17 GBq/µmol) to good (80–85 GBq/µmol) apparent molar activity, depending on the starting activity of 18F–. In addition, satisfactory radiochemical yields (35–55%, non–decay corrected) and high radiochemical purity (>98%, using gel filtration or solid-phase purification) are obtained. The mild radiolabeling procedure takes 0.5 h to complete and can be used for direct labeling of vector molecules such as peptides, protein scaffolds, and engineered antibody fragments.
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Acknowledgements
The authors thank J. Cleynhens, J. Cornelis, I. Sannen, J. Peetroons, S. Celen, H.-J. Verhaegen, and P. Haspeslagh from the Laboratory for Radiopharmaceutical Research (University of Leuven); J. De Jonge from the In vivo Cellular and Molecular Imaging Center (Vrije Universiteit Brussel); and S. Muyldermans from the Cellular and Molecular Imaging Laboratory (Vrije Universiteit Brussel). This research received support from IWT Flanders (SBO 130065 MIRIAD, G.B., N.D.; SBO S000218N MATATUM, N.D.), the EU (H2020-MSCA-ITN PET3D, C.X., J.B., N.D.), and the FWO (G0D8817N, G.B.; G066615N, C.X., N.D.). F.C. is a Postdoctoral Fellow of FWO (12R3119N).
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F.C., J.L., N.D., C.X., and G.B. designed the research. J.L. synthesized the RESCA ligands. F.C., T.T., and J.B. performed the experimental work. F.C., T.T., and G.B. wrote the manuscript. G.B. is the corresponding author.
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A patent application related to this work has been filed (WO/2016/065435; F.C., J.L., G.B.). The RESCA chelator will be made commercially available from Chematech in the near future. F.C., J.L., and G.B. will receive a part of the profit. The remaining authors declare no competing interests.
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Cleeren, F. et al. Theranostics 7, 2924–2939 (2017) http://www.thno.org/v07p2924.htm
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Cleeren, F., Lecina, J., Bridoux, J. et al. Direct fluorine-18 labeling of heat-sensitive biomolecules for positron emission tomography imaging using the Al18F-RESCA method. Nat Protoc 13, 2330–2347 (2018). https://doi.org/10.1038/s41596-018-0040-7
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DOI: https://doi.org/10.1038/s41596-018-0040-7
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