Abstract
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Objectives: PET imaging of integrin αvβ3 has been intensively studied due to its value as biomarker of angiogenesis. Several high affinity RGD peptide tracers have been successfully developed for integrin αvβ3 including [18F]FAl-NOTA-PRGD2 which provides added benefit of radiolabelling with fluorine-18 via [18F]FAl complexation. In this study we report preparation, the affinity for integrin αvβ3 and radiolabelling of a new [18F]FAl-NOTA analog of the RGD2 peptide designed using a different linker between the peptide and the NOTA moiety.
Methods: The precursor NOTA-LJ-PRDG2 was prepared by coupling PRGD2 (Peptides International, RGD-3766-PI) with NOTA-NHS (Chemmatech, C100). RP-HPLC purification provided the desired precursor, which was converted to the FAl complex by adding freshly prepared AlCl2F at 100°C in 0.1 M sodium acetate buffer. The reference FAl-NOTA-LJ-PRGD2 was recovered by RP-HPLC. In a typical labeling, 2 mM NOTA-LJ-PRGD2 in 0.2 M NaOAc was added to freshly made AlCl2[18F]F at 100°C. After 10 min the reaction mixture was subject to RP-HPLC purification. The product peak was collected, and solvents were removed by C18 cartridge. Pure [18F]FAl-NOTA-LJ-PRGD2 was eluted in ethanol followed by solvent removal and formulation in 30 mM phosphate. The tracer was ready for injection after filtration with 0.22 µm filter.
Results: The precursor NOTA-LJ-PRGD2 and the reference FAl-NOTA-LJ-PRGD2 were isolated at a yield of 63% and 33% respectively, and characterized by LCMS and ESI-MS. [18F]FAl-NOTA-LJ-PRGD2 was isolated at a yield of 9-13% with a total synthesis time of 75 minutes. The estimated specific activity was 400-1200 mCi/µmol by using activity of the final product and the total molar amount of precursor used. The in vitro characteristics of this new analog were compared with those of FPPRGD2, Alfatide II, NOTA-LJ-PRGD2 and PRGD2, and showed a comparable Ki value.
Conclusion: We successfully developed a new RGD peptide tracer that is conveniently easy to make and demonstrates a comparable Ki to other RGD2 ligands. Disclosures: All authors are employees of AbbVie. The design, study conduct, and financial support for this research were provided by AbbVie. AbbVie participated in the interpretation of data, review, and approval of the publication.