Tetrazine-trans-cyclooctene ligation for the rapid construction of integrin αvβ3 targeted PET tracer based on a cyclic RGD peptide

Labeling biomolecules with 18F is usually done through coupling with prosthetic groups, which generally requires several time-consuming radiosynthetic steps resulting in low labeling yield. Recently, the tetrazine-trans-cyclooctene ligation has been introduced as a method of bioconjugation that proceeds with fast reaction rates without need for catalysis. Herein, we report the development of an extremely fast and efficient method for generating 18F labeled probes based on the tetrazine-trans-cyclooctene ligation. Starting with only 30 μg (78 μM) of a tetrazine-RGD conjugate and 2 mCi (5 μM) of 18F-trans-cyclooctene, the 18F labeled RGD peptide could be obtained in more than 90% yield within five minutes. The 18F labeled RGD peptide demonstrated prominent tumor uptake in vivo. The receptor specificity was confirmed by blocking experiments. These results successfully demonstrate that the tetrazine-trans-cyclooctene ligation serves as an efficient labeling method for PET probe construction.