Direct Aromatic 18F-Labeling of Highly Reactive Tetrazines for Pretargeted Bioorthogonal PET Imaging

Pretargeted bioorthogonal imaging can be used to visualize and quantify slow accumulating targeting vectors with short-lived radionuclides such as fluorine-18 - the most clinically applied Positron Emission Tomography (PET) radionuclide. Pretargeting results in higher target-to-background ratios compared to conventional imaging approaches using long-lived radionuclides. Currently, the tetrazine ligation is the most popular bioorthogonal reaction for pretargeted imaging, but a direct18 F-labeling strategy for highly reactive tetrazines, which would be highly beneficial if not essential for clinical translation, has thus far not been reported. In this work, a simple, scalable and reliable direct 18 F-labeling procedure has been developed and applied to obtain a pretargeting tetrazine-based imaging agent with favorable characteristics (target-to-background ratios and clearance) that may qualify it for future clinical translation.

Direct Aromatic 18F-Labeling of Highly Reactive Tetrazines for Pretargeted Bioorthogonal PET Imaging

Pretargeted bioorthogonal imaging can be used to visualize and quantify slow accumulating targeting vectors with short-lived radionuclides such as fluorine-18 - the most clinically applied Positron Emission Tomography (PET) radionuclide. Pretargeting results in higher target-to-background ratios compared to conventional imaging approaches using long-lived radionuclides. Currently, the tetrazine ligation is the most popular bioorthogonal reaction for pretargeted imaging, but a direct18 F-labeling strategy for highly reactive tetrazines, which would be highly beneficial if not essential for clinical translation, has thus far not been reported. In this work, a simple, scalable and reliable direct 18 F-labeling procedure has been developed and applied to obtain a pretargeting tetrazine-based imaging agent with favorable characteristics (target-to-background ratios and clearance) that may qualify it for future clinical translation.

Evaluation of [64Cu]Cu-NOTA-PEG7-H-Tz for Pretargeted Imaging in LS174T Xenografts—Comparison to [111In]In-DOTA-PEG11-BisPy-Tz

Pretargeted nuclear imaging for the diagnosis of various cancers is an emerging and fast developing field. The tetrazine ligation is currently considered the most promising reaction in this respect. Monoclonal antibodies are often the preferred choice as pretargeting vector due to their outstanding targeting properties. In this work, we evaluated the performance of [64Cu]Cu-NOTA-PEG7-H-Tz using a setup we previously used for [111In]In-DOTA-PEG11-BisPy-Tz, thereby allowing for comparison of the performance of these two promising pretargeting imaging agents. The evaluation included a comparison of the physicochemical properties of the compounds and their performance in an ex vivo blocking assay. Finally, [64Cu]Cu-NOTA-PEG7-H-Tz was evaluated in a pretargeted imaging study and compared to [111In]In-DOTA-PEG11-BisPy-Tz. Despite minor differences, this study indicated that both evaluated tetrazines are equally suited for pretargeted imaging.

Concise Synthesis of Functionalized Cyclobutene Analogues for Bioorthogonal Tetrazine Ligation

Novel bioorthogonal tools enable the development of new biomedical applications. Here we report the concise synthesis of a series of aryl-functionalized cyclobutene analogues using commercially available starting materials. Our study demonstrates that cyclobutene acts as a small, strained dienophile to generate stable substrates suitable for bioorthogonal tetrazine ligation.

Interfacial tetrazine click chemistry mediated assembly of multifunctional colloidosomes

We demonstrate that tetrazine ligation chemistry can be employed to cross-link and assemble gold nanoparticles at the water-oil interface to create plasmonic colloidosomes. These biocompatible colloidosomes exhibit size tunability via...

Light-activated tetrazines enable live-cell spatiotemporal control of bioorthogonal reactions

Bioorthogonal ligations encompass coupling chemistries that have considerable utility in living systems.1–3 Among the numerous bioorthogonal chemistries described to date, cycloaddition reactions between tetrazines and strained dienophiles are widely used in proteome, lipid, and glycan labeling due to their extremely rapid kinetics.4,5 In addition, a variety of functional groups can be released after the cycloaddition reaction,6,7 and drug delivery triggered by in vivo tetrazine ligation8 is in human phase I clinical trials.9 While applications of tetrazine ligations are growing in academia and industry, it has so far not been possible to control this chemistry to achieve the high degrees of spatial and temporal precision necessary for modifying mammalian cells with single-cell resolution. Here we demonstrate visible light-activated formation of tetrazines from photocaged dihydrotetrazines, which enables live-cell spatiotemporal control of rapid biorthogonal cycloaddition reactions between tetrazines and dienophiles such as trans-cyclooctenes (TCOs). Photocaged dihydrotetrazines are stable in conditions that normally degrade tetrazines, enabling efficient early-stage incorporation of bioorthogonal handles into biomolecules such as peptides. Photocaged dihydrotetrazines allow the use of non-toxic visible light to trigger tetrazine ligations on live mammalian cells. By tagging reactive phospholipids with fluorophores, we demonstrate modification of HeLa cell membranes with single-cell spatial resolution. Finally, we show that photo-triggered therapy is possible by coupling tetrazine photoactivation with strategies that uncage prodrugs in response to tetrazine ligation, opening up new methods for photopharmacology and precision drug delivery using bioorthogonal chemistry.