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  • Pre-targeted Imaging of Protease Activity Via In Situ Assembly of Nanoparticles. Angewandte Chemie (International ed. in English) Rao, J., Chen, Z., Chen, M., Zhou, K. 2020


    Pre-targeted strategies combine high specificity of macromolecules such as antibodies for target binding and rapid clearance of small molecular ligands to image target molecules. However, pre-targeted imaging of the activity of enzymes has not been described likely due to the lack of a mechanism to retain the injected substrate in the first step for subsequent labeling. Here we report the use of  two   bioorthogonal reactions-the condensation reaction of aromatic nitriles and aminothiols, and the  inverse-electron demand Deals-Alder reaction (IEDDA) between tetrazine and trans-cyclooctene (TCO) -to develop a novel strategy for pre-targeted imaging of the activity of proteases.  The substrate  probe bearing TCO (TCO-C-SNAT4) can be selectively activated by an enzyme target (e.g. caspase-3/7), which triggers macrocyclization and subsequent in situ self-assembly into nanoaggregates retained at the target site. Our results show that tetrazine-imaging tag conjugate is able to label TCO in the nanoaggregates to generate selective signal retention for imaging in vitro, in cells and in mice. Due to the decoupling of enzyme activation and imaging tag immobilization, TCO-C-SNAT4 can be repetitively injected to generate and accumulate more TCO-nanoaggregates for click labeling. This strategy should be particularly attractive for imaging the activity of enzymes with slow kinetics using short-lived radioisotopes.

    View details for DOI 10.1002/anie.201916352

    View details for PubMedID 32056345