Drug ‘clicking’ on cell-penetrating fluorescent nanoparticles for in cellulo chemical proteomics

Chemical proteomics approaches are widely used to identify molecular targets of existing or novel drugs. This manuscript describes the development of a straightforward approach to conjugate azide-labeled drugs via click chemistry to alkyne-tagged cell-penetrating fluorescent nanoparticles as a novel tool to study target engagement and/or identification inside living cells. A modification of the Baeyer test for alkynes allows monitoring the Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) reaction, guaranteeing the presence of the drug on the solid support. As a proof of concept, the conjugation of the promiscuous kinase inhibitor dasatinib to Cy5-labeled nanoparticles is presented. Dasatinib-decorated fluorescent nanoparticles efficiently inhibited its protein target SRC in vitro, entered cancer cells, and colocalized with SRC in cellulo.