Bioorthogonally activatable methylene blue platform for selective prodrug activation and fluorescent imaging in...

The development of fluorescent prodrugs based on bioorthogonal chemistry involves broadening the range of fluorophores that exhibit changes in fluorescence signals and the spatiotemporally regulated release of therapeutic agents upon biorthogonal ligation. However, there are still certain gaps including shallow tissue-penetrating and low drug release efficiency, which limit its application.

Herein, we present a flexible and effective bioorthogonal scaffold that allows targeted medication release with simultaneous fluorescence emission when the targeting groups or prodrugs are conjugated. The scaffold consists of a tetrazine-caged methylene blue (MB-Tz), which serves as a dual switch for the activation of fluorophore and drug. Further encountering the TCO-caged molecular partner (TCO-RGD or TCO-Dox) triggers the NIR fluorescence reinstatement and simultaneously leads to spatiotemporal targeting and selective activation of prodrugs inside cancer cells. It was also demonstrated that bioorthogonal activation successfully inhibited tumor growth by controlled activation in vivo, with minimal systemic toxicity observed.

We envision that integration of fluorescence and bioorthogonal reactions will serve as a general small-molecule-based strategy for precisely targeted imaging and treatment in chemotherapy.