Cooperative bond scission by HRP/H₂O₂ for targeted prodrug activation

The prodrug strategy provides an opportunity for improving the therapeutic index of drugs and avoiding their side effects. The main challenge lies in the fast and effective release of the parent drugs at the desired site under specific stimuli. Herein, a cooperative prodrug activation approach with exogenous native enzyme and endogenous tumor small molecule biomarkers was developed. Chemically, precursors of methylene blue (MB) and resorufin (RSF) react with horseradish peroxidase (HRP)/hydrogen peroxide (H₂O₂) to quickly and quantitatively release parent dyes and drugs containing amines or carboxylic acids. The application of this approach in mammalian cells was demonstrated with cooperative-activated photodynamic therapy based on a precursor of MB. Compared with free MB, much higher selectivity toward cancer cells was achieved with this approach as evaluated by the selectivity index (SI). This study provides a new method for fast and effective targeted prodrug activation with no need for antibody modification compared with traditional enzyme/prodrug therapy.