Reduction-responsive fluorescence off–on BODIPY–camptothecin conjugates for self-reporting drug release

A reduction-responsive fluorescence off-on theranostic prodrug with self-reporting drug release was constructed based on boron dipyrromethene (BODIPY) and therapeutic drug camptothecin (CPT) with a long flexible disulfide linker. Treatment with dithiothreitol (DTT) induced cleavage of the disulfide bond, followed by intramolecular cyclization reaction to release free CPT, simultaneously perturbing electronic energy transfer (EET) and resulting in enhanced blue and green fluorescence emissions. The changes of the fluorescence ratio over time provided the opportunity for detection and real-time monitoring of drug release at the cellular levels. In addition, the disulfide-linked dyad composed of hydrophobic molecules could self-assemble into stable nanoparticles in aqueous solution, facilitating drug delivery and cancer therapy in vivo due to the enhanced permeation and retention (EPR) effect. Nanomedicines displayed similar fluorescence enhancement in tumor cells. These findings confirm that this dye-disulfide-drug system (DDD) has a significant potential for thiol-activated cancer theranostic and self-reporting drug release in a clinical setting.