A theranostic prodrug based on FRET for real-time drug release monitoring in response to biothiols.

The clinical applications of tradition prodrug are restricted to a certain extent due to its some defects such as side effects, low selectivity and single function. Herein, we designed a theranostic strategy based on the fluorescence resonance energy transfer (FRET) mechanism. The theranostic prodrug was constructed with an anticancer drug camptothecin (CPT), a cleavable linker based on disulfide bonds (SS) and a fluorophore naphthalimide derivative (NAP). For this drug delivery and reporting system (NAP-SS-CPT), FRET occurs between CPT (energy donor) and NAP (energy receptor); and upon cellular uptake by GSH-overexpressing cancer cells, disulfide bonds could be successfully cleaved by the high concentration of GSH, and FRET process was interrupted to achieve dual fluorescence response and specifically release of CPT. The drug delivery system features some favorable properties, like excellent pH-stability, high selectivity and cytotoxicity towards GSH-overexpressing cells and relatively lower cytotoxicity towards normal cells. Fluorescence analysis reveals that NAP-SS-CPT shows a ratiometric fluorescence signal under excitation at 400nm for quantitative detection of GSH. Intracellular fluorescence imaging studies indicate that the prodrug can be efficiently internalized in HeLa cells and used for real-time monitoring of drug release. Moreover, MTT and flow cytometry assay indicate that NAP-SS-CPT exhibits high pro-apoptotic effect for cancer cells. This strategy may provide a new approach for cancer diagnosis and therapy.