Dual turn-on fluorescence signal-based controlled release system for real-time monitoring of drug release dynamics in living cells and tumor tissues.

Controlled release systems with capabilities for direct and real-time monitoring of the release and dynamics of drugs in living systems are of great value for cancer chemotherapy. Herein, we describe a novel dual turn-on fluorescence signal-based controlled release system (), in which the chemotherapy drug doxorubicin () and the fluorescent dye () are conjugated by a hydrazone moiety, a pH-responsive cleavable linker. itself shows nearly no fluorescence as the fluorescence of and is essentially quenched by the C=N isomerization and N-N free rotation. However, when activated under acidic conditions, could be hydrolyzed to afford and , resulting in dual turn-on signals with emission peaks at 595 nm and 488 nm, respectively. Notably, exhibits a desirable controlled release feature as the hydrolysis rate is limited by the steric hindrance effect from both the and moieties. Cytotoxicity assays indicate that shows much lower cytotoxicity relative to , and displays higher cell inhibition rate to cancer than normal cells. With the aid of the dual turn-on fluorescence at different wavelengths, the drug release dynamics of in living HepG2 and 4T-1 cells was monitored in double channels in a real-time fashion. Importantly, two-photon fluorescence imaging of in living tumor tissues was also successfully performed by high-definition 3D imaging. We expect that the unique controlled release system illustrated herein could provide a powerful means to investigate modes of action of drugs, which is critical for development of much more robust and effective chemotherapy drugs.