Redox/ATP switchable theranostic nanoparticles for real-time fluorescence monitoring of doxorubicin delivery

In this study, redox/ATP switchable theranostic nanoparticles (TNs) with precise specificity and controllable mobility were developed for the real-time monitoring of the release of an anticancer drug. A fluorescent probe (FAM) and a quencher (BHQ-1) were covalently conjugated to one end of an adenosine-5′-triphosphate (ATP) aptamer and its complementary DNA (cDNA), respectively. Then, doxorubicin (DOX) was intercalated within the DNA duplex to form a stable physical conjugate (FBA@DOX). Poly(ethylene glycol)-block-poly (aspartic acid-graft-cystamine) (PAS), a glutathione-sensitive cationic polymer, was synthesized and complexed with the FBA@DOX, endowing it with excellent stability in physiological solutions. Fluorescence recovery/quenching, DNase degradation, in vitro drug release, cellular uptake, and intracellular trafficking results revealed that the TNs remained in the “OFF” state, with a minimal FAM fluorescent signal and negligible DOX premature release, in low-glutathione and/or low-ATP environments. In contrast, the TNs turned “ON” and rapidly released FBA@DOX in glutathione-rich environments after internalization in cancer cells. The intracellular ATP triggered the conformational changes in FBA@DOX, thereby enabling the controlled release of DOX and simultaneous recovery of the fluorescence for monitoring the DOX release. In a cytotoxicity and apoptosis study, the redox/ATP switchable TNs demonstrated strong anticancer effects, attributable to their selective release of the drug. Overall, our findings may offer a promising strategy for developing a new generation of “smart” theranostic platforms.