OFF-ON nanodiamond drug platform for targeted cancer imaging and therapy

Improving the stability of a drug system and high curative effect are imperative for efficient cancer treatments. Herein, we fabricate an excellent drug delivery system (ND-PEG-GLY-DOX, NPGD) with responsiveness toward pH based on the ester linkage between GLYlated doxorubicin (GLY-DOX) and PEGylated nanodiamonds (ND-PEG). In vitro experiments verify that NPGD can prevent the premature release of drugs, and the low pH of the intracellular lysosomes in the tumor cells regulate the drug release from the NPGD system; these result in sustained active drug release. Therefore, NPGD acts as a direct fluorescence OFF-ON messenger and therapy that can promote theranostic performances. More importantly, in vivo studies have revealed that NPGD enhanced the efficacy beyond that obtained when using free DOX and had low toxicity confirmed by blood biochemical indices and histological examinations. Such a strategy of covalently coupled drugs and controlled drug release endows the NPGD system with theranostic capabilities, which will broaden the biomedical applications of surface-nanodiamond functional design and facilitate the development of theranostic nanodiamond drug systems.