Enhanced anticancer activity of an intracellularly activatable nanomedicine based on GLYlated nanodiamond

With the purpose of enriched drug-loading and controlled drug release, a lysozyme-actived nanodiamond-methotrexate prodrug (ND-PEG-GLY-MTX, NPGM) was designed based on ester linkage between glycidylated (GLYlated) nanodiamond and methotrexate (MTX). The resulting NPGM nanoparticles exhibited a high drug load capacity and excellent stability in the physiological environment. In vitro drug release profile demonstrated that MTX could be greatly released from NPGM nanoparticles in acidic environment containing lysozyme, implying the ester bond of NPGM was broken. Confocal microscope and flow cytometer showed that NPGM entered the cells via time, temperature-dependent, energy independent and caveolin-mediated endocytosis and laid in the lysosomes of the cell. Interestingly, the cytotoxicity of NPGM nanoparticles (OFF) in the extracellular medium could be acitived (ON) by lysozyme in lysosomes, due to cleavage of ester linkages when NPGM entered tumor cells. Furthermore, MTT assay and apoptosis detection uncovered that NPGM had better therapeutic effect than that of free MTX. The results show that the well-defined NPGM is a controlled release drug nanoplatform for tumor treatment and the NPGM will open the new nanodrugs window for a broad covalent coupling spectrum of anticancer agents.