Polypeptide-Grafted Nanodiamonds for Controlled Release of Melittin to Treat Breast Cancer

A peptide vector consisting of nanodiamonds (NDs) and PEGylated polyglutamic acid (ND@PLGPEG-<i>co</i>-PLGA) has been designed and developed. The negative charges at the surface of the vector were exploited to bind a positively charged peptide drug melittin via electrostatic interaction. The surface was saturated when the weight ratio of ND@PLGPEG-<i>co</i>-PLGA to melittin (MEL) was 5 to 1. The desorption of melittin from the surface was controlled by pH, with almost no melittin released from the nanoparticles under physiological pH conditions in 2 days. However, steady release was detected in an acidic environment. The preserved structure and activity of bound melittin were demonstrated by the HPLC and 2D MCF-7 cell culture models, respectively. The bound melittin exhibited improved toxicity toward MCF-7 cells dependent on the concentration of MEL in NDs. Our results suggested that the negatively charged polymer-coated NDs were able to release the cargo upon exposure to breast cancer cells