Fluorescent nanodiamonds as innovative delivery systems for MiR-34a replacement in breast cancer

Nanodiamonds are innovative nanocrystalline carbon particles able to deliver chemically conjugated miRNAs. In oncology, the use of miRNA-based therapies may represent an advantage, based on their ability to simultaneously target multiple intra- cellular oncogenic targets. Here, nanodiamonds were tested and optimized to deliver miR-34a, a miRNA playing a key role in inhibiting tumor development and progression in many cancers. The physical-chemical properties of nanodia- monds were investigated suggesting electrical stability and uni- formity of structure and size. Moreover, we evaluated nanodia- mond cytotoxicity on two breast cancer cell models and confirmed their excellent biocompatibility. Subsequently, nanodiamonds were conjugated with miR-34a, using the chem- ical crosslinker polyethyleneimine; real-time PCR analysis re- vealed a higher level of miR-34a in cancer cells treated with the different formulations of nanodiamonds than with com- mercial transfectant. A significant and early nanodiamond- miR-34a uptake was recorded by FACS and fluorescence micro- scopy analysis in MCF7 and MDA-MB-231 cells. Moreover, nanodiamond-miR-34a significantly inhibited both cell prolif- eration and migration. Finally, a remarkable anti-tumor effect of miR-34a-conjugated nanodiamonds was observed in both heterotopic and orthotopic murine xenograft models. In conclusion, this study provides a rationale for the development of new therapeutic strategies based on use of miR-34a delivered by nanodiamonds to improve the clinical treatment of neoplasms.