Polyglycerol grafting and RGD peptide conjugation on MnO nanoclusters for enhanced colloidal stability, selective cellular uptake and cytotoxicity.

An efficient surface engineering strategy for MnO nanoparticles was developed to attain enhanced colloidal stability, selective uptake by and toxicity to specific cancer cells. Specifically, MnO nanoclusters prepared by polyol method were grafted with polyglycerol (MnO-PG), and then conjugated with arginine-glycine-aspartate peptide (MnO-PG-RGD) through stepwise organic reactions. The physicochemical properties of the surface engineered MnO nanoclusters were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, dynamic light scattering, zeta potential, transmission electron microscopy and high-resolution transmission electron microscopy. The grafted PG layer not only largely enhanced the dispersibility and colloidal stability of MnO nanoclusters in physiological media, but also effectively inhibited non-specific cellular uptake of MnO-PG. MnO-PG-RGD was selectively taken up by human glioblastoma U87MG cells overexpressing αvβ3 integrins through receptor-mediated endocytosis. The internalized MnO-PG-RGD was mainly located in the lysosomes of U87MG cells. The acidity of lysosomes accelerated Mn2+ ions releasing, which promoted intracellular oxidative stress and further led to cell damage and apoptosis. The results indicate that appropriate surface functionalization can enable MnO nanoparticles to act as a potential anticancer agent in addition to their MRI functionality.