BiologicalProfilesof CPP-FuncionalizedSiO2-GNRs for Cellular Vehicles

Over recent years, gold nanorods (GNRs) have emerged as a promising material in biomedical optics and have been proposed as contrast agents for the photothermal therapy and the photoacoustic imaging of tumors. A promising approach to target tumors is the use of cellular vehicles, i.e. immune cells that exhibit an innate tropism to tumors and that can be loaded with GNRs and used as Trojan horses. In order to improve their optical properties and thermal stability and to enhance their cellular uptake, here, GNRs are coated with silica shells, modified with polyethylene glycol (PEG) and finally functionalized with cell penetrating peptides (CPPs). Silica-coated GNRs are prepared by a modified Stöber method, with a new precursor of silica, i.e. 3-mercapto-propyl trimethoxy silane. This silica precursor enables the PEGylation of GNRs with a maleimide-PEG-carboxyl cross linker, without any further modification, which enables a simple click chemistry reaction with amino-terminated CPPs. Different silica shell thicknesses (5 and 30 nm) were chosen and samples were characterized both morphologically by TEM and DLS and optically by spectrophotometry. A murine macrophagic cellular line was used to evaluate the biological profiles of CPP-functionalized silica-coated GNRs. Their kinetics of cellular uptake were investigated at different particle concentrations (100 and 400 uM Au) and results were reported as a function of incubation time. Their cytotoxicity was addressed by a colorimetric WST-8 assay at different time points (from 4 to 48 hours) and particle concentrations (up to 400 uM Au). A good uptake, similar to CPP-GNRs without silica shell, was observed already after 4 hour of incubation for CPP-conjugate gold nanorods with 5 nm of silica coating. For the same Au concentration and incubation time it was observed a better uptake for 5 nm silica shell. We analyze cytotoxicity of CPP-conjugate silica-coated GNRs with two different shell thickness. Results show a good cell viability (>99%) up to 200 uM of CPP-SiO2@GNRs and for incubation time up to 24 hours. More work are necessary to better understand the mechanism of cytotoxicity and to remove toxic reagents before the injection into cells.