Click Chemistry-Assisted Synthesis of a beta-D-Galactose-Targeted SiO2@RC Shell-Core Structure as a Nanoplatform for Metal-Based Complex Delivery

A facile reversed-phase microemulsion method was used to synthesize shell-core nanospheres of SiO2@RCs (SiO2-encapsuled rare-earth metal complexes). beta-D-Galactose was then grafted onto the surfaces of the nanospheres through the copper(I)-catalyzed azide-alkyne cycloaddition click reaction for targeted delivery. The chemical characteristics and surface profiles of the nanocarriers were investigated by Fourier transform infrared spectroscopy, dynamic light scattering, transmission electron microscopy, and scanning electron microscopy. A high-efficiency microwave synthesis method was applied to prepare five complex cores by the reaction of different rare-earth metal salts with two isomeric ligands, o-CPA (2-chlorophenoxyacetic acid) and m-CPA (3-chlorophenoxyacetic acid). The crystal structures of the five synthesized RC cores were confirmed through X-ray diffraction, which revealed the formulas of five RCs, [Dy(o-CPA)(3)(H2O)]center dot H2O RC1 [Ho(o-CPA)(3)(H2O)]center dot H2O RC2, 2[Er(m-CPA)(3)(H2O)]center dot 3H(2)O RC3, 2[Gd(m-CPA)(3)(H2O)]center dot 3H(2)O RC4, and [Ce-2(m-CPA)(6)(H2O)(3)]center dot 2H(2)O RC5. An in vitro cell study revealed that all RCs exhibited certain anticancer activities. RC2, in particular, showed the strongest cytotoxicity against HepG2 cells. The enhanced cell permeability and drug retention considerably improved the cytotoxicity of all SiO2@RCs-gal relative to that of RC2. The selective uptake of the beta-D-galactoseconjugated nanospheres by HepG2 cells through mechanisms mediated by cell surface receptors resulted in fewer side effects on extrahepatic tissues. Our contribution provides a novel design concept of a target SiO2@RCs-gal nanocarrier for delivering affordable antitumor complexes in cancer therapy.