Development of magnetic nanoparticles with double silica shells of different porosities for efficient siRNA delivery to breast cancer cells

A nanosystem integrating silica and Fe3O4 faces multiple challenges in small interfering RNA (siRNA) delivery, such as inefficient loading of siRNA due to siRNA being a macromolecule compared to silica pore sizes and easy oxidation of Fe3O4 due to exposure to oxygen through the porous silica shell. To tackle these challenges, here we developed novel Fe3O4-based larger-pore silica-coated nanoparticles (FLSNs) by forming clusters of Fe3O4-based amorphous silica-coated nanoparticles (FASNs) first and then coating the clusters with a mesoporous silica shell with larger pores of similar to 6-50 nm. The densely-packed less-porous amorphous silica shell on the FASNs was designed to prevent the oxidation of the Fe3O4 cores, while the larger-pore mesoporous silica shell was intended for loading siRNA macromolecules. FLSNs were synthesized in three steps. Firstly, Fe3O4 nanoparticles with a super-paramagnetic magnetite structure were fabricated. Subsequently, amorphous silica was coated onto the surface of the Fe3O4 nanoparticles through a reverse-microemulsion method to obtain FASNs. Then, FASNs were aggregated into clusters in the emulsion system formed through ultrasonic treatment and a layer of larger-pore mesoporous silica was coated onto the surface of the FASN clusters to form FLSNs using mesitylene as a pore-swelling agent. The FLSNs were further employed as a novel siRNA delivery system for inducing cancer cell apoptosis. siRNA against polo-like kinase 1 (siPLK1) was delivered by FLSNs as a model siRNA, which could induce the apoptosis of triple-negative breast cancer cells (MDA-MB-231) upon efficient cellular uptake and endosome escape. After being modified with amino groups, the FLSNs not only show a significantly higher siRNA loading efficiency, but also can be efficiently taken up by MDA-MB-231 cells. The delivered siRNA could successfully enter the cellular cytoplasm and escape from endosomal entrapment to trigger cellular apoptosis. With the aid of an external magnetic field, the siRNA delivery efficiency was further enhanced, significantly reducing the viability of the breast cancer cells. Hence, the FLSNs are promising gene delivery carriers that can be used in gene therapy. Silica-based magnetic nanoparticles are designed to deliver siRNA to triple negative breast cancer cells. The cells are killed due to siRNA-induced apoptosis upon the magnetic field-enhanced efficient cellular uptake and endosome escape of siRNA.