Ion Doped Hollow Silica Nanoparticles as Promising Oligonucleotide Delivery Systems to Mesenchymal Stem Cells

Oligonucleotide (ON) therapy is a promising treatment for a wide range of complex genetic disorders, but inefficient intracellular ON delivery has hindered clinical translation. Hollow silica nanoparticles (HSN) hold potential as effective ON delivery vehicles since ON can be encapsulated in the hollow core in situ where they are protected from degradation by eg nucleases. However, HSN must be modified to allow degradation and subsequent (sub)cellular ON release. In this report, we investigated the use of ion and fluorescent dye co-doping in the HSN silica matrix to enable HSN degradability and in vitro visualization.

HSN were core encapsulated with ON, doped with Ca²⁺, Cu²⁺, Zn²⁺, Se²⁺ and Sr²⁺ ions and co-condensed with rhodamine b isothiocyanate (RITC) by a modified reverse microemulsion method. HSN were physiochemically characterized and their biological activity such as uptake and toxicity were evaluated in mesenchymal stem cells (hMSCs).

We successfully doped HSN with RITC and Ca²⁺, Cu²⁺, Zn²⁺ and Sr²⁺ ions. We observed that doping HSN with Ca²⁺ and Sr²⁺ enhanced RITC incorporation while ON encapsulation in HSN increased Cu²⁺ and Zn²⁺ doping efficiency. Moreover, our dual-doped HSN demonstrated controlled ON release in the presence of intracellular mimicking levels of glutathione (GSH) and limited release in the absence of GSH over 14 days. HSN were biocompatible in hMSCs up to 300 µg/mL except for Cu²⁺ doped HSNs which were cytotoxic even at ~10 µg/mL. HSN uptake was influenced by the dopant ion, DNA encapsulation, and HSN concentration, where Zn-HSN showed the lowest and Sr-HSN and Se-HSN_D, the highest uptake in hMSCs.

We report a straightforward one-pot procedure to create ion and fluorescent dye co-doped HSN that can efficiently incorporate ON, as promising new gene vectors.