Silica-coated polyion complexes for enhanced pulmonary messenger RNA delivery with optimized silica layer stability

Pulmonary administration of messenger RNA (mRNA) therapeutics holds great promise for the treatment of lung diseases, as it facilitates local drug accumulation while reducing systemic side effects. However, the fragile nature and inefficient cellular internalization of mRNA in the respiratory epithelium are inherent bottlenecks to mRNA therapy. Although various nanomedicines, mainly lipid and polymeric nanoparticles, have been explored to protect mRNA payloads, their stability in harsh bioenvironments remains severely limited. This study highlighted silica-coated polyion complexes (SPICs) as reversibly stabilized mRNA vehicles for pulmonary mRNA delivery. A silica shell was formed on the surface of mRNA-loaded polyion complexes (PICs) through silicic acid condensation. The silica content of the shells was modulated by altering the concentration of the silica precursor during preparation. Higher silica content more effectively maintained particle uniformity, including size, in simulated lung fluids, whereas uncoated PICs aggregated immediately. However, the mRNA releasability of SPICs was compromised by an increase in silica content. Accordingly, SPICs with optimized silica content induced efficient mRNA expression in cultured lung cancer cells, which was associated with facilitated cellular uptake of mRNA payloads. Ultimately, the optimized SPICs exhibited an order of magnitude higher mRNA expression in the lungs than the uncoated PIC after administration through murine oropharyngeal aspiration. These results demonstrate that SPICs are a promising platform for local mRNA delivery with enhanced mRNA expression by balancing particle stability for payload protection and release.