A Neutralized Noncharged Polyethylenimine-Based System for Efficient Delivery of siRNA into Heart without Toxicity

Cationic polymers constitute an important class of materials in development of delivery vehicles for nucleic acid-based therapeutics. Among them, polyethylenimine (PEI) has been a classical cationic carrier intensively studied for therapeutic delivery of DNA, RNA, and short RNA molecules to treat diseases. However, the development of PEI for in vivo applications has been hampered by the inherent problems associated with the material, particularly its cytotoxicity and the instability of the nucleic acid complexation systems formed via electrostatic interactions. Here, we demonstrate a strategy to modify PEI polymers via hydrazidation to create neutralized, stable, and multifunctional system for delivering siRNA molecules. Through substitution of the primary amino groups of PEI with neutral hydrazide groups, cross-linked nanoparticles with surface decorated with a model targeting ligands were generated. The neutral cross-linked siRNA nanoparticles not only showed favorable biocompatibility and cell internalization efficiency in vitro but also allowed for significant tissue uptake and gene silencing efficiency in zebrafish heart in vivo. Our study suggests transformation of conventional branched PEI into a neutral polymer that can lead to a new category of nonviral carriers, and the resulting functional delivery systems may be further explored for development of siRNA therapeutics for treating cardiovascular disease/injury.