Guanidinium-functionalized Block Copolyelectrolyte Micelleplexes for Safe and Efficient siRNA Delivery

RNAi-based therapeutics utilizing small interfering RNAs (siRNAs) are of significance in the clinic as it serves great potentials for gene-based treatment of human diseases. Currently, siRNA-based RNAi efficiency has been limited by facile degradation, poor cell membrane penetration, and short half-life time of siRNA. In this study, block copolyelectrolytes containing a poly(ethylene oxide) (PEO) neutral block and a cationic block were synthesized by anionic polymerization and post-polymerization modification. In the cationic block, guanidinium and ammonium groups were randomly incorporated with various fractions to achieve micelleplexes for safe and efficient siRNA delivery. Compared to traditional polyethylenimine-based polyplexes, all micelleplexes exhibited enhanced cellular internalization and better gene silencing efficiency with higher stability. As the fraction of guanidinium groups increased, the uptake level and siRNA transfection were enhanced due to stronger binding of guanidinium groups with siRNA. However, the trade-off between cellular internalization and toxicity was inevitable with increasing guanidinium fraction. The fraction of guanidinium group in block copolyelectrolytes was optimized by the systemic evaluation of cytotoxicity and gene silencing efficiency of the micelleplexes.