Synthesis of Amphiphilic Cationic Poly(β-amino acid) Derivatives and Their PEG Length Optimization for mRNA Transfection.

We synthesized a series of amphiphilic cationic poly(ethylene glycol)-b-poly(β-amino acid) derivatives with various lengths of PEG to investigate the effects of PEG lengths on mRNA transfection. The surface charges of the polyplexes with a DPOEG ≥ 4 gradually decreased as DPOEG increased. This indicated that hydrophilic PEG with a DPOEG ≥ 4 was exposed on the surface of the polyplexes, which was further confirmed using 1H NMR. Polyplexes with a DPOEG ≤ 4 exhibited mRNA transfection efficacy similar to that of homopolymers. However, the transfection efficacy of the polyplex with a DPOEG ≥ 12 markedly decreased, mainly because of the decreased cellular uptake and stability of the polyplexes against serum albumin. This indicated that the PEG length considerably affected the delivery efficacy of IVT mRNA. Our results provide useful information for the fundamental polymer design to optimize the PEG length of amphiphilic cationic polymers for systemic IVT mRNA delivery.