Guanidine-phosphate interactions stabilize polyion complex micelles based on flexible catiomers to improve mRNA delivery

Abstract

Messenger RNA (mRNA) holds great potential as therapeutic agent, though its broad applicability is hampered by its rapid degradation by nuclease attacks and poor access to cells. Polyion complex (PIC) micelles comprising block catiomers are promising mRNA carriers, because of their effective mRNA protection in the PIC core and the capability to promote mRNA cellular uptake. We have recently shown that flexible polycations can promote the interaction between catiomers and mRNA toward improving delivery efficiency, demonstrating that, by engineering the PIC formation, the efficacy of mRNA-loaded PIC micelles (mRNA/m) can be improved. Herein, we focused on the valency between the polycation segment and mRNA, and studied its ability to promote, in collaboration with the flexible catiomers, mRNA stability and delivery efficiency for producing potent nanocarriers. The functionalities of guanidine and primary amine were compared through preparation of two different block copolymers, namely, poly(ethylene glycol)-poly(glycidyl methyl guanidine) (PEG-PGMG) and PEG-poly(glycidyl methyl amine (PEG-PGMA)). mRNA/m from PEG-PGMG (mRNA/mPGMG) showed enhanced stability against biological molecules, including polyanions, urea and nucleases compared to mRNA/m prepared from PEG-PGMA (mRNA/mPGMA), resulting in high efficiency of cellular uptake and protein translation. Our results indicate that multivalent interactions between the guanidine moieties in the polycation segments of block copolymers and the phosphate groups in mRNA are a key factor for stabilizing mRNA/m toward improving mRNA delivery efficiency.