Polysarcosine functionalised cationic polyesters efficiently deliver self-amplifying mRNA

Messenger RNA (mRNA) technology is a potent platform for new vaccines and therapeutics. To deliver RNA medicines effectively, safe delivery vectors are crucial. Among these, poly(β-amino ester)s (PBAEs) complexes with nucleic acids have been shown as promising alternatives to conventional lipid nanoparticles, but toxicity and colloidal stability concerns still remain. Conjugation of poly(ethylene glycol) (PEG) has been used to mitigate these issues, but challenges associated with PEG-induced reactogenicity have emerged. Polysarcosine (pSar) has shown promise as a PEG alternative, demonstrating reduced reactogenicity when incorporated into lipid nanoparticles. We therefore developed a synthetic route to conjugate pSar on to PBAE end-groups, resulting in a pSar-PBAE-pSar triblock copolymer. Polyplexes containing various ratios (0, 20, 50, 80, 100% pSar) of the pSarylated and a non-pSarylated PBAE were prepared with self-amplifying messenger RNA, to examine the effect of surface pSar density. RNA encapsulation efficiencies, formulation properties and gene transfectability in vitro were then assessed indicating complete encapsulation of the cargo and sub-200 nm particle diameters in all cases. Despite high gene transfection in HEK293T cells, only the 50%-pSar displayed significantly higher expression of the reporter gene than the negative control in Caco-2. Further evaluation of 50%-pSar was conducted using 3D human colorectal cancer organoids, which displayed high transfection ability within the core of the organoid indicating high penetration of these nanoparticles. As a result, these findings indicate that pSarylated PBAEs have the potential to serve as a promising component material for enhancing delivery of nucleic acid therapeutics.