Charge-Shifting Polycations Based on N,N‑(dimethylamino)ethyl Acrylate for Improving Cytocompatibility During DNA Delivery

Synthetic polycations are studied extensively as DNA delivery agents because of their ease of production, good chemical stability, and low cost relative to viral vectors. This report describes the synthesis of charge-shifting polycations based on N,N-(dimethylamino)ethyl acrylate (DMAEA) and 3-aminopropylmethacryamide (APM), called PAD copolymers, and their use for in vitro DNA delivery into HeLa cells. PAD copolymers of varying compositions were prepared by RAFT polymerization to yield polymers of controlled molecular weights with low dispersities. Model hydrolysis studies were carried out to assess the rate of charge-shifting of the polycations by loss of the cationic dimethylaminoethanol side chains. They showed reduction in the net cationic charge by about 10-50% depending on composition after 2 days at pH 7, forming polyampholytes comprising permanent cationic groups, residual DMAEA, as well as anionic acrylic acid groups. HeLa cells exposed for 4 h to PAD copolymers with the greatest charge-shifting ability showed comparable or higher viability at high concentrations, relative to the noncharge shifting polycations PAPM and polyethyleneimine (PEI) 2 days post-exposure. Cell uptake efficiency of PAD/60bp-Cy3 DNA polyplexes at 2.5:1 N/P ratio was very high (>95%) for all compositions, exceeding the uptake efficiency of PEI polyplexes of equivalent composition. These results suggest that these PAD copolymers, and in particular PAD₈₀ containing 80 mol % DMAEA, have suitable rates of charge-shifting hydrolysis for DNA delivery, as PAD₈₀ showed reduced cytotoxicity at high concentrations, while still retaining high uptake efficiencies. In addition, the polyampholytes formed during DMAEA hydrolysis in PAD copolymers can offer enhanced long-term cytocompatibility.