Role of boronic acid moieties in poly(amido amine)s for gene delivery

The effects of the presence of two different types of phenylboronic acids as side groups in disulfide-containing poly(amido amine)s (SS-PAA) were investigated in the application of these polymers as gene delivery vectors. To this purpose, a para-carboxyphenylboronic acid was grafted on a SS-PAA with pending aminobutyl side chains, resulting in p(DAB-4CPBA) and an ortho-aminomethylphenylboronic acid was incorporated through copolymerization, resulting in p(DAB-2AMPBA). Both polymers have 30% of phenylboronic acid side chains and 70% of residual aminobutyl side chains and were compared with the non-boronated benzoylated analogue p(DAB-Bz) of similar M(w). It was found that the presence of phenylboronic acid moieties improved polyplex formation with plasmid DNA since smaller and more monodisperse polyplexes were formed as compared to their non-boronated counterparts. The transfection efficiency of polyplexes of p(DAB-4CPBA) was approximately similar to that of p(DAB-Bz) and commercial PEI (Exgen), both in the absence and the presence of serum, indicating that p(DAB-4CPBA) and p(DAB-Bz) are potent gene delivery vectors. However, the polymers with phenylboronic acid functionalities showed increased cytotoxicity, which is stronger for the ortho-aminophenylboronic acid containing polyplexes of p(DAB-2AMPBA) than for the p(DAB-4CPBA) analog. The cytotoxic effect may be caused by increased membrane disruptive interaction as was indicated by the increased hemolytic activity observed for these polymers.