Unmodified and tyrosine-modified polyethylenimines as potential carriers for siRNA: Biophysical characterization and toxicity.

Polyethylenimines (PEIs) are being explored as efficient non-viral nanocarriers for nucleic acid delivery in vitro and in vivo. To address limitations regarding PEI efficacy and biocompatibility, modifications of the chemical structure of linear and branched PEIs have been introduced, including grafting with tyrosine. The aim has been to compare linear and branched polyethylenimines of a wider range of different molecular mass with their tyrosine-modified derivatives. To do so, physico-chemical and biological properties of the polymers were investigated. Even in the absence of a negatively charged nucleic acid counterpart, PEIs form particle structures with defined size and surface potential. Tyrosine modification of PEI led to significantly reduced toxicity, while simultaneously increasing interaction with cellular membranes. All the effects were also dependent on the PEI molecular weight and structure (i.e., linear vs. branched). Especially in the case of linear PEIs, the improved membrane interaction also translated into slightly enhanced hemolysis, whereas their genotoxic potential was essentially abolished. Due to the improvement of properties critical for nano-vector efficacy and biocompatibility, our data demonstrate that tyrosine-modified PEIs are very promising and safe nanocarriers for the delivery of small RNAs, like siRNAs and miRNAs.