Reversible stabilization of DNA/PEI complexes by reducible click-linkage between DNA and polymer. A new polyplex concept for lowering polymer quantity.

Nonviral transfection of mammalian cells can be performed with electrostatic complexes (polyplexes) between a plasmid DNA (pDNA) encoding a foreign gene and a cationic polymer. However, an excess of the cationic polymer is required for pDNA condensation and polyplexes formation, which generate in vivo toxicity. Here, we present a new concept of polyplexes preparation aiming to reduce the polymer quantity. pDNA was functionalized with 3,6,9-trioxaundecan-1- {4 - [(2-chloroethyl) ethylamino)] - benzylamino}, 11-azide, and polyethyleneimine (lPEI) with reducible dibenzocyclooctyl (SS-DBCO) groups allowing azide-alkyne cycloaddition between pDNA and lPEI after condensation. The size of polyplexes with DBCO-SS-lPEI was smaller than with lPEI due to a stronger DNA condensation thanks to linkages between polymer and pDNA preventing dissociation until disulfide bridges reduction. In vitro transfection showed that the amount of DBCO-SS-lPEI leading to the most efficient polyplexes was three times lower than lPEI. As expected, toxicity in mice was significantly reduced upon intravenous injection of DBCO-SS-lPEI polyplexes at doses where the lPEI polyplexes killed mice. This is probably due to the high stability of the DBCO-SS-lPEI polyplexes which prevented their aggregation in the pulmonary capillaries. Overall, this new concept of polyplexes with DBCO-SS-lPEI offering the possibility of administering higher doses of polyplexes than lPEI and their ability to pass the pulmonary barrier could be favorably exploited for transfection of distant organs or tissues, such as tumors.