The prospective use of the block copolymers poly(ethylene oxide)-b-poly[2-(diethylamino)ethyl methacrylate] (PEO-b-PDEA) and poly[oligo(ethylene glycol)methyl ether methacrylate]-b-poly[oligo(ethylene glycol)methyl ether methacrylate-co-2-(diethylamino)ethyl methacrylate-co-2-(diisopropylamino)ethyl methacrylate] (POEGMA-b-P(OEGMA-co-DEA-co-DPA)) as nonviral gene vectors was evaluated. The polymers are able to properly condense DNA into nanosized particles (R ≈ 75 nm), which are marginally cytotoxic and can be uptaken by cells. However, the green fluorescent protein (GFP) expression assays evidenced that DNA delivery is essentially negligible meaning that intracellular trafficking hampers efficient gene release. Subsequently, we demonstrate that cellular uptake and particularly the quantity of GFP-positive cells are substantially enhanced when the block copolymer polyplexes are produced and further supplemented by BPEI chains (branched polyethylenimine). The dynamic light scattering/electrophoretic light scattering/isothermal titration calorimetry data suggest that such a strategy allows the adsorption of BPEI onto the surface of the polyplexes, and this phenomenon is responsible for increasing the size and surface charge of the assemblies. Nevertheless, most of the BPEI chains remain freely diffusing in the systems. The biological assays confirmed that cellular uptake is enhanced in the presence of BPEI and principally, the free highly charged polymer chains play the central role in intracellular trafficking and gene transfection. These investigations pointed out that the transfection efficiency versus cytotoxicity issue can be balanced by a mixture of BPEI and less cytotoxic agents such as for instance the proposed block copolymers.

The use of sugar-functionalized polyplexes as a nonviral gene delivery vector with lower cytotoxicity than the well-known polymeric carrier branched polyethyleneimine (BPEI) is investigated. The substitution of primary amine groups in the BPEI chains with lactose residues leads to larger polyplexes, presumably due to the higher amount of polymer required to complete DNA condensation. Nevertheless, the sugar functionalization substantially reduces the cytotoxicity of the assemblies. The nanocomplexes are taken up by the cells to a greater extent, whereas the levels of gene expression are maintained compared to those obtained using BPEI, which is known for its excellent transfection efficiency. Accordingly, the preparation of lower-cytotoxicity polyplexes while maintaining gene expression, which is highly relevant to the field, is demonstrated.