Charge Density and Molecular Weight of Polyphosphoramidate Gene Carrier Are Key Parameters Influencing Its DNA Compaction Ability and Transfection Efficiency

Abstract

A series of polyphosphoramidates (PPA) with different molecular weights (MWs) and charge densities were synthesized and examined for their DNA compaction ability and transfection efficiency. A strong correlation was observed between the transfection efficiency of PPA/DNA nanoparticles and the MW and net positive charge density of the PPA gene carriers in three different cell lines (HeLa, HEK293 and HepG2 cells). An increase in MW and/or net positive charge density of PPA carrier yielded higher DNA compaction capacity, smaller nanoparticles with higher surface charges and higher complex stability against challenges by salt and polyanions. These favorable physicochemical properties of nanoparticles led to enhanced transfection efficiency. PPA/DNA nanoparticles with the highest complex stability showed comparable transfection efficiency as PEI/DNA nanoparticles likely by compensating the low buffering capacity with higher cellular uptake and affording higher level of protection to DNA in endolysosomal compartment. The differences in transfection efficiency were not attributed by any difference in cytotoxicity among the carriers, as all nanoparticles showed minimal level of cytotoxicity under the transfection conditions. Using PPA as a model system, we demonstrated the structural dependence of transfection efficiency of polymer gene carrier. These results offer more insights into nanoparticle engineering for non-viral gene delivery.

Polyethylenimine-based nanocarriers in co-delivery of drug and gene: a developing horizon

“…The results are in complete agreement with the proton sponge hypothesis and show that PEI-mediated transfection is effective in avoiding lysosomal trafficking [39]. Polymer/DNA, using a number of possible mechanisms that include DNA protection from enzymatic degradation, faciliting cellular absorption, promoting endolysosomal escape, DNA unpacking in the cytosol, the nucleus and escorting nuclear translocation of DNA or nanoparticles [40]. The excess PEI significantly improves the efficiency of transfection of amounts of polyplex [38].…”

“…Particle aggregation results from colloidal instability and particle swelling due to charge screening, are two factors contributing to increasing particle size. Salt ions increase the size of PEI-DNA complex and the transfer efficiency, and the longer incubation period has the opposite effect [40,44]. In 2004, Grosse et al, found that cytotoxic effects of PEI could be due to its ability to eliminate endosomes.…”

Branched polyethylenimine-grafted-carboxymethyl chitosan copolymer enhances the delivery of pDNA or siRNA in vitro and in vivo

“…Many reports suggest that the higher transfection efficiency of polyplexes that include nucleic acids might be attributed to the higher buffering capacity of these complexes and rapid unpackaging of nucleic acids from polymers when they are transfected into the cells. 29,39,40 As described in the above results, OCMPEI copolymers permitted easy unpackaging ability, which might account for their capacity for high rates of transfection.…”

Peptides as Promising Non-Viral Vectors for Gene Therapy

“…A large library of poly( -amino ester)s has been synthesised and systematically screened for transfection efficiency (Green et al, 2006). The effects of molecular weight and charge density of polyphosphoramidates (PPA) on DNA binding and buffering capacity have been reported (Ren et al, 2010). A series of novel enzyme-degradable polycarbonates (PC) with various aliphatic side-chains attached were prepared and shown to effectively transfect cells with virtually no toxicity (Seow & Yang, 2009a).…”