Influence of the molecular weight of bioreducible oligoethylenimine conjugates on the polyplex transfection properties.

The purpose of the present study was to investigate the influence of molecular weights on the chemical, biophysical, and biological properties of bioreducible oligoethylenimine conjugates. The cationic conjugates were synthesized by polyaddition between branched oligoethylenimine 800 Da (OEI) and the disulfide bond containing N,N'-cystamine bisacrylamide (CBA) linker. A correlation between the copolymer molecular weights and the polyplex transfection properties was found. The OEI-CBA copolymers differing in molecular weights (from 8.6 to 37 kDa) showed good plasmid DNA binding ability resulting in compact 90- to 150-nm-sized polyplexes. Colloidal stability of the polyplexes was lost in reductive environment. A low concentration of dithiothreitol of 5 microM was sufficient to render polyplexes unstable in size. Reducing conditions at physiological salt concentration triggered polyplex dissociation. The bioreducible polymers displayed much lower cytotoxicity (IC(50) approximately 100 microg/mL in cell culture) than branched polyethylenimine 25 kDa (BPEI) and linear polyethylenimine 22 kDa (LPEI). Reporter gene transfection experiments were done with CHO-K1 and B16-F10 cells. The largest (37 kDa) copolymer HC-6-8 demonstrated highest transfection levels among all the bioreducible copolymers, which was comparable with LPEI and much more effective than BPEI.