A reducible polycationic gene vector derived from thiolated low molecular weight branched polyethyleneimine linked by 2-iminothiolane

To improve transfection efficiency and reduce the cytotoxicity of polymeric gene vectors, reducible polycations (RPC) were synthesized from low molecular weight (MW) branched polyethyleneimine (bPEI) via thiolation and oxidation. RPC (RPC-bPEI0.8 kDa) possessed MW of 5 kDa–80 kDa, and 50%–70% of the original proton buffering capacity of bPEI0.8 kDa was preserved in the final product. The cytotoxicity of RPC-bPEI0.8 kDa was 8–19 times less than that of the gold standard of polymeric transfection reagents, bPEI25 kDa. Although bPEI0.8 kDa exhibited poor gene condensing capacities (∼2 μm at a weight ratio (WR) of 40), RPC-bPEI0.8 kDa effectively condensed plasmid DNA (pDNA) at a WR of 2. Moreover, RPC-bPEI0.8 kDa/pDNA (WR ≥2) formed 100–200 nm-sized particles with positively charged surfaces (20–35 mV). In addition, the results of the present study indicated that thiol/polyanions triggered the release of pDNA from RPC-bPEI0.8 kDa/pDNA via the fragmentation of RPC-bPEI0.8 kDa and ion-exchange. With negligible polyplex-mediated cytotoxicity, the transfection efficiencies of RPC-bPEI0.8 kDa/pDNA were approximately 1200–1500-fold greater than that of bPEI0.8 kDa/pDNA and were equivalent or superior (∼7-fold) to that of bPEI25 kDa/pDNA. Interestingly, the distribution of high MW RPC-bPEI0.8 kDa/pDNA in the nucleus of the cell was higher than that of low MW RPC-bPEI0.8 kDa/pDNA. Thus, the results of the present study suggest that RPC-bPEI0.8 kDa has the potential to effectively deliver genetic materials with lower levels of toxicity.