Bioreducible polymers as a determining factor for polyplex decomplexation rate and transfection.

Polyplex formation (complexation) and gene release from the polyplexes (decomplexation) are major events in polymeric gene delivery; however, the effect of the decomplexation rate on transfection has been rarely investigated. This study employed mixed polymers of poly((L)-lysine) (PLL: MW ~7.4 kDa) and reducible PLL (RPLL) (MW ~6.7 kDa) to design decomplexation rate-controllable PLL(100-x)RPLL(x)/pDNA complexes (PRL(x) polyplexes). The transfection efficiency of a model gene (luciferase) in MCF7 and HEK293 cell lines increased with increasing x (RPLL content) in the PRL(x) polyplexes until peaking at x = 2.5 and 10, respectively, after which point transfection efficiency declined rapidly. In MCF7 cells, PRL(2.5) polyplex produced 3 or 223 times higher gene expression than PLL or RPLL polyplexes, respectively. Similarly, the transfection efficiency of PRL(10) polyplex-transfected HEK293 cells was 3.8 or 67 times higher than that of PLL or RPLL polyplexes, respectively. The transfection results were not apparently related to the particle size, surface charge, complexation/compactness, cellular uptake, or cytotoxicity of the tested polyplexes. However, the decomplexation rate varied by RPLL content in the polyplexes, which in turn influenced the gene transfection. The nuclear localization of pDNA delivered by PRL(x) polyplexes showed a similar trend to their transfection efficiencies. This study suggests that an optimum decomplexation rate may result in high nuclear localization of pDNA and transfection. Understanding in decomplexation and intracellular localization of pDNA may help develop more effective polyplexes.