Background The reduction-sensitive cationic polymer is a promising nonviral carrier for gene delivery. Until now, disulfide bonds have been the only golden standard for its design. The aim of this research was to develop a novel reduction-responsive cationic polymer as a gene carrier. Methods Polycationic carriers were synthesized by addition of branched oligoethylenimine 800 Da (OEI800) via an active ester containing diselenide bonds. Disulfide bonds cross-linked with OEI800-SSx and monoselenide bonds linked with OEI800-Sex were synthesized and compared. Their molecular weights and degradation properties were determined using gel permeation chromatography. Changes in particle size, morphology, and DNA binding were investigated by dynamic light scattering, transmission electron microscopy, and electrophoresis assay in a reduction environment. Cytotoxicity and transfection in vitro were evaluated in a murine melanoma cell line (B16F10) and a human cervical epithelial carcinoma cell line (HeLa), while intracellular degradation and dissociation with DNA were studied by confocal laser scanning microscopy with FITC-labeled OEI800 derivatives and Cy5-labeled DNA. Results Diselenide-conjugated OEI800 (OEI800-SeSex) polymer carriers of high molecular weight were successfully synthesized. After compacting with DNA, the OEI800-SeSex polymers formed nanoparticles with an average size of 140 nm at an adequate C/P ratio. OEI800-SeSex showed reduction-responsive degradation properties similar to those of the OEI800-SSx via gel permeation chromatography, dynamic light scattering, and transmission electron microscopy. OEI800-SeSex showed much lower cytotoxicity than PEI25k, and significantly higher transfection efficiency than OEI800 in both B16F10 and HeLa cells. Transfection of luciferase in the OEI800-SeSex group was comparable with that of standard PEI25k and traditional reduction-sensitive polymer OEI800-SSx groups. Furthermore, intracellular degradation of OEI800-SeSex and dissociation with DNA were also confirmed by confocal laser scanning microscopy. Conclusion The OEI800-SeSex obtained was able to bind plasmid DNA efficiently to yield nanosized particles and had reduction sensitivity which is as efficient as that for OEI800-SSx. In vitro experiments confirmed its low cytotoxicity and high transfection ability. Diselenide bonds can be used as effective and novel reduction-sensitive linkages for gene delivery.
