Novel reduction-responsive cross-linked polyethylenimine derivatives by click chemistry for nonviral gene delivery

Novel reducible disulfide-containing cross-linked polyethylenimines (PEI-SS-CLs) were synthesized via click chemistry and evaluated as nonviral gene delivery vectors. First, about four azide pendant groups were introduced into a low-molecular-weight (LMW) PEI (1.8 kDa) to get an azide-terminated PEI. Then, click reaction between a disulfide-containing dialkyne cross-linker and the azide functionalized LMW PEI resulted in a high-molecular-weight disulfide-containing cross-linked PEI composed of LMW constitute via a reducible cross-linker. The synthesized polymers were characterized by (1)H NMR, FTIR, and size-exclusion chromatography (SEC). It was shown that the obtained disulfide-containing cross-linked PEIs were able to condense plasmid DNA into positively charged nanoparticles. The degradation of the disulfide cross-linked polymers PEI-SS-CLs induced by DTT was confirmed by a gel retardation assay and SEC analysis. In vitro experiments revealed that the reducible PEI-SS-CLs were less cytotoxic and more effective in gene transfection (in both the presence and absence of serum) than the control nondegradable 25-kDa PEI. This study demonstrates that a reducibly degradable cationic polymer composed of LMW PEI cross-linked via a disulfide-containing linker possesses both higher gene transfection efficiency and lower cytotoxicity than PEI (25 kDa). These polymers are therefore attractive candidates for further in vivo evaluations.