Synthesis of amphoteric curdlan derivatives for delivery of therapeutic nucleic acids

Cationic polymers are powerful carriers for intracellular delivery of therapeutic nucleic acids. However, the positively charged macromolecules have considerable cytotoxicity and often induce irreversible damages to the cells and tissues, which greatly negate the clinical application of such materials as drug delivery system. Herein, we report the synthesis of novel amphoteric polymers based on curdlan, and the evaluation of their cytotoxicity as well as the nucleic acid delivery efficiency. β-(1,3)-polyglucuronic acid, a TEMPO-oxidized derivative of curdlan, was chemically modified by conjugation of tetraethylenepentamine. The resulting amphoteric polymers, denoted tetraethylenepentamine-curdlan (TEPAC) polymers have the degree of substitution (DS) ranging from 25% to 48%. The result of MTT assay indicated that TEPAC polymers have negligible cytotoxicity on HeLa cells and A549 cells. The novel amphoteric polymers efficiently bound with plasmid DNA and delivered pcDNA-eGFP plasmid to 293T cells and induced expression of GFP 48 h after the transfection. Moreover, TEPAC polymers delivered siRNA to HeLa cells and HepG2 cells in high efficiency, and induced significant RNAi for the expression of an endogenous gene. Collectively, our data demonstrate that the novel curdlan-based amphoteric polymers are biocompatible and may provide a highly efficient system for the delivery of therapeutic nucleic acids.