Reducible polyrotaxane-based pseudo-comb polycations via consecutive ATRP processes for gene delivery.

Supramolecular cyclodextrin polyrotaxane (PR) has attracted much attention due to their unique flexible properties. In this work, the reducible PR-based cationic block copolymer (SS-PR) was prepared via ATRP of DMAEMA based on the self-assembled pseudo-PR. A series of pseudo-comb polycations (SS-PR-pDM) with different molecular weights were subsequently produced via two-step ATRP of DMAEMA by using bromoisobutylryl-functionalized SS-PR as the macroinitiator. Incorporation of disulfide linkages in the backbone of PR permits the SS-PR and pseudo-comb SS-PR-pDM to be readily disassembled upon reductive stimuli. SS-PR-pDM exhibited the enhanced pDNA-condensing ability and similarly low toxicity compared with SS-PR. Meanwhile, SS-PR-pDM displayed higher cell internalization rates (88% for SS-PR-pDM3 vs. 77% for SS-PR) and luciferase gene transfection efficiency. The percentages of the EGFP-positive HeLa cells mediated by SS-PR-pDM3 and SS-PR were 44% and 22%, respectively. Furthermore, the favorable property of the pseudo-comb SS-PR-pDM benefited pDNA entering the nucleus. The present work demonstrates that properly grafting cationic side chains from reducible PR backbones via consecutive ATRP processes was one effective means to produce new PR-based supramolecular polycations. STATEMENT OF SIGNIFICANCE: Supramolecular cyclodextrin polyrotaxanes (PR) had been attracted much attention due to their unique flexible properties. In this work, two kinds of bioreducible PR-based polycations were synthesized via consecutive ATRP processes for gene delivery. The bioreducible PR-based cationic block copolymer (SS-PR) was prepared via ATRP of DMAEMA based on the self-assembled pseudopolyrotaxane of α-cyclodextrins (α-CD) with a disulfide-linked bromoisobutylryl-terminated PEG. Then, a series of pseudo-comb polycations (SS-PR-pDM) with different molecular weights were subsequently produced by using SS-PR-Br macroinitiators via step-two ATRP of DMAEMA. Incorporation of disulfide linkages in bromoisobutylryl-terminated PEG permits the SS-PR and pseudo-comb SS-PR-pDM to be readily disassembled upon reductive stimuli, contributing to gene delivery efficiency. SS-PR-pDM displayed higher cell internalization and gene transfection efficiency. In addtion, the favorable property of the pseudo-comb SS-PR-pDM benefited pDNA entering the nucleus. The present work demonstrates that properly grafting pDMAEMA side chains from bioreducible polyrotaxane backbones via consecutive ATPR processes was one effective means to produce new PR-based supramolecular polycations.