Hongzhe Li

Pentablock copolymers of poly(ethylene glycol), poly((2-dimethyl amino)ethyl methacrylate) and poly(2-hydroxyethyl methacrylate) from consecutive atom transfer radical polymerizations for non-viral gene delivery.

Well-defined pentablock copolymers (PBPs) of P(HEMA)-b-P(DMAEMA)-b-PEG-b-P(DMAEMA)-b-P(HEMA) (in which PEG=poly(ethylene glycol), P(DMAEMA)=poly((2-dimethyl amino)ethyl methacrylate), and P(HEMA)=poly(2-hydroxyethyl methacrylate)), with different block lengths of P(DMAEMA), for non-viral gene delivery were prepared via consecutive atom transfer radical polymerizations (ATRPs) from the same di-2-bromoisobutyryl-terminated PEG (Br-PEG-Br) center block. The PBPs demonstrate good ability to condense plasmid DNA (pDNA) into 100-160 nm size nanoparticles with positive zeta potentials of 25-35 mV at PBPs/pDNA weight ratios of 5-25. The PBPs exhibit very low in vitro cytotoxicity and excellent gene transfection efficiency in HEK293 and COS7 cells. In particular, the transfection efficiencies of all the PBPs in HEK293 cells are comparable to, or higher than those of polyethylenimine (PEI, 25 kDa) at most weight ratios. The ability of the copolymers to condense plasmid DNA and the transfection efficiency of the resulting complexes are dependent on the chain length of P(DMAEMA) blocks. In addition to reducing the cytotoxicity and increasing the stability of the plasmid complexes, the PEG center block and the short P(HEMA) end blocks also help to enhance the gene transfection efficiency. Thus, the approach to well-defined block copolymers via ATRP provides a versatile means for tailoring the structure of non-viral gene vectors to meet the requirements of low cytotoxicity, good stability and high transfection capability for gene therapy applications.

Cationic polyrotaxanes as gene carriers: physicochemical properties and real-time observation of DNA complexation, and gene transfection in cancer cells.

Cationic polymers have been studied as promising nonviral gene delivery vectors. In contrast to the conventional polycations with long sequences of covalently bonded repeating units, we have developed a series of novel cationic polyrotaxanes consisting of multiple oligoethyleneimine-grafted beta-cyclodextrin rings threaded on a poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) triblock copolymer chain. In this study, these cationic polyrotaxanes with different oligoethyleneimine chain lengths were investigated for DNA binding ability, cytotoxicity, and gene transfection efficiency in cancer cells. Fluorescent titration assay results indicated that all the polyrotaxanes could completely condense plasmid DNA and form stable complexes at N/P ratio of 2, where the N/P ratio is the molar ration of amine groups in the cationic molecule to phosphate groups in the DNA. Particularly, tapping mode AFM imaging in aqueous environment was conducted to observe the morphology of the polyrotaxane/DNA complexes and their formation processes in real time. In both SK-OV-3 and PC3 cancer cells, these polyrotaxanes showed low cytotoxicity and high transfection efficiency which is comparable to or significantly higher than that of high molecular weight branched polyethylenimine (25 kDa), one of the most effective gene-delivery polymers studied to date. In addition, the synthesized polyrotaxanes displayed sustained gene delivery capability in PC3 cells in the presence or absence of serum. Therefore, these cationic polyrotaxanes with strong DNA binding ability, low cytotoxicity, and high and sustained gene delivery capability have a high potential as novel nonviral gene carriers in clinical cancer gene therapy.

Cationic supramolecules consisting of oligoethylenimine-grafted α-cyclodextrins threaded on poly(ethylene oxide) for gene delivery

In this study, three cationic polyrotaxanes composed of multiple oligoethylenimine-grafted alpha-cyclodextrin rings threaded on a poly(ethylene oxide) chain have been synthesized and characterized, and investigated for gene delivery. All three cationic polyrotaxanes could efficiently compact pDNA into small nanoparticles, with diameters ranging from 100 to 200 nm. In both BHK-21 and MES-SA cell lines, the transfection efficiency mediated by the cationic polyrotaxanes were comparable or even higher than that of branched polyethylenimine (PEI) with a molecular weight of 25 kDa, which is one of the most efficient gene-delivery vectors to date. Moreover, the cationic polyrotaxanes showed much lower cytotoxicity than branched PEI (25 kDa). Hence, these cationic poly rotaxanes have high potentials as new carriers for gene delivery.

Injectable Supramolecular Hydrogels Self-Assembled by Polymers and Cyclodextrins for Controlled Drug Delivery

Of many polymeric biomaterials, hydrogels are of special importance because of their favorable biocompatibility and pertinence in delivering delicate bioactive agents such as proteins. Physical hydrogels have attracted much attention for controlled drug delivery because of the mild and aqueous conditions involved in trapping bioactive agents. This paper reviews our recent progress on developing a new class of physical hydrogels based on the supramolecular self-assembly between cyclodextrins and bioabsorbable poly(ethylene oxide) (PEO) or its copolymers. Being thixotropic, the hydrogels can be injected through needles and applied as injectable drug delivery systems. The properties of the hydrogels also can be fine-tuned with triblock copolymers where PEO segments flank hydrophobic or biodegradable segments in the middle.