Fu-Jian Xu

Star-Shaped Cationic Polymers by Atom Transfer Radical Polymerization from β-Cyclodextrin Cores for Nonviral Gene Delivery

Cationic polymers with low cytotoxicity and high transfection efficiency have attracted considerable attention as nonviral carriers for gene delivery. Herein, well-defined and star-shaped CDPD consisting of beta-CD cores and P(DMAEMA) arms, and CDPDPE consisting of CDPD and P(PEGEEMA) end blocks (where CD = cyclodextrin, P(DMAEMA) = poly(2-(dimethylamino)ethyl methacrylate), P(PEGEEMA) = poly(poly(ethylene glycol)ethyl ether methacrylate)) for gene delivery were prepared via atom transfer radical polymerization (ATRP) from the bromoisobutyryl-terminated beta-CD core. The CDPD and CDPDPE exhibit good ability to condense plasmid DNA (pDNA) into 100-200 nm size nanoparticles with positive zeta potentials of 25-40 mV at nitrogen/phosphate (N/P) ratios of 10 or higher. CDPD and CDPDPE exhibit much lower cytotoxicity and higher gene transfection efficiency than high molecular weight P(DMAEMA) homopolymers. A comparison of the transfection efficiencies between CDPD and P(DMAEMA) homopolymer indicates that the unique star-shaped architecture involving the CD core can enhance the gene transfection efficiency. In addition to reducing cytotoxicity, the introduction of a biocompatible P(PEGEEMA) end block to the P(DMAEMA) arms in CDPDPE can further enhance the gene transfection efficiency.

Surface functionalization of polycaprolactone films via surface-initiated atom transfer radical polymerization for covalently coupling cell-adhesive biomolecules.

The ability to manipulate and control the surface properties, without altering the substrate properties, is of crucial importance in the designing of biomedical materials. In this work, surface-initiated atom transfer radical polymerization (ATRP) is employed to tailor the functionality of polycaprolactone (PCL) film surfaces in a well-controlled manner. Functional polymer brushes of glycidyl methacrylate (GMA) were prepared via surface-initiated ATRPs from the PCL film surfaces. Kinetics study revealed that the chain growth from the PCL films was consistent with a controlled process. The dense and reactive epoxide groups of the grafted P(GMA) brushes were used for the direct coupling of cell-adhesive collagen and Arg-Gly-Asp-Ser (RGDS) peptides to improve the cell-adhesion properties of the PCL film surface. These modified surfaces were evaluated by culturing of a cell line, 3T3 fibroblasts. The cell attachment and proliferation were improved remarkably on the collagen (or RGDS) functionalized PCL film surfaces. The adhesion results also indicated that the collagen-coupled PCL film surface is better for the cell-adhesion process. With the versatility of surface-initiated ATRP and the good biocompatibility nature of biomolecules, the PCL films with desirable surface functionalities can be precisely tailored to cater to various biomedical applications.

Improvement of hemocompatibility of polycaprolactone film surfaces with zwitterionic polymer brushes.

Polycaprolactone (PCL) has been widely adopted as a scaffold biomaterial, but further improvement of the hemocompatibility of a PCL film surface is still needed for wide biomedical applications. In this work, the PCL film surface was functionalized with zwitterionic poly(3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate) (P(DMAPS)) brushes via surface-initiated atom transfer radical polymerization (ATRP) for enhancing hemocompatibility. Kinetics study revealed an approximately linear increase in graft yield of the functional P(DMAPS) brushes with polymerization time. The blood compatibilities of the modified PCL film surfaces were studied by platelet adhesion tests of platelet-rich plasma and human whole blood, hemolysis assay, and plasma recalcification time (PRT) assay. The improvement of hemocompatibility is dependent on the coverage of the grafted P(DMAPS) brushes on the PCL film. Lower or no platelet and blood cell adhesion was observed on the P(DMAPS)-grafted film surfaces. The P(DMAPS) grafting can further decrease hemolysis and enhance the PRT of the PCL surface. With the versatility of surface-initiated ATRP and the excellent hemocompatibility of zwitterionic polymer brushes, PCL films with desirable blood properties can be readily tailored to cater to various biomedical applications.

Drug release behaviors of a pH sensitive semi-interpenetrating polymer network hydrogel composed of poly(vinyl alcohol) and star poly[2-(dimethylamino)ethyl methacrylate]

A series of pH sensitive semi-interpenetrating polymer network (semi-IPN) structural hydrogels composed of poly(vinyl alcohol) (PVA) and 21-arm star poly[2-(dimethylamino)ethyl methacrylate] (star PDMAEMA) with different molecular weight were prepared. Riboflavin was used as a model drug to evaluate the drug loading capacities and drug release behaviors of the semi-IPN structural hydrogels. The molecular weight of the star PDMAEMA polymers was calculated by GPC, and the formation of semi-IPN structure was confirmed by FTIR and SEM. It was found that the molecular weight of star PDMAEMA has significant effect on the structure, swelling ratio and drug release behaviors of the semi-IPN hydrogel at different pH conditions. The results suggested that the PVA/star PDMAEMA-50,000 hydrogel exhibited highest swelling ratio and drug loading capacity. The pH-sensitive semi-IPN hydrogel based on star PDMAEMA could be a promising drug delivery system due to the controllable porous structure.

Comb-shaped copolymers composed of hydroxypropyl cellulose backbones and cationic poly((2-dimethyl amino)ethyl methacrylate) side chains for gene delivery.

Cationic polymers have been of interest and importance as nonviral gene delivery carriers. Herein, well-defined comb-shaped cationic copolymers (HPDs) composed of long biocompatible hydroxypropyl cellulose (or HPC) backbones and short poly((2-dimethyl amino)ethyl methacrylate) (or P(DMAEMA)) side chains were prepared as gene vectors via atom transfer radical polymerization (ATRP) from the bromoisobutyryl-terminated HPC biopolymers. The P(DMAEMA) side chains of HPDs can be further partially quaternized to produce the quaternary ammonium HPDs (QHPDs). HPDs and QHPDs were assessed in vitro for nonviral gene delivery. HPDs exhibit much lower cytotoxicity and better gene transfection yield than high-molecular-weight P(DMAEMA) homopolymers. QHPDs exhibit a stronger ability to complex pDNA, due to increased surface cationic charges. Thus, the approach to well-defined comb-shaped cationic copolymers provides a versatile means for tailoring the functional structure of nonviral gene vectors to meet the requirements of strong DNA-condensing ability and high transfection capability.

Bioreducible POSS-cored star-shaped polycation for efficient gene delivery.

The bioreducible star-shaped gene vector (POSS-(SS-PDMAEMA)8) with well-defined structure and relatively narrow molecular weight distribution was synthesized via atom transfer radical polymerization (ATRP) of (2-dimethylamino)ethyl methacrylate (DMAEMA) from a polyhedral oligomeric silsesquioxane (POSS) macroinitiator. POSS-(SS-PDMAEMA)8 was composed of a biocompatible POSS core and eight disulfide-linked PDMAEMA arms, wherein the PDMAEMA chain length could be adjusted by controlling polymerization time. POSS-(SS-PDMAEMA)8 can effectively bind pDNA into uniform nanocomplexes with appropriate particle size and zeta potential. The incorporation of disulfide bridges gave the POSS-(SS-PDMAEMA)8 material facile bioreducibility. In comparison with POSS-(PDMAEMA)8 without disulfide linkage, POSS-(SS-PDMAEMA)8 exhibited much lower cytotoxicity and substantially higher transfection efficiency. The present work would provide useful information for the design of new POSS-based drug/gene carriers.

Biocleavable comb-shaped gene carriers from dextran backbones with bioreducible ATRP initiation sites.

It is of crucial importance to design reduction-sensitive polysaccharide-based copolymers for intracellular triggered gene and drug delivery. In this work, a simple two-step method involving the reaction of hydroxyl groups of dextran with cystamine was first developed to introduce reduction-sensitive disulfide linked initiation sites of atom transfer radical polymerization (ATRP) onto dextran. Well-defined biocleavable comb-shaped vectors consisting of nonionic dextran backbones and disulfide-linked cationic P(DMAEMA) side chains were subsequently prepared via ATRP for highly efficient gene delivery. The P(DMAEMA) side chains can be readily cleavable from the dextran backbones under reducible conditions. Moreover, the bioreducible P(DMAEMA) side chains can be functionalized by poly(poly(ethylene glycol)ethyl ether methacrylate) (P(PEGEEMA)) end blocks to reduce the cytotoxicity and further enhance the gene transfection efficiency. This present study demonstrated that properly grafting short bioreducible polycation side chains from a nonionic polysaccharide backbone with biocleavable ATRP initiation sites is an effective means to produce a class of polysaccharide-based gene delivery vectors.

In vivo treatment of tumors using host-guest conjugated nanoparticles functionalized with doxorubicin and therapeutic gene pTRAIL

The combination of gene therapy and chemotherapy may increase the therapeutic efficacy in the treatment of patients. In this work, the anti-cancer drug Dox and therapeutic gene pTRAIL-loaded host-guest co-delivery system was assayed for the possibility of in vivo synergistically treating tumors. The introduced Dox could act as an auxiliary component to human tumor necrosis factor-related apoptosis-inducing ligand-encoding plasmid gene pTRAIL. Such delivery system possessed the good ability of in vivo retention of chemotherapeutic drugs, achieved good therapeutic effects in the inhibition of tumor growth and significantly prolonged the survival time of tumor-bearing mice. With the efficient ability to co-deliver drug and gene, such host-guest assembly should have great potential applications in cancer therapy.

Cationic microRNA-delivering nanovectors with bifunctional peptides for efficient treatment of PANC-1 xenograft model

Therapeutic strategies based on modulation of microRNA activity possess much promise in cancer therapy, but the in vivo delivery of microRNA to target sites and its penetration into tumor tissues remain great challenge. In this work, miR-34a-delivering therapeutic nanocomplexes with a tumor-targeting and -penetrating bifunctional CC9 peptide were proposed for efficient treatment of pancreatic cancers. In vitro study indicated that the nanoparticle-based miR-34a delivery systems could effectively facilitate cellular uptake and greatly up-regulate the mRNA level of miR-34a in PANC-1 cell lines. The up-regulation of miR-34a remarkably induced cell cycle arrest and apoptosis, suppressed the tumor cell migration and inhibited the target gene expressions such as E2F3, Bcl-2, c-myc and cyclin D1. More importantly, the in vivo systemic administration of the developed targeting miR-34a delivery systems in a pancreatic cancer model significantly inhibited tumor growth and induced cancer cell apoptosis. Such bifunctional peptide-conjugated miRNA-delivering nanocomplexes should have great potential applications in cancer therapy.

Supramolecular pseudo-block gene carriers based on bioreducible star polycations

A series of supramolecular pseudo-block polycations (CD-SS-pDM/Ad-pPEGs) were realized by assembling bioreducible β-cyclodextrin-cored star poly (2-dimethyl amino)ethyl methacrylate with different molecular weight and an adamantine-ended linear poly(poly(ethylene glycol)ethyl ether methacrylate) (pPEGEEMA) via the host-guest interaction. The pseudo-block CD-SS-pDM/Ad-pPEG carriers were investigated in terms of DNA binding capability, cytotoxicity, gene transfection in HepG2 and COS7 cell lines, and in vivo anti-tumor activity. The pseudo-block carriers exhibited undiminished pDNA-condensing abilities compared with the starting star carriers. Meanwhile, the pseudo-block carriers displayed lower cytotoxicity and higher gene transfection efficiencies at various N/P ratios. These results are consistent with the favorable properties of pPEGEEMA as expected. Furthermore, cellular internalization results and in vivo anti-tumor activity analysis demonstrated that assembled pPEGEEMA could enhance the stability of pseudo-block carriers, thus improving their cellular internalization and gene transfection efficiency. The present study demonstrated that supramolecular pseudo-block polycations via the host-guest interaction is an effective means to produce new gene carriers.