Wan-Xia Wu

Ring-Opening Polymerization for Hyperbranched Polycationic Gene Delivery Vectors with Excellent Serum Tolerance

In order to improve the transfection efficiency (TE) and biocompatibility, we synthesized a series of hyperbranched cationic polymers by ring-opening polymerization between diepoxide and several polyamines. These materials can condense plasmid DNA efficiently into nanoparticles that have much lower cytotoxicity than those derived from bPEI. In vitro transfection experiments showed that polymers prepared from branched or cyclic polyamine (P1 and P5) exhibited TE several times higher than 25KDa bPEI. More significantly, serum seemed to have no negative effect on P1-P5 mediated transfection. On the contrary, the TE of P1 improved, even when the serum concentration reached 70%. Several assays demonstrated the excellent serum tolerance of such polycationic vectors: bovine serum albumin (BSA) adsorption assay revealed considerably lower protein adsorption of P1-P5 than PEI; P1 showed better DNA protection ability from degradation by DNase I than PEI; flow cytometry results suggested that any concentration of serum may not decrease the cellular uptake of P1/DNA polyplex; and confocal laser scanning microscopy also found that serum has little effect on the transfection. By using specific cellular uptake inhibitors, we found that the polyplexes enter the cells mainly via caveolae and microtubule-mediated pathways. We believe that this ring-opening polymerization may be an effective synthetic approach toward gene delivery materials with high biological activity.

Trypsin-catalyzed tandem reaction: One-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones by in situ formed acetaldehyde

A simple, mild, one-pot tandem method catalyzed by trypsin was developed for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones by the Biginelli reaction of urea, β-dicarbonyl compounds, and in situ-formed acetaldehyde. Trypsin was found to display dual promiscuous functions to catalyze transesterification and the Biginelli reaction in sequence.

Lipase-catalyzed synthesis of azido-functionalized aliphatic polyesters towards acid-degradable amphiphilic graft copolymers

A series of novel aliphatic polyesters with azido functional groups were synthesized via the direct lipase-catalyzed polycondensation of dialkyl diester, diol and 2-azido-1,3-propanediol (azido glycerol) using immobilized lipase B from Candida antarctica (CALB). The effects of polymerization conditions including reaction time, temperature, enzyme amount, substrates and monomer feed ratio on the molecular weights of the products were studied. The polyesters with pendant azido groups were characterized by (1)H NMR, (13)C NMR, 2D NMR, FTIR, GPC and DSC. Alkyne end-functionalized poly(ethylene glycol) containing a cleavable acetal group was then grafted onto the polyester backbone by copper-catalyzed azide-alkyne cycloaddition (CuAAC, click chemistry). Using fluorescence spectroscopy, dynamic light scattering (DLS) and transmission electron microscopy (TEM), these amphiphilic graft copolymers were found to readily self-assemble into nanosized micelles in aqueous solution with critical micelle concentrations between 0.70 and 1.97 mg L(-1), and micelle sizes from 20-70 nm. The degradation of these polymers under acidic conditions was investigated by GPC and (1)H NMR spectroscopy. Cell cytotoxicity tests indicated that the micelles had no apparent cytotoxicity to Bel-7402 cells, suggesting their potential as carriers for controlled drug delivery.

Lipase-catalyzed synthesis of oxidation-responsive poly(ethylene glycol)-b-poly(β-thioether ester) amphiphilic block copolymers

A series of novel oxidation-responsive amphiphilic diblock copolymers with β-thioether ester groups were synthesized via the one-step lipase-catalyzed polycondensation of methyl 3-((2-hydroxyethyl)thio)propanoate (MHETP) with monomethoxy poly(ethylene glycol) (mPEG) using immobilized lipase B from Candida antarctica (CALB) as the catalyst. The amphiphilic poly(ethylene glycol)-b-poly(β-thioether ester) (mPEG-b-PTE) diblock copolymers could self-assemble to form nanosized micelles in aqueous solution with low critical micelle concentration (CMC). The micelles were able to undergo a H2O2-triggered disassembly due to the oxidizable thioether groups and degradable ester groups in the hydrophobic PTE core. The oxidation-responsive behaviour of the micelles was further investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Nile Red, a hydrophobic model drug, was encapsulated into the polymeric micelles and showed fast release upon the addition of H2O2. Cell cytotoxicity tests indicated that the micelles had low cytotoxicity toward HeLa cells. The oxidation-insensitive poly(ethylene glycol)-b-poly(e-caprolactone) (mPEG-b-PCL) diblock copolymer was also prepared for comparison. All these findings demonstrated the potential of mPEG-b-PTE diblock copolymers as a promising oxidation-responsive nanocarrier for controlled drug delivery.

Lipase-catalyzed regioselective domino reaction for the synthesis of chromenone derivatives

An efficient synthesis of 2H-chromenones and 2-hydroxyl-2H-chromenones derivatives has been developed from 1,3-dicarbonyls and α,β-unsaturated aldehydes by a controllable regioselective domino cyclization reaction under catalysis of different lipases. 2H-Chromenones derivatives were synthesized by bovine pancreatic lipase (BPL) in acetonitrile, while lipase from Pseudomonas fluorescens (PFL) can catalyze the synthesis of the 2-hydroxyl-2H-chromenones derivatives in dichloromethane with moderate to high yields.

Linear TACN-based cationic polymers as non-viral gene vectors

A series of linear cationic polymers were synthesized by the ring-opening polymerization between diglycidyl ethers and 1-Cbz-1,4,7-triazacyclononane (TACN). Besides the good pH buffering capacity in endosome pH range caused by TACN, these polymers have evenly distributed hydroxyl groups, which may benefit not only the water solubility but also their biocompatibility and serum tolerance. The polymers could condense DNA into nanoparticles with appropriate sizes and zeta-potentials. Cytotoxicity assays reveal that most of the polyplexes formed from title polymers have lower cytotoxicity than those derived from PEI. In vitro transfection assays show that some of these materials have higher transfection efficiency than bPEI, especially in tumor cells with the presence of serum. Flow cytometry and confocal microscopy were applied to further confirm their good serum tolerance. The structure–activity relationship of such type of polymeric vectors was also discussed. Results suggest that the ring-opening polymerization may be an effective synthetic approach toward gene delivery materials with high biological activity.

Novel biocompatible fluorescent polymeric micelles based on 1,8-naphthalimide derivatives for cell imaging

Two novel fluorescent polymeric nanoparticles developed by the aqueous self-assembly of micelles exhibited the desired permeability for cell imaging. In particular, one of the fluorescent polymeric nanoparticles has been successfully used as an excellent intracellular pH sensor in whole living cells, based on PET inhibition.

Investigation on the microstructure of as-deformed NiCr microwires using TEM

Ultra-fine NiCr (80/20 wt%) wires with a nanocrystalline (nc) grain and diameters that range from 21 μm to 25 μm were fabricated using a cold-drawing method. The engineering strains were 8.8%, 17.3%, 26.4%, 36.1%, and 46.6%. The microstructures of the drawn direction and wire cross-section were characterized using transmission electron microscopy (TEM). Two thinning preparation techniques were used in preparing the TEM specimens. The grain size was approximately 3 nm to 20 nm. The deformed microstructures include amorphous GBs, crystal GBs, edge dislocations and twins. Amorphous boundaries may be produced by phase transition or dislocation pile-up. Several edge dislocations existed at the grain boundaries (GBs) and grain interior. Twinning deformation microstructures were found in cross-sections with an asymmetrical relationship. The possible deformation mechanism for the formation of the microstructure is discussed.

Water-soluble mitochondria-targeting polymeric prodrug micelles for fluorescence monitoring and high intracellular anticancer efficiency

A series of mitochondria-targeting amphipathic prodrugs were developed and subsequently the relationship of different locations of TPP modification and molecular weights of mPEG for selective imaging and therapeutic targeting were tested. The aqueous self-assembled micelles can realize controlled release of free drug, with a faster release at alkaline pH.