A strategy to improve serum-tolerant transfection activity of polycation vectors by surface hydroxylation.

The aim of this contribution is to develop a universal method to promote the serum-tolerant capability of polycation-based gene delivery system. A "hydroxylation camouflage" strategy was put forward by coating the polycation vectors with hydroxyl-enriched "skin". Branched polyethyleneimine (PEI) was herein used as the polycation model and modified via the catalyst-free aminolysis reaction with 5-ethyl-5-(hydroxymethyl)-1,3-dioxan-2-oxo (EHDO). PEI-g-EHDO, PEI and alkylated PEI derivative termed as PEI-g-DPA were comparatively explored with respect to the transfection efficiency in the serum-free and serum-conditioned medium. The resultant data indicate that the serum-tolerant capability largely depended on the surface composition and substitution degree. In addition to the reduced surface charge, the introduced function caused by hydroxyl coating is believed to play a crucial role for the improved properties of PEI-g-EHDOs. The EHDO modification can effectively inhibit the adsorption of BSA proteins onto polyplexes surface. And the polyplexes stability was remarkably enhanced in the presence of DNase and heparin after EHDO modification. Note that the transfection activity of PEI-g-EHDO(34.5%) in the serum-conditioned medium was even higher than that without serum addition. In contrast, serum addition led to appreciable reduction in the transfection efficiency mediated by PEI and PEI-g-DPAs. Specifically, as far as the transfection activity in the presence of serum is concerned, PEI-g-EHDO could be up to 30-fold higher than unmodified PEI25k. PEI-g-EHDO(34.5%) displayed little to no hemolytic effect and high cell-biocompatibility with nearly no cytotoxicity detected in 293T cells and HeLa cells. Taking into account the high biocompatibility and serum-tolerant transfection activity, PEI-g-EHDO(34.5%) holds great potential for the use as efficient gene vector. More importantly, it is expected that such "hydroxylation camouflage" strategy may be universally applicable for a majority of existing polycation vectors.

Fabrication of lactobionic-loaded chitosan microcapsules as potential drug carriers targeting the liver.

This paper demonstrates a general approach for fabrication of lactobionic chitosan microcapsules using layer-by-layer assembly via click chemistry. Chitosan was selectively modified with either azide (CHI-Az) or alkyne (CHI-Alk) groups. The growth of the CHI-Az/CHI-Alk click multilayer was studied experimentally by multilayer assembly on planar supports. Linear buildup of the film was observed. The chitosan click capsules were also analyzed with confocal laser scanning microscopy and transmission electron microscopy. Capsules were found to have regular spherical shapes. In addition, (CHI-Az/CHI-Alk)-coated particles were modified with fluorescein isothiocyanate to ensure that the particles can be easily post-functionalized. Finally, lactobionic acid was conjugated onto the (CHI-Az/CHI-Alk)-coated particles and the lactobionic particles exhibited hepatoma cell (HepG2) targeting behavior.

Self-Assembled Micelles Based on PEG-Polypeptide Hybrid Copolymers for Drug Delivery.

A series of amphiphilic poly(L-leucine)-block-poly(ethylene glycol)-block-poly(L-leucine) (PLL-PEG-PLL) hybrid triblock copolymers have been synthesized. All the blocks in this system have good biocompatibility and low toxicity. The PLL-PEG-PLL copolymers could self-assemble into micelles with PLL blocks as the hydrophobic core and PEG blocks as the hydrophilic shell, which were characterized by FT-IR, (1) H NMR, and transmission electron microscopy analysis. The critical micellar concentration of the copolymer was 95.0 mg · L(-1) . The circular dichroism spectrum shows that the PLL segments adopt a unique α-helical conformation, which is found to play an important role in controlling the drug release rate. The drug release could be effectively sustained by encapsulation in the micelles. The copolymers may have potential applications in drug delivery.

Peptide-functionalized thermo-sensitive hydrogels for sustained drug delivery.

In this study, a KRGDKK (Lys-Arg-Gly-Asp-Lys-Lys) peptide with a RGD sequence is utilized as a functional group to synthesize a novel thermo-sensitive hydrogel. The KRGDKK peptide prepared by a solid phase synthesis approach is coupled to the ends of a poly[(epsilon-caprolactone)-co-lactide]-poly(ethylene glycol)-poly[(epsilon-caprolactone)-co-lactide] (PCLA-PEG-PCLA) triblock copolymer to obtain peptide-PCLA-PEG-PCLA-peptide. The self-assembly behavior of both PCLA-PEG-PCLA and peptide-PCLA-PEG-PCLA-peptide copolymers in aqueous solution is investigated, and hydrogels prepared from PCLA-PEG-PCLA and peptide-PCLA-PEG-PCLA-peptide are also prepared. An in vitro cell viability study demonstrated that the peptide-PCLA-PEG-PCLA-peptide hydrogels do not exhibit an apparent cytotoxicity, which suggests that the hydrogels have promising potential as injectable drug-delivery systems. Furthermore, compared with the PCLA-PEG-PCLA hydrogels, the peptide-PCLA-PEG-PCLA-peptide hydrogels display improved mechanical properties because of hydrogen bonding between the amino groups of KRGDKK. An in vitro drug release study showed that the peptide-PCLA-PEG-PCLA-peptide hydrogels exhibit outstanding controlled release properties and the release of the drug could be sustained for more than a month without initial burst.

Facile fabrication of diblock methoxy poly(ethylene glycol)-poly(tetramethylene carbonate) and its self-assembled micelles as drug carriers.

AB type diblock methoxy poly(ethylene glycol)-b-poly(tetramethylene carbonate) (mPEG-PTeMC) copolymers were designed for the first time and used as carriers for the sustained release of the hydrophobic drug ibuprofen. In this paper, we developed a facile ring-opening polymerization (ROP) method to prepare mPEG-PTeMC copolymers under the catalysis of Novozym-435 lipase. Attractively, the polymerization has been successfully performed at 30 degrees C, close to room temperature. The data show that the copolymer compositions agree well with the feed ratio of TeMC to mPEG, indicating the controllable feature of the polymerization. The copolymer structures were characterized by (1)H NMR, IR, SEC, and DSC measurements. mPEG-PTeMC exhibits no apparent in vitro cytotoxicity toward human embryonic kidney transformed 293T cells. Those amphiphilic copolymers can readily self-assemble into nanosized micelles (about 150 nm) in aqueous solution. Their critical micelle concentrations are in the range of (1.6-9.3) x 10(-7) mol/L, determined by fluorescence spectroscopy. The micelles present high stability in PBS solution, with no obvious change in micelle diameters over 5 days. Ibuprofen can be loaded effectively in mPEG-PTeMC micelles, and its sustained release behavior is observed. Transmission electron microscopy shows that the well-dispersed spherical micelles are around 25 nm in diameter, while the diameter is 30 nm after loading ibuprofen. The release rate increases when the chain length of the PTeMC block decreases. These properties show that the micelles self-assembled from mPEG-PTeMC copolymers would have great potential as carriers for the effective encapsulation as well as sustained release of hydrophobic drugs.