The relationship between social support and professional identity of health professional students from a two-way social support theory perspective: chain mediating effects of achievement motivation and meaning in life.

BACKGROUND: Studies has suggested that receiving social support improves the professional identity of health professional students. According to the two-way social support theory, social support includes receiving social support and giving social support. However, the effect of the two-way social support on health professional students' professional identity has not been clarified yet. METHODS: To explore the mechanism of how two-way social support affects health professional students' professional identity, an observational, cross-sectional study was conducted among a convenience and cluster sample of 1449 health professional students from two medical schools in western China. Measures included a short version of the two-way social support scale, a health professional students' professional identity questionnaire, an achievement motivation scale, and a meaning in life scale. Data were analyzed by use of SPSS26.0 software and PROCESSv4.0 plug-in. RESULTS: Receiving social support, giving social support, achievement motivation, meaning in life, and professional identity were positively correlated with each other. Receiving and giving social support not only directly predicted health professional students' professional identity, but also indirectly predicted health professional students' professional identity through the mediating roles of achievement motivation and meaning in life, and the chain mediating roles of achievement motivation and meaning in life, respectively. The effectiveness of predicting health professional students' professional identity varied among different types of two-way social support, which could be depicted as two-way social support > mainly giving social support > mainly receiving social support > low two-way social support. CONCLUSION: In the medical education, the awareness and ability of health professional students to receive and give social support should be strengthened. More attention should be drawn on the chain mediating effect of achievement motivation and meaning in life between two-way social support and professional identity. The current results shed new light on exploring effective ways of improving health professional students' professional identity, which suggested that more attention should be paid to the positive effects of mainly giving social support and two-way social support rather than only on the effects of receiving social support.

[Construction of serum-resistant cationic polymer α-CD-PAMAM and evaluation of its performances as gene delivery vector].

Polyamidoamine (PAMAM) dendrimers as synthetic gene vectors are efficient gene delivery systems. In this study, a kind of α-cyclodextrin-PAMAM conjugates polymer (Cy D-G1) was synthesized as a gene delivery vector. Based on ~1H NMR detectation, about 6.4 PAMAM-G1 molecules was grafted onto an α-CD core. Agarose gel electrophoresis revealed that Cy D-G1 could efficiently bind with DNA to condense them into nano-scale particles, which showed a similar binding capacity of PEI-25 K. Besides, it could protect DNA from DNase I degradation in a low N/P ratio. When N/P ratio in the CyD-G1/DNA polyplex was 40, the average particle size of CyD-G1/DNA polyplex was about 120 nm, and zeta potential was +21 mV. This polyplex could maintain its particle size in serum-containing solution within 360 min. In comparison with PEI-25 K carrier, CyD-G1 showed low cytotoxicity in various cell lines. Cell transfection results showed that CyD-G1 efficiently delivered DNA into cells at N/P = 80 compared with Lipofectamine 2000 and PEI-25 K. Unlike Lipofectamine 2000 and PEI-25 K, in serum-containing test condition, CyD-G1/DNA polyplex could maintain the transgene activities. The results of confocal laser scanning microscopy indicated that most DNA entered into cell nuclei within 4 h, and this phenomenon was consistent with the results calculated by flow cytometry. Taken together, CyD-G1 showed good transgene activities and the gene delivery vector could be used not only in vitro but also in vivo.

Divalent folate modification on PEG: an effective strategy for improving the cellular uptake and targetability of PEGylated polyamidoamine-polyethylenimine copolymer.

The stability and targeting ability of nanocarrier gene delivery systems are necessary conditions to ensure the good therapeutic effect and low nonspecific toxicity of cancer treatment. Poly(ethylene glycol) (PEG) has been widely applied for improving stability and as a spacer for linking ligands and nanocarriers to improve targetability. However, the cellular uptake and endosomal escape capacity of nanocarriers has been seriously harmed due to the introduction of PEG. In the present study, we synthesized a new gene delivery vector by coupling divalent folate-PEG (PEG3.4k-FA2) onto polyamidoamine-polyethylenimine (PME) copolymer (PME-(PEG3.4k-FA2)1.72). Both PEG and monovalent folate-PEG (PEG3.4k-FA1) modified PME were prepared as control polymers, which were named as PME-(PEG3.5k)1.69 and PME-(PEG3.4k-FA1)1.66, respectively. PME-(PEG3.4k-FA2)1.72 exhibited strong DNA condensation capacity like parent polymer PME which was not significantly influenced by PEG. PME-(PEG3.4k-FA2)1.72/DNA complexes at N/P = 10 had a diameter ∼143 nm and zeta potential ∼13 mV and showed the lowest cytotoxicity and hemolysis and the highest transfection efficiency among all tested polymers. In folate receptor positive (FR-positive) cells, the cellular uptake and transfection efficiency were increased with the increase in the number of folates coupled on PEG; the order was PME-(PEG3.4k-FA2)1.72 > PME-(PEG3.4k-FA1)1.66 > PME-(PEG3.5k)1.69. Folate competition assays showed that PME-(PEG3.4k-FA2)1.72 complexes had stronger targeting ability than PME-(PEG3.5k)1.69 and PME-(PEG3.4k-FA1)1.66 complexes due to their higher folate density per PEG molecule. Cellular uptake mechanism study showed that the folate density on PEG could change the endocytosis pathway of PME-(PEG3.5k)1.69 from clathrin-mediated endocytosis to caveolae-mediated endocytosis, leading to less lysosomal degradation. Distribution and uptake in 3D multicellular spheroid assays showed that divalent folate could offer PME-(PEG3.4k-FA2)1.72 complexes stronger penetrating ability and higher cellular uptake. With these advantages, PME-(PEG3.4k-FA2)1.72 may be a promising nonviral vector candidate for efficient gene delivery. This study also indicates that divalent folate modification on PEG can serve as an efficient strategy to improve the cellular uptake and targeting ability of PEGylated cationic polymers for gene delivery.

Dilution-stable PAMAM G1-grafted polyrotaxane supermolecules deliver gene into cells through a caveolae-dependent pathway.

Numerous preclinical studies have demonstrated that polycation mediated gene delivery systems successfully achieved efficient gene transfer into cells and animal models. However, results of their clinical trials to date have been disappointing. That self-assembled gene and polycation systems should be stable undergoing dilution in the body is one of the prerequisites to ensuring efficiency of gene transfer in clinical trials, but it was neglected in most preclinical studies. In this account, we developed the dilution-stable PAMAM G1-grafted polyrotaxane (PPG1) supermolecules in which PAMAM G1-grafted α-cyclodextrins are threaded onto a PEG chain capped with hydrophobic adamantanamine. The PPG1/pDNA polyplex (approximate 100 nm in diameter) was very stable and kept its initial particle size and a uniform size distribution at ultrahigh dilution, whereas DNA/PEI 25K polyplex was above three times bigger at a 16-fold dilution than the initial size and their particle size distribution indicated multiple peaks mainly due to forming loose and noncompacted aggregates. PPG1 supermolecules showed significantly superior transfection efficiencies compared to either PEI 25K or Lipofectamine 2000 in most cell lines tested including normal cells (HEK293A) and cancer cells (Bel7402, HepG2, and HeLa). Furthermore, we found that the PPG1 supermolecules delivered DNA into HEK293A through a caveolae-dependent pathway but not a clathrin-dependent pathway as PEI 25K did. These findings raised the intriguing possibility that the caveolae-dependent pathway of PPG1 supermolecule/pDNA polyplex avoiding lysosomal degradation was attributed to their high transfection efficiency. The dilution-stable PPG1 supermolecule polyplex facilitating caveolae-dependent internalization has potential applications to surmount the challenges of high dilutions in the body and lysosomal degradation faced by most gene therapy clinical trials.

Charge shielding effects on gene delivery of polyethylenimine/DNA complexes: PEGylation and phospholipid coating.

Polyethylenimine (PEI) is an efficient cationic polymer for gene delivery, but defective in biocompatibility. In this study, we developed two different strategies to shield the positively charged PEI/DNA complexes: PEGylation and lipid coating. The physicochemical properties, cytotoxicity and transfection efficiency of the two gene delivery systems were investigated. Both PEGylation and lipid coating succeeded in reducing the zeta-potential of the complexes. Lipid-coated PEI/DNA complexes (LPD complexes) and PEI/DNA complexes exhibited similar cytotoxicity, whereas PEG-PEI/DNA complexes showed lower cytotoxicity, especially at high N/P ratios. LPD complexes were less efficient in transfection compared to PEG-PEI/DNA complexes. The transfection efficiency was influenced remarkably by cytotoxicity and surface charge of the complexes. Intracellular processes studies revealed that endosomal release might be one of the rate-limiting steps in cell transfection with PEI as a gene delivery carrier.

Insulin-loaded pH-sensitive hyaluronic acid nanoparticles enhance transcellular delivery.

In the present study, we developed novel insulin-loaded hyaluronic acid (HA) nanoparticles for insulin delivery. The insulin-loaded HA nanoparticles were prepared by reverse-emulsion-freeze-drying method. This method led to a homogenous population of small HA nanoparticles with average size of 182.2 nm and achieved high insulin entrapment efficiencies (approximately 95%). The pH-sensitive HA nanoparticles as an oral delivery carrier showed advantages in protecting insulin against the strongly acidic environment of the stomach, and not destroying the junction integrity of epithelial cells which promise long-term safety for chronic insulin treatment. The results of transport experiments suggested that insulin-loaded HA nanoparticles were transported across Caco-2 cell monolayers mainly via transcellular pathway and their apparent permeability coefficient from apical to basolateral had more than twofold increase compared with insulin solution. The efflux ratio of P (app) (B to A) to P (app) (A to B) less than 1 demonstrated that HA nanoparticle-mediated transport of insulin across Caco-2 cell monolayers underwent active transport. The results of permeability through the rat small intestine confirmed that HA nanoparticles significantly enhanced insulin transport through the duodenum and ileum. Diabetic rats treated with oral insulin-loaded HA nanoparticles also showed stronger hypoglycemic effects than insulin solution. Therefore, these HA nanoparticles could be a promising candidate for oral insulin delivery.

Efficient intracellular gene delivery using the formulation composed of poly (L-glutamic acid) grafted polyethylenimine and histone.

PURPOSE: Inefficient endosomal escape and poor nuclear import are thought to contribute to low gene transfer efficiency of polycations. To overcome these drawbacks, we prepared multiple gene delivery formulations including low cytotoxic polycation, histone containing NLSs and chloroquine as the endosomolytic agent. METHODS: Comb-shaped poly (L-glutamic acid) grafted low-molecular-weight polyethylenimine (PLGE) copolymer was synthesized by aminolysis of poly-γ-benzyl-L-glutamate using low-molecular-weight polyethylenimine (800 Da). The formation of DNA/histone/PLGE terplex was observed by atomic force microscope and gel retardation assay. The particle size and zeta potential of DNA complexes with varying content of histone were also measured to confirm the terplex formation. Cytotoxicity of vectors was assayed by MTT. Multiple gene delivery formulations were optimized to their best transfection efficiency that was monitored by fluorescence microscope and flow cytometry. In vivo gene delivery of the optimal formulation was evaluated by the GFP-expression levels in drosophila melanogaster. RESULTS: The DNA/histone/PLGE terplex was successfully formed. The PLGE and histone together condensed DNA into small, discrete particles (less than 200 nm in diameter) in isotonic solution. Cytotoxicity of PLGE and histone were much lower than that of PEI 25 K. Either histone or chloroquine contributed to enhancing the levels of transfection activity of PLGE polymer. However, chloroquine and histone did not show a synergistic effect on the improvement of transfection efficiency. The optimal formulation was the DNA/histone/PLGE terplex at the N/P ratio of 15 and histone/ DNA weight ratio of 0.8. Compared with Lipofectamine 2000 and PEI 25 K, the optimal formulation showed significantly increased levels of GFP-expression both in vitro and in vivo. CONCLUSION: This formulation provided a versatile approach for preparing high efficiency of the polycation-based gene vectors. It also reinforced the finding of earlier studies that nuclear import and endosomal escape were rate-limiting steps for nonviral gene delivery.

A novel dendrimer based on poly (L-glutamic acid) derivatives as an efficient and biocompatible gene delivery vector.

Non-viral gene delivery systems based on cationic polymers have faced limitations related to their relative low gene transfer efficiency, cytotoxicity and system instability in vivo. In this paper, a flexible and pompon-like dendrimer composed of poly (amidoamine) (PAMAM) G4.0 as the inner core and poly (L-glutamic acid) grafted low-molecular-weight polyethylenimine (PLGE) as the surrounding multiple arms was synthesized (MGI dendrimer). The novel MGI dendrimer was designed to combine the merits of size-controlled PAMAM G4.0 and the low toxicity and flexible chains of PLGE. In phosphate-buffered saline dispersions the well-defined DNA/MGI complex above a N/P ratio of 30 showed good stability with particle sizes of approximately 200 nm and a comparatively low polydispersity index. However, the particle size of the DNA/25 kDa polyethylenimine (DNA/PEI 25K) complex was larger than 700 nm under the same salt conditions. The shielding of the compact amino groups at the periphery of flexible PAMAM and biocompatible PLGE chains in MGI resulted in a dramatic decrease of the cytotoxicity compared to native PAMAM G4.0 dendrimer. The in vitro transfection efficiency of DNA/MGI dendrimer complex was higher than that of PAMAM G4.0 dendrimer. Importantly, in serum-containing medium, DNA/MGI complexes at their optimal N/P ratio maintained the same high levels of transfection efficiency as in serum-free medium, while the transfection efficiency of native PAMAM G4.0, PEI 25K and Lipofectamine 2000 were sharply decreased. In vivo gene delivery of pVEGF165/MGI complex into balloon-injured rabbit carotid arteries resulted in significant inhibition of restenosis by increasing VEGF165 expression in local vessels. Therefore, the pompon-like MGI dendrimer may be a promising vector candidate for efficient gene delivery in vivo.

[PEGylation of polyamidoamine dendrimer and the properties for gene vectors].

Polyamidoamine-polyethylene glycol (PAMAM-PEG) copolymers were synthesized using IPDI as coupling reagent by two-step method. The copolymers were characterized by IR spectrum and 1H NMR spectrum, and the PEG conjugating ratios of the copolymers were calculated equal to 10% and 30% separately. MTT assay indicated that after PEGylation a lower cytotoxicity of the copolymers could be found, and with increasing PEG conjugating ratio the cytotoxicity decreased obviously. Agarose gel retardation assay demonstrated that PAMAM-PEG copolymers could be combined with DNA and PAMAM-PEG/DNA complexes were prepared by self-assembly. DLS measurement showed that when N/P > or = 50, the particle size of copolymer/ gene complexes was in a range of 150-200 nm, and the zeta potential was in a range of 10-25 mV. In vitro gene transfection illustrated that when N/P < or = 50, the gene transfection efficiency of PAMAM-PEG copolymers was a little less than that of PAMAM-G5, but the transfection efficiency can be raised by increasing N/P ratio or transfection time. Considering both cytotoxicity and transfection efficiency aspects PAMAM-PEG-13 was more effect than PAMAM-PEG-39 in PEGylation.

Interaction of DNA/nuclear protein/polycation and the terplexes for gene delivery.

Nuclear transport of exogenous DNA is a major barrier to nonviral gene delivery that needs to be addressed in the design of new vectors. In this study, we prepared pDNA/HMGB1/PEG-PEI terplexes to promote nuclear import. HMGB1 in the terplexes was used to assist the transportation of pDNA into the nucleus of cells, since it contained nuclear localization signal (NLS); PEG chains were introduced to stabilize pDNA/vector terplexes and reduce the cytotoxicity. HMGB1/PEG-PEI combined vectors have been investigated specifically for their structure interaction by atomic force microscopy and circular dichroic spectroscopy. The results demonstrated that the HMGB1 molecule could bind with the pDNA chains, but not condense pDNA well. The PEG-PEI further compacted pDNA/HMGB1 complexes into nanosized spherical terplexes. The pDNA delivered by HMGB1/PEG-PEI combined vectors was significantly accumulated in the nucleus of cells, as observed by confocal laser scanning microscopy. The percentage of GFP-transfected cells and VEGF protein expression level induced by HMGB1/PEG-PEI were 2.6-4.9-fold and 1.4-2.8-fold higher, respectively, than that of a common cationic polymer PEI 25 kDa. Therefore, the HMGB1/PEG-PEI combined vector could be used as a versatile vector for promoting exogenous DNA nuclear localization, thereby enhancing its expression.

Prevention of postoperative peritoneal adhesions by O-carboxymethyl chitosan in a rat cecal abrasion model.

PURPOSE: Post-surgical adhesion formation can result in significant morbidity and mortality. N,O-carboxymethyl chitosan (N,O-CMC) has been previously shown to be effective in the prevention of postsurgical adhesion formation. In this study, we evaluated the ability of O-carboxymethyl chitosan (O-CMC), another chitosan derivative generated by carboxymethylation of chitosan's oxygen centers, to reduce postsurgical adhesion development. METHODS: Twenty male Sprague-Dawley rats (250 +/- 20 g) were divided into two equal groups: O-CMC group and saline (control) group. All rats underwent a midline laparotomy and the cecum was abraded to cause petechial hemorrhages. Following peritoneal injections of either saline or O-CMC, the incisions were closed. Seven days after surgery, the animals were killed and adhesion formation was scored. Tissue samples from the adhesions were examined histochemically. RESULTS: Adhesion formation was significantly decreased in the O-CMC group (P < .001) in comparison with the control group. Furthermore, significantly less collagen (P < .001) and fewer inflammatory cells and fibroblasts were detected in the O-CMC-treated animals. Additionally, a significantly (P < .05) lower level of TGF-beta1 expression was found in the O-CMC group. CONCLUSION: O-CMC appears to be effective in the prevention of postoperative peritoneal adhesion formation, which may be attributed to decreased accumulation of inflammatory cells and fibroblasts and reduced collagen synthesis.

Stability of poly(ethylene glycol)-graft-polyethylenimine copolymer/DNA complexes: influences of PEG molecular weight and PEGylation degree.

Polyethylenimine (PEI) is one of the most widely investigated cationic polymers for gene delivery. However, PEI/DNA complexes are unstable and tend to aggregate. PEGylation was used to improve the stability. The stability of polymer/DNA complexes was investigated including complexation stability, aggregation stability, sedimentation stability, and nuclease stability. PEI25K/DNA complexes were liable to aggregate to large particles (500-700 nm). The aggregation was proved to be induced by phosphate anion. In the medium without phosphate anion, aggregation was prevented by electrostatic repulsion. Owing to more efficient steric repulsion, PEG2 and PEG5K excelled PEG750 in facilitating copolymers to form stable small polyplexes (below 100 nm) without aggregation regardless of phosphate anion. The steric repulsion predominated over electrostatic repulsion in stabilization.

A biodegradable low molecular weight polyethylenimine derivative as low toxicity and efficient gene vector.

Polyethylenimine (PEI) is a class of cationic polymers proven to be effective for gene delivery. However, PEI is nondegradable and the molecular weight of PEI affects the cytotoxicity and gene transfer activity. Aiming to prepare a biodegradable gene vector with high transfection efficiency and low cytotoxicity, we conjugated low molecular weight (LMW) PEIs to the biodegradable backbone polyglutamic acids derivative (PEG-b-PBLG) by aminolysis to form PEIs combined PEG-b-PLG-g-PEIs (GGI). Two copolymers, GGI 30 and GGI 40, were synthesized. The chemistry of GGI was characterized using IR, 1H NMR and 13C NMR, GPC, and CD, respectively. The degradation behaviors of copolymer GGI in papain solution were investigated. GGIs showed good DNA condensation ability and high protection of DNA from nuclease degradation. The zeta potential of the GGI/pDNA polyplexes was approximately 15 mV, and the particle size was in the range 102-138 nm at N/P ratios between 10 and 30. The particle size and the morphology of the polyplex was further confirmed by transmission electron microscope (TEM). In cytotoxicity assay, GGIs were significantly less toxic than PEI 25k. The degradation product of GGI exhibited negligible effects on cells even at high copolymer concentration. The results of GFP flow cytometry and fluorescence imaging showed that the trasnfection efficiencies of GGIs were all markedly higher than PEI 25k in Hela, HepG2, Bel 7402, and 293 cell lines. Importantly, the presence of serum had a lower inhibitive effect on the transfection activity of GGI in comparison to PEI 25k and Lipofectamine 2000. Therefore, PEG-b-PLG-g-PEI copolymers may be attractive cationic polymers for nonviral gene therapy.

Novel thermo-sensitive core-shell nanoparticles for targeted paclitaxel delivery.

Novel thermo-sensitive nanoparticles self-assembled from poly(N,N-diethylacrylamide-co-acrylamide)-block-poly(gamma-benzyl L-glutamate) were designed for targeted drug delivery in localized hyperthermia. The lower critical solution temperature (LCST) of nanoparticles was adjusted to a level between physiological body temperature (37 degrees C) and that used in local hyperthermia (about 43 degrees C). The temperature-dependent performances of the core-shell nanoparticles were systemically studied by nuclear magnetic resonance (NMR), circular dichroism (CD), fluorescence spectroscopy, dynamic light scattering (DLS), and atom force microscopy (AFM). The mean diameter of the nanoparticles increased slightly from 110 to 129 nm when paclitaxel (PTX), a poorly water-soluble anti-tumor drug, was encapsulated. A stability study in bovine serum albumin (BSA) solution indicated that the PTX loaded nanoparticles may have a long circulation time under physiological environments as the LCST was above physiological body temperature and the shell remained hydrophilic at 37 degrees C. The PTX release profiles showed thermo-sensitive controlled behavior. The proliferation inhibiting activity of PTX loaded nanoparticles was evaluated against Hela cells in vitro, compared with Taxol (a formulation of paclitaxel dissolved in Cremophor EL and ethanol). The cytotoxicity of PTX loaded nanoparticles increased obviously when hyperthermia was performed. The nanoparticles synthesized here could be an ideal candidate for thermal triggered anti-tumor PTX delivery system.

Blood compatibility improvement of titanium oxide film modified by doping La(2)O(3).

La(2)O(3) doped titanium oxide (TiO(2)) films with different concentration were deposited by means of the Radio-Frequency magnetron sputtering technique. The microstructure and surface properties of TiO(2) films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and contact angle test. The blood compatibility of the specimens was evaluated by tests of platelet adhesion. Results show that pure rutile phase is formed in doped samples and La(2)O(3) incorporation significantly improves the wettability and hemocompatibility of TiO(2) films. Our studies demonstrate that La(2)O(3) doped TiO(2) films are potentially useful biomaterials with good blood compatibility.

[Experimental study on prevention of postsurgical adhesions by using O-carboxymethylchitosan solution after an abdominal operation].

O-Carboxymethylchitosan (O-CMC) in 1000 g batch was prepared from chitin as starting material and its chemical structure was confirmed by analysis of IR and NMR. O-CMC solution, sodium hyaluronate (HA) solution and physiological saline were used in Sprague-Dawley rat model for prevention of postsurgical adhesions; after 7 days of an abdominal operation, the 3 groups were evaluated according to Belluco standard, the mean scores of O-CMC group, HA group and physiological saline group were 2.5 +/- 3.1, 3.3 +/- 3.6 and 10.3 +/- 1.0, respectively. Histological inspection showed that in O-CMC group, mesothelial cells on peritonaeum or cecum surfaces were almost restored; in HA group the injured surface of peritonaeum was mostly repaired, but in physiological saline group the injured surface of cecum was just a little repaired; there were extensive adhesions between peritonaeum and cecum, and inflammatory response was quite serious. Experimental results indicated that O-CMC and HA had excellent efficiency and O-CMC was slightly better than HA for the prevention of postsurgical adhesions.

Surface modification of polyaniline using tetraethyl orthosilicate.

A well-dispersible conducting polyaniline/silica hybrid is prepared by the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) on the surface of polyaniline in water/ethanol solution. It provides a simple and environmentally sound route for preparing the processable conducting polyaniline/silica hybrid at the nanometre level. The conductivity of polyaniline/silica hybrid is 2.43 S cm(-1) at 25 degrees C, and its powder is easily dispersed in the anhydrous ethanol or aqueous solution without any stabilizer. In addition, the structure, morphology and cyclic voltammorgram of this hybrid are also reported.

[Preparation and properties of self-assemble paclitaxel-loaded core-shell type nano-micelles].

Polyethylene glycol-polybenzyl-L-glutamate copolymer (PEG-PBLG) was synthesized and paclitaxel-loaded core-shell type nano-micelles with amphiphilic copolymer PEG-PBLG was prepared by the dialysis method. The drug loading content and entrapment efficiency were determined by HPLC. The average size and its distribution were determined by dynamic light scattering method. The paclitaxel release rate in vitro from micelles was measured by HPLC. The cell cytotoxicity in vitro was observed with MTT assay. The anti-tumor activity of paclitaxel-loaded micelles were evaluated in tumor-inhibiting test of nude mice using human liver cancer HepG-2. The results indicated that paclitaxel could be entrapped in PEG-PBLG copolymer micelles and its size was in the range of 80-265 nm which increased with an increase in molecular weight of PBLG in copolymer; in vitro the paclitaxel could be released sustainably from the micelles. In high concentration of paclitaxel (>20 microg x mL(-1)) the paclitaxel-loaded PEG-PBLG micelles displayed much less cell cytotoxicity than paclitaxel injections with Cremophor EL (P<0.05); the tumor inhibiting activity of paclitaxel-loaded PEG-PBLG micelles was similar to that of paclitaxel injections with Cremophor EL in the same paclitaxel concentration. It was concluded that the paclitaxel-loaded PEG-PBLG micelles had more uniform size and size distribution, excellent drug sustainable-release behavior, less cytotoxicity, good anti-tumor activity similar to paclitaxel injections with Cremophor EL. So paclitaxel-loaded PEG-PBLG micelles would be a novel paclitaxel preparation in clinic for the treatment of tumor.

[In vitro study on polyethylene glycol-chitosan copolymer as a gene delivery vector].

Chitosan and its derivatives are extensively studied as non-viral gene delivery vectors nowadays. Polyethylene glycol-chitosan (mPEG-CS) copolymers were synthesized by oxidation of mPEG-OH and then combined mPEG-CHO with amino groups on chitosan chains. The in vitro cytotoxicity of copolymers was evaluated by MTT method. The results showed > 70% cell viability of HeLa and A549 cells after incubation with mPEG-CS copolymer from concentration 5 to 100 microg x mL(-1). The mPEG-CS copolymers with various degrees of PEG substitution were combined with DNA and the properties of mPEG-CS/DNA complexes were investigated such as nanoparticle size, zeta potential and agarose gel analysis. The best one among all these mPEG-CS copolymers was mPEG (3.55) -CS, for its capability to condense plasmid DNA was most efficient. For this reason, mPEG (3.55) -CS was picked out to mediate plasmid enhanced green fluorescence protein (pEGFP) and transfect HeLa and A549 cells. The expression of green fluorescence protein was observed by fluorescence microscope and the transfection efficiency was detected by flow cytometry. The gene expression mediated by mPEG-CS was resistant to serum, and the optimal transfection efficiency (8.1% for HeLa cells and 4.8% for A549 cells) of mPEG-CS/EGFP system was obtained under the condition of N/P 40 and 48 h transfection time. These results indicate that mPEG-CS copolymer is an efficient non-viral gene vector.