Preparation of magnetic polybutylcyanoacrylate nanospheres encapsulated with aclacinomycin A and its effect on gastric tumor

AIM: To evaluate the effect of aclacinomycin A-loaded magnetic polybutylcyanoacrylate nanoparticles on gastric tumor growth in vivo and in vitro.METHODS: Magnetic polybutylcyanoacrylate (PBCA)nanospheres encapsulated with aclacinomycin A (MPNS-ACM) were prepared by interracial polymerization. Particle size, shape and drug content were examined. Female BABL/c nude mice were implanted with MKN-45 gastric carcinoma tissues subcutaneously to establish human gastric carcinoma model. The mice were randomly divided into 5 groups of 6 each: ACM group (8 mg/kg bin); group of high dosage of MPNS-ACM (8 mg/kg bin); group of low dosage of MPNS-ACM (1.6 mg/kg bin); group of magnetic PBCA nanosphere (MPNS) and control group(normal saline). Magnets (2.5 T) were implanted into the tumor masses in all of the mice one day before the therapy.Above-mentioned drugs were administered intravenously to the mice of every group on the first day and sixth day.When the mice were sacrificed, tumor weight was measured, and the assay of granulocyte- macrophage colony forming-unit (CFU-GM) was performed on semi-solid culture. White blood cell, alanine aminotransferase and creatine were examined. 3-[4-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) was used to examine the viability of MKN-45 cells afger incubation with different concentrations of ACM, MPNS and MPNS-ACM suspension respectively for 48 h.RESULTS: Content of ACM in MPNS-ACM was 12.0% and the average diameter of the particles was 210 nm. The inhibitory rates of ACM (8 mg/kg bin), high dosage of MPNS-ACM (8 mg/kg bin), low dosage of MPNS-ACM (1.6 mg/kg bin)and MPNS on human gastric carcinoma in nude mice were 22.63%, 52.55%, 30.66% and 10.22%, respectively. There was a significant decrease in the number of CFU-GM of bone marrow in ACM group compared with control group,whereas no obvious change was observed in that of the nanosphere groups. The values of 50% inhibition concentration (IC50) of ACM, MPNS and MPNS-ACM were 0.09, 97.78 and 1.07 μg/mL, respectively.CONCLUSION: The tumor inhibitory rate of MPNS-ACM was much higher than that of ACM under magnetic field and the inhibition on bone marrow was alleviated significantly compared with ACM group.

Transfection of mEpo gene to intestinal epithelium in vivo mediated by oral delivery of chitosan-DNA nanoparticles

AIM: To prepare the chitosan-pmEpo nanoparticles and to study their ability for transcellular and paracellular transport across intestinal epithelia by oral administration. METHODS: ICR mice were fed with recombinant plasmid AAV-tetO-CMV-mEpo (containing mEpo gene) or pCMVβ(containing LacZ gene), whether it was wrapped by chitosan or no. Its size and shape were observed by transmission electron microscopy. Agarose gel electrophoresis was used to assess the efficiency of encapsulation and stability against nuclease digestion. Before and after oral treatmant, blood samples were collected by retro-orbital puncture, and hematocrits were used to show the physiological effect of mEpo. RESULTS: Chitosan was able to successfully wrap the plasmid and to protect it from DNase degradation. Transmission electron microscopy showed that freshly prepared particles were approximately 70-150 nm in size and fairly spherical.Three days after fed the chitosan-pCMVβ complex was fed,the mice were killed and most of the stomach and 30% of the small intestine were stained. Hematocrit was not modified in naive and ‘naked' mEpo-fed mice, a rapid increase of hematocrit was observed during the first 4 days of treatment in chitosan-mEpo-fed animals, reaching 60.9±1.2% (P<0.01),and sustained for a week. The second feed (6 days after the first feed) was still able to promote a second hematocrit increase in chitosan-mEpo-fed animals, reaching 65.9±1.4%(P<0.01), while the second hematocrit increase did not appearin the ‘naked' mEpo-second-fed mice. CONCLUSION: Oral chitosan-DNA nanoparticles can efficiently deliver genes to enterocytes, and may be used as a useful tool for gene transfer.

STRUCTURING & RHEOLOGY OF MOLTEN POLYMER/CLAY NANOCOMPOSITES

The evolution and the origin of“solid-like state”in molten polymer/clay nanocomposites are studied.Usingpolypropylene/clay hybrid(PPCH)with sufficient maleic anhydride modified PP(PP-MA)as compatibilizer,well exfoliationyet solid-like state was achieved after annealing in molten state.Comprehensive linear viscoelasticity and non-lineartheological behaviors together with WAXD and TEM are studied on PPCH at various dispersion stages focusing on time,temperature and deformation dependencies of the“solid-like”state in molten nanocomposites.Based on these,it is revealedthat the solid-structure is developed gradually along with annealing through the stages of inter-layer expansion by PP-MA,the diffusion and association of exfoliated silicate platelets,the formation of band/chain structure and,finally,a percolatedclay associated network,which is responsible for the melt rigidity or solid-like state.The network will be broken down bymelt frozen/crystallization and weakened at large shear or strong flow and,even more surprisingly,may be disrupted by usingtrace amount of silane coupling agent which may block the edge interaction of platelets.The solid-like structure causescharacteristic non-linear rheological behaviors,e.g.residual stress after step shear,abnormal huge stress overshoots in stepflows and,most remarkably,the negative first normal stress functions in steady shear or step flows.The rheological andstructural arguments challenge the existing models of strengthened entangled polymer network by tethered polymer chainsconnecting clay particles or by chains in confined melts or frictional interaction among tactoids.A scheme of percolatednetworking of associated clay platelets,which may in band form of edge connecting exfoliated platelets,is suggested toexplain previous experimental results.

Negative cooperative effect of cytotoxicity of a di-component initiating system for a novel injectable tissue engineering hydrogel

Chemically cross-linked hydrogels constitute a novel injectable tissue engineering material. At present, one of the key problems is to find an appropriate initiator. This study evaluated the cytotoxicity in vitro of a water-soluble redox initiating system consisting of ammonium persulfate (APS) and N, N, N′, N′-tetramethylethylenediamine (TEM- ED). Gelation time of PEG diacrylate macromer in phos- phate buffer saline solution was first adjusted to guarantee that the examined initiator concentrations are sufficiently high to trigger polymerization of macromers. NIH/3T3 fi- broblasts were employed to examine cytotoxicity via MTT measurements and optical microscopic observations. It has been found that the combined APS/TEMED system exhibits negative cooperative effect, for the underlying cytotoxicity is even lower than that of APS or TEMED at certain concen- trations.