Carbohydrate-directed conjugation of cobra venom factor to antibody by selective derivatization of the terminal galactose residues

NEW DEVELOPMENTS FOR THE SITE-SPECIFIC ATTACHMENT OF PROTEIN TO SURFACES

Protein immobilization on surfaces is of great importance in numerous applications in biology and biophysics. The key for the success of all these applications relies on the immobilization technique employed to attach the protein to the corresponding surface. Protein immobilization can be based on covalent or noncovalent interaction of the molecule with the surface. Noncovalent interactions include hydrophobic interactions, hydrogen bonding, van der Waals forces, electrostatic forces, or physical adsorption. However, since these interactions are weak, the molecules can get denatured or dislodged, thus causing loss of signal. They also result in random attachment of the protein to the surface. Site–specific covalent attachment of proteins onto surfaces, on the other hand, leads to molecules being arranged in a definite, orderly fashion and uses spacers and linkers to help minimize steric hindrances between the protein and the surface. This work reviews in detail some of the methods most commonly used as well as the latest developments for the site-specific covalent attachment of protein to solid surfaces.

Chitosan?RGDSGGC conjugate as a scaffold material for musculoskeletal tissue engineering

In the present study, we have developed a novel and versatile method for the preparation of chitosan-peptide complex based on the selective reaction of chitosan with 2-iminothiolane. The new type of SH-chitosan derivative showed an excellent solubility to aqueous solution even in the alkaline conditions. This characteristic greatly facilitated further modification study of chitosan with a variety of bioactive substances. A synthetic peptide, RGDSGGC containing RGDS moiety that is known as one of the most important cell adhesive peptides, was readily coupled by disulfide bonds formation with sulfhydryl groups of SH-chitosan in the presence of dimethyl sulfoxide. Next, the effect of the introduction of RGDSGGC moiety to chitosan on cell adhesion and proliferation activity of chondrocytes and fibroblasts were evaluated. As a result, it was suggested that this polysaccharide-peptide conjugate exhibited excellent capacities for both cell adhesion and cell proliferation of chondrocytes and fibroblasts. Considering the growing importance of the biocompatible scaffolds in the recent tailored tissue engineering technique, these results indicate that the present strategy of 2-iminothiolane-based conjugation of polysaccharides with biologically active peptides will become a key and potential technology to develop desirable scaffold materials for the tissue regenerations.

Serum from rabbit orally administered cobra venom inhibits growth of implanted hepatocellular carcinoma cells in mice

AIM: To investigate the inhibitory effect of serum preparation from rabbits orally administered cobra venom (SRCV) on implanted hepatocellular carcinoma (HCC) cells in mice.

METHODS: An HCC cell line, HepA, was injected into mice to prepare implanted tumors. The animals (n = 30) were divided randomly into SRCV, 5-fluorouracil (5-FU), and distilled water (control) groups. From the second day after transplantation, 20 mg/kg 5-FU was administered intraperitoneally once a day for 9 d. SRCV (1000 mg/kg) or distilled water (0.2 mL) was given by gastrogavage. Tumor growth inhibition was described by the inhibitory rate (IR). Apoptosis was detected by transmission electron microscopy (TEM), flow cytometry (FCM), and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL). Student’s t-test was performed for statistical analysis.

RESULTS: The tumor growth was inhibited markedly by SRCV treatment compared to that in the control group (P < 0.01). The treatment resulted in a significant increase in the apoptotic rate of cancer cells by the factors of 10.5% ± 2.4% and 20.65% ± 3.2% as demonstrated through TUNEL and FCM assays, respectively (P < 0.01). The apoptotic cells were also identified by characteristic ultrastructural features.

CONCLUSION: SRCV can inhibit the growth of implanted HepA cells in mice, and the apoptosis rate appears to elevate during the process.

Conjugation of folate via gelonin carbohydrate residues retains ribosomal-inactivating properties of the toxin and permits targeting to folate receptor positive cells

Conjugation of folate to proteins permits receptor-mediated endocytosis via the folate receptor (FR) and delivery of the conjugate into the cytoplasm of cells. Since many cancers up-regulate the FR it has enabled the targeting of toxins to tumor cells resulting in specific cell death. However, current conjugation methods rely on chemistries that can affect certain catalytic subunits, such as the A-chain of the plant toxin gelonin. As a result many folate-targeted toxins are a compromise between receptor/ligand interaction and toxin activity. We describe the first example of folate conjugated to a protein via carbohydrate residues, using a novel SH-folate intermediate. The folate-gelonin conjugate retains over 99% of toxin activity in a cell-free translational assay compared with unmodified gelonin and is able to bind the FR at the same affinity as free folic acid (10(-10) m). Additionally, the conjugate exhibits prolonged inhibition of protein synthesis in FR positive cell lines in vitro. Folate linked to gelonin via amino conjugation exhibits the same affinity for FR as free folic acid but the toxin is 225-fold less active in a cell-free translational assay. The effect of different conjugation methods on toxin activity and the implications for folate targeting of other glycoproteins are discussed.