Following the clinical success of Bevacizumab, a humanized monoclonal antibody that affects the interaction between vascular endothelial growth factor (VEGF) and its receptors, blocking tumor-induced angiogenesis has become one of the most important targets for the development of new cancer therapeutic drugs and procedures. Among the latter, therapeutic vaccination using VEGF as antigen presents itself as very attractive, with the potential of generating not only a growth factor blocking antibody response but also a cellular response against tumor cells and stromal elements, which appear to be a major source of tumor VEGF. In this paper, we report the development of a protein vaccine candidate, based on a human modified VEGF antigen that is expressed at high levels in E. coli. With respect to controls, immunization experiments in C57BL/6 mice using weekly doses of this antigen and three adjuvants of different chemical natures show that time for tumor development after subcutaneous injection of Melanoma B16-F10 cells increases, tumors that develop grow slower, and overall animal survival is higher. Immunization also prevents tumor development in some mice, making them resistant to second tumor challenges. Vaccination of mice with the human modified VEGF recombinant antigen produces antibodies against the human antigen and the homologous mouse VEGF molecule. We also show that sera from immunized mice block human VEGF-induced HUVEC proliferation. Finally, a possible contribution of T cell cytotoxicity to the overall anti-tumor effect is suggested from the results of vaccination experiments where CD8+ lymphocytes were impaired using neutralizing rat antibodies.
We have previously reported the isolation of a novel single-chain variable fragment (scFv) against vascular endothelial growth factor (VEGF), from a phage-displayed human antibody repertoire. This scFv, denominated 2H1, was shown to block the binding of VEGF to its receptor but exhibited a moderate binding affinity. Here, we describe the affinity maturation of the 2H1 scFv. Two phage-displayed libraries were constructed by diversification of the third complementarity-determining regions (CDRs) of the light (VL) and heavy (VH) chain variable domains of 2H1 using parsimonious mutagenesis. A competitive phage-selection strategy in the presence of the parental scFv as a competitor was used to eliminate low affinity binders. High affinity variants were retrieved from both libraries. An optimized VL variant was designed and constructed by combining recurrent replacements found among selected variants in a single molecule, resulting in an additional affinity increase. Further affinity improvements were achieved by combining this optimized VL with the best VH variants. The final variant obtained here, L3H6, showed an overall affinity improvement of 18-fold over the parental scFv and exhibited an enhanced potency to block the binding of VEGF to its receptor. Using phage display and extensive mutagenesis of VEGF, we determined the fine specificity of L3H6. This functional mapping revealed a novel neutralizing epitope on human VEGF defined by the residues Y25, T71, E72, N100, K101, E103 and R105. The conformational epitope recognized by L3H6 was recapitulated by grafting human VEGF residues into the mouse molecule, providing further confirmation of the nature of the identified epitope.
Yerba Mate (Ilex paraguariensis St. Hill. Aquifoliaceae) is a native South American tree and has a large amount of bioactive compounds. Colorectal cancer (CRC) is one of the so‐called westernized diseases and is the third most common cancer in both men and women. Efficient strategies for the treatment of CRC are extensively being explored including dietary intervention. The objective of our research was to evaluate the effects of Yerba Mate extract on cell proliferation, invasive capacity of tumor cells, and angiogenesis. For this, in vitro and in vivo experimentation was carried out using CRC models. The extract was generated by aqueous extraction and prepared according to traditional American procedure of preparing mate infusion. In vitro results showed that the Yerba Mate extract inhibits CT26 and COLO 205 cell proliferation with IC50 values of 0.25 and 0.46 mg/mL, respectively. We demonstrated by TUNEL assay that one of the mechanisms by which Yerba Mate extract decreases cell proliferation is by induction of apoptosis. In a murine syngeneic tumor model, oral administration of Yerba Mate extract in a dose of 1.6 g/kg/day significantly inhibited angiogenesis and tumor growth without affecting biological parameters or body weight. Our findings suggest that Yerba Mate may be a promising agent for the treatment of colon cancer and could be used as an herbal medicine or functional food ingredient.Practical ApplicationConsidering the chemical composition and presence of phenolic compounds with their free‐radical scavenging activities and bioactivities against colon cancer cells, Yerba Mate can be a promising candidate as healthy food sources in human nutrition, and also be considered a natural source of potential antitumor agents. Taking into account the economic importance of Yerba Mate in Argentina, this vegetable would have a greater commercial value as a functional food.
Human VEGF121 (vascular endothelial growth factor isoform 121) was produced as a recombinant fusion protein with GST (glutathione S-transferase) in Escherichia coli. After affinity purification with glutathione, the GST-VEGF121 fusion protein preparation was used to obtain antibodies in mice against commercial hrVEGF (human recombinant VEGF) through immunization. It was also employed successfully to select specific antihuman VEGF antibody fragments of human origin employing phage-display technology. The fusion protein preparation was separated in monomeric, dimeric and oligomeric forms using size-exclusion chromatography. The dimers were recognized by a soluble VEGF receptor 2-Fc chimaera, and stimulated the growth of human umbilical-vein endothelial cells in vitro in a similar fashion to a commercial hrVEGF. The presence of GST in the fusion protein apparently did not affect the correct assembly of dimers and display of residues critical for receptor recognition. The two-step purification method reported in the present paper involves no laborious renaturalization methods, yields 10 mg/l of the mixture of different aggregation states after affinity chromatography, and 5 mg/l of the biologically active dimer after gel filtration, thus providing a source of material for the development of new anti-angiogenic therapeutic molecules.
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