Molecular cloning and chimerisation of CDI 315B monoclonal antibody

Monoclonal antibody to cytokeratin VKIALEVEIATY sequence motif reduces plasminogen activation in breast tumour cells

Cytokeratins (CKs) are the main structural proteins of epithelial cells. Although they mainly form cytoplasmic structures, they are also localized at the plasma membrane or secreted from the cells. Some CKs are over-expressed in tumour cells and are used as diagnostic and prognostic biomarkers. A stable hybridoma cell line producing anti-cytokeratin monoclonal antibody (anti-CK MAb) was prepared after immunizing mice with breast cancer MCF-7 cell lysate. As shown by 2D electrophoresis, immunoblotting and mass spectroscopy, the monoclonal antibody recognizes an epitope on CK1, CK2, CK8, CK10 and CK18 in MCF-7 cells. To identify the binding site of the antibody three peptides of 12 amino acids were synthesized, each overlapping a 27 amino acid consensus sequence of the recognized CKs. Anti-CK MAb expressed high affinity for a dodecapeptide with the sequence VKIALEVEIATY, localized in the CK alpha-helical B2 domain, as shown by ELISA and surface plasmon resonance. Treatment of MCF-7 cells by anti-CK MAb impaired plasminogen activation and consequently invasiveness of the cells. Our results show that, besides their use in diagnosis, anti-cytokeratin antibodies could be used in therapy of invasive breast cancer.

Immunonanoparticles − an effective tool to impair harmful proteolysis in invasive breast tumor cells

Breast cancer cells exhibit excessive proteolysis, which is responsible for extensive extracellular matrix degradation, invasion and metastasis. Besides other proteases, lysosomal cysteine protease cathepsin B has been implicated in these processes and the impairment of its intracellular activity was suggested to reduce harmful proteolysis and hence diminish progression of breast tumors. Here, we present an effective system composed of poly(D,L-lactide-coglycolide) nanoparticles, a specific anti-cytokeratin monoclonal IgG and cystatin, a potent protease inhibitor, that can neutralize the excessive intracellular proteolytic activity as well as invasive potential of breast tumor cells. The delivery system distinguishes between breast and other cells due to the monoclonal antibody specifically recognizing cytokeratines on the membrane of breast tumor cells. Bound nanoparticles are rapidly internalized by means of endocytosis releasing the inhibitor cargo within the lysosomes. This enables intracellular cathepsin B proteolytic activity to be inhibited, reducing the invasive and metastatic potential of tumor cells without affecting proteolytic functions in normal cells and processes. This approach may be applied for treatment of breast and other tumors in which intracellular proteolytic activity is a part of the process of malignant progression.

Molecular cloning and chimerisation of an inhibitory anti-cathepsin B antibody and its expression in Chinese hamster ovary cells

The lysosomal cysteine protease cathepsin B is one of several proteases that have been linked to tumour progression. Its increased expression and secretion in tumour cells may facilitate the degradation of extracellular matrix proteins, leading to tumour cell invasion and metastasis. Specific inhibitory monoclonal antibodies are a possible alternative to synthetic inhibitors as a therapeutic tool for cancer treatment. An inhibitory monoclonal antibody, which binds to an epitope near the active site of cathepsin B and inhibits its proteolytic activity, was prepared and its effect on invasion of ras-transformed MCF-10A neoT cells was tested in vitro. Here we present the nucleotide sequences of the heavy and light chains of the inhibitory antibody and compare them to the murine immunoglobulin germline sequences for possible somatic hypermutations. Since no harmful mutations were found, a mouse/human chimeric antibody was constructed by fusing murine V(H) and V(L) variable regions of the inhibitory antibody with human gamma 1 and K constant regions, respectively. Chinese hamster ovary K1 cells were co-transfected with expression vectors pcD-NA3L and pcDNA3H and the reactivity of the isolated chimeric antibody was tested by ELISA and Western blotting. We could demonstrate an inhibitory effect of the chimeric antibody.