A novel monoclonal antibody to a defined peptide epitope in MUC16

The MUC16 mucin is overexpressed and aberrantly glycosylated in ovarian carcinomas. Immunodetection of circulating MUC16 is one of the most used cancer biomarker assays, but existing antibodies to MUC16 fail to distinguish normal and aberrant cancer glycoforms. Although all antibodies react with the tandem-repeat region, their epitopes appear to be conformational dependent and not definable by a short peptide. Aberrant glycoforms of MUC16 may constitute promising targets for diagnostic and immunotherapeutic intervention, and it is important to develop well-defined immunogens for induction of potent MUC16 immunity. Here, we developed a MUC16 vaccine based on a 1.7TR (264 aa) expressed in Escherichia coli and in vitro enzymatically glycosylated to generate the aberrant cancer-associated glycoform Tn. This vaccine elicited a potent serum IgG response in mice and we identified two major immunodominant linear peptide epitopes within the tandem repeat. We developed one monoclonal antibody, 5E11, reactive with a minimum epitope with the sequence FNTTER. This sequence contains potential N- and O-glycosylation sites and, interestingly, glycosylation blocked binding of 5E11. In immunochemistry of ovarian benign and cancer lesions, 5E11 showed similar reactivity as traditional MUC16 antibodies, suggesting that the epitope is not efficiently glycosylated. The study provides a vaccine design and immunodominant MUC16 TR epitopes.

Expression of ST3Gal, ST6Gal, ST6GalNAc and ST8Sia in human hepatic carcinoma cell lines, HepG-2 and SMMC-7721 and normal hepatic cell line, L-02

We measured ST3Gal, ST6Gal, ST6GalNAc and ST8Sia expression in human hepatic carcinoma cell lines, HepG-2 and SMMC-7721 and normal hepatic cell line, L-02 to reveal the relationship between hepatic carcinoma cell lines sialyltransferases expression and cell membrane sialic acid sugar chains. Membrane sialic acid sugar chains in L-02, HepG-2 and SMMC-7721 cell lines were measured with lectin microarrays to find expression profiles. Expression of 20 sialyltransferases was measured with DNA microarray. qRT-PCR and Western blot were used to verify DNA microarrays data. Siaα 2-3Galβ1-3[Siaα2-6GalNAc]α-R and Siaα 2-6Gal/GalNAc sugar chains in hepatic carcinoma cell lines, HepG-2 and SMMC-7721 were upregulated, and 7differentially expressed sialyltransferases were captured. ST3Gal-IV and ST6Gal I were overexpressed and ST3Gal-I, ST3Gal-V, ST3Gal-VI, ST6GalNAcII and ST6GalNAcVI were downregulated in HepG-2 and SMMC-7721 cell Lines, compared with control cell line. ST6GalNAc-IV and ST8sia expressions were not detected. Other sialyltransferases were not different among cell lines. Results from qRT-PCR and Western blot were consistent with DNA microarray. Overexpression of ST3Gal-IV and ST6Gal I in HepG-2 and SMMC-7721 cell lines may correlate with upregulation of Siaα 2-3Galβ1-3[Siaα2-6GalNAc]α-R and Siaα 2-6Gal/GalNAc sugar chains on cell membranes.

Transmembrane mucins as novel therapeutic targets

Membrane-tethered mucin glycoproteins are abundantly expressed at the apical surfaces of simple epithelia, where they play important roles in lubricating and protecting tissues from pathogens and enzymatic attack. Notable examples of these mucins are MUC1, MUC4 and MUC16 (also known as cancer antigen 125). In adenocarcinomas, apical mucin restriction is lost and overall expression is often highly increased. High-level mucin expression protects tumors from killing by the host immune system, as well as by chemotherapeutic agents, and affords protection from apoptosis. Mucin expression can increase as the result of gene duplication and/or in response to hormones, cytokines and growth factors prevalent in the tumor milieu. Rises in the normally low levels of mucin fragments in serum have been used as markers of disease, such as tumor burden, for many years. Currently, several approaches are being examined that target mucins for immunization or nanomedicine using mucin-specific antibodies.