The CA125 antigen, recognized by the OC125 antibody, is a tissue-specific circulating antigen expressed in ovarian cancer. The CA125 antigen is encoded by the MUC16 gene cloned by Yin and Lloyd. The full-length gene describes a complex tethered mucin protein present primarily in a variety of gynecologic tissues, especially neoplasms. OC125 and other related antibodies react with glycosylation-dependent antigens present exclusively in the cleaved portion of the molecule. These antibodies are not useful as screening tools, nor can they detect the proximal residual MUC16 protein fragment after cleavage. This has limited its diagnostic and therapeutic applications. Using synthetic peptides, we raised novel-specific antibodies to the carboxy-terminal portion of MUC16 retained by the cell proximal to the putative cleavage site. These antibodies were characterized using fluorescence-activated cell-sorting analysis, enzyme-linked immunoassay, Western blot analysis, and immunohistochemistry. Each of the selected monoclonal antibodies was reactive against recombinant GST-ΔMUC16 protein and the MUC16-transfected SKOV3 cell line. Three antibodies, 4H11, 9C9, and 4A5 antibodies showed high affinities by Western blot analysis and saturation-binding studies of transfected-SKOV3 cells and displayed antibody internalization. Immunohistochemical positivity with novel antibody 4H11 was similar to OC125 but with important differences, including diffuse positivity in lobular breast cancer and a small percentage of OC125-negative ovarian carcinomas that showed intense and diffuse 4H11. Development of such antibodies may be useful for the characterization of MUC16 biology and allow for future studies in targeted therapy and diagnostics.
"An explanation for the bias toward antibodies that recognize the tandem repeat region of MUC16 is not available but is likely due to higher immunogenicity of these epitopes. Antibodies against defined epitopes that are outside of the tandem repeat region (against peptides from the carboxy terminal end [90,91], for example) will serve an important purpose in modifying the CA125 assays and also in attempts to understand the biology of this mucin. "
[Show abstract][Hide abstract] ABSTRACT: Over three decades have passed since the first report on the expression of CA125 by ovarian tumors. Since that time our understanding of ovarian cancer biology has changed significantly to the point that these tumors are now classified based on molecular phenotype and not purely on histological attributes. However, CA125 continues to be, with the recent exception of HE4, the only clinically reliable diagnostic marker for ovarian cancer. Many large-scale clinical trials have been conducted or are underway to determine potential use of serum CA125 levels as a screening modality or to distinguish between benign and malignant pelvic masses. CA125 is a peptide epitope of a 3-5 million Da mucin, MUC16. Here we provide an in-depth review of the literature to highlight the importance of CA125 as a prognostic and diagnostic marker for ovarian cancer. We focus on the increasing body of literature describing the biological role of MUC16 in the progression and metastasis of ovarian tumors. Finally, we consider previous and on-going efforts to develop therapeutic approaches to eradicate ovarian tumors by targeting MUC16. Even though CA125 is a crucial marker for ovarian cancer, the exact structural definition of this antigen continues to be elusive. The importance of MUC16/CA125 in the diagnosis, progression and therapy of ovarian cancer warrants the need for in-depth research on the biochemistry and biology of this mucin. A renewed focus on MUC16 is likely to culminate in novel and more efficient strategies for the detection and treatment of ovarian cancer.
Molecular Cancer 05/2014; 13(1):129. DOI:10.1186/1476-4598-13-129 · 4.26 Impact Factor
"Other studies have also shown the lack MUC16 tissues expression in 15% to 25% of serous EOC (Lu et al., 2004; Rosen et al., 2005; Breitenecker et al., 1989). MUC16 was also found to be expressed in a small percentage (3%-4%) of invasive breast carcinomas and 13% of lung carcinomas (Rao et al., 2010). Because MUC16 is expressed in a limited subset of early stage OC, in other types of cancers and in a number of benign conditions, its serum level is neither a sensitive nor a specific marker to detect early diseases. "
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