Abstract
Epithelial cell adhesion molecule (EpCAM) is a transmembrane protein expressed at intercellular junctions in epithelial cells. As an epithelial biomarker, it used for immunologic-based capture of epithelial-derived circulating tumor cells (CTCs) in human patients with different carcinomas. EpCAM expression has not been described in normal or neoplastic epithelial tissues in cats. Our goal was to find a commercial antibody that recognizes surface EpCAM expression for CTC detection. We tested two anti-human EpCAM antibodies, designated for use with flow cytometry, for detection of surface EpCAM expression on feline cell lines derived from normal mammary and renal epithelia and mammary and oropharyngeal squamous cell carcinomas in cats. Only one of the antibodies, a goat polyclonal antibody, labeled normal and neoplastic feline mammary epithelial cells and oropharyngeal squamous cell carcinoma cells; no labeling was observed for normal feline kidney epithelial cells. At low dilution, this antibody immunohistochemically stained the intercellular junctions of normal pancreatic, intestinal and mammary epithelium, as well as neoplastic mammary epithelium in feline tissues; however, oral mucosa, skin, and an oropharyngeal squamous cell carcinoma showed no positive immunostaining. The antibody only weakly bound feline squamous cell carcinoma cell lines under static adhesion. Our results indicate that EpCAM is expressed in specific epithelia in cats but is variably expressed in feline mammary tumors and oropharyngeal squamous cell carcinoma. A higher avidity cross-reactive or feline-specific antibody will be required to further investigate EpCAM expression in normal and neoplastic feline tissue or for detecting CTCs in the blood of tumor-bearing cats.
Highlights
Blood-based “liquid biopsies” are becoming more prevalent in clinical diagnostic medicine because they can be readily performed and are minimally invasive, making them ideal for detection and monitoring of disease
All feline cell lines were tested with both antibodies, with the exception of FMEC and Norden Laboratory feline kidney (NLFK), which were not tested with the SB epithelial cell adhesion molecule (EpCAM) antibody
Positive staining was seen with the goat polyclonal R&D EpCAM antibody on the feline normal and neoplastic mammary cell lines and the oropharyngeal squamous cell carcinoma cell lines, whereas no staining was evident on the NLFK normal renal epithelial cell line (Figures 3, 4 and Table 2)
Summary
Blood-based “liquid biopsies” are becoming more prevalent in clinical diagnostic medicine because they can be readily performed and are minimally invasive, making them ideal for detection and monitoring of disease. Most techniques used for identification of CTCs rely upon the immunologic detection of lineage-associated markers. One such marker for epithelial tumors is epithelial cell adhesion molecule (EpCAM), known as epithelial glycoprotein 2 (EGP-2), epithelial specific antigen (ESA), GA733-2, 17-1A, HEA125, MK-1, KSA, Trop-1, tumor-associated calcium signal transducer 1 (TACSTD1) and CD326 [7, 8]. EpCAM is considered a marker of carcinogenesis, because it is over-expressed in many tumors of epithelial origin, even tumors arising from tissue which normally lack expression of the protein, such as squamous cell carcinoma [7,8,9,10,11,12]. Analyzers have been built for the specific purpose of detecting EpCAM-positive CTCs (e.g., CellSearch R ) [5, 18]
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