Epitope Mapping of a Cancer-Specific Anti-Podocalyxin Monoclonal Antibody (PcMab-60) Using Enzyme-Linked Immunosorbent Assay and Surface Plasmon Resonance.

Podocalyxin (PODXL) is a type I transmembrane sialoglycoprotein that is overexpressed in human cancers, including breast, oral, and lung. PODXL promotes tumor progression, and its expression is associated with poor prognosis. Since PODXL is expressed in normal cells, including kidney podocytes and vascular endothelial cells (VECs), cancer-specific monoclonal antibodies (mAbs) are necessary to reduce the adverse effects of antibody therapy on PODXL-expressing cancers. Previously, we established a cancer-specific mAb against PODXL, PcMab-60 (mouse IgM, kappa), by immunizing mice with soluble PODXL produced by LN229 glioblastoma cells. PcMab-60 reacted with PODXL-expressing cancer cells, but did not react with VECs. In this study, we investigated an epitope of PcMab-60 using flow cytometry, surface plasmon resonance (SPR), and enzyme-linked immunosorbent assay (ELISA). The results of SPR revealed that the PcMab-60 epitope consisted of Thr105, Arg109, Gly110, Gly111, Gly112, Ser113, Gly114, Asn115, Pro116, and Thr117. In contrast, the results of ELISA revealed that the PcMab-60 epitope consisted of Arg109, Gly110, Gly111, Gly112, Ser113, Gly114, Asn115, and Pro116. These results demonstrate the cancer-specific epitope, which was recognized by PcMab-60.