PTK7 is a catalytically defective receptor protein tyrosine kinase upregulated in various cancers, including esophageal squamous cell carcinoma (ESCC). In previous studies, we observed a positive correlation between PTK7 expression levels and tumorigenicity in various ESCC cell lines and xenograft mice with ESCC KYSE-30 cells. In this study, we analyzed the effects of anti-PTK7 monoclonal antibodies (mAbs) on the tumorigenic activity in KYSE-30 cells and in mouse xenograft models. PTK7 mAb-32 and mAb-43 bind with a high affinity to the extracellular domain of PTK7. PTK7 mAbs significantly reduced three-dimensional cell proliferation, adhesion, wound healing, and migration. PTK7 mAbs also reduce chemotactic invasiveness by decreasing MMP-9 secretion. PTK7 mAbs decreased actin cytoskeleton levels in the cortical region of KYSE-30 cells. PTK7 mAbs reduced the phosphorylation of ERK, SRC, and FAK. In a mouse xenograft model of ESCC using KYSE-30 cells, PTK7 mAbs reduced tumor growth in terms of volume, weight, and the number of Ki-67-positive cells. These results demonstrated that PTK7 mAbs can inhibit the tumorigenicity of ESCC at the cellular level and in vivo by blocking the function of PTK7. Considering the anticancer activities of PTK7 mAbs, we propose that PTK7 mAbs can be used in an effective treatment strategy for PTK7-positive malignancies, such as ESCC.
Keywords: anticancer agent; esophageal squamous cell carcinoma; monoclonal antibody; protein tyrosine kinase 7 (PTK7); tumorigenesis.