Monoclonal antibody targeting of the EphA2 receptor tyrosine kinase in cancer
EphA2 is a transmembrane receptor tyrosine kinase that is upregulated on a large number of aggressive carcinomas. Despite its overexpression, the EphA2 on malignant cells fails to bind its ligand, ephrinA1, which is anchored to the membrane of adjacent cells. Unlike other receptor tyrosine kinases, EphA2 demonstrates kinase activity independent of ligand binding. However, ligand binding causes EphA2 to negatively regulate tumor cell growth and migration. Herein, we translate knowledge of EphA2 into strategies that selectively target malignant cells. We generated monoclonal antibodies that bind epitopes on the extracellular domains of EphA2. EphA2 antibodies were screened for their capabilities to mimic the biochemical and biological consequences of ligand binding. A subset of EphA2 monoclonal antibodies was found able to induce EphA2 autophosphorylation and subsequent degradation. These EphA2 agonistic antibodies inhibited anchorage-independent growth by MDA-MB-231 breast cancer cells but did not affect monolayer growth. Antibody targeting of EphA2 decreased tumor cell growth and extended survival as measured using xenograft tumor models. Moreover, we demonstrated that EphA2 antibodies inhibit tumor progression by inducing apoptosis. Investigation of the cellular basis of EphA2 antibody activity revealed that the EphA2 in malignant cells causes fibronectin production and that EphA2 antibodies prevent fibronectin production. We further showed that fibronectin regulates the ability of malignant cells to colonize an inhospitable microenvironment. We also identified certain antibodies that may distinguish the EphA2 on malignant versus non-transformed cells. The differential binding arises as a result of steric occlusion of the EphA2 on normal cells by stable cell-cell adhesions. Consequently, antibodies that recognize these epitopes should be able to selectively target malignant cells without inducing toxicities to normal cells. These results suggest an opportunity for antibody-based targeting of the many cancers that overexpress EphA2.
Kinch, Purdue University.
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