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Vascular endothelial cadherin (VE-cadherin) is an endothelial cell-specific adhesion molecule localized exclusively at the adherens junctions. VE-cadherin homophilic adhesion is mediated through its five extracellular domains and is crucial for the proper assembly of vascular endothelium during angiogenesis, as well as for the maintenance of vascular integrity. Therefore, developing monoclonal antibodies (mAbs) that block VE-cadherin mediated assembly, while not disrupting established vasculature, could be an effective approach to inhibit tumor angiogenesis. We have previously identified a number of mAbs against murine VE-cadherin that exhibit differential binding activities on established versus neovasculature. Two of these mAbs, BV13 and 10G4, inhibit angiogenesis and tumor growth; however they target all the established vessels in vivo resulting in vascular leakage. In contrast, another mAb, E4G10, which targets only the neovasculature in vivo, inhibits angiogenesis and tumor growth without the disruptive effects. Using a variety of experimental approaches we mapped the epitopes of the mAbs. We determined that both disruptive mAbs target an epitope within amino acids 45-56, and identified the epitope of E4G10 within the first 10 amino acids. The epitope of E4G10 includes conserved residues necessary for VE-cadherin mediated adhesion. Our structural homology modeling of VE-cadherin suggests that BV13 and 10G4 target an epitope that appears not to be involved in trans-adhesion, and is accessible regardless of the status of VE-cadherin interactions. Conversely, E4G10 targets only the unbound form of the molecule found in the neovasculature, where VE-cadherin has not yet engaged in trans-adhesion and its epitope is fully exposed. Thus, E4G10 can inhibit junction formation and angiogenesis, yet it does not target normal vasculature because its epitope is masked in established endothelium, while BV13 and 10G4 target an epitope that is accessible all the time, resulting in the disruption of adherens junctions. Our findings establish the immediate N-terminal region of VE-cadherin as a novel target for inhibiting angiogenesis. In addition, the unique targeting of E4G10 to the neovasculature may allow us to generate immunoconjugates that deliver effector molecules specifically to the tumor.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]