Collaborative Enhancement of Antibody Binding to Distinct PECAM-1 Epitopes Modulates Endothelial Targeting

Abstract

Antibodies to platelet endothelial cell adhesion molecule-1 (PECAM-1) facilitate targeted drug delivery to endothelial cells by “vascular immunotargeting.” To define the targeting quantitatively, we investigated the endothelial binding of monoclonal antibodies (mAbs) to extracellular epitopes of PECAM-1. Surprisingly, we have found in human and mouse cell culture models that the endothelial binding of PECAM-directed mAbs and scFv therapeutic fusion protein is increased by co-administration of a paired mAb directed to an adjacent, yet distinct PECAM-1 epitope. This results in significant enhancement of functional activity of a PECAM-1-targeted scFv-thrombomodulin fusion protein generating therapeutic activated Protein C. The “collaborative enhancement” of mAb binding is affirmed in vivo, as manifested by enhanced pulmonary accumulation of intravenously administered radiolabeled PECAM-1 mAb when co-injected with an unlabeled paired mAb in mice. This is the first demonstration of a positive modulatory effect of endothelial binding and vascular immunotargeting provided by the simultaneous binding a paired mAb to adjacent distinct epitopes. The “collaborative enhancement” phenomenon provides a novel paradigm for optimizing the endothelial-targeted delivery of therapeutic agents.

Influence of PECAM-1 ligand interactions on PECAM-1-dependent cell motility and filopodia extension

“…2010; Chacko et al. 2012). Although of tumor cell origin, REN cells have several features that have made them an appealing system for modeling the vascular endothelium.…”

Thrombomodulin and the vascular endothelium: insights into functional, regulatory, and therapeutic aspects

“…The fusion protein subsequently demonstrated significantly higher fold efficacy in the resolution of DIC in rats than either sTM or Ab(TF) alone (176). Similarly, linking a PECAM-1-directed antibody single-chain fragment (scFv) to TM recently yielded a fusion protein, scFv(PECAM-1)-TM, for enhanced vascular immunotargeting of TM in mice (21). Moreover, fusion of TM to a red blood cell-directed scFv was recently shown to prolong the circulation time and bioavailability of soluble TM (192).…”

Towards Effective and Safe Thrombolysis and Thromboprophylaxis

“…39 In addition to fibrin-and platelet-targeting approaches, there are several other components of the vasculature and blood that have been targeted, such as platelet endothelial cell adhesion molecule-1, glycophorin A on RBCs, and thrombomodulin, to anchor PAs to the arterial or venous lumen. [40][41][42][43] Platelet endothelial cell adhesion molecule-1 fused with urokinase in a model of cerebrovascular thromboembolism mediated almost complete clot lysis without exacerbating the characteristic side effects such as intracerebral hemorrhage. 44 Targeting RBCs was shown to have effective prophylaxis against arterial and venous thrombosis for ≈24 hours.…”