The cellular and molecular mechanisms by which
adrenomedullin (AM) blockade suppresses
tumor neovessels are not well defined. Herein, we show that AM blockade using anti-AM and anti-AM receptors
antibodies targets vascular endothelial cells (ECs) and vascular smooth muscle cells (VSMCs), and induces regression of unstable nascent
tumor neovessels. The underlying mechanism involved, and shown in vitro and in vivo in mice, is the disruption of the molecular engagement of the endothelial cell-specific junctional molecules
vascular endothelial-cadherin (
VE-cadherin)/β-
catenin complex. AM blockade increases endothelial cell permeability by inhibiting cell-cell contacts predominantly through disruption of
VE-cadherin/β-
catenin/Akt signalling pathway, thereby leading to vascular collapse and regression of
tumor neovessels. At a molecular level, we show that AM blockade induces
tyrosine phosphorylation of
VE-cadherin at a critical
tyrosine, Tyr731, which is sufficient to prevent the binding of β-
catenin to the cytoplasmic tail of
VE-cadherin leading to the inhibition of cell barrier function. Furthermore, we demonstrate activation of
Src kinase by phosphorylation on Tyr416, supporting a role of Src to phosphorylate Tyr731-VE-cadherin. In this model, Src inhibition impairs αAM and αAMR-induced Tyr731-VE-cadherin phosphorylation in a dose-dependent manner, indicating that Tyr731-VE-cadherin phosphorylation state is dependent on Src activation. We found that AM blockade induces β-
catenin phosphorylation on Ser33/Ser37/Thr41 sites in both ECs and VSMCs both in vitro and in vivo in mice. These data suggest that AM blockade selectively induces regression of unstable
tumor neovessels, through disruption of
VE-cadherin signalling. Targeting AM system may present a novel therapeutic target to selectively disrupt assembly and induce regression of nascent
tumor neovessels, without affecting normal stabilized vasculature.