Loïc Vincent

Combretastatin A4 phosphate induces rapid regression of tumor neovessels and growth through interference with vascular endothelial-cadherin signaling

The molecular and cellular pathways that support the maintenance and stability of tumor neovessels are not well defined. The efficacy of microtubule-disrupting agents, such as combretastatin A4 phosphate (CA4P), in inducing rapid regression of specific subsets of tumor neovessels has opened up new avenues of research to identify factors that support tumor neoangiogenesis. Herein, we show that CA4P selectively targeted endothelial cells, but not smooth muscle cells, and induced regression of unstable nascent tumor neovessels by rapidly disrupting the molecular engagement of the endothelial cell-specific junctional molecule vascular endothelial-cadherin (VE-cadherin) in vitro and in vivo in mice. CA4P increases endothelial cell permeability, while inhibiting endothelial cell migration and capillary tube formation predominantly through disruption of VE-cadherin/beta-catenin/Akt signaling pathway, thereby leading to rapid vascular collapse and tumor necrosis. Remarkably, stabilization of VE-cadherin signaling in endothelial cells with adenovirus E4 gene or ensheathment with smooth muscle cells confers resistance to CA4P. CA4P synergizes with low and nontoxic doses of neutralizing mAbs to VE-cadherin by blocking assembly of neovessels, thereby inhibiting tumor growth. These data suggest that the microtubule-targeting agent CA4P selectively induces regression of unstable tumor neovessels, in part through disruption of VE-cadherin signaling. Combined treatment with anti-VE-cadherin agents in conjunction with microtubule-disrupting agents provides a novel synergistic strategy to selectively disrupt assembly and induce regression of nascent tumor neovessels, with minimal toxicity and without affecting normal stabilized vasculature.

Simulated Microgravity Impairs Leukemic Cell Survival Through Altering VEGFR-2/VEGF-A Signaling Pathway

Motile cells capable of undergoing transendothelial migration, such as hematopoietic and leukemic cells, have been shown to sense and respond to a decrease in their surrounding gravity. In this study, we investigated the effects of microgravity on human leukemic cell proliferation and expression of receptors that control cell survival, such as the tyrosine kinase vascular endothelial growth factor receptor-2 (VEGFR-2). VEGFR-2 is shuttled between the nucleus and membrane, and through an autocrine activation of its ligand, VEGF-A, conveys signals that control cell survival. Autocrine or paracrine stimulation of VEGFR-2 facilitates localization of this receptor from the membrane to the nucleus—a process that results in increased survival of the leukemic cells. Here, we provide evidence that the mechanical forces altered by simulated microgravity localize and maintain VEGFR-2 in the membrane, and also block VEGF-A expression. This interferes with the shuttling of VEGFR-2 to the nucleus, resulting in a decrease in signaling and enhanced leukemic cell death. These data suggest that microgravity modulates cell survival through altering the cellular trafficking and activation state of tyrosine kinase receptors. This study has potential implications for understanding the regulation of receptor biology in pathophysiology, particularly VEGFR trafficking, thereby providing for the development of appropriate therapeutic strategies to abrogate intracrine stimulation triggered by VEGFR internalization.

Kaplan et al. reply

Replying to: M. R. Dawson et al. 461, 10.1038/nature08254 (2009)Commenting on ref. 1, Dawson et al. claim that metastasis formation is independent of VEGFR1 activity, contradicting work by us and many others, including the original description of flt1TK-/- (VEGFR1-TK-/-) mice in the metastatic setting. Contrasting the findings by Dawson et al., here we show that VEGFR1 knockdown in myelomonocytic cells eradicates micro- and macrometastases in a non-amputation/resection tumour model.

147. Adenovirus Vector E4 Gene Regulates Connexin 40 and 43 Expression in Endothelial Cells Via PKA and PI3K Signal Pathways

Connexins (Cxs) provide a means for intercellular communication and play important roles in the pathophysiology of vascular cardiac diseases. Infection of endothelial cells (ECs) with first-generation E1/E3-deleted E4+ adenovirus (AdE4+) selectively modulates the survival and angiogenic potential of ECs by as of yet unrecognized mechanisms. We show here that AdE4+ vectors potentiate Cx expression in ECs in vitro and in mouse heart tissue. Infection of ECs with AdE4+, but not AdE4-, resulted in a time- and dose-dependent induction of junctional Cx40 expression and suppression of Cx43 protein and mRNA expression. Treatment of ECs with PKA inhibitor H89 or PI3K inhibitor LY294002 prevented the AdE4+-mediated regulation of Cx40 and Cx43 that was associated with diminished AdE4+-mediated survival of ECs. Moreover, both PKA activity and cAMP-response element (CRE)-binding activity were enhanced by treatment of ECs with AdE4+. However, there is no causal evidence of a cross-talk between the 2 modulatory pathways, PKA and PI3K. Remarkably, Cx40 immunostaining was markedly increased and Cx43 was decreased in the heart tissue of mice treated with intra-tracheal AdE4+. Taken together, these results suggest that AdE4+ may play an important role in the regulation of Cx expression in ECs, and that these effects are mediated by both the PKA/CREB and PI3K signaling pathways.