Loss of Notch signalling induced by Dll4 causes arterial calibre reduction by increasing endothelial cell response to angiogenic stimuli

<p>Abstract</p> <p>Background</p> <p>In the vascular system, Notch receptors and ligands are expressed mainly on arteries, with Delta-like 4 (Dll4) being the only ligand known to be expressed early during the development of arterial endothelial cells and capillaries. <it>Dll4 </it>null embryos die very early in development with severely reduced arterial calibre and lumen and loss of arterial cell identity.</p> <p>Results</p> <p>The current detailed analysis of these mutants shows that the arterial defect precedes the initiation of blood flow and that the arterial <it>Dll4</it>^-/-endothelial cells proliferate and migrate more actively. <it>Dll4</it>^-/-mutants reveal a defective basement membrane around the forming aorta and increased endothelial cell migration from the dorsal aorta to peripheral regions, which constitute the main causes of arterial lumen reduction in these embryos. The increased proliferation and migration of <it>Dll4</it>^-/-endothelial cells was found to coincide with increased expression of the receptors VEGFR-2 and Robo4 and with downregulation of the TGF-β accessory receptor Endoglin.</p> <p>Conclusion</p> <p>Together, these results strongly suggest that Notch signalling can increase arterial stability and calibre by decreasing the response of arterial endothelial cells to local gradients of pro-angiogenic factors like VEGF.</p

Combination of Dll4/Notch and Ephrin-B2/EphB4 targeted therapy is highly effective in disrupting tumor angiogenesis

<p>Abstract</p> <p>Background</p> <p>Dll4/Notch and Ephrin-B2/EphB4 pathways play critical roles in tumor vessel development and maturation. This study evaluates the efficacy of the inhibition of both signaling pathways, alone and in combination, in reducing the growth of an autochthonous mouse tumor and assesses potential adverse effects.</p> <p>Methods</p> <p>We used the transgenic RIP1-Tag2 tumor model to study the effects of 1) inhibition of Dll4/Notch by either <it>Dll4 </it>allelic deletion or use of a soluble extracellular Dll4 (sDll4), 2) inhibition of Ephrin-B2/EphB4 signaling by a soluble extracellular EphB4 fused to albumin (sEphB4-Alb), and 3) inhibition of both pathways by sEphB4-Alb combined with either <it>Dll4 </it>allelic deletion or sDll4. To investigate adverse effects, we used inducible endothelial-specific <it>Dll4 </it>knock-out mice, treated with sEphB4-Alb, and carried out histopathological analysis.</p> <p>Results</p> <p><it>Dll4 </it>allele deletion or soluble Dll4 treatment resulted in increased tumor vessel density, reduced mural cell recruitment and vessel perfusion which resulted in reduced tumor size. The soluble EphB4 instead reduced vessel density and vessel perfusion, leading to reduction of tumor size. Greater efficacy was observed when sEphB4-Alb was combined with either <it>Dll4 </it>allele deletion or sDll4 in regards to tumor size, vessel perfusion and mural cell recruitment. Induced endothelial specific <it>Dll4 </it>loss-of-function caused hepatic vascular alterations, which were prevented by concomitant sEphB4-Alb treatment.</p> <p>Conclusion</p> <p>Combination targeting of Dll4/Notch and Ephrin-B2/EphB4 has potential for clinical investigation, providing cumulative efficacy and increased safety over Dll4/Notch inhibition alone.</p

PET Imaging of Dll4 Expression in Glioblastoma and Colorectal Cancer Xenografts Using 64 Cu-Labeled Monoclonal Antibody 61B

Delta-like ligand 4 (Dll4) expressed in tumor cells plays a key role to promote tumor growth of numerous cancer types. Based on a novel anti-human Dll4 monoclonal antibody (61B), we developed a (64)Cu-labeled probe for positron emission tomography (PET) imaging of tumor Dll4 expression. In this study, 61B was conjugated with the (64)Cu-chelator DOTA through lysine on the antibody. Human IgG (hIgG)-DOTA, which did not bind to Dll4, was also prepared as a control. The Dll4 binding activity of the probes was evaluated through the bead-based binding assay with Dll4-alkaline phosphatase. The resulting PET probes were evaluated in U87MG glioblastoma and HT29 colorectal cancer xenografts in athymic nude mice. Our results demonstrated that the 61B-DOTA retained (77.2 ± 3.7) % Dll4 binding activity of the unmodified 61B, which is significantly higher than that of hIgG-DOTA (0.06 ± 0.03) %. Confocal microscopy analysis confirmed that 61B-Cy5.5, but not IgG-Cy5.5, predominantly located within the U87MG and HT29 cells cytoplasm. U87MG cells showed higher 61B-Cy5.5 binding as compared to HT29 cells. In U87MG xenografts, 61B-DOTA-(64)Cu demonstrated remarkable tumor accumulation (10.5 ± 1.7 and 10.2 ± 1.2 %ID/g at 24 and 48 hour post injection, respectively). In HT29 xenografts, tumor accumulation of 61B-DOTA-(64)Cu was significantly lower than that of U87MG (7.3 ± 1.3 and 6.6 ± 1.3 %ID/g at 24 and 48 hour post injection, respectively). The tumor accumulation of 61B-DOTA-(64)Cu was significantly higher than that of hIgG-DOTA-(64)Cu in both xenografts models. Immunofluorescence staining of the tumor tissues further confirmed that tumor accumulation of 61B-Cy5.5 was correlated well with in vivo PET imaging data using 61B-DOTA-(64)Cu. In conclusion, 61B-DOTA-(64)Cu PET probe was successfully synthesized and demonstrated prominent tumor uptake by targeting Dll4. 61B-DOTA-(64)Cu has great potential to be used for noninvasive Dll4 imaging, which could be valuable for tumor detection, Dll4 expression level evaluation, and Dll4-based treatment monitoring

The EphB4 Receptor Tyrosine Kinase Promotes Lung Cancer Growth: A Potential Novel Therapeutic Target

Despite progress in locoregional and systemic therapies, patient survival from lung cancer remains a challenge. Receptor tyrosine kinases are frequently implicated in lung cancer pathogenesis, and some tyrosine kinase inhibition strategies have been effective clinically. The EphB4 receptor tyrosine kinase has recently emerged as a potential target in several other cancers. We sought to systematically study the role of EphB4 in lung cancer. Here, we demonstrate that EphB4 is overexpressed 3-fold in lung tumors compared to paired normal tissues and frequently exhibits gene copy number increases in lung cancer. We also show that overexpression of EphB4 promotes cellular proliferation, colony formation, and motility, while EphB4 inhibition reduces cellular viability in vitro, halts the growth of established tumors in mouse xenograft models when used as a single-target strategy, and causes near-complete regression of established tumors when used in combination with paclitaxel. Taken together, these data suggest an important role for EphB4 as a potential novel therapeutic target in lung cancer. Clinical trials investigating the efficacy of anti-EphB4 therapies as well as combination therapy involving EphB4 inhibition may be warranted.</p

Low-Dosage Inhibition of DII4 Signaling Promotes Wound Healing by Inducing Functional Neo-Angiogenesis

Recent findings regarding Dll4 function in physiological and pathological conditions indicate that this Notch ligand may constitute an important therapeutic target. Dll4 appears to be a major anti-angiogenic agent, occupying a central role in various angiogenic pathways. The first trials of anti-Dll4 therapy in mice demonstrated a paradoxical effect, as it reduced tumor perfusion and growth despite leading to an increase in vascular density. This is seen as the result of insufficient maturation of the newly formed vasculature causing a circulatory defect and increased tumor hypoxia. As Dll4 function is known to be closely dependent on expression levels, we envisioned that the therapeutic anti-Dll4 dosage could be modulated to result in the increase of adequately functional blood vessels. This would be useful in conditions where vascular function is a limiting factor for recovery, like wound healing and tissue hypoxia, especially in diabetic patients. Our experimental results in mice confirmed this possibility, revealing that low dosage inhibition of Dll4/Notch signaling causes improved vascular function and accelerated wound healing