Tie2 Agonist Research Articles

Effects of angiopoietin (Ang) 1/endothelial-enriched Tunica interna endothelial cell kinase 2 (Tie2) signaling pathway on autophagy-based neuroprotection and expression of aquaporin 4

We investigated Ang-1/Tie2 signaling’s role in cellular autophagy-based neuroprotection and aquaporins expression. 40 mice were randomized into sham surgery group, model group, Tie2-antagonist group, and Ang-1+Tie2 agonist group, followed by observing brain pathological changes, and mRNA levels of LC3-I, LC3-II and aquaporin 4 (AQP4), together with levels of TNF-α and IL-1β. A certain regularity of brain tissue structure was observed in sham surgery group but not in model group. In Ang-1+Tie2 agonist group, the brain tissue structure was more disordered, which was ameliorated in Tie2-antagonist group, along with a proportion of intact cells. The neurological score of mice in Tie2 antagonist group was lower than Ang-1+Tie2 agonist and model groups. Levels of LC3-I and AQP4 in Tie2 antagonist group were also lower, along with higher levels of LC3-I and AQP4. LC3-II levels were higher in Tie2 antagonist group compared with those in Ang-1+Tie2 agonist and model groups. Whereas LC3-II and IL-1β/TNF-α levels in Ang-1+Tie2 agonist group were lower with higher levels of IL-1β and TNF-α. Inhibition of Ang-1/Tie2 signaling could have a restorative effect on neural function in stroke mice.

Report of the first seven agents in the I-SPY COVID trial: a phase 2, open label, adaptive platform randomised controlled trial

An urgent need exists to rapidly screen potential therapeutics for severe COVID-19 or other emerging pathogens associated with high morbidity and mortality. Using an adaptive platform design created to rapidly evaluate investigational agents, hospitalised patients with severe COVID-19 requiring ≥6L/min oxygen were randomised to either a backbone regimen of dexamethasone and remdesivir alone (controls) or backbone plus one open-label investigational agent. Patients were enrolled to the arms described between July 30, 2020 and June 11, 2021 in 20 medical centres in the United States. The platform contained up to four potentially available investigational agents and controls available for randomisation during a single time-period. The two primary endpoints were time-to-recovery (<6L/min oxygen for two consecutive days) and mortality. Data were evaluated biweekly in comparison to pre-specified criteria for graduation (i.e., likely efficacy), futility, and safety, with an adaptive sample size of 40-125 individuals per agent and a Bayesian analytical approach. Criteria were designed to achieve rapid screening of agents and to identify large benefit signals. Concurrently enrolled controls were used for all analyses. https://clinicaltrials.gov/ct2/show/NCT04488081. The first 7 agents evaluated were cenicriviroc (CCR2/5 antagonist; n=92), icatibant (bradykinin antagonist; n=96), apremilast (PDE4 inhibitor; n=67), celecoxib/famotidine (COX2/histamine blockade; n=30), IC14 (anti-CD14; n=67), dornase alfa (inhaled DNase; n=39) and razuprotafib (Tie2 agonist; n=22). Razuprotafib was dropped from the trial due to feasibility issues. In the modified intention-to-treat analyses, no agent met pre-specified efficacy/graduation endpoints with posterior probabilities for the hazard ratios [HRs] for recovery ≤1.5 between 0.99 and 1.00. The data monitoring committee stopped Celecoxib/Famotidine for potential harm (median posterior HR for recovery 0.5, 95% credible interval [CrI] 0.28-0.90; median posterior HR for death 1.67, 95% CrI 0.79-3.58). None of the first 7 agents to enter the trial met the prespecified criteria for a large efficacy signal. Celecoxib/Famotidine was stopped early for potential harm. Adaptive platform trials may provide a useful approach to rapidly screen multiple agents during a pandemic. Quantum Leap Healthcare Collaborative is the trial sponsor. Funding for this trial has come from: the COVID R&D Consortium, Allergan, Amgen Inc., Takeda Pharmaceutical Company, Implicit Bioscience, Johnson & Johnson, Pfizer Inc., Roche/Genentech, Apotex Inc., FAST Grant from Emergent Venture George Mason University, The DoD Defense Threat Reduction Agency (DTRA), The Department of Health and Human ServicesBiomedical Advanced Research and Development Authority (BARDA), and The Grove Foundation. Effort sponsored by the U.S. Government under Other Transaction number W15QKN-16-9-1002 between the MCDC, and the Government.

Adjunctive therapy with the Tie2 agonist Vasculotide reduces pulmonary permeability in Streptococcus pneumoniae infected and mechanically ventilated mice

Community acquired pneumonia, mainly caused by Streptococcus pneumoniae (S.pn.), is a common cause of death worldwide. Despite adequate antibiotic therapy, pneumococcal pneumonia can induce pulmonary endothelial hyperpermeability leading to acute lung injury, which often requires mechanical ventilation (MV) causing ventilator-induced lung injury (VILI). Endothelial stabilization is mediated by angiopoietin-1 induced Tie2 activation. PEGylated (polyethylene glycol) Tie2-agonist Vasculotide (VT) mimics Angiopietin-1 effects. Recently, VT has been shown to reduce pulmonary hyperpermeability in murine pneumococcal pneumonia. The aim of this study was to determine whether VT reduces lung damage in S.pn. infected and mechanically ventilated mice. Pulmonary hyperpermeability, immune response and bacterial load were quantified in S.pn. infected mice treated with Ampicillin + /−VT and undergoing six hours of MV 24 h post infection. Histopathological lung changes, Tie2-expression and -phosphorylation were evaluated. VT did not alter immune response or bacterial burden, but interestingly combination treatment with ampicillin significantly reduced pulmonary hyperpermeability, histological lung damage and edema formation. Tie2-mRNA expression was reduced by S.pn. infection and/or MV but not restored by VT. Moreover, Tie2 phosphorylation was not affected by VT. These findings indicate that VT may be a promising adjunctive treatment option for prevention of VILI in severe pneumococcal pneumonia.

Platelets docking to VWF prevent leaks during leukocyte extravasation by stimulating Tie-2

AbstractNeutrophil extravasation requires opening of the endothelial barrier but does not necessarily cause plasma leakage. Leaks are prevented by contractile actin filaments surrounding the diapedesis pore, keeping this opening tightly closed around the transmigrating neutrophils. We have identified the receptor system that is responsible for this. We show that silencing, or gene inactivation, of endothelial Tie-2 results in leak formation in postcapillary venules of the inflamed cremaster muscle at sites of neutrophil extravasation, as visualized by fluorescent microspheres. Leakage was dependent on neutrophil extravasation, because it was absent upon neutrophil depletion. We identified the Cdc42 GTPase exchange factor FGD5 as a downstream target of Tie-2 that is essential for leakage prevention during neutrophil extravasation. Looking for the Tie-2 agonist and its source, we found that platelet-derived angiopoietin-1 (Angpt1) was required to prevent neutrophil-induced leaks. Intriguingly, blocking von Willebrand factor (VWF) resulted in vascular leaks during transmigration, indicating that platelets interacting with endothelial VWF activate Tie-2 by secreting Angpt1, thereby preventing diapedesis-induced leakiness.

Angiopoietin-Tie Signaling Pathway in Endothelial Cells: A Computational Model.

SummaryThe angiopoietin-Tie signaling pathway is an important vascular signaling pathway involved in angiogenesis, vascular stability, and quiescence. Dysregulation in the pathway is linked to the impairments in vascular function associated with many diseases, including cancer, ocular diseases, systemic inflammation, and cardiovascular diseases. The present study uses a computational signaling pathway model validated against experimental data to quantitatively study various mechanistic aspects of the angiopoietin-Tie signaling pathway, including receptor activation, trafficking, turnover, and molecular mechanisms of its regulation. The model provides mechanistic insights into the controversial role of Ang2 and its regulators vascular endothelial protein tyrosine phosphatase (VE-PTP) and Tie1 and predicts synergistic effects of inhibition of VE-PTP, Tie1, and Tie2 cleavage on enhancing the vascular protective actions of Tie2.

Structural basis of Tie2 activation and Tie2/Tie1 heterodimerization

The endothelial cell (EC)-specific receptor tyrosine kinases Tie1 and Tie2 are necessary for the remodeling and maturation of blood and lymphatic vessels. Angiopoietin-1 (Ang1) growth factor is a Tie2 agonist, whereas Ang2 functions as a context-dependent agonist/antagonist. The orphan receptor Tie1 modulates Tie2 activation, which is induced by association of angiopoietins with Tie2 in cis and across EC-EC junctions in trans Except for the binding of the C-terminal angiopoietin domains to the Tie2 ligand-binding domain, the mechanisms for Tie2 activation are poorly understood. We report here the structural basis of Ang1-induced Tie2 dimerization in cis and provide mechanistic insights on Ang2 antagonism, Tie1/Tie2 heterodimerization, and Tie2 clustering. We find that Ang1-induced Tie2 dimerization and activation occurs via the formation of an intermolecular β-sheet between the membrane-proximal (third) Fibronectin type III domains (Fn3) of Tie2. The structures of Tie2 and Tie1 Fn3 domains are similar and compatible with Tie2/Tie1 heterodimerization by the same mechanism. Mutagenesis of the key interaction residues of Tie2 and Tie1 Fn3 domains decreased Ang1-induced Tie2 phosphorylation and increased the basal phosphorylation of Tie1, respectively. Furthermore, the Tie2 structures revealed additional interactions between the Fn 2 (Fn2) domains that coincide with a mutation of Tie2 in primary congenital glaucoma that leads to defective Tie2 clustering and junctional localization. Mutagenesis of the Fn2-Fn2 interface increased the basal phosphorylation of Tie2, suggesting that the Fn2 interactions are essential in preformed Tie2 oligomerization. The interactions of the membrane-proximal domains could provide new targets for modulation of Tie receptor activity.

Tie1: an orphan receptor provides context for angiopoietin-2/Tie2 signaling.

Angiopoietin-1/Tie2 (ANG1/Tie2) signaling is well documented as regulating angiogenesis and vessel maturation. This pathway is complicated by involvement of the orphan receptor Tie1, which has been implicated as both a positive and negative regulator of ANG1/Tie2 signaling, and ANG2, which can serve as both a Tie2 agonist and antagonist, depending on the context. Two papers in this issue of the JCI provide new insight into this complicated pathway. Korhonen et al. reveal that Tie1 acts to modulate the effects of ANG1 and ANG2 on Tie2 in vitro and in vivo. Kim et al. demonstrate that ANG2 acts as a Tie2 agonist in non-pathological conditions, whereas in the setting of inflammation, ANG2 functions as a Tie2 antagonist and promotes vascular dysfunction. Both studies indicate that inflammation promotes cleavage of the ectodomain of Tie1 and that this cleavage event corresponds with the switch of ANG2 from a Tie2 agonist to an antagonist. The results of these studies lay the groundwork for future strategies to therapeutically exploit this pathway in diseases characterized by adverse vascular remodeling and increased permeability.

Tie1 controls angiopoietin function in vascular remodeling and inflammation.

The angiopoietin/Tie (ANG/Tie) receptor system controls developmental and tumor angiogenesis, inflammatory vascular remodeling, and vessel leakage. ANG1 is a Tie2 agonist that promotes vascular stabilization in inflammation and sepsis, whereas ANG2 is a context-dependent Tie2 agonist or antagonist. A limited understanding of ANG signaling mechanisms and the orphan receptor Tie1 has hindered development of ANG/Tie-targeted therapeutics. Here, we determined that both ANG1 and ANG2 binding to Tie2 increases Tie1-Tie2 interactions in a β1 integrin-dependent manner and that Tie1 regulates ANG-induced Tie2 trafficking in endothelial cells. Endothelial Tie1 was essential for the agonist activity of ANG1 and autocrine ANG2. Deletion of endothelial Tie1 in mice reduced Tie2 phosphorylation and downstream Akt activation, increased FOXO1 nuclear localization and transcriptional activation, and prevented ANG1- and ANG2-induced capillary-to-venous remodeling. However, in acute endotoxemia, the Tie1 ectodomain that is responsible for interaction with Tie2 was rapidly cleaved, ANG1 agonist activity was decreased, and autocrine ANG2 agonist activity was lost, which led to suppression of Tie2 signaling. Tie1 cleavage also occurred in patients with hantavirus infection. These results support a model in which Tie1 directly interacts with Tie2 to promote ANG-induced vascular responses under noninflammatory conditions, whereas in inflammation, Tie1 cleavage contributes to loss of ANG2 agonist activity and vascular stability.

Role of angiopoietin-2 in infection – A double-edged sword?

The endothelial angiopoietin (Angpt)/Tie2 ligand receptor system maintains vascular quiescence and modulates the response to injury. Angpt-1 is considered the natural Tie2 agonist and receptor ligation leads to its phosphorylation inducing various protective downstream pathways. The natural antagonist – Angpt-2 – appears to inhibit these protective effects. In sepsis, the balance between both ligands is shifted in favor for Angpt-2 and the vasculature is highly dysfunctional, activated and leaky. Circulating levels of Angpt-2 strongly predict mortality in septic patients. Consistently, experimental strategies that target Angpt-2 (e.g. antibody, RNAi, etc.) can protect the vascular barrier and improve survival. However, in vitro is has also been shown that Angpt-2 can act as a dose-dependent Tie2 agonist/antagonist. Based on this, people have wondered if Angpt-2 is per se injurious or if it might have protective effects dependent on the scenario. A recent paper by Safioleas and colleagues showed survival benefits after a therapeutic injection of recombinant Angpt-2 in experimental pyelonephritis. Here, we discuss their counter-intuitive but interesting findings and put them into a global context with respect to the existent literature in the angiopoietin/Tie2 sepsis field.

The Synthetic Tie2 Agonist Peptide Vasculotide Protects Renal Vascular Barrier Function In Experimental Acute Kidney Injury.

Microvascular barrier dysfunction plays a major role in the pathophysiology of acute kidney injury (AKI). Angiopoietin-1, the natural agonist ligand for the endothelial-specific Tie2 receptor, is a non-redundant endothelial survival and vascular stabilization factor. Here we evaluate the efficacy of a polyethylene glycol-clustered Tie2 agonist peptide, vasculotide (VT), to protect against endothelial-cell activation with subsequent microvascular dysfunction in a murine model of ischemic AKI. Renal ischemia reperfusion injury (IRI) was induced by clamping of the renal arteries for 35 minutes. Mice were treated with VT or PEGylated cysteine before IRI. Sham-operated animals served as time-matched controls. Treatment with VT significantly reduced transcapillary albumin flux and renal tissue edema after IRI. The protective effects of VT were associated with activation of Tie2 and stabilization of its downstream effector, VE-cadherin in renal vasculature. VT abolished the decline in renal tissue blood flow, attenuated the increase of serum creatinine and blood urea nitrogen after IRI, improved recovery of renal function and markedly reduced mortality compared to PEG [HR 0.14 (95% CI 0.05–0.78) P < 0.05]. VT is inexpensive to produce, chemically stable and unrelated to any Tie2 ligands. Thus, VT may represent a novel therapy to prevent AKI in patients.

Vasculotide can attenuate the immune inflammatory response and airway remodeling in chronic experimentally-induced airway inflammation in mice. (HYP2P.343)

Abstract Inflammation and airway remodeling are features associated with chronic asthmatic lungs. Previous reports have shown the benefits of the angiopoietin-1/Tie2 signaling axis on acute experimentally-induced asthma in mice. However, the more chronic effects as well as the interaction between the inflammatory and vascular components is poorly. Thus, we evaluated the impact of vasculotide, a synthetic Tie2 agonist in a chronic model of asthma. During the chronic allergic response in mice, we show that in addition to endothelial Tie2 receptor expression, there is an increased proportion of dendritic cells and monocytes expressing Tie2. Treatment of experimentally-induced chronic airway inflammation in mice with vasculotide correlated with a skewed CD4+ TH subsets and cytokine profile in the bronchoalveolar lavage of animals. This modified cytokine milieu promoted an altered endothelial cell response characterized by reduced expression of CD62E, CD54 and CD106 on endothelial cells, decreased cellular migration of inflammatory cells to the lung as well as reduced mucus accumulation. Analysis of lung tissues of animals treated with vasculotide revealed a decrease in collagen deposition and thinning of the smooth muscle cell layer in the airways of mice with chronic allergic airway inflammation. Our results demonstrate that vasculotide can impact the inflammatory and remodeling components in chronic asthma through its action on both cells of the immune response and on endothelial cells.

Structural basis for angiopoietin-1–mediated signaling initiation

Angiogenesis is a complex cellular process involving multiple regulatory growth factors and growth factor receptors. Among them, the ligands for the endothelial-specific tunica intima endothelial receptor tyrosine kinase 2 (Tie2) receptor kinase, angiopoietin-1 (Ang1) and Ang2, play essential roles in balancing vessel stability and regression during both developmental and tumor-induced angiogenesis. Despite possessing a high degree of sequence identity, Ang1 and Ang2 have distinct functional roles and cell-signaling characteristics. Here, we present the crystal structures of Ang1 both unbound and in complex with the Tie2 ectodomain. Comparison of the Ang1-containing structures with their Ang2-containing counterparts provide insight into the mechanism of receptor activation and reveal molecular surfaces important for interactions with Tie2 coreceptors and associated signaling proteins. Using structure-based mutagenesis, we identify a loop within the angiopoietin P domain, adjacent to the receptor-binding interface, which confers the specific agonist/antagonist properties of the molecule. We demonstrate using cell-based assays that an Ang2 chimera containing the Ang1 loop sequence behaves functionally similarly to Ang1 as a constitutive Tie2 agonist, able to efficiently dissociate the inhibitory Tie1/Tie2 complex and elicit Tie2 clustering and downstream signaling.

Angiopoietin-2 Functions as a Tie2 Agonist in Tumor Models, Where It Limits the Effects of VEGF Inhibition

The angiopoietins Ang1 (ANGPT1) and Ang2 (ANGPT2) are secreted factors that bind to the endothelial cell-specific receptor tyrosine kinase Tie2 (TEK) and regulate angiogenesis. Ang1 activates Tie2 to promote blood vessel maturation and stabilization. In contrast, Ang2, which is highly expressed by tumor endothelial cells, is thought to inhibit Tie2 activity and destabilize blood vessels, thereby facilitating VEGF-dependent vessel growth. Here, we show that the inhibition of tumor xenograft growth caused by an Ang2-specific antibody (REGN910) is reversed by systemic administration of the Tie2 agonist Ang1. These results indicate that Ang2 blockade inhibits tumor growth by decreasing Tie2 activity, showing that Ang2 is a Tie2 activator. REGN910 treatment of tumors resulted in increased expression of genes that are repressed by Tie2 activation, providing further evidence that REGN910 inhibits Tie2 signaling. Combination treatment with REGN910 plus the VEGF blocker aflibercept reduced tumor vascularity and tumor perfusion more dramatically than either single agent, resulting in more extensive tumor cell death and more potent inhibition of tumor growth. Challenging the prevailing model of Ang2 as a destabilizing factor, our findings indicate that Ang2 plays a protective role in tumor endothelial cells by activating Tie2, thereby limiting the antivascular effects of VEGF inhibition. Thus, blockade of Ang2 might enhance the clinical benefits currently provided by anti-VEGF agents. .

Role of p38 MAPK and Tie2 in the Pathogenesis of MDS and Their Inhibition by Dual Inhibitor ARRY-614.

AbstractAbstract 2825Myelodysplastic syndromes (MDS) are a heterogeneous collection of disorders characterized by dysfunctional bone marrow progenitors leading to peripheral cytopenias. The molecular mechanisms underlying MDS pathophysiology are unclear, but emerging data support a role for both p38 MAPK (p38) and TEK (Tie2). Over-activation of the p38 pathway and increased apoptosis have been reported in the bone marrow of MDS patients, and dysregulation of Tie2 signaling, a potential regulator of hematopoiesis via maintenance of normal hematopoietic stems cell (HSC) quiescence, is associated with worse outcome.To better understand the role of Tie2 in hematopoiesis, CD34+ cells from human cord blood were separated by multi-parameter flow cytometry and cell sorted into HSCs (i.e., CD34+, CD38−) or the more differentiated common myeloid progenitors (CMPs; i.e., CD38+, IL-3Rαlo, CD45RA−), myeloid erythroid progenitors (MEPs; i.e., CD38+, IL-3Rα−, CD45RA−), and granulocyte myeloid progenitors (GMPs; i.e., CD38+, IL-3Rαlo, CD45RA+). Expression of Tie2, Tie1, Ang-1 (Tie2 agonist) and Ang-2 (Tie2 antagonist) was determined by qPCR. The data showed that Tie2, Tie1, and Ang-1 were expressed in CD34+ cells and appeared to be regulated during differentiation, with reduced Tie2 expression observed in the GMP population.To further understand the roles of p38 and Tie2 in MDS, bone marrow and plasma samples were analyzed from a Phase 1 clinical study conducted with ARRY-614, a p38/Tie2 inhibitor, in patients with IPSS Low/Int-1 Risk MDS. At baseline, 65% (13/20) of the MDS patients showed aberrant p38 activation (≥5% phospho-p38 positive cells). Following treatment with ARRY-614, the median percent of cells positive for phospho-p38 was decreased by 85% through up to 4 cycles of treatment (∼112 days). Apoptosis in patient bone marrow samples was reduced as well (monitored by cleaved caspase-3).In cell-based assays, ARRY-614 inhibits both p38-mediated HSP27 phosphorylation (IC50 = 1 nM) and Tie2-dependent AKT phosphorylation (IC50 = 13 nM). Cellular IC50 values, corrected for plasma protein binding, and preliminary pharmacokinetic parameters were used to predict inhibition of these targets in patients. Analysis of the highest administered dose (1200 mg QD) of ARRY-614 as a powder-in-capsule (PiC) formulation in the Phase 1 clinical study predicted robust suppression of phospho-p38 (≥ 50% for 24 hours), consistent with bone marrow and plasma biomarker findings. However, partial inhibition of Tie2 (≥ 50% for 17.1 hours) was predicted. In a second Phase 1 clinical study, an optimized ARRY-614 formulation has demonstrated decreased intra- and inter-patient variability and increased peak plasma concentrations. With this new formulation, peak plasma concentrations of the 400 mg QD cohort were ∼50% higher than those of the 1200 mg QD PiC formulation cohort, possibly affording more extensive Tie2 inhibition.In summary, these observations suggest that inhibition of both p38 and Tie2 may be important for the effects of ARRY-614 in MDS patients. The ongoing Phase 1 dose escalation trial of the optimized ARRY-614 formulation may further our understanding of the contributions of these targets to the pathogenesis of MDS. Disclosures:Winski:Array Biopharma Inc.: Employment. Cable:Array Biopharma Inc.: Employment. Hogeland:Array Biopharma Inc.: Employment. Brown:Array Biopharma Inc.: Employment. Weaver:Array Biopharma Inc.: Employment. Garrus:Array Biopharma Inc.: Employment. Rhodes:Array Biopharma Inc.: Employment. Maloney:Array Biopharma Inc.: Employment. Ptaszynski:Array BioPharma: Consultancy. Chantry:Array Biopharma Inc.: Employment.

Tie2-Dependent Neovascularization of the Ischemic Hindlimb Is Mediated by Angiopoietin-2

The angiopoietins (ANGPT) are ligands for the endothelial cell (EC) receptor tyrosine kinase, Tie2. Angpt-1 is a Tie2 agonist that promotes vascular maturation and stabilization, whereas Angpt-2 is a partial agonist/antagonist involved in the initiation of postnatal angiogenesis. Therefore, we hypothesized that overexpression of Angpt-2 would be more effective than Angpt-1 for enhancing the perfusion recovery in the ischemic hindlimb. Perfusion recovery was markedly impaired in Tie2-deficient animals at day 35 in a model of chronic hindlimb ischemia. Injections of Angpt-2 or VEGFA plasmid at 7 days post femoral artery resection enhanced recovery and improved arteriogenesis as assessed by angiographic scores, whereas Angpt-1 or null plasmid had no effect. In addition, Angpt-2 together with VEGF resulted in greater improvement in perfusion and collateral vessel formation than VEGF alone. Similarly, conditional overexpression of Angpt-2 in mice improved ischemic limb blood flow recovery, while Angpt-1 overexpression was ineffective. These data from Tie2 heterozygote deficient mice demonstrate, for the first time, the importance of the Tie2 pathway in spontaneous neovascularization in response to chronic hindlimb ischemia. Moreover, they show that overexpression of the partial agonist, Angpt-2, but not Angpt-1, enhanced ischemic hind limb perfusion recovery and collateralization, suggesting that a coordinated sequence antagonist and agonist activity is required for effective therapeutic revascularization.

Angiopoietin2 and Tie2: Tied to Lymphangiogenesis and Lung Metastasis. New Perspectives in Antimetastatic Antiangiogenic Therapy

Angiopoietin2 and Tie2: Tied to Lymphangiogenesis and Lung Metastasis. New Perspectives in Antimetastatic Antiangiogenic Therapy

Tie1 regulates the Tie2 agonistic role of angiopoietin-2 in human lymphatic endothelial cells

Although Angiopoietin (Ang) 2 has been shown to function as a Tie2 antagonist in vascular endothelial cells, several recent studies on Ang2-deficient mice have reported that, like Ang1, Ang2 acts as a Tie2 agonist during in vivo lymphangiogenesis. However, the mechanism governing the Tie2 agonistic activity of Ang2 in lymphatic endothelial cells has not been investigated. We found that both Ang1 and Ang2 enhanced the in vitro angiogenic and anti-apoptotic activities of human lymphatic endothelial cells (HLECs) through the Tie2/Akt signaling pathway, while only Ang1 elicited such effects in human umbilical vein vascular endothelial cells (HUVECs). This Tie2-agonistic effect of Ang2 in HLECs resulted from low levels of physical association between Tie2 and Tie1 receptors due to a reduced level of Tie1 expression in HLECs compared to HUVECs. Overexpression of Tie1 and the resulting increase in formation of Tie1/Tie2 heterocomplexes in HLECs completely abolished Ang2-mediated Tie2 activation and the subsequent cellular responses, but did not alter the Ang1 function. This inhibitory role of Tie1 in Ang2-induced Tie2 activation was also confirmed in non-endothelial cells with adenovirus-mediated ectopic expression of Tie1 and/or Tie2. To our knowledge, this study is the first to describe how Ang2 acts as a Tie2 agonist in HLECs. Our results suggest that the expression level of Tie1 and its physical interaction with Tie2 defines whether Ang2 functions as a Tie2 agonist or antagonist, thereby determining the context-dependent differential endothelial sensitivity to Ang2.

Expression profile of heat shock proteins in acute myeloid leukaemia patients reveals a distinct signature strongly associated with FLT3 mutation status – consequences and potentials for pharmacological intervention

Heat shock proteins (HSPs) are molecular chaperones that assist proteins in their folding to native structures. HSPs are regarded as possible therapeutic targets in acute myeloid leukaemia (AML). We used bioinformatical approaches to characterize the HSP profile in AML cells from 75 consecutive patients, in addition to the effect of the HSP90 inhibitor 17-DMAG. Patients harbouring a FLT3-internal tandem duplication (FLT3-ITD) were extensively overrepresented in the cluster with high HSP levels, indicating a strong dependence of HSPs in stabilizing FLT3-ITD encoded oncoproteins. FLT3 ligation further increased the levels of HSP90 and its co-chaperone HSP70. HSP90 inhibition had a stronger pro-apoptotic effect for AML cells with FLT3-ITD than for cells with wild-type FLT3, whereas the anti-proliferative effect of HSP90 inhibition was similar for the two patient subsets. HSP90 inhibition altered the constitutive cytokine release profile in an anti-angiogenic direction independent of FLT3 mutational status: (i) pro-angiogenic CXCL8, MMP-2 and MMP-9 showed a stronger decrease than anti-angiogenic CXCL9-11, (ii) the Tie-2 agonist Ang-1 showed a stronger decrease than the potentially antagonistic Ang-2, and (iii) VEGF and HGF levels were decreased. Finally, HSP90 inhibition counteracted the leukaemia-stimulating effect of endothelial cells. Our studies demonstrate that HSP90 inhibition mediates anti-leukaemic effects through both direct and indirect activity.

Effects of a synthetic PEG-ylated Tie-2 agonist peptide on endotoxemic lung injury and mortality

A synthetic 7-mer, HHHRHSF, was recently identified by screening a phage display library for binding to the Tie-2 receptor. A polyethylene-oxide clustered version of this peptide, termed vasculotide (VT), was reported to activate Tie-2 and promote angiogenesis in a mouse model of diabetic ulcer. We hypothesized that VT administration would defend endothelial barrier function against sepsis-associated mediators of permeability, prevent lung vascular leakage arising in endotoxemia, and improve mortality in endotoxemic mice. In confluent human microvascular endothelial cells, VT prevented endotoxin-induced (lipopolysaccharides, LPS O111:B4) gap formation, loss of monolayer resistance, and translocation of labeled albumin. In 8-wk-old male C57Bl6/J mice given a ∼70% lethal dose of endotoxin (15 mg/kg ip), VT prevented lung vascular leakage and reversed the attenuation of lung vascular endothelial cadherin induced by endotoxemia. These protective effects of VT were associated with activation of Tie-2 and its downstream mediator, Akt. Echocardiographic studies showed only a nonsignificant trend toward improved myocardial performance associated with VT. Finally, we evaluated survival in this mouse model. Pretreatment with VT improved survival by 41.4% (n = 15/group, P = 0.02) and post-LPS administration of VT improved survival by 33.3% (n = 15/group, P = 0.051). VT-mediated protection from LPS lethality was lost in Tie-2 heterozygous mice, in agreement with VT's proposed receptor specificity. We conclude that this synthetic Tie-2 agonist, completely unrelated to endogenous Tie-2 ligands, is sufficient to activate the receptor and its downstream pathways in vivo and that the Tie-2 receptor may be an important target for therapeutic evaluation in conditions of pathological vascular leakage.

The synthetic Tie2 agonist peptide vasculotide protects against vascular leakage and reduces mortality in murine abdominal sepsis

IntroductionAngiopoietin-1 (Angpt1), the natural agonist ligand for the endothelial Tie2 receptor, is a non-redundant endothelial survival and vascular stabilization factor that reduces endothelial permeability and inhibits leukocyte-endothelium interactions. Here we evaluate the efficacy of a novel polyethylene glycol (PEG)-clustered Tie2 agonist peptide, vasculotide (VT), to protect against vascular leakage and mortality in a murine model of polymicrobial abdominal sepsis.MethodsPolymicrobial abdominal sepsis in C57BL6 mice was induced by cecal-ligation-and-puncture (CLP). Mice were treated with different dosages of VT or equal volume of phosphate-buffered saline (PBS). Sham-operated animals served as time-matched controls.ResultsSystemic administration of VT induced long-lasting Tie2 activation in vivo. VT protected against sepsis-induced endothelial barrier dysfunction, as evidenced by attenuation of vascular leakage and leukocyte transmigration into the peritoneal cavity. Histological analysis revealed that VT treatment ameliorated leukocyte infiltration in kidneys of septic mice, probably due to reduced endothelial adhesion molecule expression. VT-driven effects were associated with significantly improved organ function and reduced circulating cytokine levels. The endothelial-specific action of VT was supported by additional in vitro studies showing no effect of VT on either cytokine release from isolated peritoneal macrophages, or migratory capacity of isolated neutrophils. Finally, administration of VT pre-CLP (hazard ratio 0.39 [95% confidence interval 0.19-0.81] P < 0.001) and post-CLP reduced mortality in septic mice (HR 0.22 [95% CI 0.06-0.83] P < 0.05).ConclusionsWe provide proof of principle in support of the efficacious use of PEGylated VT, a drug-like Tie2 receptor agonist, to counteract microvascular endothelial barrier dysfunction and reduce mortality in a clinically relevant murine sepsis model. Further studies are needed to pave the road for clinical application of this therapeutic concept.