Targeting the Ang2/Tie2 Axis with Tanshinone IIA Elicits Vascular Normalization in Ischemic Injury and Colon Cancer.

Pathological angiogenesis, as exhibited by aberrant vascular structure and function, has been well deemed to be a hallmark of cancer and various ischemic diseases. Therefore, strategies to normalize vasculature are of potential therapeutic interest in these diseases. Recently, identifying bioactive compounds from medicinal plant extracts to reverse abnormal vasculature has been gaining increasing attention. Tanshinone IIA (Tan IIA), an active component of Salvia miltiorrhiza, has been shown to play significant roles in improving blood circulation and delaying tumor progression. However, the underlying mechanisms responsible for the therapeutic effects of Tan IIA are not fully understood. Herein, we established animal models of HT-29 human colon cancer xenograft and hind limb ischemia to investigate the role of Tan IIA in regulating abnormal vasculature. Interestingly, our results demonstrated that Tan IIA could significantly promote the blood flow, alleviate the hypoxia, improve the muscle quality, and ameliorate the pathological damage after ischemic insult. Meanwhile, we also revealed that Tan IIA promoted the integrity of vascular structure, reduced vascular leakage, and attenuated the hypoxia in HT-29 tumors. Moreover, the circulating angiopoietin 2 (Ang2), which is extremely high in these two pathological states, was substantially depleted in the presence of Tan IIA. Also, the activation of Tie2 was potentiated by Tan IIA, resulting in decreased vascular permeability and elevated vascular integrity. Mechanistically, we uncovered that Tan IIA maintained vascular stability by targeting the Ang2-Tie2-AKT-MLCK cascade. Collectively, our data suggest that Tan IIA normalizes vessels in tumors and ischemic injury via regulating the Ang2/Tie2 signaling pathway.

The Angiopoietin-2 and TIE Pathway as a Therapeutic Target for Enhancing Antiangiogenic Therapy and Immunotherapy in Patients with Advanced Cancer.

Despite significant advances made in cancer treatment, the development of therapeutic resistance to anticancer drugs represents a major clinical problem that limits treatment efficacy for cancer patients. Herein, we focus on the response and resistance to current antiangiogenic drugs and immunotherapies and describe potential strategies for improved treatment outcomes. Antiangiogenic treatments that mainly target vascular endothelial growth factor (VEGF) signaling have shown efficacy in many types of cancer. However, drug resistance, characterized by disease recurrence, has limited therapeutic success and thus increased our urgency to better understand the mechanism of resistance to inhibitors of VEGF signaling. Moreover, cancer immunotherapies including immune checkpoint inhibitors (ICIs), which stimulate antitumor immunity, have also demonstrated a remarkable clinical benefit in the treatment of many aggressive malignancies. Nevertheless, the emergence of resistance to immunotherapies associated with an immunosuppressive tumor microenvironment has restricted therapeutic response, necessitating the development of better therapeutic strategies to increase treatment efficacy in patients. Angiopoietin-2 (ANG2), which binds to the receptor tyrosine kinase TIE2 in endothelial cells, is a cooperative driver of angiogenesis and vascular destabilization along with VEGF. It has been suggested in multiple preclinical studies that ANG2-mediated vascular changes contribute to the development and persistence of resistance to anti-VEGF therapy. Further, emerging evidence suggests a fundamental link between vascular abnormalities and tumor immune evasion, supporting the rationale for combination strategies of immunotherapy with antiangiogenic drugs. In this review, we discuss the recent mechanistic and clinical advances in targeting angiopoietin signaling, focusing on ANG2 inhibition, to enhance therapeutic efficacy of antiangiogenic and ICI therapies. In short, we propose that a better mechanistic understanding of ANG2-mediated vascular changes will provide insight into the significance of ANG2 in treatment response and resistance to current antiangiogenic and ICI therapies. These advances will ultimately improve therapeutic modalities for cancer treatment.

Targeting Angiopoietin in Retinal Vascular Diseases: A Literature Review and Summary of Clinical Trials Involving Faricimab.

This review summarizes the latest findings in the literature of Angiopoietin-2 (Ang-2), Tyrosine-protein kinase receptor (Tie-2) complex, and faricimab along with their involvement for the treatment of retinal vascular diseases in various clinical trials. In ischemic diseases, such as diabetic retinopathy, Ang-2 is upregulated, deactivating Tie-2, resulting in vascular leakage, pericyte loss, and inflammation. Recombinant Angiopeotin-1 (Ang-1), Ang-2-blocking molecules, and inhibitors of vascular endothelial protein tyrosine phosphatase (VE-PTP) decrease inflammation-associated vascular leakage, showing therapeutic effects in diabetes, atherosclerosis, and ocular neovascular diseases. In addition, novel studies show that angiopoietin-like proteins may play an important role in cellular metabolism leading to retinal vascular diseases. Current therapeutic focus combines Ang-Tie targeted drugs with other anti-angiogenic or immune therapies. Clinical studies have identified faricimab, a novel bispecific antibody designed for intravitreal use, to simultaneously bind and neutralize Ang-2 and VEGF-A for treatment of diabetic eye disease. By targeting both Ang-2 and vascular endothelial growth factor-A (VEGF-A), faricimab displays an improved and sustained efficacy over longer treatment intervals, delivering superior vision outcomes for patients with diabetic macular edema and reducing the treatment burden for patients with neovascular age-related macular degeneration and diabetic macular edema. Phase 2 results have produced promising outcomes with regard to efficacy and durability. Faricimab is currently being evaluated in global Phase 3 studies.

Molecular insight of regorafenib treatment for colorectal cancer.

Regorafenib is a multi-targeting kinase inhibitor approved for the treatment of metastatic colorectal cancer patients in refractory to standard chemotherapy. Similarly to sorafenib, this agent was originally developed as a RAF1 inhibitor. However, the kinase inhibitory profile is distinct from sorafenib. A broad-spectrum of kinase inhibition induces wide-range drug sensitivity, irrespective of mutation status of major oncogenes. This agent's main therapeutic effects are anti-angiogenesis and the remodeling of tumor microenvironment through several mechanisms of action. The dual blockade of VEGF receptors and TIE2 can lead to both additive anti-angiogenesis effects and the suggestive unique regulation of vessel stability. Additionally, it inhibits molecular escape pathways to VEGF inhibition (e.g., FGF, PIGF, and PDGF signaling), enabling its continuous antiangiogenic effect even in tumors resistant to VEGF inhibitors. Furthermore, regorafenib has the important effect of enhancing anti-tumor immunity via macrophage modulation. Based on this concept, clinical trials have been recently launched for the development of a combination strategy with immune checkpoint inhibitors. Contrary to regorafenib induced clinical benefits and advances in the novel strategy, currently no predictive biomarkers have been identified. In the present review, we revisit and summarize regorafenib's unique mechanisms of action. The review could highlight molecular insights and provide some perspective for the search of predictive biomarkers used in metastatic colorectal cancer patients treated with regorafenib.

Probing 2H-Indazoles as Templates for SGK1, Tie2, and SRC Kinase Inhibitors.

The broader and systematic application of a novel scaffold is often hampered by the unavailability of a short and reliable synthetic access. We investigated a new strategy for the design and synthesis of an array of N2-substituted aza-2H-indazole derivatives as potential kinase inhibitors. Guided by a rational ligand alignment approach to qualify the so-far underrepresented aza-2H-indazole scaffold, indazoles were connected at the N2 position with a phenyl spacer and an arylsulfonamide or amide linkage. Initial profiling against a panel of 30 kinases confirmed the in silico predicted selectivity bias. A synthesized focused library of 52 different aza-2H-indazole derivatives showed good initial selective inhibition against SGK1, Tie2, and SRC kinases, with the best representatives having IC50 values in the range of 500 nm. In a comparative computational study, these data were analyzed and rationalized in light of docking studies.

Discovery of novel anti-angiogenesis agents. Part 9: Multiplex inhibitors suppressing compensatory activations of RTKs.

Aberrant angiogenesis is a hallmark of various diseases including cancers. VEGFR-2 inhibitors have been utilized as anti-angiogenic agents for several years. However, compensatory activation of various receptor tyrosine kinases (RTK) could induce the occurrence of resistance. We previously reported a series of multi-target inhibitors of VEGFR-2, Tie-2, and EphB4 as anti-angiogenic agents. These inhibitors might be a promising strategy to overcome the resistance induced by compensatory activation. In order to expand the structural diversity of these multiple RTK inhibitors, we described herein the design, synthesis, and evaluation of a novel class of triplet VEGFR-2/TIE-2/EphB4 inhibitors. The biological evaluation indicated that five compounds (6b, 6d, 6e, 7e, and 7g) exhibited simultaneous VEGFR-2/Tie-2/EphB4 inhibitory activities with IC50 values less than 50 nM.

Discovery of novel anti-angiogenesis agents. Part 10: Multi-target inhibitors of VEGFR-2, Tie-2 and EphB4 incorporated with 1,2,3-triazol.

VEGFR-2, Tie-2, and EphB4 are essential for both angiogenesis and tumorigenesis. Herein, we developed a series of pyridines incorporated with 1,2,3-triazole as multi-target inhibitors based on the crystal structure alignment of the kinase domain of angiogenic RTKs. Biological results indicated that these multi-target inhibitors displayed considerable potential as novel anti-angiogenic agents. Among them, compound BD7 exhibited the most potent inhibition against the three RTKs simultaneously, and good activity on inhibiting viability of human umbilical endothelial cells. Therefore, 1,2,3-triazole could serve as a promising DFG binding group for multi-target inhibitors of VEGFR-2, Tie-2 and EphB4 bearing pyridine as hinge binding group.

Angiopoietin-1/Tie2 signaling pathway contributes to the therapeutic effect of thymosin ß4 on diabetic peripheral neuropathy.

Angiopoietin-1 (Ang1) and its receptor Tie2 regulate vascular function. Our previous study demonstrated that thymosin beta 4 (Tß4) ameliorates neurological function of diabetic peripheral neuropathy. Mechanisms underlying the therapeutic effect of Tß4 on diabetic peripheral neuropathy have not been fully investigated. The present in vivo study investigated whether the Ang1/Tie2 signaling pathway is involved in Tß4-improved neurovascular remodeling in diabetic peripheral neuropathy. Diabetic BKS. Cg-m+/+Leprdb/J (db/db) mice at age 20 weeks were treated with Tß4 and neutralizing antibody against mouse Tie2 for 4 consecutive weeks. Neurological functional and neurovascular remodeling were measured. Administration of the neutralizing antibody against Tie2 attenuated the therapeutic effect of Tß4 on improved diabetic peripheral neuropathy as measured by motor and sensory nerve conduction velocity and thermal hypoesthesia compared to diabetic db/db mice treated with Tß4 only. Histopathological analysis revealed that the neutralizing antibody against Tie2 abolished Tß4-increased microvascular density in sciatic nerve and intraepidermal nerve fiber density, which were associated with suppression of Tß4-upregulated occludin expression and Tß4-reduced protein levels of nuclear factor-κB (NF-κB) and vascular cell adhesion molecule-1 (VCAM1). Our data provide in vivo evidence that the Ang1/Tie2 pathway contributes to the therapeutic effect of Tß4 on diabetic peripheral neuropathy.

Novel 5,6-disubstituted pyrrolo[2,3-d]pyrimidine derivatives as broad spectrum antiproliferative agents: Synthesis, cell based assays, kinase profile and molecular docking study.

Two new series of 5-subtituted and 5,6-disubstituted pyrrolo[2,3-d]pyrimidine octamides (4a-o and 6a-g) and their corresponding free amines 5a-m and 7a-g have been synthesized and biologically evaluated for their antiproliferative activity against three human cancer cell lines. The 5,6-disubstituted octamides 6d-g as well as the amine derivative 7b have shown the best anticancer activity with single digit micromolar GI50 values over the tested cancer cells, and low cytotoxic effects (GI50 > 10.0 µM) against HFF-1 normal cell. A structure activity relationship (SAR) study has been established and disclosed that terminal octamide moiety at C2 as well as disubstitution with fluorobenzyl piperazines at C5 and C6 of pyrrolo[2,3-d]pyrimidine are the key structural features prerequisite for best antiproliferative activity. Moreover, the most active member 6f was tested for its antiproliferative activity over a panel of 60 cancer cell lines at NCI, and exhibited distinct broad spectrum anticancer activity with submicromolar GI50 and TGI values over multiple cancer cells. Kinase profile of compound 6f over 53 oncogenic kinases at 10 µM concentration showed its highly selective inhibitory activity towards FGFR4, Tie2 and TrkA kinases. The observed activity of 6f against TrkA (IC50 = 2.25 µM), FGFR4 (IC50 = 6.71 µM) and Tie2 (IC50 = 6.84 µM) was explained by molecular docking study, which also proposed that 6f may be a type III kinase inhibitor, binding to an allosteric site rather than kinase hinge region. Overall, compound 6f may serve as a promising anticancer lead compound that could be further optimized for development of potent anticancer agents.

Tie2 signalling through Erk1/2 regulates TLR4 driven inflammation.

The inflammatory response is essential for eradication of lipopolysaccharide (LPS) presenting microbial invaders but requires exquisite regulation to prevent detrimental vascular inflammation. Endothelial cells play active roles in both the initiation of inflammation, through the detection of LPS by Toll-like Receptor 4 (TLR4), and the resolution of inflammation, through the actions of the receptor tyrosine kinase, Tie2. The process by which Tie2 attenuates LPS-TLR4 driven inflammation is poorly understood. To investigate the effects of Tie2 on TLR4 signalling, Nf-κB activation was monitored in cells expressing Tie2 mutants harboring tyrosine (Y) to phenylalanine (F) substitutions in the cytoplasmic domain. Tie2 attenuated LPS induced Nf-κB activation in a manner requiring Tie2 kinase activation, the carboxy-terminal tyrosine residue Y1100 and downstream Erk1/2 signalling. Tyrosine 1100 was also required for the Tie2 dependent decrease in expression of the TLR4 signalling proteins, TRAF6 and IRAK1 and stabilization of the Nf-κB inhibitor, IκBα. In contrast, upregulation of known TLR4 antagonist miRNA-146b-5p required all three tyrosine phosphorylation sites in Tie2. Finally, we confirmed in an in vivo model that activation of Tie2 signalling reduces LPS mediated inflammation. Our results show that Y1100 initiated Erk1/2 signalling is essential for the anti-inflammatory effect of Tie2 on TLR4 mediated inflammation.

Targeting the Tie2-αvß3 integrin axis with bi-specific reagents for the inhibition of angiogenesis.

BACKGROUND: Increased activity of the receptor tyrosine kinase Tie2 has been implicated in the promotion of pathological angiogenesis. This activity is mainly mediated through angiopoietin (Ang)1- and Ang2-dependent activation of integrins by Tie2, rendering the Ang/Tie2/integrin axis an attractive putative target for cancer therapeutics. RESULTS: To target this axis, we developed single domain, non-immunoglobulin high-affinity bi-specific protein inhibitors against both Tie2 and αvß3 integrin. We have previously engineered the Ang2-binding domain of Tie2 (Ang2-BD) as a Tie2 inhibitor. Here, we engineered an exposed loop in Ang2-BD to generate variants that include an integrin-binding Arg-Gly-Asp (RGD) motif and used flow cytometry screening of a yeast-displayed Ang2-BD RGD loop library to identify the integrin antagonists. The bi-specific antagonists targeting both Tie2 and αvß3 integrin inhibited adhesion and proliferation of endothelial cells cultured together with the αvß3 integrin ligand vitronectin, as well as endothelial cell invasion and tube formation. The bi-specific reagents inhibited downstream signaling by Tie2 intracellularly in response to its agonist Ang1 more effectively than the wild-type Ang2 BD that binds Tie2 alone. CONCLUSIONS: Collectively, this study-the first to describe inhibitors targeting all the known functions resulting from Tie2/integrin αvß3 cross-talk-has created new tools for studying Tie2- and integrin αvß3-dependent molecular pathways and provides the basis for the rational and combinatorial engineering of ligand-Tie2 and ligand-integrin αvß3 receptor interactions. Given the roles of these pathways in cancer angiogenesis and metastasis, this proof of principle study paves the route to create novel Tie2/integrin αvß3-targeting proteins for clinical use as imaging and therapeutic agents.

Development of Molecular Therapies for Venous Malformations.

Vascular anomalies are localized defects of morphogenesis that can affect lymphatic and blood vessels. They are generally called birthmarks, typically observed soon after birth and occurring in up to 10% of children. Based on their clinical and histological characteristics, they are classified into vascular tumours and vascular malformations. The most common malformations are venous malformations (VMs) resulting in chronic vascular diseases that can be associated with significant morbidity necessitating often demanding and repeating clinical management. The current treatment is based on surgical resection and sclerotherapy, which can be impossible due to the size or location of lesions or ineffective due to the regrowth of malformed vessels. Therefore, medical therapies for VMs are highly desired. Recent studies have identified genetic defects that result in the constantly active endothelial cell receptor tyrosine kinase TIE2/phosphoinositide 3-kinase PI3K signalling pathway as a frequent cause for VMs. The first treatment to inhibit this pathway with sirolimus indicated that molecular treatment can be effective against VMs. In addition, certain VM 'hotspot' mutations have been previously found in tumours, providing the rationale for the exploration and repurposing of existing and investigational cancer drugs for VMs. Finally, discoveries of molecular and cellular abnormalities that characterize a large proportion of VMs and the generation of pre-clinical VM mouse models provide the necessary basis for the development of the targeted molecular treatment strategies we discuss in this MiniReview.

Angiopoietins bind thrombomodulin and inhibit its function as a thrombin cofactor.

Angiopoietin-1 (Ang1) and Angiopoietin-2 (Ang2) are ligands for Tie2, an endothelial-specific receptor tyrosine kinase that is an essential regulator of angiogenesis. Here we report the identification, via expression cloning, of thrombomodulin (TM) as another receptor for Ang1 and Ang2. Thrombomodulin is an endothelial cell surface molecule that plays an essential role as a coagulation inhibitor via its function as a cofactor in the thrombin-mediated activation of protein C, an anticoagulant protein, as well as thrombin-activatable fibrinolysis inhibitor (TAFI). Ang1 and Ang2 inhibited the thrombin/TM-mediated generation of activated protein C and TAFI in cultured endothelial cells, and inhibited the binding of thrombin to TM in vitro. Ang2 appears to bind TM with higher affinity than Ang1 and is a more potent inhibitor of TM function. Consistent with a potential role for angiopoietins in coagulation, administration of thrombin to mice rapidly increased plasma Ang1 levels, presumably reflecting release from activated platelets (previously shown to contain high levels of Ang1). In addition, Ang1 levels were significantly elevated in plasma prepared from wound blood, suggesting that Ang1 is released from activated platelets at sites of vessel injury. Our results imply a previously undescribed role for angiopoietins in the regulation of hemostasis.

Discovery of novel anti-angiogenesis agents. Part 7: Multitarget inhibitors of VEGFR-2, TIE-2 and EphB4.

Herein, we embarked on a structural optimization campaign aiming at the discovery of second generation anti-angiogenesis agents with our previously reported BPS-7 as lead compound. A library of 27 compounds has been afforded based on the highly conserved ATP-binding pocket of VEGFR-2, Tie-2, and EphB4. Several title compounds exhibited simultaneous inhibitory effects against three angiogenic RTKs. These compounds with a 'triplet' inhibition profile have been identified as novel anti-angiogenic and anticancer agents. The representative VDAU11 displayed prominent anti-angiogenic and anticancer potency and could be considered as a candidate for further optimization. These results indicate that N-(pyridin-2-yl)acrylamide could serve as a novel hinge-binding group of triple inhibitors.

The Selective Tie2 Inhibitor Rebastinib Blocks Recruitment and Function of Tie2Hi Macrophages in Breast Cancer and Pancreatic Neuroendocrine Tumors.

Tumor-infiltrating myeloid cells promote tumor progression by mediating angiogenesis, tumor cell intravasation, and metastasis, which can offset the effects of chemotherapy, radiation, and antiangiogenic therapy. Here, we show that the kinase switch control inhibitor rebastinib inhibits Tie2, a tyrosine kinase receptor expressed on endothelial cells and protumoral Tie2-expressing macrophages in mouse models of metastatic cancer. Rebastinib reduces tumor growth and metastasis in an orthotopic mouse model of metastatic mammary carcinoma through reduction of Tie2+ myeloid cell infiltration, antiangiogenic effects, and blockade of tumor cell intravasation mediated by perivascular Tie2Hi/Vegf-AHi macrophages in the tumor microenvironment of metastasis (TMEM). The antitumor effects of rebastinib enhance the efficacy of microtubule inhibiting chemotherapeutic agents, either eribulin or paclitaxel, by reducing tumor volume, metastasis, and improving overall survival. Rebastinib inhibition of angiopoietin/Tie2 signaling impairs multiple pathways in tumor progression mediated by protumoral Tie2+ macrophages, including TMEM-dependent dissemination and angiopoietin/Tie2-dependent angiogenesis. Rebastinib is a promising therapy for achieving Tie2 inhibition in cancer patients. Mol Cancer Ther; 16(11); 2486-501. ©2017 AACR.

Utilizing combinatorial engineering to develop Tie2 targeting antagonistic angiopoetin-2 ligands as candidates for anti-angiogenesis therapy.

In many human cancers, the receptor tyrosine kinase (RTK) Tie2 plays important roles in mediating proliferation, survival, migration and angiogenesis. Thus, molecules that could potently inhibit activation of the Tie2 receptor would have a significant impact on cancer therapy. Nevertheless, attempts to develop Tie2-targeted inhibitors have met with little success, and there is currently no FDA-approved therapeutic selectively targeting Tie2. We used a combinatorial protein engineering approach to develop a new generation of angiopoietin (Ang)2-derived Tie2 antagonists as potential cancer therapeutics and as tools to study angiogenesis. The construct for designing a yeast surface display (YSD) library of potential antagonists was an Ang2 binding domain (Ang2-BD) that retains Tie2 binding ability but prevents ligand multimerization and receptor dimerization and activation. This mutant library was then screened by quantitative high-throughput flow cytometric sorting to identify Ang2-BD variants with increased expression, stability and affinity to Tie2. The selected variants were recombinantly expressed and showed high affinity to soluble and cellular Tie2 and strongly inhibited both Tie2 phosphorylation and endothelial capillary tube formation and cell invasion compared to the parental Ang2-BD. The significance of the study lies in the insight it provides into the sequence-structure-function relationships and mechanism of action of the antagonistic Ang mutants. The approach of using a natural protein ligand as a molecular scaffold for engineering high-affinity agents can be applied to other ligands to create functional protein antagonists against additional biomedical targets.

Angiogenesis in Dermatology - Insights of Molecular Mechanisms and Latest Developments.

Angiogenesis is the growth of new blood vessels from pre-existing vessels. It is a biological process essential in physiological wound healing or pathological inflammation and tumor growth, which underlies a complex interplay of stimulating and inhibiting signals. Extracellular matrix, cells of innate and adaptive immunity and endothelial cells itself are a major source of angiogenic factors that activate or inhibit specific receptors and consequently influence intracellular signaling pathways. Most inflammatory and neoplastic diseases in dermatology are characterized by excessive angiogenesis, such as psoriasis, atopic dermatitis, as well as melanoma, non-melanoma skin cancer, but also benign vascular neoplasia. In this article we describe current knowledge of angiogenesis and its most relevant mechanisms in different dermatological disorders with particular emphasis on the angiogenic factors (vascular endothelial growth factor) and angiopoietins as a target of current and future directions of anti-angiogenic therapy.

Binding Pose Flip Explained via Enthalpic and Entropic Contributions.

The anomalous binding modes of five highly similar fragments of TIE2 inhibitors, showing three distinct binding poses, are investigated. We report a quantitative rationalization for the changes in binding pose based on molecular dynamics simulations. We investigated five fragments in complex with the transforming growth factor ß receptor type 1 kinase domain. Analyses of these simulations using Grid Inhomogeneous Solvation Theory (GIST), pKA calculations, and a tool to investigate enthalpic differences upon binding unraveled the various thermodynamic contributions to the different binding modes. While one binding mode flip can be rationalized by steric repulsion, the second binding pose flip revealed a different protonation state for one of the ligands, leading to different enthalpic and entropic contributions to the binding free energy. One binding pose is stabilized by the displacement of entropically unfavored water molecules (binding pose determined by solvation entropy), ligands in the other binding pose are stabilized by strong enthalpic interactions, overcompensating the unfavorable water entropy in this pose (binding pose determined by enthalpic interactions). This analysis elucidates unprecedented details determining the flipping of the binding modes, which can elegantly explain the experimental findings for this system.