Thermodynamic and structural description of allosterically regulated VEGFR-2 dimerization

Computer-Aided Design of VEGFR-2 Inhibitors as Anticancer Agents: A Review

Due to its intricate molecular and structural characteristics, vascular endothelial growth factor receptor 2 (VEGFR-2) is essential for the development of new blood vessels in various pathological processes and conditions, especially in cancers. VEGFR-2 inhibitors have demonstrated significant anticancer effects by blocking many signaling pathways linked to tumor growth, metastasis, and angiogenesis. Several small compounds, including the well-tolerated sunitinib and sorafenib, have been approved as VEGFR-2 inhibitors. However, the widespread side effects linked to these VEGFR-2 inhibitors-hypertension, epistaxis, proteinuria, and upper respiratory infection-motivate researchers to search for new VEGFR-2 inhibitors with better pharmacokinetic profiles. The key molecular interactions required for the interaction of the small molecules with the protein target to produce the desired pharmacological effects are identified using computer-aided drug design (CADD) methods such as pharmacophore and QSAR modeling, structure-based virtual screening, molecular docking, molecular dynamics (MD) simulation coupled with MM/PB(GB)SA, and other computational strategies. This review discusses the applications of these methods for VEGFR-2 inhibitor design. Future VEGFR-2 inhibitor designs may be influenced by this review, which focuses on the current trends of using multiple screening layers to design better inhibitors.

Targeting the interaction of pleiotrophin and VEGFA165 with protein tyrosine phosphatase receptor zeta 1 inhibits endothelial cell activation and angiogenesis

Protein tyrosine phosphatase receptor zeta 1 (PTPRZ1) is a transmembrane tyrosine phosphatase (TP) that serves as a receptor for pleiotrophin (PTN) and vascular endothelial growth factor A 165 (VEGFA165) to regulate endothelial cell migration. In the present work, we identify a PTN peptide fragment (PTN97-110) that inhibits the interaction of PTN and VEGFA165 with PTPRZ1 but not VEGF receptor 2. This peptide abolishes the stimulatory effect of PTN and VEGFA165 on endothelial cell migration, tube formation on Matrigel, and Akt activation in vitro. It also partially inhibits VEGFA165-induced VEGF receptor 2 activation but does not affect ERK1/2 activation and cell proliferation. In vivo, PTN97-110 inhibits or dysregulates angiogenesis in the chick embryo chorioallantoic membrane and the zebrafish assays, respectively. In glioblastoma cells in vitro, PTN97-110 abolishes the stimulatory effect of VEGFA165 on cell migration and inhibits their anchorage-independent growth, suggesting that this peptide might also be exploited in glioblastoma therapy. Finally, in silico and experimental evidence indicates that PTN and VEGFA165 bind to the extracellular fibronectin type-III (FNIII) domain to stimulate cell migration. Collectively, our data highlight novel aspects of the interaction of PTN and VEGFA165 with PTPRZ1, strengthen the notion that PTPRZ1 is required for VEGFA165-induced signaling, and identify a peptide that targets this interaction and can be exploited for the design of novel anti-angiogenic and anti-glioblastoma therapeutic approaches.

Analytical and Functional Similarity of Aflibercept Biosimilar ABP 938 with Aflibercept Reference Product

INTRODUCTION

ABP 938 is being developed as a biosimilar candidate to aflibercept reference product (RP), a biologic used for certain angiogenic eye disorders. This study was designed to provide a comparative analytical assessment of the structural and functional attributes of ABP 938 and aflibercept RP sourced from the United States (US) and the European Union (EU).

METHODS

Structural and functional characterization studies were performed using state-of-the-art analytical techniques that were appropriate to assess relevant quality attributes and capable of detecting qualitative and quantitative differences in primary structure, higher-order structure and biophysical properties, product-related substances and impurities, general properties, and biological activities.

RESULTS

ABP 938 had the same amino acid sequence and exhibited similar secondary and tertiary structures, and biological activity as aflibercept RP. There were minor differences in a small number of biochemical attributes which are not expected to impact clinical performance. In addition, aflibercept RP sourced from the US and EU were analytically similar.

CONCLUSIONS

ABP 938 was structurally and functionally similar to aflibercept RP. Since aflibercept RP sourced from the US and EU were analytically similar, this allows for the development of a scientific bridge such that a single-source RP can be used in nonclinical and clinical studies.

An Ensemble Docking Approach for Analyzing and Designing Aptamer Heterodimers Targeting VEGF165

Vascular endothelial growth factor 165 (VEGF165) is a prominent isoform of the VEGF-A protein that plays a crucial role in various angiogenesis-related diseases. It is homodimeric, and each of its monomers is composed of two domains connected by a flexible linker. DNA aptamers, which have emerged as potent therapeutic molecules for many proteins with high specificity and affinity, can also work for VEGF165. A DNA aptamer heterodimer composed of monomers of V7t1 and del5-1 connected by a flexible linker (V7t1:del5-1) exhibits a greater binding affinity with VEGF165 compared to either of the two monomers alone. Although the structure of the complex formed between the aptamer heterodimer and VEGF165 is unknown due to the highly flexible linkers, gaining structural information will still be valuable for future developments. Toward this end of accessing structural information, we adopt an ensemble docking approach here. We first obtain an ensemble of structures for both VEGF165 and the aptamer heterodimer by considering both small- and large-scale motions. We then proceed through an extraction process based on ensemble docking, molecular dynamics simulations, and binding free energy calculations to predict the structures of the VEGF165/V7t1:del5-1 complex. Through the same procedures, we reach a new aptamer heterodimer that bears a locked nucleic acid-modified counterpart of V7t1, namely RNV66:del5-1, which also binds well with VEGF165. We apply the same protocol to the monomeric units V7t1, RNV66, and del5-1 to target VEGF165. We observe that V7t1:del5-1 and RNV66:del5-1 show higher binding affinities with VEGF165 than any of the monomers, consistent with experiments that support the notion that aptamer heterodimers are more effective anti-VEGF165 aptamers than monomeric aptamers. Among the five different aptamers studied here, the newly designed RNV66:del5-1 shows the highest binding affinity with VEGF165. We expect that our ensemble docking approach can help in de novo designs of homo/heterodimeric anti-angiogenic drugs to target the homodimeric VEGF165.

Novel small molecule inhibitors targeting renal cell carcinoma: Status, challenges, future directions

Renal cell carcinoma (RCC) is the most common renal malignancy with a rapidly increasing morbidity and mortality rate gradually. RCC has a high mortality rate and an extremely poor prognosis. Despite numerous treatment strategies, RCC is resistant to conventional radiotherapy and chemotherapy. In addition, the limited clinical efficacy and inevitable resistance of multiple agents suggest an unmet clinical need. Therefore, there is an urgent need to develop novel anti-RCC candidates. Nowadays many promising results have been achieved with the development of novel small molecule inhibitors against RCC. This paper reviews the recent research progress of novel small molecule inhibitors targeting RCC. It is focusing on the structural optimization process and conformational relationships of small molecule inhibitors, as well as the potential mechanisms and anticancer activities for the treatment of RCC. To provide a theoretical basis for promoting the clinical translation of novel small molecule inhibitors, we discussed their application prospects and future development directions. It could be capable of improving the clinical efficacy of RCC and improving the therapy resistance for RCC.

Differential antiangiogenic and anticancer activities of the active metabolites of ginsenoside Rg3

Background

Epimers of ginsenoside Rg3 (Rg3) have a low bioavailability and are prone to deglycosylation, which produces epimers of ginsenoside Rh2 (S-Rh2 and R-Rh2) and protopanaxadiol (S-PPD and R-PPD). The aim of this study was to compare the efficacy and potency of these molecules as anti-cancer agents.

Methods

Crystal violet staining was used to study the anti-proliferatory action of the molecules on a human epithelial breast cancer cell line, MDA-MB-231, and human umbilical vein endothelial cells (HUVEC) and compare their potency. Cell death and cell cycle were studied using flow cytometry and mode of cell death was studied using live cell imaging. Anti-angiogenic effects of the drug were studied using loop formation assay. Molecular docking showed the interaction of these molecules with vascular endothelial growth factor receptor-2 (VEGFR2) and aquaporin (AQP) water channels. VEGF bioassay was used to study the interaction of Rh2 with VEGFR2, in vitro.

Results

HUVEC was the more sensitive cell line to the anti-proliferative effects of S-Rh2, S-PPD and R-PPD. The molecules induced necroptosis/necrosis in MDA-MB-231 and apoptosis in HUVEC. S-Rh2 was the most potent inhibitor of loop formation. In silico molecular docking predicted a good binding score between Rh2 or PPD and the ATP-binding pocket of VEGFR2. VEGF bioassay showed that Rh2 was an allosteric modulator of VEGFR2. In addition, SRh2 and PPD had good binding scores with AQP1 and AQP5, both of which play roles in cell migration and proliferation.

Conclusion

The combination of these molecules might be responsible for the anti-cancer effects observed by Rg3.

NRP1 interacts with endoglin and VEGFR2 to modulate VEGF signaling and endothelial cell sprouting

Endothelial cells express neuropilin 1 (NRP1), endoglin (ENG) and vascular endothelial growth factor receptor 2 (VEGFR2), which regulate VEGF-A-mediated vascular development and angiogenesis. However, the link between complex formation among these receptors with VEGF-A-induced signaling and biology is yet unclear. Here, we quantify surface receptor interactions by IgG-mediated immobilization of one receptor, and fluorescence recovery after photobleaching (FRAP) measurements of the mobility of another coexpressed receptor. We observe stable ENG/NRP1, ENG/VEGFR2, and NRP1/VEGFR2 complexes, which are enhanced by VEGF-A. ENG augments NRP1/VEGFR2 interactions, suggesting formation of tripartite complexes bridged by ENG. Effects on signaling are measured in murine embryonic endothelial cells expressing (MEEC+/+) or lacking (MEEC-/-) ENG, along with NRP1 and/or ENG overexpression or knockdown. We find that optimal VEGF-A-mediated phosphorylation of VEGFR2 and Erk1/2 requires ENG and NRP1. ENG or NRP1 increase VEGF-A-induced sprouting, becoming optimal in cells expressing all three receptors, and both processes are inhibited by a MEK1/2 inhibitor. We propose a model where the maximal potency of VEGF-A involves a tripartite complex where ENG bridges VEGFR2 and NRP1, providing an attractive therapeutic target for modulation of VEGF-A signaling and biological responses.

Recent advances of anti-angiogenic inhibitors targeting VEGF/VEGFR axis

Vascular endothelial growth factors (VEGF), Vascular endothelial growth factor receptors (VEGFR) and their downstream signaling pathways are promising targets in anti-angiogenic therapy. They constitute a crucial system to regulate physiological and pathological angiogenesis. In the last 20 years, many anti-angiogenic drugs have been developed based on VEGF/VEGFR system to treat diverse cancers and retinopathies, and new drugs with improved properties continue to emerge at a fast rate. They consist of different molecular structures and characteristics, which enable them to inhibit the interaction of VEGF/VEGFR, to inhibit the activity of VEGFR tyrosine kinase (TK), or to inhibit VEGFR downstream signaling. In this paper, we reviewed the development of marketed anti-angiogenic drugs involved in the VEGF/VEGFR axis, as well as some important drug candidates in clinical trials. We discuss their mode of action, their clinical benefits, and the current challenges that will need to be addressed by the next-generation of anti-angiogenic drugs. We focus on the molecular structures and characteristics of each drug, including those approved only in China.

Anti-angiogenic Potential of Trans-chalcone in an In Vivo Chick Chorioallantoic Membrane Model: An ATP Antagonist to VEGFR with Predicted Blood-brain Barrier Permeability

BACKGROUND

Glioblastoma multiforme (GBM) is characterized by massive tumorinduced angiogenesis aiding tumorigenesis. Vascular endothelial growth factor A (VEGF-A) via VEGF receptor 2 (VEGFR-2) constitutes majorly to drive this process. Putting a halt to tumordriven angiogenesis is a major clinical challenge, and the blood-brain barrier (BBB) is the prime bottleneck in GBM treatment. Several phytochemicals show promising antiangiogenic activity across different models, but their ability to cross BBB remains unexplored.

METHODS

We screened over 99 phytochemicals having anti-angiogenic properties reported in the literature and evaluated them for their BBB permeability, molecular interaction with VEGFR-2 domains, ECD2-3 (extracellular domains 2-3) and TKD (tyrosine kinase domain) at VEGF-A and ATP binding site, cell membrane permeability, and hepatotoxicity using in silico tools. Furthermore, the anti-angiogenic activity of predicted lead Trans-Chalcone (TC) was evaluated in the chick chorioallantoic membrane.

RESULTS

Out of 99 phytochemicals, 35 showed an efficient ability to cross BBB with a probability score of > 0.8. Docking studies revealed 30 phytochemicals crossing benchmark binding affinity < -6.4 kcal/mol of TKD with the native ligand ATP alone. Out of 30 phytochemicals, 12 showed moderate to low hepatotoxicity, and 5 showed a violation of Lipinski's rule of five. Our in silico analysis predicted TC as a BBB permeable anti-angiogenic compound for use in GBM therapy. TC reduced vascularization in the CAM model, which was associated with the downregulation of VEGFR-2 transcript expression.

CONCLUSION

The present study showed TC to possess anti-angiogenic potential via the inhibition of VEGFR-2. In addition, the study predicted TC to cross BBB as well as a safe alternative for GBM therapy, which needs further investigation.

Structure-Based Design of Peptides Targeting VEGF/VEGFRs

Vascular endothelial growth factor (VEGF) and its receptors (VEGFRs) play a main role in the regulation of angiogenesis and lymphangiogenesis. Furthermore, they are implicated in the onset of several diseases such as rheumatoid arthritis, degenerative eye conditions, tumor growth, ulcers and ischemia. Therefore, molecules able to target the VEGF and its receptors are of great pharmaceutical interest. Several types of molecules have been reported so far. In this review, we focus on the structure-based design of peptides mimicking VEGF/VEGFR binding epitopes. The binding interface of the complex has been dissected and the different regions challenged for peptide design. All these trials furnished a better understanding of the molecular recognition process and provide us with a wealth of molecules that could be optimized to be exploited for pharmaceutical applications.

Structural insights into regulation of CCN protein activities and functions

CCN proteins play important functions during development, in repair mechanisms following tissue injury, as well as in pathophysiologic mechanisms of metastasis of cancer. CCNs are secreted proteins that have a multimodular structure and are categorized as matricellular proteins. Although the prevailing view is that CCN proteins regulate biologic processes by interacting with a wide array of other proteins in the microenvironment of the extracellular matrix, the molecular mechanisms of action of CCN proteins are still poorly understood. Not dissuading the current view, however, the recent appreciation that these proteins are signaling proteins in their own right and may even be considered preproproteins controlled by endopeptidases to release a C-terminal bioactive peptide has opened new avenues of research. Also, the recent resolution of the crystal structure of two of the domains of CCN3 have provided new knowledge with implications for the entire CCN family. These resolved structures in combination with structural predictions based upon the AlphaFold artificial intelligence tool provide means to shed new light on CCN functions in context of the notable literature in the field. CCN proteins have emerged as important therapeutic targets in several disease conditions, and clinical trials are currently ongoing. Thus, a review that critically discusses structure - function relationship of CCN proteins, in particular as it relates to interactions with other proteins in the extracellular milieu and on the cell surface, as well as to cell signaling activities of these proteins, is very timely. Suggested mechanism for activation and inhibition of signaling by the CCN protein family (graphics generated with BioRender.com ).

The plant defensins PaDef and γ-thionin inhibit the endothelial cell response to VEGF

Angiogenesis is involved in wound repair and tissue maintenance but is associated with diverse diseases. Pro-angiogenic factors such as vascular endothelial growth factor (VEGF) regulate this process. Therefore, searching for treatments to inhibit or promote angiogenesis is attractive. Reports from our group showed that plant antimicrobial peptides (PAPs) PaDef from avocado and γ-thionin from habanero pepper are cytotoxic on cancer cells. However, their functions as angiogenic regulators are unknown. In this work, we evaluate the effect of PaDef and γ-thionin on the angiogenic processes of two different endothelial cell lines: bovine endothelial cells (BUVEC) and the human endothelial cell line EA.hy926. The results showed that VEGF (10ng/mL) stimulated the BUVEC (40 ± 7%) and EA.hy926 cell proliferation (30 ± 9%); however, peptides (5-500ng/mL) reverted this effect. Besides, VEGF increased the migration of BUVEC (20 ± 8%) and EA.hy926 cells (50 ± 6%), but both PAPs (5ng/mL) inhibited the VEGF stimulus (100%). Furthermore, DMOG 50μM (an inhibitor of HIF-hydroxylase) was used in BUVEC and EA.hy926 cells to determine the effect of hypoxia on VEGF and peptide activities. The DMOG reverted the inhibitory action of both peptides (100%), indicating that peptides act through a HIF-independent pathway. Also, the PAPs do not affect the tube formation but decrease it in EA.hy926 cells stimulated with VEGF (100%). Additionally, docking assays showed a possible interaction between PAPs and the VEGF receptor. These results suggest that plant defensins PaDef and γ-thionin are potential angiogenic modulators of the VEGF activity on endothelial cells.

Elucidating activation and deactivation dynamics of VEGFR-2 transmembrane domain with coarse-grained molecular dynamics simulations

The vascular endothelial growth factor receptor 2 (VEGFR-2) is a member of receptor tyrosine kinases (RTKs) and is a dimeric membrane protein that functions as a primary regulator of angiogenesis. As is usual with RTKs, spatial alignment of its transmembrane domain (TMD) is essential toward VEGFR-2 activation. Experimentally, the helix rotations within TMD around their own helical axes are known to participate importantly toward the activation process in VEGFR-2, but the detailed dynamics of the interconversion between the active and inactive TMD forms have not been clearly elucidated at the molecular level. Here, we attempt to elucidate the process by using coarse grained (CG) molecular dynamics (MD) simulations. We observe that inactive dimeric TMD in separation is structurally stable over tens of microseconds, suggesting that TMD itself is passive and does not allow spontaneous signaling of VEGFR-2. By starting from the active conformation, we reveal the mechanism of TMD inactivation through analyzing the CG MD trajectories. We observe that interconversions between a left-handed overlay and a right-handed one are essential for the process of going from an active TMD structure to the inactive form. In addition, our simulations find that the helices can rotate properly when the overlaying structure of the helices interconverts and when the crossing angle of the two helices changes by larger than ~40 degrees. As the activation right after the ligand attachment on VEGFR-2 will take place in the reverse manner of this inactivation process, these structural aspects will also appear importantly for the activation process. The rather large change in helix configuration for activation also explains why VEGFR-2 rarely self-activate and how the activating ligand structurally drive the whole VEGFR-2. This mechanism of TMD activation / inactivation within VEGFR-2 may help in further understanding the overall activation processes of other RTKs.

Receptors that bind to PEDF and their therapeutic roles in retinal diseases

Retinal neovascular, neurodegenerative, and inflammatory diseases represented by diabetic retinopathy are the main types of blinding eye disorders that continually cause the increased burden worldwide. Pigment epithelium-derived factor (PEDF) is an endogenous factor with multiple effects including neurotrophic activity, anti-angiogenesis, anti-tumorigenesis, and anti-inflammatory activity. PEDF activity depends on the interaction with the proteins on the cell surface. At present, seven independent receptors, including adipose triglyceride lipase, laminin receptor, lipoprotein receptor-related protein, plexin domain-containing 1, plexin domain-containing 2, F1-ATP synthase, and vascular endothelial growth factor receptor 2, have been demonstrated and confirmed to be high affinity receptors for PEDF. Understanding the interactions between PEDF and PEDF receptors, their roles in normal cellular metabolism and the response the initiate in disease will be accommodating for elucidating the ways in which inflammation, angiogenesis, and neurodegeneration exacerbate disease pathology. In this review, we firstly introduce PEDF receptors comprehensively, focusing particularly on their expression pattern, ligands, related diseases, and signal transduction pathways, respectively. We also discuss the interactive ways of PEDF and receptors to expand the prospective understanding of PEDF receptors in the diagnosis and treatment of retinal diseases.

Novel hKDR mouse model depicts the antiangiogenesis and apoptosis-promoting effects of neutralizing antibodies targeting vascular endothelial growth factor receptor 2

Vascular endothelial growth factor receptor 2 (VEGFR2)/KDR plays a critical role in tumor growth, diffusion, and invasion. The amino acid sequence homology of KDR between mouse and human in the VEGF ligand-binding domain was low, thus the WT mice could not be used to evaluate Abs against human KDR, and the lack of a suitable mouse model hindered both basic research and drug developments. Using the CRISPR/Cas9 technique, we successfully inserted different fragments of the human KDR coding sequence into the chromosomal mouse Kdr exon 4 locus to obtain an hKDR humanized mouse that can be used to evaluate the marketed Ab ramucirumab. In addition, the humanized mAb VEGFR-HK19 was developed, and a series of comparative assays with ramucirumab as the benchmark revealed that VEGFR-HK19 has higher affinity and superior antiproliferation activity. Moreover, VEGFR-HK19 selectively inhibited tumor growth in the hKDR mouse model but not in WT mice. The most important binding epitopes of VEGFR2-HK19 are D257, L313, and T315, located in the VEGF binding region. Therefore, the VEGFR2-HK19 Ab inhibits tumor growth by blocking VEGF-induced angiogenesis, inflammation, and promoting apoptosis. To our best knowledge, this novel humanized KDR mouse fills the gaps both in an animal model and the suitable in vivo evaluation method for developing antiangiogenesis therapies in the future, and the newly established humanized Ab is expected to be a drug candidate possibly benefitting tumor patients.

Preparation, In Vitro Affinity, and In Vivo Biodistribution of Receptor-Specific 68Ga-Labeled Peptides Targeting Vascular Endothelial Growth Factor Receptors

As angiogenesis plays a key role in tumor growth and metastasis, the angiogenic process has attracted scientific interest as a target for diagnostic and therapeutic agents. Factors influencing angiogenesis include the vascular endothelial growth factor (VEGF) family and the two associated receptor types (VEGFR-1 and VEGFR-2). VEGFR-1/-2 detection and quantification in cancer lesions are essential for tumor process management. As a result of the advantageous pharmacokinetics and image contrast, peptides radiolabeled with PET emitters have become interesting tools for the visualization of VEGFR-1/-2-positive tumors. In this study, we prepared ⁶⁸Ga-labeled peptides containing 15 (peptide 1) and 23 (peptide 2) amino acids as new PET tracers for tumor angiogenic process imaging.

METHODS

The peptides were conjugated with NODAGA-tris(t-Bu ester) and subsequently radiolabeled with [⁶⁸Ga]Ga-chloride. The prepared [⁶⁸Ga]Ga-NODAGA-peptide 1 and [⁶⁸Ga]Ga-NODAGA-peptide 2 were tested for radiochemical purity and saline/plasma stability. Consequently, the binding affinity toward VEGFRs was assessed in vitro on human glioblastoma and kidney carcinoma cells. The found peptide receptor affinity was compared with the calculated values in the PROtein binDIng enerGY prediction (PRODIGY) server. Finally, the biodistribution study was performed on BALB/c female mice to reveal the basic pharmacokinetic behavior of radiopeptides.

RESULTS

The in vitro affinity testing of [⁶⁸Ga]Ga-NODAGA-peptides 1 and 2 showed retained receptor binding as characterized by equilibrium dissociation constant (K_D) values in the range of 0.5-1.2 μM and inhibitory concentration 50% (IC₅₀) values in the range of 3.0-5.6 μM. Better binding properties of peptide 2 to VEGFR-1/-2 were found in the PRODIGY server. The biodistribution study on mice showed remarkable accumulation of both peptides in the kidneys and urinary bladder with a short half-life after intravenous application. The in vitro plasma stability of [⁶⁸Ga]Ga-NODAGA-peptide 2 was superior to that of [⁶⁸Ga]Ga-NODAGA-peptide 1.

CONCLUSIONS

The obtained results demonstrated a high radiolabeling yield with no need for purification and preserved binding potency of ⁶⁸Ga-labeled peptides 1 and 2 toward VEGFRs in cancer cells. The peptide-receptor protein interaction assessed in protein-peptide docking determined the strongest interaction of peptide 2 with domain 2 of VEGFR-2 in addition to a more acceptable plasma stability (t_1/2 = 120 min) than that for peptide 1. We found both radiolabeled peptides very potent in their receptor binding, which makes them suitable imaging agents. The rapid transition of the radiopeptides into the urinary tract indicates suitable pharmacokinetic characteristics.

Anti-Angiogenetic and Anti-Lymphangiogenic Effects of a Novel 2-Aminobenzimidazole Derivative, MFB

Background and Purpose

Benzimidazoles have attracted much attention over the last few decades due to their broad-spectrum pharmacological properties. Increasing evidence is showing the potential use of benzimidazoles as anti-angiogenic agents, although the mechanisms that impact angiogenesis remain to be fully defined. In this study, we aim to investigate the anti-angiogenic mechanisms of MFB, a novel 2-aminobenzimidazole derivative, to develop a novel angiogenesis inhibitor.

Experimental Approach

MTT, BrdU, migration and invasion assays, and immunoblotting were employed to examine MFB’s effects on vascular endothelial growth factor (VEGF)-induced endothelial cell proliferation, migration, invasion, as well as signaling molecules activation. The anti-angiogenic effects of MFB were analyzed by tube formation, aorta ring sprouting, and matrigel plug assays. We also used a mouse model of lung metastasis to determine the MFB’s anti-metastatic effects.

Key Results

MFB suppressed cell proliferation, migration, invasion, and endothelial tube formation of VEGF-A-stimulated human umbilical vascular endothelial cells (HUVECs) or VEGF-C-stimulated lymphatic endothelial cells (LECs). MFB suppressed VEGF-A and VEGF-C signaling in HUVECs or LECs. In addition, MFB reduced VEGF-A- or tumor cells-induced neovascularization in vivo. MFB also diminished B16F10 melanoma lung metastasis. The molecular docking results further showed that MFB may bind to VEGFR-2 rather than VEGF-A with high affinity.

Conclusions and Implications

These observations indicated that MFB may target VEGF/VEGFR signaling to suppress angiogenesis and lymphangiogenesis. It also supports the role of MFB as a potential lead in developing novel agents for the treatment of angiogenesis- or lymphangiogenesis-associated diseases and cancer.

Identification of VEGFR2 as the Histatin-1 receptor in endothelial cells

Histatin-1 is a salivary peptide with antimicrobial and wound healing promoting activities, which was previously shown to stimulate angiogenesis in vitro and in vivo via inducing endothelial cell migration. The mechanisms underlying the proangiogenic effects of Histatin-1 remain poorly understood and specifically, the endothelial receptor for this peptide, is unknown. Based on the similarities between Histatin-1-dependent responses and those induced by the prototypical angiogenic receptor, vascular endothelial growth factor receptor 2 (VEGFR2), we hypothesized that VEGFR2 is the Histatin-1 receptor in endothelial cells. First, we observed that VEGFR2 is necessary for Histatin-1-induced endothelial cell migration, as shown by both pharmacological inhibition studies and siRNA-mediated ablation of VEGFR2. Moreover, Histatin-1 co-immunoprecipitated and co-localized with VEGFR2, associating spatial proximity between these proteins with receptor activation. Indeed, pulldown assays with pure, tagged and non-tagged proteins showed that Histatin-1 and VEGFR2 directly interact in vitro. Optical tweezers experiments permitted estimating kinetic parameters and rupture forces, indicating that the Histatin-1-VEGFR2 interaction is transient, but specific and direct. Sequence alignment and molecular modeling identified residues Phe26, Tyr30 and Tyr34 within the C-terminal domain of Histatin-1 as relevant for VEGFR2 binding and activation. This was corroborated by mutation and molecular dynamics analyses, as well as in direct binding assays. Importantly, these residues were required for Histatin-1 to induce endothelial cell migration and angiogenesis in vitro. Taken together, our findings reveal that VEGFR2 is the endothelial cell receptor of Histatin-1 and provide insights to the mechanism by which this peptide promotes endothelial cell migration and angiogenesis.

Computational assessment of pigment epithelium-derived factor as an anti-cancer protein during its interaction with the receptors

Pigment epithelium-derived factor (PEDF) is a member of the serine proteinase inhibitor (serpin) with antiangiogenic, anti-tumorigenic, antioxidant, anti-atherosclerosis, antithrombotic, anti-inflammatory, and neuroprotective properties. The PEDF can bind to low-density lipoprotein receptor-related protein 6 (LRP6), laminin (LR), vascular endothelial growth factor receptor 1 (VEGFR1), vascular endothelial growth factor receptor 2 (VEGFR2), and ATP synthase β-subunit receptors. In this study, we aimed to investigate the structural basis of the interaction between PEDF and its receptors using bioinformatics approaches to identify the critical amino acids for designing anticancer peptides. The human ATP synthase β-subunit was predicted by homology modeling. The molecular docking, molecular dynamics (MD) simulation, and Molecular mechanics/Poisson-Boltzmann surface area (MM/PBSA) were used to study this protein-receptor complex. The molecular docking showed PEDF could bind to the Laminin and VEGFR2 much stronger than ATP synthase β-subunit, VEGFR1, and LRP6. The PEDF could effectively interact with various receptors during the simulation. The N-terminal of PEDF has an important role in the interaction with the receptors. The MM/PBSA showed the electrostatic (ΔE_Elec) and van der Waals interactions (ΔE_VdW) contributed positively to the binding process of the complexes. The critical amino acids in the binding interaction of PEDF to its receptors in the MD simulation were determined. The interaction mode of 34-mer PEDF to laminin, VEGFR2, and LRP6 were different from VEGFR1, ATP synthase β-subunit. The 34-mer PEDF has an important role in the interaction with different receptors and these critical amino acids can be used for designing peptides for future therapeutic aims.Communicated by Ramaswamy H. Sarma.

Structure-Based Virtual Screening, Molecular Docking, and Molecular Dynamics Simulation of VEGF inhibitors for the clinical treatment of Ovarian Cancer

Vascular endothelial growth factor (VEGF) and its receptor play an important role both in physiologic and pathologic angiogenesis, which is identified in ovarian cancer progression and metastasis development. The aim of the present investigation is to identify a potential vascular endothelial growth factor inhibitor which is playing a crucial role in stimulating the immunosuppressive microenvironment in tumor cells of the ovary and to examine the effectiveness of the identified inhibitor for the treatment of ovarian cancer using various in silico approaches. Twelve established VEGF inhibitors were collected from various literatures. The compound AEE788 displays great affinity towards the target protein as a result of docking study. AEE788 was further used for structure-based virtual screening in order to obtain a more structurally similar compound with high affinity. Among the 80 virtual screened compounds, CID 88265020 explicates much better affinity than the established compound AEE788. Based on molecular dynamics simulation, pharmacophore and comparative toxicity analysis of both the best established compound and the best virtual screened compound displayed a trivial variation in associated properties. The virtual screened compound CID 88265020 has a high affinity with the lowest re-rank score and holds a huge potential to inhibit the VGFR and can be implemented for prospective future investigations in ovarian cancer.

Modulating Angiogenesis by Proteomimetics of Vascular Endothelial Growth Factor

Angiogenesis, formation of new blood vessels from the existing vascular network, is a hallmark of cancer cells that leads to tumor vascular proliferation and metastasis. This process is mediated through the binding interaction of VEGF-A with VEGF receptors. However, the balance between pro-angiogenic and anti-angiogenic effect after ligand binding yet remains elusive and is therefore challenging to manipulate. To interrogate this interaction, herein we designed a few sulfono-γ-AA peptide based helical peptidomimetics that could effectively mimic a key binding interface on VEGF (helix-α1) for VEGFR recognition. Intriguingly, although both sulfono-γ-AA peptide sequences V2 and V3 bound to VEGF receptors tightly, in vitro angiogenesis assays demonstrated that V3 potently inhibited angiogenesis, whereas V2 activated angiogenesis effectively instead. Our findings suggested that this distinct modulation of angiogenesis might be due to the result of selective binding of V2 to VEGFR-1 and V3 to VEGFR-2, respectively. These molecules thus provide us a key to switch the angiogenic signaling, a biological process that balances the effects of pro-angiogenic and anti-angiogenic factors, where imbalances lead to several diseases including cancer. In addition, both V2 and V3 exhibited remarkable stability toward proteolytic hydrolysis, suggesting that V2 and V3 are promising therapeutic agents for the intervention of disease conditions arising due to angiogenic imbalances and could also be used as novel molecular switching probes to interrogate the mechanism of VEGFR signaling. The findings also further demonstrated the potential of sulfono-γ-AA peptides to mimic the α-helical domain for protein recognition and modulation of protein-protein interactions.

Cholenic acid derivative UniPR1331 impairs tumor angiogenesis via blockade of VEGF/VEGFR2 in addition to Eph/ephrin

Angiogenesis, the formation of new blood vessels from preexisting ones, is crucial for tumor growth and metastatization, and is considered a promising therapeutic target. Unfortunately, drugs directed against a specific proangiogenic growth factor or receptor turned out to be of limited benefit for oncology patients, likely due to the high biochemical redundancy of the neovascularization process. In this scenario, multitarget compounds that are able to simultaneously tackle different proangiogenic pathways are eagerly awaited. UniPR1331 is a 3β-hydroxy-Δ⁵-cholenic acid derivative, which is already known to inhibit Eph-ephrin interaction. Here, we employed an analysis pipeline consisting of molecular modeling and simulation, surface plasmon resonance spectrometry, biochemical assays, and endothelial cell models to demonstrate that UniPR1331 directly interacts with the vascular endothelial growth factor receptor 2 (VEGFR2) too. The binding of UniPR1331 to VEGFR2 prevents its interaction with the natural ligand vascular endothelial growth factor and subsequent autophosphorylation, signal transduction, and in vitro proangiogenic activation of endothelial cells. In vivo, UniPR1331 inhibits tumor cell-driven angiogenesis in zebrafish. Taken together, these data shed light on the pleiotropic pharmacological effect of UniPR1331, and point to Δ⁵-cholenic acid as a promising molecular scaffold for the development of multitarget antiangiogenic compounds.

Functional antibody characterization via direct structural analysis and information-driven protein-protein docking

Detailed description of the mechanism of action of the therapeutic antibodies is essential for the functional characterization and future optimization of potential clinical agents. We recently developed KD035, a fully human antibody targeting vascular endothelial growth factor receptor 2 (VEGFR2). KD035 blocked VEGF‐A, and VEGF‐C‐mediated VEGFR2 activation, as demonstrated by the in vitro binding and competition assays and functional cellular assays. Here, we report a computational model of the complex between the variable fragment of KD035 (KD035(Fv)) and the domains 2 and 3 of the extracellular portion of VEGFR2 (VEGFR2(D2‐3)). Our modeling was guided by a priori experimental information including the X‐ray structures of KD035 and related antibodies, binding assays, target domain mapping and comparison of KD035 affinity for VEGFR2 from different species. The accuracy of the model was assessed by molecular dynamics simulations, and subsequently validated by mutagenesis and binding analysis. Importantly, the steps followed during the generation of this model can set a precedent for future in silico efforts aimed at the accurate description of the antibody–antigen and more broadly protein–protein complexes.

A Structural Overview of Vascular Endothelial Growth Factors Pharmacological Ligands: From Macromolecules to Designed Peptidomimetics

The vascular endothelial growth factor (VEGF) family of cytokines plays a key role in vasculogenesis, angiogenesis, and lymphangiogenesis. VEGF-A is the main member of this family, alongside placental growth factor (PlGF), VEGF-B/C/D in mammals, and VEGF-E/F in other organisms. To study the activities of these growth factors under physiological and pathological conditions, resulting in therapeutic applications in cancer and age-related macular degeneration, blocking ligands have been developed. These have mostly been large biomolecules like antibodies. Ligands with high affinities, at least in the nanomolar range, and accurate structural data from X-ray crystallography and NMR spectroscopy have been described. They constitute the main focus of this overview, which evidences similarities and differences in their binding modes. For VEGF-A ligands, and to a limited extent also for PlGF, a transition is now observed towards developing smaller ligands like nanobodies and peptides. These include unnatural amino acids and chemical modifications for designed and improved properties, such as serum stability and greater affinity. However, this review also highlights the scarcity of such small molecular entities and the striking lack of small organic molecule ligands. It also shows the gap between the rather large array of ligands targeting VEGF-A and the general absence of ligands binding other VEGF members, besides some antibodies. Future developments in these directions are expected in the upcoming years, and the study of these growth factors and their promising therapeutic applications will be welcomed.

A Cyclic Peptide Epitope of an Under-Explored VEGF-B Loop 1 Demonstrated In Vivo Anti-Angiogenic and Anti-Tumor Activities

Pathological angiogenesis is mainly initiated by the binding of abnormal expressed vascular endothelial growth factors (VEGFs) to their receptors (VEGFRs). Blocking the VEGF/VEGFR interaction is a clinically proven treatment in cancer. Our previous work by epitope scan had identified cyclic peptides, mimicking the loop 1 of VEGF-A, VEGF-B and placental growth factor (PlGF), inhibited effectively the VEGF/VEGFR interaction in ELISA. We described here the docking study of these peptides on VEGFR1 to identify their binding sites. The cellular anti-angiogenic activities were examined by inhibition of VEGF-A induced cell proliferation, migration and tube formation in human umbilical vein endothelial cells (HUVECs). The ability of these peptides to inhibit MAPK/ERK1/2 signaling pathway was examined as well. On chick embryo chorioallantoic membrane (CAM) model, a cyclic peptide named B-cL1 with most potent in vitro activity showed important in vivo anti-angiogenic effect. Finally, B-cL1 inhibited VEGF induced human gastric cancer SGC-7901 cells proliferation. It showed anti-tumoral effect on SGC-7901 xenografted BALB/c nude mouse model. The cyclic peptides B-cL1 constitutes an anti-angiogenic peptide drug lead for the design of new and more potent VEGFR antagonists in the treatment of angiogenesis related diseases.

Glioma-Targeted Therapeutics: Computer-Aided Drug Design Prospective

Amongst the several types of brain cancers known to humankind, glioma is one of the most severe and life-threatening types of cancer, comprising 40% of all primary brain tumors. Recent reports have shown the incident rate of gliomas to be 6 per 100,000 individuals per year globally. Despite the various therapeutics used in the treatment of glioma, patient survival rate remains at a median of 15 months after undergoing first-line treatment including surgery, radiation, and chemotherapy with Temozolomide. As such, the discovery of newer and more effective therapeutic agents is imperative for patient survival rate. The advent of computer-aided drug design in the development of drug discovery has emerged as a powerful means to ascertain potential hit compounds with distinctively high therapeutic effectiveness against glioma. This review encompasses the recent advances of bio-computational in-silico modeling that have elicited the discovery of small molecule inhibitors and/or drugs against various therapeutic targets in glioma. The relevant information provided in this report will assist researchers, especially in the drug design domains, to develop more effective therapeutics against this global disease.

[Design of Synthetic Polymer Nanoparticles That Capture and Neutralize Target Molecules]

Protein affinity reagents that specifically and strongly bind to target molecules are widely used in disease detection, diagnosis, and therapy. Although antibodies and their fragments are the gold standard in protein-protein inhibitors (PPIs), synthetic polymers such as linear polymers, dendrimers, and nanoparticles as cost-effective PPIs have attracted great attention as alternatives to antibodies. These polymers exhibit high affinity to the target by imitating natural protein-protein interactions. However, only a few in vivo applications have been reported. Here, our recent advances in the development of synthetic polymers for in vivo application are reviewed. Poly(N-isopropylacrylamide) (pNIPAm) was used as a model of synthetic affinity reagents. Incorporation of both sulfated carbohydrate and hydrophobic monomers into lightly crosslinked pNIPAm nanoparticles (NPs) captured and neutralized vascular endothelial growth factor (VEGF) and inhibited tumor growth upon intravenous injection into tumor-bearing mice. Modification of a liposome with the pNIPAm-based linear polymer increased the polymer circulation time after intravenous injection and improved the affinity for the target. The pNIPAm-based NPs delivered by oral administration captured the target small molecules and inhibited their absorption from the intestine. Our recent findings provide useful information for the design of synthetic polymers that capture target molecules in vivo.

A Novel Human Long Noncoding RNA SCDAL Promotes Angiogenesis through SNF5-Mediated GDF6 Expression

Angiogenesis is essential for vascular development. The roles of regulatory long noncoding RNAs (lncRNAs) in mediating angiogenesis remain under-explored. Human embryonic stem cell-derived mesenchymal stem cells (hES-MSCs) are shown to exert more potent cardioprotective effects against cardiac ischemia than human bone marrow-derived MSCs (hBM-MSCs), associated with enhanced neovascularization. The purpose of this study is to search for angiogenic lncRNAs enriched in hES-MSCs, and investigate their roles and mechanisms. AC103746.1 is one of the most highly expressed intergenic lncRNAs detected in hES-MSCs versus hBM-MSCs, and named as SCDAL (stem cell-derived angiogenic lncRNA). SCDAL knockdown significantly reduce the angiogenic potential and reparative effects of hES-MSCs in the infarcted hearts, while overexpression of SCDAL in either hES-MSCs or hBM-MSCs exhibits augmented angiogenesis and cardiac function recovery. Mechanistically, SCDAL induces growth differentiation factor 6 (GDF6) expression via direct interaction with SNF5 at GDF6 promoter. Secreted GDF6 promotes endothelial angiogenesis via non-canonical vascular endothelial growth factor receptor 2 activation. Furthermore, SCDAL-GDF6 is expressed in human endothelial cells, and directly enhances endothelial angiogenesis in vitro and in vivo. Thus, these findings uncover a previously unknown lncRNA-dependent regulatory circuit for angiogenesis. Targeted intervention of the SCDAL-GDF6 pathway has potential as a therapy for ischemic heart diseases.

VEGFR-2 redirected CAR-T cells are functionally impaired by soluble VEGF-A competition for receptor binding

Background

The adoptive transfer of chimeric antigen receptor (CAR)-T cells has emerged as a potent immunotherapy against some hematological malignancies but not yet for epithelial-derived solid tumors. One critical issue is the paucity of broadly expressed solid tumor antigens (TAs), and another is the presence of suppressive mechanisms in the tumor microenvironment (TME) that can impair CAR-T cell homing, extravasation and effector functions. TAs expressed by endothelial cells of the tumor vasculature are of clinical interest for CAR therapy because of their genomic stability and accessibility to circulating T cells, as well as their expression across multiple tumor types. In this study, we sought to explore limitations to the efficacy of second-generation (2G) murine CAR-T cells redirected against the vascular endothelial growth factor receptor-2 (VEGFR-2) with the well-characterized single-chain variable fragment DC101.

Methods

Primary murine T cells were retrovirally transduced to express a 2G anti-VEGFR-2-CAR, and the in vitro binding to VEGFR-2, as well as reactivity against TA-expressing cells, was evaluated in the absence versus presence of exogenous VEGF-A. The CAR-T cells were further tested in vivo for tumor control alone and in combination with anti-VEGF-A antibody. Finally, we performed ex vivo phenotypic analyses of tumor-infiltrating CAR-T cells for the two treatment groups.

Results

In line with previous reports, we observed poor control of B16 melanoma by the 2G anti-VEGFR-2 CAR-T cells as a monotherapy. We further showed that VEGFR-2 is not downregulated by B16 melanoma tumors post treatment, but that its soluble ligand VEGF-A is upregulated and furthermore competes in vitro with the CAR-T cells for binding to VEGFR-2. This competition resulted in impaired CAR-T cell adhesion and effector function in vitro that could be restored in the presence of anti-VEGF-A antibody. Finally, we demonstrated that coadministration of anti-VEGF-A antibody in vivo promoted CAR-T cell persistence and tumor control and was associated with reduced frequencies of PD-1⁺ Ki67^- and LAG-3⁺ Ki67^- CAR-T cells in the TME.

Conclusions

This study represents the first example of impaired function of a vasculature-targeted CAR by an angiogenic ligand and rationalizes the use of combinatorial therapies that target the tumor vasculature and augment CAR-T cell effector function.

Use of NanoBiT and NanoBRET to monitor fluorescent VEGF-A binding kinetics to VEGFR2/NRP1 heteromeric complexes in living cells

BACKGROUND AND PURPOSE

VEGF-A is a key mediator of angiogenesis, primarily signalling via VEGF receptor 2 (VEGFR2). Endothelial cells also express the co-receptor neuropilin-1 (NRP1) that potentiates VEGF-A/VEGFR2 signalling. VEGFR2 and NRP1 had distinct real-time ligand binding kinetics when monitored using BRET. We previously characterised fluorescent VEGF-A isoforms tagged at a single site with tetramethylrhodamine (TMR). Here, we explored differences between VEGF-A isoforms in living cells that co-expressed both receptors.

EXPERIMENTAL APPROACH

Receptor localisation was monitored in HEK293T cells expressing both VEGFR2 and NRP1 using membrane-impermeant HaloTag and SnapTag technologies. To isolate ligand binding pharmacology at a defined VEGFR2/NRP1 complex, we developed an assay using NanoBiT complementation technology whereby heteromerisation is required for luminescence emissions. Binding affinities and kinetics of VEGFR2-selective VEGF165 b-TMR and non-selective VEGF165 a-TMR were monitored using BRET from this defined complex.

KEY RESULTS

Cell surface VEGFR2 and NRP1 were co-localised and formed a constitutive heteromeric complex. Despite being selective for VEGFR2, VEGF165 b-TMR had a distinct kinetic ligand binding profile at the complex that largely remained elevated in cells over 90 min. VEGF165 a-TMR bound to the VEGFR2/NRP1 complex with kinetics comparable to those of VEGFR2 alone. Using a binding-dead mutant of NRP1 did not affect the binding kinetics or affinity of VEGF165 a-TMR.

CONCLUSION AND IMPLICATIONS

This NanoBiT approach enabled real-time ligand binding to be quantified in living cells at 37°C from a specified complex between a receptor TK and its co-receptor for the first time.

Heparin-binding VEGFR1 variants as long-acting VEGF inhibitors for treatment of intraocular neovascular disorders

Neovascularization is a key feature of ischemic retinal diseases and the wet form of age-related macular degeneration (AMD), all leading causes of severe vision loss. Vascular endothelial growth factor (VEGF) inhibitors have transformed the treatment of these disorders. Millions of patients have been treated with these drugs worldwide. However, in real-life clinical settings, many patients do not experience the same degree of benefit observed in clinical trials, in part because they receive fewer anti-VEGF injections. Therefore, there is an urgent need to discover and identify novel long-acting VEGF inhibitors. We hypothesized that binding to heparan-sulfate proteoglycans (HSPG) in the vitreous, and possibly other ocular structures, may be a strategy to promote intraocular retention, ultimately leading to a reduced burden of intravitreal injections. We designed a series of VEGF receptor 1 variants and identified some with strong heparin-binding characteristics and ability to bind to vitreous matrix. Our data indicate that some of our variants have longer duration and greater efficacy in animal models of intraocular neovascularization than current standard of care. Our study represents a systematic attempt to exploit the functional diversity associated with heparin affinity of a VEGF receptor.

Anti-Angiogenic Properties of Ginsenoside Rg3 Epimers: In Vitro Assessment of Single and Combination Treatments

Tumour angiogenesis plays a key role in tumour growth and progression. The application of current anti-angiogenic drugs is accompanied by adverse effects and drug resistance. Therefore, finding safer effective treatments is needed. Ginsenoside Rg3 (Rg3) has two epimers, 20(S)-Rg3 (SRg3) and 20(R)-Rg3 (RRg3), with stereoselective activities. Using response surface methodology, we optimised a combination of these two epimers for the loop formation of human umbilical vein endothelial cell (HUVEC). The optimised combination (C3) was tested on HUVEC and two murine endothelial cell lines. C3 significantly inhibited the loop formation, migration, and proliferation of these cells, inducing apoptosis in HUVEC and cell cycle arrest in all of the cell lines tested. Using molecular docking and vascular endothelial growth factor (VEGF) bioassay, we showed that Rg3 has an allosteric modulatory effect on vascular endothelial growth factor receptor 2 (VEGFR2). C3 also decreased the VEGF expression in hypoxic conditions, decreased the expression of aquaporin 1 and affected AKT signaling. The proteins that were mostly affected after C3 treatment were those related to mammalian target of rapamycin (mTOR). Eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1) was one of the important targets of C3, which was affected in both hypoxic and normoxic conditions. In conclusion, these results show the potential of C3 as a novel anti-angiogenic drug.

Design and synthesis of novel (S)-Naproxen hydrazide-hydrazones as potent VEGFR-2 inhibitors and their evaluation in vitro/in vivo breast cancer models

Naproxen is a common non-steroidal anti-inflammatory drug, which is the most usually used propionic acid derivative for the treatment of many types of diseases. In this study, a series of novel (S)-Naproxen derivatives bearing hydrazide-hydrazone moiety were designed, synthesized, and evaluated for anticancer activity. The structures of these compounds were characterized by spectral (1H-13C NMR, FT-IR, and HR-MS analyses) methods. All synthesized compounds were screened for anticancer activity against two different human breast cancer cell lines (MDA-MB-231 and MCF-7). Among them, (S)-2-(6-methoxynaphthalen-2-yl)-N'-{(E)-[2-(trifluoromethoxy)phenyl]methylidene} propanehydrazide (3a) showed the most potent anticancer activity against both cancer cell lines with a good selectivity (IC50 = 22.42 and 59.81 µM, respectively). Furthermore, the molecular modeling of these compounds was studied on Vascular Endothelial Growth Factor Receptor 2. Inhibition of VEGFR-2 and apoptotic protein Bcl-2 was investigated in MDA-MB-231 cells treated with compound 3a by using Western Blotting. Apoptosis was also detected by staining with DAPI in fluorescence microscopy. Flow Cytometry analyses related to cell cycle phases showed that a dramatic increase in S and M phases was established compared to untreated control cells indicating the cancer cell cycle arrest. The anticancer activity of compound 3a was investigated in the Ehrlich acid tumor model, a well-validated in vivo ectopic breast cancer model, in mice. Our results showed that compound 3a had anticancer activity and decreased the tumor volume in both low (60 mg/kg) and high (120 mg/kg) doses in mice.

A Non-immunogenic Bivalent d-Protein Potently Inhibits Retinal Vascularization and Tumor Growth

We report a general approach to engineering multivalent d-proteins with antibody-like activities in vivo. Mirror-image phage display and structure-guided design were utilized to create a d-protein that uses receptor mimicry to antagonize vascular endothelial growth factor A (VEGF-A). Selections against the d-protein form of VEGF-A using phage-displayed libraries of two different domain scaffolds yielded two proteins that bound distinct receptor interaction sites on VEGF-A. X-ray crystal structures of the d-protein/VEGF-A complexes were used to guide affinity maturation and to construct a heterodimeric d-protein VEGF-A antagonist with picomolar activity. The d-protein VEGF-A antagonist prevented vascular leakage in a rabbit eye model of wet age-related macular degeneration and slowed tumor growth in the MC38 syngeneic mouse tumor model with efficacies comparable to those of approved antibody drugs, and in contrast with antibodies, the d-protein was non-immunogenic during treatment and following subcutaneous immunizations.

A dose-escalating toxicology study of the candidate biologic ELP-VEGF

Vascular Endothelial Growth Factor (VEGF), a key mediator of angiogenesis and vascular repair, is reduced in chronic ischemic renal diseases, leading to microvascular rarefaction and deterioration of renal function. We developed a chimeric fusion of human VEGF-A₁₂₁ with the carrier protein Elastin-like Polypeptide (ELP-VEGF) to induce therapeutic angiogenesis via targeted renal VEGF therapy. We previously showed that ELP-VEGF improves renal vascular density, renal fibrosis, and renal function in swine models of chronic renal diseases. However, VEGF is a potent cytokine that induces angiogenesis and increases vascular permeability, which could cause undesired off-target effects or be deleterious in a patient with a solid tumor. Therefore, the current study aims to define the toxicological profile of ELP-VEGF and assess its risk for exacerbating tumor progression and vascularity using rodent models. A dose escalating toxicology assessment of ELP-VEGF was performed by administering a bolus intravenous injection at doses ranging from 0.1 to 200 mg/kg in Sprague Dawley (SD) rats. Blood pressure, body weight, and glomerular filtration rate (GFR) were quantified longitudinally, and terminal blood sampling and renal vascular density measurements were made 14 days after treatment. Additionally, the effects of a single administration of ELP-VEGF (0.1-10 mg/kg) on tumor growth rate, mass, and vascular density were examined in a mouse model of breast cancer. At doses up to 200 mg/kg, ELP-VEGF had no effect on body weight, caused no changes in plasma or urinary markers of renal injury, and did not induce renal fibrosis or other histopathological findings in SD rats. At the highest doses (100-200 mg/kg), ELP-VEGF caused an acute, transient hypotension (30 min), increased GFR, and reduced renal microvascular density 14 days after injection. In a mouse tumor model, ELP-VEGF did not affect tumor growth rate or tumor mass, but analysis of tumor vascular density by micro-computed tomography (μCT) revealed significant, dose dependent increases in tumor vascularity after ELP-VEGF administration. ELP-VEGF did not induce toxicity in the therapeutic dosing range, and doses one hundred times higher than the expected maximum therapeutic dose were needed to observe any adverse signs in rats. In breast tumor-bearing mice, ELP-VEGF therapy induced a dose-dependent increase in tumor vascularity, demanding caution for potential use in a patient suffering from kidney disease but with known or suspected malignancy.

Structural Basis for Vascular Endothelial Growth Factor Receptor Activation and Implications for Disease Therapy

Vascular endothelial growth factors (VEGFs) bind to membrane receptors on a wide variety of cells to regulate diverse biological responses. The VEGF-A family member promotes vasculogenesis and angiogenesis, processes which are essential for vascular development and physiology. As angiogenesis can be subverted in many disease states, including tumour development and progression, there is much interest in understanding the mechanistic basis for how VEGF-A regulates cell and tissue function. VEGF-A binds with high affinity to two VEGF receptor tyrosine kinases (VEGFR1, VEGFR2) and with lower affinity to co-receptors called neuropilin-1 and neuropilin-2 (NRP1, NRP2). Here, we use a structural viewpoint to summarise our current knowledge of VEGF-VEGFR activation and signal transduction. As targeting VEGF-VEGFR activation holds much therapeutic promise, we examine the structural basis for anti-angiogenic therapy using small-molecule compounds such as tyrosine kinase inhibitors that block VEGFR activation and downstream signalling. This review provides a rational basis towards reconciling VEGF and VEGFR structure and function in developing new therapeutics for a diverse range of ailments.

Molecular Bases of VEGFR-2-Mediated Physiological Function and Pathological Role

The vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs) play crucial roles in vasculogenesis and angiogenesis. Angiogenesis is an important mechanism in many physiological and pathological processes, and is involved in endothelial cell proliferation, migration, and survival, then leads to further tubulogenesis, and finally promotes formation of vessels. This series of signaling cascade pathways are precisely mediated by VEGF/VEGFR-2 system. The VEGF binding to the IgD2 and IgD3 of VEGFR-2 induces the dimerization of the receptor, subsequently the activation and trans-autophosphorylation of the tyrosine kinase, and then the initiation of the intracellular signaling cascades. Finally the VEGF-activated VEGFR-2 stimulates and mediates variety of signaling transduction, biological responses, and pathological processes in angiogenesis. Several crucial phosphorylated sites Tyr801, Try951, Try1175, and Try1214 in the VEGFR-2 intracellular domains mediate several key signaling processes including PLCγ-PKC, TSAd-Src-PI3K-Akt, SHB-FAK-paxillin, SHB-PI3K-Akt, and NCK-p38-MAPKAPK2/3 pathways. Based on the molecular structure and signaling pathways of VEGFR-2, the strategy of the VEGFR-2-targeted therapy should be considered to employ in the treatment of the VEGF/VEGFR-2-associated diseases by blocking the VEGF/VEGFR-2 signaling pathway, inhibiting VEGF and VEGFR-2 gene expression, blocking the binding of VEGF and VEGFR-2, and preventing the proliferation, migration, and survival of vascular endothelial cells expressing VEGFR-2.

Structure-Guided Molecular Engineering of a Vascular Endothelial Growth Factor Antagonist to Treat Retinal Diseases

Background

Ocular neovascularization is a hallmark of retinal diseases including neovascular age-related macular degeneration and diabetic retinopathy, two leading causes of blindness in adults. Neovascularization is driven by the interaction of soluble vascular endothelial growth factor (VEGF) ligands with transmembrane VEGF receptors (VEGFR), and inhibition of the VEGF pathway has shown tremendous clinical promise. However, anti-VEGF therapies require invasive intravitreal injections at frequent intervals and high doses, and many patients show incomplete responses to current drugs due to the lack of sustained VEGF signaling suppression.

Methods

We synthesized insights from structural biology with molecular engineering technologies to engineer an anti-VEGF antagonist protein. Starting from the clinically approved decoy receptor protein aflibercept, we strategically designed a yeast-displayed mutagenic library of variants and isolated clones with superior VEGF affinity compared to the clinical drug. Our lead engineered protein was expressed in the choroidal space of rat eyes via nonviral gene delivery.

Results

Using a structure-informed directed evolution approach, we identified multiple promising anti-VEGF antagonist proteins with improved target affinity. Improvements were primarily mediated through reduction in dissociation rate, and structurally significant convergent sequence mutations were identified. Nonviral gene transfer of our engineered antagonist protein demonstrated robust and durable expression in the choroid of treated rats one month post-injection.

Conclusions

We engineered a novel anti-VEGF protein as a new weapon against retinal diseases and demonstrated safe and noninvasive ocular delivery in rats. Furthermore, our structure-guided design approach presents a general strategy for discovery of targeted protein drugs for a vast array of applications.

Pleiotrophin selectively binds to vascular endothelial growth factor receptor 2 and inhibits or stimulates cell migration depending on ανβ3 integrin expression

Pleiotrophin (PTN) has a moderate stimulatory effect on endothelial cell migration through α_νβ₃ integrin, while it decreases the stimulatory effect of vascular endothelial growth factor A (VEGFA) and inhibits cell migration in the absence of α_νβ₃ through unknown mechanism(s). In the present work, by using a multitude of experimental approaches, we show that PTN binds to VEGF receptor type 2 (VEGFR2) with a K_D of 11.6 nM. Molecular dynamics approach suggests that PTN binds to the same VEGFR2 region with VEGFA through its N-terminal domain. PTN inhibits phosphorylation of VEGFR2 at Tyr1175 and still stimulates endothelial cell migration in the presence of a selective VEGFR2 tyrosine kinase inhibitor. VEGFR2 downregulation by siRNA or an anti-VEGFR2 antibody that binds to the ligand-binding VEGFR2 domain also induce endothelial cell migration, which is abolished by a function-blocking antibody against α_νβ₃ or the peptide PTN_112-136 that binds α_νβ₃ and inhibits PTN binding. In cells that do not express α_νβ₃, PTN decreases both VEGFR2 Tyr1175 phosphorylation and cell migration in a VEGFR2-dependent manner. Collectively, our data identify VEGFR2 as a novel PTN receptor involved in the regulation of cell migration by PTN and contribute to the elucidation of the mechanism of activation of endothelial cell migration through the interplay between VEGFR2 and α_νβ₃.

Elements of the Endomucin Extracellular Domain Essential for VEGF-Induced VEGFR2 Activity

Endomucin (EMCN) is the type I transmembrane glycoprotein, mucin-like component of the endothelial cell glycocalyx. We have previously shown that EMCN is necessary for vascular endothelial growth factor (VEGF)-induced VEGF receptor 2 (VEGFR2) internalization and downstream signaling. To explore the structural components of EMCN that are necessary for its function and the molecular mechanism of EMCN in VEGF-induced endothelial functions, we generated a series of mouse EMCN truncation mutants and examined their ability to rescue VEGF-induced endothelial functions in human primary endothelial cells (EC) in which endogenous EMCN had been knocked down using siRNA. Expression of the mouse full-length EMCN (FL EMCN) and the extracellular domain truncation mutants ∆21-81 EMCN and ∆21-121 EMCN, but not the shortest mutant ∆21-161 EMCN, successfully rescued the VEGF-induced EC migration, tube formation, and proliferation. ∆21-161 EMCN failed to interact with VEGFR2 and did not facilitate VEGFR2 internalization. Deletion of COSMC (C1GalT1C1) revealed that the abundant mucin-type O-glycans were not required for its VEGFR2-related functions. Mutation of the two N-glycosylation sites on ∆21-121 EMCN abolished its interaction with VEGFR2 and its function in VEGFR2 internalization. These results reveal ∆21-121 EMCN as the minimal extracellular domain sufficient for VEGFR2-mediated endothelial function and demonstrate an important role for N-glycosylation in VEGFR2 interaction, internalization, and angiogenic activity.

Creation of different bioluminescence resonance energy transfer based biosensors with high affinity to VEGF

In age-related macular degeneration (AMD) or diabetic retinopathy (DR), hypoxia and inflammatory processes lead to an upregulation of the vascular endothelial growth factor (VEGF) expression and thereby to pathological neovascularisation with incorrectly formed vessels prone to damage, thus increasing the vascular permeability and the risk of bleeding and oedema in the retina. State of the art treatment is the repeated intraocular injection of anti-VEGF molecules. For developing improved individualized treatment approaches, a minimally invasive, repeatable method for in vivo quantification of VEGF in the eye is necessary. Therefore, we designed single molecule eBRET2 VEGF biosensors by directly fusing a Renilla luciferase mutant (Rluc8) N-terminal and a green fluorescent protein (GFP2) C-terminal to a VEGF binding domain. In total, 10 different VEGF biosensors (Re01- Re10) were generated based on either single domains or full length of VEGF receptor 1 or 2 extracellular regions as VEGF binding domains. Full length expression of the biosensors in HEK293-T cells was verified via Western Blot employing an anti-Rluc8-IgG. Expression of alternative splice variants was eliminated through the deletion of the donor splice site by introduction of a silent point mutation. In all ten biosensors the energy transfer from the Rluc8 to the GFP2 occurs and generates a measurable eBRET2 ratio. Four biosensors show a relevant change of the BRET ratio (ΔBR) after VEGF binding. Furthermore, each biosensor shows a unique detection range for VEGF quantification and especially Re06 and Re07 have a high sensitivity in the range of in vivo VEGF concentrations in the eye, previously measured by invasive methods. In conclusion, we generated several eBRET2 biosensors that are suitable for VEGF quantification in vitro and could identify two eBRET2 biosensors, which may be suitable for non-invasive in vivo VEGF quantification with an implantable device.

Specific humoral response in cancer patients treated with a VEGF-specific active immunotherapy procedure within a compassionate use program

BACKGROUND

CIGB-247 is a cancer therapeutic vaccine that uses as antigen a variant of human vascular endothelial growth factor (VEGF) mixed with the bacterially-derived adjuvant VSSP. CIGB-247 has been already evaluated in two phase I clinical trials (CENTAURO and CENTAURO-2), showing to be safe and immunogenic in advanced cancer patients selected under well-defined and controlled clinical conditions. Surviving patients were submitted to monthly re-immunizations and some of them showed objective clinical benefits. Based on these results, a compassionate use program (CUP) with CIGB-247 was initiated for patients that did not meet the strict entry criteria applied for the CENTAURO and CENTAURO-2 clinical trials, but could potentially benefit from the application of this cancer therapeutic vaccine.

RESULTS

Polyclonal IgM, IgA and IgG antibodies specific for VEGF were detected by ELISA in serum samples from patients vaccinated with 400 μg of antigen combined with 200 μg of VSSP. Polyclonal antibody response showed no cross reactivity for other VEGF family member molecules like VEGF-C and VEGF-D. Serum from immunized individuals was able to block the binding of VEGF to its receptors VEGFR2 and VEGFR1. IgG fraction purified from immune sera shared the aforementioned characteristics and also inhibited the interaction between VEGF and the therapeutic recombinant antibody bevacizumab, an anti-angiogenic drug approved for the treatment of different tumors. No serious adverse events attributable to CIGB-247 have been documented yet in participants of the CIGB-247 CUP. The present paper is a first report of our findings concerning the humoral response and safety characteristics in treated CIGB-247 CUP cancer patients. The study has provided the unique opportunity of not only testing CIGB-247 in a broader clinical spectrum sample of Cuban cancer patients, but also within the context of the day-to-day clinical practice and treatment settings for these diseases in Cuban medical institutions.

CONCLUSIONS

The CIGB-247 CUP has demonstrated that immunization and follow-up of a variety of cancer patients, under day-to-day clinical practice conditions in several Cuban medical institutions, replicate our previous findings in clinical trials: CIGB-247 is safe and immunogenic.

Biochemical and Conformational Characterization of Recombinant VEGFR2 Domain 7

Angiogenesis is a biological process finely tuned by a plethora of pro- and anti-angiogenic molecules, among which vascular endothelial growth factors (VEGFs). Their biological activity is expressed through the interaction with three cognate receptor tyrosine kinases, VEGFR1, 2, and 3. VEGFR2 is the primary regulator of angiogenesis. Ligand-induced VEGFR2 dimerization and activation depend on direct ligand binding to extracellular domains 2 and 3 of receptor and in the establishment of interactions between proximal membrane domains. VEGFR2 domain 7 has been shown to play a crucial role in receptor dimerization and regulation, therefore, representing a convenient target for the allosteric modulation of VEGFR2 activity. The ability to prepare a functional VEGFR2D7 domain represents the starting point to the development of novel VEGFR2 binders acting as allosteric inhibitors of receptor activity. Here, we describe a robust and efficient procedure for the preparation in E. coli of the VEGFR2 domain 7. The protein was obtained with a good yield and was properly folded. It was investigated in a biochemical and structural study, providing information on its conformational arrangement and in solution properties.

VEGFR2-Specific Ligands Based on Affibody Molecules Demonstrate Agonistic Effects when Tetrameric in the Soluble Form or Immobilized via Spider Silk

Strategies to promote vascularization are being developed in order to improve long-term survival of artificial tissue constructs. Vascular endothelial growth factor A (VEGFA) has an important role in both pathological and physiological angiogenesis, mediated by binding to VEGF receptors (VEGFRs). In nature, signaling can be modulated by presentation of growth factors in either soluble form or bound to the extracellular matrix. Herein, a previously reported VEGFR2-binding antagonistic affibody heterodimer (di-Z_VEGFR2) was formatted into a tetrameric construct (tetra-Z_VEGFR2) with the intention of generating artificial agonistic ligands for VEGFR2 signaling. In vitro cell assays demonstrated that tetra-Z_VEGFR2 induced VEGFR2 phosphorylation and increased cell proliferation, in contrast to di-Z_VEGFR2. In order to simulate matrix-bound factors, both constructs were fused at the genetic level to a partial spider silk protein, 4RepCT. Assembly of the silk fusion proteins onto a solid surface was verified by quartz crystal microbalance with dissipation analysis. Moreover, surface plasmon resonance studies demonstrated retained VEGFR2 binding ability of di-Z_VEGFR2-silk and tetra-Z_VEGFR2-silk after silk-mediated immobilization. Cell culture studies demonstrated that VEGFR2-overexpressing cells adhered to di-Z_VEGFR2-silk and tetra-Z_VEGFR2-silk and had activated VEGFR2 signaling. Altogether, we demonstrate the potential of especially tetra-Z_VEGFR2-silk to promote angiogenesis in tissue-engineering applications. The results from the study also show that molecules can obtain completely new functions when presented on materials, and verifying the biological effects after functionalizing materials is thus always recommended.

Dual Action of Sulfated Hyaluronan on Angiogenic Processes in Relation to Vascular Endothelial Growth Factor-A

Pathological healing characterized by abnormal angiogenesis presents a serious burden to patients’ quality of life requiring innovative treatment strategies. Glycosaminoglycans (GAG) are important regulators of angiogenic processes. This experimental and computational study revealed how sulfated GAG derivatives (sGAG) influence the interplay of vascular endothelial growth factor (VEGF)₁₆₅ and its heparin-binding domain (HBD) with the signaling receptor VEGFR-2 up to atomic detail. There was profound evidence for a HBD-GAG-HBD stacking configuration. Here, the sGAG act as a “molecular glue” leading to recognition modes in which sGAG interact with two VEGF₁₆₅-HBDs. A 3D angiogenesis model demonstrated the dual regulatory role of high-sulfated derivatives on the biological activity of endothelial cells. While GAG alone promote sprouting, they downregulate VEGF₁₆₅-mediated signaling and, thereby, elicit VEGF₁₆₅-independent and -dependent effects. These findings provide novel insights into the modulatory potential of sGAG derivatives on angiogenic processes and point towards their prospective application in treating abnormal angiogenesis.

A novel 2-aminobenzimidazole-based compound Jzu 17 exhibits anti-angiogenesis effects by targeting VEGFR-2 signalling

BACKGROUND AND PURPOSE

Recent development in drug discovery have shown benzimidazole to be an important pharmacophore,. Benzimidazole derivatives exhibit broad-spectrum pharmacological properties including anti-microbial, anti-diabetic and anti-tumour activity. However, whether benzimidazole derivatives are effective in suppressing angiogenesis and its underlying mechanisms remain incompletely understood. In this study, we aim to characterize the anti-angiogenic mechanisms of a novel 2-aminobenzimidazole-based compound, Jzu 17, in an effort to develop novel angiogenesis inhibitor.

EXPERIMENTAL APPROACH

Effects of Jzu 17 on endothelial cell proliferation, migration, invasion, and activation of signalling molecules induced by VEGF-A, were analysed by immunoblotting, MTT, BrdU, migration, and invasion assays. We performed tube formation assay, aorta ring sprouting assay, matrigel plug assay, and a mouse model of metastasis to evaluate ex vivo and in vivo anti-angiogenic effects of Jzu 17.

KEY RESULTS

Jzu 17 inhibited VEGF-A-induced cell proliferation, migration, invasion, and endothelial tube formation of HUVECs. Jzu 17 suppressed VEGF-A-induced microvessel sprouting ex vivo and attenuated VEGF-A- or tumour cell-induced neovascularization in vivo. Jzu 17 also reduced B16F10 melanoma lung metastasis. In addition, Jzu 17 inhibited the phosphorylation of VEGFR-2 and its downstream signalling molecules in VEGF-A-stimulated HUVECs. Results from computer modelling further showed that Jzu 17 binds to VEGFR-2 with high affinity.

CONCLUSIONS AND IMPLICATIONS

Jzu 17 may inhibit endothelial remodelling and suppress angiogenesis through targeting VEGF-A-VEGFR-2 signalling. These results also suggest Jzu 17 as a potential lead compound and warrant the clinical development of similar agents in the treatment of cancer and angiogenesis-related diseases.

Identification of Potent VEGF Inhibitors for the Clinical Treatment of Glioblastoma, A Virtual Screening Approach

Vascular endothelial growth factor (VEGF) expression could be found in all glioblastomas. VEGF takes part in numerous changes including the endothelial cell proliferation, the vasculature of solid tumor: its survival invasion, and migration, chemotaxis of bone marrow-derived progenitor cells, vasodilation and vascular permeability. VEGF inhibition can be a smart therapeutic strategy because it is extremely specific and less toxic than cytotoxic therapy. To establish better inhibition of VEGF than the current inhibitors, present study approach is by molecular docking, virtual screening to illustrate the inhibitor with superior affinity against VEGF to have a cautious pharma profile. To retrieve the best established and high-affinity high affinity molecule, Molegro Virtual Docker software was executed. The high-affinity scoring compounds were subjected to further similarity search to retrieve the drugs with similar properties from pubchem database. The completion of virtual screening reveals that PubChem compound SCHEMBL1250485 (PubChem CID: 66965667) has the highest affinity. The study of the drug-likeness was verified using OSIRIS Property Explorer software which supported the virtual screened result. Further ADMET study and drug comparative study strongly prove the superiority of the new established inhibitor with lesser rerank score and toxicity. Overall, the new inhibitor has higher potential to stop the expression of VEGF in glioblastoma and positively can be further analysed through In vitro studies.

Human Recombinant VEGFR2D4 Biochemical Characterization to Investigate Novel Anti-VEGFR2D4 Antibodies for Allosteric Targeting of VEGFR2

VEGF-A/VEGFR2 complex is the major signaling pathway involved in angiogenesis and the inhibition of this axis retards tumor growth and inflammatory disorders progression, reducing vessel sprouting. Signaling by VEGFR2 requires receptor dimerization and a well-defined orientation of monomers in the active dimer. The extracellular portion of receptor is composed of seven Ig-like domains, of which D2-3 are the ligand binding domains, while D4 and D7, establishing homotypic contacts, allosterically regulate receptor activity. The allosteric targeting of VEGFR2 represents a promising alternative to study neovascular disorders overcoming drawbacks related to competition with VEGF. In this work, we expressed in bacterial host domain 4 of VEGFR2 (VEGFR2D4). After protein refolding, we characterized the purified domain and administered it in mice for monoclonal antibodies production. One of them, mAbD4, was tested in ELISA assays, showing a nanomolar affinity for VEGFR2D4. Finally, the methodology here described could contribute to the development of antibodies which can allosterically bind VEGFR2 and therefore to be used for imaging purposes or to modulate receptor signaling.

Complex Formation between VEGFR2 and the β2-Adrenoceptor

Vascular endothelial growth factor (VEGF) is an important mediator of endothelial cell proliferation and angiogenesis via its receptor VEGFR2. A common tumor associated with elevated VEGFR2 signaling is infantile hemangioma that is caused by a rapid proliferation of vascular endothelial cells. The current first-line treatment for infantile hemangioma is the β-adrenoceptor antagonist, propranolol, although its mechanism of action is not understood. Here we have used bioluminescence resonance energy transfer and VEGFR2 genetically tagged with NanoLuc luciferase to demonstrate that oligomeric complexes involving VEGFR2 and the β₂-adrenoceptor can be generated in both cell membranes and intracellular endosomes. These complexes are induced by agonist treatment and retain their ability to couple to intracellular signaling proteins. Furthermore, coupling of β₂-adrenoceptor to β-arrestin2 is prolonged by VEGFR2 activation. These data suggest that protein-protein interactions between VEGFR2, the β₂-adrenoceptor, and β-arrestin2 may provide insight into their roles in health and disease.

Suppression of migratory and metastatic pathways via blocking VEGFR1 and VEGFR2

BACKGROUND

Vascular endothelial growth factor (VEGF) A and B are endothelial cell mitogens whose ligation to VEGFR1/VEGFR2 drives tumor angiogenesis and metastasis, and epithelial-mesenchymal transition (EMT). Blockade of these signaling axes could be obtained by disturbing the interactions between VEGFA and/or VEGFB with VEGFR1 and/or VEGFR2.

METHODS

A 14-mer peptide (VGB) that recognizes both VEGFR1 and VEGFR2 were investigated for its inhibitory effects on the VEGF-induced proliferation and migration using MTT and scratch assay, respectively. Downstream signaling pathways were also assessed by quantitative estimation of gene and protein expression using real-time PCR and immunohistochemistry (IHC).

RESULTS

We investigated the inhibitory effects of VGB on downstream mediators of metastasis, including epithelial-cadherin (E-cadherin), matrix metalloprotease-9 (MMP-9), cancer myelocytomatosis (c-Myc), and nuclear factor-κβ (NF-κβ), and migration, comprising focal adhesion kinase (FAK) and its substrate Paxilin. VGB inhibited the VEGF-induced proliferation of human umbilical vein endothelial cells (HUVECs), 4T1 and U87 cells in a time- and dose-dependent manner and migration of HUVECs. Based on IHC analyses, treatment of 4T1 mammary carcinoma tumor with VGB led to the suppression of p-AKT, p-ERK_1/2, MMP-9, NF-κβ, and activation of E-cadherin compared with PBS-treated controls. Moreover, quantitative real-time PCR analyses of VGB-treated tumors revealed the reduced expression level of FAK, Paxilin, NF-κβ, MMP-9, c-Myc, and increased expression level of E-cadherin compared to PBS-treated controls.

CONCLUSIONS

Our results demonstrated that simultaneous blockade of VEGFR1/VEGFR2 is an effective strategy to fight solid tumors by targeting a wider range of mediators involved in tumor angiogenesis, growth, and metastasis.