Characterization of a Designed Vascular Endothelial Growth Factor Receptor Antagonist Helical Peptide with Antiangiogenic Activity in Vivo

A TLR4-Targeting Bioactive Peptide Hydrogel to Regulate Immune-Microenvironment for Diabetic Wound Repair

Persistent inflammation and disrupted immunoregulation are critical factors in impeding diabetic wound healing. While immunoregulatory hydrogel dressings hold significant promise for clinical applications in diabetic wound healing, the current application often demands intricate interventions and high-cost treatments involving cytokines and cell therapies. The development of single component immunoregulatory hydrogels remains a complex challenge. To address this issue, an active peptide hydrogel with immunoregulatory properties targeting the TLR4/NF-kB pathway, aiming to promote rapid diabetic wound healing, is engineered. The hydrogel sequence comprises naphthalene derivative, phenylalanine, and glycine to modulate hydrophilic/hydrophobic characteristics. The amino group on arginine contributes to tissue adhesion and regulation of intermolecular forces, ultimately yielding stable gels. The results underscore the formation of the peptide hydrogel (NFA) via the physical crosslinking of self-assembled nanofibers in water, thereby affording both excellent injectability and tissue adhesion. Notably, NFA demonstrates significant potential in promoting wound healing in a mouse model with full-thickness wounds by regulating macrophage responses in the inflammatory microenvironment through the TLR4/NF-kB pathway.

Radiolabeled 15-mer peptide internalization is mediated by megalin (LRP2 receptor) in a CRISPR/Cas9-based LRP2 knockout human kidney cell model

BACKGROUND

Megalin (LRP2 receptor) mediates the endocytosis of radiolabeled peptides into proximal tubular kidney cells, which may cause nephrotoxicity due to the accumulation of a radioactive tracer. The study aimed to develop a cellular model of human kidney HK2 cells with LRP2 knockout (KO) using CRISPR/Cas9 technique. This model was employed for the determination of the megalin-mediated accumulation of 68Ga- and 99mTc-labeled 15-mer peptide developed to target the vascular endothelial growth factor (VEGF) receptor in oncology radiodiagnostics.

RESULTS

The gene editing in the LRP2 KO model was verified by testing two well-known megalin ligands when higher viability of KO cells was observed after gentamicin treatment at cytotoxic concentrations and lower FITC-albumin internalization by the KO cells was detected in accumulation studies. Fluorescent-activated cell sorting was used to separate genetically modified LRP2 KO cell subpopulations. Moreover, flow cytometry with a specific antibody against megalin confirmed LRP2 knockout. The verified KO model identified both 68Ga- and 99mTc-radiolabeled 15-mer peptides as megalin ligands in accumulation studies. We found that both radiolabeled 15-mers enter LRP2 KO HK2 cells to a lesser extent compared to parent cells. Differences in megalin-mediated cellular uptake depending on the radiolabeling were not observed. Using biomolecular docking, the interaction site of the 15-mer with megalin was also described.

CONCLUSION

The CRISPR/Cas9 knockout of LRP2 in human kidney HK2 cells is an effective approach for the determination of radiopeptide internalization mediated by megalin. This in vitro method provided direct molecular evidence for the cellular uptake of radiolabeled anti-VEGFR 15-mer peptides via megalin.

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.

RGD and Scutellarin Conjugate (WK001) Targeting Platelet Glycoprotein IIb/IIIa Receptor Protects from Myocardial Ischemia/Reperfusion Injury: Synthesis, Characterization, and Bioactivity Evaluation

Myocardial ischemia/reperfusion (MI/R) injury is an unresolved clinical challenge. The blockade of binding fibrinogen by glycoprotein IIb/IIIa (GPIIb-IIIa) inhibitors has become a new therapeutic approach against MI/R injury. In this study, we modified the RGD structure to combine with scutellarin and synthesized a novel peptide, scutellarin-HomoArg-Gly-Asp-Trp-NH₂ (WK001). Herein, reported experimental and docking evidence indicates that WK001 provides immediate and potent platelet inhibition, with stronger inhibition of platelet aggregation than eptifibatide and scutellarin. In particular, it is administered intravenously to prevent thrombus formation and attenuate myocardial fibrosis progression in vivo. Therefore, WK001 could be developed as an antiplatelet drug to treat thrombosis-associated diseases, such as stroke and myocardial infarction.

Sulfono-γ-AApeptides as Protein Helical Domain Mimetics to Manipulate the Angiogenesis

Sulfono-γ-AApeptides recently developed in our group have been proven to be a new class of unnatural foldamer with well-defined helical structure and have been demonstrated to mimic protein helical domains and disrupt biomedically relevant protein-protein interactions (PPIs). Based on our design concept in a recent report, we discovered two similar sulfono-γ-AApeptides V2 and V3 which were designed to mimic the VEGF N-terminal helix α1 known to directly interact with VEGFRs. Interestingly, V2 was shown to possess the pro-angiogenic effect, whereas V3 was proved to be a potent inhibitor for angiogenesis. We speculate that the distinct angiogenesis signaling was due to the selective binding of the two molecules to VEGFR1 and VEGFR2, respectively. Together with their remarkable resistance to proteolytic degradation, relatively small sizes, and amenability to modification with diverse functional groups, V2 and V3 could serve as lead molecules for the development of potential therapeutic agents and molecular probes. These findings highlight sulfono-γ-AApeptides as an alternative paradigm to mimic the α-helical domain to modulate a wide variety of PPIs in the future.

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.

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.

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.

α/Sulfono-γ-AApeptide Hybrid Analogues of Glucagon with Enhanced Stability and Prolonged In Vivo Activity

Peptide drugs have the advantages of target specificity and good drugability and have become one of the most increasingly important hotspots in new drug research in biomedical sciences. However, peptide drugs generally have low bioavailability and metabolic stability, and therefore, the modification of existing peptide drugs for the purpose of improving stability and retaining activity is of viable importance. It is known that glucagon is an effective therapy for treating severe hypoglycemia, but its short half-life prevents its wide therapeutic use. Herein, we report that combined unnatural residues and long fatty acid conjugation afford potent α/sulfono-γ-AApeptide hybrid analogues of Glucagon with enhanced stability and prolonged in vivo activity. This strategy could be adopted to develop stabilized analogues of other short-acting bioactive peptides.

Metabolic and conformational stabilization of a VEGF-mimetic beta-hairpin peptide by click-chemistry

HPLW is a Vascular Endothelial Growth Factor (VEGF)-mimicking beta-hairpin peptide endowed of proangiogenic effect and showing valuable biomedical application in the proangiogenic therapy. However, the translational potential of HPLW is limited by its low metabolic stability, which would shorten the in vivo efficacy of the molecule. Here, we developed a peptide analog of HPLW, named HPLW2, that retains the structural and biological properties of the original peptide but features an impressive resistance to degradation by human serum proteases. HPLW2 was obtained by covalently modifying the chemical structure of the peptide with molecular tools known to impart protease resistance. Notably, the peptide was cyclized by installing an interstrand triazole bridge through Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) reaction. HPLW2 appears as a novel and promising drug candidate with potential biomedical application in the proangiogenic therapy as a low molecular weight drug, alternative to the use of VEGF. Our work points out the utility of the interstrand triazole bridge as effective chemical platform for the conformational and metabolic stabilization of beta-hairpin bioactive peptides.

Considering both small and large scale motions of vascular endothelial growth factor (VEGF) is crucial for reliably predicting its binding affinities to DNA aptamers

Considering both small and large scale motions of VEGF is crucial to predict its relative binding affinities to DNA aptamer variants with docking.

Neurotrophic Effects of Vascular Endothelial Growth Factor B and Novel Mimetic Peptides on Neurons from the Central Nervous System

Vascular endothelial growth factor B (VEGFB) is a pleiotropic trophic factor, which in contrast to the closely related VEGFA is known to have a limited effect on angiogenesis. VEGFB improves survival in various tissues including the nervous system, where the effect was observed mainly for peripheral neurons. The neurotrophic effect of VEGFB on central nervous system neurons has been less investigated. Here we demonstrated that VEGFB promotes neurite outgrowth from primary cerebellar granule, hippocampal, and retinal neurons in vitro. VEGFB protected hippocampal and retinal neurons from both oxidative stress and glutamate-induced neuronal death. The VEGF receptor 1 (VEGFR1) is required for VEGFB-induced neurotrophic and neuroprotective effects. Using a structure-based approach, we designed short peptides, termed Vefin1-7, mimicking the binding interface of VEGFB to VEGFR1. Vefins were analyzed for their secondary structure and binding to VEGF receptors and compared with previously described peptides derived from VEGFA, another ligand of VEGFR1. We show that Vefins have neurotrophic and neuroprotective effects on primary hippocampal, cerebellar granule, and retinal neurons in vitro with potencies comparable to VEGFB. Similar to VEGFB, Vefins were not mitogenic for MCF-7 cancer cells. Furthermore, one of the peptides, Vefin7, even dose-dependently inhibited the proliferation of MCF-7 cells in vitro. Unraveling the neurotrophic and neuroprotective potentials of VEGFB, the only nonangiogenic factor of the VEGF family, is promising for the development of neuroprotective peptide-based therapies.

The activity of sulfono-γ-AApeptide helical foldamers that mimic GLP-1

Existing long α-helix mimicking necessitates the retention of most natural amino acid residues to maintain their biological activity. Here, we report the exploration of helical sulfono-γ-AApeptides with entire unnatural backbones for their ability to structurally and functionally mimic glucagon-like peptide 1 (GLP-1). Our findings suggest that efficient construction of novel GLP-1 receptor (GLP-1R) agonists could be achieved with nanomolar potencies. In addition, the resulting sulfono-γ-AApeptides were also proved to display remarkable stability against enzymatic degradation compared to GLP-1, augmenting their biological potential. This alternative strategy of α-helix mimicking, as a proof of concept, could provide a new paradigm to prepare GLP-1R agonists.

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.

Rational Design of Antiangiogenic Helical Oligopeptides Targeting the Vascular Endothelial Growth Factor Receptors

Tumor angiogenesis, essential for cancer development, is regulated mainly by vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs), which are overexpressed in cancer cells. Therefore, the VEGF/VEGFR interaction represents a promising pharmaceutical target to fight cancer progression. The VEGF surface interacting with VEGFRs comprises a short α-helix. In this work, helical oligopeptides mimicking the VEGF-C helix were rationally designed based on structural analyses and computational studies. The helical conformation was stabilized by optimizing intramolecular interactions and by introducing helix-inducing C^α,α-disubstituted amino acids. The conformational features of the synthetic peptides were characterized by circular dichroism and nuclear magnetic resonance, and their receptor binding properties and antiangiogenic activity were determined. The best hits exhibited antiangiogenic activity in vitro at nanomolar concentrations and were resistant to proteolytic degradation.

A cyclic peptide reproducing the α1 helix of VEGF-B binds to VEGFR-1 and VEGFR-2 and inhibits angiogenesis and tumor growth

Vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs) are pivotal regulators of angiogenesis. The VEGF–VEGFR system is therefore an important target of anti-angiogenesis therapy. Based on the X-ray structure of VEGF-B/VEGFR-1 D2, we designed a cyclic peptide (known as VGB1) reproducing the α1 helix and its adjacent region to interfere with signaling through VEGFR-1. Unexpectedly, VGB1 bound VEGFR-2 in addition to VEGFR-1, leading to inhibition of VEGF-stimulated proliferation of human umbilical vein endothelial cells and 4T1 murine mammary carcinoma cells, which express VGEFR-1 and VEGFR-2, and U87 glioblastoma cells that mostly express VEGFR-2. VGB1 inhibited different aspects of angiogenesis, including proliferation, migration and tube formation of endothelial cells stimulated by VEGF-A through suppression of extracellular signal-regulated kinase 1/2 and AKT (Protein Kinase B) phosphorylation. In a murine 4T1 mammary carcinoma model, VGB1 caused regression of tumors without causing weight loss in association with impaired cell proliferation (decreased Ki67 expression) and angiogenesis (decreased CD31 and CD34 expression), and apoptosis induction (increased TUNEL staining and p53 expression, and decreased Bcl-2 expression). According to far-UV circular dichroism (CD) and molecular dynamic simulation data, VGB1 can adopt a helical structure. These results, for the first time, demonstrate that α1 helix region of VEGF-B recognizes both VEGFR-1 and VEGFR-2.

A peptide mimicking the binding sites of VEGF-A and VEGF-B inhibits VEGFR-1/-2 driven angiogenesis, tumor growth and metastasis

Interfering with interactions of vascular endothelial growth factors (VEGFs) with their receptors (VEGFRs) effectively inhibits angiogenesis and tumor growth. We designed an antagonist peptide of VEGF-A and VEGF-B reproducing two discontinuous receptor binding regions of VEGF-B (loop 1 and loop3) covalently linked together by a receptor binding region of VEGF-A (loop3). The designed peptide (referred to as VGB4) was able to bind to both VEGFR1 and VEGFR2 on the Human Umbilical Vein Endothelial Cells (HUVECs) surface and inhibited VEGF-A driven proliferation, migration and tube formation in HUVECs through suppression of ERK1/2 and AKT phosphorylation. The whole-animal fluorescence imaging demonstrated that fluorescein isothiocyanate (FITC)-VGB4 accumulated in the mammary carcinoma tumors (MCTs). Administration of VGB4 led to the regression of 4T1 murine MCT growth through decreased expression of p-VEGFR1 and p-VEGFR2 and abrogation of ERK1/2 and AKT activation followed by considerable decrease of tumor cell proliferation (Ki67 expression) and angiogenesis (CD31 and CD34 expression), induction of apoptosis (increased p53 expression, TUNEL staining and decreased Bcl2 expression), and suppression of metastasis  (increased E-cadherin and decreased N-cadherin, NF-κB and MMP-9 expression). These findings indicate that VGB4 may be applicable for antiangiogenic and antitumor therapy.

Unveiling a VEGF-mimetic peptide sequence in the IQGAP1 protein

The ability to modulate angiogenesis by chemical tools has several important applications in different scientific fields. With the perspective of finding novel proangiogenic molecules, we searched peptide sequences with a chemical profile similar to that of the QK peptide, a well described VEGF mimetic peptide. We found that residues 1617-1627 of the IQGAP1 protein show molecular features similar to those of the QK peptide sequence. The IQGAP1-derived synthetic peptide was analyzed by NMR spectroscopy and its biological activity was characterized in endothelial cells. These studies showed that this IQGAP1-derived peptide has a biological activity similar to that of VEGF and could be considered as a novel tool for reparative angiogenesis.

Disrupting VEGF-VEGFR1 Interaction: De Novo Designed Linear Helical Peptides to Mimic the VEGF13-25 Fragment

The interaction between vascular endothelial growth factor (VEGF) and its receptors (VEGFR) has important implications in angiogenesis and cancer, which moved us to search for peptide derivatives able to block this protein–protein interaction. In a previous work we had described a collection of linear 13-mer peptides specially designed to adopt helical conformations (Ac-SSEEX⁵ARNX⁹AAX¹²N-NH₂), as well as the evaluation of seven library components for the inhibition of the interaction of VEGF with its Receptor 1 (VEGFR1). This study led to the discovery of some new, quite potent inhibitors of this protein–protein system. The results we found prompted us to extend the study to other peptides of the library. We describe here the evaluation of a new selection of peptides from the initial library that allow us to identify new VEGF-VEGFR1 inhibitors. Among them, the peptide sequence containing F, W, and I residues at the 5, 9, and 12 positions, show a very significant nanomolar IC₅₀ value, competing with VEGF for its receptor 1, VEGFR1 (Flt-1), which could represent a new tool within the therapeutic arsenal for cancer detection and therapy.

RGD-mediated delivery of small-molecule drugs

Conjugates of cytotoxic agents with RGD peptides (Arg-Gly-Asp) addressed to α_νβ₃, α₅β₁ and α_νβ₆ integrin receptors overexpressed by cancer cells, have recently gained attention as potential selective anticancer chemotherapeutics. In this review, the design and the development of RGD conjugates coupled to different small molecules including known cytotoxic drugs and natural products will be discussed.

Miniaturizing VEGF: Peptides mimicking the discontinuous VEGF receptor-binding site modulate the angiogenic response

The angiogenic properties of VEGF are mediated through the binding of VEGF to its receptor VEGFR2. The VEGF/VEGFR interface is constituted by a discontinuous binding region distributed on both VEGF monomers. We attempted to reproduce this discontinuous binding site by covalently linking into a single molecular entity two VEGF segments involved in receptor recognition. We designed and synthesized by chemical ligation a set of peptides differing in length and flexibility of the molecular linker joining the two VEGF segments. The biological activity of the peptides was characterized in vitro and in vivo showing a VEGF-like activity. The most biologically active mini-VEGF was further analyzed by NMR to determine the atomic details of its interaction with the receptor.

Long range Trp-Trp interaction initiates the folding pathway of a pro-angiogenic β-hairpin peptide

HPLW, a designed VEGF (Vascular Endothelium Growth Factor) receptor-binding peptide, assumes a well folded β-hairpin conformation in water and is able to induce angiogenesis in vivo. In this study, we investigated at atomic resolution the thermal folding/unfolding pathway of HPLW by means of an original multi-technique approach combining DSC, NMR, MD and mutagenesis analyses. In particular, careful NMR investigation of the single proton melting temperatures together with DSC analysis accurately delineate the peptide folding mechanism, which is corroborated by computational folding/unfolding simulations. The HPLW folding process consists of two main events, which are successive but do not superimpose. The first folding step initiates at 320 K upon the hydrophobic collapse of the Trp5 and Trp13 side-chains which stabilizes the concurrent β-turn formation, whose COi-HNi + 3 hydrogen bond (Asp10 → Arg7) appears particularly stable. At 316 K, once the β-turn is completely formed, the two β-strands pair, very likely starting by Trp5 and Trp13, which thus play a key role also in the final step of the β-hairpin folding. Overall, here we describe a multi-state hierarchical folding pathway of a highly structured β-hairpin, which can be classified as a broken-zipper mechanism.

Synthesis, Characterization, and Biological Evaluation of a Dual-Action Ligand Targeting αvβ3 Integrin and VEGF Receptors

A dual-action ligand targeting both integrin αVβ3 and vascular endothelial growth factor receptors (VEGFRs), was synthesized via conjugation of a cyclic peptidomimetic αVβ3 Arg-Gly-Asp (RGD) ligand with a decapentapeptide. The latter was obtained from a known VEGFR antagonist by acetylation at the Lys13 side chain. Functionalization of the precursor ligands was carried out in solution and in the solid phase, affording two fragments: an alkyne VEGFR ligand and the azide integrin αVβ3 ligand, which were conjugated by click chemistry. Circular dichroism studies confirmed that both the RGD and VEGFR ligand portions of the dual-action compound substantially adopt the biologically active conformation. In vitro binding assays on isolated integrin αVβ3 and VEGFR-1 showed that the dual-action conjugate retains a good level of affinity for both its target receptors, although with one order of magnitude (10/20 times) decrease in potency. The dual-action ligand strongly inhibited the VEGF-induced morphogenesis in Human Umbilical Vein Endothelial Cells (HUVECs). Remarkably, its efficiency in preventing the formation of new blood vessels was similar to that of the original individual ligands, despite the worse affinity towards integrin αVβ3 and VEGFR-1.

The anti-apoptotic BAG3 protein is expressed in lung carcinomas and regulates small cell lung carcinoma (SCLC) tumor growth

BAG3, member the HSP70 co-chaperones family, has been shown to play a relevant role in the survival, growth and invasiveness of different tumor types. In this study, we investigate the expression of BAG3 in 66 specimens from different lung tumors and the role of this protein in small cell lung cancer (SCLC) tumor growth. Normal lung tissue did not express BAG3 while we detected the expression of BAG3 by immunohistochemistry in all the 13 squamous cell carcinomas, 13 adenocarcinomas and 4 large cell carcinomas. Furthermore, we detected BAG3 expression in 22 of the 36 SCLCs analyzed. The role on SCLC cell survival was determined by down-regulating BAG3 levels in two human SCLC cell lines, i.e. H69 and H446, in vitro and measuring cisplatin induced apoptosis. Indeed down-regulation of BAG3 determines increased cell death and sensitizes cells to cisplatin treatment. The effect of BAG3 down-regulation on tumor growth was also investigated in an in vivo xenograft model by treating mice with an adenovirus expressing a specific bag3 siRNA. Treatment with bag3 siRNA-Ad significantly reduced tumor growth and improved animal survival. In conclusion we show that a subset of SCLCs over express BAG3 that exerts an anti-apoptotic effect resulting in resistance to chemotherapy.

Functional binding surface of a β-hairpin VEGF receptor targeting peptide determined by NMR spectroscopy in living cells

In this study, the functional interaction of HPLW peptide with VEGFR2 (Vascular Endothelial Growth Factor Receptor 2) was determined by using fast (15)N-edited NMR spectroscopic experiments. To this aim, (15)N uniformly labelled HPLW has been added to Porcine Aortic Endothelial Cells. The acquisition of isotope-edited NMR spectroscopic experiments, including (15)N relaxation measurements, allowed a precise characterization of the in-cell HPLW epitope recognized by VEGFR2.

Design and synthesis of C-terminal modified cyclic peptides as VEGFR1 antagonists

Previously designed cyclic peptide antagonist c[YYDEGLEE]-NH2 disrupts the interaction between vascular endothelial growth factor (VEGF) and its receptors (VEGFRs). It represents a promising tool in the fight against cancer and age-related macular degeneration. We described in this paper the optimization of the lead peptide by C-terminal modification. A new strategy for the synthesis of cyclic peptides is developed, improving the cyclisation efficiency. At 100 µM, several new peptides with an aromatic group flexibly linked at C-terminal end showed significantly increased receptor binding affinities in competition ELISA test. The most active peptide carrying a coumarin group may be a useful tool in anti-angiogenic biological studies.

De novo designed library of linear helical peptides: an exploratory tool in the discovery of protein-protein interaction modulators

Protein-protein interactions (PPIs) have emerged as important targets for pharmaceutical intervention because of their essential role in numerous physiological and pathological processes, but screening efforts using small-molecules have led to very low hit rates. Linear peptides could represent a quick and effective approach to discover initial PPI hits, particularly if they have inherent ability to adopt specific peptide secondary structures. Here, we address this hypothesis through a linear helical peptide library, composed of four sublibraries, which was designed by theoretical predictions of helicity (Agadir software). The 13-mer peptides of this collection fixes either a combination of three aromatic or two aromatic and one aliphatic residues on one face of the helix (Ac-SSEEX(5)ARNX(9)AAX(12)N-NH2), since these are structural features quite common at PPIs interfaces. The 81 designed peptides were conveniently synthesized by parallel solid-phase methodologies, and the tendency of some representative library components to adopt the intended secondary structure was corroborated through CD and NMR experiments. As proof of concept in the search for PPI modulators, the usefulness of this library was verified on the widely studied p53-MDM2 interaction and on the communication between VEGF and its receptor Flt-1, two PPIs for which a hydrophobic α-helix is essential for the interaction. We have demonstrated here that, in both cases, selected peptides from the library, containing the right hydrophobic sequence of the hot-spot in one of the protein partners, are able to interact with the complementary protein. Moreover, we have discover some new, quite potent inhibitors of the VEGF-Flt-1 interaction, just by replacing one of the aromatic residues of the initial F(5)Y(9)Y(12) peptide by W, in agreement with previous results on related antiangiogenic peptides. Finally, the HTS evaluation of the full collection on thermoTRPs has led to a few antagonists of TRPV1 and TRPA1 channels, which open new avenues on the way to innovative modulators of these channels.