Inhibition of angiogenesis in vitro and in vivo: comparison of the relative activities of triflavin, an Arg-Gly-Asp-containing peptide and anti-alpha(v)beta3 integrin monoclonal antibody

γ-Bungarotoxin impairs the vascular endothelial barrier function by inhibiting integrin α5

γ-bungarotoxin (γ-BGT) is an RGD motif-containing protein, derived from the venom of Bungarus multicinctus, leading to acute death in mice. These RGD motif-containing proteins from snake venom belonging to the disintegrin family can interfere with vascular endothelial homeostasis by directly binding cell surface integrins. Targeting integrins that generate vascular endothelial dysfunction may contribute to γ-BGT poisoning, however, the underlying mechanisms have not been investigated in detail. In this study, the results showed that γ-BGT played a role in -promoting the permeability of the vascular endothelial barrier. Depending on its selective binding to integrin α5 in vascular endothelium (VE), γ-BGT initiated downstream events, including focal adhesion kinase dephosphorylation and cytoskeleton remodeling, resulting in the intercellular junction interruption. Those alternations facilitated paracellular permeability of VE and barrier dysfunction. Proteomics profiling identified that as a downstream effector of the integrin α5 / FAK signaling pathway cyclin D1 partially mediated the cellular structural changes and barrier dysfunction. Furthermore, VE-released plasminogen activator urokinase and platelet-derived growth factor D could serve as potential diagnostic biomarkers for γ-BGT-induced vascular endothelial dysfunction. Our results indicate the mechanisms through which γ-BGT as a novel disintegrin directly interacts with the VE, with consequences for barrier dysfunction.

Peptide modulators of cell migration: Overview, applications and future development

Cell migration is a key physiological process in the development and homeostasis of multicellular organisms; errors in this complex system can trigger the development of cancer or inflammatory disorders. Therefore, modulating cell migration provides opportunities for drug discovery. Peptides are gaining importance on the global therapeutics market, given their unique properties compared with established small-molecule drugs or biologics. In this review, we identified over 470 peptides modulating cell migration and analyzed their characteristics. Over 95% of these peptides are in the discovery or preclinical stage, because the transition of peptide hits into drug leads often results in a bottleneck in the development process. We summarize chemical strategies in (pre-)clinical development to enhance drug-like properties of bioactive peptides.

Recent developments in animal venom peptide nanotherapeutics with improved selectivity for cancer cells

Animal venoms are a rich source of bioactive peptides that efficiently modulate key receptors and ion channels involved in cellular excitability to rapidly neutralize their prey or predators. As such, they have been a wellspring of highly useful pharmacological tools for decades. Besides targeting ion channels, some venom peptides exhibit strong cytotoxic activity and preferentially affect cancer over healthy cells. This is unlikely to be driven by an evolutionary impetus, and differences in tumor cells and the tumor microenvironment are probably behind the serendipitous selectivity shown by some venom peptides. However, strategies such as bioconjugation and nanotechnologies are showing potential to improve their selectivity and potency, thereby paving the way to efficiently harness new anticancer mechanisms offered by venom peptides. This review aims to highlight advances in nano- and chemotherapeutic tools and prospective anti-cancer drug leads derived from animal venom peptides.

Structural Insight into Integrin Recognition and Anticancer Activity of Echistatin

Echistatin (Ech) is a short disintegrin with a long ⁴²NPHKGPAT C-terminal tail. We determined the 3-D structure of Ech by X-ray crystallography. Superimposition of the structures of chains A and B showed conformational differences in their RGD loops and C-termini. The chain A structure is consistent with our NMR analysis that the GPAT residues of the C-terminus cannot be observed due to high flexibility. The hydrogen bond patterns of the RGD loop and between the RGD loop and C-terminus in Ech were the same as those of the corresponding residues in medium disintegrins. The mutant with C-terminal HKGPAT truncation caused 6.4-, 7.0-, 11.7-, and 18.6-fold decreases in inhibiting integrins αvβ3, αIIbβ3, αvβ5, and α5β1. Mutagenesis of the C-terminus showed that the H44A mutant caused 2.5- and 4.4-fold increases in inhibiting αIIbβ3 and α5β1, and the K45A mutant caused a 2.6-fold decrease in inhibiting αIIbβ3. We found that Ech inhibited VEGF-induced HUVEC proliferation with an IC₅₀ value of 103.2 nM and inhibited the migration of A375, U373MG, and Panc-1 tumor cells with IC₅₀ values of 1.5, 5.7, and 154.5 nM. These findings suggest that Ech is a potential anticancer agent, and its C-terminal region can be optimized to improve its anticancer activity.

Inhibition of αvβ3 integrin impairs adhesion and uptake of tumor-derived small extracellular vesicles

BACKGROUND

Extracellular vesicles (EVs) are lipid-bound particles that are naturally released from cells and mediate cell-cell communication. Integrin adhesion receptors are enriched in small EVs (SEVs) and SEV-carried integrins have been shown to promote cancer cell migration and to mediate organ-specific metastasis; however, how integrins mediate these effects is not entirely clear and could represent a combination of EV binding to extracellular matrix and cells.

METHODS

To probe integrin role in EVs binding and uptake, we employed a disintegrin inhibitor (DisBa-01) of integrin binding with specificity for αvβ3 integrin. EVs were purified from MDA-MB-231 cells conditioned media by serial centrifugation method. Isolated EVs were characterized by different techniques and further employed in adhesion, uptake and co-culture experiments.

RESULTS

We find that SEVs secreted from MDA-MB-231 breast cancer cells carry αvβ3 integrin and bind directly to fibronectin-coated plates, which is inhibited by DisBa-01. SEV coating on tissue culture plates also induces adhesion of MDA-MB-231 cells, which is inhibited by DisBa-01 treatment. Analysis of EV uptake and interchange between cells reveals that the amount of CD63-positive EVs delivered from malignant MDA-MB-231 breast cells to non-malignant MCF10A breast epithelial cells is reduced by DisBa-01 treatment. Inhibition of αvβ3 integrin decreases CD63 expression in cancer cells suggesting an effect on SEV content.

CONCLUSION

In summary, our findings demonstrate for the first time a key role of αvβ3 integrin in cell-cell communication through SEVs. Video Abstract.

Effect of Integrin Binding Peptide on Vascularization of Scaffold-Free Microtissue Spheroids

BACKGROUND

Three-dimensional (3D) biomimetic models via various approaches can be used by therapeutic applications of tissue engineering. Creating an optimal vascular microenvironment in 3D model that mimics the extracellular matrix (ECM) and providing an adequate blood supply for the survival of cell transplants are major challenge that need to be overcome in tissue regeneration. However, currently available scaffolds-depended approaches fail to mimic essential functions of natural ECM. Scaffold-free microtissues (SFMs) can successfully overcome some of the major challenges caused by scaffold biomaterials such as low cell viability and high cost.

METHODS

Herein, we investigated the effect of soluble integrin binding peptide of arginine-glycine-aspartic acid (RGD) on vascularization of SFM spheroids of human umbilical vein endothelial cells. In vitro-fabricated microtissue spheroids were constructed and cultivated in 0 mM, 1 mM, 2 mM, and 4 mM of RGD peptide. The dimensions and viability of SFMs were measured.

RESULTS

Maximum dimension and cell viability observed in 2 mM RGD containing SFM. Vascular gene expression of 2 mM RGD containing SFM were higher than other groups, while 4 mM RGD containing SFM expressed minimum vascularization related genes. Immunofluorescent staining results indicating that platelet/endothelial cell adhesion molecule and vascular endothelial growth factor protein expression of 2 mM RGD containing SFM was higher compared to other groups.

CONCLUSION

Collectively, these findings demonstrate that SFM spheroids can be successfully vascularized in determined concentration of RGD peptide containing media. Also, soluble RGD incorporated SFMs can be used as an optimal environment for successful prevascularization strategies.

Investigating the cytotoxic effects of the venom proteome of two species of the Viperidae family (Cerastes cerastes and Cryptelytrops purpureomaculatus) from various habitats

Animal secretions are of great interest in terms of drug development due to their complex protein and peptide composition. Especially, in the field of therapeutic medications such as anti-cancer drugs snake venoms receive attention. In this study, we address two Viperidae species from various habitats with a particular focus on the cytotoxic potential along with the decomplexation of the venom proteome: the horned desert viper (Cerastes cerastes), native to desert regions of North Africa and the mangrove pit viper (Cryptelytrops purpureomaculatus), found in coastal forests of Southeast Asia. Initial cytotoxic screenings of the crude venoms revealed diverse activity, with the highest effect against SHSY5Y human glioblastoma carcinoma cells compared to other cancerous and non-cancerous cell lines. In-depth cytotoxicity studies of SHSY5Y cells with purified venom fractions revealed heterodimeric disintegrins from C. cerastes venom, which exerted a high cytotoxic activity with IC₅₀ values from 0.11 to 0.58 μM and a disintegrin-like effect on SHSY5Y morphology was observed due to cell detachment. Furthermore, two polyproline BPP-related peptides, one PLA₂ and a peptide-rich fraction were determined for C. purpureomaculatus with moderate IC₅₀ values between 3 and 51 μM. Additionally, the decryption of the venom proteomes by snake venomic mass spectrometry and comparison of the same species from different habitats revealed slight differences in the composition.

Venom as therapeutic weapon to combat dreadful diseases of 21st century: A systematic review on cancer, TB, and HIV/AIDS

Cancer and infectious diseases are the preeminent causes of human morbidities and mortalities worldwide. At present, chemotherapy, radiotherapy, immunotherapy, and gene therapy are considered as predominant options in order to treat cancer. But these therapies provide inadequate consequences by affecting both the normal and tumor cells. On the other hand, tuberculosis (TB), and HIV (human immunodeficiency virus) infections are significant threats, causing over a million mortalities each year. The extensive applications of antibiotics have caused the microbes to acquire resistance to the existing antibiotics. With the emerging dilemma of drug resistant microbes, it has become imperative to identify novel therapeutic agents from natural sources as emphatic alternative approach. Over the past few decades, venoms derived from several reptiles, amphibians, and arthropods including snakes, scorpions, frogs, spiders, honey bees, wasps, beetles, caterpillars, ants, centipedes, and sponges have been identified as efficient therapeutics. Venoms constitute plethora of bioactive components, particularly peptides, enzymes, and other chemical entities, which exhibit a large array of anticancer and anti-pathogenic activities. This review highlights the panorama of bioactive components of animal venoms divulging the anticancer, anti-tubercular, and anti-HIV activities. In a nutshell, this context discloses the decisive role of animal venoms as alternative natural resources to combat these deadly diseases of 21^st century, and propounding the plausible development of new therapeutic drugs in the present era.

Venom-based peptide therapy: insights into anti-cancer mechanism

The 5-year relative survival rate of all types of cancer has increased significantly over the past three decades partly due to the targeted therapy. However, still there are many targeted therapy drugs could play a role only in a portion of cancer patients with specific molecular alternation. It is necessary to continue to develop new biological agents which could be used alone and/or in combination with current FDA approved drugs to treat complex cancer diseases. Venom-based drugs have been used for hundreds of years in human history. Nevertheless, the venom-origin of the anti-cancer drug do rarely appear in the pharmaceutical market; and this is due to the fact that the mechanism of action for a large number of the venom drug such as venom-based peptide is not clearly understood. In this review, we focus on discussing some identified venom-based peptides and their anti-cancer mechanisms including the blockade of cancer cell proliferation, invasion, angiogenesis, and metastasis (hallmarks of cancer) to fulfill the gap which is hindering their use in cancer therapy. Furthermore, it also highlights the importance of immunotherapy based on venom peptide. Overall, this review provides readers for further understanding the mechanism of venom peptide and elaborates on the need to explore peptide-based therapeutic strategies.

Disintegrins from snake venoms and their applications in cancer research and therapy

Integrins regulate diverse functions in cancer pathology and in tumor cell development and contribute to important processes such as cell shape, survival, proliferation, transcription, angiogenesis, migration, and invasion. A number of snake venom proteins have the ability to interact with integrins. Among these are the disintegrins, a family of small, non-enzymatic, and cysteine-rich proteins found in the venom of numerous snake families. The venom proteins may have a potential role in terms of novel therapeutic leads for cancer treatment. Disintegrin can target specific integrins and as such it is conceivable that they could interfere in important processes involved in carcinogenesis, tumor growth, invasion and migration. Herein we present a survey of studies involving the use of snake venom disintegrins for cancer detection and treatment. The aim of this review is to highlight the relationship of integrins with cancer and to present examples as to how certain disintegrins can detect and affect biological processes related to cancer. This in turn will illustrate the great potential of these molecules for cancer research. Furthermore, we also outline several new approaches being created to address problems commonly associated with the clinical application of peptide-based drugs such as instability, immunogenicity, and availability.

Enhanced trophic factor secretion by mesenchymal stem/stromal cells with Glycine-Histidine-Lysine (GHK)-modified alginate hydrogels

Recombinant proteins and cytokines are under broad preclinical and clinical investigation to promote angiogenesis, but their success is limited by ineffective delivery, lack of long-term stability and excessive cost. Mesenchymal stem/stromal cells (MSC) secrete bioactive trophic factors, and thus, may provide an effective alternative to address these challenges. Glycine-Histidine-Lysine (GHK) is a peptide fragment of osteonectin, a matricellular protein with reported proangiogenic potential. We examined the capacity of GHK to up-regulate secretion of proangiogenic factors from human MSC in culture and when covalently coupled to alginate hydrogels. GHK had no apparent cytotoxic effects on MSC in culture over a wide range of concentrations. We detected a dose-dependent increase in vascular endothelial growth factor (VEGF) concentration in media conditioned by GHK-treated MSC, which increased endothelial cell proliferation, migration and tubule formation. We covalently coupled GHK to alginate using carbodiimide chemistry, and human MSC were entrapped in alginate hydrogels to assess VEGF secretion. Similar to monolayer culture, MSC responded to GHK-modified gels by secreting increased concentrations of VEGF and basic fibroblast growth factor compared to unmodified gels. The pre-treatment of MSC with antibodies to α6 and β1 integrins prior to entrapment in GHK-modified gels abrogated VEGF secretion, suggesting that the proangiogenic response of MSC was integrin-mediated. These data demonstrate that the proangiogenic potential of MSC can be significantly increased by the presentation of GHK with a biodegradable carrier, therefore increasing their clinical potential when used for tissue repair.

Anti-angiogenic activities of two recombinant disintegrins derived from the Mohave and Prairie rattlesnakes

Angiogenesis plays a crucial role in the growth and spread of cancer. New vascularization nourishes cancer cells with oxygen and nutrients, allowing these cells to grow, invade nearby tissue, spread to other parts of the body, and form new colonies of cancer cells. Tumor angiogenesis consists of endothelial cell proliferation, migration, and tube formation into the tumor mass. The study of natural and synthetic angiogenesis inhibitors is a promising area for therapeutics since tumors cannot grow or spread without the formation of new blood vessels. Anti-angiogenic activities have been identified in peptides known as disintegrins. Disintegrins are a family of small proteins (45-84 amino acids in length), many which are found in snake venom that function as potent inhibitors of both platelet aggregation and integrin-dependent cell adhesion. This study reports two recombinant disintegrins (r-mojastin 1 and r-viridistatin 2) inhibiting, with similar effectiveness, distinct steps in angiogenesis such as proliferation, adhesion to fibronectin, migration, and tube formation in vitro and in vivo. Both recombinant disintegrins bind to α(v)β₃ and α(v)β₅ receptors that are upregulated in tumor endothelial cells, having a higher binding activity to α(v)β₃ integrin.

Latent KSHV infection of endothelial cells induces integrin beta3 to activate angiogenic phenotypes

Kaposi's Sarcoma (KS), the most common tumor of AIDS patients, is a highly vascularized tumor supporting large amounts of angiogenesis. The main cell type of KS tumors is the spindle cell, a cell of endothelial origin, the primary cell type involved in angiogenesis. Kaposi's Sarcoma-associated herpesvirus (KSHV) is the etiologic agent of KS and is likely involved in both tumor formation and the induction of angiogenesis. Integrins, and specifically integrin αVβ3, have known roles in both tumor induction and angiogenesis. αVβ3 is also important for KSHV infection as it has been shown to be involved in KSHV entry into cells. We found that during latent infection of endothelial cells KSHV induces the expression of integrin β3 leading to increased surface levels of αVβ3. Signaling molecules downstream of integrins, including FAK and Src, are activated during viral latency. Integrin activation by KSHV is necessary for the KSHV-associated upregulation of a number of angiogenic phenotypes during latent infection including adhesion and motility. Additionally, KSHV-infected cells become more reliant on αVβ3 for capillary like formation in three dimensional culture. KSHV induction of integrin β3, leading to induction of angiogenic and cancer cell phenotypes during latency, is likely to be important for KS tumor formation and potentially provides a novel target for treating KS tumors.

Kaposi's Sarcoma (KS) is the most common tumor of AIDS patients world-wide and is characterized by very high vascularization. The main KS tumor cell type is the spindle cell, a cell of endothelial origin. Kaposi's Sarcoma-associated herpesvirus (KSHV), the etiologic agent of KS, is found predominantly in the latent state in spindle cells. In this study we examined how KSHV alters endothelial cells to induce phenotypes common to angiogenesis and tumor formation. Integrins are cell surface adhesion and signaling proteins that can be involved in tumor growth and tumor angiogenesis. We found that KSHV infection of endothelial cells leads to increased expression of integrin β3, a molecule that, when paired with its cognate α subunit, αV, has been shown to be critical for tumor-associated angiogenesis. KSHV infection promotes angiogenic phenotypes in endothelial cells including adhesion, motility and capillary morphogenesis, and these phenotypes require expression and signaling through integrin β3. Therefore, KSHV induction of integrin beta3 and downstream signaling is required for the induction of phenotypes thought to be critical for KS tumor formation. αVβ3 inhibitors are in clinical trials for inhibition of tumors and we propose that these inhibitors may be clinically relevant for treatment of KS tumors.

"Insularin, a disintegrin from Bothrops insularis venom: inhibition of platelet aggregation and endothelial cell adhesion by the native and recombinant GST-insularin proteins"

Insularin (INS) was obtained from Bothrops insularis venom by reversed-phase high-performance liquid chromatography using a C(18) column and characterized as a disintegrin by peptide mass fingerprint and inhibition of ADP-induced platelet aggregation. A cDNA coding for P-II a metalloproteinase/disintegrin was cloned from a cDNA library from B. insularis venom glands. The deduced protein sequence possesses 73 amino acid residues, including the N-terminal, internal peptides of native insularin, the ARGDNP-sequence and 12 cysteines in a conserved alignment. This cDNA fragment was subcloned in the pGEX-4T-1 vector and expressed in a prokaryotic expression system as a fusion protein with glutathione S-transferase (GST-INS). Both native and recombinant insularin inhibited ADP-induced platelet aggregation and endothelial cells (HUVEC) adhesion with similar activities indicating that GST-INS folded correctly and preserved the integrin-binding loop. Insularin may be a tool in studies that involve platelets and endothelial cell adhesion dependent on alphaIIbeta3 and alphavbeta3 integrins.

Snake venom disintegrins and cell migration

Cell migration is a key process for the defense of pluricellular organisms against pathogens, and it involves a set of surface receptors acting in an ordered fashion to contribute directionality to the movement. Among these receptors are the integrins, which connect the cell cytoskeleton to the extracellular matrix components, thus playing a central role in cell migration. Integrin clustering at focal adhesions drives actin polymerization along the cell leading edge, resulting in polarity of cell movement. Therefore, small integrin-binding proteins such as the snake venom disintegrins that inhibit integrin-mediated cell adhesion are expected to inhibit cell migration. Here we review the current knowledge on disintegrin and disintegrin-like protein effects on cell migration and their potential use as pharmacological tools in anti-inflammatory therapy as well as in inhibition of metastatic invasion.

Acurhagin-C, an ECD disintegrin, inhibits integrin alphavbeta3-mediated human endothelial cell functions by inducing apoptosis via caspase-3 activation

BACKGROUND AND PURPOSE

Acurhagin, a member of versatile metalloproteinase disintegrins from Agkistrodon acutus venom, has been identified as a platelet aggregation inhibitor, previously. Here, acurhagin-C, the C-terminal Glu-Cys-Asp (ECD)-containing fragment of acurhagin, was evaluated for its biological activities and potential applications in anti-angiogenic therapy.

EXPERIMENTAL APPROACH

Human umbilical vein endothelial cells (HUVECs) were treated with acurhagin-C to assay effects on viability, apoptosis, adhesion, migration, invasion, proliferation and angiogenesis. The recognition site and signalling involved for the interactions of acurhagin-C with HUVEC were determined using flow cytometric, electrophoresis and immunoblotting analyses.

KEY RESULTS

Acurhagin-C decreased viability and induced apoptosis in HUVEC. It also dose-dependently inhibited HUVEC adhesion to immobilized extracellular matrices fibronectin, collagen I and vitronectin with respective IC(50) values of approximately 0.6, 0.3 and 0.1 microM. Acurhagin-C prevented migration and invasion of HUVEC through vitronectin- and Matrigel-coated barriers respectively. Furthermore, acurhagin-C attenuated fibroblast growth factor-2-primed angiogenesis both in vitro and in vivo, and specifically blocked the binding of anti-alphavbeta3 monoclonal antibody 23C6 to HUVEC in an ECD-dependent manner. However, purified alphavbeta3 also dose-dependently bound to immobilized acurhagin and acurhagin-C with a saturable pattern. Interference with integrin alphavbeta3-mediated functions and promotion of caspase-3 activation by acurhagin-C affected morphology of HUVEC and induced apoptosis.

CONCLUSIONS AND IMPLICATIONS

Acurhagin-C elicited endothelial anoikis via disruption of alphavbeta3/focal adhesion kinase/phosphatidylinositol 3-kinase/Akt survival cascade and subsequent initiation of the procaspase-3 apoptotic signalling pathway.

Angiopoietin-2 stimulation of endothelial cells induces alphavbeta3 integrin internalization and degradation

The angiopoietins (Ang-1 and Ang-2) have been identified as agonistic and antagonistic ligands of the endothelial receptor tyrosine kinase Tie2, respectively. Both ligands have been demonstrated to induce translocation of Tie2 to cell-cell junctions. However, only Ang-1 induces Tie2-dependent Akt activation and subsequent survival signaling and endothelial quiescence. Ang-2 interferes negatively with Ang-1/Tie2 signaling, thereby antagonizing the Ang-1/Tie2 axis. Here, we show that both Ang-1 and Ang-2 recruit beta3 integrins to Tie2. This co-localization is most prominent in cell-cell junctions. However, only Ang-2 stimulation resulted in complex formation among Tie2, alphavbeta3 integrin, and focal adhesion kinase as evidenced by co-immunoprecipitation experiments. Focal adhesion kinase was phosphorylated in the FAT domain at Ser(910) upon Ang-2 stimulation and the adaptor proteins p130Cas and talin dissociated from alphavbeta3 integrin. The alphavbeta3 integrin was internalized, ubiquitinylated, and gated toward lysosomes. Taken together, the experiments define Tie2/alphavbeta3 integrin association-induced integrin internalization and degradation as mechanistic consequences of endothelial Ang-2 stimulation.

MVL-PLA2, a snake venom phospholipase A2, inhibits angiogenesis through an increase in microtubule dynamics and disorganization of focal adhesions

Integrins are essential protagonists of the complex multi-step process of angiogenesis that has now become a major target for the development of anticancer therapies. We recently reported and characterized that MVL-PLA2, a novel phospholipase A2 from Macrovipera lebetina venom, exhibited anti-integrin activity. In this study, we show that MVL-PLA2 also displays potent anti-angiogenic properties. This phospholipase A2 inhibited adhesion and migration of human microvascular-endothelial cells (HMEC-1) in a dose-dependent manner without being cytotoxic. Using Matrigel and chick chorioallantoic membrane assays, we demonstrated that MVL-PLA2, as well as its catalytically inactivated form, significantly inhibited angiogenesis both in vitro and in vivo. We have also found that the actin cytoskeleton and the distribution of alphav beta3 integrin, a critical regulator of angiogenesis and a major component of focal adhesions, were disturbed after MVL-PLA2 treatment. In order to further investigate the mechanism of action of this protein on endothelial cells, we analyzed the dynamic instability behavior of microtubules in living endothelial cells. Interestingly, we showed that MVL-PLA2 significantly increased microtubule dynamicity in HMEC-1 cells by 40%. We propose that the enhancement of microtubule dynamics may explain the alterations in the formation of focal adhesions, leading to inhibition of cell adhesion and migration.

Arg-Gly-Asp (RGD) peptide conjugated poly(lactic acid)-poly(ethylene oxide) micelle for targeted drug delivery

In this study, a new poly(lactic acid)-poly (ethylene oxide)-Arg-Gly-Asp (PLA-PEO-RGD) derivative was synthesized, and paclitaxel-loaded PLA-PEO-RGD micelles were prepared by this derivative. The solubility assay showed that micelles mixed with Pluronic F-68 as surfactant could increase the solubility of this hydrophobic paclitaxel in aqueous solution. The cell-binding assay showed that PLA-PEO-RGD micelle (IC(50) = 11.13 +/- 1.38 nmol/L) had about 3.6-fold higher integrin avidity than PLA-PEO-RGD conjugates (IC(50) = 40.33 +/- 3.12 nmol/L). The avidity of micelle was also higher than RGD4C peptide (IC(50) = 24.44 +/- 1.21 nmol/L). The in vitro drug release profile of drug-loaded PLA-PEO-RGD micelles exhibited initial burst release to 37% +/- 2% (w/w) during the first 12 h, and then the release rate became steady in a controlled release manner. Furthermore, treatment of the MDA-MB-435 breast cancer cell line with paclitaxel-loaded PLA-PEO-RGD micelles yielded cytotoxicities, with EC(50) values of approximately 30 mumol/L. The paclitaxel-loaded PLA-PEO-RGD micelles treated group showed the most dramatic tumor reduction in MDA-MB-435 tumor-bearing nude mice, and the final mean tumor load was 31 +/- 16 mm(3) (mean +/- SD; n = 8). (125)I-labeled micelles administration resulted in significant (p < 0.001) higher tumor uptake (2.68% +/- 0.14%, ID/g) of PLA-PEO-RGD micelles compared to PLA-PEO micelles (0.84% +/- 0.09%, ID/g) after 2.5 h postinjection. Biodistribution study showed the best blood clearance of PLA-PEO-RGD micelles after 4.5 h postinjection. The results of this study suggest that paclitaxel-loaded PLA-PEO-RGD micelles based on the specific recognition of alpha(V)beta(3) integrin represent a potential and powerful target delivery technology.

Differences in binding of (99m)Tc-disintegrins to integrin alphavbeta3 on tumor and vascular cells

Disintegrins, which contain an Arg-Gly-Asp sequence in their binding domains are antagonists of integrins such as alphavbeta3. The purpose of this study was to compare a range of disintegrins with different integrin selectivities for their binding behavior in vitro to vascular endothelial cells bearing alphavbeta3 and to cultured tumor cells which express alphavbeta3.

METHODS

Five disintegrins (bitistatin, kistrin, flavoridin, VLO4 and echistatin) and a cyclic pentapeptide, c[RGDyK], were radiolabeled with (99m)Tc and tested for binding to cells in vitro.

RESULTS

(99m)Tc-Kistrin, flavoridin and VLO4 had the highest binding, (99m)Tc-echistatin had moderate binding, and (99m)Tc-bitistatin and (99m)Tc-c[RGDyK] had low binding to cells. The observed binding was attributed to alphavbeta3 to various extents: echistatin, bitistatin>kistrin>flavoridin>VLO4. Cancer cells internalized bound disintegrins after binding, but endothelial cells did not. After binding to endothelial cells, (99m)Tc-kistrin was not displaced by competing peptide or plasma proteins.

CONCLUSIONS

These data suggest that radiolabeled kistrin, flavoridin and VLO4 may have advantages over labeled bitistatin and small cyclic peptides for targeting alphavbeta3 in vivo. Since receptor-bound radioligand is not internalized by endothelial cells, disintegrins may provide an advantage for targeting alphavbeta3 on vasculature because they bind strongly to surface receptors and are not readily displaced.

Modulation of in vitro and in vivo angiogenesis by alternagin-C, a disintegrin-like protein from Bothrops alternatus snake venom and by a peptide derived from its sequence

We have previously demonstrated that alternagin-C (ALT-C), a disintegrin-like protein from the venom of the Brazilian snake Bothrops alternatus, induces human vascular endothelial cell (HUVEC) proliferation by up-regulating the expression of vascular endothelial growth factor (VEGF). Here, we show that ALT-C is also able to induce in vivo angiogenesis using the model of matrigel plug in nude mice. Fibroblast growth factor (FGF) alone or supplemented with ALT-C was mixed with melted matrigel and subcutaneously injected in nude mice. After two weeks, the matrigel plugs were removed and analyzed to verify endothelial cell migration and new vessel formation. ALT-C (1 and 10 ng) strongly induced endothelial cell migration as well as the formation of new vessels. However, in higher concentrations, ALT-C strongly inhibited angiogenesis. In low concentrations (1 and 10nM), ALT-C also up-regulates the expression of VEGF receptor 2 (VEGFR2, KDR) mostly after 48 h, but it did not affect VEGFR1 (Ftl-1) in HUVEC cells as demonstrated by real-time PCR analysis. However, in higher concentrations (100 nM) the expression of both receptors is down-regulated. A peptide derived from ALT-C primary structure also affects HUVEC proliferation in vitro and angiogenesis in vivo. In conclusion, the present study shows for the first time the in vivo angiogenesis induced by a disintegrin-like molecule and the modulation of VEGFRs as well.

Alpha v integrins mediate beta-amyloid induced inhibition of long-term potentiation

Beta-amyloid (Abeta) is the principal component of the extracellular plaques present in patients with Alzheimer's disease. Several studies have recently shown that acutely applied Abeta inhibits the induction of LTP in the hippocampus. In the present studies, we have investigated the role of integrins in such Abeta-mediated block of LTP in the dentate gyrus in vitro and in the CA1 in vivo. Selective antibodies to the alpha v integrin subunit were found to prevent the Abeta inhibition of LTP, both in the dentate gyrus in vitro and in the CA1 in vivo. In contrast, two control antibodies did not prevent such action of Abeta. In addition, a small molecule nonpeptide antagonist of alpha v-containing integrins and two other antagonistic ligands of integrins, superfibronectin and the disintegrin echistatin, also prevented the Abeta inhibition of LTP. These studies indicate that alpha v integrins may be important mediators of synaptic dysfunction prior to neurodegeneration in Alzheimer's disease.

RGD-peptide presents anti-adhesive effect, but not direct pro-apoptotic effect on endothelial progenitor cells

Circulating endothelial progenitor cells (EPCs) contribute to neovascularization in tumor or ischemic tissues by multi-step events, including adhesion, migration, chemoattraction, and differentiation to endothelial cells. Anti-angiogenic RGD-peptides have been shown to directly induce apoptosis in human umbilical vein endothelial cells (HUVECs) and T cells. Here, we examined the effects of RGD-peptides on EPCs in terms of adhesive differentiation and apoptosis. When mononuclear cells (MNCs) isolated from human cord blood were cultured on fibronectin-coated plates for 7 days, RGD-peptide treatment decreased dose-dependently the number of adherent cells double positive for DiI-ac-LDL uptake and UEA-1 binding. The cells treated with RGD peptide were also stained less strongly by vWF or KDR antibody by immunofluorescence staining. Immobilization of the RGD-peptide promoted cell adhesion, but resulted in a deficiency in the development of ability of ac-LDL uptake and UEA-1 binding, showing an antagonistic effect. Accordingly, ex vivo-cultivated EPCs expressed integrin alpha5, alphav, beta1, beta3, and beta5, and antibodies to integrins alpha5, alphav, and beta1 decreased the number of adherent cells. However, viability of total MNCs containing early EPCs was not affected by RGD-peptide. In addition, neither an increase in apoptotic cell death nor a direct activation of caspase-3 by RGD-peptide was detected in ex vivo-cultivated EPCs, unlike in HUVECs. Interestingly, RGD-peptide rather enhanced Bcl-2 expression in ex vivo-cultivated EPCs and the EPCs themselves with a high Bcl-2/Bax ratio are comparatively resistant to apoptosis. Therefore, these results suggest that RGD-peptides may inhibit EPC differentiation by anti-adhesive effect, but not by a direct pro-apoptotic effect.

An improved method of 18F peptide labeling: hydrazone formation with HYNIC-conjugated c(RGDyK)

Radiolabeled alpha(v)beta(3)-integrin antagonists are increasingly investigated as a means of imaging angiogenesis. Several methods of labeling alpha(v)beta(3)-integrin binding peptide with (18)F have been reported recently. In the present study, we devised a straightforward means for labeling Arg-Gly-Asp (RGD) peptide with (18)F via hydrazone formation between c(RGDyK)-hydrazinonicotinic acid (HYNIC) (3) and 4-[(18)F]-fluorobenzaldehyde ([(18)F]4). The resulting reaction mixture was purified by HPLC to give 4'-[(18)F]-fluorobenzylidenehydrazone-6-nicotinamide-c(RGDyK) ([(18)F]5). The conjugation efficiency of 3 and 4 to form [(18)F]5 was 95.2%, and the radiochemical purity of [(18)F]5 after purification was >99%. The specific activity of [(18)F]5 estimated by radio-HPLC was 20.5 GBq/mumol (end of synthesis). Competitive binding assay of c(RGDyK) (1) and 5 was performed using [(125)I]iodo-c(RGDyK) as a radioligand, and K(i) values were found to be 2.8 and 21.7 nM, respectively. For the biodistribution study, the angiogenic mouse model was established by inducing unilateral ischemia on the left hindlimbs of ICR mice after femoral artery ablation. Seven days after inducing ischemia, [(18)F]5 was administered to the mice through the tail vein. Ischemic muscle uptake of [(18)F]5 was significantly higher than that of normal muscle (P<.01). Specific uptake was confirmed by coinjection of 1 with [(18)F]5. Here, we successfully labeled RGD peptide with (18)F via hydrazone formation between 3 and 4, resulting to [(18)F]5. [(18)F]5 was found to have high affinity for alpha(v)beta(3)-integrin and to accumulate specifically in ischemic hindlimb muscle of mice. We suggest that (18)F labeling via formation of hydrazone between HYNIC peptide and [(18)F]4 is a useful method for labeling c(RGDyK), which can be applied for imaging angiogenesis.

Snake venom metalloproteases--structure and function of catalytic and disintegrin domains

Snake venoms are relevant sources of toxins that have evolved towards the engineering of highly active compounds. In the last years, research efforts have produced great advance in their understanding and uses. Metalloproteases with disintegrin domains are among the most abundant toxins in many Viperidae snake venoms. This review will focus on the structure, function and possible applications of the metalloprotease and disintegrin domains.

Lebestatin, a disintegrin from Macrovipera venom, inhibits integrin-mediated cell adhesion, migration and angiogenesis

Lebestatin, a new member of the lysine-threonine-serine (KTS)-disintegrin family, was purified to homogeneity from Tunisian snake (Macrovipera lebetina) venom. It is a single-chain polypeptide composed of 41 amino acids. The amino-acid sequence of lebestatin shows that it displays a pattern of cysteines similar to other short disintegrins, but contains the sequence KTS rather than RGD in its integrin-binding loop. Lebestatin presents a high homology with obtustatin and viperistatin. Lebestatin interacts specifically with the alpha1beta1 integrin. It was thus able to inhibit both adhesion and migration of PC12 and alpha1beta1 integrin-expressing CHO cells (CHO-alpha1) to type I and IV collagens. This disintegrin also affected adhesion and migration of endothelial cells and exhibited an anti-angiogenic effect in vivo when using the 8-day-old embryo chick chorioallantoic membrane model.

Disintegrins: integrin selective ligands which activate integrin-coupled signaling and modulate leukocyte functions

Extracellular matrix proteins and cell adhesion receptors (integrins) play essential roles in the regulation of cell adhesion and migration. Interactions of integrins with the extracellular matrix proteins lead to phosphorylation of several intracellular proteins such as focal adhesion kinase, activating different signaling pathways responsible for the regulation of a variety of cell functions, including cytoskeleton mobilization. Once leukocytes are guided to sites of infection, inflammation, or antigen presentation, integrins can participate in the initiation, maintenance, or termination of the immune and inflammatory responses. The modulation of neutrophil activation through integrin-mediated pathways is important in the homeostatic control of the resolution of inflammatory states. In addition, during recirculation, T lymphocyte movement through distinct microenvironments is mediated by integrins, which are critical for cell cycle, differentiation and gene expression. Disintegrins are a family of low-molecular weight, cysteine-rich peptides first identified in snake venom, usually containing an RGD (Arg-Gly-Asp) motif, which confers the ability to selectively bind to integrins, inhibiting integrin-related functions in different cell systems. In this review we show that, depending on the cell type and the microenvironment, disintegrins are able to antagonize the effects of integrins or to act agonistically by activating integrin-mediated signaling. Disintegrins have proven useful as tools to improve the understanding of the molecular events regulated by integrin signaling in leukocytes and prototypes in order to design therapies able to interfere with integrin-mediated effects.

Alphavbeta5-integrins mediate early steps of metastasis formation

Tumour cell adhesion within the microvasculature of host organs, its stabilisation and cell invasion into the host organs, appear to be important steps in the formation of distant metastases. Intravital fluorescence-video microscopy was used to investigate the early steps in metastasis formation of colon carcinoma cells within the liver, which is the main target organ of colorectal carcinomas. The involvement of alphav-integrins was analysed in vivo using HT-29 cells after treatment with different function-blocking antibodies [pan-alphav (n=9 animals), specific alphavbeta3 (n=8 animals) and alphavbeta5 (n=8 animals)] or linear Arg-Gly-Asp (RGD)-containing peptides (RGD-peptides) (n=6 animals). Treatment with anti-alphav and anti-alphavbeta5 antibodies resulted in significantly (P<0.001) decreased tumour cell adhesion in vivo within the hepatic microvasculature. Cells treated with anti-alphavbeta3 antibodies or unspecific immunoglobulin-G (IgG) did not show significant changes in their adhesive properties. Furthermore, inhibition of cell adhesion was achieved by linear RGD-peptides in a dose-dependent manner. Relative numbers of migrated cells were not affected by any of the treatments. These results suggest that alphav-integrins, especially alphavbeta5, can influence the ability of circulating tumour cells to adhere within the hepatic microvessels. In contrast, migration of adherent cells into the liver parenchyma was not affected by alphav-integrin inhibition. Our findings support the hypothesis that specific interactions between circulating tumour cells and host organs are required for organ-specific tumour cell arrest.

Jararhagin, a snake venom metalloproteinase-disintegrin, stimulates epithelial cell migration in an in vitro restitution model

The snake venom metalloproteinase-disintegrin jararhagin (JG) has no chemotactic activity but stimulates the migration of neutrophils in vivo through a mechanism still unclear. In this study we investigated the effects of jararhagin on epithelial cell adhesion and migration in vitro. F-actin arrangement and the distribution of laminin, fibronectin, several integrins and phosphorylated Focal Adhesion Kinase (FAK) were studied using rhodamine-phalloidin and immunofluorescence. Maximum stimulation of migration (about 100%) was obtained with 5 microg/ml JG, with about 38% inhibition of cellular adhesion. In migratory cells the toxin stimulated the formation of filopodia, lamellipodia and stress fibers. The pericellular fibronectin matrix was lost in migrating cells, while laminin was less affected. The toxin stimulated FAK phosphorylation and the recruitment of alphav-containing integrins to focal contacts, whereas integrins containing the alpha2 subunit were reduced in these junctions. Inactivation of the toxin with 1,10 phenanthroline showed that the catalytic activity is important for the effect of jararhagin on cell migration, FAK phosphorylation and for the recruitment of alphav, but not as much for the anti-adhesive effect. In conclusion, jararhagin stimulates the migration of epithelial cells in vitro through a mechanism that involves its proteolytic activity, qualitative changes in cellular adhesion and the formation of actin-rich cellular processes.

The involvement of integrin αvβ3 in polymorphonuclear leukocyte-induced angiogenesis in bovine aortic endothelial cells

We have previously reported that angiogenesis stimulated by adhesion of polymorphonuclear leukocytes (PMNs) to endothelial cells (ECs) via intercellular adhesion molecule-1 (ICAM-1) might be mediated by a transcription factor, ets-1, which regulates adhesion molecules such as integrins related to angiogenesis. However, the regulation mechanisms of PMN-induced angiogenesis mediated by ICAM-1 remain unclear. Therefore, we investigated the effects of PMN on EC attachment to the extracellular matrix (ECM), which is one of the critical elements for angiogenesis development. After the addition of PMNs, attachment of bovine aortic endothelial cells (BAECs) to vitronectin, which is known as a ligand for integrin alpha(v)beta(3), increased greatly. Stimulation of BAEC with PMN induced expressions of integrin beta(3) mRNA and protein. PMN-induced angiogenesis was inhibited by Arg-Gly-Asp (RGD) peptide and LM609 anti-alpha(v)beta(3) antibody. The PMN-induced BAEC attachment to vitronectin was inhibited by ets-1 antisense oligonucleotide and anti-ICAM-1 antibody. These results suggested that enhancement of EC attachment to ECM via integrin alpha(v)beta(3) participated in the development of PMN-induced angiogenesis. Furthermore, the increase in EC attachment to ECM by ligation of PMN to ICAM-1 might be regulated by Ets-1 expression.

RGDS peptide induces caspase 8 and caspase 9 activation in human endothelial cells

Peptides containing the Arg-Gly-Asp (RGD) motif inhibit cell adhesion and exhibit a variety of other biologic effects including anticoagulant and antimetastatic activities. The aim of the present study was to examine the anchorage-independent effects of an RGD-containing peptide, Arg-Gly-Asp-Ser (RGDS), on human umbilical vein endothelial cells (HUVECs). Assays were performed on HUVECs seeded onto collagen IV; under these experimental conditions RGDS did not exert antiadhesive effects but significantly reduced FGF-2-dependent chemotaxis after 4 hours of treatment and reduced proliferation after 24 hours of treatment. Experiments carried out with caspase-specific inhibitors indicated that the observed antichemotactic effects required caspase 8 and caspase 9 activation. RGDS activated both caspase 8 and caspase 9 after 4 hours of treatment and caspase 3 after 24 hours of treatment, and markedly enhanced HUVEC apoptosis by transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL)/Hoechst staining and fluorescence-activated cell sorting (FACS) analysis. Finally, confocal microscopy showed that RGDS localizes in the cytoplasm of live HUVECs within 4 hours and in vitro experiments showed that RGDS directly interacts with recombinant caspases 8 and 9 in a specific way. In summary, these results indicate that RGDS directly binds and activates caspases 8 and 9, inhibits chemotaxis, and induces apoptosis of HUVECs with a mechanism independent from its antiadhesive effect.

Alternagin-C, a Disintegrin-like Protein, Induces Vascular Endothelial Cell Growth Factor (VEGF) Expression and Endothelial Cell Proliferation in Vitro

Alternagin-C (ALT-C), a disintegrin-like protein purified from the venom of the Brazilian snake Bothrops alternatus, interacts with the major collagen I receptor, the alpha(2)beta(1) integrin, inhibiting collagen binding. Here we show that ALT-C also inhibits the adhesion of a mouse fibroblast cell line (NIH-3T3) to collagen I (IC(50) 2.2 microm). In addition, when immobilized on plate wells, ALT-C supports the adhesion of this cell line as well as of human vein endothelial cell (HUVEC). ALT-C (3 microm) does not detach cells that were previously bound to collagen I. ALT-C (5 nm) induces HUVEC proliferation in vitro, and it inhibits the positive effect of vascular endothelial growth factor (VEGF) or FGF-2 on the proliferation of these cells, thus suggesting a common mechanism for these proteins. Gene expression analysis of human fibroblasts growing on ALT-C- or collagen-coated plates showed that ALT-C and collagen I induce a very similar pattern of gene expression. When compared with cells growing on plastic only, ALT-C up-regulates the expression of 45 genes including the VEGF gene and down-regulates the expression of 30 genes. Fibroblast VEGF expression was confirmed by RT-PCR and ELISA assay. Up-regulation of the VEGF gene and other growth factors could explain the positive effect on HUVEC proliferation. ALT-C also strongly activates Akt/PKB phosphorylation, a signaling event involved in endothelial survival and angiogenesis. In conclusion, ALT-C acts as a survival factor, promoting adhesion and endothelial cell proliferation.

Inhibition of angiogenesis as a therapeutic strategy against brain tumors

Multidisciplinary treatment strategies for patients with malignant brain tumors have resulted in only small gains in terms of prognosis in spite of the use of aggressive therapy. There is a growing realization that a paradigm shift is needed in the conceptual approaches to glioma therapy. Such approaches will rely on identification and modification of key cellular targets that define the biological behavior of these tumors. Among the targets for such treatment approaches, tumor angiogenesis has captured the attention of not only the medical field but also of the lay public because of its conceptual departure from traditional methods of cancer therapy. Angiogenesis and vascular proliferation are particularly important in the growth and progression of malignant gliomas and are used as indicators of the degree of malignancy. Recent studies have helped us gain a better understanding of the molecular mediators of this process. It is now evident that after the initial formation of malignancy the continued growth of a glioma is critically dependent on its angiogenic potential. Hence, several approaches to control angiogenesis are being developed and tested. Preliminary results from clinical studies have shown that angiogenesis inhibition is a valid approach as a therapeutic strategy against gliomas but it is also becoming evident that inhibition of individual modulators of this process may not yield the expected impact on prognosis. To fully realize the potential of antiangiogenic therapy, a deeper understanding of the interplay between the tumor vasculature and its environment is needed. Angiogenesis inhibitors have made the transition from preclinical studies to the clinical arena; it remains for ongoing human trials of such agents to fully explore the feasibility and efficacy of these agents in order to exploit the potential of this approach.

A new protein structure of P-II class snake venom metalloproteinases: it comprises metalloproteinase and disintegrin domains

A new metalloproteinase-disintegrin, named Jerdonitin, was purified from Trimeresurus jerdonii venom with a molecular weight of 36 kDa on SDS-PAGE. It dose-dependently inhibited ADP-induced human platelet aggregation with IC(50) of 120nM. cDNA cloning and sequencing revealed that Jerdonitin belonged to the class II of snake venom metalloproteinases (SVMPs) (P-II class). Different from other P-II class SVMPs, metalloproteinase and disintegrin domains of its natural protein were not separated, confirmed by internal peptide sequencing. Compared to other P-II class SVMPs, Jerdonitin has two additional cysteines (Cys219 and Cys238) located in the spacer domain and disintegrin domain, respectively. They probably form a disulfide bond and therefore the metalloproteinase and disintegrin domains cannot be separated by posttranslationally processing. In summary, comparison of the amino acid sequences of Jerdonitin with those of other P-II class SVMPs by sequence alignment and phylogenetic analysis, in conjunction with natural protein structure data, suggested that it was a new type of P-II class SVMPs.

Alpha(v)beta3 and alpha(v)beta5 integrins bind both the proximal RGD site and non-RGD motifs within noncollagenous (NC1) domain of the alpha3 chain of type IV collagen: implication for the mechanism of endothelia cell adhesion

The NC1 domains of human type IV collagen, in particular alpha3NC1, are inhibitors of angiogenesis and tumor growth (Petitclerc, E., Boutaud, A., Prestayko, A., Xu, J., Sado, Y., Ninomiya, Y., Sarras, M. P., Jr., Hudson, B. G., and Brooks, P. C. (2000) J. Biol. Chem. 275, 8051-8061). The recombinant alpha3NC1 domain contained a RGD site as part of a short collagenous sequence at the N terminus, designated herein as RGD-alpha3NC1. Others, using synthetic peptides, have concluded that this RGD site is nonfunctional in cell adhesion, and therefore, the anti-angiogenic activity is attributed exclusively to alpha(v)beta(3) integrin interactions with non-RGD motifs of the RGD-alpha3NC1 domain (Maeshima, Y., Colorado, P. C., and Kalluri, R. (2000) J. Biol. Chem. 275, 23745-23750). This nonfunctionality is surprising given that RGD is a binding site for alpha(v)beta(3) integrin in several proteins. In the present study, we used the alpha3NC1 domain with or without the RGD site, expressed in HEK 293 cells for native conformation, as an alternative approach to synthetic peptides to assess the functionality of the RGD site and non-RGD motifs. Our results demonstrate a predominant role of the RGD site for endothelial adhesion and for binding of alpha(v)beta(3) and alpha(v)beta(5) integrins. Moreover, we demonstrate that the two non-RGD peptides, previously identified as the alpha(v)beta(3) integrin-binding sites of the alpha3NC1 domain, are 10-fold less potent in competing for integrin binding than the native protein, indicating the importance of additional structural and/or conformational features of the alpha3NC1 domain for integrin binding. Therefore, the RGD site, in addition to non-RGD motifs, may contribute to the mechanisms of endothelial cell adhesion in the human vasculature and the anti-angiogenic activity of the RGD-alpha3NC1 domain.

In vitro and in vivo evaluations of THAM derived telomers bearing RGD and Ara-C for tumour neovasculature targeting

As an approach to the development of specific drug delivery systems, a new class of low macromolecular carriers called 'telomers' endowed with an antitumour agent, such as arabinofuranosylcytosine (Ara-C), RGDSK peptidic sequences, as tumour targeting moieties, and tyrosine groups labelled with 125I atoms allowing the in vivo scintigraphic follow up, were synthesized. Their tumour targeting ability was assessed in vivo in mice bearing a murine B16 melanoma. The biological results showed that the presence of RGDSK sequences onto the macromolecules leads to the selective targeting and the accumulation of telomers within the vascularized zone of the tumour. Moreover, such compounds exhibited in vitro a better IC(50) (0.015 muM) than pure Ara-C and in vivo an oncostatic index higher than 160%.

Inhibition of tumor progression and neoangiogenesis using cyclic RGD-peptides in a chemically induced colon carcinoma in rats

Integrins are cell surface molecules that mediate cell adhesion, but are also important regulators of tumor cell interactions with their microenvironment, tumor cell survival and growth. In addition, the alpha(v)beta3-integrins appear to be critical for microvessel formation in tumor-induced neoangiogenesis. The present study is the first to investigate the effects of therapeutic alpha(v)beta3-integrin inhibition in a chemically induced tumor model that largely resembles human colon carcinomas. Tumor induction was performed in 47 male Sprague-Dawley rats using 1,2 dimethylhydrazin (21 mg/kg) twice a week. After 20 weeks of tumor induction, 100% of the animals developed adenocarcinomas with a median of 13.5 macroscopic tumor nodules (range 12-17), but no distant metastases. During further tumor induction for an additional 10 weeks, rats were treated three times/week with (a) 15 mg/kg RGDfV-peptide that can block vitronectin and fibronectin receptors; (b) an equimolar amount of an ineffective cyclic control peptide; or (c) with equimolar amounts of a linear RGDS-peptide. At the end of this treatment period, rats were sacrificed, and tumor load was quantified macroscopically and confirmed by histological examination. For investigation of the involvement of tumor-induced neoangiogenesis microvessel, density was determined using CD31-immunostaining. After 30 weeks, control animals (group B) had 5-18 tumors (median 14.5). If rats were treated with RGDfV-peptide (group A), the number of tumor nodules was significantly reduced (P < 0.005) to a median of seven macroscopic tumors (range 2-10 tumors), which also represented a significant reduction (P < 0.005) compared with prior to treatment. Application of noncylic RGDS-peptides (group C) did not affect the number of tumor nodules (median 18; range 10-30 tumors). The diameters of tumor nodules were comparable (3.2-6.1 mm) in animals of all groups. In addition, microvessel density was significantly (P < 0.05) reduced in tumors in group A compared to control rats. The major side effect in the treatment group was increased susceptibility to respiratory infections. Our results demonstrate that alpha(v)beta3-integrin-receptor inhibition appears to be a therapeutic strategy for colorectal cancer. In our therapeutic model, late onset of treatment with integrin-blocking peptides resulted in an inhibition of tumor growth and a reduced tumor load which appeared to be mediated, at least in part, by inhibition of neoangiogenesis.

Chlorotoxin inhibits glioma cell invasion via matrix metalloproteinase-2

Primary brain tumors (gliomas) have the unusual ability to diffusely infiltrate the normal brain thereby evading surgical treatment. Chlorotoxin is a scorpion toxin that specifically binds to the surface of glioma cells and impairs their ability to invade. Using a recombinant His-Cltx we isolated and identified the principal Cltx receptor on the surface of glioma cells as matrix metalloproteinase-2 (MMP-2). MMP-2 is specifically up-regulated in gliomas and related cancers, but is not normally expressed in brain. We demonstrate that Cltx specifically and selectively interacts with MMP-2 isoforms, but not with MMP-1, -3, and -9, which are also expressed in malignant glioma cells. Importantly, we show that the anti-invasive effect of Cltx on glioma cells can be explained by its interactions with MMP-2. Cltx exerts a dual effect on MMP-2: it inhibits the enzymatic activity of MMP-2 and causes a reduction in the surface expression of MMP-2. These findings suggest that Cltx is a specific MMP-2 inhibitor with significant therapeutic potential for gliomas and other diseases that invoke the activity of MMP-2.

Contortrostatin, a homodimeric disintegrin, actively disrupts focal adhesion and cytoskeletal structure and inhibits cell motility through a novel mechanism

Integrins play a major role in the regulation of cell motility. They physically link the extracellular environment to the cytoskeleton and participate in large protein complexes known as focal adhesions. In this report, it is demonstrated that treatment of tumor cells with the homodimeric disintegrin contortrostatin induces integrin-mediated tyrosine phosphorylation events and causes severe disruptions in the actin cytoskeleton and disassembly of focal adhesion structures without affecting cellular adhesion to a reconstituted basement membrane. Included in this disruption is the tyrosine phosphorylation and altered subcellular localization of FAK. Through use of transfected 293 cells with specific integrin expression profiles and anti-alphavbeta3 mAbs, we demonstrate that these events are mediated exclusively by the alphavbeta3 integrin and are likely the result of contortrostatin-mediated crosslinking of this receptor at the cell surface, since monovalent disintegrins, flavoridin or echistatin do not induce such effects. Further, it is shown that contortrostatin potently inhibits motility in cells expressing the alphavbeta33 integrin. The results of this study describe a novel integrin-mediated mechanism by which cell motility can be inhibited and suggest an alternative approach to therapeutic intervention for cancer invasion and metastasis.

Inhibitory effects of salmosin, a disintegrin, on posterior capsular opacification in vitro and in vivo

The proliferation, migration and transdifferentiation of the remaining lens epithelial cells (LECs) after cataract surgery are a major cause of posterior capsular opacification (PCO). It has previously been reported that salmosin, a novel disintegrin, significantly inhibits solid tumor growth in mice by perturbation of tumor-specific angiogenesis via blocking alpha v beta 3 integrin expressed on vascular endothelial cells. In this study, the inhibitory function of salmosin in PCO was investigated and was found that salmosin inhibits the attachment of bovine LECs and rabbit lens cells (N/N1003A) to extracellular matrix-coated plates. The anti-adhesive activity of salmosin was approximately 1000 times higher than that of synthetic Arg-Gly-Asp peptide. In addition, the cell proliferation and migration of bovine LECs and N/N1003A were strongly inhibited by salmosin, whereas the proliferation of corneal endothelial cells was less affected. LEC migration and proliferation were also decreased by salmosin treatment in rabbit eyes without any toxic effect in the cornea, iris and retina. In this study, salmosin was shown to specifically inhibit LEC migration and proliferation in an animal model. Therefore, the authors suggest that further investigation may show salmosin to be a good candidate for inhibiting PCO development.