Contortrostatin activates ERK2 and tyrosine phosphorylation events via distinct pathways

Synthetic D-amino acid peptide inhibits tumor cell motility on laminin-5

Cell motility is partially dependent on interactions between the integrins and the extracellular matrix. Our previous studies have identified synthetic D-amino acid cell adhesion peptides using a combinatorial screening approach. In this study, we demonstrate that HYD1 (kikmviswkg) completely blocks random haptotactic migration and inhibits invasion of prostate carcinoma cells on laminin-5. This effect is adhesion independent and reversible. The inhibition of migration by HYD1 involves a dramatic remodeling of the actin cytoskeleton resulting in increased stress fiber formation and actin colocalization with cortactin at the cell membrane. HYD1 interacts with alpha6beta1 (not alpha6beta4) and alpha3beta1 integrins and surprisingly elevates laminin-5-dependent intracellular signals including focal adhesion kinase, mitogen-activated protein kinase kinase and extracellular signal-regulated kinase. HYD1 does not contain a previously characterized binding sequence for integrins. A scrambled derivative of HYD1, called HYDS (wiksmkivkg), does not interact with the alpha6 or alpha3 integrin subunits and is not biologically active. Taken together, these results indicate that HYD1 is a biologically active integrin-targeting peptide that reversibly inhibits tumor cell migration on laminin-5 and uncouples phosphotyrosine signaling from cytoskeletal-dependent migration.

Intravenous liposomal delivery of the snake venom disintegrin contortrostatin limits breast cancer progression

Despite significant research in this area, metastatic breast cancer remains a disease with a poor prognosis. Until an effective therapy is developed, it is imperative that new treatment modalities be investigated. In this report, we describe an effective method for delivery of a novel snake venom disintegrin, contortrostatin (CN), in an orthotopic, xenograft model of human mammary cancer in immunodeficient mice. CN (Mr 13,500) is a homodimeric disintegrin isolated from venom of the Southern Copperhead snake. The homodimer possesses two Arg-Gly-Asp sites, which modulate its interaction with integrins on tumor cells and angiogenic vascular endothelial cells. Although our laboratory has previously described the antitumor activity of CN in a mouse model of human mammary cancer, the method of delivery, daily intratumor injection, was not translatable to clinical application. We now describe a clinically relevant method of administering CN, liposomal delivery (LCN). A unique liposomal system has been designed for i.v. administration of a biologically active protein with full retention of biological activity. Pharmacokinetics, biodistribution, platelet reactivity, and immunogenicity of LCN were determined and compared with similar characteristics of native, unencapsulated CN. There are several advantages to liposomal delivery of CN: (1) LCN has a significantly prolonged circulatory half-life compared with native CN; (2) LCN is passively accumulated in the tumor; (3) LCN has no platelet reactivity; and (4) LCN is not recognized by the immune system. Finally, antiangiogenic activity is an important component of CN's mechanism of antitumor action. We have demonstrated that i.v. delivery of LCN leads to potent antiangiogenic activity in the orthotopic, xenograft human mammary tumor model.

Alternagin-C, a nonRGD-disintegrin, induces neutrophil migration via integrin signaling

Recently, a new protein containing a disintegrin domain, alternagin-C (Alt-C), was purified from Bothrops alternatus venom. Unlike other disintegrins, in Alt-C an ECD amino acid mogif takes the place of the RGD sequence. Most disintegrins contain an RGD/KGD sequence and are very potent inhibitors of platelet aggregation, as well as other cell interactions with the extracellular matrix, including tumor cell metastasis and angiogenesis. The present study investigated the effects of Alt-C on human neutrophil chemotaxis in vitro and the activation of integrin-mediated pathways. Alt-C showed a potent chemotactic effect for human neutrophils when compared to N-formyl-methionyl-leucyl-phenylalanine peptide (fMLP), a classic chemotactic agent. Moreover, preincubation of neutrophils with Alt-C significantly inhibited chemotaxis toward fMLP and itself. In addition, a peptide containing an ECD sequence presented a chemotactic activity and significantly inhibited chemotaxis induced by Alt-C and fMLP. A significant increase of F-actin content was observed in cells treated with Alt-C, showing that the chemotactic activity of Alt-C on neutrophils is driven by actin cytoskeleton dynamic changes. Furthermore, this protein was able to induce an increase of phosphotyrosine content triggering focal adhesion kinase activation and its association with phosphatidylinositol 3-kinase. Alt-C was also able to induce a significant increase in extracellular signal-regulated kinase 2 nuclear translocation. The chemotactic activity of Alt-C was partially inhibited by LY294002, a specific phosphatidylinositol 3-kinase inhibitor, and by PD98056, a Map kinase kinase inhibitor. These findings suggest that Alt-C can trigger human neutrophil chemotaxis modulated by intracellular signals characteristic of integrin-activated pathways and that these effects could be related to the ECD mogif present in disintegrin-like domain.

Integrin alphavbeta3, requirement for VEGFR2-mediated activation of SAPK2/p38 and for Hsp90-dependent phosphorylation of focal adhesion kinase in endothelial cells activated by VEGF

Endothelial cell migration, a key process in angiogenesis, requires the coordinated integration of motogenic signals elicited by the adhesion of endothelial cells to extracellular matrices and by angiogenic cytokines such as the vascular endothelial growth factor (VEGF). In this study, we found that addition of VEGF to human umbilical vein endothelial cells cultivated on vitronectin triggers a synergistic interaction between the VEGF receptor VEGFR2 and the clustered integrin receptor alphavbeta3. The interaction between VEGFR2 and alphavbeta3 is required for full phosphorylation of VEGFR2 and to drive the activation of motogenic pathways involving focal adhesion kinase (FAK) and stress-activated protein kinase-2/p38 (SAPK2/p38). The signal emanating from the VEGFR2 and alphavbeta3 interaction and leading to SAPK2/p38 activation proceeds directly from VEGFR2. The chaperone Hsp90 is found in a complex that coprecipitates with inactivated VEGFR2, and the association is increased by VEGF and decreased by geldanamycin, a specific inhibitor of Hsp90-mediated events. Geldanamycin also impairs the phosphorylation of FAK that results from the interaction between VEGFR2 and alphavbeta3, and this is accompanied by an inhibition of the recruitment of vinculin to VEGFR2. We conclude that a necessary cross talk should occur between VEGFR2 and the integrin alphavbeta3, to transduce the VEGF signals to SAPK2/p38 and FAK and that Hsp90 is instrumental in the building up of focal adhesions by allowing the phosphorylation of FAK and the recruitment of vinculin to VEGFR2.