Characterization of platelet aggregation induced by human breast carcinoma and its inhibition by snake venom peptides, trigramin and rhodostomin

Platelets in cancer metastasis: To help the "villain" to do evil

Cancer progress is accompanied by platelet activation and thrombotic complications. Platelets are a dangerous alliance of cancer cells, and are a close engager in multiple processes of cancer metastasis. Platelet adhesion to cancer cells forms a protective cloak that helps cancer cells to escape immune surveillance and natural killer cell-mediated cytolysis. Platelets facilitate tethering and arrest of disseminated cancer cells in the vasculature, enhance invasive potentials and thus extravasation of cancer cells. Moreover, platelets recruit monocytes and granulocytes to the sites of cancer cell arrest, and collaborate with them to establish a pro-metastatic microenvironment and metastatic niches. Platelets also secret a number of growth factors to stimulate cancer cell proliferation, release various angiogenic regulators to regulate tumor angiogenesis and subsequently promote cancer growth and progress. Albeit platelets are helping the "villain" cancer to do evil, the close engagements of platelets in cancer metastasis and progress can be used as the intervention targets for new anti-cancer therapeutic developments. Platelet-targeted anti-cancer strategy may bring in novel anti-cancer treatments that can synergize the therapeutic effects of chemotherapies and surgical treatments of cancer.

The mojastin mutant Moj-DM induces apoptosis of the human melanoma SK-Mel-28, but not the mutant Moj-NN nor the non-mutated recombinant Moj-WN

In this study, three recombinant mojastin peptides (Moj-WN, Moj-NN, and Moj-DM) were produced and compared functionally. Recombinant Moj peptides were purified as GST-fusions. GST-Moj-WN and GST-Moj-NN inhibited ADP-induced platelet aggregation in platelet rich plasma. The GST-Moj-WN had an IC(50) of 160nM, while the GST-Moj-NN had an IC(50) of 493nM. The GST-Moj-DM did not inhibit platelet aggregation. All three GST-Moj peptides inhibited SK-Mel-28 cell adhesion to fibronectin. The GST-Moj-WN inhibited the binding of SK-Mel-28 cells to fibronectin with an IC(50) of 11nM, followed by the GST-Moj-NN (IC(50) of 28nM), and the GST-Moj-DM (IC(50) of 46nM). The GST-Moj peptides' ability to induce apoptosis on SK-Mel-28 cells was determined using Annexin-V-FITC and nuclear fragmentation assays. Cells were incubated with 5muM GST-Moj peptides for 24h. At 5microM GST-Moj-DM peptide, 13.56%+/-2.08 of treated SK-Mel-28 cells were in early apoptosis. The GST-Moj-DM peptide also caused nuclear fragmentation as determined by fluorescent microscopy and Hoechst staining. The GST-Moj-WN and GST-Moj-NN peptides failed to induce apoptosis. We characterized the SK-Mel-28 integrin expression, as the first step in determining r-Moj binding specificity. Our results indicate that SK-Mel-28 cells express alphavbeta3, alphav, alpha6, beta1, and beta3 integrin receptors.

Review of Growth Inhibitory Peptide as a biotherapeutic agent for tumor growth, adhesion, and metastasis

This review surveys the biological activities of an alpha-fetoprotein (AFP) derived peptide termed the Growth Inhibitory Peptide (GIP), which is a synthetic 34 amino acid segment produced from the full length 590 amino acid AFP molecule. The GIP has been shown to be growth-suppressive in both fetal and tumor cells but not in adult terminally-differentiated cells. The mechanism of action of this peptide has not been fully elucidated; however, GIP is highly interactive at the plasma membrane surface in cellular events such as endocytosis, cell contact inhibition and cytoskeleton-induced cell shape changes. The GIP was shown to be growth-suppressive in nine human tumor types and to suppress the spread of tumor infiltrates and metastases in human and mouse mammary cancers. The AFP-derived peptide and its subfragments were also shown to inhibit tumor cell adhesion to extracellular matrix (ECM) proteins and to block platelet aggregation; thus it was expected that the GIP would inhibit cell spreading/migration and metastatic infiltration into host tissues such as lung and pancreas. It was further found that the cyclic versus linear configuration of GIP determined its biological and anti-cancer efficacy. Genbank amino acid sequence identities with a variety of integrin alpha/beta chain proteins supported the GIP's linkage to inhibition of tumor cell adhesion and platelet aggregation. The combined properties of tumor growth suppression, prevention of tumor cell-to-ECM adhesion, and inhibition of platelet aggregation indicate that tumor-to-platelet interactions present promising targets for GIP as an anti-metastatic agent. Finally, based on cholinergic studies, it was proposed that GIP could influence the enzymatic activity of membrane acetylcholinesterases during tumor growth and metastasis. It was concluded that the GIP derived from full-length AFP represents a growth inhibitory motif possessing instrinsic properties that allow it to interfere in cell surface events such as adhesion, migration, metastasis, and aggregation of tumor cells.

Practical applications of snake venom toxins in haemostasis

Snake venom toxins affecting haemostasis have facilitated extensively the routine assays of haemostatic parameters in the coagulation laboratory. Snake venom thrombin-like enzymes (SVTLE) are used for fibrinogen/fibrinogen breakdown product assay and for the detection of fibrinogen dysfunction. SVTLE are not inhibited by heparin and can thus can be used for assaying antithrombin III and other haemostatic variables in heparin-containing samples. Snake venoms are a rich source of prothrombin activators and these are utilised in prothrombin assays, for studying dysprothrombinaemias and for preparing meizothrombin and non-enzymic forms of prothrombin. Russell's viper (Daboia russelli) venom (RVV) contains toxins which have been used to assay blood clotting factors V, VII, X, platelet factor 3 and, importantly, lupus anticoagulants (LA). Other prothrombin activators (from the taipan, Australian brown snake and saw-scaled viper) have now been used to assay LA. Protein C and activated protein C resistance can be measured by means of RVV and Protac, a fast acting inhibitor from Southern copperhead snake venom and von Willebrand factor can be studied with botrocetin from Bothrops jararaca venom. The disintegrins, a large family of Arg-Gly-Asp (RGD)-containing snake venom proteins, show potential for studying platelet glycoprotein receptors, notably, GPIIb/IIIa and Ib. Snake venom toxins affecting haemostasis are also used in the therapeutic setting: Ancrod (from the Malayan pit viper, Calloselasma rhodostoma), in particular, has been used as an anticoagulant to achieve 'therapeutic defibrination'. Other snake venom proteins show promise in the treatment of a range of haemostatic disorders.

Snake venoms and the hemostatic system

Snake venoms are complex mixtures containing many different biologically active proteins and peptides. A number of these proteins interact with components of the human hemostatic system. This review is focused on those venom constituents which affect the blood coagulation pathway, endothelial cells, and platelets. Only highly purified and well characterized snake venom proteins will be discussed in this review. Hemostatically active components are distributed widely in the venom of many different snake species, particularly from pit viper, viper and elapid venoms. The venom components can be grouped into a number of different categories depending on their hemostatic action. The following groups are discussed in this review: (i) enzymes that clot fibrinogen; (ii) enzymes that degrade fibrin(ogen); (iii) plasminogen activators; (iv) prothrombin activators; (v) factor V activators; (vi) factor X activators; (vii) anticoagulant activities including inhibitors of prothrombinase complex formation, inhibitors of thrombin, phospholipases, and protein C activators; (viii) enzymes with hemorrhagic activity; (ix) enzymes that degrade plasma serine proteinase inhibitors; (x) platelet aggregation inducers including direct acting enzymes, direct acting non-enzymatic components, and agents that require a cofactor; (xi) platelet aggregation inhibitors including: alpha-fibrinogenases, 5'-nucleotidases, phospholipases, and disintegrins. Although many snake venoms contain a number of hemostatically active components, it is safe to say that no single venom contains all the hemostatically active components described here. Several venom enzymes have been used clinically as anticoagulants and other venom components are being used in pre-clinical research to examine their possible therapeutic potential. The disintegrins are an interesting group of peptides that contain a cell adhesion recognition motif, Arg-Gly-Asp (RGD), in the carboxy-terminal half of their amino acid sequence. These agents act as fibrinogen receptor (integrin GPIIb/IIIa) antagonists. Since this integrin is believed to serve as the final common pathway leading to the formation of platelet-platelet bridges and platelet aggregation, blockage of this integrin leads to inhibition of platelet aggregation regardless of the stimulating agent. Clinical trials suggest that platelet GPIIb/IIIa blockade is an effective therapy for the thrombotic events and restenosis frequently accompanying cardiovascular and cerebrovascular disease. Therefore, because of their clinical poten tial, a large number of disintegrins have been isolated and characterized.

Determination of tumor cell procoagulant activity by Sonoclot analysis in whole blood

Coagulation activation in cancer may be due to expression of procoagulant activity (PCA) by tumor cells. Some PCA activate coagulation, while others influence platelet aggregation. Thus, clotting time assessments of PCA may not reflect the potential for hypercoagulability. We therefore studied the effect of various malignant and non-malignant cells on whole blood coagulation using the Sonoclot Analyzer. Five human (HT29 colon, J82 bladder, MCF-7 breast, BT-474 breast and A375 malignant melanoma) and three rodent (MC28, WEHI-164 and Neuro2a) cell lines were used. Rat thymocytes and peritoneal macrophages and human endotoxin-stimulated mononuclear cells and umbilical vein endothelial cells (HUVEC) were used as non-malignant controls. All tumor cells markedly shortened the recalcification time of citrated blood and the most potent (HT29 and J82) also increased clot rate (P < 0.01). The breast cancer cells MCF-7 and BT-474 expressed only weak PCA and did not affect clotting rate. None of the non-malignant cells significantly affected clotting time or rate in whole blood. J82 and HT29 cells grown in serum-rich media shortened the recalcification time of both normal and FVII-deficient plasmas. However, cells grown in serum-free conditions had significantly less PCA in FVII-deficient plasma. We conclude that the Sonoclot Analyzer is useful for determining cellular PCA; significant PCA is a feature of malignant cells and cells grown in medium containing serum supplements cannot be reliably evaluated for PCA.