Snake venom disintegrin, saxatilin, inhibits platelet aggregation, human umbilical vein endothelial cell proliferation, and smooth muscle cell migration

Snake venom toxins: Potential anticancer therapeutics

Snake venom contains a cocktail of compounds dominated by proteins and peptides, which make up the toxin. The toxin components of snake venom attack several targets in the human body including the neuromuscular system, kidney and blood coagulation system and cause pathologies. As such, the venom toxins can be managed and used for the treatment of these diseases. In this regard, Captopril used in the treatment of cardiovascular diseases was the first animal venom toxin-based drug approved by the US Food and Drug Administration and the European Medicines Agency. Cancers cause morbidity and mortality worldwide. Due to side effects associated with the current cancer treatments including chemotherapy, radiotherapy, immunotherapy, hormonal therapy and surgery, there is a need to improve the efficacy of current treatments and/or develop novel drugs from natural sources including animal toxin-based drugs. There is a long history of earlier and ongoing studies implicating snake venom toxins as potential anticancer therapies. Here, we review the role of crude snake venoms and toxins including phospholipase A2, L-amino acid oxidase, C-type lectin and disintegrin as potential anticancer agents tested in cancer cell lines and animal tumour models in comparison to normal cell lines. Some of the anti-tumour activities of snake venom toxins include induction of cytotoxicity, apoptosis, cell cycle arrest and inhibition of metastasis, angiogenesis and tumour growth. We thus propose the advancement of multidisciplinary approaches to more pre-clinical and clinical studies for enhanced bioavailability and targeted delivery of snake venom toxin-based anticancer drugs.

Snake venom disintegrins update: insights about new findings

Snake venom disintegrins are low molecular weight, non-enzymatic proteins rich in cysteine, present in the venom of snakes from the families Viperidae, Crotalidae, Atractaspididae, Elapidae, and Colubridae. This family of proteins originated in venom through the proteolytic processing of metalloproteinases (SVMPs), which, in turn, evolved from a gene encoding an A Disintegrin And Metalloprotease (ADAM) molecule. Disintegrins have a recognition motif for integrins in their structure, allowing interaction with these transmembrane adhesion receptors and preventing their binding to proteins in the extracellular matrix and other cells. This interaction gives disintegrins their wide range of biological functions, including inhibition of platelet aggregation and antitumor activity. As a result, many studies have been conducted in an attempt to use these natural compounds as a basis for developing therapies for the treatment of various diseases. Furthermore, the FDA has approved Tirofiban and Eptifibatide as antiplatelet compounds, and they are synthesized from the structure of echistatin and barbourin, respectively. In this review, we discuss some of the main functional and structural characteristics of this class of proteins and their potential for therapeutic use.

Purification and characterization of platelet aggregation inhibitor from the venom of Bitis arietans

Disintegrins are the antagonists of integrin receptors that can be found mostly in snakes’ venom. They can inhibit platelet aggregation, thus preventing the formation of blood clots. By blocking the integrin receptors of cancer cells, disintegrins can inhibit proliferation and metastasis. Thus, the search for new sources of disintegrins and development of methods of their purification is an important task of modern biotechnolo­gy. This work was dedicated to the purification and characterization of inhibiting polypeptides from Bitis arietans­ venom. Crude venom of B. arietans was fractionated using ion-exchange chromatography on Q Sepharose followed by size-exclusion chromatography on Superdex 75 using FPLC method. Analysis of molecular weight of protein components was performed using SDS-PAGE and MALDI-TOF analysis on Voyager-DE. Aggregation of platelet-rich plasma (PRP) in the presence of platelet aggregation inhibitor was investigated using aggregometry on the AR2110. MTT test was used for measuring HeLa cells proliferation and survival in vitro. Two-step chromatography allowed us to obtain fraction that contained polypeptides possessing the dose-dependent inhibitory action on adenosine diphosphate (ADP)-induced platelet aggregation in PRP. SDS-PAGE showed that obtained fraction contained two polypeptides with molecular weight 9.0 and 13.67 kDa according­ to MALDI-TOF analysis. Purified polypeptides inhibited ADP-induced platelet aggregation with IC50 0.09 mg/ml. However, 0.005 mg/ml of fraction suppressed viability of HeLa cells according to MTT test on 20%. Discovered biological effects of fractions allowed us to conclude the possible use of these polypeptides as anti-aggregatory or anti-proliferative agents. Keywords: antithrombotic action, disintegrins, glycoprotein IIb/IIIa, platelets, snake venom

Structure-Function Relationship of the Disintegrin Family: Sequence Signature and Integrin Interaction

Disintegrins are small cysteine-rich proteins found in a variety of snake venom. These proteins selectively modulate integrin function, heterodimeric receptors involved in cell-cell and cell-matrix interaction that are widely studied as therapeutic targets. Snake venom disintegrins emerged from the snake venom metalloproteinase and are classified according to the sequence size and number of disulfide bonds. Evolutive structure and function diversification of disintegrin family involves a stepwise decrease in the polypeptide chain, loss of cysteine residues, and selectivity. Since the structure elucidation of echistatin, the description of the structural properties of disintegrins has allowed the investigation of the mechanisms involved in integrin-cell-extracellular matrix interaction. This review provides an analysis of the structures of all family groups enabling the description of an expanded classification of the disintegrin family in seven groups. Each group presents a particular disulfide pattern and sequence signatures, facilitating the identification of new disintegrins. The classification was based on the disintegrin-like domain of the human metalloproteinase (ADAM-10). We also present the sequence and structural signatures important for disintegrin-integrin interaction, unveiling the relationship between the structure and function of these proteins.

Exogenous Integrin αIIbβ3 Inhibitors Revisited: Past, Present and Future Applications

The integrin αIIbβ3 is the most abundant integrin on platelets. Upon platelet activation, the integrin changes its conformation (inside-out signalling) and outside-in signalling takes place leading to platelet spreading, platelet aggregation and thrombus formation. Bloodsucking parasites such as mosquitoes, leeches and ticks express anticoagulant and antiplatelet proteins, which represent major sources of lead compounds for the development of useful therapeutic agents for the treatment of haemostatic disorders or cardiovascular diseases. In addition to hematophagous parasites, snakes also possess anticoagulant and antiplatelet proteins in their salivary glands. Two snake venom proteins have been developed into two antiplatelet drugs that are currently used in the clinic. The group of proteins discussed in this review are disintegrins, low molecular weight integrin-binding cysteine-rich proteins, found in snakes, ticks, leeches, worms and horseflies. Finally, we highlight various oral antagonists, which have been tested in clinical trials but were discontinued due to an increase in mortality. No new αIIbβ3 inhibitors are developed since the approval of current platelet antagonists, and structure-function analysis of exogenous disintegrins could help find platelet antagonists with fewer adverse side effects.

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.

Cytotoxic and anticancer properties of the Malaysian mangrove pit viper (Trimeresurus purpureomaculatus) venom and its disintegrin (purpureomaculin)

Background

The Asiatic pit vipers from the Trimeresurus complex are medically important venomous snakes. These pit vipers are often associated with snakebite that leads to fatal coagulopathy and tissue necrosis. The cytotoxic venoms of Trimeresurus spp.; however, hold great potential for the development of peptide-based anticancer drugs.

Methods

This study investigated the cytotoxic effect of the venom from Trimeresurus purpureomaculatus, the mangrove pit viper (also known as shore pit viper) which is native in Malaysia, across a panel of human cancer cell lines from breast, lung, colon and prostate as well as the corresponding normal cell lines of each tissue.

Results

The venom exhibited dose-dependent cytotoxic activities on all cell lines tested, with median inhibition concentrations (IC₅₀) ranging from 0.42 to 6.98 µg/mL. The venom has a high selectivity index (SI = 14.54) on breast cancer cell line (MCF7), indicating that it is significantly more cytotoxic toward the cancer than to normal cell lines. Furthermore, the venom was fractionated using C₁₈ reversed-phase high-performance liquid chromatography and the anticancer effect of each protein fraction was examined. Fraction 1 that contains a hydrophilic low molecular weight (approximately 7.5 kDa) protein was found to be the most cytotoxic and selective toward the breast cancer cell line (MCF7). The protein was identified using liquid chromatography-tandem mass spectrometry as a venom disintegrin, termed purpureomaculin in this study.

Conclusion

Taken together, the findings revealed the potent and selective cytotoxicity of a disintegrin protein isolated from the Malaysian T. purpureomaculatus venom and suggested its anticancer potential in drug discovery.

Snake venom components in medicine: From the symbolic rod of Asclepius to tangible medical research and application

Both mythologically and logically, snakes have always fascinated man. Snakes have attracted both awe and fear not only because of the elegant movement of their limbless bodies, but also because of the potency of their deadly venoms. Practically, in 2017, the world health organization (WHO) listed snake envenomation as a high priority neglected disease, as snakes inflict up to 2.7 million poisonous bites, around 100.000 casualties, and about three times as many invalidities on man. The venoms of poisonous snakes are a cocktail of potent compounds which specifically and avidly target numerous essential molecules with high efficacy. The individual effects of all venom toxins integrate into lethal dysfunctions of almost any organ system. It is this efficacy and specificity of each venom component, which after analysis of its structure and activity may serve as a potential lead structure for chemical imitation. Such toxin mimetics may help in influencing a specific body function pharmaceutically for the sake of man's health. In this review article, we will give some examples of snake venom components which have spurred the development of novel pharmaceutical compounds. Moreover, we will provide examples where such snake toxin-derived mimetics are in clinical use, trials, or consideration for further pharmaceutical exploitation, especially in the fields of hemostasis, thrombosis, coagulation, and metastasis. Thus, it becomes clear why a snake captured its symbolic place at the Asclepius rod with good reason still nowadays.

Fc-saxatilin suppresses hypoxia-induced vascular leakage by regulating endothelial occludin expression

Vascular leakage due to compromised integrity of the endothelial barrier is closely associated with brain damage in several neurological disorders, including ischaemic stroke. Saxatilin, a snake venom disintegrin containing the Arg-Gly-Asp (RGD) motif, exerts thrombolytic and antiplatelet effects by interacting with multiple integrins on platelets. Integrin signalling is indispensable for regulation of endothelial permeability. Saxatilin may play a role in vascular leakage after ischaemia because it has high affinity for endothelial integrins. Here, we determined whether Fc-saxatilin, an Fc-fusion protein of saxatilin, could prevent vascular leakage under hypoxic or ischaemic conditions. In mouse brain microvascular endothelial cells, hypoxia increased the permeability to FITC-dextran, and this effect was attenuated by Fc-saxatilin treatment. Fc-saxatilin also blocked vascular leakage of Evans Blue in the ischaemic brain induced by middle cerebral artery occlusion in mice. Furthermore, the expression of occludin, a tight junction protein, was reduced by hypoxia in endothelial cells. This downregulation of occludin was attenuated by Fc-saxatilin treatment. We also determined the activity of matrix metalloproteinases (MMPs) 2 and 9 because they are implicated in the degradation of occludin and of the microvascular basal lamina. Hypoxia increased MMP-9 activity, and this increase was attenuated by Fc-saxatilin treatment. Fc-saxatilin specifically bound to integrin α_vβ₃ of the endothelial cells and inhibited hypoxia-induced activation of FAK, a downstream signalling molecule in integrin-dependent signal transduction. Taken together, these results provide new insights into the mechanism via which Fc-saxatilin, as an integrin antagonist, prevents vascular leakage under ischemic conditions by regulating occludin expression in endothelial tight junctions.

Blood Vessel Maturation by Disintegrin in Oxygen-Induced Retinopathy

PURPOSE

Although Arg-Gly-Asp (RGD) motif-containing disintegrins are associated with integrin inhibition and the activation of various biological processes, little is known about the role of RGD motif-containing disintegrin in vascular development and remodeling. We therefore investigated the role of RGD-containing disintegrin in vascular remodeling in oxygen-induced retinopathy (OIR) mouse model.

MATERIALS AND METHODS

EGT022, an RGD-containing disintegrin originated from human a disintegrin and metalloproteinase 15 (ADAM15), was used to investigate the role of the disintegrin in vascular development in OIR mouse model. To analyze the functional effects of EGT022 on retinal vascular development, the immunohistochemistry on mouse retinas after fluorescein isothiocyanate (FITC) perfusion was conducted and the vessel integrity was examined using modified Mile's permeability assay.

RESULTS

EGT022 was able to reduce overall retinopathy scores by 75%, indicating its efficacy in retinal microvessel maturation stimulation. Pericyte coverage was greatly stimulated by EGT022 treatment in OIR mouse model. EGT022 was also effective to significantly improve blood vessel integrity.

CONCLUSIONS

RGD-containing disintegrin EGT022 stimulated vascular maturation in OIR mouse model. Experimental results suggest that EGT022 is useful for treatments to improve ischemia in nonproliferative diabetic retinopathy (NPDR), the early stage of diabetic retinopathy.

rAdinbitor, a disintegrin from Agkistrodon halys brevicaudus stejneger, inhibits tumorigenicity of hepatocarcinoma via enhanced anti-angiogenesis and immunocompetence

Adinbitor is a disintegrin previously obtained from Agkistrodon halys brevicaudus stejneger by our group. Here, we investigated the in vitro and in vivo anti-tumor activities of recombinant Adinbitor (rAdinbitor). rAdinbitor stimulation can inhibit the in vitro proliferation, migration and invasion capacities of murine hepatocarcinoma H22 and Hca-F cells. The administrations of rAdinbitor either by gavage or intraperitoneal injection suppress the tumor malignancy and prolong the survival rate and time of H22-transplanted mice. The number and size of formed blood vessels decreased dramatically in tumorous tissues in that the expression levels of vascular endothelial growth factor (VEGF) and cluster of differentiation 34 (CD34) were significantly decreased in responding to rAdinbitor treatment. The protein levels of IL-18 and IgG increased significantly in the serum of H22-transplanted tumor mice with rAdinbitor treatment. rAdinbitor shows in vitro and in vivo anti-tumor effects as an angiogenesis inhibitor and immunocompetence enhancer.

A novel peptide inhibitor of platelet aggregation from stiff silkworm, Bombyx batryticatus

A novel platelet aggregation inhibitory peptide, named BB octapeptide, was isolated from stiff silkworm (Bombyx batryticatus) by gel filtration, anion-exchange, and reverse-phase high performance liquid chromatography. The molecular mass of the peptide was determined to be 885 Da using electrospray ionization mass spectrometry, and the sequence was identified as Asp-Pro-Asp-Ala-Asp-IIe-Leu-Gln using the Edman degradation method. To test its biological activity, the peptide was chemically synthesized using Fmoc solid-phase synthesis method. BB octapeptide inhibited rabbit platelet aggregation that was induced by collagen and epinephrine, with the IC50 values of 91.14 μM and 104.50 μM, respectively. After intravenous administrated in mice (30 mg/kg, 4 days), BB octapeptide showed similar ex vivo efficacy of inhibiting platelet aggregation as aspirin (10 mg/kg). In addition, this peptide prevented paralysis and death in pulmonary thromboembolism model and significantly reduced ferric chloride-induced thrombus formation in rats. Moreover, it exhibited low cytotoxicity in a cellular model. In conclusion, this is the first report that a novel platelet aggregation inhibitory peptide was isolated from stiff silkworm (B. batryticatus). Due to the excellent efficacy in reducing platelet aggregation and low toxicity, it can be a valuable lead compound for new drug design and development.

Thrombolytic effects of the snake venom disintegrin saxatilin determined by novel assessment methods: a FeCl3-induced thrombosis model in mice

Saxatilin, a novel disintegrin purified and cloned from the venom of the Korean snake Gloydius saxatilis, strongly inhibits activation and aggregation of platelets. Glycoprotein (GP) IIb/IIIa receptor antagonists can resolve thrombus, so saxatilin might also have thrombolytic effects. We investigated the thrombolytic effects of saxatilin in mice using a ferric chloride-induced carotid arterial thrombosis model. Thrombotic occlusion and thrombus resolution were evaluated quantitatively by measuring blood flow in the carotid artery with an ultrasonic flow meter and calculating the degree of flow restoration on a minute-by-minute basis; results were confirmed by histological examination. Saxatilin dissolved thrombi in a dose-dependent manner. Saxatilin at 5 mg/kg restored blood flow to baseline levels. As saxatilin dose increased, time to recanalization decreased. A bolus injection of 10% of a complete dose with continuous infusion of the remaining dose for 60 minutes resulted in effective recanalization without reocclusion. The thrombolytic effect of saxatilin was also demonstrated in vitro using platelet aggregometry by administering saxatilin in preformed thrombi. Bleeding complications were observed in 2 of 71 mice that received saxatilin. Fibrin/fibrinogen zymography and platelet aggregometry studies indicated that saxatilin does not have fibrinolytic activity, but exerted its action on platelets. Integrin-binding assays showed that saxatilin inhibited multiple integrins, specifically α2bβ3 (GP IIb/IIIa), α5β1, αvβ3, αvβ1, and αvβ5, which act on platelet adhesion/aggregation. Saxatilin inhibited multiple integrins by acting on platelets, and was safe and effective in resolving thrombi in mice.

A new dextran-graft-polybutylmethacrylate copolymer coated on 316L metallic stents enhances endothelial cell coverage

Amphiphilic copolymers based on the copolymerization of hydrophilic and hydrophobic moieties offer versatility in various biomedical material applications. Here, a new biocompatible copolymer of dextran-graft-polybutylmethacrylate is synthesized for the coating of metallic endovascular stents. Coating of metallic surfaces is performed and analyzed by X-ray photoelectron spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, contact angle measurement, atomic force microscopy and scanning electron microscopy before and after deformation corresponding to stent deployment by a balloon catheter. In the conditions described here, the resulting coating is smooth and uniform with neither cracks nor detachment after stent expansion. Interestingly, surfaces coated with the copolymer greatly improve in vitro adhesion and growth of endothelial cells. This copolymer provides new opportunities for implanted biomaterials.

The buccal gland of Lampetra japonica is a source of diverse bioactive proteins

The parasitic phase lampreys (Lampetra japonica) are bloodsuckers in the marine, and their buccal gland secretion (lamphredin) contains various regulators such as anticoagulants, ion channel blockers, and immune suppressors like those from leeches, insects, ticks, vampire bats, and snakes. This review focuses on the functions and characteristics of the active proteins from the buccal gland of L. japonica for the first time, and provides new insights into the parasitic mechanisms of lampreys and the possibilities of developing drugs such as novel anticoagulants, thrombolytic agents, local anesthetics, and immunosuppressants.

Cell growth inhibition and induction of apoptosis by snake venom toxin in ovarian cancer cell via inactivation of nuclear factor κB and signal transducer and activator of transcription 3

Snake venom toxin from Vipera lebetina turanica induces apoptosis in many cancer cell lines, but there is no study about the apoptotic effect of snake venom toxin on human ovarian cancer cells. In this study, we investigated the apoptotic effect of snake venom toxin in human ovarian cancer PA-1 and SK-OV3 cells. Snake venom toxin dose dependently (0∼10 μg/mL) inhibited ovarian cancer cell growth with IC(50) values 4.5 μg/mL in PA-1 cells, and 6.5 μg/mL in SK-OV3 cells. Our results also showed that apoptotic cell death increased by snake venom toxin in a dose dependent manner (0∼10 μg/mL). Consistent with increased cell death, snake venom toxin increased the expression of pro-apoptotic protein Bax and caspase-3, but down-regulated anti-apoptotic protein Bcl-2. Untreated ovarian cancer cells showed a high DNA binding activity of nuclear factor B (NF-κB), but it was inhibited by snake venom toxin accompanied by inhibition of p50 and p65 translocation into the nucleus as well as phosphorylation of inhibitory κB. Snake venom toxin also inhibited DNA binding activity of the signal transducer and activator of transcription 3 (STAT3). Moreover, the combination treatment of NF-κB (salicylic acid, 1 or 5 μM) and STAT3 (stattic, 1 μM) with snake venom toxin (1 μg/mL) further enhanced cell growth inhibitory effects of snake venom toxin. These results showed that snake venom toxin from Vipera lebetina turanica caused apoptotic cell death of ovarian cancer cells through the inhibition of NF-κB and STAT3 signal, and suggested that snake venom toxin may be applicable as an anticancer agent for ovarian cancer.

Conotoxin engineering: dual pharmacophoric noradrenaline transport inhibitor/integrin binding peptide with improved stability

A dual-pharmacophoric peptide was engineered by grafting the integrin binding RGD motif between the C- and N-termini of a disulfide-rich noradrenaline transporter inhibiting χ-conotoxin resulting in a stable backbone cyclized peptide. The construct maintained two independent biological activities and showed increased plasma stability with no adverse effects observed following administration to rats, highlighting the potential value of pharmacophore grafting into constrained peptide scaffolds.

"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.

A novel RGD-toxin protein, Lj-RGD3, from the buccal gland secretion of Lampetra japonica impacts diverse biological activities

RGD (Arg-Gly-Asp) motif toxin proteins from snake venoms, saliva glands secretion of leech or tick have typical characteristics of inhibiting platelet aggregation, angiogenesis, and tumor growth. Here we report cloning and characterization of a novel RGD-toxin protein from the buccal gland of Lampetra japonica. In an attempt to study the activities of anticoagulant in the buccal gland secretion of L. japonica, we established buccal gland cDNA library and identified a gene encoding a predicted protein of 118 amino acids with 3 RGD motifs. The predicted protein was named Lj-RGD3. We generated the cDNA of Lj-RGD3 and obtained the recombinant protein rLj-RGD3. The polyclonal antibodies against rLj-RGD3 recognized the native Lj-RGD3 protein in buccal gland secretion in Western blot analyses. The biological function studies reveal that rLj-RGD3 inhibited human platelet aggregation in a dose-dependent manner with IC(50) value at 5.277 μM. In addition, rLj-RGD3 repressed bFGF-induced angiogenesis in the chick chorioallantoic membrane model. rLj-RGD3 also inhibited the adhesion of ECV304 cells to vitronectin. Furthermore, rLj-RGD3 induced apoptosis and significantly inhibited proliferation, migration, and invasion evoked by bFGF in ECV304 cells. Taken together, these results suggested that rLj-RGD3 is a novel RGD-toxin protein possessing typical functions of the RGD-toxin protein.

VGD and MLD-motifs containing heterodimeric disintegrin viplebedin-2 from Vipera lebetina snake venom. Purification and cDNA cloning

We have previously demonstrated that the fibrinolytic enzyme lebetase is synthesized with disintegrin-like domain that is cleaved posttranslationally (Siigur et al., 1996). Now we isolated a heterodimeric disintegrin viplebedin-2 containing this disintegrin-like part from Vipera lebetina venom using size-exclusion chromatography on Sephadex G-100 sf and HPLC on C18 column. The molecular masses of viplebedin-2 and tryptic peptides from both chains of viplebedin-2 were determined by MALDI-TOF mass spectrometry. Using cDNA library of the venom gland of a single V. lebetina turanica snake the viplebedin-2 coding cDNAs were cloned and sequenced. Viplebedin-2 chains are synthesized from two different genes. One chain, containing VGD sequence in disintegrin loop, is synthesized as a disintegrin-like part of the PII-type metalloprotease, lebetase. The other chain, containing MLD sequence in disintegrin loop, is synthesized from the gene without metalloproteinase domain. Two polyadenylation signal sequences have been found in MLD sequence coding chain precursor cDNAs. Viplebedin-2 dose-dependently inhibited adhesion of platelets to immobilized collagen and inhibited collagen-induced platelet aggregation.

Integrin inhibitors from snake venom: exploring the relationship between the structure and activity of RGD-peptides

alphaIIbbeta3 is an integrin that is involved in platelet adhesion and aggregation. This receptor may be inhibited by cysteine-rich peptides known as disintegrins. We isolated two disintegrins from Bothrops jararaca venom called jarastatin and jararacin. We evaluated the structural characteristics and the effects on human platelet aggregation of these disintegrins. Inhibitory profiles were compared to six distinct peptides synthesized based on their RGD hairpin loop primary sequences. Both jarastatin and jararacin inhibited ADP and thrombin induction. Conversely, none of the cyclic peptides showed high-quality activity in assays induced by ADP or thrombin. We constructed homology models for all of these molecules, and theoretically evaluated their interaction with the alphaIIbbeta3 crystal structure using a molecular modeling approach. These results support the observations that the cyclic peptides had little effects, and also reinforce the observation that residues outside the disintegrin RGD sequence are required for interactions with receptor.

Anti-platelet effect of cumanastatin 1, a disintegrin isolated from venom of South American Crotalus rattlesnake

Disintegrins have been previously described in the venom of several snake families inhibiting signal transduction, cell-cell interactions, and cell-matrix interactions and may have therapeutic potential in heart attacks, thrombotic diseases, and cancers. This investigation describes the first disintegrin isolated from South American Crotalus venom (Venezuelan rattlesnake Crotalus durissus cumanensis), which inhibits platelet adhesion to matrix proteins. C. d. cumanensis crude venom was first separated on a Sephadex G-100 column into 4 fractions (SI to SIV). Crude venom and SIII fraction significantly diminished platelet adhesion to fibrinogen (Fg) and to fibronectin (Fn). Anti-adhesive SIII fraction was further separated by DEAE-Sephacel followed by C-18 reverse phase high performance liquid chromatography (HPLC). The platelet anti-adhesive fraction obtained was designated as cumanastatin-1. This disintegrin has a mass of 7.442 kDa as determined by mass spectrometry (MALDI-TOF/TOF) and pI of 8.5. Cumanastatin-1 also inhibited ADP-induced platelet aggregation with an IC(50) of 158 nM. However, it did not significantly inhibit collagen and thrombin-induced platelet aggregation. Cumanastatin-1 considerably inhibited anti-alpha(IIb)beta(3) integrin binding to platelets in a dose-dependent manner; however, it did not present any effect on the alpha(5)beta(1) integrin or on P-selectin.

Suppressive effect and mechanism of saxatilin, a disintegrin from Korean snake (Gloydius saxatilis), in vascular smooth muscle cells

RGD-peptides can inhibit the binding of ligands to certain beta3 integrins, alphaIIbbeta3 and alphavbeta3, both of which are involved in neointimal hyperplasia that contributes to atherosclerosis and restenosis of arterial walls. Saxatilin, a disintegrin from a Korean snake (Gloydius saxatilis), interacts with integrins alphaIIbbeta3 and alphavbeta3. It suppressed the adhesion of human coronary artery smooth muscle cells (HCASMCs) to vitronectin with an IC(50) of 2.5 microM, and growth factor (PDGF-BB or bFGF)-induced proliferation was inhibited at an IC(50) of 25 microM. Saxatilin disassembled the actin cytoskeleton of focal adhesion and induced cell detachment. This disassembly of focal adhesion in saxatilin-treated HCASMCs involved caspase-induced paxillin degradation. Saxatilin temporally phosphorylated FAK and ERKs and affected the cell cycle of HCASMCs by increasing CDK inhibitors (p21 and p27) and reducing cyclins (D1/2 and E). These results may have significant implications for integrin antagonistic therapy used for the treatment of atherosclerosis and restenosis.

Evaluation of the antiangiogenic potential of AQ4N

PURPOSE

A number of cytotoxic chemotherapy agents tested at low concentrations show antiangiogenic properties with limited cytotoxicity, e.g., cyclophosphamide, tirapazamine, and mitoxantrone. AQ4N is a bioreductive alkylaminoanthraquinone that is cytotoxic when reduced to AQ4; hence, it can be used to target hypoxic tumor cells. AQ4N is structurally similar to mitoxantrone and was evaluated for antiangiogenic properties without the need for bioreduction.

EXPERIMENTAL DESIGN

The effect of AQ4N and fumagillin on human microvascular endothelial cells (HMEC-1) was measured using a variety of in vitro assays, i.e., 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, wound scrape, tubule formation, rat aortic ring, and invasion assays. Low-dose AQ4N (20 mg/kg) was also given in vivo to mice bearing a tumor in a dorsal skin flap.

RESULTS

AQ4N (10(-11) to 10(-5) mol/L) had no effect on HMEC-1 viability. AQ4N (10(-9) to 10(-5)mol/L) caused a sigmoidal dose-dependent inhibition of endothelial cell migration in the wound scrape model. Fumagillin showed a similar response over a lower dose range (10(-13) to 10(-9) mol/L); however, the maximal inhibition was less (25% versus 43% for AQ4N). AQ4N inhibited HMEC-1 cell contacts on Matrigel (10(-8) to 10(-5) mol/L), HMEC-1 cell invasion, and sprouting in rat aorta explants. Immunofluorescence staining with tubulin, vimentim, dynein, and phalloidin revealed that AQ4N caused disruption to the cell cytoskeleton. When AQ4N (20 mg/kg) was given in vivo for 5 days, microvessels disappeared in LNCaP tumors grown in a dorsal skin flap.

CONCLUSIONS

This combination of assays has shown that AQ4N possesses antiangiogenic effects in normoxic conditions, which could potentially contribute to antitumor activity.

Surface immobilization of chondroitin 6-sulfate/heparin multilayer on stainless steel for developing drug-eluting coronary stents

A thin layer of gold was sputtered onto SUS316L stainless steel (SS) sheet. After thiolizing the Au layer with dimercaptosuccinic acid (DMSA), layers of chondroitin 6-sulfate (ChS) and heparin (HEP) were alternatively immobilized on the Au-treated SS. The resulting stent would be both anti-atherogenic and anti-thrombogenic. After repeating one to five cycles, one to five layers of polyelectrolyte complex (PEC) of ChS/HEP were successfully fabricated. A model drug, sirolimus, was loaded in the ChS/HEP layers. The SS-ChS-HEP surface was examined by X-ray photoelectron spectroscopy (XPS), contact angle, and atomic force microscopy (AFM) measurement. Biological tests including hemocompatibility, drug release pattern, and the inhibition of smooth muscle cell proliferation were also performed. The results show that the multilayer of ChS/HEP exhibits longer blood clotting time than pure SS substrates. Therefore, this biopolymer multilayer can avoid thrombosis on the stainless. The releasing rate of sirolimus can be controlled through the number of ChS/HEP PEC layers. With a five-layer coating, sirolimus can be released continuously for more than 20 days. Furthermore, the multilayer ChS/HEP loaded with sirolimus can suppress specifically to the growth of smooth muscle cells to avoid restenosis. This suggests that the PEC multilayer of ChS/HEP modified-SS could be applied in making drug-eluting stents.

Saxatilin suppresses tumor-induced angiogenesis by regulating VEGF expression in NCI-H460 human lung cancer cells

Tumor growth and metastasis are dependent on angiogenesis, and endothelial cell invasion and migration are apparent means of regulating tumor progression. We report here that saxatilin, a snake venom-derived disintegrin, suppresses the angiogenesis-inducing properties of NCI-H460 human lung cancer cells. Culture supernatants of NCI-H460 cells are able to induce human umbilical vascular endothelial cell (HUVEC) invasion and tube formation. However, treatment of the cancer cells with saxatilin resulted in reduced angiogenic activity of the culture supernatant. This suppressed angiogenic property was found to be associated with the level of vascular endothelial growth factor (VEGF) in the culture supernatant. Further experimental evidence indicated that saxatilin inhibits VEGF production in NCI-H460 cells by affecting hypoxia induced factor-1 alpha (HIF-1 alpha) expression via the Akt pathway.

Saxatilin, a snake venom disintegrin, suppresses TNF-alpha-induced ovarian cancer cell invasion

Saxatilin is a disintegrin known to inhibit tumor progression in vivo and in vitro. The role of saxatilin in cancer cell invasion was examined by a modified Boyden chamber assay in MDAH 2774 human ovarian cancer cell line. Saxatilin (50 nM) significantly inhibited cancer cell invasion induced by tumor necrosis factor-alpha (TNF-alpha). Saxatilin also reduced MMP-9 mRNA levels in cancer cells in a dose-dependent manner. In addition, TNF-alpha-induced MMP-9 activity was reduced by the treatment of saxatilin. These results indicate that transcriptional regulation of MMP-9 is an important mechanism for the tumor suppressive effects of saxatilin in MDAH 2774 human ovarian cancer cells.

Inhibitory effect of snake venom toxin fromVipera lebetina turanicaon hormone-refractory human prostate cancer cell growth: induction of apoptosis through inactivation of nuclear factor κB

We investigated whether the snake venom toxin (SVT) from Vipera lebetina turanica inhibits cell growth of human prostate cancer cells by inducing apoptosis and also studied possible signaling pathways involved in this cell death. SVT inhibited growth of PC-3 and DU145 cells, androgen-independent prostate cancer cells, but not LNCaP cells, a human androgen-dependent prostate cancer cell. Cells were arrested in the G(2)-M phase by SVT with a concomitant decrease in the expression of the G(2)-M phase regulatory protein cyclin B1 and were also arrested in the G(1)-S phase with decreasing expression of cyclin-dependent kinase 4, cyclin D1 and cyclin E. In addition to the growth-inhibitory effect, SVT increased the induction of apoptotic cell death. Untreated PC-3 cells show high DNA binding activity of nuclear factor kappaB (NF-kappaB), an antiapoptotic transcriptional factor, but this was inhibited by SVT and accompanied by a significant inhibition of p50 translocation into the nucleus, as well as phosphorylation of inhibitory kappaB. Consistent with the induction of apoptosis and inhibition of NF-kappaB, this toxin increased the expression of proapoptotic proteins such as p53, Bax, caspase-3, and caspase-9, but down-regulated antiapoptotic protein Bcl-2. However, SVT did not show an inhibitory effect on cell growth and caspase-3 activity in cells carrying mutant p50 and inhibitory kappaB kinase plasmids. Confocal microscopy analysis showed that SVT is taken up into the nucleus of the cells. These findings suggest that a nanogram concentration range of SVT from V. lebetina turanica could inhibit hormone-refractory human prostate cancer cell growth, and the effect may be related to NF-kappaB signal-mediated induction of apoptosis.

Saxatilin inhibits TNF-α-induced proliferation by suppressing AP-1-dependent IL-8 expression in the ovarian cancer cell line MDAH 2774

Tumor necrosis factor-alpha (TNF-alpha)-induced proliferation of cancer cell line MDAH 2774 was significantly suppressed by treating the cells with saxatilin, a snake venom disintegrin. The suppressed proliferation was found to be associated with the level of interleukin-8 (IL-8) expression in the cells. TNF-alpha-induced IL-8 promoter activation that is inhibited by saxatilin treatment was dependent on activating protein-1 (AP-1) instead of nuclear factor-kappa B (NF-kappaB). Coexpression of dominant negative p38 (DN-p38) suggested that p38 is involved in the IL-8 promoter activity which is regulated by saxatilin or TNF-alpha. Experimental evidence clearly indicated that saxatilin inhibits TNF-alpha-induced proliferation of the ovarian cancer cells by suppressing IL-8 expression in AP-1-dependent manner.

Saxatilin, a Snake Venom Disintegrin, Regulates Platelet Activation Associated with Human Vascular Endothelial Cell Migration and Invasion

BACKGROUND

Platelet activation results in platelet aggregation and the secretion of granules, which contain a variety of constituents including nonprotein molecules, adhesive proteins and hydrolases. The platelet-derived supernatant (PDS), which contains these granules, is known to trigger the activation of endothelium and chemotaxis of monocytes.

METHODS AND RESULTS

PDS derived from collagen-activated platelets stimulated human umbilical vein endothelial cell (HUVEC) migration and invasion, as measured through the use of a Boyden chamber. This collagen-induced PDS also triggered integrin alpha(v)beta(3) upregulation in HUVECs. The inclusion of a neutralizing antibody to platelet-derived growth factor (PDGF)-B abolished HUVEC migration/invasion and integrin alpha(v)beta(3) upregulation, showing that PDGF-AB mediates the proangiogenic effects of collagen-activated PDS. Saxatilin, a snake venom disintegrin known to interrupt platelet aggregation by antagonizing integrin alpha(IIb)beta(3), inhibited the collagen-induced platelet activation and abolished the angiogenic properties of PDS. Saxatilin also inhibited the collagen-induced phosphorylation of Syk, a key mediator of inside-out signaling in platelet activation.

CONCLUSION

Saxatilin inhibits platelet activation, platelet PDGF-AB release as well as subsequent endothelial cell migration and invasion.

Novel function of human ADAM15 disintegrin-like domain and its derivatives in platelet aggregation

INTRODUCTION

A Disintegrin and Metalloproteinase (ADAM) proteins are a family of multifunctional proteins containing disintegrin and metalloproteinase domains that perform both adhesive and proteolytic functions in cell-cell and cell-matrix interactions. ADAM15 is unique among these proteins in having an Arg-Gly-Asp (RGD) motif in its disintegrin-like domain. This motif is known to interact with the integrin alphaIIbbeta3 on platelets.

MATERIALS AND METHODS

We cloned and expressed the human ADAM15 disintegrin-like domain and its derivatives in Pichia pastoris, and purified them by chromatographic fractionation. We then characterized the integrin binding specificities and their antiplatelet activities of the proteins. Antiplatelet function was assessed by inhibition of platelet adhesion and aggregation.

RESULTS

The yeast-expressed ADAM15 disintegrin-like domains were able to inhibit the binding of alphaIIbbeta3 as well as alphavbeta3 to its biological ligands in a dose-dependent manner. Remarkably, mutation of the three residues proximal to the RGD tripeptide sequence, RPTRGD sequence to NWKRGD, increased its affinity for alphaIIbbeta3. The NWK mutant had a much greater inhibitory action on human platelet aggregation than the original ADAM15 disintegrin-like domain.

CONCLUSIONS

The structural context of the RGD tripeptide sequence in the disintegrin domain determines the specificity and affinity of the protein for its binding partners. The human ADAM15 disintegrin-like domain may provide useful information for developing an antithrombotic agent.

Inhibition of angiogenesis and tumor progression by hydrodynamic cotransfection of angiostatin K1-3, endostatin, and saxatilin genes

In vivo expression of angiostatin and endostatin, two different types of endothelial cell growth inhibitor, have been reported to inhibit vascularization in tumor tissues, resulting in tumor growth inhibition. Recently, in vivo expression of saxatilin, a novel disintegrin purified from snake (Gloydius saxatilis) venom, was able to strongly inhibit endothelial cell proliferation and smooth muscle cell migration, resulting in tumor growth inhibition. However, the antitumor efficacy of the individual antiangiogenic molecules expressed in vivo was not sufficiently potent to induce tumor regression in animal models. Therefore, in this study, we have systemically examined how combinational transfer of angiostatin, endostatin, and saxatilin genes affects neovascularization in tumor tissues and tumor progression in a mouse model. In Matrigel-implanted mice, cotransfection with plasmids encoding angiostatin K1-3 (pFLAG-Angio K1/3), endostatin (pFLAG-Endo), and saxatilin (pFLAG-Sax) resulted in the most effective inhibition of angiogenesis. In addition, hydrodynamic cotransfection of the three genes induced more inhibition of B16BL6 melanoma growth and pulmonary metastasis than other combinations of transfected genes. Compared with the empty vector-treated control group, cotreatment with the three plasmids reduced B16BL6 tumor growth by 89% and pulmonary metastasis by 90%. These results provide additional evidence supporting the combined systemic expression of antiangiogenic factors, such as angiostatin K1-3, endostatin, and saxatilin, as an alternative procedure for antiangiogenic cancer therapy.

A novel disintegrin, jerdonatin, inhibits platelet aggregation and sperm-egg binding

A novel disintegrin, jerdonatin, was purified to homogeneity from Trimeresurus jerdonii venom by gel filtration and reversed-phase high-pressure liquid chromatography. We isolated the cDNA encoding jerdonatin from the snake venom gland. Jerdonatin cDNA precursor encoded pre-peptide, metalloprotease and disintegrin domain. Jerdonatin is composed of 72 amino acid residues including 12 cysteines and the tripeptide sequence Arg-Gly-Asp (RGD), a well-known characteristic of the disintegrin family. Molecular mass of jerdonatin was determined to be 8011 Da by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS). Jerdonatin inhibited ADP- and collagen-induced human platelet aggregation with IC50 of 123 and 135 nM, respectively. We also investigated the effect of jerdonatin on the binding of B6D2F1 hybrid mice spermatozoa to mice zona-free eggs and their subsequent fusion. Jerdonatin significantly inhibited sperm-egg binding in a concentration-dependent manner, but had no effect on the fusion of sperm-egg. These results indicate that integrins on the egg play a role in mammalian fertilization.

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.

Purification, cloning and biological characterization of a novel disintegrin from Trimeresurus jerdonii venom

A novel disintegrin, jerdonin, was purified from the Trimeresurus jerdonii venom by means of gel filtration and reverse phase high pressure liquid chromatography. Its coding cDNA was also isolated from the venom gland. The jerdonin coding cDNA is part of a precursor composed of proprotein, metalloproteinase, and disintegrin domains. From the deduced amino acid sequence, jerdonin is composed of 71 amino acid residues including 12 cysteines and the tripeptide sequence Arg-Gly-Asp (RGD), a well-known characteristic of the disintegrin family. Molecular mass of jerdonin was determined to be 7483Da by matrix-assisted laser desorption ionization time of flight mass spectrometry. Jerdonin inhibited ADP- and collagen-induced human platelet aggregation with IC(50) of 220 and 240 nM, respectively. In vivo, jerdonin inhibited the growth of subcutaneously inoculated B16 solid tumor in C57BL/6 mice and improved the survival time of the tumor-bearing mice.

A novel disintegrin-like domain of a high molecular weight metalloprotease inhibits platelet aggregation

Disintegrin is one of the functionally distinct domains in high molecular weight metalloproteases from various snake venoms and generally has an Arg-Gly-Asp (RGD) sequence that is recognized by specific cell surface integrins. A cDNA encoding the disintegrin-like domain of a snake venom metalloprotease was cloned, expressed in Pichia pastoris, and molecular function of the recombinant protein was characterized. The cDNA sequence indicated that the disintegrin-like domain contains an Asp-Glu-Cys-Asp (DECD) sequence in place of the RGD motif. The expressed disintegrin-like protein was designated as halydin and it was able to inhibit human platelet aggregation in a dose-dependent manner. Unlike other typical RGD-disintegrins, the recombinant non-RGD disintegrin, halydin, inhibited platelet aggregation by suppressing platelet adhesion to collagen rather than by blocking fibrinogen binding to glycoprotein (GP) IIb-IIIa on the platelet surface. Experimental evidence suggests that halydin binds to integrin alpha2beta1 on the platelet surface.

Snake venom disintegrins: novel dimeric disintegrins and structural diversification by disulphide bond engineering

We report the isolation and amino acid sequences of six novel dimeric disintegrins from the venoms of Vipera lebetina obtusa (VLO), V. berus (VB), V. ammodytes (VA), Echis ocellatus (EO) and Echis multisquamatus (EMS). Disintegrins VLO4, VB7, VA6 and EO4 displayed the RGD motif and inhibited the adhesion of K562 cells, expressing the integrin alpha5beta1 to immobilized fibronectin. A second group of dimeric disintegrins (VLO5 and EO5) had MLD and VGD motifs in their subunits and blocked the adhesion of the alpha4beta1 integrin to vascular cell adhesion molecule 1 with high selectivity. On the other hand, disintegrin EMS11 inhibited both alpha5beta1 and alpha4beta1 integrins with almost the same degree of specificity. Comparison of the amino acid sequences of the dimeric disintegrins with those of other disintegrins by multiple-sequence alignment and phylogenetic analysis, in conjunction with current biochemical and genetic data, supports the view that the different disintegrin subfamilies evolved from a common ADAM (a disintegrin and metalloproteinase-like) scaffold and that structural diversification occurred through disulphide bond engineering.

Structural and functional significance of disulfide bonds in saxatilin, a 7.7 kDa disintegrin

Saxatilin is a 7.7 kDa disintegrin that belongs to a family of homologous protein found in several snake venoms. Six disulfide bond locations of the disintegrin were determined by enzymatic cleavage and matrix-assisted-laser-desorption-ionization time-of-flight mass spectrometry (MALDI-TOF). Functional implications of the disulfide bonds related to the biological activity of saxatilin were investigated with recombinant protein species produced by site-directed mutagenesis of saxatilin. Several lines of experimental evidence indicated that three disulfide bonds, Cys21-Cys35, Cys29-Cys59, and Cys47-Cys67, of the disintegrin are closely associated with its biological function such as its ability to block the binding of integrin GPIIb-IIIa and alpha(v)beta(3) with fibrinogen and extracellular matrix. Those disulfide linkages were also revealed to be important for maintaining the functional structure of the protein molecule. On the other hand, the disulfide bridges of Cys6-Cys15 and Cys8-Cys16 do not appear to be critical for the molecular structure and function of saxatilin.