Simon F. De Meyer, PhD; Guido Stoll, MD; Denisa D....

von Willebrand FactorAn Emerging Target in Stroke Therapy

Simon F. De Meyer, PhD; Guido Stoll, MD; Denisa D. Wagner, PhD*; Christoph Kleinschnitz, MD*

Thrombus formation is of paramount importance in the pathophysiology of acute ischemic stroke. Current antithromboticsused to treat or prevent cerebral ischemia are only moderately effective or bear an increased risk of severe bleeding. vonWillebrand factor (VWF) has long been known to be a key player in thrombus formation at sites of vascular damage.While the association between VWF and coronary heart disease has been well studied, knowledge about the role ofVWF in stroke is much more limited. However, in recent years, an increasing amount of clinical and preclinical evidencehas revealed the critical involvement of VWF in stroke development. This review summarizes the latest insights intothe pathophysiologic role of VWF-related processes in ischemic brain injury under experimental conditions and inhumans. Potential clinical merits of novel inhibitors of VWF-mediated platelet adhesion and activation as powerful andsafe tools to combat thromboembolic disorders including ischemic stroke are discussed. Preclinical and clinical evidenceillustrates an important role of VWF in ischemic stroke, suggesting that VWF could become a promising target in stroketherapy. (Stroke. 2012;43:599-606.)

Key Words: glycoprotein Ib � platelets � stroke � von Willebrand factor

Ischemic stroke is a devastating disease that represents theprimary reason for sustained disability and the second

leading cause of death worldwide.1 Eighty percent of strokesare caused by arterial occlusion of cerebral arteries, whereasthe remaining 20% are caused by intracerebral hemorrhages.Currently, the only established therapeutic option for acutestroke is rapid thrombolysis using the clot-breaking agenttissue-type plasminogen activator (tPA) to achieve recana-lization of occluded cerebral vessels. However, due to theincreased risk of bleeding associated with late tPA admin-istration, intravenous tPA is recommended only within thelimited therapeutic time window of 4.5 hours poststrokeand thus is available to �10% of patients.2 A recent trial toextend the therapeutic window up to 9 hours by use ofrecombinant desmoteplase, a novel plasminogen activator,failed3 as did a trial using the defibrinogenating agentancrod.4

In terms of secondary stroke prevention, the situation is verysimilar. Antiplatelet agents such as acetylsalicylic acid, dipyri-damole, and the platelet P2Y12 receptor inhibitor clopidogrelshow only limited efficacy and substantially increase the risk offatal bleeding. This holds also true for anticoagulants, particu-larly warfarin, and even the introduction of novel substance

classes such as direct thrombin inhibitors (eg, dabigatran) orfactor Xa blockers (eg, rivaroxaban, apixaban) could not over-come the threat of hemorrhage. These limitations emphasize theneed for a better understanding of the pathophysiological mech-anisms of thrombus formation in acute ischemic stroke5 tosuccessfully improve treatment.

von Willebrand Factor: Role in Hemostasis,Thrombosis, and InflammationIn 1926, Finnish physician Erik von Willebrand reported anew type of inherited bleeding disorder that was distinct fromhemophilia A.6 Thirty years later, the plasma protein that iscentral to the disease was identified and was named vonWillebrand factor (vWF). Now, �50 years later, much of thestructure and function of vWF has been elucidated and its rolein maintaining the delicate balance between bleeding andthrombosis has become an intriguing subject. vWF is a large,multimeric glycoprotein. Along with serving as a protectivecarrier molecule for clotting factor VIII, its main function ismediating initial platelet adhesion at sites of vascular injury.Indeed, whereas this is a prerequisite for normal hemostasis,adhesion of platelets is also the first step in thrombosis and animportant mediator of inflammation.7

Received June 16, 2011; final revision received August 9, 2011; accepted September 6, 2011.Jeffrey L. Saver, MD, was the Guest Editor for this paper.From the Immune Disease Institute (S.F.D.M., D.D.W.) and the Program in Cellular and Molecular Medicine (S.F.D.M., D.D.W.), Children’s Hospital

Boston, Boston, MA; the Department of Pediatrics (S.F.D.M., D.D.W.), Harvard Medical School, Boston, MA; the Laboratory for Thrombosis Research(S.F.D.M.), KULeuven Campus Kortrijk, Kortrijk, Belgium; and the Department of Neurology (G.S., C.K.), University of Wuerzburg, Wuerzburg,Germany.

*D.D.W. and C.K. contributed equally.The online-only Data Supplement is available at http://stroke.ahajournals.org/lookup/suppl/doi:10.1161/STROKEAHA.111.628867/-/DC1.Correspondence to Simon De Meyer, PhD, Laboratory for Thrombosis Research, KULeuven Campus Kortrijk, E Sabbelaan 53, 8500 Kortrijk,

Belgium. E-mail [email protected]© 2011 American Heart Association, Inc.

Stroke is available at http://stroke.ahajournals.org DOI: 10.1161/STROKEAHA.111.628867

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The critical role of vWF in normal hemostasis is exempli-fied by von Willebrand disease. von Willebrand disease is themost common inherited bleeding disorder in humans, causedby quantitative or qualitative defects in vWF.8 Bleedingsymptoms range from mild (Type 1) to severe (Type 3) andinclude mucosal hemorrhages such as epistaxis, menorrhagia,and bleeding from the gums and gastrointestinal tract.

vWF is exclusively synthesized in endothelial cells andmegakaryocytes and circulates as multimers of varying size(up to 20 000 kDa). The multidomain structure of the mono-meric vWF building blocks (Figure 1) is fundamental to thefunction of vWF (Figure 2). Rapid binding of vWF (A3domain) to exposed fibrillar collagen Type I and III immo-bilizes vWF at sites of vascular damage. This and/or highshear blood leads to conformational changes, exposing thebinding site for platelet glycoprotein (GP)Ib� in the vWF A1domain. The reversible nature of the GPIb�–vWF A1 inter-actions allows deceleration and rolling of platelets, which,especially under high shear forces, is necessary for the

definitive arrest. Firm adhesion of platelets at the site ofvascular injury is further supported by engagement of theplatelet collagen receptors (GPVI and integrin �2�1) andleads to platelet activation. On platelet activation, solubleplatelet agonists such as adenosine 5�-diphosphate, adenosine5�-triphosphate, and thromboxane A2 are released and plate-let integrins like GPIIb/IIIa shift to a high-affinity state.Subsequent platelet aggregation is promoted by binding ofactivated platelet GPIIb/IIIa to its primary ligand fibrinogenand to the Arg-Gly-Asp sequence found in the C1 domain ofvWF. Additional incoming platelets are recruited to thegrowing thrombus, primarily through engagement of theirGPIb� receptors (Figure 2). Hence, the GPIb complex isessential for both initial platelet adhesion to sites of vascularinjury and recruitment of new platelets to the growingthrombus.

Besides its role in thrombus formation, vWF has also beenshown to support inflammatory processes. In vitro experi-ments demonstrated that vWF promotes leukocyte adhe-

Figure 1. Schematic representation of vWF. vWFis a multimeric protein composed of dimeric build-ing blocks. The vWF domains, the binding sites ofmajor binding partners, and the cleavage site forADAMTS13 are indicated. Adapted from De Meyeret al.8 vWF indicates von Willebrand factor.

Figure 2. Schematic representation of vWF-mediated platelet adhesion and aggregation.vWF that is immobilized on collagen with its A3domain or released from endothelial Weibel-Palade (WP) bodies recruits platelets by bind-ing with its A1 domain to platelet GPIb�.Together with fibrinogen (not shown), vWF fur-ther crosslinks platelets through binding of itsC1 domain to platelet GPIIb/IIIa. vWF indicatesvon Willebrand factor; GP, glycoprotein.

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sion by acting as a ligand for the leukocyte receptorsP-selectin glycoprotein ligand 1 and �2 integrin.9 vWF-bound platelets also were shown to support leukocytetethering and rolling under high shear stress.10 Morerecently, Petri et al showed that vWF promotes theextravasation of leukocytes from blood vessels in a strictlyplatelet and GPIb�-dependent way.11

ADAMTS13: A Biological Regulator ofvWF ActivityvWF activity is correlated with multimer size, with ultralargemultimers spontaneously binding to platelets. Ultralarge vWFis released from endothelial and platelet storage granules onstimulation with various thrombogenic or inflammatorysecretagogues, but also during hypoxia.12,13 To prevent spon-taneous thrombosis, ADAMTS13 (a disintegrin and metallo-protease with thrombospondin Type 1 repeats 13) cleaves theY1605-M1606 bond in the vWF A2 domain (Figures 1 and2), thereby digesting ultralarge vWF into smaller, less reac-tive molecules. As seen in thrombotic thrombocytopenicpurpura, ADAMTS13 deficiency is associated with throm-botic occlusion of microvessels from multiple organs, includ-ing the brain.14–16 Experimental studies in mice have demon-strated the antithrombotic and anti-inflammatory propertiesof ADAMTS13.17,18

vWF and Stroke RiskBecause of the pivotal role of vWF in platelet adhesion andthrombus formation, it seems logical to anticipate a correla-tion between high plasma levels of vWF and development ofcardiovascular disease. Although this relationship has beenwell studied for coronary heart disease,19 much less is knownabout the association between vWF levels and stroke. Whencomparing patients with stroke with healthy control subjects,several studies found an association between high vWF levelsand stroke20–28 and even different etiologic subtypes ofischemic stroke.29 However, increased vWF levels are awell-known marker of endothelial activation and/or dysfunc-tion and a conclusive interpretation of many of these case–control studies on the causative or consequential nature ofhigh vWF levels in patients with stroke has been obscured bythe poststroke time point of vWF measurement. By alsomeasuring the vWF propeptide, a recent investigation of 2independent case–control studies elegantly indicated thatendothelial cell activation and subsequent Weibel-Paladebody secretion is indeed an important mechanism underlyingthe association between total vWF levels and the occurrenceof a first ischemic stroke.30 Several prospective studies suchas the recent longitudinal analysis embedded in the Rotter-dam study31 clearly identified high plasma levels of vWF asa strong predictor of stroke.32–37 Importantly, correlationbetween vWF levels and stroke-related mortality persistedafter adjustment for common risk factors such as age, strokeseverity, and atrial fibrillation indicating that vWF is anindependent predictor.38 On a genetic level, vWF poly-morphisms have been identified that significantly raise therisk of ischemic stroke.39–41 Not all of these are associatedwith higher vWF levels, suggesting that other mechanisms

such as increased vWF activity could contribute to the risk ofstroke as well.

A major downregulator of vWF activity is ADAMTS13.Accordingly, low levels of ADAMTS13 come along with anincreased risk of cardiovascular disease, including ischemicstroke.25,28 Analogous to vWF, single nucleotide polymor-phisms in ADAMTS13 were found to be associated with theincidence of ischemic stroke in a Swedish population.42

Together, these proof-of-principle studies established thatplasma levels of vWF and/or ADAMTS13 are associatedwith the risk of stroke in the general population. However,determination of vWF and/or ADAMTS13 levels on a regularbasis to judge the risk of thromboembolic disease in individ-ual patients cannot be recommended until larger prospectivetrials and standardized test systems are available.

Experimental Studies: Role of vWF inAcute StrokeThe importance of vWF as a risk factor for stroke occurrenceand mortality in humans recently also stimulated experimen-tal studies in models of acute stroke. Using a mouse model oftransient middle cerebral artery occlusion, we showed thatmice that are deficient in vWF due to VWF gene abrogation(VWF�/�)43 are protected from brain ischemia/reperfusioninjury.44–46 Infarct sizes in VWF�/� were approximately 60%of the infarct volumes in wild-type controls 1 day aftertransient middle cerebral artery occlusion, which was accom-panied by reduced fibrin accumulation in the infarcted brainhemisphere. Accordingly, neurological scores assessing mo-tor function and coordination were significantly better inVWF�/� mice compared with controls. Importantly, geneticdisruption of vWF did not increase the risk of intracerebralbleeding in the context of ischemic stroke.45 Reconstitution ofplasma vWF by hydrodynamic gene transfer fully restoredthe susceptibility of VWF�/� mice to cerebral ischemiaunderlining the causative role of vWF in this setting.44,45 Thisis in line with the well-established antithrombotic effects ofvWF deficiency in several experimental arterial and venousthrombosis models.43,47–50 Further illustrating the critical roleof vWF in ischemia/reperfusion injury are the findings thatADAMTS13�/� mice are more susceptible to focal cerebralischemia.46,51 These mice developed significantly larger in-farctions with an increased accumulation of immune cells andthrombi in the ischemic brain tissue, resulting in more severeneurological deficits.51 On the other hand, intravenous admin-istration of recombinant ADAMTS13 into wild-type miceimmediately before reperfusion significantly reduced infarctvolume.46

By reconstituting VWF�/� mice with different vWF mu-tants, we recently showed that binding of vWF to bothcollagen and GPIb�, but not to GPIIb/IIIa, is a mandatorystep in stroke development.44 The involvement of collagenand GPIb�-mediated platelet adhesion in stroke is corrobo-rated by the findings that blocking platelet collagen receptorGPVI or GPIb� also confers a protective effect in the mousetransient middle cerebral artery occlusion model.52 Blockadeof GPIIb/IIIa did not affect stroke size and led to an increasedincidence of intracerebral hemorrhage, whereas blocking ofGPIb� or GPVI did not increase the frequency of intracere-

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bral bleeding.52 Finally, mice in which downstream signalingof GPIb through phospholipase D1 is abrogated and mice inwhich the extracellular part of GPIb� is replaced by humaninterleukin-4 receptor (GPIb�/IL4R�)53 are also protectedagainst focal cerebral ischemia without causing excessivebleeding.54,54a These observations further underline thatblockage of the GPIb�–vWF axis or collagen–platelet axismight be a safe approach in ischemic stroke.

Inhibitors of vWF: A Promising Class ofAntithrombotics on the Brink of Reachingthe ClinicFrom this, it is clear that pharmacological interference invWF-mediated platelet adhesion and thrombus formationcould have clinical benefit as a promising strategy in stroketreatment. Although no such vWF blockers have yet achievedregulatory approval for marketing, there are promising pre-clinical and clinical studies that demonstrate the antithrom-botic potential of agents that inhibit vWF function by block-ing the vWF–collagen or vWF–GPIb� interaction (Figure 3).In this section, we discuss candidate molecules that couldprove useful in stroke therapy based on the encouragingresults they have demonstrated in the inhibition of vWF-mediated thrombosis. These inhibitors include monoclonalantibodies against vWF (82D6A3, AJvW2 and its humanizedform AJW200) or GPIb� (6B4 and its humanized formh6B4), the nanobody ALX-0081, the aptamer ARC1779, andthe recombinant GPIb� fragment GPG-290 (Table).55–57 Adetailed overview of the key features of each of theseinhibitors is given in the online-only Supplemental Table(http://stroke.ahajournals.org).

Although most attention has been focused on the develop-ment of vWF–GPIb� inhibitors, the anti-vWF antibody82D6A3 is different in that it inhibits the binding of vWF to

collagen. Preclinical studies in baboons have demonstratedthat 82D6A3 has a strong antithrombotic efficacy.58 Thisobservation indicates that, despite the existence of otherbinding partners for vWF in the extracellular matrix, vWFbinding to fibrillar collagen has an important role in mediat-ing thrombosis. A humanized version of 82D6A3 has beenconstructed for further preclinical and clinical testing.59

AJvW2, AJW200, 6B4, and h6B4 are monoclonal antibod-ies designed to disrupt the vWF–GPIb� interaction by bind-ing to the vWF A1 domain and GPIb�, respectively. Bothantibodies have been tested extensively in preclinical throm-bosis models.60–67 The clinical efficacy and tolerance of

Figure 3. Schematic representation of mode-of-action of various vWF inhibitors. vWF-mediatedplatelet adhesion can be blocked by inhibitingbinding of vWF to either collagen or GPIb� or bycleaving vWF by ADAMTS13. vWF indicates vonWillebrand factor; GP, glycoprotein.

Table. Inhibitors of vWF-Mediated Platelet Adhesion*

Compound Description

82D6A3 Monoclonal antibody against vWF A3 domain thatinhibits binding of vWF to collagen

6B4 h6B4 Fab-fragment of a monoclonal antibody againstplatelet GPIb� that inhibits binding of vWF to GPIb�

AJvW2 AJW200 Monoclonal antibody against vWF A1 domain thatinhibits binding of vWF to GPIb�

GPG-290 Chimeric recombinant protein containinggain-of-function GPIb� fragment that binds to A1

domain thereby inhibiting binding of vWF to GPIb�

ARC1779 Aptamer against vWF A1 domain that inhibitsbinding of vWF to GPIb�

ALX-0081 ALX-0681 Nanobody against vWF A1 domain that inhibitsbinding of vWF to GPIb�

rADAMTS13 Recombinant protein that cleaves vWF multimers bycleaving the Y1605-M1606 bond in the vWF A2

domain

vWF indicates von Willebrand factor; GP, glycoprotein.*A detailed description of each of these inhibitors is given in the online-only

Supplemental Table (http://stroke.ahajournals.org).




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AJW200 has been demonstrated in human volunteers withoutbleeding complications.68

GPG-290 is a homodimeric recombinant fragment ofhuman GPIb� composed of the first 290 amino acids andconjugated to human IgG1Fc to form a homodimer. GPG-290contains 2 gain-of-function mutations (G233V/M239V) re-sulting in its enhanced affinity for the vWF A1 domain (andpossibly other GPIb� ligands). Its antithrombotic activity wasdemonstrated in preclinical murine and canine models ofarterial and venous thrombosis.48,69,70

The aptamer ARC1779 represents an interesting new classof inhibitors. Aptamers are nucleic acid macromolecules thattightly bind to a specific molecular target.71 In solution, thechain of nucleotides forms intramolecular interactions thatfold the molecule into a complex 3-dimensional shape thatenhances affinity for its target molecule. A potential advan-tage of this class of molecules is that they can be inactivatedby a complementary aptamer antidote if necessary. ARC1779is a 40-nucleotide DNA/RNA aptamer conjugated to a 20-kDa polyethylene glycol to enhance its pharmacokineticproperties. ARC1779 binds to the vWF A1 domain and wasreported to effectively inhibit thrombus formation in severalpreclinical settings.72,73 The aptamer was well tolerated inhealthy volunteers in a Phase I trial. Importantly, in a PhaseII trial, ARC1779 effectively increased platelet counts incritically ill patients with thrombotic thrombocytopenic pur-pura by blocking spontaneous vWF-mediated platelet aggre-gation74–76 and even prevented desmopressin-induced throm-bocytopenia in patients with von Willebrand disease Type2B.77 High-affinity aptamers to murine vWF have recentlybeen developed, which will allow the investigation of anti-vWF aptamers in murine preclinical models of thrombosis,including stroke.78 Interestingly, a recent trial showed thatARC1779 was able to reduce cerebral emboli signals inpatients undergoing carotid endarterectomy.79

Nanobodies are antibody-derived therapeutic proteins thatcontain the structural and functional properties of naturallyoccurring heavy-chain antibodies. The cameloid bivalentNanobody ALX-0081 specifically targets exposed GPIb�-binding sites in vWF. By blocking GPIb� binding to vWF,ALX-0081 showed strong antithrombotic potency in preclin-ical baboon studies and in blood obtained from patientsundergoing percutaneous coronary intervention.80,81 In aPhase I clinical study, this nanobody was found to be welltolerated and safe. ALX-0081 (and ALX-0681, a subcutane-ous formulation of ALX-0081) entered a Phase II study inpatients undergoing percutaneous coronary intervention andrecently also a Phase II study in patients with thromboticthrombocytopenic purpura.

Apart from blocking binding of vWF to either collagen orGPIb�, another way of reducing vWF activity is decreasingits size by ADAMTS13. Recombinant ADAMTS13 is beingdeveloped as a new therapeutic agent and, as mentionedearlier, was protective in a preclinical mouse model ofischemic stroke.46 Recombinant human ADAMTS13 hasreceived orphan designation for the treatment of thromboticthrombocytopenic purpura (EU/3/08/588).

Potential Use of vWF Antagonism inStroke TherapyBecause vWF antagonists are starting to enter the first clinicaltrials, it is interesting to speculate on the potential role ofthese new drugs in stroke therapy. Inhibitors of the vWF–GPIb� or vWF– collagen interaction have no directthrombolytic properties, so their use is unlikely to result indissolution of an already existing thrombus in the acutesetting of ischemic stroke. However, when used in combina-tion with tPA, vWF antagonists could prevent ongoingmicrovascular thrombus formation during the reperfusionphase after successful or spontaneous thrombolysis,82,83 re-ducing the occurrence of rethrombosis and/or secondarystroke progression. Whether dual therapy of vWF inhibitorsand tPA would allow the use of lower and thereby safer dosesof tPA remains to be established. The use of tPA-dependentexperimental thromboembolic stroke models will have toshed more light on the possible beneficial effects of combin-ing thrombolytic therapy with vWF inhibition. Former at-tempts to prevent the apposition of further clots into analready existing thrombus during the early stage of ischemicstroke by applying heparins failed.84 Although heparins couldcounteract deterioration of stroke symptoms in some studies,the net clinical benefit was outweighed by an increased riskedof severe hemorrhages. Consequently, full-intensity paren-teral anticoagulation with heparins is no longer recommendedin the acute phase of cerebral ischemia.85 In view of theanticipated safer benefit-over-risk ratio in terms of bleeding,it will be interesting to see whether vWF antagonists are moresuccessful than heparins during the acute phase of ischemicstroke. Nevertheless, close CT or MRI monitoring of potentialhemorrhagic transformation should accompany potential futureapplications of vWF inhibitors in patients with stroke. Interest-ingly, recombinant ADAMTS13 promoted thrombus dissolutionin injured mouse mesenteric arterioles,17 calling for furtherstudies of the thrombolytic potential of ADAMTS13 in acuteischemic stroke.

With regard to stroke prevention, vWF inhibition couldbecome useful for short-term therapy during proceduresassociated with increased risk of cerebral thromboembolismsuch as angiography, carotid endarterectomy, or heart surgeryunder conditions of extracorporeal circulation. Promisingresults were recently obtained with ARC1779, which signif-icantly reduced cerebral embolization in patients undergoingcarotid endarterectomy.79 In the absence of oral formulations,the potential of vWF blockers to prevent stroke or systemicembolism in chronic conditions, for example, in patients withatrial fibrillation, cannot yet be judged.

ConclusionsThere is now compelling evidence on preclinical and clinicallevels that interactions between the cerebral blood vessels andplatelets using vWF, GPIb�, and collagen are instrumental inischemic brain disease. Early clinical testing of lead com-pounds targeting vWF-mediated platelet adhesion in healthyindividuals or selected disease states points toward a favor-able bleeding risk profile and higher efficacy as comparedwith established antithrombotic drugs. Based on the encour-aging results in rodent stroke models, larger translational




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studies in nonhuman primates and proof-of-principle clinicaltrials are now warranted to further judge the risk-to-benefitratio of interfering with the early steps of platelet activation.If these trials are as promising as the current experimentaldata, an exciting decade exploring vWF-targeted strokestrategies lies ahead. Back in 1926, Dr von Willebrand maynot have fully grasped what great implications his seminalreport6 on a bleeding disease would have on our understand-ing and treatment of thrombotic disorders. More than 90 yearslater, stroke may very well become one of them.

AcknowledgmentsWe thank Lesley Cowan for helping with the preparation of thearticle. We thank Dr Robert Schaub and Dr Karen Vanhoorelbeke forcritical reading and helpful advice.

Sources of FundingThis work was supported by National Heart, Lung, and BloodInstitute of the National Institutes of Health grant R01 HL041002 (toD.D.W.). S.F.D.M. is a postdoctoral fellow of the Research Foun-dation Flanders (Fonds voor Wetenschappelijk Onderzoek Vlaan-deren). G.S. and C.K. are supported by the Deutsche Forschungsge-meinschaft, Bonn, Germany, SFB 688, projects A13 and B1.

DisclosuresNone.

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32. Roldan V, Marín F, García-Herola A, Lip GYH. Correlation of plasmavon Willebrand factor levels, an index of endothelial damage/dysfunction, with two point-based stroke risk stratification scores in atrialfibrillation. Thromb Res. 2005;116:321–325.

33. Lip GYH, Lane D, Van Walraven C, Hart RG. Additive role of plasmavon Willebrand factor levels to clinical factors for risk stratification ofpatients with atrial fibrillation. Stroke. 2006;37:2294–2300.

34. Pinto A, Tuttolomondo A, Casuccio A, Di Raimondo D, Di Sciacca R,Arnao V, et al. Immuno-inflammatory predictors of stroke at follow-up inpatients with chronic non-valvular atrial fibrillation (NVAF). Clin Sci.2009;116:781–789.




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35. Conway DSG, Pearce LA, Chin BSP, Hart RG, Lip GYH. Prognosticvalue of plasma von Willebrand factor and soluble P-selectin as indices ofendothelial damage and platelet activation in 994 patients with nonval-vular atrial fibrillation. Circulation. 2003;107:3141–3145.

36. Tzoulaki I, Murray GD, Lee AJ, Rumley A, Lowe GDO, Fowkes FGR.Relative value of inflammatory, hemostatic, and rheological factors forincident myocardial infarction and stroke: the Edinburgh Artery Study.Circulation. 2007;115:2119–2127.

37. Folsom AR, Rosamond WD, Shahar E, Cooper LS, Aleksic N, Nieto FJ,et al. Prospective study of markers of hemostatic function with risk ofischemic stroke. The Atherosclerosis Risk in Communities (ARIC) StudyInvestigators. Circulation. 1999;100:736–742.

38. Carter AM, Catto AJ, Mansfield MW, Bamford JM, Grant PJ. Predictivevariables for mortality after acute ischemic stroke. Stroke. 2007;38:1873–1880.

39. van Schie MC, de Maat MPM, Isaacs A, van Duijn CM, Deckers JW,Dippel DWJ, et al. Variation in the von Willebrand factor gene isassociated with vWF levels and with the risk of cardiovascular disease.Blood. 2011;117:1393–1399.

40. Dai K, Gao W, Ruan C. The SMA I polymorphism in the von Willebrandfactor gene associated with acute ischemic stroke. Thromb Res. 2001;104:389–395.

41. van Schie MC, van Loon JE, de Maat MP, Leebeek FW. Genetic deter-minants of von Willebrand factor levels and activity in relation to the riskof cardiovascular disease. A review. J Thromb Haemost. 2011;9:899–908.

42. Hanson E, Jood K, Nilsson S, Blomstrand C, Jern C. Association betweengenetic variation at the ADAMTS13 locus and ischemic stroke. J ThrombHaemost. 2009;7:2147–2148.

43. Denis C, Methia N, Frenette PS, Rayburn H, Ullman-Cullere M, HynesRO, et al. A mouse model of severe von Willebrand disease: defects inhemostasis and thrombosis. Proc Natl Acad Sci U S A. 1998;95:9524–9529.

44. De Meyer SF, Schwarz T, Deckmyn H, Denis CV, Nieswandt B, Stoll G,et al. Binding of von Willebrand factor to collagen and glycoproteinIbalpha, but not to glycoprotein IIb/IIIa, contributes to ischemic stroke inmice. Arterioscler Thromb Vasc Biol. 2010;30:1949–1951.

45. Kleinschnitz C, De Meyer SF, Schwarz T, Austinat M, Vanhoorelbeke K,Nieswandt B, et al. Deficiency of von Willebrand factor protects micefrom ischemic stroke. Blood. 2009;113:3600–3603.

46. Zhao B-Q, Chauhan AK, Canault M, Patten IS, Yang JJ, Dockal M, et al.von Willebrand factor-cleaving protease ADAMTS13 reduces ischemicbrain injury in experimental stroke. Blood. 2009;114:3329–3334.

47. De Meyer SF, Vandeputte N, Pareyn I, Petrus I, Lenting PJ, Chuah MKL,et al. Restoration of plasma von Willebrand factor deficiency is sufficientto correct thrombus formation after gene therapy for severe von Wille-brand disease. Arterioscler Thromb Vasc Biol. 2008;28:1621–1626.

48. Brill A, Fuchs TA, Chauhan AK, Yang JJ, De Meyer SF, Kollnberger M,et al. von Willebrand factor-mediated platelet adhesion is critical for deepvein thrombosis in mouse models. Blood. 2011;117:1400–1407.

49. Chauhan AK, Kisucka J, Lamb CB, Bergmeier W, Wagner DD. vonWillebrand factor and factor VIII are independently required to formstable occlusive thrombi in injured veins. Blood. 2007;109:2424–2429.

50. Ni H, Denis CV, Subbarao S, Degen JL, Sato TN, Hynes RO, et al.Persistence of platelet thrombus formation in arterioles of mice lackingboth von Willebrand factor and fibrinogen. J Clin Invest. 2000;106:385–392.

51. Fujioka M, Hayakawa K, Mishima K, Kunizawa A, Irie K, Higuchi S, etal. ADAMTS13 gene deletion aggravates ischemic brain damage: apossible neuroprotective role of ADAMTS13 by ameliorating postische-mic hypoperfusion. Blood. 2010;115:1650–1653.

52. Kleinschnitz C, Pozgajova M, Pham M, Bendszus M, Nieswandt B, StollG. Targeting platelets in acute experimental stroke: impact of glycopro-tein Ib, VI, and IIb/IIIa blockade on infarct size, functional outcome, andintracranial bleeding. Circulation. 2007;115:2323–2330.

53. Kanaji T, Russell S, Ware J. Amelioration of the macrothrombocytopeniaassociated with the murine Bernard-Soulier syndrome. Blood. 2002;100:2102–2107.

54. Elvers M, Stegner D, Hagedorn I, Kleinschnitz C, Braun A, KuijpersMEJ, et al. Impaired alpha(IIb)beta(3) integrin activation and shear-dependent thrombus formation in mice lacking phospholipase D1. SciSignal. 2010;3:ra1.

54a.De Meyer SF, Schwarz T, Schatzberg D, Wagner DD. Platelet glyco-protein lb� is an important mediator of ischemic stroke in mice. ExpTransl Stroke Med. 2011;3:9.

55. De Meyer SF, De Maeyer B, Deckmyn H, Vanhoorelbeke K. von Wil-lebrand factor: drug and drug target. Cardiovasc Hematol Disord DrugTargets. 2009;9:9–20.

56. De Meyer SF, Vanhoorelbeke K, Ulrichts H, Staelens S, Feys HB, SallesI, et al. Development of monoclonal antibodies that inhibit plateletadhesion or aggregation as potential anti-thrombotic drugs. CardiovascHematol Disord Drug Targets. 2006;6:191–207.

57. Firbas C, Siller-Matula JM, Jilma B. Targeting von Willebrand factor andplatelet glycoprotein Ib receptor. Expert Rev Cardiovasc Ther. 2010;8:1689–1701.

58. Wu D, Vanhoorelbeke K, Cauwenberghs N, Meiring M, Depraetere H,Kotze HF, et al. Inhibition of the von Willebrand (vWF)–collagen inter-action by an antihuman vWF monoclonal antibody results in abolition ofin vivo arterial platelet thrombus formation in baboons. Blood. 2002;99:3623–3628.

59. Staelens S, Desmet J, Ngo TH, Vauterin S, Pareyn I, Barbeaux P, et al.Humanization by variable domain resurfacing and grafting on a humanIgG4, using a new approach for determination of non-human like surfaceaccessible framework residues based on homology modelling of variabledomains. Mol Immunol. 2006;43:1243–1257.

60. Kageyama S, Yamamoto H, Nagano M, Arisaka H, Kayahara T,Yoshimoto R. Anti-thrombotic effects and bleeding risk of AJvW-2, amonoclonal antibody against human von Willebrand factor. Br JPharmacol. 1997;122:165–171.

61. Kageyama S, Yamamoto H, Nakazawa H, Yoshimoto R. Anti-humanvWF monoclonal antibody, AJvW-2 Fab, inhibits repetitive coronaryartery thrombosis without bleeding time prolongation in dogs. ThrombRes. 2001;101:395–404.

62. Kageyama S, Yamamoto H, Yoshimoto R. Anti-human von Willebrandfactor monoclonal antibody AJvW-2 prevents thrombus deposition andneointima formation after balloon injury in guinea pigs. ArteriosclerThromb Vasc Biol. 2000;20:2303–2308.

63. Cauwenberghs N, Meiring M, Vauterin S, van Wyk V, Lamprecht S,Roodt JP, et al. Antithrombotic effect of platelet glycoprotein Ib-blockingmonoclonal antibody Fab fragments in nonhuman primates. ArteriosclerThromb Vasc Biol. 2000;20:1347–1353.

64. Fontayne A, Meiring M, Lamprecht S, Roodt J, Demarsin E, Barbeaux P,et al. The humanized anti-glycoprotein Ib monoclonal antibody h6B4-Fabis a potent and safe antithrombotic in a high shear arterial thrombosismodel in baboons. Thromb Haemost. 2008;100:670–677.

65. Fontayne A, Vanhoorelbeke K, Pareyn I, Van Rompaey I, Meiring M,Lamprecht S, et al. Rational humanization of the powerful antithromboticanti-GPIbalpha antibody: 6B4. Thromb Haemost. 2006;96:671–684.

66. Wu D, Meiring M, Kotze HF, Deckmyn H, Cauwenberghs N. Inhibitionof platelet glycoprotein Ib, glycoprotein IIb/IIIa, or both by monoclonalantibodies prevents arterial thrombosis in baboons. Arterioscler ThrombVasc Biol. 2002;22:323–328.

67. Kageyama S, Yamamoto H, Nakazawa H, Matsushita J, Kouyama T,Gonsho A, et al. Pharmacokinetics and pharmacodynamics of AJW200, ahumanized monoclonal antibody to von Willebrand factor, in monkeys.Arterioscler Thromb Vasc Biol. 2002;22:187–192.

68. Machin SJ, Clarke C, Ikemura O, Kageyama S, Mackie IJ, Talbot JA, etal. A humanized monoclonal antibody against vWF A1 domain inhibitsvWF:RiCof activity and platelet adhesion in human volunteers. J ThrombHaemost. 2003;1:Abstract OC328.

69. Hennan JK, Swillo RE, Morgan GA, Leik CE, Brooks JM, Shaw GD, etal. Pharmacologic inhibition of platelet vWF–GPIb alpha interactionprevents coronary artery thrombosis. Thromb Haemost. 2006;95:469–475.

70. Wadanoli M, Sako D, Shaw GD, Schaub RG, Wang Q, Tchernychev B,et al. The von Willebrand factor antagonist (GPG-290) prevents coronarythrombosis without prolongation of bleeding time. Thromb Haemost.2007;98:397–405.

71. Keefe AD, Schaub RG. Aptamers as candidate therapeutics for cardio-vascular indications. Curr Opin Pharmacol. 2008;8:147–152.

72. Diener JL, Daniel Lagasse HA, Duerschmied D, Merhi Y, Tanguay J-F,Hutabarat R, et al. Inhibition of von Willebrand factor-mediated plateletactivation and thrombosis by the anti-von Willebrand factor A1-domainaptamer ARC1779. J Thromb Haemost. 2009;7:1155–1162.

73. Rottman JB, Gilbert M, Marsh HN, Boomer RM, Fraone JM, Makim A,et al. An anti-von Willebrand’s factor A1 domain aptamer inhibits arterialthrombosis induced by electrical injury in cynomolgus macaques.J Thromb Haemost. 2007;5:Abstract P-S-664.

74. Cataland SR, Peyvandi F, Mannucci PM, Lammle B, Hovinga JAK,Machin SJ, et al. A randomized, double-blind, placebo-controlled, clinical




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75. Jilma-Stohlawetz P, Gorczyca ME, Jilma B, Siller-Matula J, Gilbert JC,Knobl P. Inhibition of von Willebrand factor by ARC1779 in patientswith acute thrombotic thrombocytopenic purpura. Thromb Haemost.2011;105:545–552.

76. Knobl P, Jilma B, Gilbert JC, Hutabarat RM, Wagner PG, Jilma-Stohlawetz P. Anti-von Willebrand factor aptamer ARC1779 forrefractory thrombotic thrombocytopenic purpura. Transfusion. 2009;49:2181–2185.

77. Jilma B, Paulinska P, Jilma-Stohlawetz P, Gilbert JC, Hutabarat R, KnoblP. A randomised pilot trial of the anti-von Willebrand factor aptamerARC1779 in patients with type 2b von Willebrand disease. ThrombHaemost. 2010;104:563–570.

78. Woelfel M, De Meyer SF, Wagner P, McGinness KE, Wagner DD,Schaub R. The generation of an aptamer inhibitor of murine von Wille-brand factor (vWF) mediated platelet aggregation. Blood. 2010;116:Abstract 4312.

79. Markus HS, McCollum C, Imray C, Goulder MA, Gilbert J, King A. Thevon Willebrand inhibitor ARC1779 reduces cerebral embolization aftercarotid endarterectomy: a randomized trial. Stroke. 2011;42:2149–2153.

80. Ulrichts H, Silence K, Schoolmeester A, de Jaegere P, Rossenu S, RoodtJ, et al. Antithrombotic drug candidate ALX-0081 shows superior pre-

clinical efficacy and safety compared to currently marketed antiplateletdrugs. Blood. 2011;118:757–765.

81. van Loon JE, de Jaegere PP, Ulrichts H, van Vliet HH, de Maat MP, deGroot PG, et al. The in vitro effect of the new antithrombotic drugcandidate ALX-0081 on blood samples of patients undergoing percuta-neous coronary intervention. Thromb Haemost. 2011;106:165–171.

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Simon F. De Meyer, Guido Stoll, Denisa D. Wagner and Christoph Kleinschnitzvon Willebrand Factor: An Emerging Target in Stroke Therapy

Print ISSN: 0039-2499. Online ISSN: 1524-4628 Copyright © 2011 American Heart Association, Inc. All rights reserved.

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SUPPLEMTENTAL MATERIAL

von Willebrand factor: an emerging target in stroke therapy

Simon F. De Meyer et al.

Supplemental Table. Inhibitors of VWF-mediated platelet adhesion

Compound Antithrombotic

mechanism

Development

stage

Preclinical and clinical antithrombotic

evidence

82D6A3 • Moab

• Targets VWF

A3 domain

• Interrupts

collagen-

VWF binding

preclinical • Epitope overlaps with collagen-binding

region in VWF A3 domain1

• Inhibited in vitro binding of VWF to

collagen, with a more pronounced effect

with increasing shear stress 1, 2

• Abolished thrombus formation in a

thrombosis model in baboons without

prolongation of bleeding time3

• Humanized version has been

constructed4

6B4

h6B4

• Moab (Fab)

• Targets

GPIbα

• Interrupts

VWF-GPIbα

binding

preclinical • Epitope identified as two different

regions in GPIbα5

• Inhibited ex vivo VWF-mediated

platelet agglutination and platelet

adhesion to collagen6

• Fab fragments inhibited thrombus

formation in two thrombosis models in

baboons without significant effect on

bleeding times6, 7

• Fab fragments showed a broader safe

therapeutic window compared to a

GPIIb/IIIa antagonist in baboons7

• Humanized version was constructed and

abolished thrombus formation in

baboons8, 9

AJvW2

AJW200

• Moab

• Targets VWF

A1 domain

• Interrupts

VWF-GPIbα

binding

Clinical (No

active clinical

studies

ongoing)

• Conformation epitope identified in VWF

A1 domain10

• Inhibited ex vivo VWF-mediated

platelet adhesion and agglutination10, 11

• Abolished thrombus formation and

showed a superior bleeding safety

profile in comparison to GPIIb/IIIa

antagonism in both guinea pigs and

dogs11, 12

• A humanized version (AJW200) was

generated which inhibited thrombus

formation in dogs with a safer bleeding

profile compared to GPIIb/IIIa

antagonism 13, 14

• AJW200 was well tolerated in human

volunteers without bleeding

complications15

GPG-290 • Chimeric

recombinant

protein

containing

gain-of-

function

GPIbα

fragment

preclinical • Reduced arterial thrombus formation in

dog thrombosis models16, 17

• Reduced venous thrombosis in mice18

• Showed superior bleeding safety profile

compared to clopidogrel16

• Targets VWF

A1 domain

• Interrupts

VWF-GPIbα

binding

ARC1779 • Aptamer

• Targets VWF

A1 domain

• Interrupts

VWF-GPIbα

binding

Clinical (no

active clinical

studies

ongoing)

• Inhibited VWF dependent platelet

adhesion and agglutination19

• Inhibited thrombus formation in a

cynomolgus monkey thrombosis model19

• Well tolerated in human volunteers20

• Inhibited ex vivo VWF activity in blood

from patients with acute coronary

syndrome21

• Raised platelet counts in patients with

TTP22, 23

• Prevented thrombocytopenia in patients

with VWD type 2B24

• reduced cerebral emobolization in

patiens undergoing carotid

endarterectomy.25

ALX-0081

ALX-0681

• Nanobody®

• Targets VWF

A1 domain

• Interrupts

VWF-GPIbα

binding

clinical • Abolished thrombus formation in a

baboon thrombosis model and showed

superior therapeutic window compared

to aspirin, clopidogrel and abciximab26

• Well tolerated and inhibited ex vivo

platelet adhesion in patients having TTP

or undergoing PCI26-28

• Entered a Phase II study in TTP patients

rADAMTS13 • Recombinant

protein

preclinical • Delays thrombus formation in a mouse

thrombosis model29

• Cleaves VWF

A2 domain

• Improves experimental stroke outcome

in mice30

Supplemental references

1. Vanhoorelbeke K, Depraetere H, Romijn RA, Huizinga EG, De Maeyer M,

Deckmyn H. A consensus tetrapeptide selected by phage display adopts the conformation of a dominant discontinuous epitope of a monoclonal anti-VWF antibody that inhibits the von Willebrand factor-collagen interaction. J. Biol. Chem. 2003;278:37815-37821

2. Hoylaerts MF, Yamamoto H, Nuyts K, Vreys I, Deckmyn H, Vermylen J. von Willebrand factor binds to native collagen VI primarily via its A1 domain. Biochem. J. 1997;324:185-191

3. Wu D, Vanhoorelbeke K, Cauwenberghs N, Meiring M, Depraetere H, Kotze HF, et al. Inhibition of the von Willebrand (VWF)-collagen interaction by an antihuman VWF monoclonal antibody results in abolition of in vivo arterial platelet thrombus formation in baboons. Blood. 2002;99:3623-3628

4. Staelens S, Desmet J, Ngo TH, Vauterin S, Pareyn I, Barbeaux P, et al. Humanization by variable domain resurfacing and grafting on a human IgG4, using a new approach for determination of non-human like surface accessible framework residues based on homology modelling of variable domains. Mol. Immunol. 2006;43:1243-1257

5. Cauwenberghs N, Vanhoorelbeke K, Vauterin S, Westra DF, Romo G, Huizinga EG, et al. Epitope mapping of inhibitory antibodies against platelet glycoprotein Ibalpha reveals interaction between the leucine-rich repeat N-terminal and C-terminal flanking domains of glycoprotein Ibalpha. Blood. 2001;98:652-660

6. Cauwenberghs N, Meiring M, Vauterin S, van Wyk V, Lamprecht S, Roodt JP, et al. Antithrombotic effect of platelet glycoprotein Ib-blocking monoclonal antibody Fab fragments in nonhuman primates. Arterioscler. Thromb. Vasc. Biol. 2000;20:1347-1353

7. Wu D, Meiring M, Kotze HF, Deckmyn H, Cauwenberghs N. Inhibition of platelet glycoprotein Ib, glycoprotein IIb/IIIa, or both by monoclonal antibodies prevents arterial thrombosis in baboons. Arterioscler. Thromb. Vasc. Biol. 2002;22:323-328

8. Fontayne A, Meiring M, Lamprecht S, Roodt J, Demarsin E, Barbeaux P, et al. The humanized anti-glycoprotein Ib monoclonal antibody h6B4-Fab is a potent and safe antithrombotic in a high shear arterial thrombosis model in baboons. Thromb. Haemost. 2008;100:670-677

9. Fontayne A, Vanhoorelbeke K, Pareyn I, Van Rompaey I, Meiring M, Lamprecht S, et al. Rational humanization of the powerful antithrombotic anti-GPIbalpha antibody: 6B4. Thromb. Haemost. 2006;96:671-684

10. Yamamoto H, Vreys I, Stassen JM, Yoshimoto R, Vermylen J, Hoylaerts MF. Antagonism of vWF inhibits both injury induced arterial and venous thrombosis in the hamster. Thromb. Haemost. 1998;79:202-210

11. Kageyama S, Yamamoto H, Nagano M, Arisaka H, Kayahara T, Yoshimoto R. Anti-thrombotic effects and bleeding risk of AJvW-2, a monoclonal antibody against human von Willebrand factor. Br J Pharmacol. 1997;122:165-171

12. Kageyama S, Yamamoto H, Nakazawa H, Yoshimoto R. Anti-human vWF monoclonal antibody, AJvW-2 Fab, inhibits repetitive coronary artery thrombosis without bleeding time prolongation in dogs. Thromb. Res. 2001;101:395-404

13. Kageyama S, Matsushita J, Yamamoto H. Effect of a humanized monoclonal antibody to von Willebrand factor in a canine model of coronary arterial thrombosis. Eur. J. Pharmacol. 2002;443:143-149

14. Kageyama S, Yamamoto H, Nakazawa H, Matsushita J, Kouyama T, Gonsho A, et al. Pharmacokinetics and pharmacodynamics of AJW200, a humanized monoclonal antibody to von Willebrand factor, in monkeys. Arterioscler Thromb Vasc Biol. 2002;22:187-192

15. Machin SJ, Clarke C, Ikemura O, Kageyama S, Mackie IJ, Talbot JA, et al. A humanized monoclonal antibody against VWF A1 domain inhibits VWF:RiCof activity and platelet adhesion in human volunteers. J Thromb Haemost. 2003;1:Abstract OC328

16. Hennan JK, Swillo RE, Morgan GA, Leik CE, Brooks JM, Shaw GD, et al. Pharmacologic inhibition of platelet vWF-GPIb alpha interaction prevents coronary artery thrombosis. Thromb. Haemost. 2006;95:469-475

17. Wadanoli M, Sako D, Shaw GD, Schaub RG, Wang Q, Tchernychev B, et al. The von Willebrand factor antagonist (GPG-290) prevents coronary thrombosis without prolongation of bleeding time. Thromb. Haemost. 2007;98:397-405

18. Brill A, Fuchs TA, Chauhan AK, Yang JJ, De Meyer SF, Köllnberger M, et al. von Willebrand factor-mediated platelet adhesion is critical for deep vein thrombosis in mouse models. Blood. 2011;117:1400-1407

19. Diener JL, Daniel Lagassé HA, Duerschmied D, Merhi Y, Tanguay J-F, Hutabarat R, et al. Inhibition of von Willebrand factor-mediated platelet activation and thrombosis by the anti-von Willebrand factor A1-domain aptamer ARC1779. J Thromb Haemost. 2009;7:1155-1162

20. Gilbert JC, DeFeo-Fraulini T, Hutabarat RM, Horvath CJ, Merlino PG, Marsh HN, et al. First-in-human evaluation of anti von Willebrand factor therapeutic aptamer ARC1779 in healthy volunteers. Circulation. 2007;116:2678-2686

21. Spiel AO, Mayr FB, Ladani N, Wagner PG, Schaub RG, Gilbert JC, et al. The aptamer ARC1779 is a potent and specific inhibitor of von Willebrand Factor mediated ex vivo platelet function in acute myocardial infarction. Platelets. 2009;20:334-340

22. Knöbl P, Jilma B, Gilbert JC, Hutabarat RM, Wagner PG, Jilma-Stohlawetz P. Anti-von Willebrand factor aptamer ARC1779 for refractory thrombotic thrombocytopenic purpura. Transfusion. 2009;49:2181-2185

23. Jilma B, Jilma P, Gilbert J, Hutabarat R, Siller J, Spiel A, et al. Safety, pharmacokinetics and pharmacodynamics of the anti von willebrand factor aptamer ARC1779 in patients with acute thrombotic thrombocytopenic purpura (TTP). J Thromb Haemost. 2009;7:Abstract AS-WE-014

24. Jilma B, Paulinska P, Jilma-Stohlawetz P, Gilbert JC, Hutabarat R, Knöbl P. A randomised pilot trial of the anti-von Willebrand factor aptamer ARC1779 in patients with type 2b von Willebrand disease. Thromb. Haemost. 2010;104:563-570

25. Markus HS, McCollum C, Imray C, Goulder MA, Gilbert J, King A. The von Willebrand Inhibitor ARC1779 Reduces Cerebral Embolization After Carotid Endarterectomy: A Randomized Trial. [published online ahead of print June 23, 2011]. Stroke. 2011 http://stroke.ahajournals.org/content/early/recent. Accessed July 19, 2011

26. Ulrichts H, Silence K, Schoolmeester A, de Jaegere P, Rossenu S, Roodt J, et al. Antithrombotic drug candidate ALX-0081 shows superior preclinical efficacy and safety compared to currently marketed antiplatelet drugs. [published online ahead of print May 16, 2011]. Blood. 2011 http://bloodjournal.hematologylibrary.org/content/early/recent. Accessed July 19, 2011

27. Abd-Elaziz K, Kamphuisen PW, Lyssens C, Reuvers M, den Daas I, Van Bockstaele F, et al. Safety, Tolerability, Pharmacokinetics and Pharmacodynamics of Anti-Vwf Nanobody(R) ALX-0681 After Single and Multiple Subcutaneous Administrations to Healthy Volunteers. Blood. 2009;114:Abstract 1063

28. van Loon JE, de Jaegere PP, Ulrichts H, van Vliet HH, de Maat MP, de Groot PG, et al. The in vitro effect of the new antithrombotic drug candidate ALX-0081 on blood samples of patients undergoing percutaneous coronary intervention. Thromb. Haemost. 2011;106:165-171

29. Chauhan AK, Motto DG, Lamb CB, Bergmeier W, Dockal M, Plaimauer B, et al. Systemic antithrombotic effects of ADAMTS13. J. Exp. Med. 2006;203:767-776

30. Zhao B-Q, Chauhan AK, Canault M, Patten IS, Yang JJ, Dockal M, et al. von Willebrand factor-cleaving protease ADAMTS13 reduces ischemic brain injury in experimental stroke. Blood. 2009;114:3329-3334

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