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Copyright © 2003 by Institute of Pharmacology Polish Journal of Pharmacology Polish Academy of Sciences Pol. J. Pharmacol., 2003, 55, 523–533 ISSN 1230-6002

REVIEW

PROGRESS IN PHARMACOTHERAPY OF

Krzysztof Labuzek, Robert Krysiak, Bogus³aw Okopien, Zbigniew S. Herman Department of Clinical Pharmacology, Medical University of Silesia, PL 40-752Katowice, Medyków 18, Poland

Progress in pharmacotherapy of thrombosis. K. LABUZEK, R. KRYSIAK, B. OKOPIEN, Z.S. HERMAN. Pol. J Pharmacol., 2003, 55, 523–533.

Excessive coagulation and impaired lead to many hemostatic disorders, which enhance the risk of development of life-threatening cardio- vascular diseases such as myocardial infarction, , deep venous throm- bosis and pulmonary embolism, belonging to the most important factors in- fluencing morbidity and mortality in civilized societies. The adverse events induced by currently used drugs, the need for regular monitoring of coagula- tion parameters, inconvenient, in some cases, route of administration stimu- late further search for novel, effective and safe methods of therapies of these disorders. In this paper, we describe those new agents which are now under experimental and clinical study, such us , nitroaspirin, GP IIb/IIIa receptor antagonists, derivatives, collagen-GPVI and von Willebrand factor-GPIb-IX contact blockers, direct inhibitors, in- hibitors of thrombin- interactions, factor VII inhibitors and tissue factor-factor VII contact blockers. Based on the available literature, we dis- cuss the possible role of these agents in the future prevention and treatment of thromboembolic diseases.

Key words: coagulation system, hemostasis, thrombosis, aggregation, adhesion

 correspondence; e-mail: [email protected] K. Labuzek, R. Krysiak, B. Okopien, Z.S. Herman

Abbreviations: ADP – adenosine diphosphate, dues in the active site of the consitutive form of cy- APTT – activated partial thromboplastin time, clooxygenase (COX-1) resulting in the inhibition ATA – aurin tricarboxylic acid, COX – cyclooxy- of platelet aggregation. Low doses of acetylsali- genase, DIC – disseminated intravascular coagula- cylic acid (75–150 mg/d) inhibit the synthesis of tion, GP – glycoprotein, INR – International Nor- A2, a molecule that enhances platelet malized Ratio, LAPP – leech antiplatelet protein, aggregation. As the inhibition of COX is irreversi- NAP – nematode protein, NO –ni- ble, platelet activity returns to normal only after tric oxide, PAR – protease-activated receptors, PG new have been formed, i.e. 7–10 days later – , PIVKA – protein induced by vita- [42]. Many clinical studies have shown the utility min K absence, PTCA – percutaneous transluminal of acetylsalicylic acid for the primary and secon- coronary angioplasty, RAPT – the Ridogrel vs. Aspi- dary prevention of cardiovascular diseases [7, 16, rin Patency Trial, SNAC – sodium N-[8-(hydroxy- 21, 22]. However, therapy with acetylsalicylic acid benzoyl)amino]caprylate, TAP – tick anticoagulant is associated with the increased risk of such ad- peptide, TF – tissue factor, TFPI – tissue factor verse events as gastrointestinal complaints and pathway inhibitor, TX – thromboxane bleeding, hemorrhagic stroke, renal failure and ar- terial hypertension. Introduction New agents inhibiting platelet adhesion and ag- gregation are synthase inhibitors, The coagulation system plays an important role which inhibit thromboxane A2 synthesis and en- in internal homeostasis as it protects the living or- hance synthesis by providing cyclic ganism from excessive loss of . Following endoperoxides. , an derivative, vascular injury, the hemostatic plug is formed in or- der to stop bleeding (hemostasis). Hemostatic plug INTRINSIC EXTRINSIC formation requires both soluble and morphotic PATHWAY PATHWAY blood elements. The major phases of coagulation High molecular prekallikrein TFPI + Xa and fibrinolysis as well as platelet functions are weight kininogen presented in Figure 1. Hemostatic disorders in- phospholipids XIIa inhibition crease the risk of life-threatening cardiovascular ADP VII kallikrein diseases such as myocardial infarction, stroke, deep Ca++ Ca++ venous thrombosis and pulmonary embolism. Anti- Tissue Factor + VIIa + XII XIIa phospholipids + Ca++ thrombotic therapy consists of the inhibition of platelets and activity of plasma coagulation factors XI XIa ++ and of the stimulation of plasma fibrinolytic activ- Ca ity. Fibrinolytic drugs are used exclusively in the IX IXa tenase complex VIIIa treatment of acute episodes of coronary, pulmonary Ca++ phospholipids and peripheral ischemia. These drugs cannot be XXa Ca++ Va used in chronic therapy due to their serious adverse phospholipids effects. The aim of this review is to present new complex prothrombinase agents which are under experimental and clinical study and are planned to be used in the prevention thrombin prothrombin and treatment of thromboembolic diseases. The aim of this review is to present modern therapy of fibrinogen fibrin thromboembolic diseases. We put special emphasis activation on new agents which are under experimental and plasminogen plasmin clinical study and are planned to be used in the pre- vention and treatment of these disorders. Fig. 1. The coagulation system consists of the extrinsic and in- trinsic pathways. In coagulation, the particular role is played by substances released by active blood platelets (serotonin, phos- Prostanoids pholipids, prostanoids and NO). They modulate the speed and character of coagulation. All coagulation-related processes op- Acetylsalicylic acid is the oldest effective re- erate simultaneously and in a cascade-like manner. The initia- medy for thromboembolic diseases. Its action de- tion of one coagulation pathway triggers the consecutive steps pends on the irreversible acetylation of serine resi- of the other coagulation pathways

524 Pol. J. Pharmacol., 2003, 55, 523–533 PROGRESS IN PHARMACOTHERAPY OF THROMBOSIS is one of such agents. Its in vitro antiplatelet effect some attempts to use NO donors that release NO is low, probably due to the unspecific stimulation [19]. One of the most promising agents is nitroaspi- of thromboxane receptors by excessive amounts of rin (NCX4016), a combination of acetylsalicylic PGG2 and PGH2 endoperoxides formed from ara- acid and NO-releasing nitrate. Nitroaspirin shows chidonic acid. higher antiplatelet activity than acetylsalicylic acid Another possibility to inhibit thromboxane A2 and it produces less adverse effects [50]. The dos- is the blockade of its receptors, for example by the age of nitroaspirin should be adjusted to get the compound GR32191. Some studies focused on ri- maximum antiplatelet effect with the minimal de- dogrel, a compound that both inhibits the synthesis crease in blood pressure, the major adverse effect of TXA2 and blocks TXA2 receptors. Ridogrel of nitrates. Preliminary studies have shown that ni- strongly inhibits TXA2 activity and, at the same troaspirin significantly delays the occurrence of time, it enhances prostacyclin synthesis. In the Ri- restenosis after revascularization [34]. There are dogrel vs. Patency Trial (RAPT), ridogrel ongoing studies aimed to evaluate the effect of ni- and aspirin were similarly effective in maintaining troaspirin combined with other antiplatelet drugs, the patency of coronary arteries in patients with such as antagonists of glycoproteins GPIIb/IIIa and acute myocardial infarction who underwent fibri- GPIb [19, 50]. nolytic treatment. However, patients treated with ridogrel less frequently developed reinfarction, re- GP IIb/IIIa receptor antagonists current angina and stroke [42, 47]. The glycoprotein IIb/IIIa (GPIIb/IIIa) receptor Nitric oxide and nitroaspirin on platelets plays a crucial role in the process of thrombosis. It belongs to a superfamily of cell sur- Nitric oxide (NO) effectively inhibits the adhe- face receptors known as integrins that can recog- sion and aggregation of platelets, neutrophils and nize molecules carrying the Arg-Gly-Asp (RGD) monocytes. NO is a product of the metabolism of binding sequence [41]. GPIIb/IIIa receptor antago- such drugs as nitrates. Recently, there have been nists have so far been the most effective antiaggre-

Table 1. Classifications of GP IIb/IIIa receptor antagonists on the basis of chemical structure, binding kinetic profiles to activated vs. unactivated platelets, route of administration and duration of action

Chemical structure

Monoclonal antibodies , YM337 RGD cyclic analogues DMP728, (integrilin) Non-peptide lamifiban, lefradafiban, lotrafiban, roxifiban, , xemilofiban

Binding to the activated and rested form of GPIIb/IIIa

Similar effect on both forms(ClassI) DMP802, roxifiban (DMP754), XV454 Higher activity to activated receptor (Class II) DMP728, L734217, MK852

Route of administation

Intravenous abciximab, eptifibatide (integrilin), lamifiban, tirofiban Oral lefradafiban, roxifiban (DMP754), SR121566, xemilofiban Other routes(intranasal) DMP755

Duration of action

Fast eptifibatide (integrilin), lamifiban, orbofiban, tirofiban Intermediate roxifiban (DMP 754) Slow C7E3, DMP802, XV454

ISSN 1230-6002 525 K. Labuzek, R. Krysiak, B. Okopien, Z.S. Herman gative agents. Several classes of these drugs are Thienopyridine derivatives either available on the market or in advanced stage of development (Tab. 1). The direct blockade of Adenosine diphosphate (ADP), an agonist of GPIIb/IIIa receptors effectively inhibits platelet ag- P2X and P2Y purinergic receptors, is released by gregation regardless of the way of platelet stimula- endothelial cells and blood platelets, which triggers tion [29, 37]. Antagonists of this receptor inhibit fi- platelet adhesion and aggregation. The P2X recep- brinogen binding to activated platelets independent tor is an ionotropic receptor, while the P2Y recep- of the agonist, inhibit clot retraction, and attenuate tor is a metabotropic one. Thienopyridine deriva- platelet procoagulant activity. They do not affect tives block the P2Y1 receptor. inhibits GP1b-mediated primary adhesion under shear [37]. the ADP-induced activation of GPIIb/IIIa, thus pre- The best-known GPIIb/IIIa receptor antagonist is venting fibrinogen-mediated platelet aggregation. abciximab, a chimeric human-murine monoclonal As ticlopidine requires metabolic activation, its ef- antibody Fab fragment directed against GPIIb/IIIa fect develops only after 3–7 days and disappears receptors. Abciximab also blocks receptors for vitro- about 3 days after cessation of the therapy. Ti- nectin and beta 2-integrin Mac-1 (CD11b/CD18), clopidine decreases the risk of ischemic stroke, thereby inhibiting the growth of the internal mem- death caused by acute cardiovascular events and brane in blood vessels and producing antiinflam- nonfatal myocardial infarction, it increases claudi- matory and antiatherosclerotic effects. Following cation distance and prevents cardiovascular com- intravenous (iv) administration, abciximab quickly plications in patients with coronary stents [34]. The antiplatelet efficacy of ticlopidine is similar to that and irreversibly binds to GPIIb/IIIa receptors, show- of aspirin. Prolonged ticlopidine treatment is asso- ing the maximal effect as early as 2 h after injec- ciated with such adverse effects as gastric com- tion. Platelet aggregation returns to normal 12–36 h plaints, skin rash, thrombocytopenic purpura, and after cessation of iv infusion. Trace amounts of ab- neutropenia. At present, ticlopidine is recommend- ciximab still can be found after 21 days. The long- ed for patients who do not tolerate aspirin, because term effect of abciximab may be an obstacle when the adverse effects of ticlopidine on gastric and a patient is being prepared for urgent life-saving duodenal mucosa are weaker compared to aspirin. surgery. The most important disadvantage of ab- Most recent studies have shown that combined ciximab is its immunogenecity, which hinder but treatment with ticlopidine and aspirin decreases the do not disallow its repeated administration [39]. number of cardiovascular complications compared The above-mentioned disadvantages are not ex- with a combination of aspirin and or vita- hibited by GPIIb/IIIa receptor antagonists that are min K antimetabolites [44]. not monoclonal antibodies. Eptifibatide is a peptide irreversibly modifies purinergic re- from the venom of the rattlesnake Sistrurus miliar- ceptors, thereby inhibiting the action of ADP on ius barbouri while tirofiban is a non-peptide com- blood platelets. In this manner, it indirectly reduces pound from the venom of the African viper Echis GPIIb/IIIa expression on the platelet surface. The carinatus. Both these low-molecular-weight com- antiplatelet effect of clopidogrel lasts for about 1 pounds show high and selective affinity for GPIIb/ week after cessation of the treatment. Although IIIa receptors. The effects of eptifibatide and tirofi- clopidogrel rarely causes neutropenia, it may pro- ban develop 15 min and 5 min after administration, duce gastrointestinal complaints and skin changes. respectively. The affinity of these drugs for GPIIb/ Clinical studies indicate that clopidogrel prevents IIIa receptors is lower than that of abciximab and myocardial infarctions and and that it re- their effect on platelet receptors is of very short du- duces the overall death rate due to cardiovascular ration (a few seconds) and can be quickly reversed. diseases, the effect being more marked than that of The long biological half-life of these drugs results aspirin [44]. from their slow elimination. Platelet activity nor- malizes within from 30 min to 4 h after cessation of Other antagonists of purinergic receptors administration. Treatment with GPII/IIIa receptor antagonists is beneficial to patients with unstable There are ongoing phase II studies of the selec- angina, myocardial infarction without ST eleva- tive platelet purinergic receptor antagonist tion, and those undergoing percutaneous translumi- AR-C69931 MX. After iv injection, it produces nal coronary angioplasty (PTCA) [6, 9, 35, 36]. a strong effect in patients with un-

526 Pol. J. Pharmacol., 2003, 55, 523–533 PROGRESS IN PHARMACOTHERAPY OF THROMBOSIS stable angina, non-Q wave myocardial infarction, with antiplatelet drugs showing different mecha- and revascularization [18, 46]. The risk of hemor- nisms of action, e.g. aspirin [19]. Promising results rhagic complications caused by this compound is have been obtained in studies of substances that lower than that for GPIIb/IIIa antagonists. Com- bind von Willebrand factor, thus depriving it of its pared with thienopyridine derivatives (ticlopidine affinity for GPIb glycoprotein. These substances, and clopidogrel), which indirectly impair the func- namely aurin tricarboxylic acid (ATA) and a fla- tion of purinergic receptors, selective antagonists vonoid derivative of acetic acid have an antiplatelet of PAR (protease-activated receptors) have an im- effect and they inhibit neointima formation [32]. mediate onset of action and they virtually com- pletely block the activity of these receptors [42]. Collagen – GPVI contact blockers Antithrombotic effect can be produced by com- Von Willebrand factor – GPIb – IX pounds, obtained from the saliva of insects and in- contact blockers vertebrates that feed on blood from the higher ani- mals, that impair the contact between collagen and Von Willebrand factor, a glycoprotein synthe- platelet glycoprotein GPVI [19]. The oldest and the sized by endothelial cells and megakaryocytes, sta- best known compound is a protein isolated from bilizes factor VIII and mediates the binding of gly- leech saliva termed leech antiplatelet protein (LAPP). coprotein GPIb, located on platelets and extracellu- Nowadays, it is produced by genetic recombination lar matrix, to collagen [2]. There are attempts to (rLAPP – recombinant leech antiplatelet protein). pharmacologically block this phenomenon with LAPP binds to platelet glycoproteins GPVI, GPIb substances that directly block platelet GPIb or bind and GPIa/IIa and potently inhibits platelet adhesion to a specific region of von Willebrand factor, thus, and aggregation. However, this multi-targeted ef- inhibiting its activity. Platelet adhesion can be fect is associated with serious hemorrhagic compli- blocked by monoclonal antibodies directed against cations [10, 12, 51]. Other GPVI-blocking com- guinea pig platelet GPIb. When modified, these an- pounds isolated from invertebrates’ saliva, such as tibodies show affinity for human platelet GPIb [4]. pallidipin and moubatin, also show strong antiag- Promising results were achieved in the prevention gregative activity [10, 28]. Unfortunately, animal of experimental pulmonary thromboembolism in studies have shown that the antithrombotic effects baboons treated with mouse monoclonal Fab frag- of pallidipin and moubatin were associated with ments B4-F(ab’) in order to minimize the immuno- a high risk of bleeding [20, 44, 47]. GPVI-blocking genecity of anti-GPIb antibodies [8]. Similarly the monoclonal antibody JAQ-1 shows high antithrom- AjvW2 antibody proved to be effective in the pre- botic efficacy with a minimal effect on bleeding vention of thrombosis and restenosis following time [38]. A soluble form of GPVI is being studied PTCA in guinea pigs [27]. This antibody seems to in patients with venous thrombosis [10]. prevent the growth of neointima stimulated by growth factors released by monocytes and cells re- Vitamin K antagonists siding in the vascular wall. In order to inhibit the binding of von Willebrand factor to GPIb, a modi- Vitamin K is an essential cofactor mediating the fied von Willebrand factor and inactive fragments posttranslational modification of coagulation fac- of this factor, namely VCL (Leu504-Lys728) and tors II, VII, IX and X, the process consisting in the AR545C (Ala444-Asp730) were introduced [19, g-carboxylation of glutamic acid. Vitamin K an- 20, 53]. These molecules show affinity for GPIb, tagonists inhibit this process, thereby producing an but they do not bind to collagen. As a result, they anticoagulant effect. and have a noticeable antiplatelet effect without affect- induce the formation of inactive (due to absence of ing bleeding time, which may suggest that they are g-carboxylic groups) coagulation factors (PIVKA – relatively safe for humans [8, 27]. This effect re- protein induced by vitamin K absence), thus, inhi- sults from the fact that other platelet glycoproteins biting blood coagulation. Although vitamin K anta- (GPIa/IIa and GPIIb/IIIa) bind neither modified gonists are highly effective and widely used, the the- von Willebrand factor nor its fragments, which in- rapy is difficult because of the high risk of hemor- hibits but does not block thrombus formation. This rhagic complications and the strong possibility of mechanism allows combining these compounds drug-drug interactions. What is more, therapy with

ISSN 1230-6002 527 K. Labuzek, R. Krysiak, B. Okopien, Z.S. Herman oral requires regular monitoring of heparin in the prevention of thromboembolic com- International Normalized Ratio (INR), which is plications in patients who underwent hip surgery. troublesome for outpatients and markedly decreases There are ongoing phase III studies aimed to com- their quality of life. Recently, Hurlen et al. [26] pare SNAC heparin and low-molecular-weight have shown that warfarin was more effective than in terms of efficacy and safety [40]. aspirin in the secondary prevention of myocardial infarction, but this therapy produced more side- effects. Direct thrombin inhibitors

Heparin Direct thrombin inhibitors function indepen- dently of . They do not need cofactors, Heparin is a polymeric glucosaminoglycan con- they inhibit the positive feedback processes that are sisting of alternating iduronic acid and glucuronic conducive to constant thrombin formation, they acid residues. Commercial unfractionated heparins have a particular effect on the activity of throm- are mixtures of polymers that differ in molecular bus-bound thrombin, and they cannot be inacti- weight. Heparin enhances the activity of antithrom- vated by platelet factor 4. Platelet factor 4, a catio- bin, a molecule that neutralizes thrombin, factors nic protein released by activated platelets, blocks Xa, IXa, XIa, XIIa and VIIa, and kallikrein by the active center of heparin, but has no effect on di- modifying their active sites. Although antithrombin rect thrombin inhibitors [25, 52]. As direct throm- can bind to thrombin in the absence of heparin, the bin inhibitors are not bound by endothelium and presence of heparin increases the rate of this pro- plasma proteins, their therapeutic potency depends cess over 1000-fold. In rare cases of antithrombin more on the dose, and their effects on coagulation deficiency, heparin shows no effect. Heparin ther- parameters are more predictable [25]. , apy is associated with the risk of commonly known a compound isolated from the saliva of the leech, serious complications, such as bleeding, thrombo- recombinant desirudin (desulfatohirudin) and the cytopenia, allergy, and abnormalities of adrenal synthetic derivative (Hirulog) directly cortex function. Apart from that risk, the short inactivate thrombin in the absence of antithrombin half-life of heparin (40–90 min) and the need of and other cofactors. The biological half-lifes of iv monitoring of activated partial thromboplastin time and sc injected hirudin are about 40 min and (APTT) are major drawbacks of this therapy. 120 min, respectively, about 60 min for desirudin, Low-molecular-weight heparins (4–15 kDa), and about 25 min for bivalirudin [17]. Hirudin is such as enoxaparin, dalteparin and nadroparin, en- used in patients with heparin-induced thrombocy- hance the impact of antithrombin on factor Xa, topenia. The OASIS-1 and OASIS-2 multicenter while their effects on antithrombin and platelet ac- studies confirmed the 30-day efficacy of hirudin in tivities are much smaller. Their proven efficacy, patients with either unstable angina or myocardial high bioavailability following subcutaneous (sc) infarction without ST elevation. The GUSTO-2A, injection, low protein binding, convenient admini- TIMI-9A and HIT III trials, in which hirudin was stration (1–2 sc injections daily), no need for regu- used as an adjuvant to thrombolytic treatment, were lar monitoring of APTT, and the low risk of hemor- interrupted due to higher than expected rates of rhagic complications explain the increasing popu- hemorrhagic complications. The GUSTO-2B and larity of these drugs in the prevention and treatment TIMI-9B trials, in which hirudin doses were re- of thromboembolic conditions. duced, showed no advantage of hirudin over hepa- Heparin can be administered orally when bound rin in acute coronary conditions. There are attempts to synthetic amino acids. The best-known intestinal to use bivalirudin in patients with myocardial in- carrier of heparin is sodium N-[8-(hydroxybenzo- farction undergoing PTCA. Bivalirudin seems to be yl)-amino]caprylate (SNAC). At present, attempts more effective than heparin and to have a lower are being made to use oral heparin for the preven- risk of hemorrhagic complications [52]. Its efficacy tion of thrombotic complications in patients under- and safety is still being investigated, and some going surgery for hip and knee osteoarthrosis [43]. clinical studies show that its use is associated with In phase II studies, the combination of SNAC and more hemorrhagic complications compared with heparin was as effective and safe as unfractionated heparin [19, 52].

528 Pol. J. Pharmacol., 2003, 55, 523–533 PROGRESS IN PHARMACOTHERAPY OF THROMBOSIS

Argatroban, an arginine derivative, is a throm- active thrombin. Factor Xa inhibitors exhibit either bin antagonist. As a competitive thrombin inhibi- direct or indirect action, the latter of which requires tor, it binds noncovalently to the active site of the presence of antithrombin. The direct inhibitors thrombin. Its biological half-life following iv injec- inhibit both free factor Xa dissolved in plasma and tion is about 45 min. Current studies of factor Xa coupled with the prothrombinase com- are focused on its utility in patients with unstable plex. The indirect inhibitors inhibit exclusively free angina and deep venous thrombosis who cannot be factor Xa activity. treated with heparin due to heparin-induced throm- The pentasaccharide () is a syn- bocytopenia [24]. McKeage and Plosker showed thetic analog of the heparin fragment of the lowest that argatroban was effective in patients with molecular weight with antithrombotic activity. Its thrombosis that developed in the course of heparin bioavailability is very good following sc injection, therapy [33]. and the biological half-life in serum is about 14 h. Other thrombin inhibitors include melagatran, Clinical studies have shown that the pentasaccha- (H 376/95), napsagatran, ride was more effective than enoxaparine for the and efegatran [52]. Melagatran is a low-molecu- prevention and treatment of thrombosis accompa- lar-weight compound (430 Da) with a high affinity nying prolonged orthopedic surgery [3, 30, 48, 49]. for thrombin in the forming thrombus. In the stud- Venographic studies of the deep venous system re- ies performed so far, it showed low rates of adverse vealed that the pentasaccharide reduced by up to events, of which hemorrhagic events were most 50% the incidence of deep venous thrombosis. In common. Modification of melagatran’s structure the same study, the risk of pentasaccharide-related resulted in the formation of the prodrug ximelaga- bleeding increased by about 1% compared with tran, which can be administred orally. Melagatran low-molecular-weight heparin [14, 48, 49]. At (3 mg/d sc) and ximelagatran (48 mg/d po) are present, there are ongoing studies to compare the more effective than dalteparin in the prevention of efficacy of the pentasaccharide with that of heparin thrombotic complications in patients undergoing in patients with unstable angina [52]. hip or knee surgery and produce less adverse events Direct factor Xa inhibitors include polypeptides [15]. There are ongoing studies to evaluate the effi- isolated from the saliva of ticks, e.g. tick anticoagu- cacy of melagatran and ximelagatran in the preven- lant peptide (TAP) from Ornithodoros moubata, tion of thromboembolic events in patients with and from the saliva of leeches, e.g. antistasin from atrial fibrillation [19]. Hementeria officinalis and lefaxin from Hemente- is a glycosaminoglycan that ria depressa. These compounds are now available occurs in the matrix of many tissues. Like heparin, as recombinants. There are also synthetic low- it is released by mastocytes and endothelial cells. molecular-weight non-peptide factor Xa inhibitors, Dermatan sulfate inhibits thrombin activity without such as DX9056, DX-9065a, YM416 and SK549 affecting the other coagulation factors. Natural der- [19]. Their role in the prevention and treatment of matan sulfate is being the subject of clinical studies thromboembolic conditions still awaits to be estab- now. It is used for the prevention of deep venous lished. thrombosis in patients undergoing extensive ortho- pedic or oncologic surgery [13]. Other direct throm- Inhibitors of thrombin-platelet bin inhibitors, such as bothroiacin, rhodniin, triabin interactions and dipetalin, are currently under experimental study [19, 42]. Thrombin is an activated that (i) stimulates the conversion of fibrinogen into fi- inhibitors brin, (ii) activates coagulation factors V, VIII, XI, XIII, (iii) activates blood platelets by acting on Factor X (Stuart-Prower factor) unites the in- platelet PAR, thus, enhancing platelet adhesion and trinsic and extrinsic pathways of blood coagulation. aggregation. At the same time, thrombin inhibits Once activated, factor Xa forms a complex with ac- coagulation by acting on platelet PAR receptors, es- tivated factor Va, calcium ions and platelet phos- pecially PAR 1 and PAR 4. These are serpentine pholipids which shows prothrombinase activity. receptors activated by proteases. Thrombin cleaves This complex converts inactive prothrombin into the 41-amino acid N-terminus of the receptor, there-

ISSN 1230-6002 529 K. Labuzek, R. Krysiak, B. Okopien, Z.S. Herman by unmasking a domain with affinity for the half-life. Following sc injection, it shows high bio- further fragments of the receptor’s helix. The un- availability (90–100%). RNAPc2 (3 g/kg) reduced masked domain, called the tethered agonist, binds the rate of deep venous thrombotic complications to its own receptor. The further steps of cellular sig- in patients undergoing knee arthroplasty, which was nal transmission depend on G proteins. This recep- confirmed by venography, and it insignificantly in- tor type can be activated only once because the creased the bleeding time [23, 31]. cleavage of the N-terminus is irreversible, and the There are ongoing studies aimed to compare receptors must be synthesized again in order to re- rNAPc2 and enoxaparin in patients undergoing gain their activity [42]. Knowing the structure and long orthopedic surgery or PTCA. There are also function of PAR receptors allowed the develop- ongoing studies evaluating the effect of rNAPc2 ment of antiplatelet agents, such as polyclonal anti- combined with heparin and aspirin. The results are bodies directed against the N-terminals of PAR-1 unknown yet [19, 52]. receptors and synthetic peptides that are selective Tissue Factor Pathway Inhibitor (TFPI), is a pro- antagonists of these receptors (RWJ-58259). Pre- tease inhibitor with marked anticoagulant involved liminary studies indicate that both types of these in the regulation of TF-induced coagulation. Re- agents, especially selective PAR-4 blockers, have cently, the results of two clinical studies have shown a strong anticoagulant effect with little effect on that recombinant TFPI effectively and dose-depen- bleeding time [45]. dently attenuates the endotoxin-induced coagula- tion activation in humans without influencing the Tissue factor – factor VII contact blockers fibrinolytic and cytokine response and decreases mortality in critically ill patients [1, 11]. Tissue factor (TF) is an integral membrane gly- coprotein that is activated by binding to factor VII Other coagulation inhibitors in the presence of calcium ions and platelet phos- pholipids. Then it converts factors IX (Christmas and protein S are endogenous inhibi- factor) and X (Stuart-Prower factor) into their ac- tors of coagulation which are syntheszied by the tive forms IXa and Xa. When a blood vessel is in- liver in the presence of vitamin K. The activation of tact, TF is not in contact with the lumen. Endothe- protein C requires the presence of thrombin-throm- lial injury (atherosclerotic plaque rupture) unmasks bomodulin complex. The antithrombotic effect of TF, which triggers the coagulation cascade. In re- protein C is multidirectional, as it inhibits thrombin cent years, substances with affinity for TF, factor production by inactivation of factors Va and VIIIa VII and the TF-factor VII complex were disco- and activates fibrinolysis. There are attempts to vered. These substances inhibit the initial phases of parenterally administer active recombinant protein the extrinsic coagulation pathway. Harker et al. C to patients with familial thrombophilia, a disease showed that anti-TF monoclonal antibodies inhi- characterized by a deficiency or impaired function bited procoagulant activity induced by E. coli in of proteins C and S. Therapy with protein C re- baboons. Inactive, structurally modified TF, which duces the risk of deep venous thrombosis and pul- competes for factor VII with endogenous TF, also monary thromboembolism in these patients. Clini- has an anticoagulant effect. Modified factor VII cal studies in over 1500 patients hospitalized due to (VIIai) with its active site blocked and with affinity sepsis-induced intravascular coagulation indicate for TF has a similar effect [23]. The efficacy of fac- that human recombinant active protein C reduces tor VIIai is comparable to that of heparin in by 6% the overall risk of death and by 20% the PTCA-treated patients [52]. Of greatest interest are relative risk of death compared to those who apart compounds that inhibit the activity of the TF-factor from the standard treatment received placebo. The VII complex. Nematode anticoagulant protein bleeding time increased only insignificantly in (NAP) was first isolated from the saliva of nema- these patients. It is believed that protein S may todes feeding on their hosts’ blood. Recombinant have a similar effect as it is a cofactor that accele- NAP (rNAPc2) shows affinity for the TF-factor rates the action of active protein C [5]. Because the VIIa complex after binding to either zymogen or active form of protein C requires thrombin-throm- activated factor X [23]. RNAPc2 can be adminis- bomodulin complex, this effect is limited to the area tered every 1–2 days because of its long biological where free thrombin is present, i.e. where a throm-

530 Pol. J. Pharmacol., 2003, 55, 523–533 PROGRESS IN PHARMACOTHERAPY OF THROMBOSIS botic process is going on. This and promising re- 5. Bernard G.R., Vincent J.L., Laterre P.F., LaRosa S.P., sults of clinical studies indicate that thrombomodu- Dhainaut J.F., Lopez-Rodriguez A., Steingrub J.S., lin can be used in coagulation disorders. Thanks to Garber G.E., Helterbrand J.D., Ely E.W., Fisher C.J. Jr: Efficacy and safety of recombinant human acti- its long half-life following sc injection, thrombo- vated protein C for severe sepsis. N. Engl. J. Med., modulin can be given 2 times a week. There are on- 2001, 344, 699–709. going studies to evaluate the efficacy and safety of 6. Brener S.J., Barr L.A., Burchenal J.E., Katz S., thrombomodulin in the prevention of deep venous George B.S., Jones A.A., Cohen E.D., Gainey P.C., thrombosis and the treatment of DIC (disseminated White H.J., Cheek H.B., Moses J.W., Moliterno D.J., intravascular coagulation) [19]. Effron M.B., Topol E.J.: Randomized, placebo-con- trolled trial of platelet glycoprotein IIb/IIIa blockade with primary angioplasty for acute myocardial infarc- Conclusion tion. ReoPro and Primary PTCA Organization and Randomized Trial (RAPPORT) Investigators. Circula- Acute coronary events, pulmonary thromboem- tion, 1998, 98, 734–741. bolism, cerebral stroke, deep venous thrombosis 7. Buring J.E., Hennekens C.H.: Prevention of cardio- and DIC belong to the most important factors influ- vascular disease: risks and benefits of aspirin. J. Gen. encing morbidity and mortality in civilized socie- Intern. Med., 1990, 5, 54–57. 8. ties. As the specificity of antiplatelet and anti- Cauwenberghs N., Meiring M., Vauterin S., van Wyk V., Lamprecht S., Roodt J.P., Novak L., Harsfalvi J., thrombotic drugs is low, it is of utmost importance, Deckmyn H., Kotze H.F.: Antithrombotic effect of when treating the patient, to maximize the thera- platelet glycoprotein Ib-blocking monoclonal anti- peutic effect of the used drug and at the same time body Fab fragments in non human primates. Arterio- to minimize the risk of hemorrhagic complications. scler. Thromb. Vasc. Biol., 2000, 20, 1347–1353. The drug-related adverse events, the need for regu- 9. Chan A.W., Moliterno D.J.: Defining the role of abci- lar monitoring of coagulation parameters, in- ximab for acute coronary syndromes: lessons from covenient, in some cases, route of administration CADILLAC, ADMIRAL, GUSTO IV, GUSTO V, and TARGET. Curr. Opin. Cardiol., 2001, 16, 375–383. stimulate further search for novel, effective and 10. Clemetson K.J.: Platelet collagen receptors: a new tar- safe pharmacotherapies of these disorders. Recent get for inhibition? Haemostasis, 1999, 29, 16–26. years have witnessed discoveries of novel antico- 11. de Jonge E., Dekkers P.E., Creasey A.A., Hack C.E., agulant agents which, in the nearest future, may be- Paulson S.K., Karim A., Kesecioglu J., Levi M., van come an important tool for the prevention and Deventer S.J., van Der Poll T.: Tissue factor pathway treatment of thromboembolic disorders. Great im- inhibitor dose-dependently inhibits coagulation acti- provement in the efficacy of antithrombotic phar- vation without influencing the fibrinolytic and cyto- kine response during human endotoxemia. Blood, macotherapy is impatiently awaited by scientists, 2000, 95, 1124–1129. clinicians and, first of all, by patients. 12. Depraetere H., Kerekes A., Deckmyn H.: The colla- gen-binding leech products rLAPP and calin prevent REFERENCES both von Willebrand factor and alpha2beta1(GPIa/ IIa)-I-domain binding to collagen in a different man- 1. Abraham E., Reinhart K., Svoboda P., Seibert A., Olt- ner. Thromb. Haemost., 1999, 82, 1160–1163. hoff D., Dal Nogare A., Postier R., Hempelmann G., 13. Di Carlo V., Agnelli G., Prandoni P., Coccheri S., Gen- Butler T., Martin E., Zwingelstein C., Percell S., Shu V., sini G.F., Gianese F., Mannucci P.M.: Dermatan sul- Leighton A., Creasey A.A.: Assessment of the safety phate for the prevention of postoperative venous of recombinant tissue factor pathway inhibitor in pa- thromboembolism in patients with cancer. DOS (Der- tients with severe sepsis: a multicenter, randomized, matan sulphate in Oncologic Surgery) Study Group. placebo-controlled, single-blind, dose escalation study. Thromb. Haemost., 1999, 82, 30–34. Crit. Care Med., 2001, 29, 2081–2089. 14. Eriksson B.I., Bauer K.A., Lassen M.R., Turpie A.G.: 2. Andrews R.K.: The glycoprotein Ib-IX-V complex in Fondaparinux compared with enoxaparin for the pre- platelet adhesion and signaling. Thromb. Haemost., vention of venous thromboembolism after hip-fracture 1999, 82, 357–364. surgery. N. Engl. J. Med., 2001, 345, 1298–1304. 3. Bauer K.A., Eriksson B.I., Lassen M.R., Turpie A.G.: 15. Eriksson B.I., Bergqvist D., Kalebo P., Dahl O.E., Fondaparinux compared with enoxaparin for the pre- Lindbratt S., Bylock A., Frison L., Eriksson U.G., vention of venous thromboembolism after elective major Welin L., Gustafsson D.: Ximelagatran and melaga- knee surgery. N. Engl. J. Med., 2001, 345, 1305–1310. tran compared with dalteparin for prevention of ve- 4. Becker B.H., Miller J.L.: Effects of an antiplatelet gly- nous thromboembolism after total hip or knee replace- coprotein Ib antibody on hemostatic function in the ment: the METHRO II randomised trial. Lancet, 2002, guinea pig. Blood, 1989, 74, 690–694. 360, 1441–1447.

ISSN 1230-6002 531 K. Labuzek, R. Krysiak, B. Okopien, Z.S. Herman

16. Fahey T., Peters T.J.: Interpretation of thrombosis pre- 29. Kleinschmidt K.: Acute coronary syndromes: pharma- vention trial. Randomised trial of low-intensity oral cotherapeutic interventions – guidelines for manage- anticoagulation with warfarin and low-dose aspirin in ment of patients subjected to conservative and inva- the primary prevention of ischaemic heart disease in sive treatment (Polish). Nowoœci Kardiologiczne, 2001, men at increased risk. The Medical Research Coun- 1, 10. cil’s General Practice Research Framework. Lancet, 30. Lassen M.R., Bauer K.A., Eriksson B.I., Turpie A.G.: 1998, 351, 233–241. Postoperative fondaparinux versus preoperative eno- 17. Fox I., Dawson A., Loynds P., Eisner J., Findlen K., xaparin for prevention of venous thromboembolism in Levin E., Hanson D., Mant T., Wagner J., Maraganore elective hip-replacement surgery: a randomised double- J.: Anticoagulant activity of Hirulog, a direct throm- blind comparison. Lancet, 2002, 359, 1715–1720. bin inhibitor, in humans. Thromb. Haemost., 1993, 69, 31. Lee A., Agnelli G., Büller H., Ginsberg J., Heit J., 157–163. Rote W., Vlasuk G., Costantini L., Julian J., Comp P., 18. Gachet A.: ADP receptors and their inhibition. Thromb. van der Meer J., Piovella F., Raskob G., Gent M.: Haemost., 2001, 86, 222–232. Dose-response study of recombinant factor VIIa/tis- 19. Gresele P., Agnelli G.: Novel approaches to the treat- sue factor inhibitor recombinant nematode anticoagu- ment of thrombosis. Trends Pharmacol. Sci., 2002, 23, lant protein c2 in prevention of postoperative venous 25–32. thromboembolism in patients undergoing total knee 20. Gurevitz O., Goldfarb A., Hod H., Feldman M., Shenk- replacement. Circulation, 2001, 104, 74–78. man B., Varon D., Eldar M., Inbal A.: Recombinant 32. Matsuno H., Kozawa O., Niwa M., Tanabe K., Ichi- von Willebrand factor fragment AR545C inhibits pla- maru K., Takiguchi Y., Yokota M., Hayashi H., telet aggregation and enhances with rtPA Uematsu T.: Multiple inhibition of platelet activation in a rabbit thrombosis model. Arterioscler. Thromb. by aurintricarboxylic acid prevents vascular stenosis Vasc. Biol., 1998, 18, 200–207. after endothelial injury in hamster carotid artery. 21. Hachinski V.: Aspirin and the primary prevention of Thromb. Haemost., 1998, 79, 865–871. myocardial infarction and stroke. Arch. Neurol., 1990, 33. McKeage K., Plosker G.L.: Argatroban. Drugs, 2001, 47, 1354. 61, 515–522. 22. Hansson L., Zanchetti A., Carruthers S.G., Dahlof B., 34. Momi S., Emerson M., Paul W., Leone M., Mezza- Elmfeldt D., Julius S., Menard J., Rahn K.H., Wedel soma A.M., Del Soldato P., Page C.P., Gresele P.: Pre- H., Westerling S.: Effects of intensive blood-pressure vention of pulmonary thromboembolism by NCX lowering and low-dose aspirin in patients with hyper- 4016, a nitric oxide releasing aspirin. Eur. J. Pharma- tension: principal results of the Hypertension Optimal col., 2000, 397, 177–186. Treatment (HOT) randomised trial. HOT Study Group. 35. Monassier J.P., Hamon M., Elias J., Maillard L., Lancet, 1998, 351, 1755–1762. Spaulding C., Raynaud P., Cribier A., Barragan P., 23. Harker L.A., Hanson S.R., Wilcox J.N., Kelly A.B.: Juliard J. M., Lefevre T., Aubry P., Faugier J. P., Mas- Antithrombotic and antilesion benefits without hem- quet C., Rioux P., Bedossa M., Joly P., Petiteau P.Y., orrhagic risks by inhibiting tissue factor pathway. Royer T., Morice M.C., Roriz R., Cattan S., Meyer P., Haemostasis, 1996, 26, Suppl 1, 76–82. Blanchard D., Khalife K.: Early versus late coronary 24. Hilpert K., Ackermann J., Banner D.W., Gast A., Gu- stenting following acute myocardial infarction: results bernator K., Hadvary P., Labler L., Muller K., Schmid of the STENTIM I Study. French Registry of Stenting G., Tschopp T.B.: Design and synthesis of potent and in Acute Myocardial Infarction. Catheter. Cardiovasc. highly selective thrombin inhibitors. J. Med. Chem., Diagn., 1997, 42, 243–248. 1994, 37, 3889–3901. 36. Montalescot G., Barragan P., Wittenberg O., Ecollan 25. Hull R.D., Pineo G.F.: Hirudin versus heparin and P., Elhadad S., Villain P., Boulenc J.M., Morice M.C., low-molecular-weight heparin. J. Lab. Clin. Med., 1998, Maillard L., Pansieri M., Choussat R., Pinton P.: Plate- 132, 171–174. let glycoprotein IIb/IIIa inhibition with coronary 26. Hurlen M., Abdelnoor M., Smith P., Erikssen J., Arne- stenting for acute myocardial infarction. ADMIRAL sen H.: Warfarin, aspirin, or both after myocardial in- Investigators – Abciximab before Direct Angioplasty farction. N. Engl. J. Med., 2002, 26, 969–974. and Stenting in Myocardial Infarction Regarding 27. Kageyama S., Yamamoto H., Yoshimoto R.: Anti- Acute and Long-Term Follow-up. N. Engl. J. Med., human von Willebrand factor monoclonal antibody 2001, 344, 1895–1903. AJvW-2 prevents thrombus deposition and neointima 37. Mousa S.A.: Antiplatelet therapies: from aspirin to formation after balloon injury in guinea pigs. Arterio- GPIIb/IIIa-receptor antagonists and beyond. Drug scler. Thromb. Vasc. Biol., 2000, 20, 2303–2308. Discov. Today, 1999, 4, 552–561. 28. Keller P.M., Schultz L.D., Condra C., Karczewski J., 38. Nieswandt B., Schulte V., Bergmeier W., Mokhtari- Connolly T.M.: An inhibitor of collagen-stimulated Nejad R., Rackebrandt K., Cazenave J.P., Ohlmann P., platelet activation from the salivary glands of the Hae- Gachet C., Zirngibl H.: Long-term antithrombotic pro- menteria officinalis leech. Cloning of the cDNA and tection by in vivo depletion of platelet glycoprotein VI expression. J. Biol. Chem., 1992, 267, 6899–6904. in mice. J. Exp. Med., 2001, 193, 459–469.

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39. Orford J.L., Holmes D.R. Jr.: Abciximab readminis- 48. Turpie A.G., Bauer K.A., Eriksson B.I., Lassen M.R.: tration. Rev. Cardiovasc. Med., 2002, 3, 67–70. Fondaparinux vs enoxaparin for the prevention of ve- 40. Pineo G.F., Hull R.D., Marder V.J.: Orally active nous thromboembolism in major orthopedic surgery: heparin and low-molecular-weight heparin. Curr. a meta-analysis of 4 randomized double-blind studies. Opin. Pulmon. Med., 2001, 7, 344–348. Steering Committees of the Pentasaccharide Orthope- 41. Pollina E.: Design and synthesis of RGD mimetics as dic Prophylaxis Studies. Arch. Int. Med., 2002, 162, potent inhibitors of platelet aggregation. J. Undergrad. 1833–1840. Sci., 1996, 3, 119–126. 49. Turpie A.G., Bauer K.A., Eriksson B.I., Lassen M.R.: 42. Rang H.P., Dale M.M., Ritter J.M.: Clinical Pharma- Postoperative fondaparinux versus postoperative eno- cology (Polish). Czelej Publishing, Lublin, 2001. xaparin for prevention of venous thromboembolism 43. Rivera T.M., Leone-Bay A., Paton D.R., Leipold H.R., after elective hip-replacement surgery: a randomised Baughman R.A.: Oral delivery of heparin in combina- double-blind trial. Lancet, 2002, 359, 1721–1726. tion with sodium N-[8-(2-hydroxybenzoyl)amino]ca- 50. Wallace J.L., Ignarro L.J., Fiorucci S.: Potential cardio- prylate: pharmacological considerations. Pharm. Res., protective actions of NO-releasing aspirin. Nat. Rev. 1997, 14, 1830–1834. Drug. Discov., 2002, 1, 375–382. 44. Schömig A.: Randomized comparison of antiplatelet 51. Watson S.P.: Collagen receptor signalling in platelets and anticoagulant therapy after the placement of coro- and megakaryocytes. Thromb. Haemost., 1999, 82, nary-artery stents. N. Engl. J. Med., 1996, 334, 1084– 365–376. 1089. 52. Weitz J.I., Buller H.R.: Direct thrombin inhibitors in 45. Shapiro M.J., Weiss E.J., Farugi T.R., Coughlin S.R.: acute coronary syndromes. Present and future. Circu- Protease-activated receptor 1 and 4 are shut off with lation, 2002, 105, 1004–1011. distinct kinetics after activation by thrombin. J. Biol. 53. Yao S.K., Ober J.C., Garfinkel L.I., Hagay Y., Ezov N., Chem., 2000, 275, 25216–25221. Ferguson J.J., Anderson H.V., Panet A., Gorecki M., 46. Storey F.: The P2Y12 receptor as a therapeutic target Buja L.M.: Blockade of platelet membrane glycopro- in cardiovascular disease. Platelets, 2001, 12, 197–209. tein Ib receptors delays intracoronary thrombogenesis, 47. The Ridogrel Versus Aspirin Patency Trial (RAPT). enhances thrombolysis, and delays coronary artery re- Randomized trial of ridogrel, a combined thromboxa- occlusion in dogs. Circulation, 1994, 89, 2822–2828. ne A2 synthase inhibitor and thromboxane A2/prosta- glandin endoperoxide receptor antagonist, versus aspi- rin as adjunct to thrombolysis in patients with acute myocardial infarction. Circulation, 1994, 89, 588–595. Received: March 13, 2003; in revised form: June 1, 2003.

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