EP0483261A1 - Hirudin peptide derivatives - Google Patents

Abstract

The invention relates to novel peptide derivatives having biological activity, which inhibits fibrinolytic activity but not the amidolytic activity of thrombin. Peptide derivatives, having partial homology with the carboxy terminal part of hirudin, are characterized by a tyrosine or cysteine residue modified at a predetermined site located in the molecule. The invention also relates to compositions and methods employing said peptide derivatives for therapeutic, profilactic or diagnostic purposes. The invention also relates to compositions inhibiting endothelial cells, as well as methods characterized by the peptide derivatives described above or similar peptide derivatives not containing a cysteine or tyrosine residue modified at a corresponding location in the molecule. These methods and compositions are advantageously useful for reducing or preventing platelet aggregation and platelet activation in a patient or in extracorporeal blood, in particular in patients with heparin-induced thrombocytopenia in their history.

Description

HIRUDIN PEPTIDE DERIVATIVES

TECHNICAL FIELD OF INVENTION

This invention relates to novel, biologically active peptide derivatives which inhibit the fibrinolytic, but not the amidolytic activity of thrombin. The peptide derivatives, which display partial homology to the carboxy terminal portion of hirudin, are characterized by a modified tyrosine or cysteine residue at a predetermined site in the molecule. This invention also relates to compositions and methods employing such peptide derivatives for therapeutic, prophylactic or diagnostic purposes. This invention also relates to platelet and endothelial cell inhibitory compositions and methods characterized by the above-described peptide derivatives or similar peptide derivatives which do not contain a modified cysteine or tyrosine residue at a corresponding locus in the molecule. These methods and compositions are advantageously useful for decreasing or preventing platelet aggregation and platelet activation in a patient or in extracorporeal blood, especially in patients who have a history of heparin-induced throm- bocytopenia.

BACKGROUND ART

Acute vascular diseases, such as myocardial infarction, stroke, pulmonary embolism, deep vein thrombosis, peripheral arterial occlusion, and other blood system thromboses constitute major health risks. Such diseases are caused by either partial or total occlusion of a blood vessel by a blood clot, which contains fibrin and aggregated platelets.

Current methods for treatment and prophylaxis of thrombotic diseases involve therapeutics which act in one of two different ways. The first type of therapeutic inhibits thrombin activity or thrombin formation, thus preventing clot formation. These drugs also inhibit platelet activation and aggregation. The second category of therapeutic accelerates thrombolysis and dissolves the blood clot, thereby removing it from the blood vessel and unblocking the flow of blood [J. P. Cazenave et al., Agents Action, 15, Sup l.. pp. 24-49 (1984)].

Heparin, a compound of the former class, has been widely used to treat conditions, such as venous thromboembolism, in which thrombin activity is responsible for the development or expansion of a thrombus. Although effective, heparin produces many undesirable side effects, including he orrhaging and thrombocytopenia. This has led to a search for a more specific and less toxic anticoagulant. Hirudin is a naturally occurring polypeptide which is produced by the blood sucking leech Hirudo medicinalis. This compound, which is produced in the salivary gl-nd of the leech, is the most potent natural inhibitor of coagulation known. Hirudin prevents blood from coagulating by binding tightly to thrombin (K_d = 2 x 10^""M) in a 1:1 stoichiometric complex [S. R. Stone and J. Hofsteenge, "Kinetics of the Inhibition of Thrombin by Hirudin" Biochemistry. 25, pp. 4622-28 (1986)]. This, in turn, inhibits thrombin from catalyzing the conversion of fibrinogen to fibrin (clot) .

The actual binding between hirudin and thrombin is a two-step process. Initially, hirudin binds to a "low" affinity site on the thrombin molecule (K_d = 1 x 10^"*M) which is separate from the catalytic site. Following the low affinity binding, hirudin undergoes a conformational change and then binds to the "high" affinity site on thrombin. This latter site corresponds to the active site of thrombin.

The isolation, purification and chemical composition of hirudin are known in the art [P. Walsmann and F. Markwardt, "Biochemical and Pharmacological Aspects of the Thrombin Inhibitor Hirudin", Pharmazie. 36, pp. 653-60 (1981)]. More recently, the complete amino acid sequence of the polypeptide has been elucidated [J. Dodt et al. "The Complete Covalent Structure of Hirudin: Localization of the Disulfide Bonds", Biol. Chem. Hoppe-Seyler. 366, pp. 379-85 (1985); S. J. T. Mao et al., "Rapid Purification and Revised Amino Terminal Sequence of Hirudin: A Specific Thrombin Inhibitor of the Blood- Sucking Leech", Anal. Biochem_f 161, pp. 514-18 (1987); and R. P. Harvey et al., "Cloning and Expression of a cDNA Coding for the Anti-Coagulant Hirudin from the Bloodsucking Leech, Hirudo medicinalis". Proc. Natl. Acad. Sci. USA. 83, pp. 1084-88 (1986)].

At least ten different isomorphic forms of hirudin have been sequenced anfi have been shown to differ slightly in amino acid sequence [D. Tripier, "Hirudin: A Family of Iso-Proteins. Isolation and Sequence Determination of New Hirudins", Folia Haematol.. 115, pp. 30-35 (1988)]. All forms of hirudin comprise a single polypeptide chain protein containing 65 or 66 amino acids in which the amino terminus primarily comprises hydrophobic amino acids and the carboxy terminus typically comprises polar amino acids. More specifically, all forms of hirudin are characterized by an N-terminal domain (residues 1- 39) stabilized by three disulfide bridges in a 1-2, 3- 5, and 4-6 half-cysteinyl pattern and a highly acidic C-terminal segment (residues 40-65) . In addition, the C-terminal segment of hirudin is characterized by the presence of a tyrosine residue at amino acid position 63 which is sulfated.

In animal studies, hirudin, purified from leeches, has demonstrated efficacy in preventing venous thrombosis, vascular shunt occlusion and thrombin- induced disseminated intravascular coagulation. In addition, hirudin exhibits low toxicity, little antigenicity and a very short clearance time from circulation [F. Markwardt et al., "Pharmacological Studies on the Antithrombotic Action of Hirudin in Experimental Animals", Thromb. Hae ostasis. 47, pp. 226-29 (1982)].

Despite hirudin's effectiveness, however, studies have shown that hirudin prolongs bleeding time in a dose-dependent manner, thus making the determi- nation and administration of proper dosages critically important. Furthermore, the high cost and low supply of the naturally occurring product has prevented its widespread use.

In an effort to create a greater supply of hirudin, attempts have been made to produce the polypeptide through recombinant DNA techniques. The presence of an O-sulfated tyrosine residue on native hirudin and the inability of microorganisms to perform a similar protein modification made the prospect of recombinant production of biologicaxly active hirudin highly speculative. The observation that desulfato- hirudins were almost as active as their sulfated counterparts [United States patent 4,654,302], however, led the way to the cloning and expression of hirudin in E.coli [European patent applications 158,564, 168,342 and 171,024] and yeast [European patent application 200,655]. Despite these advances, hirudin is still moderately expensive to produce and it is not wideiy available commercially. Recently, efforts have been made to identify peptide fragments of native hirudin which are also effective in lowering clotting time. An unsulfated 21 amino acid C-terminal fragment of hirudin, N^acetyl- hirudin₄₅.₆₅, inhibits clot formation in vitro. In addition, several other smaller, unsulfated peptides corresponding to the C-terminal 11 or 12 amino acids of hirudin (residues 55-65 and 54-65) have also demonstrated efficacy in inhibiting clot formation in vitro [J. L. Krstenansky et al., "Antithrombin Properties of C-terminus of Hirudin Using Synthetic Unsulfated N^β-acetyl-hirudin_4S__H", FEBS Lett. 211, pp. 10-16 (1987)]. Such peptide fragments, however, may not be fully satisfactory to dissolve blood clots in on-going therapy regimens. For example, if-acetyl- hirudin_<5_„ has a specific activity four orders of magnitude lower than native hirudin.

In addition to catalyzing the formation of a fibrin clot, thrombin has several other bioregulatory roles [J. . Fenton, II, "Throabin Bioregulatory Functions", Adv. Clin. Enzvmoi.. 6, pp. 186-93 (1988)]. For example, thrombin directly activates platelet aggregation and release reactions. This means that thrombin plays a central role in acute platelet- dependent thrombosis [S. R. Hanson and L. A. Harker, "Interruption of Acute Platelet-Dependent Thrombosis by the Synthetic Antithrombin D-Phenylalanyl-L-Prolyl-L- Arginylchloro-methyl Ketone", Pre ■ Natl. Acad. Sci. USA. 85, pp. 3184- 88 (1988)].

Thrombin can also directly activate an inflammatory response by stimulating the synthesis of platelet activating factor (PAF) by endothelial cells [S. M. Prescott et al. , "Human Endothelial Cells in Culture Produce Platelet-Activating^" Factor (l-alkyl-2- acetyl-sn-glycero-3-phosphocholine) When Stimulated with Thrombin, Proc. Natl. Acad. Sci. USA. 81, pp. 3534-38 (1984)]. PAF is exposed on the surface of endothelial cells and serves as a ligand for neutrophil adhesion and subsequent degranulation [G. M. Vercolletti et al. , "Platelet-Activating Factor Primes Neutrophil Responses to Agonists: Role in Promoting Neutrophil-Mediated Endothelial Damage", Blood. 71, pp. 1100-07 (1988)].

The mechanism by which thrombin activates platelets and endothelial cells involves a receptor and is effected at a lower concentration than that required for fibrinogen cleavage [J. T. Harmon and G. A. Ja ieson, "The Glycocalcin Portion of Glycoprotein lb Expresses Both High and Moderate Affinity Receptor Sites for Thrombin", J. Biol. Chem.. 28, pp. 13224-29 (1986)]. Reagents which block the active site of thrombin, such as hirudin, interrupt the activation of platelets and endothelial cells [C. L. Knupp, "Effect of Thrombin Inhibitors on Thrombin-Induced Release and Aggregation", Thrombosis Res... 49, pp. 23-36 (1988)]. However, there is no evidence that the mere interruption of thrombin/receptor binding is sufficient to inhibit that activation.

Accordingly, despite these developments to date, the need exists for small synthetic peptides or peptide derivatives, characterized by increased efficacy in the inhibition of clot formation, thrombin- induced platelet activation or endothelial cell activation, which may be produced in commercially feasible quantities.

SUMMARY OF THE INVENTION

The present invention solves the problems . referred to above by providing peptide derivatives ' which inhibit the fibrinolytic activity, but not the amidolytic activity of thrombin. Specifically, the peptide derivatives of this invention, as well as compositions and methods employing them, are effective as anticoagulants which cause an increase in blood clotting time. These peptide derivatives are characterized by partial homology to the C-terminus of native hirudin and by the presence of a derivatized tyrosine or cysteine residue at a functionally critical locus in the moleucle.

The present invention also provides compositions and methods which inhibit thrombin-induced platelet aggregation and platelet release (hereinafter "platelet activation") and the release of inflammatory substances from endothelial cells (hereinafter "endothelial activation") . These compositions and methods may employ the above-described peptide derivatives or other, similar peptide derivatives which do not contain a corresponding modified tyrosine or cysteine residue in the molecule.

The relatively small size of the peptides derivatives of this invention and the other peptide derivatives which characterize the compositions of this invention advantageously permits production using conventional peptide synthesis techniques. Thus, they may be produced in extremely high yields and are easily purified, as compared to either native hirudin or its full length recombinant DNA counterpart.

Advantageously, these peptide derivatives, unlike hirudin, exhibit a saturable effect on clotting time. Thus, the therapeutic and prophylatic uses of the peptides avoid the harmful and potentially fatal consequences of an overdose associated with conven¬ tional anticoagulants, such as heparin. And the small size of the peptide derivatives employed in this invention decreases the possibility of an adverse antigenic response in patients treated with them.

As will be appreciated from the disclosure to follow, the peptide derivatives, compositions and methods of ths invention are useful in the treatment, prevention or diagnosis of vascular and other diseases attributed to the undesirable effects of thrombin, as well as in the treatment of extracorporeal blood and in in vivo diagnosis techniques. And, compositions characterized the peptide derivatives of this invention are also useful for coating invasive devices to be inserted into a patient.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 depicts the effects of various concentrations of N-acetyl-TNBCys₆₃hirudin₅₃._M, N-acetyl- (3,5-diiodoTyr)_Hhirudin₅₃_₆_, N-acetyl-SCMCys₆₃hirudin_H__M, N-acetyl-SCECys₆₃hirudin_H_₆_, N-acetyl-hirudin„„_M or N- acetyl-Cys₆₃hirudin₅₃._M on the activated partial thromboplastin times of normal human plasma. DETAILED DESCRIPTION OF THE INVENTION

The following common abbreviations of amino acids are used throughout the present application:

Lys - lysine Arg - arginine

His - histidine Gly - glycine

Ala - alanine Val - valine

Leu - leucine lie - isoleucine

Pro - proline Phe - phenylalanine

Trp - tryptophan Met - methionine

Ser - serine Thr - threonine

Cys - cysteine Tyr - tyrosine

Asn - asparagine Gin - glutamine

Asp - aspartic acid Glu - glutamic acid

Asx - asparagine or Glx - glutamine or aspartic acid glutamic acid

Hyp - hydroxyproline Nle - norleucine

Sar - sarcosine D-ala - D-alanine

5-nitroTyr - 5-nitrotyrosine Ac - acetyl

Cha - cyclohexylalanine N-Ac - N-acetyl

SCMCys - S-carboxymethylcysteine

SCECys - s-carboxyethylcysteine

Tyr(S0₃H) - tyrosine sulfonate

Tyr (0S0₃H) - O-sulfate ester of tyrosine

3-nitroTyr - 3-nitrotyrosine diiodoTyr - 3,5-diiodotyrosine

SubPhe - ortho, meta or para mono- or di-substituted phenylalanine

TNBCys - 2-thio-5-nitrobenzoic acid cysteine

3,4-dehydroPro - 3,4-dehydroproline

As used in this application, an "alkyl group" and the "alkyl portion of an alkoxy group" includes straight, branched, or cyclic alkyl groups; for example, methyl, ethyl, propyl, isopropyl, butyl. isobutyl, tert-butyl, pentyl, isopentyl, sec-pentyl, cyclopentyl, hexyl, isohexyl, cyclohexyl and cyclo pentylmethvl. An "acyl group" of from 2 to 10 carbon atoms includes straight, branched, cyclic, saturated and unsaturated acyl groups having 1 or 2 carbonyl moieties per group — for example acetyl, benzoyl, aleyl, glutaryl and succinyl. A "halogen group" is a fluoro, chloro, bro o or iodo group.

The term "any amino acid" as used herein includes the L-isomers of the naturally occurring amino acids, as well as other "non-protein" α-amino acids commonly utilized by those in the peptide chemistry arts when preparing synthetic analogues of naturally occurring amino peptides. The "naturally occurring amino acids" are glycine, alanine, valine, leucine, isoleucine, serine, methionine, threonine, phenylalanine, tyrosine, tryptophan, cysteine, proline, histidine, aspartic acid, asparagine, glutamic acid, glutamine, arginine, ornithine and lysine. Examples of "non-protein" α-amino acids are norleucine, norvaline, alloisoleucine, homoarginine, thiaproline, dehydroproline, hydroxyproline (Hyp) , homoserine, cyclohexylglycine (Chg) , α-amino-n-butyric acid (Aba) , cyclohexylalanine (Cha) , aminophenylbutyric acid (Pba) , phenylalanine substituted at the ortho, meta, or para position of the phenyl moiety with one or two of the following: a (C,-C_t) alkyl, a (C,-C₄) alkoxy, halogen or nitro groups or substituted with a methylenedioxy group, β-2- and 3-thienylal-alanine, β-2- and 3- furanylalanine, β-2-, 3- and 4-pyridylalanine, β- (benzothienyl-2- and 3-yl)alanine, β-(l- and 2- naphth 1)alanine, O-alkylated derivatives of serine, threonine or tyrosine, S-alkylated cysteine, S- alkylated ho ocysteine, O-sulfate, O-phosphate and o- carboxylate esters of tyrosine, 3- and 5-sulfonyl - 11 -

tyrosine, 3- and 5-carbonyl tyrosine, 3- and 5- phosphonyl tyrosine, 4-methylsulfonyl tyrosine, 4- ethylphosphonyl tyrosine, 4-phenylacetic acid, 3,5- diiodotyrosine, 3- and 5-nitrotyrosine, e-alkyl lysine, 5 e-alkyl ornithine, 2-thio-5-nitrobenzoic acid cysteine and the D-isomers of the naturally occurring amino acids.

The term "derivatized amino acid" as used herein refers to O-sulfate esters of tyrosine, O-

10 phosphate esters of tyrosine, O-carboxylate esters of tyrosine, 3-sulfonyl tyrosine, 5-sulfonyl tyrosine, 3- phosphonyl tyrosine, 5-phosphonyl tyrosine, 3-carboηyl tyrosine, 5-carbonyl tyrosine, 4-methylsulfonyl tyrosine, 4-methylphosphonyl tyrosine, 4-r-<enylacetic

15 acid, 3,5-diiodotyrosine, 3-nitrotyrosine, 5- nitrotyrosine, S-alkylated cysteine, S-alkylated homocysteine and thionitrobenzoic acid cysteine. The term "patient" as used in this application refers to any mammal, especially humans. The term

20 "antiplatelet" as used herein means an inhibitor of both platelet aggregation and platelet release reactions.

The present invention relates to peptide derivatives of the formula:

__ ^•—' Λ **t ** **3 **4 **5 **6 **7 *"β ^*9 *"10 wherein X is a hydrogen, one or two alkyl groups of from 1 to 6 carbon atoms, one or two acyl groups of from 2 to 10 carbon atoms, carbobenzyloxy or t-butyloxy carbonyl; A, is a bond or is a peptide containing from 1 0 to 11 residues of any amino acid; A₂ is Phe, SubPhe, β- (2- and 3-thienyl) alanine, β-(2- and 3- furanyl)alanine, β-(2-, 3- and 4-pyridyl)alanine, β- (benzothienyl-2- and 3-yl)alanine, β-(l- and 2- naphthyl)alanine, Tyr or Trp; A is Glu or Asp; A. is 5 any amino acid; A₅ is lie, Val, Leu, Nle or Phe; _ is Pro, Hyp, 3,4-dehydroPro, thiazolidine-4- carboxylate, Sar, NMePgl or D-Ala; A₇ is any amino acid; A_s is any amino acid; A, is a derivatized amino acid selected from the group consisting of O-sulfate esters of tyrosine, O-phosphate esters of tyrosine, O-carboxylate esters of tyrosine, 3-sulfonyl tyrosine, 5-sulfonyl tyrosine, 3- phosphonyl tyrosine, 5-phosphonyl tyrosine, 3-carbonyl tyrosine, 5-carbonyl tyrosine, 4-methylsulfonyl tyrosine, 4-methylphosphonyl tyrosine, 4-phenylacetic acid, 3,5-diiodotyrosine, 3-nitrotyrosine, 5- nitrotyrosine, S-alkylated cysteine, S-alkylated homocysteine, thionitrobenzoic acid cysteine, and dipeptides consisting of said derivatized amino acid and any amino acid; A,₀ is a bond or a peptide con- taining from 1 to 5 residues of any amino acid; and Y is a carboxyl terminal residue selected from OH, C,-C₆ alkoxy, amino, mono- or di-(C,-C.) alkyl substituted amino or benzylamino; with the proviso that said peptide does not consist of a sequence of amino acids wherein: X is H or an amino protecting group; A, is a bond or from 1 to 11 amino acid residues consisting of any C-terminal portion of the amino acid sequence:

Thr-Pro-B-Pro-Glx-Ser-His-Asn-Asx-Gly-Asp, wherein B is Asn or Lys; A₂ is Phe; A₃ is Glu; A. is Glu; A, is lie; A_* is Pro; A₇ is Glu; A, is Glu; A, is an O- sulfate ester of tyrosine, an O-phosphate ester of tyrosine, an O-carboxylate ester of tyrosine, 3- sulfonyl tyrosine, 5-sulfonyl tyrosine, 3-phosphonyl tyrosine, 5-phosphonyl tyrosine, 3-carbonyl tyrosine, 5-carbonyl tyrosine, 4-methylsulfonyl tyrosine or 4- methylphosphonyl tyrosine; A_I0 is a bond. Leu or Leu- Gln; and Y is OH.

Preferred peptide derivatives according to this invention are characterizexl by an A, component selected from the group consisting of 3,5-diiodo- diiodotyrosine, 3-nitrotyrosine, 5-nitrotyrosine, S- carboxymethylcysteine, S-carboxyethylcysteine and thionitrobenzoic acid cysteine. The most preferred peptides according to the present invention have the amino acid formulae:

N-Ac-Asn-Gly-Asp-Phe-Glu-Glu-Ile-Pro-Glu-Glu- » (3,5-diiodoTyr)-Leu-OH (herein referred to as "N- Ac-(diiodoTyr)₆₃hirudin₅₃_₆₄") ;

N-Ac-Asn-Gly-Asp-Phe-Glu-Glu-Ile-Pro-Glu-Glu- (3-nitroTyr)-Leu-OH (herein referred to as "N-Ac- (3-nitroTyr)₆₃hirudin₅₃.₆") ;

N-Ac-Asn-Gly-Asp-Phe-Glu-Glu-Ile-Pro-Glu-Glu- (5-nitroTyr)-Leu-OH (herein referred to as "N-Ac- (5-nitroTyr)_β3hirudin„.₆₄") ; N-Ac-Asn-Gly-Asp-Phe-Glu-Glu-Ile-Pro-Glu-Glu-

(SCMCys) -Leu-OH (herein referred to as "N-Ac- SCMCys₆₃hirudin„.₆ " ) ;

N-Ac-Asn-Gly-Asp-Phe-Glu-Glu-Ile-Pro-Glu-Glu- (SCECys) -Leu-OH (herein referred to as "N-Ac- SCECys₆₃hirudin_S3.₆₄" ) ; and

N-Ac-Asn-Gly-Asp-Phe-Glu-Glu-Ile-Pro-Glu-Glu (TNBCys) -Leu-OH (herein referred to as "N-Ac- TNBCys₆₃hirudin₅₃.₆₄" ) .

The presence of a derivatized amino acid at the A, position of the peptides of this invention causes an unexpected increase in anticoagulant potency and in antiplatelet activity as compared to corresponding peptide derivatives which lack such a moiety.

Typically, this increase is 3 to 10-fold in anticoagulant potency and up to 100-fold in antiplatelet activity.

The peptide derivatives of the present invention, as well as other peptide derivatives which are utilized in the compositions of the present invention, may be synthesized by various techniques which are well known in the art. These include recombinant DNA techniques, solid-phase peptide synthesis, solution-phase peptide synthesis, organic chemical synthesis techniques, or a combination o_f these techniques. The choice of synthesis techniques will, of course, depend upon the composition of the particular peptide derivative. In the preferred embodiments of this invention, the peptide derivative is synthesized entirely by solid-phase synthesis techniques, which constitute the most cost-efficient procedure for producing commercial quantities of these molecules [see, for example, European patent application 276,104, copending United States patent application 314,756 and J. M. Maraganore et al., "Anticoagulant Activity of Synthetic Hirudin Peptides", J. Biol. Chem.. 264, pp. 8692-98 (1989) , all of which are herein incorporated by reference) . When "non-protein" amino acids are contained in the peptide derivatives, they may either be added directly to the growing chain during peptide synthesis or prepared by chemical modification of the complete synthesized peptide, depending on the nature of the desired "non-protein" amino acid. Those of skill in the chemical synthesis art are well aware of which "non-protein" amino acids may be added directly and which must be synthesized by chemically modifying the complete molecule following synthesis [see, copending United States patent application 314,756]. Examples of "non-protein" amino acids which may be added directly during synthesis are diiodoTyr, norleucine, and norvaline. Those amino acids which must be synthesized by reacting the fully synthesized molecule are exemplified by SCMCys, SCECys, 3- or 5-nitroTyr and TNBCys.

The anticoagulant activity of the peptide derivatives of the invention may be assayed using any conventional technique. For example, the assay employed may use purified thrombin and fibrinogen and measures the inhibition of release of fibrinopeptides A or B by radioimmunoassay or ELISA. Alternatively, the assay may involve direct determination of the thrombin- inhibitory activity of the peptide. Such assays measure the inhibition of thrombin-catalyzed cleavage of colorimetric substrates or, more preferably, the increase in activated partial thromboplastin times (APTT) and increase in thrombin times (TT) . The latter assays measure factors in the "intrinsic" pathway of coagulation.

The peptide derivatives of this invention are useful in compositions, combinations and methods for the treatment and prophylaxis of vascular diseases attributed to blood system thromboses. For example, the peptide derivatives of this invention, and composi¬ tions containing them, may be used for heparin replace¬ ment for prophylactic purposes, heparin replacement in the treatment of thrombocytopenia, treatment of disseminated intravascular coagulation and treatment of vascular thrombi that may arise from any disease state. The peptide derivatives of this invention, as well as compositions containing them, may be used in the treat¬ ment or prophylaxis of vascular diseases in all mammals and, in particular, humans. Alternatively, the peptide derivatives of this invention, as well as other peptide derivatives which lack a derivatized amino acid at the A, position, may be administered in combination with heparin or low molecular weight heparin. Such combinations advantageously lower the dosage of heparin or low molecular weight heparin required to produce a desired anticoagulant effect when either compound is used alone. Furthermore, these combinations advantageously reduce the potential for hemorrhagic complications often associated with heparin use. And such combi- nations surprisingly demonstrate greater anticoagulant activity than that exhibited in monotherapies based upon either of the individual components. As defined herein, the term "combination" includes a single dosage form containing at least one peptide derivative of the present invention or at least one other peptide derivative which lacks the derivatized amino acid at A, and heparin or low molecular weight heparin, a multiple dosage form wherein the peptide derivative and the heparin are administered separately, but concurrently, or a multiple dosage form wherein the two agents are administered separately, but sequentially.

According to an alternate embodiment of the present invention, the above-described peptide derivatives, as well as other similar peptide derivatives which lack the derivatized amino acid at position A,, may be formulated into compositions for inhibiting platelet activation ("antiplatelet") . The antiplatelet activity of either of the above groups of peptide derivatives may be measured by any of a number of conventional platelet assays. Preferably, the assay measures a change in the degree of aggregation of platelets or a change in the release of a platelet secretory component in the presence of thrombin. The former may be measured in a commercially available aggregometer. The latter may be measured using RIA or ELISA techniques specific for the secreted component.

The compositions of the present invention are also useful in inhibiting coagulation or platelet activation in extracorporeal blood. As used herein, the term "extracorporeal blood" includes blood removed in line from a patient, subjected to extracorporeal treatment and then returned to the patient in such processes as dialysis procedures, blood filtration, or blood bypass during surgery. "The term also includes blood products which are stored extracorporeally for eventual administration to a patient, as well as blood collected from a patient to be used for various assays. Such products include whole blood, plasma, platelets, or any blood fraction in which inhibition of either coagulation or platelet activation is desired.

According to another embodiment of the invention, the pharmaceutically acceptable compositions and methods for inhibiting platelet activation in a treated patient or in extracorporeal blood may further comprise standard dosage amounts of other platelet inhibitors such as metal chelaters, prostaglandins, other small platelet inhibitory peptides, cyclooxy- genase inhibitors, small non-peptide platelet inhibitors, inhibitors of platelet surface components, antibodies to platelet surface components, hemato- poietic factors, analogs of any of the above compounds or combinations thereof. The most preferred additional platelet inhibitors are aspirin, ticlopidine, dipyrida- mole, sulphinpyrazone, prostaglandin E, or known analogs thereof, stable prostacyclin derivatives, monoclonal antibodies against glycoprotein lib/Ilia or natural inhibitors of glycoprotein lib/Ilia, monoclonal antibodies against glycoprotein lb, natural inhibitors of glycoprotein lb, erythropoetin, arg-gly-asp- containing peptides and derivatives of arg-gly-asp- containing peptides.

This invention also relates to methods and compositions for inhibiting thrombin-induced endothelial cell activation. Such inhibiton includes the repression of platelet activating factor (PAF) synthesis by these cells. This mechanism of inhibition has important implications in the treatment of diseases characterized by thrombin-induced inflammation, which is thought to be mediated by PAF. Such diseases include, but are not limited to, adult respiratory distress syndrome, septic shock, septicemia and reperfusion damage.

The pharmaceutically acceptable compositions and combinations used in the methods of this invention may be formulated using conventional methods to prepare pharmaceutically useful compositions. Such composi¬ tions and combinations preferably include at least one pharmaceutically acceptable carrier. See, e.g., Remington's Pharmaceutical Sciences (E. W. Martin) . In addition, the compositions and combinations preferably include a pharmaceutically acceptable buffer, prefer¬ ably phosphate buffered saline, together with a pharma¬ ceutically acceptable compound for adjusting isotonic pressure, such as sodium chloride, mannitol or sor- bitol.

The dosage and dose rate of the peptide derivatives which characterize the compositions and combinations of the present invention is dependent on a variety of factors, such as the specific composition employed, the object of the treatment, i.e., therapy or prophylaxis, the nature of the thrombotic disease to be treated, antiplatelet or anticoagulant activity and the judgment of the treating physician. Various dosage forms may be employed to administer the compositions and combinations of this invention. These include, but are not limited to, parenteral administration, oral administration and topical application. The compositions and combinations may be administered to the patient in any pharmaceutically acceptable dosage form, including those which may be administered to a patient intravenously as bolus or by continued infusion, intramuscularly — including paravertebrally and periarticularly — subcutaneously, intracutan- eously, intra-articularly, intrasynovially, intra- thecally, intra-lesionally, periostally or by oral or topical routes. Such compositions and combinations are preferably adapted for oral and parenteral administration, but, most preferably, are formulated for parenteral administration.

Parenteral compositions and combinations are most preferably administered intravenously either in a bolus form or as a constant infusion. For parenteral administration, fluid unit dose forms are prepared which contain a composition of the present invention and a sterile vehicle. The peptide derivative compo¬ nent of the pharmaceutically acceptable composition or combination may be either -uspended or dissolved in the vehicle, depending on the nature of the vehicle and the nature of the component.

Parenteral compositions and combinations may be prepared by dissolving the peptide derivative in a vehicle, optionally together with other components, and filter sterilizing before filling into a suitable vial or ampule and sealing. Preferably, adjuvants such as a local anesthetic, preservatives and buffering agents are also dissolved in the vehicle. The composition may then be frozen and lyophilized to enhance stability. Parenteral suspensions may be prepared in substantially the same manner, except that the active component is suspended rather than dissolved in the vehicle. Sterilization of the compositions is preferably achieved by exposure to ethylene oxide before suspending in the sterile vehicle. A surfactant or wetting agent may advantageously be included in the composition to facilitate uniform distribution of the components.

Tablets and capsules for oral administration contain conventional excipients such as binding agents, fillers, diluents, tab eting agents, lubri- - 20 -

cants, disintegrants, and wetting agents. The tablet may be coated according to methods well known in the art. Suitable fillers which may be employed include cellulose, mannitol, lactose and other similar agents. Suitable disintegrants include, but are not limited to, starch, polyvinylpyrrolidone and starch derivatives, such as sodium starch glycolate. Suitable lubricants include, for example, magnesium stearate. Suitable wetting agents include sodium lauryl sulfate. Oral liquid preparations may be in the form of aqueous or oily suspensions, solutions, emulsions, syrups or elixirs, or may be presented as a dry product for reconstitution with water or another suitable vehicle before use. Such liquid preparations may contain conventional additives. These include suspending agents; such as sorbitol, syrup, methyl cellulose, gelatin, hydroxyethylcellulose, carboxy- methylcellulose, aluminum stearate gel or hydrogenated edible fats; emulsifying agents which include lecithin, sorbitan monooleate or acacia; non-aqueous vehicles, such as almond oil, fractionated coconut oil, and oily esters; and preservatives, such as methyl or propyl p- hydroxybenzoate or sorbic acid.

In compositions and combinations useful as anticoagulants in a treated patient, a pharmaceutically effective daily dose of the peptide derivatives of this inveniton is between about 0.1 mg/kg body weight of the patient to be treated ("body weight") and about 100 mg/kg body weight. More preferably, the daily dose of the peptide derivative is between about 0.5 mg/kg body weight to about 10 mg/kg body weight. In combinations that are additionally characterized by the presence of heparin or low molecular weight heparin, a pharmaceutically effective dosage of either of those compounds is less than that required to achieve a desired anticoagulant result when either is administered as a monotherapy. Preferably, the dosage of heparin or low molecular weight heparin is less than about 5,000 units/patient/day. To achieve an anticoagulant effect in extracorporeal blood an pharmaceutically effective amount of the peptide derivatives of this invention is between about 0.1 mg/600 ml extracorporeal blood and about 100 mg/600 ml extracorporeal blood. More preferably, the dose is between about 0.5 mg/600 ml extracorporeal blood and about 10 mg/600 ml extracorporeal blood.

In compositions where inhibition of platelet activation or inhibition of endothelial activation in a patient is desired, a pharmaceutically effective dose of the peptide derivatives of this inveniton is between about 0.0001 mg/kg body weight of the patient to be treated ("body weight") and about 100 mg/kg body weight. More preferably, the dose of the peptide derivative is between about 0.001 mg/kg body weight to about 0.05 mg/kg body weight. These lower dosages allow inhibition of platelet or endothelial cell activation without concurrent anticoagulant effects. To achieve an inhibition of platelet activation in extracorporeal blood an pharmaceutically effective amount of the peptide derivatives of this invention is between about 0.0001 mg/600 ml extracorporeal blood and about 100 mg/600 ml extracorporeal blood. More preferably, the dose is between about 0.001 mg/600 ml extracorporeal blood and about 0.05 mg/600 ml extracorporeal blood.

It should be understood that dosages outside of the above-described ranges are also encompassed by the present invention. For example, once improvement of the patient's condition has occurred, a low. maintenance dose of a combination or composition of this invention may be administered if necessary. Subsequently, the dosage or the frequency of administration, or both, may be reduced, as a function of the symptoms, to a level at which the improved condition is retained. When the symptoms have been alleviated to the desired level, treatment should cease. Patients may, however, require intermittent treatment upon any recurrence of disease symptoms. The compositions and combinations of this invention may additionally contain standard dosages of other components which are effective in fibrinolytic therapy. These inc ude, but are not limited to, tissue plasminogen activator purified from natural sources, recombinant tissue plasminogen activator, anisolated streptokinase plasminogen activator complex (ASPAC) , animal salivary gland plasminogen activator, urokinase, streptokinase and known, biologically active derivatives of any of the above. These other compounds may be present as separate components in the peptide derivative-containing combinations and compositions of this invention. Alternatively, the peptide derivative may be conjugated to such fibrinolytic agents. Conjugation may be achieved by any of the methods known in the art. The peptides derivative and fibrinolytic agent may also be present as a single molecule, i.e., in the form of a fusion protein, produced by recombinant DNA techniques or by in vitro synthesis.

The anticoagulant and antiplatelet potency of the peptide derivatives present in the compositions and combinations of this invention depend, in part, on their in vivo half-life. Accordingly, this invention also relates to pharmaceutical compositions, either co- valent or non-covalent, comprising the above-described peptide derivatives coupled to pharmaceutically acceptable polymers which increase their biological half-life. For example, a peptide derivative may be coupled to an activated derivative of polyethylene- glycol (PEG) using conventional techniques. Preferably, a PEG N-succinimidyl succinate is attached to an α-amino moiety of the peptide derivative. Such attachment is effected by reacting the peptide derivative with the PEG N-succinimidyl succinate reagent (SS-PEG) in an organic solvent or a buffered solution having a pH greater than about 7.0. Most pre¬ ferably, about a 50-fold molar excess of SS-PEG (Avg. MW = 5,000 daltons) is reacted with a peptide derivative in a 20 mM sodium borate buffer, pH 9.0.

According to an alternate embodiment of the present invention, the peptide derivatives may be used in compositions and methods for in vivo thrombus imaging in a patient. Initially, the peptide derivatives used in these compositions and methods are labeled with a radioisotope. The choice of radioisotope is based upon a number of well-known factors, for example, toxicity, biological half-life and detectability. Preferred radioisotopes include, but are not limited to, '"I, '"I and "'In. Techniques for labeling peptides and peptide derviatives are well known in the art. Most preferably, the radioisotope is '"I and labeling is achieved using '"I-Bolton Hunter Reagent. The labeled peptide derivative is administered to a patient, preferably by an intravenous route, and allowed to bind to the thrombin contained in a fibrin clot. The clot is then observed by utilizing well-known detecting means, such as a camera capable of detecting radioactivity coupled to a computer imaging system. This technique also yields images of platelet- bound thrombin and eizothrombin. According to another embodiment of the present invention, one or a combination of any of the peptide derivatives may be used in compositions and methods for coating invasive devices to be inserted into a patient. These compostions and methods result in lower risk of thrombotic complications in patients receiving such devices. Surfaces that may be coated according to the methods and compositons of this invention are exemplified by those of prostheses, artificial valves, vascular grafts, stents and catheters. Methods for achieving the coating of these surfaces are known in the art. These include chem cal cross-linking or physical adsorption of the peptide derivative-containing compositions to the surfaces of the devices.

This invention also relates to compositions containing the peptide derivatives of this invention and methods of using such compositions for the treatment of tumor metastases. The efficacy of the peptide derivatives of this invention for the treatment of tumor metastases via inhibition of metastatic growth is based upon the presence of a procoagulant enzyme present in certain cancer cells [A. Falanga and S. G. Gordon, "Isolation and Characterization of Cancer Procoagulant: A Cysteine Proteinase from Malignant Tissue", Biochemistry. 24, pp. 5558-67 (1985); S. G. Gordon et al., "Cysteine Proteinase Procoagulant from Amnion-Chorion", Blood, 66, pp. 1261-65 (1985); and A. Falanga et al., "A New Procoagulant In Acute Leukemia", Blood. 71, pp. 870-75 (1988)]. This enzyme activates the conversion of Factor X to Factor Xa in the coagulation cascade, resulting in fibrin deposition which, in turn, serves as a substrate for tumor growth. Therefore, by inhibiting fibrin-deposition through the inhibition of thrombin, the peptide derivatives of the present invention serve as effective anti-metastatic tumor agents. Examples of metastatic tumors which may be treated by the peptide derivatives of this invention include, but are not limited to, carcinoma of the brain, carcinoma of the liver, carcinoma of the lung, osteocarcinoma and neoplastic plasma cell carcinoma.

In order that this invention may be more fully understood, the following examples are set forth. It should be understood that these examples are for illustrative purposes only and are not to be construed as limiting this invention in any manner.

EXAMPLE 1 Synthesis Of N-Acetyl-(3.5-DiiodoTyrAhirudin., .. N-Acetyl-3,5-DiiodoTyr₆₃hirudin₅₃.₆₄ (herein referred to as "N-Ac-(diiodoTyr)_β3hirudin_S3_₆₄"; in which the subscript numbers represent the corresponding amino acid position in the native hirudin molecule) has the amino acid formula: N-Ac-Asn-Gly-Asp-Phe-Glu-Glu-Ile- Pro-Glu-Glu-(3,5-diiodoTyr)-Leu-OH. We prepared this peptide by conventional solid-phase peptide synthesis employing an Applied Biosystems 430 A Peptide Synthesizer (Applied Biosystems, Foster City, California) . This peptide was synthesized using Boc-L- Leu-O-divinylbenzene resin. Additional t-Boc-amino acids employed in the synthesis included Boc-L- diiodotyrosine, Boc-L-glutamic acid (r-benzyl ester) , Boc-L-proline, Boc-L-isoleucine, Boc-L-phenylalanine, Boc-_^-aspartic acid (β-benzyl ester) , Boc-glycine and Boc-L-N-acetyl-asparagine. Following synthesis, N-acetyl-

(diiodoTyr)„hirudin₅₃.₆₄ was fully deprotected and cleaved from the resin by treatment with anhydrous HF:p- cresol:ethyl methyl sulfate (1ft:1:1, v/v/v) . Following removal from the resin, the peptide was lyophilized to dryness and redissolved in a minimum volume of 0.1% TF_A in water. The crude peptide was then purified by reverse phase HPLC employing an Applied Biosystems 151A liquid chromatographic system and a Vydac C„ column (2.2 x 25 cm). The column was equilibrated in 0.1% TFA in water and developed with a linear gradient of increasing acetonitrile concentration from 0 to 80 in 0.1% TFA over 45 minutes at a flow-rate of 4.0 ml/mm. The effluent stream was monitored for absorbance at 229 nm and fractions were collected manually.

EXAMPLE 2

Synthesis Of N-Acetyl-S- Carboxymethylcvsteinyl„Hirudin.- ,.

N-acetyl-S-carboxymethylcysteinyl₆₃hirudin₅₃.₆₄ (herein referred to as "N-Ac-SCMCys₆₃hirudin₅₃_₆") has the amino acid formula: N-Ac-Asn-Gly-Asp-Phe-Glu-Glu-Ile- Pro-Glu-Glu-SCMCys-Leu-OH. We initially synthesized N- acetyl-Cys₆₃hirudin₅₃.₆₄ in the same manner as the peptide in Example 1, substituting Boc-L-cysteine for Boc-L- diiodotyrosine at the second step of synthesis. The peptide was then deprotected and purified by reverse phase HPLC in an identical manner as for the peptide in Example 1. Fractions containing the peptide were evaporated to dryness. We then dissoved 5 μg of HPLC-purified N- acetyl-Cys₆₃hirudin₅₃__M in 1.0 μl of 0.1 M Tris-HCl, pH 7.5 and immediately reacted the peptide with a 10- fold molar excess of iodoacetic acid, which had previously been dissolved in 1.4 N NaOH. The reaction proceeded for 5 hours at 25°C and was then stopped by the addition of acetic acid to a final concentration of 5%. The resulting N-acetyl-S-carboxymethylcysteinyl_β3- hirudin₅₃.₆ was purified by reverse phase HPLC on an Aquapσre C. RP-300 column (0.46 x 10 cm) which had been equilibrated in solvent A (0.1% TFA in water). The column was developed with an increasing concentration of solvent B (0.085% TFA/70% acetonitrile) from 0 to 50% over 45 minutes at a flow rate of 1.0 ml/min. The effluent stream was monitored at 214 nm for absorbance. N-acetyl-S-carboxymethyl-cysteinyl₆₃hirudin₅₃.₆₄ eluted after the unmodified N-acetyl-Cys₆₃hirudin₅₃.₆.

EXAMPLE 3 Synthesis Of N-Acetyl-S-Carboxyethylcvsteinyl.,Hirudin.,.., N-acetyl-S-carboxyethylcysteinyl₆₃hirudin₅₃__M

(herein referred to as "N-Ac-SCECys₆₃hirudin₅₃.₆₄") has the amino acid formula: N-Ac-Asn-Gly-Asp-Phe-Glu-Glu-Ile- Pro-Glu-Glu-SCECys-Leu-OH. We dissolved 5 mg of N- acetyl-Cys₆₃hirudin₅₃.₆, prepared as in Example 2, in 100 μl of dimethylformamide (DMF) and then reacted the peptide with a 50-fold molar excess of 3-iodopropionic acid at 37°C for 24 hours. Crude N-acetyl-S- carboxyethylcysteinyl₆₃hirudin₅₃.₆₄ was purified by reverse phase HPLC under identical conditions as that used for N-acetyl-S-carboxymethylcysteinyl₆₃hirudin₅₃__M in Example 2.

EXAMPLE 4

Synthesis Of N-Acetyl-Thionitrobenzoic Acid Cysteinyl„Hirudin.,,_^ N-acetyl-thionitrobenzoic acid cysteinyl„hirudin_S3.₆ (herein referred to as "N-Ac- TNBCys_Hhirudin₅₃__#4") has the amino acid formula: N-Ac- Asn-Gly-Asp-Phe-Glu-Glu-Ile-Pro-Glu-Glu-TNBCys-Leu-OH. N-acetyl-Cys_Hhirudin₅₃._M (5 mg) , prepared as in Example 2, was dissolved in 1.0 ml of 0.1 M Tris-HCl, pH 7.5. We reacted the above peptide with a 5-fold molar excess of di(thionitrobenzoic acid) (QTNB; Ellman's reagent) for 1 hour at 25°C. The peptide was then purified by reverse phase HPLC on an Aquapore C, RP-300 column under conditions described in Example 2.

EXAMPLE 5

Synthesis Of N-Acetyl-3-NitroTyr₆₃Hirudin₅₃.₆₄ And N-Acetyl-5-NitroTyr„Hirudin.,.,

N-acetyl-3-nitroTyr₆₃hirudin₅₃__M has the amino acid formula: N-Ac-Asn-Gly-Asp-Phe-Glu-Glu-Ile-Pro- Glu-Glu-(3-nitroTyr)-Leu-OH. N-acetyl-5- nitroTyr_β3hirudin₅₃.₆₄ has the amino acid formula: N-Ac- Asn-Gly-Asp-Phe-Glu-Glu-Ile-Pro-Glu-Glu-(5-nitroTyr)- Leu-OH. Initially, we synthesize N-acetyl-hirudin₅₃..₄ in an identical manner to the synthesis performed in Example 1, substituting Boc-L-tyrosine for Boc-L- diiodotyrosine at the second step of synthesis. The peptide is deprotected and purified as in Example 1.

We then react 10 mg of purified peptide with a 100-fold molar excess of tetranitromethanol in a total of l.0 ml of 0.1 M sodium bicarbonate, pH 10.0 for 24 hours at 25°C. This reaction produces both N-acetyl-3- nitroTyr₆₃hirudin₅₃._M and N-acetyl-5-nitroTyr₆₃hirudin„_₆₄. We separate unwanted reaction products and remove excess reagent by molecular sieve chromatography on a Biogel P-2 column which is equilibrated and developed with 0.1 M Tris-HCl, pH 7.5. The fractions containing the desired peptides are pooled and lyophilized. The 3- and 5-nitrated peptides are separated from each other and further purified by reverse phase HPLC using the identical purification scheme described in Example 1. EXAMPLE 6

In Vitro Assays Of Anticoagulant Activity

This example illustrates the enhanced inhibitory activity of the peptides of this invention on activated partial thromboplastin times (APTT) , as compared to control peptides N-acetyl-hirudin₅₃.₆₄ and N- acetyl-Cys₆₃hirudin„._β4. Anticoagulant activity was determined by assaying APTT of pooled, normal human plasma (George King Biomedical, Inc., Overland Park, Kansas) (diluted 4:1, v/v, plasma:water) with a Coag-A- Mate 2001 instrument (General Diagnostics, Inc. , Morris Plains, New Jersey) . Specifically, diluted plasma was mixed with varying amounts of either N-acetyl-TNB- Cys₆₃hirudin„_₆, N-acetyl-(diiodoTyr)₆₃hirudin₅₃.₆₄, N- acetyl-SCMCys₆₃hirudin₅₃._β, N-acetyl-SCECys₆₃hirudin„._M, N- acetyl-hirudin₅₃._M or N-acetyl-Cys₆₃hirudin₅₃.₆ (0.2 -293.3 μg/ml final peptide concentration). The plasma and peptides were mixed to a final volume of 125 μl prior to each APTT determination. We began the APTT assay by adding 92 μl of a crude thromboplastin suspension (General Diagnostics) and 100 μl of 0.3 M calcium chloride reagent to each well of a Coag-A-Mate dish (General Diagnostics) per APTT determination, to a final volume of assay mixture per well of 317 μl. The calcium chloride was freshly prepared prior to each assay. Activation times were constant at 180 sec. The results of such an assay comparing the APTT of the various peptides is shown in Figure 1. Figure 1 demonstrates that both N-acetyl- hirudin„.₆₄ and N-acetyl-Cys₆₃hirudin₅₃._M are weak anticoagulants in comparison to the peptides of this invention. The s-carboxymethylation or S- carboxyethylation of the Cys_β3 residue of N-acetyl- Cys₆₃hirudin₅₃.₆₄ resulted in an approximately ten-fold increase in anticoagulant potency. Thionitrobenzoation of the cysteine residue of N-acetyl-Cys₆₃hirudin₅₃.₆₄ resulted in a 2- to 3-fold increase in anticoagulant activity. And diiodination of the tyrosine residue of N-acetyl-hirudin₅₃.₆₄ produced a peptide that exhibited 5- fold more anticoagulant activity than the peptide lacking the derivatized tyrosine residue, other peptides of this invention, all of which contain either a derivatized tyrosine or cysteine residue at the A, position, may be similarly employed in APTT assays. They all display similar increases in anticoagulant potency over corresponding peptides which lack the derivatized amino acid at the A, position.

EXAMPLE 7 Inhibition Of Platelet Aggregation By

N-Acetyl- (3.5-DiiodoTyr).,Hirudin„ ..

To perform the inhibition of platelet aggregation assay, we collected blood from healthy human volunteers via a 21 gauge butterfly cannula into a 1/10 final volume of 3.8% trisodium citrate. All donors had avoided the use of medication of any kind for at least 2 weeks prior to blood collection. Platelet-rich plasma was prepared by room temperature centrifugation of the citrated whole blood for 15 minutes at 100 x g in a Sorval rotor.

We analyzed the effect of N-acetyl- (diiodoTyr)₆₃hirudin₅₃._β4 on the inhibition of platelet aggregation caused by thrombin. Specifically, varying amounts of N-acetyl-(diiodoTyr)₆₃hirudin₅₃.₆₄ (0 - 3.3 μg/ml final concentration), contained in 0.05 ml water, were added to 0.4 ml of prewarmed (37°C) platelet-rich plasma. The peptide/platelet mixture was incubated for 1 minute at 37°C. We then added 0.05 ml of human α-thrombin (a gift of^* Dr. J. Fenton II; New York Department of Health) , to a final concentration of 0.4 U/ml total assay volume. These concentrations of α-thrombin are believed to equal the levels achieved in vivo and which allow platelet aggregation studies to be performed in plasma without a major interference of clot formation.

We monitored the extent of platelet aggre¬ gation turbidometrically for 4 minutes using a Biodata 4-Channel Platelet Aggregation Profiler (PAP-4; Biodata Corp., Hatboro, Pennsylvania). Platelet aggregation was terminated by the addition of ice-cold indomethacin added to a final concentration of 10 μM. The maximum platelet aggregation observed during the 4 minutes as plotted against the concentration N-acetyl- (diiodoTyr)₆₃hirudin₅₃_₆₄ present in the assay mixture.

The data is shown below:

[N-acetyl-(diiodoTyr)₆₃ hirudin.,...1 fug/ml)

0 1.1

2.2 3.3

This data shows that N-acetyl-(diiodoTyr)₆₃- hirudin₅₃^, blocked thrombin-induced platelet aggregation in vitro at low concentrations in a dose-dependent manner with an IC₅₀ of approximately 2.4 μg/ml (the concentration of peptide required to reduce platelet aggregation to 50% of maximum) . N-acetyl- (diiodoTyr)₆₃hirudin₅₃__M was approximately 15 times as potent as hirudin₅₃.₆₄ in inhibiting platelet aggregation (data not shown) .

Compositions according to this invention which comprise other peptides described herein which similarly inhibit platelet aggregation. And, those compositions which comprise peptides containing a derivatized cysteine or tyrosine at the A, position exhibit significantly greater inhibitory activity than corresponding peptides which lack a derivatized amino acid at that position.

EXAMPLE 8 Inhibition Of Platelet Release Reactions By

N-Acetyl- (DiiodoTyr)_^Hirudin., „

The effects of N-acetyl-(diiodoTyr)₆₃hirudin₅₃.₆₄ on thrombin-induced platelet secretion may be analyzed by assaying inhibition of serotonin release and throm- boxane A₂ generation. The serotonin release assay is performed as follows. Approximately 20 ml of platelet- rich plasma, prepared as described in Example 7 , is loaded with ^uC-serotonin by incubating the plasma with 27 nCi/ml of 5-[2-^uC]serotonin binoxalate (60 mCi/mmole; DuPont-NewEngland Nuclear, Boston, Massachusetts) at 37°C for 30 minutes. Under these conditions, platelets incorporate >90% of the added serotonin, resulting in a specific activity of approx¬ imately 10,000 counts/minute/ml of platelet-rich plasma.

Platelet-rich plasma containing ^uC-serotonin loaded platelets (0.4 ml) is mixed in an aggregometer with varying concentrations (0 - 11 μg/ml total assay volume) of N-acetyl-(diiodoTyr)„hirudin₅₃._M contained in 0.05 ml saline for 1 minute at 37°C. Human α-thrombin (0.05 ml) is then added to a final concentration of either 0.25 or 0.5 U/ml of the total assay volume and the mixture is incubated at 37°C for 4 more minutes. The thrombin-induced serotonin release reaction is stopped and reuptake by the platelets is halted by the addition of a 1/lOth volume of an ice-cold cocktail containing 3.3% EDTA, 10 mM theophylline, 1 μg/ml prostaglandin E,, and 500 μM imipramine (hereinafter "ETPI") . The first three components are commonly used to prevent the platelet release reaction [J. A. Jakubowski and N. G. Ardlie, "Further Observations on the Effects of Dietary Fatty Acid Composition on Platelet Reactivity and Blood

Coagulation in Man and the Influence of Methodology on Findings", Atherosclerosis. 41, pp. 285-94 (1982)]. Imipra ine is a serotonin receptor agonist which prevents reuptake during sample handling. EPTI inhibits serotonin uptake and release by >95%. Following the addition of EPTI to the platelet samples, the platelets are removed by centrifugation at 12,000 x g for 2 minutes in a Sorval rotor. Serotonin release is assayed by measuring ^UC- radioactivity in the supernatant using liquid scintillation counting (Tri-Carb 1500; Packard Instruments). N-acetyl-(diiodoTyr)₆₃hirudin₅₃.₆₄ inhibits serotonin release in a dose-dependent manner, similar to that observed for inhibition of platelet aggregation.

For assaying inhibition of thromboxane A₂ generation, the following procedures are employed. Platelets contained in platelet-rich plasma are stimulated with thrombin in the presence of increasing concentrations of N-acetyl-(diiodoTyr)₆₃hirudin₅₃._M

(0 - 11 μg/ml). Peptide, dissolved in 0.5 ml saline, is added to 0.4 ml of platelet-rich plasma and the mixture is incubated for 1 minute at 37°C. Thrombin, contained in 0.05 ml saline, is then added to a final concentration of either 0.5 or 0.25 U/ml. The mixture is then incubated for 4 minutes at 37°C. Platelet thromboxane A₂ generation is quenched by the addition of ice-cold indomethacin to a final concentration of 10 μM, followed by centrifugation at 12,000 x g for 2 minutes. Thromboxane A₂ released into the supernatant is assayed by a radioimmunoassay that detects thromboxane B₂, a stable hydrolytic product and indicator of thromboxane A₂ [J. A. Jakubowski et al., "Cumulative Antiplatelet Effect of Low-Dose Enteric Coated Aspirin", Br. J. Haematol.. 60, pp. 635-42 (1985)].

N-acetyl-(diiodoTyr)₆₃hirudin₅₃.₆ inhibits thrombin-induced thromboxane A₂ generation in platelets in a dose-dependent manner, similar to that previously observed for inhibition of platelet aggregation.

Compositions -ccording to this invention which comprise other peptides similarly inhibit platelet release reactions. Those compositions which comprise peptides containing a derivatized cysteine or tyrosine at the A, position exhibit a significantly greater inhibitory activity than corresponding peptides which lack a derivatized amino acid at that position.

EXAMPLE 9 Activity Of N-Acetyl-(DiiodoTyr₆₃)Hirudin₅₃.₆₄ On Heparin-Induced Thrombocytopenic Blood

The efficacy of N-acetyl-(diiodoTyr)₆₃- hirudin₅₃._S4 in the treatment of patients suffering from heparin-induced thrombocytopenia is illustrated by various in vitro assays.

The platelet-rich plasma used in these assays is obtained from patients after cessation of heparin therapy and recovery from heparin-induced thrombocytopenia. Platelet-rich plasma, obtained from^" various patients and prepared as in Example 7, is incubated with varying concentrations of porcine lung sodium heparin (0.05 - 0.5 U/ml; Elkins-Sinn, Cherry Hill, New Jersey) or N-acetyl-(diiodoTyr^*)„hirudin₅₃._M (0.8 - 55 μg/ml). These concentration ranges for both heparin and N-acetyl-(diiodoTyr)₆₃hirudin₅₃.₆₄ are sufficient to increase APTT up to 200% over control plasma. Platelet aggregation is monitored turbido- metrically, as in Example 7. Heparin induces aggregation of platelets in the plasma of patients who have fully recovered from heparin-induced thrombocytopenia. N-acetyl-(diiodoTyr)₆₃hirudin₅₃.₆ does not induce platelet aggregation in similar plasma. The extent of thromboxane A₂ generation from similar platelets incubated with either heparin or N- acetyl-(diiodoTyr)₆₃hirudin_!3-64 may also be examined. Platelet-rich plasma from patients who have recovered from heparin-induced thrombocytopenia is incubated with either heparin or N-acetyl-(diiodoTyr)„hirudin₅₃._M

(1.7 - 55 μg/ml). Thromboxane A₂ secretion is stopped by the addition of indomethacin, followed by centrifugation and determined by assaying for throm¬ boxane B₂, as in Example 8. Heparin causes release of thromboxane A₂ from the platelets of patients with heparin-induced thrombocytopenia, while N-acetyl- (diiodoiyr)₆₃hirudin₅₃._β does not.

Therefore, the doses of heparin required to achieve anticoagulant effects in patients with heparin- induced thrombocytopenia lead to platelet activation and, thus, an increased risk of thrombosis. In sharp contrast, the compositions of the present invention which comprise N-acetyl-(diiodoTyr)₆₃hirudin„_₆₄ anticoagulate plasma without causing platelet activation in patients afflicted with this autoimmune disorder.

Compositions according to this invention which comprise other peptides described herein are similarly effective in increasing APTT, without causing platelet activation in patients who are suffering or who have suffered form heparin-induced thrombocyto¬ penia. Therefore, in these patients, the compositions of the present invention constitute a safe and effective alternative to heparin as anticoagulant agents and agents which inhibit platelet aggregation.

EXAMPLE 10

Anti-Metastatic Activity Of N-Acetyl- (DiiodoTyr ).,Hirudin .,

The anti-metastatic activity of the peptides of this invention, preferably, N-acetyl-(diiodoTyr)₆₃- hirudin₅₃.₆₄, is assayed using sarcoma T241 cells [L. A. Liotta et al.. Nature. 284, pp. 67-68 (1980)} and syngeneic C57BL/6 Mice (Jackson Laboratory, Bar Harbor, ME) . The mice are injected either intravenously or subcutaneously with 0 - 250 μg/kg of N-acetyl-(diiodoTyr)_β3hirudin₅₃.₆, as prepared according to Example 1, followed by intravenous injection of 10⁴ - 10⁶ T241 tumor cells. After 15 days, the animal is terminated and lung tumor colonies are quantitated. Anti-metastic activity of the peptide is measured as percent reduction in tumor colonies compared to a placebo-treated control.

EXAMPLE 11

Use Of N-Acetyl-(DiiodoTyr)₆₃ Hirudin.,... In Thrombus Imaging

The peptides of this invention, such as N- acetyl-(diiodoTyr)„hirudin₅₃__β4, may be modified by covalent attachment of ^,WI, ^,25I- or "'In-containing chemical groups. Specifically, N-acetyl-(diiodoTyr)₆₃- hirudin₅₃.₆ (as prepared in Example 1) is reacted with ^,23I-Bolton-Hunter Reagent (New England Nuclear, Boston, MA.) in 0.1 M sodium borate, pH 9.0. The I-labelled peptide (with a specific radioactivity of >5 Ci/μg) is then desalted on a column of Biogel P2 which is equilibrated in a phosphate-buffered saline. The ^,2I- labelled peptide is then tested in APTT assays to monitor any loss in antithrombin activity. Ex vivo imaging of experimental thrombi is performed essentially as described by T. M. Palabrica et al., "Thrombus Imaging in a Primate Model with Antibodies Specific For an External Membrane Protein of Activated Platelets", Proc. Natl. Acad. Sci. USA. 86, pp. 1036-40 (1989) . Specifically, imaging is performed in baboons with an external Ticoflex shunt between the femoral artery and femoral vein. An experimental thrombus is formed by placement of a segment of preclotted Dacron graft in the shunt. '"i-labelled N- acetyl-(diiodoTyr)₆₃hirudin_S3_₆₄ is injected in the venous part of the Ticoflex shunt. Serial anterior images are then obtained for 0.5 - 1 hr using an Ohio Nuclear Series 100 Gamma Camera with a PDP-11/34 computer. The kinetics of ¹²³l-peptide uptake by the graft and blood pool are derived from the radionuclide images thus obtained.

The same technique may be used to obtain ex vivo images of a deep venous thrombus obtained by stasis in the femoral vein of baboons. Because N- acetyl-(diiodoTyr)₆₃hirudin₅₃__M, as well as the c-her peptides of this invention, binds to thrombin with high specificity, the use of radiolabelled peptides of this invention allows precise ex vivo images of experimental thrombi. Also, the small size of the peptides of this invention, in contrast to native hirudin or antibodies to thrombin, provides the potential that the radio- labelled-peptide will yield images of platelet-bound thrombin and meizothrombin, as well as thrombin con¬ tained in the fibrin clot. EXAMPLE 12

Inhibition Of Endothelial Cell Activation By N-Acetyl-rDiiodoTyr)_^Hirudin.. ,.

The ability of N-acetyl-(diiodoTyr)₆₃hirudin_53-6 to inhibit thrombin-induced synthesis of platelet activating factor (PAF) is assayed using cultured human umbilical vein endothelial cells (HUVEC) . HUVECs are extracted from human umbilical cords by collagenase digestion according to established procedures [M. A. Gimbrone, Jr. , "Culture of Vascular

Endothelium", Prog. Hemost. Thromb.. 3, pp. 1-28 (1976)]. HUVECs are grown to confluence in a 96-well microtiter plate in the presence of [³H]-acetate, ells cultured in this manner produce [³H]-acetyl-PAF, which can be quantitated by extraction of HUVEC membrane phospholipids.

N-acetyl-(diiodoTyr)_β3hirudin₅₃._β4 (0 - 20 μg/ml) is added to the [³H]-acetate loaded HUVECs l minute prior to the addition of thrombin (final concentration of 1 U/ml) . The cells are incubated for 5 minutes and the supernatant is then removed. Medium containing 0.1% gelatin, 50 mM acetic acid in methanol (2:1, v/v) is then added to the HUVECs. PAF is extracted and quantitated using standard techniques [T. M. Mclntyre et al., "Cultured Endothelial Cells Synthesize Both

Platelet-Activating Factor and Prostacyclin in Response to Histamine, Bradykinin and Adenosine Triphosphate", J. Clin. Invest.. 76, pp. 271-80 (1985)]. N-acetyl- (diiodoTyr)₆₃hirudin„._β4, as well as the other peptides of this invention, significantly inhibits PAF synthesis by cultured HUVECs.

The effect of N-acetyl-(diiodoTyr)₆₃hirudin₅₃.₆₄ on thrombin-induced polymorp.ionuclear leukocyte (PMN) adhesion to HUVECs may be observed as follows. HUVECs are grown in MEM containing 1% fetal calf serum to confluency in 24-well cluster plates. The medium is removed and the cells are washed two times with fresh, serum--ree medium and incubated in the same medium for 10 - 30 minutes at 37°C to remove serum products. One ml of PMNs (2.5 x lO^'/ial) , pre-equilibrated at 37°C, is then added to each well. The PMNs are allowed to settle onto the HUVEC monolayer for 2 minutes. N- acetyl-(diiodoTyr)₆₃hirudin₅₃__M (5 μg/ml) or saline is then added to each well, immediately followed by the addition of thrombin (0.1 or 1.0 U/ml). The cells are incubated for 5 minutes at 37°C, washed twice and then examined by phase- contrast microscopy. Adherent PMNs are counted directly. PMN adherence is significantly decreased in samples containing N-acetyl- (diiodoTyr)₆₃hirudin₅₃._β4. The other peptides of this invention exhibit a similar effect on PMN adherence.

While we have hereinbefore presented a number of embodiments of this invention, it is apparent that our basic construction can be altered to provide other embodiments which utilize the processes and products of this invention. Therefore, it will be appreciated that the scope of this invention is to be defined by the claims appended hereto rather than the specific embodiments which have been presented hereinbefore by way of example.

Claims

CLAIMSI Claim:

1. A peptide derivative displaying anticoagulant activity consisting of the formula:

Λ—A|—A₂—A₃—A₄—A₅—Ag—A₇—Aj—Aq—A₎₀—x wherein X is a hydrogen, one or two alkyl groups of from l to 6 carbon atoms, one or two acyl groups of from 2 to 10 carbon atoms, carbobenzyloxy or t-butyloxy carbonyl,- A, is a bond or a peptide containing from l to

II residues of any amino acid; A₂ is Phe, SubPhe, β-(2- and 3-thienyl)alanine, β-(2- and 3-furanyl)alanine, β- (2-, 3- and 4-pyridyl)alanine, β-(benzothienyl-2- and 3-yl) alanine, β-(l- and 2-naphthyl)alanine, Tyr or Trp; A₃ is Glu or Asp; A₄ is any amino acid; A, is lie, Val, Leu, Nle or Phe; Ae is Pro, Hyp, 3,4-dehydroPro, thiazolidine-4-carboxylate, Sar, NMePgl or D-Ala; A₇ is any amino acid; A. is any amino acid; A, is a derivatized amino acid selected from the group consisting of O-sulfate esters of tyrosine, O-phosphate esters of tyrosine, O-carboxylate esters of tyrosine, 3-sulfonyl tyrosine, 5-sulfonyl tyrosine, 3-phosphonyl tyrosine, 5-phosphonyl tyrosine, 3-carbonyl tyrosine, 5-carbonyl tyrosine, 4-methylsulfonyl tyrosine, 4- methylphosphonyl tyrosine, 4-phenylacetic acid, 3,5- diiodotyrosine, 3-nitrotyrosine, 5-nitrotyrosine, S- alkylated cysteine, s-alkylated homocysteine, thionitrobenzoic acid cysteine, and dipeptides consisting of said derivatized amino acid and any amino acid; A₁₀ is a bond or a peptide containing from 1 to 5 residues of any amino acid; and Y is a carboxyl terminal residue selected from OH, C,-C₆ alkoxy, amino, mono- or di-(C,-C₄) alkyl substituted amino or benzylamino; with the proviso that said peptide derivative does not consist of a sequence of amino acids wherein: X is H or an amino protecting group; A, is a bond or a peptide consisting of from 1 to 11 amino acid residues of any C-terminal portion of the amino acid sequence:

Thr-Pro-B-Pro-Glx-Ser-His-Asn-Asx-Gly-Asp, wherein B is Asn or Lys; A₂ is Phe; A₃ is Glu; A₄ is Glu; A, is lie; A₇ is Glu; A, is Glu;

A, is an o-sulfate ester of tyrosine, an o-phosphate ester of tyrosine, an O-carboxylate ester of tyrosine, 3-sulfonyl tyrosine, 5-sulfonyl tyrosine, 3-phosphonyl tyrosine, 5-phosphonyl tyrosine, 3-carbonyl tyrosine, 5-carbonyl tyrosine, 4-methylsulfonyl tyrosine or 4- methylphosphonyl tyrosine; A₁₀ is a bond, Leu or Leu-Gin; and Y is OH.

2. The peptide derivative according to claim 1, wherein A, is selected from the group consisting of 3,5-diiodotyrosine, 3-nitrotyrosine, 5- nitrotyrosine, S-carboxymethylcysteine, S- carboxyethylcysteine, thionitrobenzoic acid cysteine and dipeptides consisting of said amino acid and any amino acid.

3. The peptide derivative according to claim 2, wherein said peptide derivative is selected from the group consisting of N-Ac-(diiodoTyr)₆₃- hirudin₅₃.₆, N-Ac-(3-nitroTyr)„hirudin₅₃_₆₄, N-Ac-(5-nitro- Tyr)₆₃hirudin₅₃._M, N-Ac-SCMCys₆₃hirudin₅₃._M , N-Ac- SCECys_β3hirudin₅₃.₆₄ , and N-Ac-TNBCys₆₃hirudin₅₃._M.

4. A pharmaceutically acceptable compo¬ sition for increasing blood clotting time in a patient or in extracorporeal blood which comprises a pharmaceutically effective amount of at least one peptide derivative according to any one of claims 1 to 3 and a pharmaceutically acceptable carrier.

5. A method for increasing blood clotting time in a patient or in extracorporeal blood comprising the step of treating said patient or said extra¬ corporeal blood in a pharmaceutically acceptable manner with a composition according to claim 4.

6. A method for preventing or treating vascular disease in a patient, comprising the step of treating said patient in a pharmaceutically acceptable manner with a composition according to claim 4.

7. A pharmaceutically acceptable compo¬ sition for inhibiting the growth of metastatic tumors, wherein said composition comprises a pharmaceutically effective amount of at least one peptide derivative according to any one of claims 1 to 3 and a pharma¬ ceutically acceptable carrier.

8. A method for inhibiting the growth of metastatic tumors in a patient, wherein said method comprises the step of treating said patient in a pharmaceutically acceptable manner with a composition according to claim 7.

9. The method according to claim 8, wherein said metastatic tumor is selected from the group consisting of carcinoma of the brain, carcinoma of the lung, carcinoma of the liver, osteocarcinoma and neoplastic cell carcinoma.

10. The peptide derivative according to claim 1, wherein said peptide derivative is labeled with a radioisotope selected from the group consisting of '²³I, ^,25I and '"In.

11. A pharmaceutically acceptable composition for ex vivo imaging of a fibrin or platelet thrombus in a patient compr-sing a peptide derivative according to claim 10.

12. A method for ex vivo imaging _ f a fibrin or platelet thrombus in a patient comprising the steps of:

(a) administering to said patient a composition according to claim 11; and

(b) using detecting means to observe said composition.

13. A composition for coating the surface of an invasive device to be inserted into a patient, wherein said composition comprises at least one peptide derivative according to any one of claims 1 to 3 and a pharmaceutically acceptable compound for adhering said peptide derivative to said surface.

14. A method for coating the surface of an invasive device to be inserted into a patient, said method comprising the step of contacting said surface with a composition according to claim 13.

15. A pharmaceutically acceptable composition for inhibiting thrombin-induced endothelial cell activation in a patient, said composition comprising a pharmaceutically acceptable carrier an_d a pharmaceutically effective amount of at least one peptide derivative selected from the group consisting of: a) a peptide derivative according to any one of claims 1 to 3; and b) other peptide derivatives of the formula:

X—Aj—A₂—A₃—A—A₅—Aj—A₇—A,—B₉—A|„— wherein X, A,, A₂, A₃, A₄, A₅, Aj, A₇, A., A₁₀ and Y are as defined in claim 1 and B„ is a lipophilic amino acid selected from the group consisting of Tyr, Trp, Phe,

Leu, Nle, lie, Val, Cha, Pro or is a dipeptide consisting of said lipophilic amino acid and any amino acid; with the proviso that said peptide derivative does not consist of a sequence of amino acids wherein:

X is H or an amino protecting group;

A, is a bond or from 1 to 11 amino acid residues consisting of any C-terminal portion of the amino acid sequence:

Thr-Pro-B-Pro-Glx-Ser-His-Asn-Asx-Gly-Asp, wherein B is Asn or Lys ; A₂ is Phe; A₃ is Glu; A is Glu; A₅ is lie; A₇ is Glu;

A, is Glu;

B, is Tyr;

A₁₀ is a bond. Leu or Leu-Gin; and Y is OH.

16. A method for inhibiting thrombin-induced endothelial cell activation in a patient, said method comprising the step of treating said patient with a composition according to claim 15.

17. A pharmaceutically acceptable compo¬ sition for treating thrombin-induced inflammation in a patient, said composition comprising a pharmaceutically effective amount of a peptide derivative according to any one of claims 1 to 3 and a pharmaceutically acceptable carrier.

18. A method for treating thrombin-induced inflammation in a patient, said method comprising the step of administering to said patient a composition according to claim 17.

19. The method according to claim 18, wherein said thrombin-induced inflammation is caused by a disease selected from the group consisting of adult respiratory distress syndrome, septic shock, septicemia and reperfusion damage.

20. A pharmaceutically acceptable composi¬ tion for inhibiting platelet aggregation in extracorporeal blood or in a patient, sa_d composition comprising a pharmaceutically acceptable carrier and a pharmaceutically effective amount of at least one peptide derivative selected from the group consisting of:

(a) a peptide derivative according to any one of claims 1 to 3; and

(b) other peptide derivatives of the formula: wherein X, A,, A₂, A₃, A₄, A₅, k_ , A₇, A,, A₁₀ and Y are as defined in claim 1 and B, is a lipophilic amino acid selected from the group consisting of Tyr, Trp, Phe,

Leu, Nle, lie, Val, Cha, Pro or is a dipeptide consisting of said lipophilic amino acid and any amino acid; with the proviso that said peptide derivative does not consist of a sequence of amino acids wherein:

X is H or an amino protecting group;

A, is a bond or from 1 to 11 amino acid residues consisting of any C-terminal portion of the amino acid sequence:

Thr-Pro-B-Pro-Glx-Ser-His-Asn-Asx-Gly-Asp, wherein B is Asn or Lys ; A₂ is Phe; A₃ is Glu; A₄ is Glu; A₅ is lie; A_s is Pro; A₇ is Glu;

A, is Glu;

B, is Tyr;

A₁₀ is a bond. Leu or Leu-Gin; and Y is OH.

21. The composition according to claim 20, wherein said composition further comprises a compound selected from the group consisting of metal chelaters, prostaglandins , small peptide platelet inhibitors, inhibitors of platelet surface components, antibodies against platelet surface components, cyclooxygenase inhibitors, small non-peptide platelet inhibitors, hematopoetic factors, analogs thereof and combinations thereof.

22. The composition according to claim 21, wherein said compound is selected from the group consisting of stable analogs of prostacyclin, pro- staglandin El, analogs of prostaglandin El, citrate- phosphate dextrose, theophylline, aspirin, ticlopidine, dipyridamole, sulphinpyrazone, monoclonal antibodies against glycoprotein lib/Ilia, natural inhibitors of glycoprotein Ilb/IIIa, monoclonal antibodies against glycoprotein lb, natural inhibitors of glycoprotein lb, erythropoietin, arg-gly-asp-containing peptides, and derivatives of arg-gly-asp-containing peptides.

23. The composition according to claim 20, wherein the pharmaceutically effective amount of said peptide derivative is between about 0.1 μg/600 ml of extracorporeal blood and about 100 mg/600 ml of extracorporeal blood.

24. The composition according to claim 23, wherein the pharmaceutically effective amount of said peptide derivative is between about 1 μg/600 ml of extracorporeal blood and about 50 μg/600 ml of extracorporeal blood.

25. The composition according to claim 20, wherein said pharmaceutically effective amount of said peptide derivative is between about 0.1 μg/kg body weight of said patient and about 100 mg/kg body weight of said patient.

26. The composition according to claim 25, wherein said pharmaceutically effective amount of said peptide derivative is between about 1 μg/kg body weight of said treated patient and about 50 μg/kg body weight of said treated patient.

27. A method for inhibiting platelet aggregation in extracorporeal blood or in a patient, said method comprising the step of treating said extracorporeal blood or said patient with a composition according to claim 20.

28. The method according to claim 27, wherein at the time of treatment, said patient is suffering from or has suffered from heparin-induced thrombocytopenia.

29. A pharmaceutically acceptable combination for increasing blood clotting time in a patient or in extracorporeal blood, wherein said combination comprises a pharmaceutically acceptable carrier; a compound selected from the group consisting of heparin and low molecular weight heparin, wherein the dosage of said heparin or low molecular weight heparin is less than about 5,000 units; and a pharmaceutically effective amount of at least one peptide derivative selected from the group consisting of: a) a peptide derivative according to any one of claims 1 to 3; and b) other peptide derivatives of the formula:

Λ—A,—A₂—A₃—A₄—A₅— A_ —A₇—A_t— Ωq—A,₀— wherein X, A,, A₂, A₃, A₄, A₅, A_*, A₇, A,, A₁₀ and Y are as defined in claim 1 and B, is a lipophilic amino acid selected from the group consisting of Tyr, Trp, Phe, Leu, Nle, lie, Val, Cha, Pro or is a dipeptide consisting of said lipophilic amino acid and any amino acid; with the proviso that said peptide does not consist of a sequence of amino acids wherein: X is H or an amino protecting group; A, is a bond or from 1 to 11 amino acid residues consisting of any C-terminal portion of the amino aci_d sequence:

Thr-Pro-B-Pro-Glx-Ser-His-Asn-Asx-Gly-Asp, wherein B is Asn or Lys; A₂ is Phe; A₃ is Glu; A₄ is Glu; A₅ is lie; A_* is Pro; A₇ is Glu;

A, is Glu;

B, is Tyr;

A,₀ is a bond, Leu or Leu-Gin; and Y is OH.

30. A method of increasing blood clotting time in a patient or in extracorporeal blood comprising the step of treating said patient or extracorporeal blood with a combination according to claim 29.

31. The method according to any one of claims 5, 6, 8, 9, 12, 14, 16, 18, 19, 27, 28 or 30, wherein said patient is a human.