Effects of Melagatran, a New Low-molecular-weight Thrombin Inhibitor, on Thrombin and Fibrinolytic Enzymes

Summary

Melagatran, a new, competitive and rapid inhibitor of thrombin with a molecular mass of 429 Da is described. Melagatran is well tolerated when administered in very high doses, and the oral bioavailability in the dog is relatively high. The aim of the study was to determine, in the preclinical setting, the degree of selectivity against the fibrinolytic system required for entering the clinical development phase. Melagatran was compared with two structurally similar thrombin inhibitors, inogatran and H 317/86. The potent inhibition of thrombin by melagatran was demonstrated by a low inhibition constant (Ki) for thrombin (0.002 μmol/l) and prolongation of clotting time to twice the control value in coagulation assays at low concentrations (0.010, 0.59 and 2.2 μmol/l for thrombin time, activated partial thromboplastin time and prothrombin time, respectively). Furthermore, thrombin-induced platelet aggregation was inhibited at the same concentration (IC_50-value 0.002 μmol/l) as the Ki-value for thrombin. In two assays of global fibrinolysis, inhibition was observed at a concentration of 1.1 μmol/l in a euglobulin plasma fraction model, while no inhibition was observed at a concentration of ≤10 μmol/l in a plasma model. In an in vivo model of endogenous fibrinolysis in the rat, inhibition of fibrinolysis was observed at ≥1.0 μmol/l. In all assays, except the Ki-ratio determinations, the compounds could be graded with regard to selectivity against the fibrinolytic system: inogatran > melagatran > H 317/86. For melagatran, inhibition of fibrinolysis was not observed at concentrations below the upper limit of the proposed therapeutic plasma concentration interval (<0.5 μmol/l). Thus, melagatran seems to have a sufficient selectivity against the fibrinolytic system, while H 317/86 was considered to be insufficient for clinical development.

• References

• 1 Eriksson BI, Ekman S, Kälebo P, Zachrisson B, Bach D, Close P. Preven tion of deep-vein thrombosis after total hip replacement: Direct thrombin inhibition with recombinant hirudin, CGP 39393.. Lancet 1996; 347: 635-9.
• 2 The global use of strategies to open occluded coronary arteries (GUSTO) IIb investigators.. A comparison of recombinant hirudin with heparin for the treatment of acute coronary syndromes.. N Engl J Med 1996; 335: 775-82.
• 3 Antman EM. Hirudin in acute myocardial infarction. Thrombolysis and thrombin Inhibition in myocardial infarction (TIMI) 9B trial.. Circulation 1996; 94: 911-21.
• 4 Bush LR. Argatroban, a selective, potent thrombin inhibitor.. Cardiovasc Drug Rev 1991; 9: 247-63.
• 5 Kimball SD. Challenges in the development of orally bioavailable thrombin active site inhibitors.. Blood Coagul Fibrinol 1995; 6: 511-9.
• 6 Antonsson KT, Bylund R, Gustafsson ND, Nilsson IO. Trypsin-like protease-inhibiting peptide derivatives, their synthesis and therapeutic use.. Patent application WO9429336-A1. CA122-285553/23.
• 7 Teger-Nilsson AC, Bylund R. Preparation of peptide derivatives as thrombin inhibitors.. Patent application WO9311152-A1. CA121-083990/07.
• 8 Kettner C, Mersinger L, Knabb R. The selective inhibition of thrombin by peptides of boroarginine.. J Biol Chem 1990; 265: 18289-97.
• 9 Åstedt B. Clinical pharmacology of tranexamic acid.. Scand J Gastroentol Suppl 1987; 137: 22-5.
• 10 Kluft C. Occurrence of C1 inactivator and other proteinase inhibitors in euglobulin fractions and their influence on fibrinolytic activity.. Haemost 1976; 5: 136-46.
• 11 Tamao Y, Yamamoto T, Kikumoto R, Hara H, Itoh J, Hirata T, Mineo K, Okamoto S. Effect of a selective thrombin inhibitor MCI-9038 on fibrinolysis in vitro and in vivo.. Thromb Haemost 1986; 56: 28-34.
• 12 Lenfors S, Gustafsson D. New model for in vivo studies of pharmacological interventions with endogenous fibrinolysis: Effects of thrombin inhibitors.. Semin Thromb Haemost 1996; 22: 335-42.
• 13 Nilsson T, Sjöling-Ericksson Å, Deinum J. The mechanism of binding of low-molecular-weight active site inhibitors to human α-thrombin.. J Enzym Inhib 1997; accepted.
• 14 Bajusz S, Szell E, Bagdy D, Barabas E, Horvath G, Dioszegi M, Fittler Z, Szabo G, Juhasz A, Tomori E, Szilagyi G. Highly active and selective anticoagulants: D-Phe-Pro-Arg-H, a free tripeptide aldehyde prone to spontaneous inactivation, and its stable N-methyl derivative, D-MePhe-Pro-Arg-H.. J Medicinal Chem 1990; 33: 1729-35.
• 15 Cousins GR, Friedrichs GS, Sudo Y, Rebello SS, Rote WE, Vlasuk GP, Nolan TG, Mendoza C, Lucchesi BR. Orally effective CVS-1123 prevents coronary artery thrombosis in the conscious dog.. Circulation 1996; 94: 1705-12.
• 16 Elg M, Gustafsson D, Deinum J. The importance of enzyme inhibition kinetics for thrombin inhibitors in a rat model of arterial thrombosis.. Thromb Haemost 1998; 78: 1286-92.
• 17 Kessels H, Willems G, Hemker C. Analysis of thrombin generation in plasma.. Comput Biol Med 1994; 24: 277-88.
• 18 Teger-Nilsson AC, Bylund R, Gustafsson D, Gyzander E, Eriksson U. In vitro effects of inogatran, a selective LMW thrombin Inhibitor.. Thromb Res 1998; 85: 133-45.
• 19 Bridey F, Dreyfus M, Parent F, Bros A, Fischer AM, Camez A, Simonneau G, Duroux P, Meyer D. Recombinant hirudin (HBW 023): Biological data of ten patients with severe venous thromboembolism.. Am J Hematol 1995; 49: 67-72.
• 20 Hauptmann J, Markwardt F. Pharmacologic aspects of the development of selective synthetic thrombin inhibitors as anticoagulants.. Semin Thromb Hemost 1992; 18: 200-17.
• 21 Hijikata-Okunomiya A, Okamoto S. A strategy for a rational approach to designing synthetic selective inhibitors.. Semin Thromb Hemost 1992; 18: 135-49.
• 22 Mattson C, Eriksson E, Nilsson S. Anticoagulant and antithrombotic effects of some protease inhibitors.. Folia Haematol (Leipzig) 1982; 109: S43-51.
• 23 Metha JL, Chen L, Mattsson C, Gustafsson D, Saldeen TGP. Melagatran, an oral active site inhibitor of thrombin, prevents or delays formation of electrically-induced occlusive thrombus in the canine coronary artery.. J Cardiovasc Pharmacol. accepted.
• 24 Pharmacokinetics of inogatran, a new low molecular weight thrombin inhibitor, in rats and dogs.. Eriksson UG, Renberg L, Vedin C, Strimfors M. Thromb Haemost 1995; 73: 1318 (Abstract 1605).
• 25 Bagdy D, Szabó G, Barabás É, Bajusz S. Inhibition by D-MePhe-Pro-ArgH (GYKI-14766) of thrombus growth in experimental models of thrombosis.. Thromb Haemost 1992; 68: 125-9.
• 26 Hussain MA, Knabb R, Aungst BJ, Kettner C. Anticoagulant activity of a peptide boronic acid thrombin inhibitor by various routes of administration.. Peptides 1991; 12: 1153-4.
• 27 Bajzar L, Manuel R, Nesheim ME. Purification and characterization of TAFI, a thrombin-activatable fibrinolysis inhibitor.. J Biol Chem 1995; 270: 14477-84.
• 28 Blombäck B, Carlsson K, Fatah K, Hessel B, Procyk R. Fibrin in human plasma: gel architectures governed by rate and nature of fibrinogen activation.. Thromb Res 1994; 75: 521-38.
• 29 Carr ME, Alving BM. Effect of fibrin structure on plasmin-mediated dissolution of plasma clots.. Blood Coagul Fibrinol 1995; 6: 567-73.
• 30 Mattsson C, Björkman JA, Ulvinge JC. Hirudin and melagatran, a reversible, low molecular weight thrombin inhibitor, as adjunctive agents to tissue type plasminogen activator in a canine model of coronary artery thrombolysis.. Fibrinol Proteol 1998; 11: 121-8.
• 31 Kopéc M, Latallo ZS, Stahl M. Wegrzynowicz. The effects of proteolytic enzymes on fibrin stabilizing factor.. Biochem Biophys Acta 1969; 181: 437-45.