ANTICOAGULANTS

1. ANTICOAGULANTS Jill Gregory Medicinal Chemistry Dr. Buynak 4.23.09

2. Overview • Review Blood basics • composition • how blood clots • Note Instances where blood clotting is bad • Discuss Anticoagulants • Heparin • Warfarin • New Drugs • F Xa inhibitors • thrombin inhibitors • Show example Clinical Trial

3. Blood Composition • connective tissue with cells suspended in plasma Plasma (55%) Cellular Elements (45%) water Ions / electrolytes (K+ Ca++) plasma proteins (Fibrinogen) transported substances erythrocytes (red blood cells) leukocytes (white blood cells) platelets

4. How blood clots • Damage to endothelium (vessels) • Platelet plug • Coagulation Factors from • plasma • platelets • and damaged cells interact and activate a cascade that leads to… • Activated Fibrin: fibers woven into a patch http://www.advanced-supplements.com/neprinol.html

5. TF VIIIa Va Coagulation Cascade Intrinsic pathway Extrinsic pathway XIIa XII VIIa XIa XI IXa IX X Xa Common pathway II (prothrombin) IIa (thrombin) XIII XIIIa • Each step requires: • Zymogen (precursor protein) • Activated Protease from step before • Cofactors like Ca++ Fibrinogen Fibrin Stabilized Fibrin

6. When would we not want clots to form?? • Clotting is good at sites of injury because it minimizes blood loss and prevents infectious agents from getting into our systems. • Clotting can be bad when occurs inappropriately in normal vessels [called thrombus] …clot can break free [called embolus] and lodge in heart, causing myocardial infarction, or in brain, causing stroke. • Thrombosis is caused by abnormalities in blood composition, vessel wall quality, and/or nature of the blood flow • Different types of thrombosis: • Venous [i.e. VTE = venous thromboembolism; DVT = Deep-vein thrombosis] • Arterial

7. When would we not want clots to form?? • Certain people are at a higher risk for thromboembolism: • Cardiovascular disease • Atrial fibrillation • Prosthetic device (i.e. replacement heart valve) • Post-surgery (i.e. hip/knee replacements) Virchow triad for the pathophysiology of thrombus formation. http://emedicine.medscape.com/article/959501-overview

8. Thromboembolism in the U.S. • “Annually, more individuals may die from DVT complications than from the combination of AIDS, breast cancer, and motor vehicle accidents combined” • 900,000 to 2,000,000 VTE cases per year in U.S. • Estimates of death rates per year vary from 50,000 to 300,000 • 700,000 Strokes per year • 15% of strokes are in people with Atrial Fibrillation • 1.2 mil Heart Attacks per year • Help prevent thromboembolism withthe anti-thrombotic drugs: Anticoagulants, Antiplatelets, Thrombolytics

9. Anticoagulants Inhibit clotting factor activation reactions in the blood TARGETED FACTOR Antithrombin (indirectly Xa and IIa) Antithrombin (indirectly Xa and IIa) Thrombin (IIa) Thrombin (IIa) Thrombin (IIa) Antithrombin Va, VIIIa Prothrombin (II), VII, IX, X Xa Xa Xa Xa Xa Xa Xa Xa Xa Thrombin (IIa) Thrombin (IIa) • CURRENT DRUGS • Unfractionated Heparin______________ • Low Molecular Weight Heparin________ • Lepirudin (DTI)____________________ • Bivalirudin (DTI) ___________________ • Argatroban(DTI)____________________ • Danaparoid_______________________ • Drotrecogin Alfa____________________ • Vitamin K antagonists (Warfarin)_______ • NEW/ in DEVELOPMENT DRUGS • Fondaparinux_____________________ • Idraparinux_______________________ • SSR 126517______________________ • Rivaroxaban______________________ • Apixaban_________________________ • LY517717________________________ • YM150__________________________ • DU-176b_________________________ • Betrixaban________________________ • Ximelagatran*_____________________ • Dabigatran etexilate________________ *taken off the market Italics are Oral Drugs

10. Aside: other Anti-thrombotic drug types • Anti-platelet agents include: • Aspirin (acetylsalicylic acid) • clopidogrel • dipyridamole • ticlopidine • glycoprotein IIb/IIIa inhibitors • Thrombolytic (/fibrinolytic) drugs include: • tissue plasminogen activator - t-PA - alteplase (Activase) • reteplase (Retavase) • tenecteplase (TNKase) • anistreplase (Eminase) • streptokinase (Kabikinase, Streptase) • urokinase (Abbokinase)

11. Heparin And other current Parenteral Anticoagulants

12. Natural anticoagulation mechanisms • Prostacyclin: • made by the endothelial cells and prevents platelets from collecting and secreting sticky substances • Antithrombin, a plasma protein • stimulated by Heparan sulfate proteoglycans from endothelial cells, inhibits coagulation factors of intrinsic and common pathways • Activated plasma zymogen Protein C with cofactor protein S • degrades certain cofactors and therefore greatly inhibits activation of prothrombin and factor X • Tissue Factor Pathway Inhibitor (TFPI) • a lipoprotein that can inhibit tissue factor bound factor Va or VIIa http://en.wikipedia.org/wiki/Coagulation

13. Basics of Heparin • Derived from mucosal tissues of slaughtered meat animals. Also exists in your body and is secreted form mast cells at the site of tissue injury • Increases Antithrombin activity. (Indirect inhibition method of IIa & Xa) • Usually intravenous adminstration • Glycosaminoglycan chains attached to a protein core = proteoglycans (750 kiloDaltons to 1000 kiloDaltons) • Low molecular weight heparin: different composition; more predictable; subcutaneous injection twice daily; use preferred over unfractionated heparin

14. Action of Heparin and similar drugs Dark shaded region is a high-affinity pentasaccharide sequence 2: Unfractionated Heparin 3: Low-molecular weight Heparin 4: Fondaparinux (discussed later) Image from Sterling T. Bennett’s chapter on Monitoring Anticoagulant Therapy

15. Crystal structure of the antithrombin-pentasaccharide complex Essentials of Glycobiology Chapter 35, Figure 2 Second Edition

16. More about Heparin • Fast action intravenously or by injection (not absorbed through the stomach or intestinal wall) • peak after injection 2 - 4 hr • Complex metabolism (long chains broken up) • half life 1 - 5 hr; cleared by the reticuloendothelial system and some excreted in urine. • A few Drug-drug interactions • Toxicities: Bleeding & Heparin-Induced Thrombocytopenia A D M E

17. Other Parenteral Anticoagulants • Lepirudin (DTI) derived from hirudin from leech salivary glands • Bivalirudin (DTI) approved for use during heparin-induced thrombocytopenia (HIT) & percutaneous coronary interventions • Argatroban (DTI) can be used in patients with risk of (HIT) • Danaparoid no longer available in the U.S. • Drotrecogin Alfa used in patients with sepsis; recombinant form of activated protein C that inhibits f Va and f VIIIa

18. Dicoumarol Phenprocoumon Warfarin Sodium Vitamin K antagonists:Parent Molecules: 4-Hydroxycoumarin & indan-1,3-dione Oral Anticoagulants Acenocoumarol Anisindione

19. Vitamin K antagonists Mechanism of Action • Some clotting factors need a carboxyl group added to their carboxyl-terminal glutamates after synthesis in the liver in order to be able to bind Ca++ during coagulation activation [these are called Vitamin K dependent clotting factors] • This γ-carboxylation reaction requires reduced Vitamin K, which leaves the reaction as a Vitamin K epoxide. • Vitamin K epoxide is then converted back to its reduced form via the enzyme vitamin K epoxidereductase and NADH • The Vitamin K antagonists inhibit the action of the reductase enzyme http://www.vet.uga.edu/VPP/clerk/Harrell/index.php http://tollefsen.wustl.edu/projects/coagulation/coagulation.html

20. Vitamin K antagonists Intrinsic pathway Extrinsic pathway XIIa XII TF VIIa XIa XI IXa IX VIIIa Va X Xa Common pathway II (prothrombin) IIa (thrombin) XIII XIIIa Fibrinogen Fibrin Stabilized Fibrin Effect on Coagulation • Vitamin K dependent clotting factors:Factors II, VII, IX, and X

21. Vitamin K antagonists History of Warfarin • 1930s: cows hemorrhaging after eating spoiled sweet clover silage • 1939: bishydroxycoumarin (dicoumarol) identified • 1948: potent form as rodenticide • Called Warfarin (Wisconsin Alumni Research Foundation) Anticoagulant in humans? No, too toxic!? • 1951: Army inductee’s failed attempt at suicide with high dose of warfarin rodenticide • Clinical use for over 60 years

22. Vitamin K antagonists Warfarin • Adminstered orally, intravenously, or rectally • Bioavailabily nearly complete; absorption dampered by food • Peak concentration 2 - 8 hr • Binds to albumin 99% of time • Can cross placental barrier • Racemic mixture: S form by CYP2C9; R by CYP1A2, minor pathway CYP2C19, and minor pathway CYP3A4 • half-life: 25 - 60 hr; Excreted in urine and stool • Food-drug & drug-drug interactions: extensive!! • Toxicities: bleeding, fetal bone abnormalities A D M E

23. Vitamin K antagonists Problems with Warfarin • Food and drug interactions • Genetic variation in metabolism • narrow therapeutic window • slow onset of action dosage adjustments & freq. monitor with INR overlap with parenteral drugs

24. Newer Anticoagulants Targeting specific factors

25. Intrinsic pathway Extrinsic pathway XIIa XII TF VIIa XIa XI IXa IX VIIIa Va X Xa Common pathway II (prothrombin) IIa (thrombin) XIII XIIIa Fibrinogen Fibrin Stabilized Fibrin Factor Xa Inhibitors • Parenteral or Oral • Direct or Indirect mech. of inhibition

26. Factor Xa Inhibitors Fondaparinux • Parenteral anticoagulant • first selective factor Xa inhibitor approved by the FDA (2001) • 55% better than enoxaparin (LMWH) at reducing risk of VTE • synthetic pentasaccharide: “represents the oligosaccharide consensus sequence of heparin” • Indirect inhibition: binds to antithrombin and increases antithrombin’s affinity for factor Xa by 300-fold http://www.fda.gov/cder/foi/nda/2001/21-345_Arixtra_chemr.pdf

27. Factor Xa Inhibitors Indraparinux & SSR 126517 • Hypermethylated form of fondaparinux = tighter binding to antithrombin • Status: phase III clinical trials • 80 hr half-life = subcutaneous injection once weekly • SSR 126517 is a biotinylated form of indraparinux, prepared to have an antidote (avidin)

28. Factor Xa Inhibitors Oral factor Xa inhibitors • Developed off of success of fondaparinux • Can affect free factor Xa OR Xa bound to prothrombinase complex! • Many different drugs of this type being developed • Rivaroxaban • Apixaban • LY517717, YM150, DU-176b, and betrixaban

29. Factor Xa Inhibitors Rivaroxaban & Apixaban A D M E

30. Factor Xa Inhibitors Two synthesis schemes of rivaroxaban

31. Intrinsic pathway Extrinsic pathway XIIa XII TF VIIa XIa XI IXa IX VIIIa Va X Xa Common pathway II (prothrombin) IIa (thrombin) XIII XIIIa Fibrinogen Fibrin Stabilized Fibrin Direct Thrombin Inhibitors

32. Direct Thrombin Inhibitors Ximelagatran • First target-specific oral anticoagulant in trials • Ximelagatran is the oral prodrug of Melagatran • Hepatatoxicity • Did not receive FDA approval in 2004 • On the market in Europe but pulled in 2006 • ‘proof of principle’ • “efficacious” as warfarin • Wider therapeutic index • Little dosage adjustment/ no monitoring

33. Direct Thrombin Inhibitors Dabigatran etexilate • Prodrug converted to Dabigatran (471 mw) by esterases in blood after absorbed in stomach in microenvironment from tartaric acid capsule • Peak 2hr; Half life 14 – 17 hr • Not metabolized by cytochrome system = no anticipated drug interactions • Farthest along in trials • History: • early 1990s: German scientists at Boehringer-Ingleheim began research • 1996 Synthesized novel drug • 1999 Phase I trials • 2001-3 Phase II trials • 2004-present Phase III trials • 2008 announced to be entering European market soon as Pradaxa® • RE-LY trial results in 2009 • Promising; improvement in liver safety

34. Direct Thrombin Inhibitors Dabigatran etexilate clinical trial example “RELY: Randomized Evaluation of Long term anticoagulant therapy (RE-LY) comparing the efficacy and safety of two blinded doses of dabigatran etexilate with open label warfarin for the prevention of stroke and systemic embolism in patients with non-valvular atrial fibrillationStudy Design:Prospective, multi-centre, randomized, open label, controlled parallel group, non-inferiority trial. Study Objective:Demonstrate that the efficacy and safety of two blinded doses of dabigatran etexilate in patients with non-valvular atrial fibrillation are non-inferior to warfarin treatment for the prevention of stroke and systemic embolism.Scope:A total of 15, 000 patients will be randomized from approximately 1,000 clinical sites within 44 countries. Patients will be randomized over a 2-year period with a minimum 1 year follow-up, maximum of 3 years and mean of 1.5 years of follow-up.” https://www.rely-trial.com/RelyWeb/resources/jsp/emergency/dabigatran_bg.jsp

35. Intrinsic pathway Extrinsic pathway XIIa XII TF VIIa XIa XI IXa IX VIIIa Va X Xa Common pathway II (prothrombin) IIa (thrombin) XIII XIIIa Fibrinogen Fibrin Stabilized Fibrin Summary Slide Vitamin K antagonists Heparin derivatives Factor Xa inhibitors Thrombin inhibitors

36. Future of Anticoagulants • Clinical trials of novel anticoagulants will continue • New drugs to be on the market soon but cost will determine how wide spread the use will be • Parallel development of f Xa inhibitors and direct thrombin inhibitors • Drugs with other targets (f VIIa - TF, f Va - VIIIa, f IXa) will go to trials • Utilize crystal structures/docking algorithms

37. References • http://tollefsen.wustl.edu/projects/coagulation/coagulation.html (Great on blood coagulation) • http://www.accessdata.fda.gov/scripts/cder/drugsatfda/ (approved drugs) • http://clinicaltrials.gov/ct2/search (searchable database for clinical trials) • http://en.wikipedia.org/wiki/Coagulation • http://my.clevelandclinic.org/drugs/antiplatelet_drugs/hic_antiplatelet_drugs.aspx • http://www.vet.uga.edu/VPP/clerk/Harrell/index.php • http://en.wikipedia.org/wiki/Thrombolytic_drug • http://www.americanheart.org/presenter.jhtml?identifier=4451 • http://www.natfonline.org/frequency_te.php • http://emedicine.medscape.com/article/959501-overview • https://www.rely-trial.com/RelyWeb/resources/jsp/emergency/dabigatran_bg.jsp • Brunton, Lazo, Parker. Goodman & Gilman’s The Pharmacological Basis of Therapeutics, 11th ed. Chapter 54: Blood Coagulation and Anticoagulant, Thrombolytic, and Antiplatelet Drugs” by Philip W. Majerus and Douglas M. Tollefsen.1467-1488. • Bauer, Kenneth A. “New Anticoagulants.” Current Opinion in Hematology 2008, 15:509-515. • Turpie, Alexander. “New oral anticoagulants in atrial fibrillation.” European Society of Cardiology, European Heart Journal 2007, 29:155-165. • Esko, Jeffrey D and Robert J. Linhart. “Proteins that bind Sulfated Glycosaminoglycans.” accessed online from Essentials of Glycobiology 2nd edition. CSH Press 2009. <http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=glyco2&part=ch35> • “Rivaroxaban.” Prous Science. Drugs of the Future 2006, 31 (6): 484-493.