Growing evidence for the effectiveness of FXa inhibition Professor Cedric HERMANS MD, MRCP(UK), PhD Division of Haematology Cliniques universitaires Saint-Luc 1200 Brussels

Conflicts of interests Participation in advisory boards and consulting activities for anti-Xa and anti-IIa anticoagulants (Bayer Schering Pharma, Boehringer Ingelheim)

Thrombin (IIa) FibrinogenFibrin Coagulation cascade

Contact Phase - FXII FIX + FVIII FX Thrombin Tissue Factor + FVIIa Intrinsic pathway Extrinsic pathway Common pathway FXI FIBRIN CLOT FV Classic theory of the coagulation cascade

Steps in blood coagulation Steps in coagulation Inhibition Initiation TF/VIIa Amplification Propagation IIa FibrinogenFibrin IX IXa X Xa II Va Antithrombin PC/PS VIII TFPI

Vitamin K Antagonists (VKA)

Heparin 1 pig = units UFH Heparin- induced skin necrosis Venous Limb Gangrene (HIT) Platelet count ?

PARENTERAL Sites of action of new anticoagulants DIRECT INDIRECT Xa IIa FT/VIIa XIX IXa VIIIa Va II Fibrin Fibrinogen Fondaparinux Idraparinux Antithrombin Dabigatran and others Rivaroxaban and others ORAL DIRECT

Pentasaccharide (Arixtra - Fondaparinux) Olson ST, et al. J. Biol. Chem. 1992; 267:12528– IIaII Fibrinogen Fibrin clot Extrinsic pathway Intrinsic pathway 3 ATIII Xa 1 ATIII 2 Arixtra Xa Pentasaccharide sequence of heparin (present in UFH and LMWH) binds to AT causing conformational change at its reactive centre accelerating 1000-fold its interaction with factor Xa. IIA Platelets

Coagulation cascade and targets of new oral anticoagulants

Rivaroxaban (XARELTO – Bayer Schering): Anti-Xa Direct, specific, competitive Factor Xa inhibitor Inhibits free and fibrin-bound Factor Xa activity and prothrombinase activity Inhibits thrombin generation No direct effect on platelet aggregation, and thus, on primary haemostasis Bioavailibility: 80–100 % C max at 2–4 h Roehrig S et al. J Med Chem 2005;48:5900–8; Perzborn E et al. J Thromb Haemost 2005;3:514–21. ~ one-third excreted as unchanged active substance in urine Of the two-thirds metabolized: half eliminated renally, half eliminated by faecal route

Dabigatran etexilate (Pradaxa – Boehringer Ingelheim) : Anti-IIa (Thrombin) –After oral administration, the prodrug dabigatran etexilate is rapidly converted to dabigatran, a potent reversible Direct Thrombin Inhibitor (DTI) –Absolute bioavailability ~ 6.5 % –Fast onset of action (C max within 2h) –Not metabolized by CYP450 / Renal excretion ~80% –Half life hours –Low potential for drug-drug interactions, no drug-food interactions –Potent antithrombotic effects are achieved by specifically blocking the activity of thrombin (both free and clot-bound)

NEW versus OLD anticoagulants Pradaxa LMWH + Vitamin K Antagonist Synthetic Per os One or two tablet(s) / day No monitoring No or little food/drug interaction Xarelto

Anti-Xa versus Anti-IIa

Many targets for new anticoagulants: Why target Factor Xa? TFPI (tifacogin) Fondaparinux Idrabiotaparinux Rivaroxaban Apixaban YM150 LY Edoxaban (DU-176b) Betrixaban (PRT054021) Ximelagatran Dabigatran OralParenteral DX-9065a Otamixaban Factor Xa XIX IXa VIIIa Va II FibrinFibrinogen AT APC (drotrecogin alfa) sTM (ART-123) TTP889 Adapted from Weitz & Bates. J Thromb Haemost 2005; Gross & Weitz. Arterioscler Thromb Vasc Biol 2008; Carriero & Ansell. Expert Opin Investig Drugs 2008 TF/Factor VIIa Factor IIa

Oral, direct FXa inhibitors in development RivaroxabanBayer and Scios LY517717Lilly YM150Astellas DU-176bDaiichi Sankyo ApixabanBMS et Pfizer GSK PRT Portola

Why is FXa an attrative target for new anticoagulants? LOCATION of FXa in the coagulation cascade Arixtra > LMWH > UFH (degree of inhibition of FXa) Inhibition of thrombin = deleterious consequences Larger therapeutic window with Xa inhibition ? Results of clinical trials ? BUT no head-to-head comparison (anti-Xa versus anti-IIa)

Initiation Amplification Propagation… Reason 1 Central role of FXa in the coagulation cascade

Targets of new anticoagulants : FXa or FIIa (Thrombin) TF Thrombin FVa FXa FVIIa Fibrinogen Thrombus

Inhibition of 1 unit of Xa prevents generation of 1000 units of thrombin Wessler & Yin. Circ 1973;47:671

X Xa Va IX IXa VIIIa II IIa Initiation phase Amplification phase Activated platelet II IIa XIa Fibrinogen Fibrin monomer X Xa XIII XIIIa Crosslinked fibrin

Reason 2 Specificity of FXa inhibtion and antithrombotic activity Higher selectivity for FXa inhibition with heparins is associated with a more potent anticoagulant effect : Fondaparinux > LMWH > UFH Fondaparinux : anti-Xa LMWH : anti-FXa > anti-IIa UFH : anti-FXa = anti-IIa

Fondaparinux better Enoxaparin better Exact 95% CI Hip replace n = 3,411 Hip fracture n = 1,250 Knee replace n = 724 Overall odds reduction % 63.1% 55.3% [59.0; 27.6] [73.4; 45.0] [75.5; 44.8] [63.2; 45.8] 61.6% p = < Fondaparinux vs enoxaparin in orthopedic surgery % odds reduction Turpie AGG. Arch Intern Med 2002;162:1833

Factor Xa inhibitors: Success in clinical trials Venous thrombo-embolic disease Fondaparinux reduced the risk of VTE compared with enoxaparin in patients undergoing hip fracture surgery and hip and knee arthroplasty Rivaroxaban reduced the risk of VTE compared with enoxaparin regimens in patients undergoing elective total hip and knee replacement surgery (RECORD programme) Acute Coronary Syndrome Fondaparinux lowered long-term morbidity, improved survival and reduced the risk of bleeding compared with enoxaparin Atrial Fibrillation None published – ongoing trials: ARISTOTLE – apixaban (vs warfarin), AVERROES – (vs ASA), ROCKET AF – rivaroxaban (vs warfarin)

Reason 3 Inhibition of thrombin could in theory have detrimental consequences, even outside the clotting system

The limited functions of Factor Xa Procoagulant Thrombin formation PAI – 1 release Cell Prolif / Inflammation Cytokine release Smooth muscle cell proliferation From J. Ansell 2007

Thrombin Platelets Platelet activation Endothelium Endothelium activation Protein C Activated protein C FVIIIa FVa Thrombomodulin Anticoagulation TAFI Anti-fibrinolytic FXIII Fibrinogen Fibrin Fibrin formation

Anticoagulant Protein C activation Prostacyclin formation Procoagulant Fibrin formation Platelet activation Feedback activation TAFI activation Inflammation P-selection expression Cell adhesion Chemotaxis Cellular Proliferation Tissue repair Growth factor secretion Angiogenesis The many functions of Thrombin

Multiplicity of thrombin’s functions Thrombin Procoagulant Cellular proliferationInflammation Anticoagulant Fibrin clot and platelet plug Feedback activation of coagulation Protein C activation Prostacyclin formation EC P-selectin expression Neutrophil–monocyte adhesion Chemotactic for PMNs Endothelial PAF formation Direct mitogen for fibroblasts PDGF and TGFβ from platelets PDGF formation in endothelium Esmon Thromb Haemost 2008

Factor Xa = an attractive target for inhibition The only known functions of Factor Xa are either procoagulant or proinflammatory Thrombin has both of these activities and indirect anticoagulant, anti-inflammatory and anti-apoptotic activities

Thrombin = anticoagulant Thrombin is essential for the activation of protein C. Activated protein C inactivates FVa and FVIIIa. Inhibition of thrombin impairs the activation of protein C and thereby the inhibition of FVa and FVIIIa. Furugohri et al. Eur J Pharmacol 2005;514:35 Morishima et al. Blood 2006;108:274a Esmon Thromb Haemost 2008

Thrombin = anticoagulant Inhibition of FXa does not interfere with the PC/PS anticoagulant pathway. Direct inhibition of FXa allows the generation of small amount of thrombin and the activation of protein C into activated protein C. Is the protein C anticoagulant pathway still needed when thrombin procoagulant activity is inhibited ??? Esmon Thromb Haemost 2008

Factor Xa = an attractive target for inhibition Inhibition of thrombin in the large vessels reduces clotting activity and facilitates the ability of blood flow to carry thrombin to the microcirculation. In the microcirculation, thrombin binds to thrombomodulin and activates protein C. The efficacy of Factor Xa inhibitors should not depend on the health of the vasculature unlike thrombin inhibitors.

Thrombin = potent platelet agonist FIIa is a potent platelet agonist. FXa does not activate platelets. Thrombin inhibition could increase the risk of bleeding. Direct FXa inhibitors allow the generation of small amounts of thrombin necessary to activate platelets and preserve primary haemostasis Ieko et al. J Thromb Haemost 2004;2:612

Reason 4 Therapeutic window of anti-Xa inhibiton

Thrombin FXa Enzyme dilution in 1:4 Human Plasma Clotting Time(s) Dose Response: Xa vs IIa C. Esmon Clotting Time vs. Enzyme Concentration

Choice of Doses Optimal Efficacy / Safety Balance BISTRO II Major + clinically relevant non-major bleeding (%) Safety Dabigatran etexilate total daily dose Efficacy Total VTE (%) Eriksson et al. J Thromb Haemost 2005; 3:103

Factor Xa = an attractive target for inhibition Factor Xa has a shallower dose–response curve than thrombin This suggests that maintaining the appropriate dose range for Factor Xa inhibitors should be easier than for thrombin inhibitors

Clinical studies

Pooled Analysis Major VTE and VTE-Related Death in major orthopaedic surgery Study Dabigatran 150 mg Dabigatran 220 mg Enoxaparin RE-NOVATE* (THR)4.3%3.1%3.9% RE-MODEL (TKR)3.8%2.6%3.5% RE-MOBILIZE (TKR)3.0%3.4%2.2% Pooled3.8%3.0%3.3% Absolute risk difference (Dabigatran – Enoxaparin) [95% CI] [-0.6 to 1.6][-1.3 to 0.9]

Pooled Analysis Bleeding Events Bleeding event Dabigatran etexilate Enoxapa rin N= mg N= mg N=2682 Major Bleeding Event 1.1%1.4% 95% CI (0.7, 1.4)(1.0, 1.9) (1.0, 2.0)

Major VTE RRR 62% Symptomatic VTE RECORD3: summary Incidence (%) 2.6%1.0%2.0% 0.7% RRR 49% Enoxaparin 40 mg once daily Rivaroxaban 10 mg once daily RRR 66% 18.9%9.6% Total VTE Rivaroxaban head-to-head comparison with enoxaparin in patients undergoing total knee replacement 0.5%0.6% Major bleeding Total VTE: any DVT, non-fatal PE and all-cause mortality Major VTE: proximal DVT, non-fatal PE and VTE-related death

Drug Class Company Half-life Bioavaila- bility Elimination Dosage (oral) Apixaban antiXa BMS/ Pfizer % 25% renal 75% liver b.i.d. Rivaroxaban antiXa Bayer/ J&J 5-13>80% 33% renal (unchanged) 33% renal (inactive metabolites) 33% biliary o.d. Dabigatran DTI B-I14-175% 80% renal 20% biliary o.d./b.i.d. Comparison of three upcoming novel specific oral anticoagulants

Conclusions Several reasons suggest that factor Xa might be a more appopriate target than IIa. The reasons are theoretical and speculative. Recent clinical studies in orthopaedic surgery indirectly support experimental observations.

Conclusions Clinical trials with oral FIIa and FXa inhibitors are ongoing and following parallel paths. Which class of drugs will be better ? –This question will remain unanswered until the appropriate head-to-head clinical trials are performed. –At the moment, both classes appear promising.

Head-to-head comparison between anti-IIa and anti-Xa inhibitors Even if we have a study which shows that the cost-benefit ratio is superior with one compound versus another one, this will be true : a) only for these two particular drugs b) and only in one well-defined clinical situation

Old versus new anticoagulants Anti-Xa versus anti-IIa ? Pradaxa LMWH + Vitamin K Antagonist Synthetic Per os One or two tablet(s) / day No monitoring No or little food/drug interaction Xarelto

Anti-Xa versus Anti-IIa ????