Coagulation the basics and recombinant Factor VIIa Mechanism

Coagulation (the basics) and recombinant Factor VIIa Mechanism of Action Jerrold H. Levy, MD Emory University School of Medicine and Emory Healthcare Atlanta, Georgia

Normal Hemostasis • First step in hemostasis is formation of a platelet aggregate • At the molecular level interaction of coagulation factors takes place on the surface of activated platelets • The Tissue Factor–FVIIa complex is the physiological activator of normal hemostasis

Hemostasis Subendothelial matrix Nitric oxide Endothelial cell

Initiation of coagulation

Coagulation Pathways Intrinsic Pathway Extrinsic Pathway IX Tissue Factor + VII Contact XI TF Pathway TF-VIIa X Common Pathway PL XIIa HKa Prothrombin XIa IXa PL (Tenase ) VIIIa PL X a Va (Prothrombinase) Protein C, Protein S, Antithrombin III XIII Thrombin Fibrinogen Fibrin (weak) XIIIa Fibrin (strong)

Normal Hemostasis: Pivotal role of TF/VIIa II X TF VIIa Xa Va IIa VIII/v. WF VIIIa TF-Bearing Cell TF VIIa IX VIIIa Va Platelet II X IXa VIIa V IX Xa Va Activated Platelet Va IXa VIIIa Xa X II IIa Hoffman et al. Blood Coagul Fibrinolysis 1998; 9(suppl 1): S 61.

Platelet Activation Pathways COLLAGEN THROMBIN ADP Aggregation Gp. IIb/IIIa Platelet G p. I Adrenaline b Adhesion v. WF Endothelium Exposed Collagen

COAGULATION and recombinant Factor VIIa ) (Novo. Seven Mechanism of Action

Bleeding through a cut in a vessel wall Tissue Factor VIIa • The first step in all coagulation: The Tissue Factor VIIa complex formation

Bleeding through a cut in a vessel wall Tissue. Factor- Factor VIIa Complex • The first step in all coagulation: The Tissue Factor VIIa complex formation • This catalysis the coagulation cascade in normal persons and in patients with bleeding disorders

Recombinant Factor VIIa Platelet Binding Tissue. Factor- Factor VIIa Complex r. Factor. VIIa Platelets Recombinant Factor VIIa (r. FVIIa) in high concentration binds to platelets; this complex catalysis further coagulation. The local coagulation activation is greatly enhanced

Further formation of a hemostatic plug Tissue. Factor- r. FVIIa Complex r. FVIIa Platelets High peak levels of recombinant Factor VIIa (r. FVIIa) induces formation of a strong fibrin network. This network cross-binds and forms a solid hemostatic plug

HEMOSTASIS : ROLE OF FACTOR VII and TISSUE FACTOR

Normal Hemostasis X TFVIIa II Xa Va TF-Bearing Cell IIa (Thrombin)

Normal Hemostasis II X TF VIIa Xa Va TF-Bearing Cell IIa VIII/v. WF VIIIa

Normal Hemostasis II X TF VIIa Xa IIa Va VIII/v. WF VIIIa TF-Bearing Cell V Va Platelet

Normal Hemostasis II X TF VIIa Xa Va IIa VIII/v. WF VIIIa TF-Bearing Cell V Va Platelet Activated Platelet

Normal Hemostasis II X TF VIIa Xa Va IIa VIII/v. WF VIIIa TF-Bearing Cell TF VIIa IX IXa Activated Platelet V Va Platelet

Normal Hemostasis II X TF VIIa Xa Va IIa VIII/v. WF VIIIa TF-Bearing Cell TF VIIa IXa V IX X II Xa IXa Va Activated Platelet VIIIa Va Platelet IIa

Normal Hemostasis II X TF VIIa Xa Va IIa VIII/v. WF VIIIa TF-Bearing Cell TF VIIa IXa V IX II X IXa VIIIa Xa Va Activated Platelet Va Platelet IIa Hoffman et al. Blood Coagul Fibrinolysis 1998; 9(suppl 1): S 61.

FACTOR VIIa Mechanism of Action • Increases the tissue factor (TF) occupancy • In pharmacological doses binds to activated platelets • Activates Factor X independent of tissue factor Proceedings of the National Academy of Sciences 97(10): 5255 -60, 2000. Circulation. 103(21): 2555 -9, 2001. Blood Coagulation & Fibrinolysis. 11 Suppl 1: S 107 -11, 2000. Proceedings of the National Academy of Sciences. 96(16): 8925 -30, 1999. Haemostasis. 30 Suppl 2: 41 -7, 2000. Thrombosis Research. 98(4): 311 -21, 2000.

Recombinant Factor VIIa (7) Mechanism of Action II X TF Xa Va TF-Bearing Cell IIa

Recombinant Factor VIIa (7) Mechanism of Action II X TF Xa Va IIa VIII/v. WF VIIIa TF-Bearing Cell V Va Platelet Activated Platelet

Recombinant Factor VIIa (7) Mechanism of Action II X TF Xa Va IIa VIII/v. WF VIIIa TF-Bearing Cell TF IX IXa Activated Platelet V Va Platelet

Recombinant Factor VIIa (7) Mechanism of Action II X TF VIIa Xa Va IIa VIII/v. WF VIIIa TF-Bearing Cell TF IXa IX X IXa VIIIa Xa Activated Platelet V Va Platelet

Recombinant Factor VIIa (7) Mechanism of Action Recombinant Factor VIIa binding to activated platelets Activated Platelet X Xa

Recombinant Factor VIIa (7) Mechanism of Action Recombinant Factor VIIa binding to activated platelets Activated Platelet X Xa II IIa

FVIIa Binding to Platelets 2. 0 Activated Unactivated Activated, without Ca+2 1. 5 Relative 1. 0 Fluorescence 0. 5 0. 0 0 150 300 [FVIIa] (n. M) Monroe et al. Br J Haematol 1997; 99: 542. 450 600

FVIIa Activates FX on Platelets in the Absence of TF 6 50 n. M VIIa 20 n. M VIIa 10 n. M VIIa 5 n. M VIIa 2 n. M VIIa None 5 [FXa] (n. M) 4 3 2 1 0 0 10 20 30 Time (min) Monroe et al. Blood Coagul Fibrinolysis 1998; 9(suppl 1): S 15. 40

Recombinant Factor VIIa Mechanism of action: Conclusion • Recombinant Factor VIIa increases the Tissue Factor occupancy • Recombinant Factor VIIa in pharmacological doses binds to activated platelets • Recombinant Factor VIIa provides Factor X activation independent of Tissue Factor