Elsevier

Journal of Biotechnology

Volume 124, Issue 4, 5 August 2006, Pages 747-757
Journal of Biotechnology

Mechanism of action, development and clinical experience of recombinant FVIIa

https://doi.org/10.1016/j.jbiotec.2006.03.042Get rights and content

Abstract

Recombinant FVIIa has been developed for treatment of bleedings in hemophilia patients with inhibitors, and has been found to induce hemostasis even during major surgery such as major orthopedic surgery. Recombinant FVIIa is being produced in BHK cell cultures and has been shown to be very similar to plasma-derived FVIIa. The use of rFVIIa in hemophilia treatment is a new concept of treatment and is based on the low affinity binding of FVIIa to the surface of thrombin activated platelets demonstrated in a cell-based in vitro model. By the administration of pharmacological doses of exogenous rFVIIa the thrombin generation on the platelet surface at the site of injury is enhanced independently of the presence of FVIII/FIX. As a result of the increased and rapid thrombin formation, a tight fibrin hemostatic plug is being formed. A tight fibrin structure has been found to be more resistant to fibrinolytic degradation thereby helping to maintain hemostasis. The general mechanism of action of pharmacological doses of rFVIIa shown to induce hemostasis not only in hemophilia, but also in patients with platelet defects, and with profuse bleedings triggered by extensive surgery or trauma, may very well be the capacity of generating a tight fibrin hemostatic plug through the increased thrombin generation. Such a fibrin plug will help to resist the overwhelming mostly local release of fibrinolytic activity triggered by the vast tissue damage occurring in extensive trauma. A release of fibrinlytic activity locally has also been demonstrated to occur in the gastrointestinal tract as well as during profuse postpartum bleedings. Pharmacological doses of rFVIIa have in fact, also been shown to induce hemostasis in such cases.

Introduction

Patients with severe hemophilia need regular treatment with a hemostatically effective product in order to avoid the development of a chronic athropathy developing as a result of repeated joint bleedings. They also require immediate effective treatment of bleedings associated with trauma or essential surgery. Around 20% of patients with severe hemophilia A develop inhibitory antibodies against the coagulation factor they are missing. The administration of factor VIII (FVIII) or factor IX (FIX) concentrates is not effective in these patients, since the respective coagulation factor is neutralized by the antibodies. Much effort has, therefore, been focused on finding a treatment which is hemostatically effective independent of the presence of FVIII/FIX. Activated prothrombin complex concentrates (APCC) containing both activated coagulation proteins and zymogens are still widely used to achieve such a FVIII by-passing effect. A hemostatic effect of these concentrates averaging between 50 and 65% was reported (Lusher et al., 1983, Sjamsoedin et al., 1981). Also, side-effects in terms of thromboembolic events have been reported (Lusher, 1991). A dog model was used to identify some of the factors involved in the development of these side-effects (Hedner et al., 1979). Based on these studies, activated coagulation FVII (FVIIa) was identified as an attractive candidate for a hemostatic agent independent of FVIII/FIX, for use in hemophilia patients. Purified FVIIa was later shown to be free of such effects in a similar dog model (Hedner and Kisiel, 1983). Furthermore, purified plasma-derived FVIIa was shown to induce hemostasis in a few severe hemophilia patients (Hedner and Kisiel, 1983, Hedner et al., 1989). It was suggested at the time that pharmacological doses of FVIIa bind to tissue factor (TF) exposed at the site of injury, activating FX and provide thrombin locally at the site of injury (Hedner and Kisiel, 1983).

Section snippets

Development of recombinant FVIIa

Based on the observed hemostatic effect of plasma-derived purified FVIIa in severe hemophilia patients, recombinant FVIIa (rFVIIa) was developed for use in the treatment of severe hemophilia complicated with inhibitors against FVIII/FIX (Thim et al., 1988, Hagen et al., 1986). The amino acid sequence and posttranslational modifications of rFVIIa from the culture medium of a transfected baby hamster kidney cell line was compared to human plasma FVIIa. The two molecules were identical as for

Preclinical development

The hemostatic effect of rFVIIa was demonstrated in hemophilia dogs (Brinkhous et al., 1989) as well as in warfarin treated rats (Diness et al., 1990). No systemic activation of the coagulation was found following the injection of rFVIIa into rabbits using a stasis model originally developed as a thrombosis model. For a comparison it was shown in the same model that the injection of activated prothrombin complex concentrate (FEIBA) did induce lowering of the platelet counts as well as of the

Clinical development

The first patient treated with rFVIIa underwent open surgical synovectomy in March 1988 without any complications and no per- or postoperative abnormal bleeding (Hedner et al., 1988). An efficacy rate of 90–100% was later confirmed in several series of severe hemophilia patients subjected to surgery including major orthopedic surgery (Ingerslev et al., 1996, Shapiro et al., 1998). A review of patients with severe hemophilia with antibodies including close to 500 subjects treated at around 1900

Normal hemostasis

According to current concept, hemostasis occurs on principally two types of surfaces, the tissue factor (TF) expressing cell and the thrombin activated platelet (Monroe et al., 2002). TF is expressed by a number of various cells localized in the deeper layers of the vessel wall and normally not exposed to the circulating blood. TF is a true receptor protein and FVII/FVIIa is its ligand. As a result of tissue injury, TF is exposed to the circulation and forms a complex with FVII or FVIIa on the

Clinical experience with rFVIIa in hemophilia patients with Inhibitors

Hemophilia patients lacking FVIII (hemophilia A) or FIX (hemophilia B) develop severe, spontaneous bleedings deep in the body, characterized by being essentially non-responding to local pressure and likely to recur several hours later. Thrombin formation is markedly impaired in hemophilia, underscoring the importance of full thrombin generation for optimal hemostasis. The administration of pharmacological doses of rFVIIa increasing the plasma level of FVII:C from the normal value of around 1 

Clinical experience with rFVIIa in other situations with an impaired thrombin generation than hemophilia

The availability of platelet procoagulant phospholipids has been demonstrated to be rate limiting for thrombin generation and accordingly, an impaired thrombin generation was described in patients with thrombocytopenia in the 1950s by Biggs and MacFarlane (1962). In accordance with this, the dependence of thrombin generation on platelet counts in a cell-based in vitro model was shown (Kjalke et al., 1999, Kjalke et al., 2001). In the same cell-based model the addition of rFVIIa in

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