Dual inhibition of factor XIIa and factor XIa as a therapeutic approach for safe thromboprotection

Stéphanie Demoulin1, Edmond Godfroid1, Cédric Hermans2

1Bioxodes S.A., Marche-en-Famenne, Belgium
2Division of Hematology, Hemostasis and Thrombosis Unit, Saint-Luc University Hospital, Université Catholique de Louvain (UCLouvain), Brussels, Belgium


Clinical practice shows that a critical unmet need in the field of medical device‐associated thrombosis prevention is the availability of an anticoagulant therapy without hemorrhagic risk. In the quest for new drugs that are at least as effective as those currently available, while avoiding bleeding complications, molecules that target nearly every step of the coagulation pathway have been developed. Among these molecules, inhibitors of factor XII (FXII) or factor XI (FXI) are promising alternatives as deficiencies in these factors protect against thrombosis without causing spontaneous hemorrhage, as revealed by epidemiological and preclinical data. Ixodes ricinus‐contact phase inhibitor (Ir‐CPI), a new anticoagulant candidate with an innovative mechanism of action could be this ideal anticoagulant agent for safe prevention from clotting on medical devices. This protein, which selectively binds to FXIIa, FXIa, and plasma kallikrein and inhibits the reciprocal activation of FXII, prekallikrein, and FXI in human plasma, was shown to prevent thrombosis in an ovine cardiopulmonary bypass system associated with cardiac surgeries. Furthermore, as opposed to unfractionated heparin, Ir‐CPI appears to be devoid of bleeding risk. This review outlines the rationale for targeting upstream coagulation factors in order to prevent medical device‐associated thrombosis; examines the novel approaches under development; and focuses on Ir‐CPI, which shows promising properties in the field of thrombosis prevention.


Anticoagulation With an Inhibitor of Factors XIa and XIIa During Cardiopulmonary Bypass

Valérie Pireaux PhDa, Joël Tassignon PhDa, Stéphanie Demoulin PhDa, Sandrine Derochette PhDa, Nicolas Borenstein DVM, PhDb, Angélique Ente DVMb, Laurence Fiette DVM, PhDb, Jonathan Douxfils PharmD, PhDc, Patrizio Lancellotti MD, PhDd, Michel Guyaux PhDa, Edmond Godfroid PhDa

aBioxodes S.A., Marche-en-Famenne, Belgium
bIMM Recherche, Institut Mutualiste Montsouris, Paris, France
cQUALIblood S.A., Namur, Belgium
dGIGA Cardiovascular Sciences, Department of Cardiology, University Hospital of Liège, CHU Sart Tilman, Liège, Belgium


Background Exposure of blood to polyanionic artificial surfaces, for example, during cardiopulmonary bypass (CPB), induces a highly procoagulant condition requiring strong anticoagulation. Unfractionated heparin (UFH) is currently used during CPB but can lead to serious bleeding complications or development of a hypercoagulable state culminating in life-threatening thrombosis, highlighting the need for safer antithrombotics. Ixodes ricinus contact phase inhibitor (Ir-CPI) is a protein expressed by I. ricinus ticks, which specifically inhibits both factors XIIa and XIa, 2 factors contributing to thrombotic disease while playing a limited role in hemostasis.

Objectives This study assessed the antithrombotic activity of Ir-CPI in animal contact phase-initiated thrombosis models, including CPB. The safety of Ir-CPI also was evaluated.

Methods The authors evaluated the antithrombotic activity of Ir-CPI by using in vitro catheter-induced clotting assays and rabbit experimental models of catheter occlusion and arteriovenous shunt. During CPB with cardiac surgery in sheep, the clinical applicability of Ir-CPI was investigated and its efficacy compared to that of UFH using an uncoated system suitable for adult therapy. Taking advantage of the similar hemostatic properties of pigs and humans, the authors performed pig liver bleeding assays to evaluate the safety of Ir-CPI.

Results Ir-CPI prevented clotting in catheter and arteriovenous shunt rabbit models. During CPB, Ir-CPI was as efficient as UFH in preventing clot formation within the extracorporeal circuit and maintained physiological parameters during and post-surgery. Unlike UFH, Ir-CPI did not promote bleeding.

Conclusions Preclinical animal models used in this study showed that Ir-CPI is an effective and safe antithrombotic agent that provides a clinically relevant approach to thrombosis prevention in bypass systems, including highly thrombogenic CPB.

Central Illustration


Ir-CPI, a FXIa/FXIIa inhibitor, provides an effective and safe thromboprotection during extracorporeal circulation associated with open-heart surgery [Abstract ISTH 2019]


1Bioxodes, Marche-en-Famenne, Belgium; 2IMMR, Paris, France

Background: Extracorporeal circulation (ECC) during cardiac surgery is a highly thrombogenic procedure involving both intrinsic and extrinsic coagulation pathways and requires strong anticoagulation to prevent thrombosis and to maintain blood fluidity. Unfractionated heparin (UFH) is currently used in such surgical procedures but can lead to serious bleeding complications, highlighting the need for new safer antithrombotic agents. Ir-CPI, a protein from the saliva of tick Ixodes ricinus, is an inhibitor of both FXIIa and FXIa which has been demonstrated to inhibit thrombotic processes in various experimental animal models.

Aims: Our objective was to evaluate the efficacy and safety of Ir-CPI in ECC during cardiac surgery using uncoated adult ECC system.

Methods: An ECC system with uncoated material was used to perform a chordae replacement and a commissuroplasty of the mitral valve on beating heart of sheep. The ECC was maintained for 90 min at full-flow systemic perfusion level. The investigative group received a bolus followed by a continuous intravenous infusion of Ir-CPI. UFH was used as comparator. Following the procedure, half the animals were kept in recovery for 7 days.

Results: Ir-CPI was proven to be as efficient as UFH in preventing clot formation within the ECC circuit. Moreover, Ir-CPI was shown to be as thromboprotective in the animal as UFH with stable physiological parameters (i.e. blood gases, hematology and biochemistry) up to 7 days post-surgery. Oxygenator membrane examination by scanning electron microscopy showed no differences between Ir-CPI and UFH treatment in terms of protein or blood cell deposits. Animals fully recovered after ECC and cardiac surgery and no hemorrhagic and thrombotic related-Ir-CPI findings were observed after histopathological analyses of organs (heart, kidney, lung, liver, brain, spleen and draining lymph nodes).

Conclusion: These results demonstrate for the first time that a FXIa/FXIIa inhibitor alone provides safe thromboprotection in ECC during cardiac surgery.

Ir-CPI: an original inhibitor of thrombosis and thrombosis-associated with cancer [Abstract ISTH SSC 2018]

Darbousset R.3, Pireaux V.1, Crescence L.2, Demoulin S.1, Panicot-Dubois L.2, Godfroid E.1, Dubois C.2

1Bioxodes, Marche-en-Famenne, Belgium; 2Aix-Marseille University, Center for CardioVascular and Nutrition Research, Marseille, France; 3The University of Sydney, Heart Research Institute, Sydney, Australia.

Background: Ir-CPI, a protein derived from saliva of the tick Ixodes ricinus, is an inhibitor of the activated form of factor XI (FXIa) and XII (FXIIa). In vitro, this molecule inhibits specifically the contact phase pathway.

Aims: Our aims were to assess the efficacy of Ir-CPI in the prevention of thrombosis dependent on the Tissue Factor (TF) pathway in mouse models of thrombosis.

Methods: Two thrombosis models dependent on TF activation were studied. First, we used a laser-injury model on a cremaster muscle arteriole that is strictly dependent on TF and independent of FXII. Second, we used a laser-induced thrombosis model in mice bearing a pancreatic tumor. This model is mainly dependent on TF expressed by cancer cell-derived microparticles. As control, we assessed the efficacy of Ir-CPI in the Deep Vein Thrombosis (DVT) model in which FXII plays a central role in thrombus formation.

Results: As expected, Ir-CPI significantly reduced thrombus weight in the DVT model. Surprisingly, Ir-CPI inhibited thrombus formation, platelet accumulation and fibrin generation in the laser-injury model in normal mice. The effects of Ir-CPI on thrombosis were confirmed in tumor-bearing mice despite their procoagulant state. Since neutrophils play a key role in the activation of the TF dependent pathway in the laser model, the presence and activation of neutrophils were compared in control and Ir-CPI-treated mice. In vivo, Ir-CPI significantly inhibited neutrophil accumulation and their secretion of Neutrophil Elastase at the site of injury. In vitro, Ir-CPI strongly diminished the activation of neutrophils leading to NETs formation.

Conclusion: As expected, Ir-CPI is an effective antithrombotic in the FXII-dependent mouse model. Surprisingly, it is effective in a laser-injury model, even in a prothrombotic tumoral state. The inhibitory effect on neutrophil recruitment in vivo and NETs formation in vitro strongly suggests that Ir-CPI has additional targets and offers new therapeutic opportunities in thrombosis-associated diseases.

Efficacy of a novel contact pathway inhibitor, Ir-CPI, on in vitro clotting induced by PCI catheter segment [Abstract ISTH 2017]

Douxfils J1, Gheldof D1, Derochette S2, Tassignon J2, Meinguet C2, Guyaux M2, Donné J-M1, Godfroid E2

1University of Namur, Pharmacy, Namur, Belgium; 2Bioxodes, Marche-en-Famenne, Belgium

Background: Ir-CPI, a protein derived from the tick Ixodes ricinus salivary, is a serine protease inhibitor of both factor XIa (FXIa) and FXIIa. In patients undergoing percutaneous coronary intervention (PCI), catheter thrombosis may occur as catheters trigger activation of FXII/FXI.

Aims: The aim of this study was to evaluate the effect of Ir-CPI on in vitro clotting induced by PCI catheter segment.

Methods: Catheter segments were pressed flat, shaped into rings and placed around the perimeter of wells (96-well plate), leaving the center of the well unobstructed. To the wells were added serial dilution of Ir-CPI (until 10 µM) with normal pooled plasma (NPP) or plasmas deficient in FXI or FXII. After incubation at 37°C and addition of a CaCl2 solution, clot formation was assessed by monitoring absorbance at 340nm. Time to reach one-half maximal absorbance (IC50) was defined as the clotting time. Thrombin generation test (TGT) was also assessed using catheter segment as trigger of the process. Positive inhibitory controls were used (fondaparinux, enoxaparin).

Results: Presence of the catheter reduced the clotting time of NPP; an effect reversed by the addition of Ir-CPI. At high concentrations (≥ 5µM), Ir-CPI allowed to overpass the clotting time without catheter. On TGT, catheter segments decreased lag time and time to peak while the endogenous thrombin potential (ETP) and the peak were increased. The presence of Ir-CPI allowed the restoration of baseline value, i.e. value of the NPP without exposition to catheter segments, in a concentration-dependent manner. When clotting was triggered with FXII deficient plasma, we confirmed that catheter thrombosis is linked to FXI activation and that clotting can be abrogated with 3µM of Ir-CPI.

Conclusion: Ir-CPI can be used to inhibit the clotting induced by catheter segments and achieve antithrombotic effect. Ir-CPI is a promising agent with a better safety profile than heparins to face the problem of catheter thrombosis during PCI procedures.  

Antithrombotic effects of Ir-CPI in an arterio-venous shunt model in the rabbit [Abstract ISTH 2015]

Guyaux M1, Gueret P2,3, Becher F4, Amiral J5, Simon S4, Godfroid E1

1Bioxodes, Marche-en-Famenne, Belgium; 2Hemostasis Unit, University Hospital Rennes; 3GETBO EA3878 Brest, France, 4Laboratoire Etudes et Recherches Immunoanalyse, CEA Saclay, Gif sur Yvette; 5Hyphen BioMed, Neuville sur Oise, France

Background: Ir-CPI is a 67 aa protein derived from the salivary glands of the tick Ixodes ricinus. It is a contact phase inhibitor targeting specifically factors XIa and XIIa.

Aims: The aim of the current study was to evaluate the antithrombotic potential and the pharmacokinetic-pharmacodynamic relationships of Ir-CPI.

Methods: The experiment was performed on New Zealand rabbits (n=34) anesthetized with ketamine-xylazine. An arterio-venous (AV) shunt device containing a silk thread was connected between the femoral artery and vein. Ir-CPI was administered intravenously at variable doses as a bolus alone or followed by a continuous infusion starting 5 min before the opening the AV-shunt. Thrombus weight was measured at the end of a 40 min shunt period. Blood samples were taken 10 min before and 45 min after administration. Plasma was prepared to monitor the activated partial thromboplastin time (aPTT), FXI and FXII activities and Ir-CPI concentration. The aPTT was measured using actin FS as reagent. Factors XI and XII activities were measured using FXI or FXII deficient plasmas and aPTT (Cephen) method. Ir-CPI plasma concentration was determined by mass spectrometry and enzyme-linked immunosorbent assay.

Results: Ir-CPI reduced thrombus weight by 36.8%, 62.1% and 97.2% at 1, 3 and 5 mg/kg, iv and by 90.4% at 3 mg/kg,iv followed by 2.3 mg/kg.h infusion. Ir-CPI plasma concentrations increased proportionally with the dose. Antithrombotic activity (>90 %) corresponded to an Ir-CPI plasma level of 2500 ng/mL, a prolongation of the aPTT of 50%, an inhibition of FXI and FXII activities of 35-40%. The effects on aPTT, FXI and FXII and Ir-CPI exposure level measured in vivo were consistent with the data obtained in vitro using rabbit plasma spiked with Ir-CPI.

Conclusion: These results demonstrate the antithrombotic potential of Ir-CPI in a model of AV-shunt in the rabbit whilst establishing the relationships between the antithrombotic efficacy, the Ir-CPI circulating concentration, the aPTT prolongation and FXI and FXII inhibition.

Efficacy of a novel contact pathway inhibitor, Ir-CPI, in an extracorporeal membrane oxygenator model [Abstract ISTH 2015]

Combe S1,2, Fromes Y3, Krezel C2, Gueret P4,5, Amiral J6, Guyaux M2 and Godfroid E2

1Hopitaux Universitaires Paris Centre, Paris, France; 2Bioxodes, Marche en Famenne, Belgium; 3Universite Pierre et Marie Curie, Paris; 4GETBO EA3878, Brest; 5Hemostasis Unit Hematology Laboratory, University Hospital, Rennes; 6Hyphen Biomed, Neuville sur Oise, France

Background: Ir-CPI, a protein derived from the tick Ixodes ricinus salivary, is a serine protease inhibitor of both FXIIa and FXIa. Heparins remain suboptimal in managing bleeding complications when extracorporeal life support is required.

Aims: The aim of this study was to evaluate whether inhibition of the contact phase of the coagulation cascade might confer antithrombotic activity.

Methods: Twelve Beagle dogs were included. A pediatric ECMO system was connected between the carotid artery and the jugular vein, and a cardiopulmonary bypass was maintained for 90 min at the level of full-flow systemic perfusion. Anticoagulation was performed by UFH (300 IU kg-1) with protamine reversal at the end of the procedure (N = 3). Three investigative groups (3x N = 3) received various doses of Ir-CPI (bolus and infusion) total dose 4.5 to 24 mg kg-1. After disconnection, circuits and cannulae were examined for clot and protein deposits. All animals were followed-up and sampled for determination of Ir-CPI plasma concentration (Mass Spectrometry), aPTT, FXI and FXII residual activities, before necropsy on Day 7.

Results: All 12 animals completed procedure. First Ir-CPI group showed fibrin deposits, increased pressure gradient in the circuit, and subsequent decreased gas exchanges. In further animals perfusion of Ir-CPI was initiated earlier in order to decrease the observed clot initiation and to improve gas exchanges. High dose achieved close to optimal control. Low dose was less satisfactory but perfusion remained possible. A dose-dependent and related increase in Ir-CPI plasma concentration, increase in aPTT ratio and inhibition of factors XI and XII (20% and >70% respectively) were measured over the course of the procedure. No side effects were observed and necropsies confirm the absence of thrombosis or hemorrhage.

Conclusion: Ir-CPI can be used as a single agent to inhibit the intrinsic coagulation pathway and achieve anticoagulation. Efficiency can be improved without increasing bleeding risk.

Evaluation of the effects of a novel contact pathway inhibitor, Ir-CPI, on in vitro platelet function and coagulation [Abstract ISTH 2015]

Jennings LK1,2, Kotha J2, Cardenas J2, Herr M2, Bhal V2, Dixon M2, White MM2, Combe S3 and Godfroid E3

1Vascular Biology/Medicine, University of Tennessee Health Science Center; 2CirQuest Labs, Memphis, USA; 3Bioxodes SA, Marche-en-Famenne, Belgium

Background: Ir-CPI, the tick Ixodes ricinus salivary protein, is a serine protease inhibitor under development as a novel anticoagulant. Ir-CPI inhibits Factors (F) XIIa, XIa, and kallikrein generation, prolongs the activated partial thromboplastin time, and confers antithrombotic activity in preclinical models.

Aims: The study aim was to test Ir-CPI effects on platelet function using light transmission aggregometry (LTA), clot retraction, and Pselectin expression and to characterize Ir-CPI inhibition of the contact activated coagulation pathway by assessing FXa and FIXa activation time and activity.

Methods: Ir-CPI effects on LTA in response to 20 µM ADP and 1.6 mM arachidonic acid (AA) were studied using consented blood donors (n = 5). Platelet P-selectin expression was evaluated using flow cytometry (n = 4) following activation by contact pathway initiation. Ir-CPI effects on PRP clot retraction was measured (n = 5), and FXa and FIXa generation were determined by quantitative chromogenic assays (n = 3).

Results: LTA response as well as clot retraction were unaffected by Ir-CPI pretreatment. However, the percent of P-selectin positive platelets was decreased following Ir-CPI treatment (0.5, 1, and 2 µM) by 5%, 9%, and 18%, respectively, vs. control. FXa activation lag times were prolonged to 704, 752, 826, 1013 s with increasing concentrations of Ir-CPI (1, 2, 4, 8 µM, respectively) vs. control (611 s). Similarly, FIXa activation lag times were 790, 834, 876, and 902 s, respectively, vs. 581 s (control). Also, the mean reaction rates (OD min -1) of FXa and FIXa with added Ir-CPI were decreased ~2.3-fold.

Conclusion: We demonstrated that Ir-CPI does not affect in vitro platelet aggregation response or clot retraction. However, Ir-CPI dose dependently blocked contact pathway mediated platelet P-selectin expression and the rate of FXa and FIXa activation and activity. This study confirms specific effects of Ir-CPI on the contact pathway of coagulation and provides a basis for monitoring Ir-CPI.

Ir-CPI, a coagulation contact phase inhibitor from the tick Ixodes ricinus, inhibits thrombus formation without impairing hemostasis

Decrem, Y., et al., Ir-CPI, a coagulation contact phase inhibitor from the tick Ixodes ricinus, inhibits thrombus formation without impairing hemostasis. J Exp Med, 2009. 206(11): p. 2381-95.


Blood coagulation starts immediately after damage to the vascular endothelium. This system is essential for minimizing blood loss from an injured blood vessel but also contributes to vascular thrombosis. Although it has long been thought that the intrinsic coagulation pathway is not important for clotting in vivo, recent data obtained with genetically altered mice indicate that contact phase proteins seem to be essential for thrombus formation. We show that recombinant Ixodes ricinus contact phase inhibitor (Ir-CPI), a Kunitz-type protein expressed by the salivary glands of the tick Ixodes ricinus, specifically interacts with activated human contact phase factors (FXIIa, FXIa, and kallikrein) and prolongs the activated partial thromboplastin time (aPTT) in vitro. The effects of Ir-CPI were also examined in vivo using both venous and arterial thrombosis models. Intravenous administration of Ir-CPI in rats and mice caused a dose-dependent reduction in venous thrombus formation and revealed a defect in the formation of arterial occlusive thrombi. Moreover, mice injected with Ir-CPI are protected against collagen- and epinephrine-induced thromboembolism. Remarkably, the effective antithrombotic dose of Ir-CPI did not promote bleeding or impair blood coagulation parameters. To conclude, our results show that a contact phase inhibitor is an effective and safe antithrombotic agent in vivo.