In vitro studies show synergistic effects of a procoagulant bispecific antibody and bypassing agents

Abstract

Background Investigational non-factor products such as emicizumab offer a treatment option for patients with hemophilia and inhibitors. However, their mechanism of action raises questions regarding safety when they are combined with treatments for breakthrough bleeding. Objectives To evaluate in vitro thrombin generation (TG) and clot formation for combinations of activated prothrombin complex concentrate (aPCC), recombinant activated factor VII (rFVIIa), and a sequence-identical analog of emicizumab (SIA). Methods Therapeutic concentrations of SIA (20-600 nm) alone or with aPCC (0.05-1 U mL ), isolated aPCC components or rFVIIa (0.88-5.25 μg mL ) were tested for TG and compared with reference ranges for healthy donor plasma. Coagulation of FVIII-inhibited blood was determined with a widely established method, i.e. rotational thromboelastometry (ROTEM), and confirmed with the Total Thrombus-formation Analysis System. Results and conclusions SIA (600 nm) or aPCC (0.5 U mL ) alone resulted in peak thrombin levels of 21.4 nm and 38.6 nm, respectively, both of which are lower than normal (83.7 ± 29.8 nm). SIA plus aPCC (0.5 U mL ) increased the peak thrombin level 17-fold over SIA alone, exceeding the reference plasma value by 4.2-fold. This hypercoagulable effect occurred with 600 nmSIA combined with as little as 0.25 U mL aPCC, confirmed by ROTEM. FIX was the main driver for enhanced TG. SIA plus rFVIIa (1.75 μg mL ) induced a 1.8-fold increase in the peak thrombin level in platelet-rich plasma, but it did not reach the normal range. These in vitro experiments demonstrate excessive TG after administration of a combination of aPCC and SIA at clinically relevant doses. Careful judgement may be required when breakthrough bleeding is treated in patients receiving emicizumab.

Immune tolerance induction in paediatric patients with haemophilia A and inhibitors receiving emicizumab prophylaxis

“…Endogenous fVIIIa has high affinity and specificity for factors IXa and X in the presence of a phospholipid surface in addition to a short half‐life and feedback regulatory mechanisms. Excess thrombin generation with fVIII in combination with emicizumab was not observed . Moreover, addition of VWF‐containing pdfVIII to haemophilia A plasma with emicizumab did not show an additive effect in thrombin generation studies .…”

“…Emicizumab, which has the ability to bind factors IXa, IX, Xa and X, is constitutively active in plasma and does not have a regulatory system that inhibits its mechanism of action . In vitro studies using a sequence‐identical analog of emicizumab demonstrated excess thrombin generation in combination with aPCC . The authors postulated that the combination of these two drugs induces a hypercoagulable state that may contribute to thrombotic events.…”

Management of bleeding and invasive procedures in haemophilia A patients with inhibitor treated with emicizumab (Hemlibra®): Proposals from the French network on inherited bleeding disorders (MHEMO), the French Reference Centre on Haemophilia, in collaboration with the French Working Group on Perioperative Haemostasis (GIHP)

“…The concomitant use of activated prothrombin complex concentrates (aPCC) such as FEIBA ® (FEIBA NF, Baxalta US Inc, a Takeda company) for controlling breakthrough bleedings in doses exceeding 100 U/kg/24 h with a duration of treatment longer than 24 hours in patients treated with emicizumab has been associated with the development of thrombotic microangiopathies (TMA) and venous thrombotic events . In vitro studies have confirmed a synergistic effect between emicizumab and aPCC . No cases of thrombosis or TMA have been reported in the literature so far following administration of recombinant FVIIa (rFVIIa, eptacog alpha, NovoSeven ® ; Novo Nordisk) in patients receiving emicizumab .…”

Use of global assays to monitor emicizumab prophylactic therapy in patients with haemophilia A with inhibitors

“…5 To our knowledge, there is one published case report and one in vitro study that have proposed using TGA to monitor emicizumab therapy during concomitant FVIII BPA therapy. 8,9 Therefore, to better understand the effects of emicizumab on routine and global coagulation assays, we report herein the results from two patients that received emicizumab prophylaxis. Notable laboratory findings following emicizumab dosing include the spurious "normal" aPTTs in the 20-25 second range, respectively, and the undetermined FVIII levels at both 1 and 2 months following therapy.…”