The in Vitro Effect on Thrombin Generation of Adding rFVIII or rFIX to Hemophilia a or b Plasma in the Absence or Presence of Concizumab

Introduction: Lack of factor VIII/IX (FVIII/FIX) in hemophilia A/B (HA/HB), respectively, results in reduced thrombin generation, leading to recurrent/spontaneous bleeds. Concizumab is an anti-tissue factor pathway inhibitor (TFPI) monoclonal antibody, currently under clinical investigation for subcutaneous prophylaxis of HA/HB patients with/without inhibitors. Breakthrough bleeds occurring in HA/HB patients while on concizumab prophylaxis may be treated with FVIII/FIX. We aimed to compare the in vitro effect of recombinant FVIII (rFVIII) and FIX (rFIX) in HA and HB plasma, respectively, in the absence or presence of concizumab. Methods: rFVIII/rFIX was added to HA/HB pooled plasma at 0.25, 0.5 or 1 IU/mL (corresponding to post-administration plasma concentrations of 12.5, 25 and 50 IU/kg rFVIII and 12.5−25, 25−50 and 50−100 IU/kg rFIX) in the absence or presence of concizumab (1,500, 4,500 or 15,000 ng/mL). In a separate experiment, 33 plasma samples from eight HA patients, who were on concizumab prophylaxis as part of the phase 2 explorer5 trial (NCT03196297), were spiked with 0.5, 1 and 1.5 IU/mL rFVIII. Pre-dose samples (before concizumab prophylaxis) from seven of these patients were also included. Thrombin generation was measured after initiation with 1 pM tissue factor (PPP-Low, Thrombinoscope). Statistical analysis of the effects conferred by each (combination of) drug(s) was performed by ANOVA analyses. Results: A significant (p 1,500 ng/mL and 0.5 IU/mL rFIX combined with 15,000 ng/mL concizumab, i.e., a 10% smaller effect of rFIX was observed in the presence of concizumab than in its absence. The thrombin peak obtained upon adding 1.0 IU/mL rFIX to plasma without concizumab was similar to the thrombin peak in the presence of concizumab and 0.5 IU/mL rFIX. This suggests that in the presence of concizumab, a 2-fold reduced dose of rFIX would be sufficient to obtain the same plasma thrombin generation capacity as with 1.0 IU/mL rFIX in the absence of concizumab. Conclusion: rFVIII/rFIX increased the thrombin peak in HA and HB plasma, respectively, both in the absence and presence of concizumab. The combined effects of rFVIII/rFIX with concizumab were mainly additive with an up to 20% additional effect caused by drug-drug interaction with rFVIII and a 10% reduction with rFIX. No signs of exaggerated thrombin generation were observed by combining concizumab with rFVIII/rFIX. Therefore, the data support rFVIII/rFIX use for bleed treatment in patients on concizumab prophylaxis. As rFVIII/rFIX and concizumab have additive effects in terms of thrombin generation capacity, data suggest that clinical effectiveness could be achieved with rFVIII/rFIX doses in the lower range recommended for such products. Download : Download high-res image (264KB) Download : Download full-size image Disclosures Kjalke: Novo Nordisk A/S: Current Employment, Current equity holder in publicly-traded company. Andersen: Novo Nordisk A/S: Current Employment, Current equity holder in publicly-traded company.