A Phase II clinical trial of a mixture of plasma-derived factor VIIa and factor X (MC710) in haemophilia patients with inhibitors: haemostatic efficacy, safety and pharmacokinetics/pharmacodynamics

Reduced plasma factor X is associated with a lack of response to recombinant activated factor VII in patients with hemophilia A and inhibitor, but does not impair emicizumab-driven hemostasis in vitro

BACKGROUND

The hemostatic effect of recombinant (r) factor (F)VIIa after repetitive intermittent administration may be attenuated in patients with hemophilia A (PwHA) with inhibitors (PwHAwI) creating a clinically unresponsive status, although mechanism(s) remain to be clarified. In patients receiving prophylaxis treatment with emicizumab, concomitant rFVIIa is sometimes utilized in multiple doses for surgical procedures or breakthrough bleeding.

AIM AND METHODS

We identified 'unresponsiveness' to rFVIIa, based on global coagulation function monitored using rotational thromboelastometry (ROTEM) in 11 PwHAwI and 5 patients with acquired HA, and investigated possible mechanisms focusing on the association between plasma FX levels and rFVIIa-mediated interactions.

RESULTS

Our data demonstrated that FX antigen levels were lower in the rFVIIa-unresponsive group than in the rFVIIa-responsive group (0.46 ± 0.14 IU/mL vs. 0.87 ± 0.15 IU/mL, p < 0.01). This relationship was further examined by thrombin generation assays using a FX-deficient PwHAwI plasma model. The addition of FX with rFVIIa was associated with increased peak thrombin (PeakTh) generation. At low levels of FX (<0.5 IU/mL), rFVIIa failed to increase PeakTh to the normal range, consistent with clinical rFVIIa-unresponsiveness. In the presence of emicizumab (50 μg/mL), PeakTh was increased maximally to 80 % of normal, even at low levels of FX (0.28 IU/mL).

CONCLUSIONS

Unresponsiveness to rFVIIa was associated with reduced levels of FX in PwHAwI. Emicizumab exhibited in vitro coagulation potential in the presence of FX at concentrations that appeared to limit the clinical response to rFVIIa therapy.

Plasma-derived factor VIIa and factor X mixture agent (MC710) prophylaxis in haemophilia B patients with inhibitors

INTRODUCTION

Haemophilia B patients with factor IX inhibitors have particularly unmet needs for conventional therapy.

AIM

Phase II/III clinical trial, multicentre, open-label, prospective, self-controlled study was conducted to assess MC710 prophylaxis in haemophilia B patients with inhibitors.

METHODS

We enrolled haemophilia patients who had received episodic or prophylactic treatment with bypassing agents up to that time. The participants continued their conventional therapy for 24 weeks and then MC710 was prophylactically infused intravenously every 2 or 3 days at 60 to 120 μg as FVIIa per kilogram of body weight for 24 weeks. The primary endpoint was the annual bleeding rate (ABR) requiring bypassing agents, which was compared intraindividually between the conventional therapy period and the MC710 prophylaxis period.

RESULTS

A total of 11 male haemophilia B patients were enrolled. The median ABR ratio for each participant (the prophylaxis period ABR divided by the conventional therapy period ABR) was .33 (2.1/6.5), range from .00 to 3.77. ABR ratios for 9 of the 11 patients ranged from .00 to .60, and 3 of the 9 patients had zero bleeding events during the prophylaxis period. Meanwhile, ABR ratios for the remaining two patients were 2.53 and 3.77, respectively. Although a fibrinogen decrease recovered by the dose reduction was reported for only one participant as the sole adverse drug reaction in this study, no thrombotic events or other safety concerns were reported.

CONCLUSION

MC710 prophylaxis is considered to be decrease the bleeding rate in haemophilia B patients with inhibitors without safety concerns.

Origins, Development, Current Challenges and Future Directions with Activated Prothrombin Complex Concentrate for the Treatment of Patients with Congenital Haemophilia with Inhibitors

Congenital haemophilia A (HA) is caused by deficiency of coagulation factor VIII (FVIII) activity, leading to spontaneous or traumatic bleeding events. While FVIII replacement therapy can treat and prevent bleeds, approximately 30% of patients with severe HA develop inhibitor antibodies that render FVIII replacement therapy ineffective. The bypassing agents (BPAs), activated prothrombin complex concentrate (aPCC) and recombinant activated FVII, first approved in 1977 and 1996, respectively, act to generate thrombin independent of pathways that involve factors IX and VIII. Both may be used in patients with congenital haemophilia and inhibitors (PwHIs) for the treatment and prevention of acute bleeds and quickly became standard of care. However, individual patients respond differently to different agents. While both agents are approved for on-demand treatment and perioperative management for patients with congenital haemophilia with inhibitors, aPCC is currently the only BPA approved worldwide for prophylaxis in PwHI. Non-factor therapies (NFTs) have a mechanism of action distinct from BPAs and have reported higher efficacy rates as prophylactic regimens. Nonetheless, treatment challenges remain with NFTs, particularly regarding the potential for synergistic action on thrombin generation with concomitant use of other haemostatic agents, such as BPAs, for the treatment of breakthrough bleeds and in perioperative management. Concomitant use of NFTs with other haemostatic agents could increase the risk of adverse events such as thromboembolic events or thrombotic microangiopathy. This review focuses on the origins, development and on-going role of aPCC in the evolving treatment landscape in the management of PwHI.

Perioperative safety and haematostatic efficacy of a new bypassing agent pd-FVIIa/FX (Byclot) in haemophilia patients with high-responding type inhibitors

: The novel agent pd-FVIIa/FX is a 1 : 10 protein weight mixture of activated factor VII (FVIIa) and factor X (FX) derived from donated blood plasma. A phase III clinical trial of pd-FVIIa/FX revealed high efficacy for bleeding episodes in haemophilia patients with inhibitors. However, up to now, only one case of this new agent being used for surgery had been reported. The objective of this study is to evaluate the perioperative haemostatic efficacy and safety of pd-FVIIa/FX in haemophilia patients with inhibitors. We retrospectively reviewed 25 operation charts from 14 haemophilia patients with high-responding inhibitors using pd-FVIIa/FX during the perioperative period. Efficacy was evaluated by attending physicians and results divided into four groups (excellent, good, fair, and poor). The operation chart was provided by nine Japanese medical institutes with expertise in haemophilia management. Out of the total of 25 surgical procedures, 44% (11/25) were classified as major surgery and the remainders were minor surgeries. In all of the surgeries but one, rFVIIa and/or APCC were administered in combination or sequential method. In all cases except one, the haemostatic efficiency rate was judged as excellent or good by treating physicians for an overall efficacy rate of 96%. No thrombotic adverse effects were reported. This study's results suggest that both combination and sequential therapy of pd-FVIIa/FX and other bypassing agents are well tolerated and effective for the control of perioperative bleeding in haemophilia patients with high-responding inhibitors.

Advances in the clinical management of inhibitors in hemophilia A and B

Inhibitors to factor (F)VIII or FIX are the most serious and challenging complication of hemophilia treatment, increasing morbidity and mortality because bleeds no longer respond to standard clotting factor replacement therapy. For patients with high-titer inhibitors, immune tolerance induction achieved through regular factor exposure is the only proven therapy capable of Inhibitor eradication and is almost always indicated for inhibitors of recent onset. Bypassing therapy is used to treat and prevent bleeding, but neither of the two currently available bypassing agents has the predictable hemostatic efficacy of factor replacement in hemophilia patients without inhibitors. Major research efforts are focused on the development of new, more potent therapies for the management of patients with inhibitors.

Novel products for haemostasis

The primary major issue in haemophilia treatment remains the development of inhibitors. Recently two novel bypassing products have been developed. First, a humanized bispecific antibody against FIXa and FX, termed hBS23, was produced utilizing these two molecules placed into a spatially appropriate position to mimic FVIIIa, and recently this mimetic activity and the pharmacokinetics of the original antibody were improved by engineering the charge properties of the variable region within the immunoglobulin. Using the new antibody, termed ACE910, a phase 1 study in 64 Japanese and Caucasian healthy adults was performed and data from this trial suggested that the product had medically acceptable safety and tolerability profiles. The other new bypassing agent is named MC710, and consists of a mixture of plasma-derived FVIIa and FX. Preclinical studies using in vitro and in vivo haemophilia B inhibitor monkey models indicated that the haemostatic effects of FVIIa and FX were enhanced by simultaneous administration. Results from phase I and II clinical studies suggested that MC710 had equal or greater pharmacokinetic (PK), pharmacodynamic (PD), efficacy and safety profiles than conventional bypassing agents in the treatment of joint bleeding in haemophilia patients with inhibitors. Another significant current issue in this context is the increased medical cost of conventional treatment due to the higher consumption of concentrates. Biosimilar products may offer advantages in these circumstances and may offer a less expensive alternative. Regulatory issues, however, together with acceptability of biosimilar materials and reimbursement policies as well as supply and demand incentives remain to be considered. Rare bleeding disorders (RBDs) have attracted less attention from the pharmaceutical industry than haemophilia or von Willebrand disease due to the limited number of patients involved. Many cases of this type have been treated, therefore, using fresh frozen plasma (FFP) or prothrombin complex concentrates (PCCs) which carry serious risks of infections, allergic reactions and fluid overload. Several specific plasma-derived or recombinant products including fibrinogen, FVIIa, FXI and FXIII have now become available, however, and a phase III clinical study of recombinant FXIIIa has recently been completed demonstrating safety and efficacy of substances of this nature.