Evaluation of Factor VIII Polysialylation: Identification of a Longer-Acting Experimental Therapy in Mice and Monkeys

Selective human factor VIII activity measurement after analytical in-line purification

Background

It is essential to measure the activity of factor VIII (FVIII) throughout the life cycle of a coagulation FVIII concentrate. Such measurement in nonclinical pharmacokinetic studies is potentially biased by the presence of endogenous nonhuman FVIII, and certain manufacturing process-related additives can also impact the assay performance. Finally, the presence of FVIII activity-mimicking antibodies poses challenges when measuring FVIII in samples. Therefore, we developed an antibody-based chromogenic FVIII assay, which facilitates the selective and sensitive activity measurement of human FVIII in the presence of animal plasma and interfering agents.

Methods

Plate-bound monoclonal anti-FVIII antibody specifically captured human FVIII, which was then measured with a chromogenic activity assay. A human reference plasma preparation was used to construct the calibration curve. Spike recovery was carried out in a citrated cynomolgus monkey plasma-solvent/detergent mixture and in the presence of the bispecific antibody emicizumab.

Results

The calibration curve ranged from 3.03 to 97.0 mIU FVIII/ml and was obtained repeatedly with good accuracy. B domain-deleted and full-length FVIII did not differ in their responses. Recovery of spiked human FVIII in citrated cynomolgus monkey plasma was 102.7%, while neither native monkey plasma nor the other animal specimen tested showed any activity. Solvent/detergent solution and the bispecific antibody emicizumab had no influence on the assay.

Conclusion

Combining antibody-mediated specific capture of human FVIII and a chromogenic activity assay resulted in a selective and sensitive measurement of human FVIII with no interference by endogenous, nonhuman FVIII, manufacturing process additives, or an FVIII activity-mimicking antibody.

BIVV001, a new class of factor VIII replacement for hemophilia A that is independent of von Willebrand factor in primates and mice

Factor VIII (FVIII) replacement products enable comprehensive care in hemophilia A. Treatment goals in severe hemophilia A are expanding beyond low annualized bleed rates to include long-term outcomes associated with high sustained FVIII levels. Endogenous von Willebrand factor (VWF) stabilizes and protects FVIII from degradation and clearance, but it also subjects FVIII to a half-life ceiling of ∼15 to 19 hours. Increasing recombinant FVIII (rFVIII) half-life further is ultimately dependent upon uncoupling rFVIII from endogenous VWF. We have developed a new class of FVIII replacement, rFVIIIFc-VWF-XTEN (BIVV001), that is physically decoupled from endogenous VWF and has enhanced pharmacokinetic properties compared with all previous FVIII products. BIVV001 was bioengineered as a unique fusion protein consisting of a VWF-D'D3 domain fused to rFVIII via immunoglobulin-G1 Fc domains and 2 XTEN polypeptides (Amunix Pharmaceuticals, Inc, Mountain View, CA). Plasma FVIII half-life after BIVV001 administration in mice and monkeys was 25 to 31 hours and 33 to 34 hours, respectively, representing a three- to fourfold increase in FVIII half-life. Our results showed that multifaceted protein engineering, far beyond a few amino acid substitutions, could significantly improve rFVIII pharmacokinetic properties while maintaining hemostatic function. BIVV001 is the first rFVIII with the potential to significantly change the treatment paradigm for severe hemophilia A by providing optimal protection against all bleed types, with less frequent doses. The protein engineering methods described herein can also be applied to other complex proteins.

SHP656, a polysialylated recombinant factor VIII (PSA-rFVIII): First-in-human study evaluating safety, tolerability and pharmacokinetics in patients with severe haemophilia A

Introduction

SHP656 is the first factor VIII (FVIII) product developed using polysialylation (PSA) technology, in which full‐length recombinant (r) FVIII (anti‐haemophilic factor [recombinant]) is conjugated with a 20 kDa PSA polymer.

Aim

To compare the safety, immunogenicity and pharmacokinetics of SHP656 vs the parent rFVIII (octocog alfa) after single infusions of 25‐75 IU/kg in patients with severe haemophilia A (FVIII activity <1%).

Methods

Multinational, phase 1, prospective, open‐label, two‐period, fixed‐sequence, dose‐escalation trial (clinicaltrials.gov NCT02716194). Patients received single doses of rFVIII and then SHP656 sequentially at the same dose: 25 ± 3 IU/kg (Cohort 1), 50 ± 5 IU/kg (Cohort 2) and 75 ± 5 IU/kg (Cohort 3).

Results

Forty patients received rFVIII: 11 in Cohort 1, 16 in Cohort 2 and 13 in Cohort 3. Two patients withdrew before receiving SHP656, leaving 38 patients who completed the study and received both treatments. No treatment‐related adverse events (AEs), serious AEs, deaths, study withdrawals, thrombotic events or allergic reactions were reported; and no significant treatment‐related changes in laboratory parameters or vital signs. No patients developed FVIII inhibitors or antibodies to PSA. FVIII activity was significantly prolonged following SHP656 administration vs rFVIII with an approximately 1.5‐fold extension in mean residence time (P < .05). Exposure increased proportional to the SHP656 dose over the 25‐75 IU/kg dose range.

Conclusion

Polysialylation of rFVIII confers a half‐life extension similar to that of approved extended half‐life products that use either PEGylation or Fc fusion technology and was not associated with any treatment‐related adverse events.

Polysialic Acid-Mediated Activity Measurement of Polysialylated Recombinant Coagulation Factor VIII

Measurement of modified biologic including coagulation factors with extended half-life obtained, for example, by polysialylation pose an analytical challenge especially if both biological activity and presence of modification have to be determined. Analytical methods applied so far address only 1 of the 2 quality attributes of modified biologics. Here, we describe the development and bioanalytical validation of a polysialic acid-mediated factor VIII activity assay: Polysialic acid-specific capture of polysialylated recombinant factor VIII is combined with a chromogenic FVIII activity test using commercially available reagents. This assay principle enabled measurement of FVIII activity down to the pico mole-range without any interference by nonmodified factor VIII. To the best of our knowledge, this is the first method to selectively, accurately, and precisely measure simultaneously activity and modification integrity of a polysialylated biologic in complex matrices, as shown by the bioanalytical validation data. The convenience, robustness, and reliability of using this method has been demonstrated by its application for the nonclinical development of the polysialylated recombinant FVIII preparation. The method principle could be applied to protein modifications other than polysialylation and to activity tests other than the chromogenic FVIII assay.