FIXing postinfusion monitoring: Assay experiences with N9‐GP (nonacog beta pegol; Refixia^®; Rebinyn^®)

Abstract

N9‐GP (nonacog beta pegol; Refixia®; Rebinyn®, Novo Nordisk A/S, Bagsværd, Denmark) is a glycoPEGylated extended half‐life recombinant factor IX (rFIX) that exhibits efficacy and potency comparable to unmodified FIX molecules in non‐clinical models. Phase 3 clinical trials have confirmed the efficacy and tolerability of N9‐GP for the prevention and on‐demand treatment of bleeding episodes in patients with haemophilia B. Recent studies have shown that PEGylation affects clotting times in activated partial thromboplastin time (aPTT)‐based one‐stage activity assays due to interaction between the FIX molecule and certain aPTT reagents. In recognition of the challenges surrounding FIX activity assessment, the identification of consistent, reproducible and accurate assays to measure FIX activity has been a priority for Novo Nordisk, running in parallel to the clinical development program for N9‐GP. N9‐GP activity can be reliably measured using chromogenic substrate assays and specific aPTT reagents. The conjugation of the PEG moiety to the FIX molecule may affect one‐stage aPTT‐based clotting assays in a reagent‐dependent manner. Many aPTT reagents that use silica as the contact activator dramatically overestimate N9‐GP activity due to premature activation. On the other hand, the contact activator in some other aPTT reagents negatively affects the enzymatic activity of FXIa, causing the underestimation of N9‐GP activity. While N9‐GP activity cannot be measured consistently with all available aPTT reagents, accurate N9‐GP measurements can be achieved with certain aPTT reagents. Here, we review the studies that led to these findings and summarize the current options for accurate measurement of N9‐GP in patient samples.

Outcome measures in Haemophilia: Beyond ABR (Annualized Bleeding Rate)

“…Afstyla (rFVIII SC, CSL Behring) prescribing information advises that results obtained with one‐stage assay should be multiplied by two to approximate results with chromogenic assay 12 Pegylated FIX (N9‐GP, Rebinyn, Refixia, Novo Nordisk) interacts with certain aPTT reagents resulting in over‐ or under‐estimation of activity; N9‐GP must be assayed in a chromogenic assay or a one‐stage assay using certain reagents 13 Assay variability with rFIXFc is reagent dependent 14 …”

Nanosized Delivery Systems for Therapeutic Proteins: Clinically Validated Technologies and Advanced Development Strategies

“…Refixia R (nonacog beta pegol), a PEGylated factor IX (rFIX), is used against hemophilia B. The protein is modified by a selective glycoPEGylation (DeFrees et al, 2006;Ezban et al, 2019). Release of the activation peptide by physiologic activators converted the PEGylated recombinant factor IX to recombinant native factor IX and proceeded normal kinetics for factor IX (Østergaard et al, 2011).…”

Current therapeutic approaches in the management of hemophilia—a consensus view by the Romanian Society of Hematology

“…However, with these drugs, there are concerns about the accumulation of PEG throughout time, especially during long-term administrations of a PEGylated drug. A clinical trial concluded that there is an initial increase in PEG level in the blood and afterward it reaches a plateau, remaining at the same concentration even after (137,138).…”