Activity and Regulation of Long-Acting Factor VIIa Analogs.

Recombinant coagulation factor VIIa (rFVIIa) has proven to be a safe and effective drug for treatment of bleeding episodes in hemophilia patients with inhibitors. However, rFVIIa is cleared from the circulation relatively fast, with circulating half-life of about 2–4 h, requiring repeated administration of rFVIIa for the effective treatment. Therefore, development of FVIIa analogs that could remain in the circulation for a longer period of time would be of a great value for improving the treatment options of rFVIIa. e.g., by prophylaxis. PEGylation of plasma proteins was shown to extend their circulatory half-lives but the PEGylation may also disrupt macromolecular interactions. In the present study we characterized the interaction of two glycoPEGylated analogs of rFVIIa, rFVIIa-10K PEG and rFVIIa-40K PEG, with its cofactor tissue factor (TF), substrate factor X (FX) and plasma inhibitors, tissue factor pathway inhibitor (TFPI) and antithrombin (AT). Both the PEGylated FVIIa analogs exhibited similar amidolytic activity as of wild-type rFVIIa (wt-rFVIIa) in the absence or presence of relipidated TF. The analogs were as effective as wt-rFVIIa in activating FX in the absence of TF. No significant differences were found between the PEGylated rFVIIa analogs and wt-rFVIIa in TF-dependent FX activation at saturating concentrations of rFVIIa, however, at lower concentrations of rFVIIa (10 to 50 pM), rFVIIa-10K PEG and rFVIIa-40K PEG activated FX at a slightly lower rate, 50% and 75%, respectively, of wt-rFVIIa. Further studies revealed that both AT/heparin and TFPI inhibited the PEGylated rFVIIa-TF complexes effectively but slightly at a lower rate compared to that was noted for wt-rFVIIa-TF. TFPI-Xa inhibited the PEGylated rFVIIa-TF and wt-rFVIIa-TF at a similar rate. On unperturbed HUVEC, wt-FVIIa (10 nM) could activate FX, albeit slowly, (1.7 nM/h) and the PEGylated rFVIIa activated FX even at much lower rates (0.23 nM/h for rFVIIa-10K PEG and 0.15 nM/h for rFVIIa-40K PEG). On stimulated HUVEC expressing TF, the PEGylated rFVIIa variants were slightly less effective at lower concentrations compared to wt-rFVIIa in activating FX, but no significant differences were found among them in activating factor X at saturating concentrations of rFVIIa (80–100 nM/h). The PEGylated rFVIIa analogs bound to cell surface TF were inhibited by TFPI-Xa complex at a similar rate as that was observed for wt-rFVIIa (IC₅₀ in nM: 0.102 ± 0.032 for wt-rFVIIa, 0.111 ± 0.024 for rFVIIa-10K PEG, and 0.096 ± 0.019 for rFVIIa-40K PEG). AT/heparin inhibited rFVIIa-10K PEG bound to endothelial cell TF at a similar rate as it inhibited wt-rFVIIa (IC₅₀ in μg/ml: wt-rFVIIa, 3.42 ± 068; rFVIIa-10K PEG, 3.56 ± 0.073), but the inhibition rate was slightly lower for rFVIIa-40K PEG bound to TF (IC₅₀ 5.92 ± 0.44 μg/ml). Overall, our present data suggest that long-acting PEGylated FVIIa analogs retain full enzymatic activity and can interact TF and FX effectively, and are inhibited by AT/heparin and TFPI-Xa as for wt-rFVIIa. Although the pegylated rFVIIa variants exhibited somewhat lower affinity towards TF, this may not critically affect the TF-driven FXa generation. Further work is needed to fully characterize these molecules.