Receptor-mediated clearance of factor VIII: implications for pharmacokinetic studies in individuals with haemophilia

Lonoctocog alfa (rVIII-SingleChain) for the treatment of haemophilia A

INTRODUCTION

The administration of factor VIII (FVIII) concentrates on-demand or on long-term prophylaxis is the effective and safe standard of care of patients with hemophilia A (HA). Development of neutralizing antibodies against exogenous FVIII and the short half-life of the current available products remain major challenges. There is currently a great interest towards newer FVIII products with the goal of reducing the inhibitor risk and increasing the half-life. Area covered: In this review, the authors describe the efficacy and safety of rVIII-SingleChain (Lonoctocog alfa), the first and only single chain recombinant FVIII (rFVIII) molecule developed for the prevention and treatment of bleeding episodes in HA patients. The pre-clinical and clinical studies of rVIII-SingleChain as well as the results of the AFFINITY trial program in previously treated patients both adults and pediatric are presented and discussed. Expert opinion: The results from PTP studies document the efficacy and safety profile of the rVIII-SingleChain. However, even if rFVIII-SingleChain presents advantageous pharmacokinetic features compared to conventional rFVIII, it should not be considered as an EHL-FVIII while its immunogenicity is currently being studied in PUPs. The slightly better PK profile of rFVIII-SingleChain could however allow a small number of selected patients to be treated with a less intensive regimen.

Non-clinical pharmacokinetics and pharmacodynamics of rVIII-SingleChain, a novel recombinant single-chain factor VIII

INTRODUCTION

rVIII-SingleChain (CSL627), a novel recombinant coagulation factor VIII (FVIII), is under investigation in a phase I/III clinical programme (AFFINITY) for the treatment of haemophilia A. Non-clinical studies were conducted to investigate the pharmacokinetic/pharmacodynamic profile of rVIII-SingleChain in comparison with full-length recombinant FVIII.

MATERIALS AND METHODS

Binding affinity of rVIII-SingleChain for von Willebrand factor was investigated by surface plasmon resonance analysis. The pharmacokinetic profile of rVIII-SingleChain was compared with a marketed full-length recombinant FVIII concentrate (Advate(®)) in haemophilia A mice, von Willebrand factor knock-out mice, Crl:CD (SD) rats, rabbits and cynomolgus monkeys. Systemic FVIII activity or antigen levels were recorded. Procoagulant activity was measured in an FeCl3-induced arterial occlusion model and by recording thrombin generation activity (ex vivo) after administration of 200-250 IU/kg rVIII-SingleChain or full-length FVIII to haemophilia A mice.

RESULTS

rVIII-SingleChain displayed a high affinity for von Willebrand factor (KD=44 pM vs. 139 pM for full-length recombinant FVIII). In all animal species tested, rVIII-SingleChain had more favourable pharmacokinetic properties than full-length recombinant FVIII: clearance was decreased and area under the curve and terminal half-life were enhanced vs. full-length recombinant FVIII, while in vivo recovery and volume of distribution were equivalent. rVIII-SingleChain showed a prolonged thrombin generation potential and prolonged procoagulant activity vs. full-length recombinant FVIII in an FeCl3-induced arterial occlusion model.

CONCLUSIONS

rVIII-SingleChain had a higher affinity for von Willebrand factor than full-length recombinant FVIII and displayed favourable pharmacokinetic/pharmacodynamic properties in non-clinical models.

Immunogenicity and pharmacokinetic studies of recombinant factor VIII containing lipid cochleates

Replacement therapy using recombinant factor VIII (rFVIII) is currently the most common therapy for hemophilia A, a bleeding disorder caused by the deficiency of FVIII. However, 15-30% of patients develop inhibitory antibodies against administered rFVIII, which complicates the therapy. Encapsulation or association of protein with lipidic structures can reduce this immune response. Previous studies developed and characterized rFVIII-containing phosphatidylserine (PS) cochleate cylinders using biophysical techniques. It was hypothesized that these structures may provide a reduction in immunogenicity while avoiding the rapid clearance by the reticuloendothelial system (RES) previously observed with liposomal vesicles of similar composition. This study investigated in vivo behavior of the cochleates containing rFVIII including immunogenicity and pharmacokinetics in hemophilia A mice. The rFVIII-cochleate complex significantly reduced the level of inhibitory antibody developed against rFVIII following intravenous (i.v.) administration. Pharmacokinetic modeling allowed assessment of in vivo release kinetics. Cochleates acted as a delayed release delivery vehicle with an input peak of cochleates showed limited RES uptake and associated rFVIII displayed a similar disposition to the free protein upon release from the structure. Incomplete disassociation from the complex limits systemic availability of the protein. Further formulation efforts are warranted to regulate the rate and extent of release of rFVIII from cochleate complexes.

Phosphatidylinositol containing lipidic particles reduces immunogenicity and catabolism of factor VIII in hemophilia a mice

Factor VIII (FVIII) is an important cofactor in blood coagulation cascade. It is a multidomain protein that consists of six domains, NH2-A1-A2-B-A3-C1-C2-COOH. The deficiency or dysfunction of FVIII causes hemophilia A, a life-threatening bleeding disorder. Replacement therapy using recombinant FVIII (rFVIII) is the first line of therapy, but a major clinical complication is the development of inhibitory antibodies that abrogate the pharmacological activity of the administered protein. FVIII binds to anionic phospholipids (PL), such as phosphatidylinositol (PI), via lipid binding region within the C2 domain of FVIII. This lipid binding site not only consists of immunodominant epitopes but is also involved in von Willebrand factor binding that protects FVIII from degradation in vivo. Thus, we hypothesize that FVIII-PL complex will influence immunogenicity and catabolism of FVIII. The biophysical studies showed that PI binding did not alter conformation of the protein but improved intrinsic stability as measured by thermal denaturation studies. ELISA studies confirmed the involvement of the C2 domain in binding to PI containing lipid particles. PI binding prolonged the in vivo circulation time and reduced catabolism of FVIII in hemophilia A mice. FVIII-PI complex reduced inhibitor development in hemophilia A mice following intravenous and subcutaneous administration. The data suggest that PI binding reduces catabolism and immunogenicity of FVIII and has potential to be a useful therapeutic approach for hemophilia A.