Preclinical pharmacokinetics and biodistribution of subcutaneously administered glycoPEGylated recombinant factor VIII (N8-GP) and development of a human pharmacokinetic prediction model

Essentials N8-GP is an extended half-life recombinant factor VIII (FVIII) for the treatment of hemophilia A. Subcutaneous (SC) FVIII dosing might reduce the treatment burden of prophylaxis. SC N8-GP has a favorable PK profile in animal models and disappears from skin injection sites. Combined animal (SC) and clinical (IV) data suggest that daily SC dosing may provide prophylaxis.

SUMMARY

Background N8-GP is an extended half-life recombinant factor VIII (FVIII) for the treatment of hemophilia A. Subcutaneous administration of FVIII may reduce the treatment burden of prophylaxis; however, standard FVIII products have low bioavailability after subcutaneous dosing in animals. Objective To evaluate the pharmacokinetics, effectiveness and local distribution of subcutaneously administered N8-GP in preclinical models and predict the human pharmacokinetic (PK) profile. Methods The pharmacokinetics of subcutaneously administered N8-GP were evaluated in FVIII knockout (F8-KO) mice and cynomolgus monkeys; a human PK prediction model in hemophilia A patients was developed. The hemostatic effect was evaluated in a tail vein bleeding model in F8-KO mice. The injection-site distribution and absorption of subcutaneously administered N8-GP were assessed in F8-KO mice by the use of temporal fluorescence imaging and immunohistochemistry. Results Subcutaneously administered N8-GP had a bioavailability, a first-order absorption rate and a half-life, respectively, of 24%, 0.094 h-1 and 14 h in F8-KO mice, and 26%, 0.33 h-1 and 15 h in cynomolgus monkeys. A dose-dependent effect of subcutaneously administered N8-GP on blood loss was observed in mice. A minimal amount of N8-GP was detected at the injection site 48-72 h after single or multiple dose(s) in F8-KO mice. Subcutaneously administered N8-GP was localized to the skin around the injection site, with time-dependent disappearance from the depot. PK modeling predicted that subcutaneously administered N8-GP at a daily dose of 12.5 IU kg-1 will provide FVIII trough levels of 2.5-10% in 95% of patients with severe hemophilia A. Conclusions Subcutaneously administered N8-GP may provide effective hemophilia A prophylaxis. A phase I clinical trial is underway to investigate this possibility.

Phase I, randomized, double-blind, placebo-controlled, single-dose escalation study of the recombinant factor VIIa variant BAY 86-6150 in hemophilia

BACKGROUND

BAY 86-6150 is a new human recombinant factor VIIa variant developed for high procoagulant activity and longer action in people with hemophilia with inhibitors.

OBJECTIVES

To investigate the safety, tolerability, pharmacodynamics, pharmacokinetics and immunogenicity of BAY 86-6150 in non-bleeding hemophilia subjects.

METHODS

The study included non-bleeding men (18-65 years of age) with moderate or severe hemophilia A or B with or without inhibitors. Sixteen subjects were randomized 3 : 1 to four cohorts of escalating doses of BAY 86-6150 (6.5, 20, 50 or 90 μg kg(-1) [n = 3 per cohort]) or placebo (n = 1 per cohort); an independent data-monitoring committee reviewed previous cohort data before the next dose escalation. Blood sampling was performed predose and postdose; subjects were monitored for 50 days postdose.

RESULTS

At the tested doses, BAY 86-6150 was not associated with clinically significant adverse events or dose-limiting toxicities. BAY 86-6150 pharmacokinetics exhibited a linear dose response, with a half-life of 5-7 h. Subjects demonstrated consistent, dose-dependent thrombin generation ex vivo in platelet-poor plasma (PPP) (mean peak effect, 26-237 nm thrombin from 6.5 to 90 μg kg(-1)). Peak thrombin levels over time paralleled BAY 86-6150, with thrombin kinetics appearing to be slightly shorter; thus, circulating BAY 86-6150 retained activity. There were corresponding decreases in activated partial thromboplastin and prothrombin times. No subject developed de novo anti-BAY 86-6150 neutralizing antibodies during the 50-day follow-up.

CONCLUSIONS

In this first-in-human, multicenter, randomized, double-blind, placebo-controlled, single-dose escalation study, BAY 86-6150 was tolerated at the highest dose (90 μg kg(-1)), with no safety concerns. Safety and efficacy will be further evaluated in phase II/III studies.

Expression of recombinant human pregnancy-associated plasma protein-A and identification of the proform of eosinophil major basic protein as its physiological inhibitor

Pregnancy-associated plasma protein-A (PAPP-A), originally known from human pregnancy serum, has recently been demonstrated to be a metzincin superfamily metalloproteinase involved in normal and pathological insulin-like growth factor (IGF) physiology. PAPP-A specifically cleaves IGF-binding protein (IGFBP)-4, one of six antagonists of IGF action, which results in release of IGF bound to IGFBP-4. IGFBP-4 is the only known PAPP-A substrate. Its cleavage by PAPP-A uniquely depends on the presence of IGF. We here report mammalian expression and purification of recombinant 1547-residue PAPP-A (rPAPP-A). The recombinant protein is secreted as a homodimer of about 400 kDa composed of two 200-kDa disulfide-bound subunits. Antigenically and functionally, rPAPP-A behaves like the native protein. In human pregnancy, PAPP-A is known to circulate as a 500-kDa disulfide-bound 2:2 complex with the proform of eosinophil major basic protein (proMBP), PAPP-A/proMBP. A comparison between rPAPP-A and pregnancy serum PAPP-A/proMBP complex surprisingly reveals a difference greater than 100-fold in proteolytic activity, showing that proMBP functions as a proteinase inhibitor in vivo. We find that polyclonal antibodies against PAPP-A abrogate all detectable IGFBP-4 proteolytic activity in pregnancy serum, pointing at PAPP-A as the dominating, if not the only, IGFBP-4 proteinase present in the circulation. We further show that pregnancy serum and plasma contain traces (<1%) of uncomplexed PAPP-A with a much higher specific activity than the PAPP-A/proMBP complex. The measurable activity of the PAPP-A/proMBP complex probably results from the presence of a minor subpopulation of partly inhibited PAPP-A that exists in a 2:1 complex with proMBP. Inhibition of PAPP-A by proMBP represents a novel inhibitory mechanism with the enzyme irreversibly bound to its inhibitor by disulfide bonds.

Messenger ribonucleic acid levels of pregnancy-associated plasma protein-A and the proform of eosinophil major basic protein: expression in human reproductive and nonreproductive tissues

PAPP-A/proMBP, the complex of pregnancy-associated plasma protein-A (PAPP-A) and the proform of eosinophil major basic protein (proMBP), circulates at increasing levels during pregnancy. The major site of synthesis is the placenta, in which PAPP-A mRNA has been localized to the syncytiotrophoblast and the placental X cells, whereas proMBP mRNA has been localized to the placental X cells only. The function of PAPP-A/proMBP and its components has remained speculative for years. Recently, however, it has been shown that PAPP-A specifically cleaves insulin-like growth factor (IGF) binding protein-4 in an IGF-dependent manner. Female reproductive and nonreproductive tissues have previously been reported to contain PAPP-A immunoreactivity, based on studies using preparations of anti(PAPP-A/proMBP), now known to recognize both PAPP-A and proMBP, and other irrelevant antigens. To analyze for the presence of PAPP-A and proMBP mRNA, a sensitive semiquantitative reverse transcription (RT) polymerase chain reaction (PCR) method was developed. Reverse-transcribed poly(A)(+) RNA was used as a template in a competitive PCR. PAPP-A and proMBP mRNA levels were normalized against the level of beta-actin mRNA. Both mRNA species were significantly more abundant in term placenta than in other tissues analyzed. All analyzed tissues, including endometrium, myometrium, colon, and kidney, contained both PAPP-A and proMBP mRNA.

Characterisation of bovine structure-specific recognition protein 1 (SSRP1) cDNA

A partial bovine SSRP1 (structure-specific recognition protein 1) cDNA has been isolated from a osteoblast cDNA library and sequenced. The bovine SSRP1 cDNA of 1870 bp encoding 460 amino acid residues showed 86% and 98% sequence identity with human SSRP1 at the DNA and protein level, respectively. Expression of SSRP1 mRNA was detected in many human tissues, with a particularly high level in kidney.

Simple and reliable procedure for PCR amplification of genomic DNA from yeast cells using short sequencing primers

Yeast is widely used in molecular biology. Heterologous expression of recombinant proteins in yeast involves screening of a large number of recombinants. We present an easy and reliable procedure for amplifying genomic DNA from freshly grown cells of the methylotrophic yeast Pichia pastoris by means of PCR without any prior DNA purification steps. This method involves a simple boiling step of whole yeast cells in the presence of detergent, and subsequent amplification of genomic DNA using short sequencing primers in a polymerase chain reaction assay with a decreasing annealing temperature.

Complete cDNA sequence of the preproform of human pregnancy-associated plasma protein-A. Evidence for expression in the brain and induction by cAMP

A cDNA that encodes the prepropeptide of pregnancy-associated plasma protein-A (preproPAPP-A), a putative metalloproteinase, has been cloned and sequenced. PAPP-A is synthesized in the placenta as a 1627-residue precursor preproprotein with a putative 22-residue signal peptide and a highly basic propeptide of 58 residues. The prepro-PAPP-A-encoding transcript contains a region with an extremely high G+C content and has an unusually long 5' untranslated region with several upstream short ORF. No alternatively spliced products could be identified by means of Northern blotting experiments or with rapid amplification of 5' cDNA ends experiments. A stretch within the 5' untranslated region shows sequence identities to a partial cDNA isolated from brain and a to cAMP-inducible sequence from a choriocarcinoma cell line.

Identification of angiotensinogen and complement C3dg as novel proteins binding the proform of eosinophil major basic protein in human pregnancy serum and plasma

In sera from pregnant women, pregnancy-associated plasma protein-A (PAPP-A) circulates as a disulfide-bound complex (approximately 474 kDa) with the proform of eosinophil major basic protein (proMBP) (Oxvig, C., Sand, O., Kristensen, T., Gleich, G. J., and Sottrup-Jensen, L. (1993) J. Biol. Chem. 268, 12243-12246). We have produced monoclonal antibodies (mAbs) against the PAPP-A.proMBP complex and established a radioimmunoassay utilizing a mAb recognizing the PAPP-A subunit. Surprisingly, serum levels of proMBP exceed those of PAPP-A four to 10-fold on a molar basis throughout pregnancy. This result prompted an investigation of the status of proMBP in pregnancy. Using a proMBP-specific mAb two novel proMBP complexes have been isolated by chromatographic techniques. Based on sequence analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and reaction with specific antibodies, one is shown to be a 2:2 disulfide-bound complex (approximately 200 kDa) between proMBP and angiotensinogen. The other is a 2:2:2 complex (approximately 300 kDa) between proMBP, angiotensinogen, and complement C3dg. Circulating proMBP in pregnancy is thus present in three types of complexes. These results suggest that specific interactions between the complexed proteins occur in pregnancy, and the possibility is raised that their interactions are important in the pathophysiology of pregnancies associated with hypertension.

Location and nature of carbohydrate groups in proform of human major basic protein isolated from pregnancy serum

From human pregnancy serum we have isolated the proform of eosinophil major basic protein (proMBP), which forms a complex with pregnancy-associated plasma protein-A (PAPP-A), PAPP-A/proMBP. It is shown that proMBP contains O-linked glycan bound to Ser-24, Thr-25 (fully substituted), and to Thr-23 and Thr-34 (partially substituted). N-linked glycan is bound to Asn-86 and O-linked glycosaminoglycan is bound to Ser-62 (both fully substituted). From the RP-HPLC elution profile and mass spectra of tryptic peptides it is found that proMBP is extremely heterogeneous with respect to glycosylation.