Biomedical Engineering Reference
In-Depth Information
similar way to that described in Section 7.5. In the case of
FVIII, generation of the rFVIIIFc monomer was enabling to
the Fc fusion technology since the homodimer was not well
produced, presumably because the large size of the homo-
dimer (
Two of the dogs also received a single dose of ReFacto,
114 IU/kg for one dog and 120 IU/kg for the other, 72 h prior
to receiving rFVIIIFc (125 IU/kg) in a cross over design.
Awashout period of 3 days was chosen to allow the clotting
to return to baseline. Clotting was corrected to normal
immediately after dosing with rFVIII (determined by
WBCT and clotting activity measured using an aPTT assay)
similar to what was observed following dosing with
rFVIIIFc. However, the WBCT normalization after rFVIIIFc
dosing lasted for approximately twice as long compared to
rFVIII. In addition, the half-life of rFVIIIFc determined by
ELISA or chromogenic activity was approximately twice as
long as that determined for rFVIII (7.0 h and 6.7 h, respec-
tively). No adverse clinical signs were detected with any of
the infusions. Therefore, construction of a monomeric Fc
fusion of rFVIII produces a molecule with a defined mech-
anism of action that has an increased half-life and the
potential to provide prolonged protection from bleeding.
The safety, tolerability, and PK of a single intravenous
dose of rFVIIIFc in previously treated severe hemophilia A
patients were evaluated in a two-arm Phase I/IIa study in 16
male patients [54,55]. Patients were administered intra-
venously with either a single low dose (25 IU/kg) of rFVIII
(Advate 1 [octocog alfa]—rFVIII full-length product) fol-
lowed by an equal dose of rFVIIIFc, or a single high dose
(65 IU/kg) of rFVIII followed by an equal dose of rFVIIIFc.
PK assessments were performed following administration of
a single dose of rFVIII and rFVIIIFc. rFVIIIFc was well
tolerated. The primary PK estimates were derived from
FVIII activity data measured by a one-stage (aPTT) clotting
assay. rFVIIIFc showed a 1.54- to 1.70-fold longer half-life
compared with rFVIII [54,55] and the C max increased pro-
portionally to the dose, but was comparable between equal
doses of rFVIII and rFVIIIFc (Figure 7.3a and b) [55]. The
total exposure (AUC INF ) also increased proportionally to the
380 kDa) prevented secretion from the cells.
The PKs and clotting activity of the rFVIIIFc monomer
(rFVIIIFc) were studied in mouse and dog models of hemo-
philia A. The ability of rFVIIIFc to clot blood was evaluated in
hemophilia A mice by measuring whole blood clotting time
(WBCT) after a single 50 IU/kg dose of rFVIIIFc or BDD-
rFVIII (ReFacto 1 [moroctocog alfa]). At selected time points
after dosing, blood was collected and visually inspected once
per minute for the formation of a clot. Baseline clotting in these
mice was
60min, but after administration of rFVIIIFc or
rFVIII, WBCT was achieved in 2-5min. Blood from mice
treated with rFVIII lost the ability to clot after 42 h. In contrast,
all of the mice treated with rFVIIIFc (50 IU/kg) maintained
effective clotting through 96 h, but lost the ability to clot at
120 h after dosing. These data suggest that there is a threefold
improvement in WBCT for rFVIIIFc compared with rFVIII.
The PKs and pharmacodynamics of rFVIIIFc were also
evaluated in the in-bred Chapel Hill colony of hemophilia A
dogs [51-52]. These dogs have a severe hemophilic phenotype
that is comparable to the severe form of human disease with
plasma FVIII levels of < 1%. A single intravenous dose
(125 IU/kg) of rFVIIIFc was administered to four dogs, which
immediately corrected blood clotting to normal as measured
by WBCT and activated partial thromboplastin time (aPTT)
[53]. WBCT remained below 20min, which is consistent with
FVIII levels of
>
96 h. The concentration of
rFVIIIFc in the plasma was measured both by ELISA and by a
chromogenic activity assay, which showed that the concentra-
tion versus time curves were similar using both methods. The
terminal half-life was also similar for both methods [53] at
15.7
1%, through
>
1.7 h (ELISA) and 15.4
0.3 h (chromogenic activity).
(A)
(B)
Advate (25 IU/kg)
rFVIIIFc (25 IU/kg)
Advate (65 IU/kg)
rFVIIIFc (65 IU/kg)
100
100
10
10
1
1
0.1 0
0.1 0
48 96
Time after start of infusion (h)
144
192
240
48 96
Time after start of infusion (h)
144
192
240
FIGURE 7.3 Group mean plasma FVIII activity pharmacokinetic profiles for low-dose and high-
dose cohorts in patients with severe hemophilia A. The plasma FVIII activity (one stage aPTT assay)
versus time curve after a single intravenous injection of rFVIIIFc or Advate are shown for (A)
25 IU/kg (low-dose cohort, n ¼ 6) and (B) 65 IU/kg (high-dose cohort, n ¼ 10 [Advate]; n ¼ 9
[rFVIIIFc]). Results presented are group mean standard error of mean (SEM) Source: This
research was originally published in Reference [55].
 
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