Summary
The development of inhibitory antibodies is a serious complication in hemophilic patients,
severely compromising therapeutic success. Bleeding episodes in affected patients
are controlled by treatment with a plasma-derived prothrombin complex concentrate
(PCC), activated PCC (APCC) or recombinant activated factor VII. We hypothesized that
a recombinant two-component agent consisting of recombinant prothrombin (rfII) and
activated factor X (rfXa) would have substantial fVIII bypassing activity and could
be a safe alternative therapeutic option. To test this hypothesis we assembled an
agent in vitro solely consisting of rfII and rfXa at a molar ratio of 37,500:1. These factors are
believed to be responsible for the activity of APCC preparations. Recombinant fX,
used as the source for fXa generation, and rfII were purified from serum-free and
protein-free conditioned media of stably transfected CHO and BHK tissue culture cells,
respectively. Activation of rfX to rfXa was accomplished by the plant protease ficin,
obviating the need for a protease derived from a human or animal source. We found
that in vitro the complex reduced the abnormally prolonged activated partial thromboplastin time
(APTT) of a high-titer fVIII inhibitor plasma similar to an APCC preparation. Furthermore,
addition of increasing amounts of rfII/rfXa to inhibitor plasma resulted in a linear
dose-dependent increase in the rate of thrombin generation. In a rabbit fVIII inhibitor
model, treatment with rfII/rfXa statistically significantly reduced the intensity
of the abnormal cuticle bleeding. In the Wessler test, rfII/rfXa showed no thrombogenicity.
These data show that a well-defined, particularly safe and efficacious agent with
fVIII bypassing activity can be generated from recombinant fII and fXa.
Keywords
Recombinant fII - recombinant fXa - fII/fXa complex - fVIII bypassing activity - hemophilic
patient with inhibitors - ficin