An unusual antibody that blocks tissue factor/factor VIIa function by
inhibiting cleavage only of macromolecular substrates
MM Fiore, PF Neuenschwander and JH Morrissey
Cardiovascular Biology Research Program, Oklahoma Medical Research
Foundation, Oklahoma City 73104.
Tissue factor (TF), the cell surface receptor and cofactor for factor VIIa
(FVIIa), is considered the major physiologic trigger of the coagulation
cascade. Most monoclonal antibodies to TF have been reported to inhibit TF
activity by blocking association of FVII(a) with TF. Using solution-phase
kinetic analyses, we have reexamined two strongly inhibitory anti-TF
monoclonal antibodies (TF8-11D12 and TF9- 9C3) previously reported to block
FVII binding in cell-binding assays. Kinetic analysis of TF9-9C3 was
consistent with direct competition with FVIIa for binding to TF. However,
antibody TF8-11D12 did not block FVIIa binding to TF as measured by ability
of the TF:FVIIa complex to cleave a small peptide substrate or by enhanced
reactivity of FVIIa with a tripeptidyl-chloromethylketone. Interestingly,
TF8-11D12 strongly inhibited cleavage of all three known macromolecular
substrates (factors VII, IX, and X) of the TF:FVIIa complex. We hypothesize
that TF8-11D12 blocks access of macromolecular substrates to the active
site of FVIIa by steric hindrance. This study identifies a useful probe for
TF function and provides insights into the inhibitory mechanism of an
unusual class of antibody proposed for therapeutic intervention in
thrombotic disease.
Volume 80,
Issue 12,
pp. 3127-3134,
12/15/1992
Copyright © 1992 by The American Society of Hematology
