Coagulation in blood is initiated when coagulation factor VII (FVII) binds to exposed TF and is activated to FVIIa, and the TF/
FVIIa complex may therefore provide a marker of vascular injury potentially applicable in diagnostic imaging of acute
gastrointestinal (GI) bleeding. Methods: Recombinant FVIIa (rFVIIa) was radiolabeled with technetium-99m in a direct
labeling reaction using the ‘carbonyl approach’ using the IsoLink
s
carbonyl labeling agent. The properties of 99mTc(CO)3-
rFVIIa complex was analyzed by TCA precipitation, HPLC and FVIIa functional integrity was tested in in vitro assays.
Results: Labeling of rFVIIa was possible without tagging with a chelater. Incorporation of radioactivity depended strongly
on rFVIIa concentration and temperature. More than 95% incorporation was achieved after 30 min at 451C with 0.76 mg/ml
rFVIIa. 99mTc(CO)3-rFVIIa was obtained in 46% radiochemical yield and in 495% radiochemical purity. Pull down
experiments showed that the biological activity (binding to tissue factor and to anti-FVII antibody) of the radiolabelled
product remained intact in the formulation mixture as well as in human serum. By computer modeling analysis, two
candidate sites for stabilizing the 99mTc(CO)3
1-ligand structure in FVIIa were identified. Conclusion: Radiolabelled rFVIIa
derivatives may represent a novel tool for the diagnosis of acute gastrointestinal bleeding lesions.