DTPA Groups Research Articles

Characterization of indium-111 labeled recombinant tissue plasminogen activator for the imaging of thrombi.

The in vitro functional properties of recombinant tissue plasminogen activator (rt-PA), its biodistribution in mice, and its pharmacokinetics and clot localization properties in dogs have been investigated after labeling rt-PA with 111In. The rt-PA was coupled with the bicyclic anhydride of DTPA using standard methodology. Amidolytic and fibrinolytic assays showed retention of protein activity when rt-PA was conjugated with an average of one DTPA group or less per molecule. Size exclusion HPLC showed each preparation to be radiochemically pure with 111In bound exclusively to the attached DTPA groups. Biodistribution in mice showed major accumulation of activity in the liver and kidneys. After administration of 0.5-1.0 mg of the labeled protein to dogs, blood activity decreased with a half time of approximately 5 min in agreement with previous reports of rapid blood clearance. Largely because of decreased blood levels, clot: blood ratios of labeled protein increased rapidly, in one study reaching 6.3 after 31 min, and satisfactory images of fibrin thrombi were obtained. The rt-PA may be labeled with 111In without destroying the ability of the protein to localize in clot and images of forming clot can be obtained with this agent within 1 h after administration.

Binding properties of 111In-diethylenetriaminepentaacetic acid (DTPA)-fragment E 1,2, a fibrin-specific probe, are dependent on use of protecting complex during attachment of DTPA groups

Fragments E 1 and E 2, plasmic degradation products of crosslinked fibrin, bind specifically to polymers of fibrin. A mixture of these fragments, denoted as fragment E 1,2, was radiolabeled with 111In after covalently attaching metal chelating groups (diethylenetriaminepentaacetic acid, DTPA) to the fragment, using two approaches. In the first approach, DTPA groups were attached directly to purified fragment E 1,2. In the second approach, attachment sites of DTPA groups were directed away from the active region of the molecule by having fragment E 1,2 bound in complex, with its active sites protected during the derivatization. Direct attachment of DTPA groups to fragment E 1,2 resulted in complete loss of binding to fibrin in vitro. When derivatized in complex, 111In-DTPA-fragment E 1,2 retained a higher degree of binding to human fragment DD and human plasma clots in vitro than did radioiodinated fragment E 1, even when up to eight DTPA groups were attached per molecule of fragment E 1,2.