LABELING OF POLYPEPTIDES WITH TC-99M USING A DEXTRAN SPACER

Radioimmunoscintigraphy and other forms of scintigraphy are becoming i ncreasingly important as tools in detection and evaluation of cancer d iseases. Several radionuclides can be considered as radiolabel; howeve r, Tc-99m may be the most suitable because of easy availability and ne ar ideal physical properties. This study describes how dextran is coup led to a monoclonal anticytokeratin antibody, epidermal growth factor, and somatostatin through stable amine bonds. The dextran moiety could then be labeled with 40-62 MBq of Tc-99m. The labeling efficiency was 60-94%, determined by gel filtration or TLC. The specific binding cou ld be con -siderably preserved after the dextranation, the antibody re tained >90% of its activity, epidermal growth factor bound with >90% s pecificity to receptor-expressing tumor cells, and somatostatin showed similar to 40% specific binding to rat adrenal homogenates. Because s omatostatin only has a transient half-life in vivo, the in vivo plasma half-life of somatostatin-dextran was tested in normal female Sprague -Dawley rats. The result showed a strong enhancement of the plasma hal f-life that was dependent on two compartments, 4 and 8 h.