Studies on high specific activity labeling of proteins using bifunctional chelates: Ga-67-DF-HSA

In the present work, carbodiimide was chosen as a coupling agent, and desferrioxamine as the chelating agent. Desferrioxamine forms high stability complexes with trivalent metals such as Fe(III), Ga(III), and In(III). The stability of the Ga-desferrioxamine complex appears to be higher than that of the Ga-transferrin complex. However, the specific activity of such a Ga-67-labeled desferrioxamine-HSA (DF-HSA) conjugate was significantly lower than theoretically calculated. Some of the possible reasons for this low radiolabeling are: 1) the coupling efficiency is extremely low, 2) the coupling efficiency is acceptable but the coupled chelons are not available to bind metals because they are ''buried'' in the protein molecule, or 3) the metal binding capability has been altered through the coupling process. The present work was intended to determine which, if any, of these explanations might be valid