Proteins labelling with indium

Open-chain ligands were the first evaluated for complexation studies with indium and yttrium. The use of diethylenetriaminepentaacetic acid (DTPA) anhydride permitted early evaluation of labeled chelate-conjugates (Figure 2).80 The use of this activated chelating agent was quite popular, until the drawbacks associated with its crosslinking of proteins became apparent. 

Initial work on radiolabeling of autologous polymorphonuclear leukocytes was performed by McAfee and Thakur [30]. One of the compounds they examined was the nonpolar, lipid-soluble complex 8-hydroxyquinoline (oxine) (Fig. 2). Indium forms a neutral, lipid-soluble complex with oxine which will penetrate cellular membranes. Subsequently, studies showed that this technique could be used to label leukocytes and platelets with retention of biological activity [31]. After diffusing intracellularly, the ln-oxine complex dissociates and the " In is bound to nuclear and cytoplasmic proteins (Fig. 3) [32-34]. Due to the high stability of indium with the blood protein transferrin, it is necessary to label platelets or WBCs in the absence of plasma. In addition, a final wash of the labeled cells using plasma will remove any loosely bound indium by complexation with transferrin [35,36]. 

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