Comparison of several indium-111 ligands in labeling blood cells: effect of diethylpyrocarbonate and CO2

The effect of oxine sulfate, oxine sulfonate, tropolone, and Merc (2 mercaptopyridine-1-oxide) were compared with oxine, with respect to their capability of labeling blood cells when complexed to indium-111 (111In). Indium-111 oxine sulfate performed similarly to [111In]oxine with regard to cell labeling capability. Indium-111 oxine sulfonate had no labeling ability. Indium-111 tropolone and Merc were not superior to [111In]oxine as cell labeling agents. Carbon dioxide (CO2) and a CO2 generating compound, diethyl pyrocarbonate, dramatically improved the cell labeling ability in plasma of [111In]tropolone and Merc. In the case of oxine, this improvement was less distinct. Theoretical aspects of the CO2 cell labeling stimulating effect are discussed in terms of intra- and extracellular transferrin and lactoferrin iron (indium) binding capacity. Indium-111 tropolone behaved favorably with respect to inhibition of leukocyte migration, compared with oxine and Merc. Combined with the property of easy cell labeling and good solubility in water, also in the complexed state, tropolone must be regarded as the most suitable cell labeling ligand.