Transferrin receptors and gallium-67 uptake in vitro

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Abstract
The relationship was studied between the number of transferrin-receptor positive cells and in vitro uptake of67Ga and125I-labeled transferrin in human cell lines, including two normal cell lines (WI-38 and foreskin fibroblasts), two transformed cell lines (AV-3 amnionic cells and Chang liver cells), and two neoplastic cell lines (HEp-2, larynx cancer and HeLa, cervical cancer). Transferrin receptors were determined by an indirect immunofluorescence technique based on their ability to bind purified human transferrin. Gallium-67 uptake was determined after a 24-h incubation of cells with Ga-67 in the presence and absence of transferrin (0–2.5 mg/ml).125I-labeled transferrin uptake was also obtained after a 24-h incubation. The fraction of cells with transferrin receptors was low in normal cell lines (3% and 9%), intermediate with transformed cell lines (33% and 49%), and high in neoplastic cell lines (59% and 61%). Transferrin stimulated67Ga uptake by all six cell lines. However, there was poor correlation between the number of transferrin-receptor positive cells and67Ga uptake either in the presence (r=0.21) or absence (r=0.46) of human transferrin. Likewise, there was poor correlation between the number of transferrin-receptor positive cells and125I-labeled transferrin uptake (r=0.35). In contrast, the correlation between67Ga uptake (in the presence of transferrin) and125I-labeled transferrin uptake was highly significant (r=0.96). These results suggest that human cell lines in culture are capable of both transferrin-dependent and transferrin-independent uptake of67Ga.