Studies on the uptake of 67 Ga and 59 Fe and the binding of transferrin by cultured mouse tumour cells.

Abstract

Two cultured mouse tumour cell lines, HPC-108 (myeloma) and WEHI-22 (T lymphoma), were used in an investigation of transferrin promotion of 67 Ga. and 59 Fe uptake by malignant cells. The effectiveness of added human transferrin could be readily demonstrated on the cells in culture medium containing foetal calf serum, but transferrin-promoted uptake varied considerably between different batches of the serum. In serum-free medium, transferrin at concentrations as low as 1 μg ml −1 promoted substantial uptake of 67 Ga and maximal uptake of 59 Fe. Saturation of the transferrin with iron pre-empted its activity toward both tracers, indicating their transport requires binding to the same sites on transferrin. High affinity receptors for transferrin on the tumour cells were characterized by measurement of the binding of diferric 125 I-labelled human transferrin to whole cells at 15°C. The HPC-108 line possessed 4 × 10 5 receptors per cell, WEHI-22 1.5 × 10 5 per cell, the EMT6 sarcoma line only 5 × 10 4 per cell, all with a dissociation constant of 1.4–2.3 nM. Some aspects of 67 Ga. and 59 Fe uptake were explained by the characteristics of this receptor and the previously demonstrated difference between the two tracers in affinity for transferrin.