Human serum transferrin cobalt complex: Stability and cellular uptake of cobalt

Transferrin (Tf) receptor expression is up-regulated on tumour cells. The human serum iron transport protein transferrin (Tf) can bind to many metals including gallium and cobalt. Cobalt has a positron-emitting isotope with a half-life of 18 h and would thus be a useful isotope for imaging purposes. This study has examined the stability of the Co–Tf in the presence of serum and albumin and the uptake of radioactive Co from Co–Tf by tumour cells. Dialysis of 57Co–Tf with serum or with apo-Tf resulted in loss of most 57Co from the complex. The time course of Co uptake from cells incubated with Co–Tf showed an initial rapid association with cells, then a slower rate of accumulation, that is, a similar uptake profile to that of iron. Competition and displacement experiments showed that uptake specifically occurred by interaction with Tf receptors.

Tumours express higher levels of transferrin receptors than do normal tissues. To investigate the suitability of human serum transferrin (Tf) complexed with radioisotopes of Co for tumour imaging, the stability and accumulation of 57Co by tumour cells incubated with 57Co-Tf were investigated. Stability studies were carried out by dialysis of trace quantities of 57Co-Tf with challenge solutions and by measurement of change in absorbance at 405 nm of Co-Tf during incubation with albumin. Figure shows uptake of 57Co by MCF7 cells incubated with 57Co-human serum transferrin.Figure optionsDownload as PowerPoint slide