Transferrin receptors associate with drug resistance in cancer cells.

Transferrin mediates its growth promoting properties through transferrin receptors, which are increased on cancer cells. We have studied drug-sensitive and drug-resistant cancer cells by using quantitative flow cytomerty with fluorochrome labelled transferrin and antibody to transferrin receptor, and we have found that drug-resistant cells have more transferrin receptors than drug-sensitive cells. This finding was confirmed and extended by using isotopically labelled ligand and by correcting for differences in cell surface areas. We also found that the number of transferrin receptors could be down-regulated by calcium channel blockers, and that such down-regulation diminished drug resistance, suggesting a hitherto unrecognised role for transferrin receptors in drug resistance.