Common Pathway for K562 Cells Endocytosis and Release of GaC‐Tf and Ga2‐Tf via a Transferrin Receptor

Abstract There has been an increasing interest in the use of gallium in anticancer activity. However, whether the uptakes of two species of transferrin, including digallium transferrin (Ga 2 ‐Tf) and the C‐terminal monogallium transferrin (Ga C ‐Tf) by cells, are different is not well understood. In this work the mechanism of both species passing in and out K562 cells has been established by using 125 I‐labeled transferrin. There were about (1.5±0.08)×10 5 binding sites per cell surface. Both Ga 2 ‐Tf and Ga C ‐Tf were recycled to the cell exterior with a protracted endocytic cycle compared to apotransferrin (apoTf). The cycling time from the internalization to release was calculated about t 1/2 = (3.15±0.055) min for apoTf, t 1/2 = (4.69±0.09) min for Ga 2 ‐Tf and t 1/2 = (4.78±0.15) min for Ga C ‐Tf. The result implies that metal dissociating from transferrin in acidic endosomes was likely to be the key step. Both Ga 2 ‐Tf and Ga C ‐Tf into K562 cells are transferrin receptor‐mediated process with a similar rate of endocytosis and release. Our present observations provide useful information for better targeted drugs in specific therapy.