67Ga and 59Fe uptake in human melanoma cells

Abstract

Human melanoma cells were incubated with 67Ga-transferrin and 59Fe-transferrin in the presence of free unlabeled iron as well as 59Fe and 67Ga and increasing P0 4 3− ion concentration. It was observed that factors which influence the uptake of 59Fe by melanoma cells have a similar effect on the uptake of 67Ga by the tumor cells. Furthermore, it was noted that when melanoma cells were incubated with either 125SI-transferrin- 59Fe or 125I-transferrin- 67Ga the 1251 activity associated with the cells was similar in both cases and remained constant over the various incubation times. However, the rate of uptake of 59Fe and 67Ga by the tumor cells differed. The uptake of 59Fe was very rapid over the first 1 1 2 h . After that time the rate of uptake was reduced, while in the case of gallium the uptake was linear over the time period tested. This would suggest that 125I-transferrin- 59Fe has a higher affinity for the cell surface binding site than does 125I-transferrin- 67Ga. It may also further suggest that for 59Fe the rate of transferrin receptor complexation is close to, or exceeds, the rate-limiting step which is responsible for transporting the 59Fe across the melanoma cell membrane. This does not appear to be the case with gallium.