The mechanism of action of the clinically used iron(III) chelator, desferrioxamine (DFO), on preventing iron (Fe) uptake from transferrin (Tf) has been investigated using the human melanoma cell line SK-MEL-28. This investigation was initiated due to the paucity of information on the mechanisms of action of DFO in neoplastic cells and because recent studies have suggested that DFO may be a useful antitumor agent. The effect of DFO was dependent on incubation time. After a 2-h incubation, DFO acted like the extracellular chelators, EDTA and diethylenetriaminepentaacetic acid, because there was little inhibition of Fe-59 uptake from Tf. In contrast, after a 24-h incubation, DFO (0.5 mM) efficiently reduced internalized Fe-59 uptake from Tf to 18% of the control value. These observations suggested the existence of a kinetic block to the entry of the apochelator to intracellular Fe pools and/or to the exit of the DFO-Fe-59 complex. Indeed, cellular fractionation demonstrated that, in contrast to the decrease in the percentage of Fe-59 in the ferritin and membrane fractions, a marked increase in the percentage of Fe-59 present in the ferritin-free cytosol occurred. These observations suggested an accumulation of the DFO-Fe-59 complex within the cell. The highly lipophilic Fe chelator, pyridoxal isonicotinoyl hydrazone, was far more effective than DFO at preventing Fe-59 uptake from Tf, illustrating the importance of membrane permeability for effective Fe chelation. Desferrioxamine at a concentration of 1 mm decreased internalized I-125-Tf uptake to 70% of the control. However, the decrease in Fe-59 uptake observed could only be partially accounted for by a decrease in Tf uptake, and it appeared that DFO was chelating Fe-59 at an intracellular site consistent with the transit Fe pool. The results are discussed in the context of the use of Fe chelators as effective antineoplastic agents.
|Publication status||Published - 1994|