Effects of different transferrin forms on transferrin receptor expression, iron uptake, and cellular proliferation of human leukemic HL60 cells. Mechanisms responsible for the specific cytotoxicity of transferrin-gallium.

Abstract

We have previously shown that human leukemic cells proliferate normally in serum-free media containing various transferrin forms, but the addition of transferrin-gallium leads to inhibition of cellular proliferation. Because gallium has therapeutic potential, the effects of transferrin-gallium on leukemic cell proliferation, transferrin receptor expression, and cellular iron utilization were studied. The cytotoxicity of gallium is considerably enhanced by its binding to transferrin and cytotoxicity can be reversed by transferrin-iron but not by other transferrin forms. Exposure to transferrin-gallium leads to a marked increase in cell surface transferrin binding sites, but despite this, cellular 59Fe incorporation is inappropriately low. Although shunting of transferrin-gallium to another cellular compartment has not been ruled out, other studies suggest that transferrin-gallium impairs intracellular release of '9Fe from transferrin by interfering with processes responsible for intracellular acidification. These studies, taken together, demonstrate that inhibition of cellular iron incorporation by transferrin-gallium is a prerequisite for inhibition of cellular proliferation.

Resistance to the Antitumor Agent Gallium Nitrate in Human Leukemic Cells Is Associated with Decreased Gallium/Iron Uptake, Increased Activity of Iron Regulatory Protein-1, and Decreased Ferritin Production

“…Whereas the inhibitory effect of gallium on iron uptake by S and R CCRF-CEM cells was consistent with earlier results in other gallium-sensitive cell lines (9), an unexpected finding was that iron uptake by R cells was consistently less than that by S cells even after extended growth of R cells in the absence of gallium. Since earlier studies have shown that cells incorporate iron and gallium by similar Tf-dependent and -independent transport systems (6 -8), we questioned whether the uptake of gallium by R cells was also decreased.…”

“…Since Tf is known to enhance gallium uptake by cells (6,7,9), further experiments were performed to determine whether increasing the amount of exogenous Tf would enhance gallium uptake and increase its cytotoxicity in R cells. As shown in Fig.…”

Supplementation of Endothelial Cells with Mitochondria-targeted Antioxidants Inhibit Peroxide-induced Mitochondrial Iron Uptake, Oxidative Damage, and Apoptosis

“…On the day of treatment the medium was replaced with DMEM containing 2% FBS, and the cells were allowed to adjust to the medium conditions. 0.2 Ci of 55 Fe (as ferric chloride) was added to the medium, and its levels were measured after 4 h. Cells were washed with DPBS and lysed with PBS containing 0.1% Triton X-100, and the radioactivity was counted in a beta counter (37,38).…”

Role of oxidative stress in the induction of metallothionein-2A and heme oxygenase-1 gene expression by the antineoplastic agent gallium nitrate in human lymphoma cells

“…Investigations directed at elucidating gallium's mechanism of action are important since they may provide insight into tumor biology and may help identify subtypes of lymphomas and other malignancies more likely to respond to treatment with this agent. Prior studies have shown that gallium shares properties with iron in that it binds to transferrin in the circulation and can be incorporated into cells via transferrin receptor-mediated endocytosis [12][13][14][15][16]. Within the cell, gallium disrupts iron homeostasis and interferes with deoxyribonucleotide synthesis by inhibiting the activity of the iron-dependent R2 subunit of ribonucleotide reductase [15,[17][18][19].…”

“…Prior studies have shown that gallium shares properties with iron in that it binds to transferrin in the circulation and can be incorporated into cells via transferrin receptor-mediated endocytosis [12][13][14][15][16]. Within the cell, gallium disrupts iron homeostasis and interferes with deoxyribonucleotide synthesis by inhibiting the activity of the iron-dependent R2 subunit of ribonucleotide reductase [15,[17][18][19]. Lymphoma cells exposed to gallium nitrate undergo apoptosis through the "intrinsic" pathway that involves proapoptotic Bax, release of cytochrome c from mitochondria, and the activation of effector caspase-3 [20].…”