Toxic effects of gallium nitrate on Friend erythroleukemia cells

Background: Gallium (Ga), is a group III transition metal with proven antitumor activity which shares certain characteristics with iron in that it binds tightly to transferrin and lactoferrin and can be incorporated into ferritin. Iron is essential for cell growth and viability, while iron deprivation results in inhibition in the synthesis of deoxyribonucleotides. Due to the essential role of iron in erythroleukemic cells, we were interested in assessing whether Ga could inhibit growth of these cells, whether Ga-induced blockade of iron utilization induces cell death and, if so, whether this effect could be reversed by addition of hemin. Methods: The effects of Ga nitrate on several parameters of cell viability were examined. Cell cycle status and cellular porphyrins were analyzed by flow cytometry. The effect of intracellular iron on the growth-inhibitory properties of Ga was studied by loading Friend erythroleukemic cells (FLC) with iron from hemin. Results: Following treatment of FLC with Ga, flow cytometry revealed cell cycle changes and increased fluorescence intensity. Transmission electron microscopy and spectral imaging analysis revealed morphological changes as well as changes in chromatin condensation and cytoplasmic integrity. X-ray microanalysis revealed Na⁺ and Cl^- influx. Hemin was unable to reverse the Ga-induced effects. Conclusions: Addition of Ga to the growth medium of cultured FLC results in an intracellular iron deficiency which cannot be reversed by hemin, and consequently leads to cell death.