Comparative Effect of the Oral Iron Chelators ICL670A and CP20 on Cell Proliferation, Apoptosis and Polyamine Metabolism in Rat and Human Liver Cell Cultures.

Iron overload increases the mitotic index in rat hepatocyte cultures stimulated by EGF. Iron, implicated in tumoral cell proliferation, promotes the development of the hepatocellular carcinoma. Conversely, iron chelation decreases cell proliferation. Polyamines play also an important role in cell proliferation. The purpose of the present work was to compare the effect of the two oral iron chelators ICL670A and CP20 on cell proliferation, apoptosis and polyamine metabolism in rat and human liver cell cultures.

We used three experimental models: the rat hepatoma cell line FAO, the rat liver epithelial cell line RLEC and the human hepatoma cell line HUH7. Chelator cell uptake was analyzed by mass spectrometry. DNA replication and cell viability were measured by thymidine incorporation and mitochondrial succinate dehydrogenase activity. Cytotoxicity was evaluated by extracellular LDH activity. Cell cycle analysis was performed by flow cytometry. Apoptosis was quantified by DNA fragmentation and caspase 3 activity. Polyamine metabolism was analyzed by measuring their intracellular concentrations by mass spectrometry as well as the ornithine decarboxylase (ODC) and spermine-spermidine acetyl transferase (SSAT) mRNAs levels. ICL670A entered the cells four times better than CP20. We observed that ICL670A (20 μM) decreased DNA replication (−75%) and cell viability (−40%) while a comparable CP20 stoechiometric concentration (30 μM) had no significant effect. ICL670A exhibited also a higher cytotoxicity than CP20. The decrease in DNA replication induced by ICL670A was correlated to a cell cycle block in S phase; CP20 (30 μM) increased slightly the cell number in G2/M phase while a higher CP20 concentration (150 μM) blocked clearly cell cycle in G2/M phase. By measuring DNA fragmentation and the activity of the executioner caspase 3, we demonstrated a high apoptotic effect of ICL670A (20 μM) compared to CP20 (30 μM). In the HUH7 human cell line, we observed that ICL670A (20 μM) decreased the intracellular levels of polyamines which was correlated to a drop in ODC and SSAT mRNAs levels. Conversely, an increase in SSAT mRNA level was observed in the presence of CP20 (150 μM) leading to an enhancement of putrescine and spermidine levels.

In conclusion, ICL670A and CP20 inhibit cell proliferation by two distinct ways. ICL670A compared to CP20:

1. enters better the cells;

2. exerts a higher antiproliferative and apoptotic effect;

3. modulates polyamine metabolism by inhibiting ODC and SSAT enzyme activities.