Polyimidazole ligands: Copper(II) complexes and antiproliferative activity in cancer cells

The design of novel chelators for therapeutic applications has been the subject of extensive research to address various diseases. Many chelators can manipulate the levels of metal ions within cells and effectively modulate the metal excess. In some cases, chelators show significant toxicity to cells. We investigated polyimidazole ligands by potentiometry and UV-Vis spectroscopy for their ability to form copper(II) complexes. We also compared the antiproliferative activity of the polyimidazole ligands and their copper(II) complexes with polypyridine ligands in CaCo-2 (colorectal adenocarcinoma), SH-SY5Y (neuroblastoma) and K562 (chronic myelogenous leukemia) cells and normal HaCaT (keratinocyte) cells. Polyimidazole ligands are less cytotoxic than their analogous polypyridine ligands. All polyimidazole ligands, except the tetraimidazole ligand for K562 cells, did not show any significant effect on the viability of cancer and normal cells. In contrast, the cytotoxic activity of polypiridine ligands was also observed in normal cells with IC₅₀ values similar to those of cancer cells. Tetraimidazole ligand, the only ligand active on the leukemic K562 cell line, induced caspase-dependent apoptosis and increased intracellular reactive oxygen species production with mitochondrial damage. The low cytotoxicity of the polyimidazole ligands, even if it limits their use as anticancer agents, could make them useful in other medical applications, such as in the treatment of metal overload, microbial infections, inflammation or neurodegenerative disorders.