To improve the solubility in aqueous media of bis(citronellalthiosemicarbazonato)copper(II) [Cu(S-tcitr)2], a compound that is effective in inhibiting cell growth of U937 cell line, the ligand was modified adding an ethylmorpholine group. [Cu(S-tcitr)2] and [Cu(Etmorph-S-tcitr)2] cytotoxic effects are compared using as a model U937 cells. [Cu(Etmorph-S-tcitr)2] results more effective in cell growth inhibition (IC50: 2.3 vs 14.8 μM). Apoptosis in [Cu(Etmorph-S-tcitr)2] treated cells was apparent after 8 h, with increased caspase activities, and these effects were not observed for [Cu(S-tcitr)2]. During the exposure to [Cu(Etmorph-S-tcitr)2], ROS (reactive oxygen species) and TBARS (Thiobarbituric acid reactive substances) significantly increased, coupled with reduced glutathione (GSH) levels and significant activation of superoxide dismutase (SOD). These intracellular scavengers seem to limit the early ROS and TBARS increases in U937 cells exposed to [Cu(S-tcitr)2]. Both complexes interacted in vitrowith naked DNA: UV–visible and CD titration reveal that they can induce DNA structure modifications in a distinct way. Furthermore, the complexes induced DNA damage on U937 cells at concentrations higher than IC50. The mechanisms of action and the effects of these two complexes are remarkably different even though they have the same coordination geometry around copper(II) and differ only for the presence of the ethylmorpholine group.
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