Structure-activity relationships of ATCUN-based Cu(II) complexes with large chelate rings: interplay of ROS...

Since the discovery of DNA cleavage and anticancer activity of the simplest Cu(II) ATCUN complex (peptide ligand: Gly-Gly-His, GGH) in 1983, systematic biological enhancements by derivatives have not been achieved. The stable 5,5,6-chelate ring structure provided by the original GGH ligand hampers efficient ROS production via Cu redox cycling (Cu(II/I)). In this work, we demonstrate that the incorporation of 7,5,6- and 7,6,6-chelates (Gly or β-alanine in the second peptide position, respectively) in combination with N-terminal design elements, such as γ-aminobutyric acid (GABA), 3,5-substituted (CF₃-, CH₃-) pyrazolyl and triazolyl units, provides an effective strategy to reinstate biological activity regarding ROS generation (determined via fluorescence spectroscopy and gel electrophoresis), DNA cleavage (gel electrophoresis) and DNA binding (fluorescence, UV/VIS and CD spectroscopy). Among the series of studied Cu(II) complexes, the metallopeptide with an amine group at the N-terminus (GABA) combined with a 7,6,6-chelate (β-alanine) system exhibits the highest overall biological activity, whereas a triazolyl moiety, independent of the chelate ring size (Gly: 7,5,6 and β-alanine: 7,6,6), leads to efficient hydroxyl radical generation. Computational studies based on an extensive conformational search of the metallopeptides, followed by an energy refinement at the level of Density Functional Theory (DFT), were used to elucidate the structure-activity relationship.