Complexes of copper(II) with tetradentate S,O-ligands: Synthesis, characterization, DNA/albumin interactions, molecular docking simulations and antitumor activity.

Four new complexes of copper(II) with S,O-tetradentate ligands, derivatives of thiosalicylic acid, encompassing an ethylene-, propylene-, butylene- and pentylene- bridge, were synthesized and characterized by microanalysis, molecular conductance and infrared (IR) spectra. The structures were assumed based on the previously mentioned analyses and confirmed with the results of electron paramagnetic resonance (EPR) spectra. The reactivity of complexes towards L-methionine (L-Met), L-cysteine (L-Cys) and guanosine-5'-monophosphate (5'-GMP) was also examined. Complex C1 ([Cu(S,O-ethylene-thiosalicylic acid)(HO)]) containing two inert methylene groups in the side chain of ligand shows the highest reactivity, while the least reactive is complex C4 ([Cu(S,O-pentylene-thiosalicylic acid)(HO)]) with five methylene groups. All complexes showed the highest reactivity towards L-Met and the lowest reactivity towards 5'-GMP. The interactions of complexes C1-C4 with calf thymus DNA (ct-DNA) were examined by ultraviolet-visible (UV-Vis) absorption and fluorescence spectral studies, revealing good DNA interaction abilities. All synthesized complexes C1-C4 show to interact with human serum albumin (HSA) with high values of binding constants. Complexes interaction with DNA/HSA was also confirmed using molecular docking simulations. All synthesized complexes reduce viability of human colon, breast and lung cancer cells, evaluated by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) colorimetric technique. The complex [Cu(S,O-pentylene- thiosalicylic acid)(HO)] showed the highest binding affinity constants to DNA/HSA and highest cytotoxicity, thus presenting a good candidate for further pharmacological research in the field of colon, breast and lung cancer therapy.