Anti-Proliferation and DNA Cleavage Activities of Copper(II) Complexes of N₃O Tripodal Polyamine Ligands

Four ligands based on the 2-tert-butyl-4-X-6-{Bis[(6-methoxy-pyridin-2-ylmethyl)-amino]-methyl}-phenol unit are synthesized: X = CHO (HLCHO), putrescine-pyrene (HLpyr), putrescine (HLamine), and 2-tert-butyl-4-putrescine-6-{Bis[(6-methoxy-pyridin-2-ylmethyl)-amino]-methyl}-phenol (H2Lbis). Complexes 1, 2, 3, and 4 are formed upon chelation to copper(II). The crystal structure of complex 1 shows a square pyramidal copper center with a very weakly bound methoxypridine moiety in the apical position. The pKa of the phenol moiety is determined spectrophotometrically at 2.82-4.39. All the complexes show a metal-centered reduction in their CV at E-p(c,red) = -0.45 to -0.5 V vs. SCE. The copper complexes are efficient nucleases towards the phi X174 DNA plasmid in the presence of ascorbate. The corresponding IC50 value reaches 7 mu M for 2, with a nuclease activity that follows the trend: 2 > 3 > 1. Strand scission is promoted by the hydroxyl radical. The cytotoxicity is evaluated on bladder cancer cell lines sensitive (RT112) or resistant to cisplatin (RT112 CP). The IC50 of the most active complexes (2 and 4) is 1.2 and 1.0 mu M, respectively, for the RT112 CP line, which is much lower than cisplatin (23.8 mu M).