Synthesis, characterization, DNA/BSA interactions and anticancer activity of achiral and chiral copper complexes

Abstract

Six novel copper(II) complexes of [CuL¹Cl]ClO₄ (1), [CuL¹(acac)]PF₆ (2), [CuL^2(R)Cl]₂(PF₆)₂ (3), [CuL^2(S)Cl]₂(PF₆)₂ (4), [CuL^2(R)(acac)]PF₆ (5) and [CuL^2(S)(acac)]PF₆ (6), (L¹ = 1-naphthyl-N,N-[bis(2-pyridyl)methyl]amine, L² = R/S-1-naphthyl-N,N-[bis(2-pyridyl)methyl]ethanamine, acac = diacetone) were synthesized to serve as artificial nucleases. All complexes were structurally characterized using X-ray crystallography. The crystal structures showed the presence of distorted square-planar CuLCl (1, 3 and 4) and distorted tetragonal-pyramidal CuL(acac) (2, 5 and 6) geometry. The interaction of these complexes with calf thymus DNA (CT-DNA) was researched by means of several spectroscopy methods, which indicated that the complexes were bound to CT-DNA by an intercalation binding mode. DNA cleavage experiments revealed that the complexes exhibited remarkable DNA cleavage activities in the presence of H₂O₂, and single oxygen (¹O₂) or hydroxyl radicals may serve as the major cleavage active species. In particular, the in vitro cytotoxicity of the complexes on four human cancer cell lines (HeLa, MCF-7, Bel-7404 and HepG-2) demonstrated that the six compounds had broad-spectrum anti-cancer activity with low IC₅₀ values. The stronger cytotoxicity and DNA cleavage activity of the chiral enantiomers compared with chiral analogues verified the influence of chirality on the antitumor activity of complexes. Meanwhile, the protein binding ability was revealed by quenching of tryptophan emission with the addition of complexes using BSA as a model protein. The results indicated that the quenching mechanism of BSA by the complexes was a static process.