The invention relates to a CuII complex in which the copper ion is coordinated to an aromatic, non-aromatic or aliphatic dicarboxylate ligand via an oxygen atom of one of the carboxylate groups, and two phenanthroline, or phenanthroline derivative, ligands, and the use of the metal complexes as self-activating nucleases to treat cancer and other proliferative disorders. In one embodiment, the CuII complex is a dinuclear complex comprising two CuII ions, in which the aromatic, non-aromatic or aliphatic dicarboxylate ligand is a bridging ligand, and in which each copper is coordinated to the bridging ligand via the carboxylate groups.
