Bis-phenanthroline derivatives as suitable scaffolds for effective G-quadruplex recognition

Selective recognition of DNA folding is central to multiple biological and pharmacological applications aimed at precise targeting of distinct genomic regions. Here, we focused on the recognition of physiologically relevant G-quadruplex (G-4) structures by bis-phenanthroline (bis-Phen) ligands containing two Phen moieties covalently linked through an amine or thioether bond. The transition metal ions Mn2+, Ni2+, Cu2+, and the biologically relevant Mg2+ and Zn2+ efficiently form 1 : 1 bis-Phen complexes characterised by a large planar structure fit to successfully recognise G-quartet arrangements. Interestingly, metal ion complexation dramatically affects ligand-stabilising effects on G-quadruplex, the melting temperature of the folded structure being increased up to 30 ◦C at ligand concentrations as low as 1 mM in the presence of Ni2+ and Cu2+. In addition, the test complexes were able to induce G-4 formation from essentially unfolded G-rich sequences even in the absence of K+ ions as shown by gel shift and circular dichroism experiments. In line with their G-4 stabilising properties bis-Phen complexes are effective inhibitors of telomerase activity, Ni(II) complexes being effective in the sub-micromolar range. This is combined with lack of unselective DNA-damaging activity and short-term cellular toxicity, which makes the novel compounds (above all their Ni(II) complexes) interesting antiproliferative drug leads.