Mono- vs. Bis-Guanyl Hydrazone-Decorated Tricyclic Scaffolds: Effects on G-Quadruplex Binding and Selectivity

Mono- and bis-guanyl hydrazone-functionalized tricyclic compounds were here designed and investigated as putative G-quadruplex ligands in the context of anticancer drug development. The G-quadruplex on Controlled Pore Glass (G4-CPG) assay, a fast and easy screening method based on affinity chromatography for identifying potential G-quadruplex binders, together with biophysical techniques such as circular dichroism and fluorescence spectroscopy, demonstrated a higher selectivity of mono- with respect to disubstituted derivatives in recognizing G-quadruplexes from telomeric and oncogenic DNA regions vs. duplexes. Among the mono-substituted compounds, higher G-quadruplex selectivity was found for those containing the pyrido [3,4-b]indole and dibenzofuran scaffolds compared to the 9H-fluorene, 9H-carbazole, and dibenzothiophene ones. Molecular docking studies suggested that the investigated ligands bound the hybrid telomeric G-quadruplex model by adopting a coplanar arrangement of the core and guanyl hydrazone moieties, both stacked on the 5′-G-quartet, while in the interaction with the parallel oncogenic G-quadruplex model the guanyl hydrazone moieties pointed towards the grooves/loops. Finally, biological assays highlighted the higher potential of mono-guanyl hydrazone-derivatized tricyclic compounds as selective anticancer agents, showing higher anticancer activity and selectivity of action than the bis-guanyl hydrazone derivatives.