Tuning the ring strain effect in acridine derivatives on binding affinity with G-quadruplex-DNA: A computational and experimental study

Structure-Activity Study on Substituted, Core-Extended, and Dyad Naphthalene Diimide G-Quadruplex Ligands Leading to Potent Antitrypanosomal Agents

Several G-quadruplex nucleic acid (G4s) ligands have been developed seeking target selectivity in the past decade. Naphthalene diimide (NDI)-based compounds are particularly promising due to their biological activity and red-fluorescence emission. Previously, we demonstrated the existence of G4s in the promoter region of parasite genomes, assessing the effectiveness of NDI-derivatives against them. Here, we explored the biological activity of a small library of G4-DNA ligands, exploiting the NDI pharmacophore, against both Trypanosoma brucei and Leishmania major parasites. Biophysical and biological assays were conducted. Among the various families analyzed, core-extended NDIs exhibited the most promising results concerning the selectivity and antiparasitic effects. NDI 16 emerged as the most potent, with an IC50 of 0.011 nM against T. brucei and remarkable selectivity vs MRC-5 cells (3454-fold). Fascinating, 16 is 480-fold more potent than the standard drug pentamidine (IC50 = 5.3 nM). Cellular uptake and parasite localization were verified by exploiting core-extended NDI red-fluorescent emission.

Enhanced sampling molecular dynamics simulations correctly predict the diverse activities of a series of stiff-stilbene G-quadruplex DNA ligands

Ligands with the capability to bind G-quadruplexes (G4s) specifically, and to control G4 structure and behaviour, offer great potential in the development of novel therapies, technologies and functional materials. Most known ligands bind to a pre-formed topology, but G4s are highly dynamic and a small number of ligands have been discovered that influence these folding equilibria. Such ligands may be useful as probes to understand the dynamic nature of G4 in vivo, or to exploit the polymorphism of G4 in the development of molecular devices. To date, these fascinating molecules have been discovered serendipitously. There is a need for tools to predict such effects to drive ligand design and development, and for molecular-level understanding of ligand binding mechanisms and associated topological perturbation of G4 structures. Here we study the G4 binding mechanisms of a family of stiff-stilbene G4 ligands to human telomeric DNA using molecular dynamics (MD) and enhanced sampling (metadynamics) MD simulations. The simulations predict a variety of binding mechanisms and effects on G4 structure for the different ligands in the series. In parallel, we characterize the binding of the ligands to the G4 target experimentally using NMR and CD spectroscopy. The results show good agreement between the simulated and experimentally observed binding modes, binding affinities and ligand-induced perturbation of the G4 structure. The simulations correctly predict ligands that perturb G4 topology. Metadynamics simulations are shown to be a powerful tool to aid development of molecules to influence G4 structure, both in interpreting experiments and to help in the design of these chemotypes.

Human telomere double G-quadruplex recognition by berberine-bisquinolinium imaging conjugates in vitro and cells

Molecular tools of double or multimeric G-quadruplexes have been given higher requirements on detection sensitivity, thermal stabilization and cell imaging to establish functions of these G-quadruplex aggregates and biological mechanisms as anticancer reagents. Here, two smart berberine-bisquinolinium conjugates (Ber-360A and Ber-PDS) by linking the berberine fluorophore ligand and an established G-quadruplex binder (i.e. bisquinolinium scaffold), have been designed and evaluated their activities and mechanisms for G-quadruplex aggregation. Two conjugates, especially Ber-PDS, are two highly selective, sensitive and fluorescent sensors which can distinguish human telomere double G-quadruplexes from other type G-quadruplexes and ds DNA. These two ligands could be the first example to stack two adjacent G-quadruplex units and fluorescently recognize human telomere double G-quadruplexes. Furthermore, conjugate Ber-PDS could enter the nucleoli and target G-quadruplex DNA through microscopy experiments, and also display strong telomerase inhibition and antitumor activities.