Energetics of ligand binding to G-quadruplexes.

G-quadruplex ligands are potential anticancer agents as telomerase inhibitors and potential transcriptional regulators of oncogenes. The search for best-in-class drugs is addressed to identify small molecules able to promote and stabilize G-quadruplex structures. What features should the G-quadruplex ligands possess? They should have selective antiproliferative effects on cancer cells and induce telomerase inhibition or oncogene suppression. One of the main challenges in their design and synthesis is to make the ligands selective for G-quadruplex DNA. These features should be amplified by careful analyses of physico-chemical aspects of G-quadruplex-drug interactions. In particular, the study of the energetics of G-quadruplex-drug interactions can enhance drug design by providing thermodynamic parameters that give quantitative information on the biomolecular interactions important for binding. The main methodologies used to gain information on energetics of binding are based on spectroscopic or calorimetric principles. Spectroscopic techniques such as fluorescence and circular dichroism are rapid and cheap methods, but are not sufficient to characterize completely the thermodynamics of interaction. Calorimetric techniques such as isothermal titration calorimetry offer a direct measure of binding enthalpy, in addition to the stoichiometry and affinity constants. With the complete thermodynamic signature of drug-target interaction, dissecting the enthalpic and entropic components of binding is possible, which can be a useful aid to decision-making during drug optimization.