Calixarenes meet (TG4T)4 G-quadruplex: Exploring reciprocal interactions to develop innovative biotechnological applications

This study investigates, for the first time, the ability of calixarene ligands to interact with G-quadruplex (GQ) DNA assemblies, which play a critical role in many biological processes, including gene expression regulation, telomere maintenance, and the surveillance of genome stability and DNA repair mechanisms. Specifically, the interaction between two calix[4]arene compounds, featuring cationic or zwitterionic functional groups on their upper rim, and the parallel tetramolecular (TG4T)4 G-quadruplex used as a model, was analyzed using circular dichroism, NMR, and molecular dynamics simulations. The results revealed that both derivatives interact favorably with the GQ model, inducing aggregation at higher ligand concentrations. Notably, the interaction varied depending on the functional groups present on the calixarene upper rim. Calixarene 1, which bears four proline units, showed a stronger affinity for GQ termini, whereas calixarene 2, functionalized with four positively charged guanidinium groups, displayed a stronger affinity for the GQ lateral phosphate groups. These findings unveiled the calixarene ability to recognize different GQ structural features depending on the type of functional groups installed on their upper rim, paving the way for their use as GQ-targeting ligands, with positive implications for therapeutic and biotechnological applications.