A Rationally Designed Azobenzene Photoswitch for DNA G-Quadruplex Regulation in Live Cells.

G-quadruplex (G4) DNA structures are increasingly acknowledged as promising targets in cancer research, and the development of G4-specific stabilizing compounds may lay a fundamental foundation in precision medicine for cancer treatment. Here, we propose a light-responsive G4-binder for precise modulation of drug activation, providing dynamic and spatiotemporal control over G4-associated biological processes contributing to cancer cell death. We developed a specialized fluorinated azobenzene (AB) switch equipped with a quinoline unit and a positively charged carboxamide side chain, Q-Azo4F-C, designed for targeted binding to G4 structures within cells. Biophysical studies, combined with molecular dynamics simulations, provide insights into the unique coordination modes of the photoswitchable ligand in its trans and cis configurations when interacting with G4s. The observed variations in complexation processes between the two isomeric states in different cancer cell lines manifest in more than 25-fold reversible cytotoxic activity. Immunostaining conducted with the structure-specific G4 antibody (BG4), establishes a direct correlation between cytotoxicity and the varying extent of G4 induction regulated by the two isoforms. Finally, we demonstrate the photo-driven reversible regulation of G4 structures in lung cancer cells by Q-Azo4F-C. Our findings highlight the potential of light-responsive G4-binders in advancing precision cancer therapy through dynamic control of G4-mediated pathways.