Phototherapeutic β-Cyclodextrin-Branched Polymer Releasing Nitric Oxide with Fluorescent Self-Reporting and Its Combination with Doxorubicin

In this contribution, we report the design, synthesis, photochemical characterization, and biological validation of a novel, photoresponsive beta-cyclodextrin branched polymer (Poly-beta CD1) and its nanoassembly with doxorubicin (DOX). This tailored polymer covalently integrates multiple bichromophoric dyads based on nitroaniline- and coumarin-derived motifs within its macromolecular scaffold. Excitation of the Poly-beta CD1 with visible blue light results in the generation of nitric oxide (NO) from the nitroaniline moiety, and the parallel restoration of the typical emission of the coumarin fluorogenic unit, initially suppressed by Forster Resonance Energy Transfer (FRET), which acts as an optical self-reporter for the photoreleased NO. These photochemical properties are enhanced relative to those of the isolated monomer beta CD1, synthesized as a model compound, and are well preserved after DOX entrapment within the polymeric network. This feature enables real-time optical monitoring of the NO photodelivery in cancer cells using fluorescence microscopy. Preliminary toxicity experiments carried out with DOX-sensitive and DOX-resistant cancer cells demonstrate that Poly-beta CD1 is well tolerated in the dark but induces cell death under light irradiation. Besides, the negligible cytotoxic action of DOX, used well below the therapeutic doses, alone or in combination with the polymer in the dark, is enhanced in both cell lines under light irradiation exclusively when the drug is combined with Poly-beta CD1 as a result of the combined action of NO.