Calixarene-Based Nanostructures for Delivering Coumarin 6 for Tumor-Cell Imaging and Photoinduced Toxicity

Fluorescence imaging techniques are emerging as safer and more sensitive alternatives to radionuclide-based approaches for cancer diagnosis. Entrapping fluorophores that also act as photosensitizers within nanocarriers is an effective strategy to enhance their stability, performance, and selective delivery to tumor tissues, enabling the development of advanced nanosystems for cancer cell imaging and theranostic applications. In this work, we report a fluorescent nanosystem obtained by entrapping Coumarin 6 in biocompatible nanostructures formed through the self-assembly of an amphiphilic calix[4]-arene derivative functionalized with choline ligands for targeting tumor cells. The nanosystem was characterized using diverse techniques, which confirmed nanoscale organization, colloidal stability, excellent resistance to freeze-drying, good fluorescence quantum yield, and visible-light-triggered photodynamic activity, as evidenced by methylene blue photodegradation. Molecular modeling simulations provided mechanistic insight into the host-guest interactions governing Coumarin 6 stabilization in the nanocarrier. The nanosystem selectively imaged breast carcinoma (MCF-7 and MDA-MB-231) and hepatocarcinoma (Hep3B and SNU398) cells that overexpress the choline transporter, while negligible uptake was observed in nonmalignant human fibroblasts (HuDe cells). Intracellular fluorescence intensity correlated with choline transporter expression levels, and the competitive inhibition assay supported a transporter-mediated cellular uptake mechanism. Upon biocompatible visible-light irradiation, the nanosystem effectively induced cancer cell death through activation of the Coumarin 6 photosensitizer. The integration of targeted cancer cell imaging and phototriggered cytotoxicity highlights this fluorescent nanosystem as a promising photoresponsive nanotheranostic candidate.