Light-controllable systems based on TiO₂-ZIF-8 composites for targeted drug release: communicating with tumour cells

Drug delivery systems based on the zeolitic imidazolate framework ZIF-8 have recently attracted viable research interest owing to their capability of decomposing in acidic media and thus performing targeted drug delivery. In vivo realization of this mechanism faces a challenge of relatively slow decomposition rates, even at elevated acidic conditions that are barely achievable in diseased tissues. In this study we propose to combine drug delivery nanocomposites with a semiconductor photocatalytic agent that would be capable of inducing a local pH gradient in response to external electromagnetic radiation. In order to test this principle, a model drug-releasing nanocomposite comprising photocatalytic titania nanotubes, ZIF-8, and the antitumor drug doxorubicin has been investigated. This system was demonstrated to release the drug in a quantity sufficient for effectively suppressing IMR-32 neuroblastoma cells that were used as a model diseased tissue. With locally applied UV irradiation, this result was achieved within 40 minutes, which is a relatively short time compared to the release duration in systems without photocatalyst, typically taking from several hours to several days.