A "Chase and Block" Strategy for Enhanced Cancer Therapy with Hypoxia-Promoted Photodynamic Therapy and Autophagy Inhibition Based on Upconversion Nanocomposites

The combination of hypoxia-promoted photodynamic therapy (PDT) and autophagy modulation has shown strong potential in the treatment of hypoxic tumors. Here, a novel design is put forward for synergistic PDT and autophagy inhibition to amplify the effect of cancer therapy by a "chase and block" strategy. Specifically, the organic photosensitive molecule (denoted FL) is encapsulated in a hydrophobic layer between multi-band emitted upconversion nanoparticles (UCNPs) and the amphiphilic polymer DSPE-PEG-COOH, allowing FL to fully exploit the luminescence spectrum of UCNPs under near-infrared (NIR) light irradiation. The FL is specifically activated by nitroreductase in the tumor microenvironment (TME), enabling hypoxia-promoted PDT and thus performing a "chase" strategy for cancer therapy. Additionally, the nanosystem is combined with an autophagy-inhibiting melittin pro-peptide (denoted as MEL), which could be triggered by the highly expressed legumain in tumor cells to inhibit the autophagy procedure by disrupting the lysosomal membrane, thus "blocking" the cancer cells from rescuing themselves and amplifying the killing effect of PDT. Both FL and MEL can be specifically activated by TME and the upconversion luminescence imaging of UCNPs offers a tracer function for the treatment. Therefore, UCNPs@FL-MEL might be an important reference for the design and development of future nanotherapeutic agents.