Cu²⁺-pyropheophorbide-a-cystine conjugate-mediated multifunctional mesoporous silica nanoparticles for photo-chemodynamic therapy/GSH depletion combined with immunotherapy cancer

Photodynamic therapy (PDT) and chemodynamic therapy (CDT) can activate immunogenicity, so PDT and CDT combined immunotherapy is a promising treatment strategy. However, insufficient hydrogen peroxide activity, hypoxia, and overexpressed glutathione in the tumor microenvironment (TME) significantly impaired the ability to activate immunogenicity. Thus, in this paper, self-reinforcing conjugates Cu²⁺-Pyropheophorbide-a-Cysteine (CuPPaCC), combined synergetic NIR and pH triggered PDT/CDT with glutathione depletion ability was constructed. CuPPaCC was encapsulated in mesoporous silica, and spherical HSCuPPaCC nanoparticles were prepared by Hyaluronic acid (HA) on the silica surface by Schiff base modification. HSCuPPaCC has tumor-specific targeting via HA mediated. In acidic solution, the Schiff base of HSCuPPaCC is destroyed and CuPPaCC is released (>70%), with excellent pH response release function. The results of the MTT analysis showed that the PDT/CDT synergistic anti-tumor effect was significant. HSCuPPaCC was activated in TME, catalyzing the decomposition of hydrogen peroxide to generate hydroxyl radicals and oxygen, alleviating TME hypoxia, replenishing oxygen to PDT, and significantly down regulating hypoxia factor HIF-1α expression. HSCuPPaCC has an excellent dual ROS mechanism and a dual depleting GSH mechanism resulting in a surge in intracellular ROS levels to efficiently kill cancer cells, enhance the ability to induce immunogenicity, and make tumors more sensitive to checkpoint PD-L1 blockade therapy. With the CT26 mouse model, not only the primary tumor was eradicated, but also the distal tumor at the end of treatment was completely suppressed by HSCuPPaCC combined with anti-PD-L1 immune checkpoint blockade therapy.