MnO2@Ce6-loaded mesenchymal stem cells as an "oxygen-laden guided-missile" for the enhanced photodynamic therapy on lung cancer

The critical issue in nanoscale medicine delivery systems is the targeted efficiency to guarantee the maximum accumulation of nanodrugs in tumors to exert better therapeutic action. In this study, we adopted an active and potent strategy based on mesenchymal stem cells (MSCs) certified with excellent tumor-tropism ability to load and ship MnO2@Ce6 nanoparticles into a tumor site. Notably, under the premise of the negligible cellular toxicity of MnO2@Ce6 on MSCs, its considerable uptake by MSCs enabled this nanoplatform (MnO2@Ce6-MSCs) to distribute increasingly inside the tumor. Briefly, a Ce6 photosensitizer was bound to MnO2 nanospheres by physical adsorption, improving its own stability in blood circulation. Furthermore, the delivered MnO2@Ce6 could modulate the tumor microenvironment (TME) by high sensitivity to excess hydrogen protons (H+) and H2O2. Thus, O-2 generated by these reactions served as an abundant source for O-1(2) conversion under a 633 nm laser exposure, which overcame the crucial bottleneck of the unfavorable hypoxia condition in TME for photodynamic therapy (PDT). In addition, MnO2 decomposed into Mn2+, which was represented by high T-1 relaxivity in magnetic resonance imaging (MRI). The Mn2+ was finally removed rapidly from the body by liver metabolism and kidney filtration. These results endowed the original nanoplatform with striking potential for MSC-guided, Ce6-converted, MRI-monitored PDT for further innovation of a clinical cancer diagnosis-treatment agent.