Smart MnO ₂ Nanosheet-Copper Carbon Dot Nanoplatform Enabling Multimodal Therapy to Reverse Hypoxia and Reprogram the Tumor Immune Microenvironment

The core obstacle to tumor metastasis and recurrence lies in the hypoxic and immunosuppressive microenvironment, and a single therapeutic modality cannot achieve synergistic intervention. In this study, a multimodal theranostic nanoplatform (MDCC) integrating copper-doped carbon dots (CuCDs), MnO₂ nanosheets, and doxorubicin was constructed, which realized the organic integration of multimodal synergistic therapy, <i>in situ</i> oxygen self-supply, immunogenic cell death (ICD) induction, and tumor immune microenvironment remodeling. MDCC exhibited a photothermal conversion efficiency of 53% under an 808 nm laser irradiation. It could reverse tumor hypoxia through two pathways, including oxygen release via MnO₂ response to the acidic environment and oxygen production via a CuCD-mediated Fenton-like reaction, thus significantly downregulating the expressions of HIF-1α and PD-L1. Meanwhile, MDCC could generate singlet oxygen (¹O₂) under 660 nm laser irradiation and achieve quadruple killing effects of photodynamic therapy (PDT), photothermal therapy (PTT), chemodynamic therapy (CDT), and chemotherapy (CT) by combining hydroxyl radical (^•OH) production from Fenton-like reaction and the chemotherapeutic effect of doxorubicin. <i>In vitro</i> experiments confirmed that MDCC could efficiently induce ICD in 4T1 cells, upregulate markers such as calreticulin (CRT), and promote dendritic cell maturation and macrophage M1 polarization. <i>In vivo</i> experiments based on the Balb/c mouse bilateral tumor model showed that MDCC combined with dual lasers and αPD-L1 could completely eliminate primary tumors and reduce the volume of distant tumors by 68.7% via the abscopal effect without obvious organ damage. This platform realizes tumor immune microenvironment remodeling through the synergy of multiple mechanisms, providing a novel strategy for the precise treatment of malignant tumors.