Reduction-responsive RNAi nanoplatform for enhanced cancer sonoimmunotherapy via dual inhibition of mitophagy and Nrf2 pathways

<b>Rationale:</b> Sonodynamic therapy (SDT) has emerged as a promising non-invasive modality with deeper tissue penetration than photodynamic or chemodynamic therapies. However, its therapeutic efficacy remains limited due to inadequate reactive oxygen species (ROS) generation, largely attributed to tumor-intrinsic antioxidant systems and mitophagy. Existing combinations of SDT with immunotherapy are primarily additive and fail to address the mechanistic interplay between ROS suppression and immune evasion. <b>Methods:</b> To overcome these limitations, we developed a redox-responsive RNA interference (RNAi) nanoplatform (NP) for the co-delivery of Nrf2 siRNA, the mitophagy inhibitor 3-Methyladenine (3-MA), and the sonosensitizer purpurin-18 (P-18). This NP enables tumor-specific release in high-glutathione environments and facilitates dual-pathway inhibition upon ultrasound activation. <b>Results:</b> This synergistic platform simultaneously disrupted Nrf2-mediated antioxidant defenses and mitophagy-dependent mitochondrial clearance, resulting in enhanced intracellular ROS accumulation. Elevated ROS levels triggered immunogenic cell death (ICD), promoting dendritic cells maturation and antigen presentation. Concurrently, 3-MA inhibited NF-κB signaling, downregulating PD-L1 expression and mitigating T cell exhaustion. In murine breast cancer models, this dual-action approach elicited robust CD8⁺ T cell responses and significantly suppressed tumor growth and metastasis. <b>Conclusions:</b> This study introduces a mechanistically integrated sonoimmunotherapeutic strategy that concurrently overcomes ROS suppression and immune checkpoint resistance. By orchestrating redox disruption and immune reprogramming, our nanoplatform provides a compelling framework for next-generation SDT-based immunotherapy.