Leveraging Mitochondria-Endoplasmic Reticulum Functional Interplay With an On-Demand Nanoparticle to Boost mtDNA-Based STING Immunotherapy.

Endogenous STING activation by mitochondrial DNA (mtDNA) offers a tumor-context-dependent strategy with potentially reduced off-target toxicity, but is often limited by weak and transient mtDNA-driven STING signaling that fails to sustain robust STING clustering. Here, we developed an on-demand nanoparticle system that harnesses mitochondrial-ER functional interplay by concurrently inducing mtDNA release and ER stress, thereby relieving the STIM1-mediated brake on STING and enabling robust STING-TBK1 assembly and downstream signaling. This strategy markedly increased the phosphorylation levels of STING, TBK1, and IRF3 by 11.50-, 9.70-, and 8.95-fold, respectively, compared with PBS, outperforming the commercial STING agonist MSA-2 by more than 2-fold. In addition, the nanoparticles enabled spatially controlled co-delivery, allowing extracellular release of a PD-1/PD-L1 inhibitor and intracellular release of mtDNA-releasing and ER stress-inducing agents. Consequently, this on-demand nanoparticle system potently enhanced both innate and adaptive antitumor immunity in vivo, significantly increasing CD8+ and CD4+ T cell infiltration while reducing Tregs, ultimately suppressing tumor progression, metastasis, and recurrence in mouse models of breast and colon cancer. This strategy advances STING-based immunotherapy by integrating spatially staged drug release with organelle-level immune modulation.