Programming Mn(II) coordination in self-assembling peptides amplifies mtDNA-driven STING signaling for potent antitumor immunity.

Activation of the cGAS-STING pathway is a powerful antitumor strategy, but its therapeutic performance is often constrained by insufficient cytosolic DNA cues. Here, we report a bioinspired metallopeptide nanoassembly, RKLAHE-Mn, formed through dynamic N,O-bidentate coordination between Mn(II) and a programmable hexapeptide scaffold. By leveraging specific interactions between histidine and glutamic acid, we achieve robust chelation that orchestrates the self-assembly of uniform, chain-like assemblies of spherical nanoparticles, with DFT calculations supporting a thermodynamically favorable Mn-His/Glu N,O-coordination mode. Upon internalization, RKLAHE-Mn triggers a rapid ROS burst and perturbs intracellular redox homeostasis. These cationic assemblies preferentially accumulate in mitochondria, leading to loss of mitochondrial membrane potential and promoting mitochondrial DNA (mtDNA) leakage into the cytosol. The released mtDNA, together with Mn(II)-dependent potentiation, amplifies STING signaling and elicits immunogenic cell death-associated responses. Notably, RKLAHE-Mn also potentiates STING-related innate immune signaling in dendritic cells, driving maturation with upregulated CD80, CD86, and MHC class II expression, increased secretion of IL-6, TNF-α, and CXCL10, and enhanced antigen presentation and cross-presentation. In a murine breast cancer model, RKLAHE-Mn remodels the immunosuppressive tumor microenvironment by promoting dendritic cell maturation and CD8+ T cell infiltration, and it significantly enhances the therapeutic efficacy of anti-PD-L1 checkpoint blockade. Collectively, this work establishes metal-coordination-guided peptide self-assembly as a versatile paradigm for converting ionic cofactors into targeted, immunostimulatory nanotherapeutics for cancer immunotherapy.