Copper complexes Cu1 triggers synergistic immunogenic cell death and pyroptosis for chemoimmunotherapy of triple-negative breast cancer.

Metal complexes possess unique spatial coordination frameworks and tunable biological functions, rendering them promising candidates for antitumor drug development. Herein, we rationally designed and synthesized a novel copper(II) complex Cu1 with the molecular formula Cu1(Cu(L)₂(ClO₄)₂·2H₂O, C₃₆H₂₆Br₂Cl₂CuN₈O₁₀S₂, where the ligand L corresponds to 2-([2,2':6',2″-terpyridin]-4'-yl)-4-bromothiazole. We systematically characterized its antitumor potency toward triple-negative breast cancer (TNBC) and dissected the underlying immunomodulatory mechanisms. UV-vis absorption titration and viscosity assays validated that Cu1 binds tightly to duplex DNA primarily via an intercalative binding mode. In cellular experiments, Cu1 exhibited potent cytotoxicity against both MDA-MB-231 and 4T1 cells, accompanied by pronounced nuclear accumulation and DNA damage. Mechanistically, Cu1 triggered massive intracellular reactive oxygen species (ROS) accumulation, activated the cGAS-STING axis coupled with endoplasmic reticulum (ER) stress, and elicited canonical immunogenic cell death (ICD), as validated by calreticulin (CRT) membrane translocation, HMGB1 cytoplasmic release, and elevated extracellular ATP secretion. Furthermore, Cu1 initiated Caspase-1/GSDMD-mediated pyroptosis. In both tumor vaccination and 4T1 orthotopic tumor-bearing mouse models, Cu1 displayed robust in vivo antitumor activity by orchestrating systemic antitumor immunity: it promoted dendritic cell (DC) maturation, boosted intratumoral CD8+ T cell infiltration, diminished immunosuppressive Foxp3+ regulatory T cells (Tregs), and established long-lasting tumor-specific immune memory. Collectively, Cu1 represents a multifunctional copper coordination complex that integrates direct tumoricidal activity and immunoregulatory capacity. This work delivers comprehensive experimental evidence supporting the translational development of copper-based therapeutic agents for TNBC chemoimmunotherapy.