Echinacoside inhibits breast cancer metastasis by targeting PAD4 to reduce NETs formation

Distant metastasis is the leading cause of mortality in breast cancer patients. Neutrophil extracellular traps (NETs) have been increasingly recognized as key promoters of metastasis, and targeting NETs has emerged as a promising antimetastatic strategy. In this study, we identified Echinacoside, a phenylethanoid glycoside derived from Rehmannia glutinosa, a traditional blood-activating herb, as a novel inhibitor of NET formation and breast cancer metastasis. Echinacoside effectively suppressed NET release from neutrophils and reduced metastatic spread in vivo. Mechanistically, Echinacoside binds directly to peptidylarginine deiminase 4 (PAD4), a key enzyme in NET formation, thereby inhibiting PAD4-mediated histone citrullination. Structural docking analysis revealed specific interaction sites between Echinacoside and PAD4. In addition, Echinacoside alleviated the NET-induced proinflammatory and immunosuppressive tumor microenvironment, inhibited epithelial–mesenchymal transition (EMT), and ultimately restrained NET-driven metastasis. Notably, Echinacoside also blocked the chemotherapy-induced exacerbation of metastasis mediated by NETs. Taken together, our findings highlight Echinacoside as a promising PAD4-targeting small molecule with significant potential for clinical application in preventing breast cancer metastasis.