Bi-magnolignan suppresses triple-negative breast cancer by triggering TBK1-dependent mitophagy

BACKGROUND: Triple-negative breast cancer (TNBC) represents an aggressive malignancy characterized by a lack of specific therapeutic targets and poor clinical prognosis, underscoring an urgent need for novel treatment strategies. Bi-magnolignan (BM), a natural lignan isolated from Magnolia officinalis, exhibits antitumor potential; however, its therapeutic efficacy and underlying mechanisms in TNBC remain to be investigated. This study aims to characterize BM-induced tumor inhibition and elucidate the specific signaling pathways involved. METHODS: The antitumor effects of BM were evaluated using integrated in vitro TNBC cell models and an in vivo 4T1 orthotopic mouse model. Mitophagy was assessed via transmission electron microscopy (TEM) and mt-Keima fluorescence imaging, while mitochondrial function was analyzed using JC-1 staining and qRT-PCR. Mechanistic validation was performed through pharmacological inhibition and genetic knockout of TBK1 to confirm the direct linkage between signaling events and apoptosis. RESULTS: BM treatment triggered rapid mitochondrial membrane potential (MMP) depolarization in TNBC cells, activating TBK1 to induce lethal mitophagy independently of the canonical PINK1-Parkin pathway. Mechanistically, activated TBK1 phosphorylated the autophagy receptor p62 at Ser403, facilitating the sequestration and elimination of damaged mitochondrial, which culminated in irreversible mitochondrial dysfunction and apoptosis. Blocking TBK1 significantly attenuated these effects, confirming its central role. In vivo, BM effectively suppressed tumor growth without inducing notable systemic toxicity. CONCLUSIONS: Our findings demonstrate that BM effectively suppresses TNBC progression through a distinct mechanism of TBK1-mediated lethal mitophagy. Consequently, BM serves as a promising lead compound, suggesting that pharmacological activation of the TBK1-mitophagy axis represents a novel therapeutic strategy for the clinical management of TNBC.