Herbal Composition Inhibits Mitochondrial Oxidative Phosphorylation to Prevent HER2-Positive Breast Cancer and Identifies Potential Active Compounds

Human Epidermal Growth Factor Receptor 2 (HER2)-positive breast cancer is an aggressive malignancy with limited treatment options. The herbal composition SLC contains Salvia miltiorrhiza Bunge (Dan shen), Ligusticum wallichii Franch. (Chuan xiong), and Carthamus tinctorius L. (Hong hua), three herbs that have demonstrated antitumor properties. This study aims to investigate the inhibitory effects and mechanisms of SLC against HER2-positive breast cancer. UPLC-Q/TOF-MS identified 113 compounds in SLC. SLC inhibited the proliferation, migration, and mitochondrial function of HER2-positive cells by reducing glucose uptake, ATP production, and oxygen consumption rate (OCR). Furthermore, SLC downregulated the levels of p-HER2/HER2, p-AKT/AKT, and p-ERK/ERK by Western blot, thereby inhibiting the HER2 signaling pathway. Mechanistically, SLC decreased the protein expression of PDK1 and inhibited the phosphorylation of PDHA1 (Ser293), and also inhibited mitochondrial-related proteins in SIRT1/PGC-1α/NRF1/TFAM signaling axes. Additionally, through the overexpression of PDK1, SLC repressed PDK1, downregulated PDHA1, and induced apoptosis. In vivo xenograft model studies demonstrated that SLC inhibited tumor growth. Molecular docking highlighted Monomethyl lithospermate as a key active component. Overall, SLC influences oxidative phosphorylation via the PDK1/PDHA1 and SIRT1/PGC-1α/NRF1/TFAM signaling pathways and downregulates the HER2 pathway, thereby ultimately inhibiting HER2-positive breast cancer progression.