Compound Kushen Injection (CKI), a traditional Chinese medicine that has been clinically used for the treatment of various malignancies for over two decades, is prepared by purifying two traditional Chinese medicinal herbs: Sophora flavescens Aiton (Kushen) and Heterosmilax japonica Kunth (Baituling). The most abundant active component, matrine, which is derived from Sophora flavescens Aiton, has also been reported in cancer treatment. However, it has effects on breast cancer lung metastasis and underlying molecular mechanisms that remain incompletely understood.

To investigate the effects of CKI on breast cancer lung metastasis and elucidate its underlying mechanisms.

CKI's effects on breast cancer cells were evaluated using CCK-8, crystal violet staining, apoptosis, scratch, and Transwell assays; tumor progression and lung metastasis were studied in 4T1 tumor-bearing mice. H&E staining and blood analyses assessed CKI's organ toxicity. Proteomic analysis identified CKI-affected proteins; expression levels of target proteins, epithelial-mesenchymal transition markers, and F-actin were validated via Western blotting, immunohistochemistry, and immunofluorescence. Flow cytometry assessed CKI's effects on immune cells. LC-MS identified CKI's chemical components. Matrine, a CKI component, was investigated for its impact on cell viability, invasion, target proteins, EMT markers, and F-actin.

CKI reduced the viability and proliferation of 4T1, MCF-7, and MDA-MB-231 breast cancer cell lines, induced apoptosis, and inhibited migration and invasion. In vivo, CKI suppressed the growth and lung metastasis of 4T1 tumors in mice without affecting liver, kidney, or heart function. CKI treatment upregulated MTSS1 and downregulated ARPC3 expression in breast cancer cells and tumor tissues. Additionally, CKI significantly altered the structure of F-actin in breast cancer cells. In CKI-treated cells and tumor tissues, E-cadherin expression was significantly upregulated, while N-cadherin and vimentin expressions were significantly downregulated, indicating inhibition of the EMT process. LC-MS identified matrine as the main active component of CKI. Matrine similarly inhibited proliferation and invasion, modulated MTSS1, E-cadherin, ARPC3, N-cadherin, and vimentin expression, and significantly affected F-actin structure.

CKI and matrine inhibit breast cancer cell proliferation, migration, invasion, and induce apoptosis, thereby preventing lung metastasis by modulating the MTSS1/ARPC3/F-actin pathway and inhibiting the EMT process. This study reinforces their theoretical basis and clinical potential in tumor therapy.