RÉSUMÉ
BACKGROUND: Breast cancer is the most common malignant disease in women. The patients with advanced breast cancer develop metastasis to bone. Bone metastasis and skeletal-related events by breast cancer are frequently associated with the invasiveness of breast cancer cells and osteoclasts-mediated bone resorption. Forsythia koreana is used in oriental traditional medicine to treat asthma, atopy, and allergic diseases. The aim of this study was to evaluate the inhibitory effects of F. koreana extracts on the invasion of breast cancer cells and bone resorption by osteoclasts. METHODS: Cell viability was measured by an MTT assay and the migration and invasion of MDA-MB-231 cells were detected by a Boyden chamber assay. The formation of osteoclasts and pit was detected using tartrate-resistant acid phosphatase staining and calcium phosphate-coated plates, respectively. The activities of matrix metalloproteinases (MMPs) and cathepsin K were evaluated by gelatin zymography and a cathepsin K detection kit. RESULTS: The fruit and leaf extracts of F. koreana significantly inhibited the invasion of MDA-MB-231 cells at noncytotoxic concentrations. The fruit extract of F. koreana reduced the transforming growth factor β1-induced migration, invasion and MMPs activities of MDA-MB-231 cells. In addition, the fruit, branch, and leaf extracts of F. koreana also inhibited the receptor activator of nuclear factor kappa-B ligand-induced osteoclast formation and osteoclast-mediated bone-resorbing activity by reducing the activities of MMPs and cathepsin K. CONCLUSIONS: The extracts of F. koreana may possess the potential to inhibit the breast cancer-induced bone destruction through blocking invasion of breast cancer cells, osteoclastogenesis, and the activity of mature osteoclasts.