Background: Metastatic breast cancer cells are frequently associated with osteoclast-mediated bone resorption, resulting in severe bone destruction and increased mortality in patients. Platycodin D (PD) isolated from Platycodon grandiflorum is a triterpenoid saponin with anti-cancer and anti-angiogenic potential. Methods: The in vivo activity was determined in mice with the intratibial injection of human metastatic breast cancer cells. Osteoclast formation and activity were detected using tartrate-resistant acid phosphatase staining and calcium phosphate-coated plates. The expression of osteoclastogenesis-inducing molecules was detected by RT-PCR and western blotting in RANKL-treated bone marrow macrophages (BMMs). Cell viability and DNA synthesis were measured with MTT and BrdU incorporation assays. The induction of apoptosis was estimated using TUNEL staining and a caspase-3 activity assay. Results: The oral administration of PD inhibited MDA-MB-231 cell-induced osteolysis in an intratibial mouse model. PD treatment blocked RANKL-induced osteoclast formation by inhibiting the expression and nuclear translocation of NFATc1 and c-Fos in BMMs and consequently reduced osteoclast-mediated bone resorption. Furthermore, PD treatment induced apoptosis in osteoclasts and inhibited the growth of MDA-MB-231 cells. Conclusion: PD may block breast cancer-induced bone loss by suppressing the formation, activity, and survival of osteoclasts, as well as the growth of metastatic breast cancer cells.
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