Breast cancer frequently spreads to bone. The interaction between bone
metastases and microenvironment, referred as the "vicious cycle", increases both
tumor burden and bone destruction. Therefore, inhibition at any point in this "vicious cycle" can reduce malignant osteolytic lesions in patients with advanced
breast cancer. In this study, we evaluated whether tetrahydrofurofuran-type
lignans derived from Magnoliae Flos, commonly used in traditional Asian medicine to treat inflammatory diseases, could block
breast cancer-mediated bone loss. Aschatin,
fargesin,
lirioresinol B dimethyl ether, and
magnolin at noncytotoxic concentrations suppressed
mRNA expression and secretion of osteolytic factor
PTHrP in MDA-MB-231 metastatic human
breast cancer cells.
Fargesin inhibited TGF-β-stimulated cell viability, migration, and invasion and decreased TGF-β-induced
PTHrP production in MDA-MB-231 cells. In addition, these
lignans reduced RANKL/OPG ratio in
PTHrP-treated hFOB1.19 human osteoblastic cells and inhibited RANKL-mediated osteoclast differentiation in mouse bone marrow macrophages. Aschatin,
fargesin,
lirioresinol B dimethyl ether, and
magnolin substantially reduced
bone-resorbing activity of osteoclasts by inhibiting MMP-9 and
cathepsin K activities. Furthermore, orally administered
fargesin inhibited
tumor growth and
cancer-mediated bone destruction in mice with MDA-MB-231 cells injected into calvarial tissues. Aschatin,
fargesin,
lirioresinol B dimethyl ether, and
magnolin blocked initiation and progression of the "vicious cycle" between
breast cancer metastases and bone microenvironment by inhibiting
PTHrP production in
breast cancer cells and osteoclastic
bone resorption. Therefore, these tetrahydrofurofuran-type
lignans have the potential to serve as beneficial agents to prevent and treat
cancer-induced bone destruction in
breast cancer patients.