Legumain inhibitor prevents breast cancer bone metastasis by attenuating osteoclast differentiation and function

Breast cancer is the main lethal disease among females, and metastasis to lung and bone poses a serious threat to patients' life. Therefore, identification of novel molecular mediators that can potentially be exploited as therapeutic targets for treating osteolytic bone metastases is needed. A murine model of breast cancer bone metastasis was developed by injection of 4 T1.2 cells into the left ventricle and hence directly into the arterial system leading to bone. AEP (Asparagine endopeptidase) inhibitor combined with epirubicin or epirubicin alone was administered by intraperitoneal injection into animal model. The presence of bone metastatic and osteolytic lesions in bone were assessed by bioluminescent imaging and X-rays analysis. The expression of EMT (Epithelial-Mesenchymal Transition) relevant genes were examined by Western blotting. Cell migration and invasion were investigated with a transwell assay. Compound BIC-113, small molecule inhibitors of AEP, inhibited AEP enzymatic activity in breast cancer cell lines, and affected invasion and migration of cancer cells, but had no effect on cell growth. In animal model of breast cancer bone metastasis, compound BIC-113 combined with epirubicin inhibited breast cancer bone metastasis and attenuated breast cancer osteolytic lesions in bone by inhibiting osteoclast differentiation and EMT. These results indicate that compound BIC-113 combined with epirubicin has the potential to be used in breast cancer therapy by preventing bone metastasis via improving E-cadherin expression and inhibition of osteoclast formation.