Morusin inhibits breast cancer-induced osteolysis by decreasing phosphatidylinositol 3-kinase (PI3K)-mTOR signalling.

Bone metastases caused by breast cancer pose a major challenge to the successful treatment of breast cancer patients. Many researchers have suggested that herbal medicines are extremely effective at preventing and treating cancer-associated osteolysis. Previous studies have revealed that Morusin (MOR) is cytotoxic to many cancer cells ex vivo. Nevertheless, how MOR contributes to osteolysis induced by breast cancer is still unknown, and the potential mechanism of action against osteolysis is worthy of further study. The protective effect and molecular mechanism of MOR in inhibiting breast cancer cell-induced osteolysis were verified by experiments and network pharmacology. Cell function was assessed by cell proliferation, osteoclast (OC) formation, bone resorption, and phalloidin staining. Tumour growth was examined by micro-CT scanning in vivo. To identify potential MOR treatments, the active ingredient-target pathway of breast cancer was screened using network pharmacology and molecular docking approaches. This study is the first to report that MOR can prevent osteolysis induced by breast cancer cells. Specifically, our results revealed that MOR inhibits RANKL-induced osteoclastogenesis and restrains the proliferation, invasion and migration of MDA-MB-231 breast cells through restraining the PI3K/AKT/MTOR signalling pathway. Notably, MOR prevented bone loss caused by breast cancer cell-induced osteolysis in vivo, indicating that MOR inhibited the development of OCs and the resorption of bone, which are essential for cancer cell-associated bone distraction. This study showed that MOR treatment inhibited osteolysis induced by breast cancer in vivo. MOR inhibited OC differentiation and bone resorption ex vivo and in vivo and might be a potential drug candidate for treating breast cancer-induced osteolysis.