Polyphyllin I suppresses human osteosarcoma growth by inactivation of Wnt/β-catenin pathway in vitro and in vivo

Osteosarcoma is the most common primary bone cancer in children and adolescents. In spite of aggressive treatment, osteosarcoma has a high mortality rate with minimal improvements in survival over past few decades. Polyphyllin I (PPI), a component in the traditional Chinese medicinal herb Paris polyphylla Smith, has been shown to have anti-tumor properties. However, its mechanism as an anti-osteosarcoma agent has not been well elucidated. In this study, we found that PPI suppressed osteosarcoma cell viability, arrested cell cycle in G2/M phase, induced apoptosis and inhibited invasion and migration of osteosarcoma cells. Moreover, PPI significantly suppressed intratibial primary tumor growth in xenograft orthotopic mouse model without any obvious side effects. These therapeutic efficacies were associated with inactivation of Wnt/beta-catenin pathway, as PPI treatment decreased the amount of p-GSK-3 beta, leading to down-regulated levels of active beta-catenin. PPI induced inhibition of osteosarcoma cell viability was abolished upon addition of GSK-3 beta specific inhibitor, CHIR99021, while PPI induced inhibition of osteosarcoma cell viability and migration were potentiated by beta-catenin silencing. These findings suggested that, in vitro and in vivo, PPI treatment inhibited osteosarcoma, at least in part, via the inactivation of Wnt/beta-catenin pathway. Thus, PPI could serve a novel therapeutic option for osteosarcoma patients.