Oxysophocarpine Retards the Growth and Metastasis of Oral Squamous Cell Carcinoma by Targeting the Nrf2/HO-1 Axis

Background/Aims: Nuclear factor erythroid 2-related factor 2 (Nrf2) is an oncogene in various types of cancers, including oral squamous cell carcinoma (OSCC). Oxysophocarpine (OSC) is a natural alkaloid that has multiple pharmacological activities. However, the biological functions and molecular mechanism underlying the effects of OSC on the growth and metastasis of OSCC are unclear. Methods: Nrf2 levels were determined in OSCC tissues and non-cancerous specimens by quantitative real-time PCR, western blotting, and immunohistochemistry (IHC) assays. The effects of OSC on OSCC cell growth and metastasis were explored (1) using 5-ethynyl-20-deoxyuridine staining and Cell Counting Kit-8, colony formation, flow cytometry, wound-healing, Transwell, and tube formation assays in vitro; and (2) by establishing a xenograft nude mouse model in vivo. The molecular mechanisms underlying the effects of OSC on the growth and metastasis of OSCC were investigated in vitro by western blotting, caspase-3 activity, and enzyme-linked immunosorbent assays, and in vivo by western blotting and IHC assays. Results: The expression levels of Nrf2 in OSCC tissues and in cell lines were much higher than in non-cancerous tissues and normal oral keratinocytes. The upregulation of Nrf2 was positively correlated with a high incidence of lymph node metastasis and advanced histological grade and TNM stage, but inversely associated with differentiation and survival of OSCC patients. OSC reduced the expression of Nrf2 and heme oxygenase 1 (HO-1) in OSCC cells. OSC also inhibited proliferation, migration, invasion, and pro-angiogenesis of OSCC cells. Moreover, OSC induced cell cycle arrest, enhanced apoptosis of OSCC cells in vitro, and decreased OSCC tumor growth in vivo. Mechanically, OSC reduced the aggressive behavior of OSCC cells by inactivation of the Nrf2/HO-1 signaling pathway. Conclusion: Our findings provide evidence that OSC inhibits the growth and metastasis of OSCC by targeting the Nrf2/ HO-1 axis, suggesting that OSC may be a potential therapeutic agent for OSCC.