Effect of Spicatoside a on Anti-Osteosarcoma MG63 Cells through Reactive Oxygen Species Generation and the Inhibition of the PI3K-AKT-mTOR Pathway

Abstract

Osteosarcoma is a primary malignant tumor found in the bones of children and adolescents. Unfortunately, many patients do not respond well to treatment and succumb to the illness. Therefore, it is necessary to discover novel bioactive compounds to overcome therapeutic limitations. Liriope platyphylla Wang et Tang is a well-known herb used in oriental medicine. Studies have shown that metabolic diseases can be clinically treated using the roots of L. platyphylla. Recent studies have demonstrated the anticarcinoma potential of root extracts; however, the exact mechanism remains unclear. The aim of this study was to examine the anti-osteosarcoma activity of a single compound extracted from the dried roots of L. platyphylla. We purified Spicatoside A (SpiA) from the dried roots of L. platyphylla. SpiA significantly inhibited the proliferation of human osteosarcoma MG63 cells in a dose- and time-dependent manner. SpiA also regulated the expression of various downstream proteins that mediate apoptosis (PARP, Bcl-2, and Bax), cell growth (cyclin D1, Cdk4, and Cdk6), angiogenesis (VEGF), and metastasis (MMP13). The Proteome Profiler Human Phospho-Kinase Array Kit showed that the AKT signaling protein was a target of SpiA in osteosarcoma cells. We also found that SpiA suppressed the constitutive activation of the PI3K-AKT-mTOR-p70S6K1 signaling pathway. We further validated the effects of SpiA on the AKT signaling pathway. SpiA induced autophagosome formation and suppressed necroptosis (a form of programmed cell death). SpiA increased the generation of reactive oxygen species (ROS) and led to the loss of mitochondrial membrane potential. N-acetylcysteine (NAC)-induced inhibition of ROS generation reduced SpiA-induced AKT inhibition, apoptotic cell death, and anti-metastatic effects by suppressing cell migration and invasion. Overall, these results highlight the anti-osteosarcoma effect of SpiA by inhibiting the AKT signaling pathway through ROS generation, suggesting that SpiA may be a promising compound for the treatment of human osteosarcoma.