A monomer purified from Paris polyphylla (PP-22) triggers S and G2/M phase arrest and apoptosis in human tongue squamous cell carcinoma SCC-15 by activating the p38/cdc25/cdc2 and caspase 8/caspase 3 pathways

Recent studies have shown that the aqueous, ethanolic extracts and a monomer compound of Paris polyphylla exhibit anticancer activity toward several types of cancer cell lines, but the anticancer activity of (3β,17α,25R)-spirost-5-ene-3,17-diol 3-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-glucopyranoside, a monomer isolated from P. polyphylla (PP), named PP-22, has not been reported previously. In this study, we investigated the effect of PP-22 on human tongue squamous cell carcinoma SCC-15 cells in vitro. MTT assays showed that PP-22 inhibited the growth of SCC-15 cells and had no obvious inhibitory effects on human liver L02 cells. Flow cytometry assays showed that the percentages of apoptotic cells were increased. In addition, cleaved caspase-8, cleaved caspase-3 and cleaved poly (ADP-ribose) polymerase (PARP) could be detected by Western blotting. Flow cytometry also showed that PP-22 triggered S and G2/M phases arrest in SCC-15 cells, and on the other hand, the expression of cyclin A, cyclin E2, cyclin B1, phospho-cell division cycle2 (p-cdc2)(Tyr15), p-Wee1, Myt1, and p53 was upregulated. Moreover, p-p38 levels increased, p-extracellular signal-regulated kinase (ERK) levels decreased, and cdc25B expression was inhibited. Furthermore, the p38/mitogen-activated protein kinase (MAPK) inhibitor SB203580 reversed the increase of the expression level of p38, p-cdc2 (Tyr15), cleaved caspase 3, cleaved PARP, p-p53, and p53 and reversed the decrease in cdc25B expression. In conclusion, these results demonstrated that PP-22 activated p38, inhibited cdc25B, increased p-cdc2 (Tyr15), and triggered S and G2/M phase arrest, as well as activated p53 through the p38-p53 pathway, inhibited the MAPK/ERK pathway, activated the caspase 8/caspase 3 pathway, and triggered the extrinsic apoptotic pathway in SCC-15 cells.