Inhibition of growth, migration and invasion of human bladder cancer cells by antrocin, a sesquiterpene lactone isolated from Antrodia cinnamomea, and its molecular mechanisms

Bladder cancer is the ninth most common cancer around the world, and is a severe urological cancer irrespective of sex. Approximately 65% of the bladder cancers will recur following surgery; with more than 20% of those patients showing an advanced and metastatic stage, with reducing prognosis. Metastasis causes the most death of bladder cancer yet current therapeutic options remain limited. Antrocin, a sesquiterpene lactone isolated from Antrodia cinnamomea, has been identified as a strong cytotoxic agent against lung and metastatic breast cancer cells; however, the effects and mechanisms of antrocin on cancer growth and metastasis remain largely unclear. This study showed that treatment with cytotoxic concentration of antrocin induced both intrinsic and extrinsic apoptotic pathways in human bladder cancer 5637 cells, evidenced by increase of Fas, DR5, Bax expression and caspase-3, -8 and -9 activation. Exposure to non-cytotoxic concentrations of antrocin significantly inhibited cell growth, migration, and invasion, which was associated with decreased phosphorylation of focal adhesion kinase (FAK) and paxillin. Antrocin also reduced subcellular distribution of FAK and paxillin at the focal adhesion contacts of the cell periphery site, and disrupted the formation of filopodia and lamellipodia. Moreover, antrocin increased epithelial-to-mesenchymal transition-related gene E-cadherin and decreased vimentin expression. Real-time PCR analysis showed that antrocin downregulated the expression of mRNA of several MMPs, including MMP-2. Moreover, the phosphorylation of ERK and c-Fos were also attenuated by antrocin. Data from chromatin immunoprecipitation assay demonstrated that antrocin decreased the DNA binding activity of c-Fos to the upstream/enhancer region of MMP-2 promoter, an action likely to result in the reducing MMP-2 expression. Overall, this is the first study which demonstrates that antrocin-inhibited migration and invasion of bladder cancer cells is partly via inactivation of FAK-paxillin and ERK-c-Fos-MMP2 signaling pathways. Both antrocin-induced intrinsic and extrinsic apoptosis is through upregulation of pro-apoptotic proteins, including Bax, Fas, and DR5. These results provide insights for understanding the anti-cancer effects and mechanisms of antrocin in human bladder cancer cells and indicate that antrocin may be a potential therapeutic agent for invasive bladder cancer cells by inhibition of metastasis and induction of apoptosis.