Flaccidoxide Induces Apoptosis Through Down-regulation of PI3K/AKT/mTOR/p70S6K Signaling in Human Bladder Cancer Cells

Background/Aim: Urothelial carcinoma (UC) is the most common type of genitourinary cancer with high incidence and mortality rates in men. In this study, we used the BFTC-905 and T24 bladder cancer cell lines as in vitro models to investigate the pathways involved in flaccidoxideinduced apoptosis. Materials and Methods: We utilized MTT assays, colony assays, wound-healing assays and fluorescence with TUNEL to confirm the cytotoxicity of flaccidoxide in bladder cancer cell lines. Potential proliferative and apoptotic molecular mechanisms were evaluated by western blotting. Results: The expression of anti-apoptotic proteins Bcl-2 and phosphorylated Bad (p Bad) was attenuated with an increasing flaccidoxide concentration, while the expression of proapoptotic proteins Bax, Bad, cleaved caspase-3, cleaved caspase-9 and cleaved PARP-1 was found increased. Additionally, phosphorylation of phosphoinositide 3-kinases (PI3K), protein kinase B (AKT) and mammalian target of rapamycin (mTOR) in the PI3K/AKT/mTOR pathway was reduced, leading to a reduction in the phosphorylation of downstream 70-kDa ribosomal protein S6 kinase 1 (p70S6K), S6 ribosomal protein (S6) and eukaryotic translation initiation factor 4B (eIF4B). However, eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) protein phosphorylation was increased due to attenuation of the upstream phosphorylation of mTOR protein. Conclusion: Flaccidoxide-induced apoptosis in BFTC-905 and T24 cells is mediated by mitochondrial dysfunction and down-regulation the PI3K/AKT/mTOR/p70S6K signaling pathway.