Recently, the interplay between autophagy and apoptosis has become an important factor in chemotherapy for cancer treatment. Inhibition of autophagy may be an effective strategy to improve the treatment of chemo-resistant cancer by consistent exposure to chemotherapeutic drugs. However, no reports have clearly elucidated the underlying mechanisms. Therefore, in this study, we assessed whether salinomycin, a promising anticancer drug, induces apoptosis and elucidated potential antitumor mechanisms in chemo-resistant prostate cancer cells. Cell viability assay, Western blot, annexin V/propidium iodide assay, acridine orange (AO) staining, caspase-3 activity assay, reactive oxygen species (ROS) production, and mitochondrial membrane potential were assayed. Our data showed that salinomycin alters the sensitivity of prostate cancer cells to autophagy. Pretreatment with 3-methyladenine (3-MA), an autophagy inhibitor, enhanced the salinomycin-induced apoptosis. Notably, salinomycin decreased phosphorylated of AKT and phosphorylated mammalian target of rapamycin (mTOR) in prostate cancer cells. Pretreatment with LY294002, an autophagy and PI3K inhibitor, enhanced the salinomycin-induced apoptosis by decreasing the AKT and mTOR activities and suppressing autophagy. However, pretreatment with PD98059 and SB203580, an extracellular signal-regulated kinases (ERK), and p38 inhibitors, suppressed the salinomycin-induced autophagy by reversing the upregulation of ERK and p38. In addition, pretreatment with N-acetyl-l-cysteine (NAC), an antioxidant, inhibited salinomycin-induced autophagy by suppressing ROS production. Our results suggested that salinomycin induces apoptosis, which was related to ROS-mediated autophagy through regulation of the PI3K/AKT/mTOR and ERK/p38 MAPK signaling pathways.

Background: Monensin is a carboxyl polyether ionophore that potently inhibits the growth of various cancer cells. Recently, the anticancer effects of monensin have been recognized based on its ability to induce apoptosis in cancer cells. However, anticancer effect of monensin and its mechanism of action have yet to be investigated, especially against human prostate cancer cells. Materials and Methods: Cell viability assay, western blot, cell-cycle arrest, annexin V/propidium iodide assay, reactive oxygen species (ROS) production and intracellular Ca²⁺ flux were assayed. Results: In this study, monensin significantly inhibited cell viability in a dose-dependent manner in prostate cell lines. Moreover, cell growth inhibition by monensin induced G₁ phase cell-cycle arrest and apoptosis via regulation of cell cycle- and apoptosis-related proteins in PC-3 cells. In addition, monensin induced the production of ROS and the disruption of Ca²⁺ homeostasis, that was restored by diphenyleneiodonium, a mitochondrial ROS inhibitor and verapamil, a Ca²⁺ channel blocker, respectively, as confirmed by pro-caspase-3 activation and poly ADP ribose polymerase cleavage. Conclusion: Monensin induces cell-cycle arrest and apoptosis through regulation of cell cycle- and apoptosis-related proteins, resulting in induction of mitochondrial ROS- and Ca²⁺-dependent apoptosis, respectively.

Mitochondrial ROS activates ERK/autophagy pathway as a protected mechanism against deoxypodophyllotoxin-induced apoptosis Mitochondrial ROS activates ERK/autophagy pathway as a protected mechanism against deoxypodophyllotoxin-induced apoptosis