Neuroblastoma is the most common extracranial childhood tumor and accounts for approximately 15% of pediatric cancer-related deaths. Further studies are needed to identify potential therapeutic targets for neuroblastoma. Monensin is an ionophore antibiotic obtained from Streptomyces cinnamonensis with known antibacterial and antiparasitic effects. No study has reported the effects of monensin on SH-SY5Y neuroblastoma cells by targeting the PI3K/AKT signaling pathway. The aim of this study was to investigate the antiproliferative effects of monensin alone and in combination with rapamycin in human SH-SY5Y neuroblastoma cells mediated by the PI3K/AKT signaling pathway. The effects of single and combination applications of monensin and rapamycin on SH-SY5Y cell proliferation were investigated by XTT, and their effects on the PI3K/AKT signaling pathway by RT-PCR, immunohistochemistry, immunofluorescence, and Western blotting. The combined effects of monensin and rapamycin on SH-SY5Y proliferation were most potent at 72 h (combination index < 1). The combination of monensin and rapamycin caused a significant decrease in the expression of P21RAS, AKT, and MAPK1 genes. Single and combined administrations of monensin and rapamycin caused a significant decrease in PI3K/AKT expression. Our results showed for the first time that monensin exerts an antiproliferative effect by targeting the PI3K/AKT signaling pathway in neuroblastoma cells. It is suggested that monensin and its combination with rapamycin may be an effective therapeutic candidate for treating neuroblastoma.

Neuroblastoma is the most common pediatric solid tumor originating from the neural crest. New treatment options are needed to improve treatment outcomes and the survival of patients with neuroblastoma. Monensin is an ionophore antibiotic with antiparasitic, antibacterial, and anticancer properties isolated from Streptomyces cinnamonensis. The aim of this study was to investigate the therapeutic effects of single and combined monensin and rapamycin treatments on mTOR (mammalian target of rapamycin) signaling pathway-mediated apoptosis and tumor growth in an SH-SY5Y neuroblastoma cell xenograft model. Control, monensin, rapamycin, and monensin + rapamycin groups were formed in the xenograft neuroblastoma model obtained from CD1 nude mice, and tumor volumes and animal weights were recorded throughout the treatment. In xenograft neuroblastoma tumor tissues, apoptosis was determined by TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling) and cleaved-caspase 3 immunohistochemistry, and PI3K (phosphoinositide-3-kinase)/AKT/mTOR expression was determined by the immunohistochemistry and immunofluorescence methods. The combination of monensin and rapamycin was to reduce the growth of xenograft neuroblastoma tumor tissues, trigger apoptosis, and suppress the expression of PI3K/AKT/mTOR. A significant increase in apoptotic cell rate was demonstrated in the combination group, supported by cleaved-caspase 3 immunohistochemistry results. In addition, it was reported that the combination treatment regime triggered apoptosis by reducing the expression of phosphorylated PI3K/AKT/mTOR. Our preclinical results may be a precursor to develop new therapeutic approaches to treat neuroblastoma.