Honokiol triggers receptor-interacting protein kinase 3-mediated cell death of neuroblastoma cells by upregulating reactive oxygen species

Neuroblastoma is the most common form of childhood extracranial tumor and almost half of neuroblastoma cases occur in infants under two years old. Neuroblastoma accounts for similar to 6-10% of childhood cancers and 15% of cancer-associated childhood mortality. However, an effective treatment remains to be developed. Honokiol exhibits long-lasting central muscle relaxation, anti-inflammatory, antibacterial, antimicrobial, antiulcer, antioxidation, antiaging and antitumor effects. Honokiol has been previously demonstrated to kill neuroblastoma cells, however, the underlying mechanism of action remains unclear. The present study reports that honokiol inhibits the growth of neuroblastoma cells via upregulation of reactive oxygen species (ROS). MTT assays demonstrated that treatment of Neuro-2a neuroblastoma cells with honokiol resulted in time-and dose-dependent inhibition of cell proliferation, which was associated with upregulation of the protein expression of receptor-interacting protein kinase 3 (RIP3), as demonstrated by western blot analysis. Furthermore, knockdown of RIP3 by small interfering RNA, or pharmacological inhibition of RIP3 by the RIP3 specific inhibitor necrosulfonamide, reversed honokiol-induced loss of cell viability in Neuro-2a cells. Importantly, honokiol significantly increased the intracellular ROS levels as determined by a 2',7'dichlorofluorescin diacetate assay, while ROS scavenger N-acetyl cysteine significantly prevented the induction of ROS and RIP3 by honokiol. The results of the present study indicate that honokiol may suppress the growth of neuroblastoma Neuro-2a cells, at least partially, through ROS-mediated upregulation of RIP3.