Efficacy of glycogen synthase kinase-3β targeting against osteosarcoma via activation of β-catenin

Development of innovative more effective therapy is required for refractory osteosarcoma patients. We previously established that glycogen synthase kinase-3 beta (GSK-3 beta) is a therapeutic target in various cancer types. In the present study, we explored the therapeutic efficacy of GSK-3 beta inhibition against osteosarcoma and the underlying molecular mechanisms in an orthotopic mouse model. Expression and phosphorylation of GSK-3 beta in osteosarcoma and normal osteoblast cell lines was examined, together with efficacy of GSK-3 beta inhibition on cell survival, proliferation and apoptosis and on the growth of orthotopically-transplanted human osteosarcoma in nude mice. We also investigated changes in expression, phosphorylation and co-transcriptional activity of beta-catenin in osteosarcoma cells following GSK-3 beta inhibition. Expression of the active form of GSK-3 beta (tyrosine 216-phosphorylated) was higher in osteosarcoma than osteoblast cells. Inhibition of GSK-3 beta activity by pharmacological inhibitors or of its expression by RNA interference suppressed proliferation of osteosarcoma cells and induced apoptosis. Treatment with GSK-3 beta-specific inhibitors attenuated the growth of orthotopic osteosaroma in mice. Inhibition of GSK-3 beta reduced phosphorylation at GSK-3 beta-phospho-acceptor sites in beta-catenin and increased beta-catenin expression, nuclear localization and co-transcriptional activity. These results suggest the efficacy of GSK-3 beta inhibitors is associated with activation of beta-catenin, a putative tumor suppressor in bone and soft tissue sarcoma and an important component of osteogenesis. Our study thereby demonstrates a critical role for GSK-3 beta in sustaining survival and proliferation of osteosarcoma cells, and identifies this kinase as a potential therapeutic target against osteosarcoma.