Napabucasin, a novel STAT3 inhibitor suppresses proliferation, invasion and stemness of glioblastoma cells

BACKGROUND: Glioblastoma (GBM) cells with stem cell-like properties are called glioma stem cells (GSCs). GSCs display highly treatment resistance and are responsible for tumor recurrence. Napabucasin (BBI608), a novel small molecule inhibitor of STAT3, has been identified to eliminate stemness-like tumor cells in some cancers. However, the influence of Napabucasin on GBM cells, especially on GSCs, is currently unclear. In this study, we explored the influence and underlying mechanisms of Napabucasin on GBM cells. METHODS: STAT3 expression and its correlation with the glioma grade and patient survival were analyzed using CGGA and TCGA glioma databases. The influence of Napabucasin on proliferation, stemness, the cell cycle, apoptosis, and invasion of human GBM cell lines U87MG and LN229 was tested by CCK8, EdU incorporation, colony formation, Transwell invasion, and three-dimensional spheroid assays as well as flow cytometry, qPCR, and western blot analysis. The ability of Napabucasin to inhibit cell proliferation of U87MG tumor xenografts in mice was assessed using a live animal bioluminescence imaging system and immunohistochemistry. RESULTS: Napabucasin suppressed the proliferation, colony formation, and invasion of U87MG and LN229 cells. Furthermore, Napabucasin induced cell cycle arrest and apoptosis. More importantly, Napabucasin treatment obviously inhibited expression of stemness-associated genes including STAT3 and suppressed the spheroid formation of glioma cells in vitro. Napabucasin also disrupted the NF-κB signaling pathway via downregulation of RelA (p65). Finally, glioma growth was effectively impaired by Napabucasin in nude mice bearing intracranial glioma xenografts. CONCLUSIONS: Napabucasin treatment may be a novel approach for the treatment of GBM, particularly GSCs.