E804 induces growth arrest, differentiation and apoptosis of glioblastoma cells by blocking Stat3 signaling

Glioblastoma, the most common type of primary malignant brain tumor, is a devastating disease associated with a median survival of approximately 12 months. Here, we have tested E804, the commercially available indirubin derivatives, against U251 and U87 glioblastoma cells. Treatment with E804 significantly inhibits the growth of human glioblastoma cells lines via induction of differentiation and apoptosis. Differentiation induction is coupled with increased expression of glial fibriliary acidic protein, a marker for mature astrocytes. Apoptosis is associated with activation of Caspase 3 and reduction of Bcl-xL and Mcl-1. Furthermore, we demonstrate that E804 reduces signal transducer and activator of transcription-3 (Stat3) signaling to a remarkable extent, suggesting that inactivation of Stat3, at least in part, mediates the effects of this indirubin derivative. Consistently, reduction of Stat3 activity promotes E804-mediated anti-tumor effects, whereas overexpression of Stat3C mutant recues cell apoptosis induced by E804. Taken together, our results indicate that E804 can effectively suppress tumor cell growth, induce tumor cell differentiation and apoptosis mediated partially by Stat3 signaling pathway, suggesting that E804 could be useful for a potential anti-glioblastoma therapeutic approach.