Activation of Akt predicts poor outcome in neuroblastoma

Whereas aberrant activation of the phosphatidylinositol 3'-kinase (PI3K)/Akt pathway, a key survival cascade, has prevously been linked to poor prognosis in several human malignan cies, its prognostic effect in neuroblastorna has not yet been explored. We therefore investigated the phosphorylation status of Ak-t, S6 ribosomal protein as target of mammalian target of rapamycin, and extracellular signalregulated kinase (ERK) in 116 primary neuroblastoma samples by tissue microarray and its correlation with established prognostic markers and survival outcome. Here, we provide for the first time evidence that phosphorylation of Ak-t at serine 473 (S473) and/or threonine 308 (T308), S6 ribosomal protein, and ERK frequently occurs in primary neuroblastoma. Importantly, we identified Akt activation as a novel prognostic indicator of decreased event-free or overall survival in neuroblastoma, whereas phosphorylation of S6 ribosomal protein or ERK had no prognostic effect. In addition, AU activation correlated with variables of aggressive disease, including AlYCA1 amplification, Ip36 aberrations, advanced disease stage, age at diagnosis, and unfavorable histology. Monitoring Akt at T308 or both phosphorylation sites improved the prognostic significance of Akt activation in neuroblastoma specimens compared with S473 phosphorylation. Parallel experiments in neuroblastoma cell lines revealed that activation of Akt bv insulin-like growth factor (IGF)-I significantly inhibited tumor necrosis factor-related apoptosisinducing ligand- or chemotherapy-induced apoptosis in a PI3K-dependent manner because the PI3K inhibitor LY294002 completely reversed the IGF-1-mediated protection of neuroblastoma cells from apoptosis. By showing that activation of Akt correlates with poor prognosis in primary neuroblastoma in vivo and with apoptosis resistance in vitro, our findings indicate that Akt presents a clinically relevant target in neuroblastoma that warrants further investigation.