Activation of phosphatidylinositol-3'-kinase/AKT signaling is essential in hepatoblastoma survival.

Purpose: Hepatoblastoma represents the most frequent malignant liver tumor in childhood. The phosphatidylinositol-3′-kinase (PI3K)/AKT pathway is crucial in downstream signaling of multiple receptor tyrosine kinases of pathogenic importance in hepatoblastoma. Increased PI3K/AKT signaling pathway activity and activating mutations of PIK3CA , encoding a PI3K catalytic subunit, have been reported in different childhood tumors. The current study was done to analyze the role of PI3K/AKT signaling in hepatoblastoma. Experimental Design: Immunohistochemical stainings of (Ser473)-phosphorylated (p)-AKT protein, its targets p-(Ser9)-GSK-3β and p-(Ser2448)-mTOR, as well as the cell cycle regulators Cyclin D1, p27 KIP1 , and p21 CIP1 were done and the PIK3CA gene was screened for mutations. In vitro , two hepatoblastoma cell lines treated with the PI3K inhibitor LY294002 were analyzed for AKT and GSK-3β phosphorylation, cell proliferation, and apoptosis. Additionally, simultaneous treatments of hepatoblastoma with LY294002 and cytotoxic drugs were carried out. Results: Most tumors strongly expressed p-AKT, p-GSK-3β, and p-mTOR; subgroups showed significant Cyclin D1, p27 KIP1 , and p21 CIP1 expression. One hepatoblastoma carried an E545A mutation in the PIK3CA gene. In vitro , PI3K inhibition diminished hepatoblastoma cell growth being accompanied by reduced AKT and GSK-3β phosphorylation. Flow cytometry and 49, 6-diamidino-2-phenylindole stainings showed that PI3K pathway inhibition leads to a substantial increase in apoptosis and a decrease in cellular proliferation linked to reduced Cyclin D1 and increased p27 KIP1 levels. Simultaneous treatment of hepatoblastoma cell lines with LY294002 and cytotoxic drugs resulted in positive interactions. Conclusions: Our findings imply that PI3K signaling plays an essential role in growth control of hepatoblastoma and might be successfully targeted in multimodal therapeutic strategies.