Targeting PI3K in neuroblastoma.

PURPOSE: This work employs pharmacological targeting of phosphoinositide 3-kinases (PI3K) in selected neuroblastoma (NB) tumors with the inhibitor AS605240, which has been shown to express low toxicity and relative specificity for the PI3K species γ. METHODS: The expression pattern of PI3K isoforms in 7 NB cell lines and 14 tumor patient samples was determined by Western blotting and immunocytochemistry. The effect of AS605240 on the growth of four selected tumor cell lines was assessed. Two cell lines exhibiting (SK-N-LO) or lacking (SK-N-AS) PI3Kγ expression were chosen for further in vitro analysis, which involved propidium iodide (PI)-based cell cycle staining, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL-staining) of apoptotic cells and analysis of PI3K/Akt-related signaling pathways via Western blotting and translocation experiments. The action of AS605240 in vivo was addressed by xenograft experiments in severe combined immunodeficiency (SCID) mice, thereby comparing SK-N-LO and SK-N-AS derived tumors. Apoptosis induced in SK-N-LO tumors was shown by immunohistochemical TUNEL-staining. RESULTS: Significant expression of PI3Kγ in neuroblastoma patient biopsies and tumor cell lines was detected. AS605240 induced apoptosis in NB cell lines proportional to this expression and suppressed growth of PI3Kγ positive, but not negative, tumors in a xenograft mouse model. No adverse effects of the inhibitor treatment were observed. CONCLUSIONS: Our observations hint to an oncogenic function of PI3Kγ in distinct neuroblastoma entities and reveal PI3K targeting by AS605240 as a promising molecular therapy of these tumors.