Protein Kinase B Modulates the Sensitivity of Human Neuroblastoma Cells to Insulin-like Growth Factor Receptor Inhibition

The potential of the novel insulin-like growth factor receptor (IGF-IR) inhibitor NVP-AEW541 as an antiproliferative agent in human neuroblastoma was investigated. Proliferation of a panel of neuroblastoma cell lines was inhibited by NVP-AEW541 with IC(50) values ranging from 0.15 to 5 microM. Experiments using an IGF-IR neutralizing antibody confirmed that the IGF-IR was essential to support growth of neuroblastoma cell lines. The expression levels of the IGF-IR in individual neuroblastoma cell lines did not correlate with the sensitivities to NVP-AEW541, while coexpression of the IGF-IR and the insulin receptor (IR) correlated with lower sensitivity to the inhibitor in some cell lines. Intriguingly, high levels of activation of Akt/protein kinase B (PKB) and phosphorylation of the ribosomal S6 protein were observed in neuroblastoma cell lines with decreased sensitivities to NVP-AEW541. Inhibition of Akt/PKB activity restored the sensitivity of neuroblastoma cells to the IGF-IR inhibitor. Transfection of neuroblastoma cells with activated Akt or ribosomal protein S6 kinase (S6K) decreased the sensitivity of the cells to NVP-AEW541. IGF-I-stimulated proliferation of neuroblastoma cell lines was completely blocked by NVP-AEW541, or by a combination of an inhibitor of phosphoinositide 3-kinase and rapamycin. In addition to its antiproliferative effects, NVP-AEW541 sensitized neuroblastoma cells to cisplatin-induced apoptosis. Together, our data demonstrate that NVP-AEW541 in combination with Akt/PKB inhibitors or chemotherapeutic agents may represent a novel approach to target human neuroblastoma cell proliferation.