Data from Phosphoprotein Pathway Mapping: Akt/Mammalian Target of Rapamycin Activation Is Negatively Associated with Childhood Rhabdomyosarcoma Survival

Abstract

<div>Abstract<p>Mapping of protein signaling networks within tumors can identify new targets for therapy and provide a means to stratify patients for individualized therapy. Despite advances in combination chemotherapy, the overall survival for childhood rhabdomyosarcoma remains ∼60%. A critical goal is to identify functionally important protein signaling defects associated with treatment failure for the 40% nonresponder cohort. Here, we show, by phosphoproteomic network analysis of microdissected tumor cells, that interlinked components of the Akt/mammalian target of rapamycin (mTOR) pathway exhibited increased levels of phosphorylation for tumors of patients with short-term survival. Specimens (<i>n</i> = 59) were obtained from the Children's Oncology Group Intergroup Rhabdomyosarcoma Study (IRS) IV, D9502 and D9803, with 12-year follow-up. High phosphorylation levels were associated with poor overall and poor disease-free survival: Akt Ser<sup>473</sup> (overall survival <i>P</i> < 0.001, recurrence-free survival <i>P</i> < 0.0009), 4EBP1 Thr<sup>37/46</sup> (overall survival <i>P</i> < 0.0110, recurrence-free survival <i>P</i> < 0.0106), eIF4G Ser<sup>1108</sup> (overall survival <i>P</i> < 0.0017, recurrence-free survival <i>P</i> < 0.0072), and p70S6 Thr<sup>389</sup> (overall survival <i>P</i> < 0.0085, recurrence-free survival <i>P</i> < 0.0296). Moreover, the findings support an altered interrelationship between the insulin receptor substrate (IRS-1) and Akt/mTOR pathway proteins (<i>P</i> < 0.0027) for tumors from patients with poor survival. The functional significance of this pathway was tested using CCI-779 in a mouse xenograft model. CCI-779 suppressed phosphorylation of mTOR downstream proteins and greatly reduced the growth of two different rhabdomyosarcoma (RD embryonal <i>P</i> = 0.00008; Rh30 alveolar <i>P</i> = 0.0002) cell lines compared with controls. These results suggest that phosphoprotein mapping of the Akt/mTOR pathway should be studied further as a means to select patients to receive mTOR/IRS pathway inhibitors before administration of chemotherapy. [Cancer Res 2007;67(7):3431–40]</p></div>