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Abstract

Gene expression profiling of tumors, clinically designated as either metastatic (M+) or non-metastatic (M0), identifies genes whose expression differed significantly between classes. A class-prediction algorithm based on these medulloblastoma genes assigned the sample class to these tumors (M+ or M0) with 72% accuracy and to four additional independent tumors with a 100% accuracy. Class prediction also assigned the metastatic medulloblastoma cell line Daoy to the metastatic class. Notably upregulated in the M+ tumors were platelet derived growth factor receptor alpha (PDGFRA) and members of the downstream RAS/mitogen-activated protein kinase (MAPK) signal transduction pathway. Immunohistochemical validation on an independent set of tumors showed significant overexpression of PDGFRA in M+ tumors as compared to M0 tumors. In in vitro assays, PDGFA enhanced medulloblastoma migration and increased downstream MAP2K1 (MEK1), MAP2K2 (MEK2), MAPK1 (p42 MAPK), and MAPK3 (p44 MAPK) phosphorylation in a dose-dependent manner. Neutralizing antibodies to PDGFRA or U0126, a highly specific chemical inhibitor of MAP2K1 and MAP2K2 known as U0126, blocked MAP2K1, MAP2K2, and MAPK1/3 phosphorylation, inhibited migration, and prevented PDGFA-stimulated migration. These results provide the first insight into the genetic regulation of medulloblastoma metastasis and are the first to suggest a role for and the RAS/MAPK signaling pathway in medulloblastoma metastasis. Inhibitors of PDGFRA and RAS proteins, among others overexpressed M+ genes identified herein, represent novel therapeutic targets in medulloblastomas and other M+/MO tumors. The inventive method of prediction and targeted therapy is applicable to any tumor that exists in both M+ and MO forms, such as the neurotumors glioma, neuroblastoma and ependymoma, as well as lung and breast cancers.

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First Claim