Disruption of parallel and converging signaling pathways contributes to the synergistic antitumor effects of simultaneous mTOR and EGFR inhibition in GBM cells.

Elevated epidermal growth factor receptor (EGFR) and mammalian target of rapamycin (mTOR) signaling are known to contribute to the malignant properties of glioblastoma multiforme (GBM), which include uncontrolled cell proliferation and evasion of apoptosis. Small molecule inhibitors that target these protein kinases have been evaluated in multiple clinical trials for cancer patients, including those with GBM. Here we have examined the cellular and molecular effects of a combined kinase inhibition of mTOR (rapamycin) and EGFR (EKI-785) in U87 and U251 GBM cells. Simultaneous treatment with rapamycin and EKI-785 results in synergistic antiproliferative as well as proapoptotic effects. At a molecular level, rapamycin alone significantly decreases S6 phosphorylation, whereas EKI-785 alone promotes substantially reduced signal transducer and activator of transcription (STAT3) phosphorylation. Treatment with rapamycin alone also increases Akt phosphorylation on Ser-473, but this effect is blocked by a simultaneous administration of EKI-785. Individually, EKI-785 diminishes while rapamycin promotes the binding of the translation inhibitor eukaryotic initiation factor 4E binding protein (4EBP1) to the eukaryotic translation initiation factor 4E (eIF4E). In spite of these opposing effects, the highest level of 4EBP1-eIF4E binding occurs with the combination of the two inhibitors. These results indicate that the inhibition of EGFR and mTOR has distinct as well as common signaling consequences and provides a molecular rationale for the synergistic antitumor effects of EKI-785 and rapamycin administration.

[1]  D. Guertin,et al.  Phosphorylation and Regulation of Akt/PKB by the Rictor-mTOR Complex , 2005, Science.

[2]  R. McLendon,et al.  Combination therapy of inhibitors of epidermal growth factor receptor/vascular endothelial growth factor receptor 2 (AEE788) and the mammalian target of rapamycin (RAD001) offers improved glioblastoma tumor growth inhibition. , 2005, Molecular cancer therapeutics.

[3]  J. Sarkaria,et al.  Mammalian target of rapamycin (mTOR) inhibitors as anti-cancer agents. , 2004, Current cancer drug targets.

[4]  J. Baselga,et al.  Combined Epidermal Growth Factor Receptor Targeting with the Tyrosine Kinase Inhibitor Gefitinib (ZD1839) and the Monoclonal Antibody Cetuximab (IMC-C225) , 2004, Clinical Cancer Research.

[5]  T. Hunter,et al.  Inappropriate Activation of the TSC/Rheb/mTOR/S6K Cassette Induces IRS1/2 Depletion, Insulin Resistance, and Cell Survival Deficiencies , 2004, Current Biology.

[6]  Y. Yarden,et al.  Oncogenic growth factor receptors: implications for signal transduction therapy. , 2004, Seminars in cancer biology.

[7]  Prakash Chinnaiyan,et al.  Dual-Agent Molecular Targeting of the Epidermal Growth Factor Receptor (EGFR) , 2004, Cancer Research.

[8]  J. Blenis,et al.  Target of rapamycin (TOR): an integrator of nutrient and growth factor signals and coordinator of cell growth and cell cycle progression , 2004, Oncogene.

[9]  Nahum Sonenberg,et al.  Signaling control of mRNA translation in cancer pathogenesis , 2004, Oncogene.

[10]  J. Dancey.  Epidermal growth factor receptor inhibitors in clinical development. , 2004, International journal of radiation oncology, biology, physics.

[11]  C. Thompson,et al.  Differential effects of rapamycin on mammalian target of rapamycin signaling functions in mammalian cells. , 2003, Cancer research.

[12]  S. Schreiber,et al.  Integration of growth factor and nutrient signaling: implications for cancer biology. , 2003, Molecular cell.

[13]  Huang Shao,et al.  Identification and characterization of signal transducer and activator of transcription 3 recruitment sites within the epidermal growth factor receptor. , 2003, Cancer research.

[14]  Paul S Mischel,et al.  Analysis of the phosphatidylinositol 3'-kinase signaling pathway in glioblastoma patients in vivo. , 2003, Cancer research.

[15]  C. Sawyers,et al.  The phosphatidylinositol 3-Kinase–AKT pathway in human cancer , 2002, Nature Reviews Cancer.

[16]  P. Houghton,et al.  4E-binding Proteins, the Suppressors of Eukaryotic Initiation Factor 4E, Are Down-regulated in Cells with Acquired or Intrinsic Resistance to Rapamycin* , 2002, The Journal of Biological Chemistry.

[17]  G. Thomas,et al.  Target of Rapamycin , 2002, Current Biology.

[18]  R. Jove,et al.  Activated STAT signaling in human tumors provides novel molecular targets for therapeutic intervention. , 2002, Clinical cancer research : an official journal of the American Association for Cancer Research.

[19]  C. Proud,et al.  The Extracellular Signal-regulated Kinase Pathway Regulates the Phosphorylation of 4E-BP1 at Multiple Sites* , 2002, The Journal of Biological Chemistry.

[20]  E. Hafen,et al.  dS6K-regulated cell growth is dPKB/dPI(3)K-independent, but requires dPDK1 , 2002, Nature cell biology.

[21]  M. Kay Washington,et al.  Importance of epidermal growth factor receptor signaling in establishment of adenomas and maintenance of carcinomas during intestinal tumorigenesis , 2002, Proceedings of the National Academy of Sciences of the United States of America.

[22]  S K Burley,et al.  Hierarchical phosphorylation of the translation inhibitor 4E-BP1. , 2001, Genes & development.

[23]  G. Mills,et al.  Linking molecular therapeutics to molecular diagnostics: Inhibition of the FRAP/RAFT/TOR component of the PI3K pathway preferentially blocks PTEN mutant cells in vitro and in vivo , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[24]  C. James,et al.  PTEN mutation, EGFR amplification, and outcome in patients with anaplastic astrocytoma and glioblastoma multiforme. , 2001, Journal of the National Cancer Institute.

[25]  J. Blenis,et al.  An inhibitor of mTOR reduces neoplasia and normalizes p70/S6 kinase activity in Pten+/− mice , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[26]  Hong Wu,et al.  Enhanced sensitivity of PTEN-deficient tumors to inhibition of FRAP/mTOR , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[27]  Y. Yarden,et al.  Untangling the ErbB signalling network , 2001, Nature Reviews Molecular Cell Biology.

[28]  J. Olefsky,et al.  A rapamycin-sensitive pathway down-regulates insulin signaling via phosphorylation and proteasomal degradation of insulin receptor substrate-1. , 2000, Molecular endocrinology.

[29]  C. James,et al.  Diversity and frequency of epidermal growth factor receptor mutations in human glioblastomas. , 2000, Cancer research.

[30]  S. Gygi,et al.  Regulation of 4E-BP1 phosphorylation: a novel two-step mechanism. , 1999, Genes & development.

[31]  W. Earnshaw,et al.  Comparison of Paclitaxel-, 5-Fluoro-2′-deoxyuridine-, and Epidermal Growth Factor (EGF)-induced Apoptosis , 1999, The Journal of Biological Chemistry.

[32]  A. Guha.  Ras Activation in Astrocytomas and Neurofibromas , 1998, Canadian Journal of Neurological Sciences / Journal Canadien des Sciences Neurologiques.

[33]  Y Chen,et al.  Treatment of polycystic kidney disease with a novel tyrosine kinase inhibitor. , 2000, Kidney international.

[34]  A. Gingras,et al.  eIF4E activity is regulated at multiple levels. , 1999, The international journal of biochemistry & cell biology.

[35]  T. Chou,et al.  Quantitative analysis of dose-effect relationships: the combined effects of multiple drugs or enzyme inhibitors. , 1984, Advances in enzyme regulation.

[36]  P. Goodfellow,et al.  A monoclonal antibody to the human epidermal growth factor receptor , 1982, Journal of cellular biochemistry.