title: Incomplete inhibition of phosphorylation of 4E-BP1 as a mechanism of primary resistance to ATP-competitive mTOR inhibitors.
abstract: The mammalian target of rapamycin (mTOR) regulates cell growth by integrating nutrient and growth factor signaling and is strongly implicated in cancer. But mTOR is not an oncogene, and which tumors will be resistant or sensitive to new adenosine triphosphate (ATP) competitive mTOR inhibitors now in clinical trials remains unknown. We screened a panel of over 600 human cancer cell lines to identify markers of resistance and sensitivity to the mTOR inhibitor PP242. RAS and phosphatidylinositol 3-kinase catalytic subunit alpha (PIK3CA) mutations were the most significant genetic markers for resistance and sensitivity to PP242, respectively; colon origin was the most significant marker for resistance based on tissue type. Among colon cancer cell lines, those with KRAS mutations were most resistant to PP242, whereas those without KRAS mutations most sensitive. Surprisingly, cell lines with co-mutation of PIK3CA and KRAS had intermediate sensitivity. Immunoblot analysis of the signaling targets downstream of mTOR revealed that the degree of cellular growth inhibition induced by PP242 was correlated with inhibition of phosphorylation of the translational repressor eIF4E-binding protein 1 (4E-BP1), but not ribosomal protein S6 (rpS6). In a tumor growth inhibition trial of PP242 in patient-derived colon cancer xenografts, resistance to PP242-induced inhibition of 4E-BP1 phosphorylation and xenograft growth was again observed in KRAS mutant tumors without PIK3CA co-mutation, compared with KRAS wild-type controls. We show that, in the absence of PIK3CA co-mutation, KRAS mutations are associated with resistance to PP242 and that this is specifically linked to changes in the level of phosphorylation of 4E-BP1.
authors.affiliation: Department of Chemistry, University of California, Berkeley, Berkeley, CA, USA.
authors.forename: G S
authors.initials: GS
authors.lastname: Ducker
authors.affiliation: Department of Medicine, University of California, San Francisco, San Francisco, CA, USA.
authors.forename: C E
authors.initials: CE
authors.lastname: Atreya
authors.affiliation: Department of Pathology, University of California, San Francisco, San Francisco, CA, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Simko
authors.affiliation: 1] Preclinical Therapeutics Core, University of California, San Francisco, San Francisco, CA, USA [2] Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA, USA.
authors.forename: Y K
authors.initials: YK
authors.lastname: Hom
authors.affiliation: 1] Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA, USA [2] Section of Surgical Oncology, Department of Surgery, University of California, San Francisco, San Francisco, CA, USA.
authors.forename: M R
authors.initials: MR
authors.lastname: Matli
authors.affiliation: Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, MA, USA.
authors.forename: C H
authors.initials: CH
authors.lastname: Benes
authors.affiliation: 1] Preclinical Therapeutics Core, University of California, San Francisco, San Francisco, CA, USA [2] Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA, USA.
authors.forename: B
authors.initials: B
authors.lastname: Hann
authors.affiliation: 1] Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA, USA [2] Section of Surgical Oncology, Department of Surgery, University of California, San Francisco, San Francisco, CA, USA.
authors.forename: E K
authors.initials: EK
authors.lastname: Nakakura
authors.affiliation: Department of Medicine, University of California, San Francisco, San Francisco, CA, USA.
authors.forename: E K
authors.initials: EK
authors.lastname: Bergsland
authors.affiliation: 1] Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA, USA [2] Section of Surgical Oncology, Department of Surgery, University of California, San Francisco, San Francisco, CA, USA.
authors.forename: D B
authors.initials: DB
authors.lastname: Donner
authors.affiliation: Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, MA, USA.
authors.forename: J
authors.initials: J
authors.lastname: Settleman
authors.affiliation: 1] Department of Chemistry, University of California, Berkeley, Berkeley, CA, USA [2] Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA, USA [3] Howard Hughes Medical Institute and Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Shokat
authors.affiliation: 1] Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA, USA [2] Section of Surgical Oncology, Department of Surgery, University of California, San Francisco, San Francisco, CA, USA.
authors.forename: R S
authors.initials: RS
authors.lastname: Warren
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001667:Binding, Competitive / Q000187:drug effects*; D002352:Carrier Proteins / Q000378:metabolism*; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D058534:Class I Phosphatidylinositol 3-Kinases; D003110:Colonic Neoplasms / Q000473:pathology; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D039642:Eukaryotic Initiation Factors; D005260:Female; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000235:genetics; D016283:Proto-Oncogene Proteins p21(ras); D011687:Purines / Q000494:pharmacology*; D038601:Ribosomal Protein S6 / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays; D018631:ras Proteins / Q000235:genetics
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000255:Adenosine Triphosphate; D000970:Antineoplastic Agents; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D058534:Class I Phosphatidylinositol 3-Kinases; D039642:Eukaryotic Initiation Factors; D007211:Indoles; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D016283:Proto-Oncogene Proteins p21(ras); D011687:Purines; D038601:Ribosomal Protein S6; D058570:TOR Serine-Threonine Kinases; D018631:ras Proteins; C499527:Eif4ebp1 protein, mouse; C117307:KRAS protein, human; C484760:PIK3CA protein, human; C572919:PP242
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