title: Rapamycin-mediated FOXO1 inactivation reduces the anticancer efficacy of rapamycin.
abstract: BACKGROUND
  Mammalian target of rapamycin (mTOR) inhibitors such as rapamycin have shown modest effects in cancer therapy due in part to the removal of a negative feedback loop leading to the activation of the phosphatidylinositol 3-kinase/Akt (PI3K/Akt) signaling pathway. In this report, we have investigated the role of FOXO1, a downstream substrate of the PI3K/Akt pathway in the anticancer efficacy of rapamycin.
  
  
  METHODS
  Colon cancer cells were treated with rapamycin and FOXO1 phosphorylation was determined by Western blot. Colon cancer cells transfected with a constitutively active mutant of FOXO1 or a control plasmid were treated with rapamycin and the antiproliferative efficacy of rapamycin was monitored.
  
  
  RESULTS
  Rapamycin induced the phosphorylation of FOXO1 as well as its translocation from the nucleus to the cytoplasm, leading to FOXO1 inactivation. The expression of an active mutant of FOXO1 in colon cancer cells potentiated the antiproliferative efficacy of rapamycin in vitro and its antitumor efficacy in vivo.
  
  
  CONCLUSIONS
  Taken together these results show that rapamycin-induced FOXO1 inactivation reduces the antitumor efficacy of rapamycin.
authors.affiliation: Department of Visceral Surgery, University Hospital of Lausanne, Pavillon 3/CHUV, Av de Beaumont, 1011 Lausanne, Switzerland.
authors.forename: Etienne
authors.initials: E
authors.lastname: Abdelnour-Berchtold
authors.forename: Yannick
authors.initials: Y
authors.lastname: Cerantola
authors.forename: Didier
authors.initials: D
authors.lastname: Roulin
authors.forename: Anne
authors.initials: A
authors.lastname: Dormond-Meuwly
authors.forename: Nicolas
authors.initials: N
authors.lastname: Demartines
authors.forename: Olivier
authors.initials: O
authors.lastname: Dormond
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D048708:Cell Growth Processes / Q000187:drug effects; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D005260:Female; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D019073:HT29 Cells; D006801:Humans; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D008819:Mice, Nude; D046912:Multiprotein Complexes; D011506:Proteins; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000378:metabolism; D014162:Transfection; D023041:Xenograft Model Antitumor Assays
chemical_list: D000903:Antibiotics, Antineoplastic; C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D046912:Multiprotein Complexes; D011506:Proteins; D014157:Transcription Factors; D000076222:Mechanistic Target of Rapamycin Complex 1; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus