title: Counteracting autophagy overcomes resistance to everolimus in mantle cell lymphoma.
abstract: OBJECTIVE
  Mantle cell lymphoma (MCL) is an aggressive B-lymphoid neoplasm with poor response to conventional chemotherapy and short survival. The phosphatidylinositol 3-kinase/Akt/mTOR survival pathway is constitutively activated in MCL cells, thereby making the mTOR inhibition an attractive therapeutic strategy. The first clinical studies of everolimus (RAD001), an mTOR inhibitor, in relapsed MCL patients have reported a significant response. Our aim was to analyze the mechanism related to everolimus resistance/sensitivity in MCL cells.
  
  
  METHODS
  Sensitivity to everolimus was analyzed in MCL cell lines and primary MCL cells. Everolimus mechanism of action was determined by flow cytometry and Western blot. Particularly, autophagy was studied by LC3BI/II expression, autophagolysosomes detection by flow cytometry and fluorescence microscopy, and siRNA-mediated gene silencing.
  
  
  RESULTS
  Everolimus exerted antitumoral effect on MCL cells while sparing normal cells. In MCL cell lines, this phenomenon was associated to G(1) cell-cycle arrest, dephosphorylation of the mTOR downstream targets, 4E-BP1 and S6RP, and rephosphorylation of Akt. A synergistic cytotoxic effect was observed between everolimus and an Akt inhibitor, which overcame the compensatory reactivation within the mTOR signaling pathway. Interestingly, MCL cells with low response to this combination showed high levels of autophagy. Accordingly, selective triple knockdown of the autophagy genes ATG7, ATG5 and ATG3, and pretreatment with the autophagy inhibitor hydroxychloroquine, efficiently overcame the resistance to Akt/mTOR inhibitors, leading to the activation of the mitochondrial apoptotic pathway.
  
  
  CONCLUSIONS
  These results suggest that autophagy induction protects MCL cells from Akt/mTOR targeting and counteracting autophagy may represent an attractive strategy for sensitizing MCL cells to everolimus-based therapy.
authors.affiliation: Universitat de Barcelona, Barcelona, Spain.
authors.forename: Laia
authors.initials: L
authors.lastname: Rosich
authors.forename: Sílvia
authors.initials: S
authors.lastname: Xargay-Torrent
authors.forename: Mónica
authors.initials: M
authors.lastname: López-Guerra
authors.forename: Elías
authors.initials: E
authors.lastname: Campo
authors.forename: Dolors
authors.initials: D
authors.lastname: Colomer
authors.forename: Gaël
authors.initials: G
authors.lastname: Roué
mesh_terms: D000970:Antineoplastic Agents / Q000627:therapeutic use; D001343:Autophagy / Q000235:genetics*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D000068338:Everolimus; D006801:Humans; D020522:Lymphoma, Mantle-Cell / Q000188:drug therapy* / Q000473:pathology; D058990:Molecular Targeted Therapy; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D020123:Sirolimus / Q000031:analogs & derivatives* / Q000627:therapeutic use; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D000068338:Everolimus; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; C546842:MTOR protein, human