title: Temsirolimus downregulates p21 without altering cyclin D1 expression and induces autophagy and synergizes with vorinostat in mantle cell lymphoma.
abstract: OBJECTIVE
  To investigate the mechanisms of antiproliferative effect induced by the mammalian target of rapamycin (mTOR) inhibitor temsirolimus in mantle cell lymphoma (MCL).
  
  
  METHODS
  The antiproliferative effect of temsirolimus on three well-defined MCL cell lines was examined by the MTS assay. Induction of cell-cycle arrest, autophagy, and apoptosis were determined by fluorescence-activated cell sorting analysis. The molecular mechanisms underlining these effects were determined by Western blot. Synergy between temsirolimus and vorinostat were examined by MTS assay and the combination index was calculated.
  
  
  RESULTS
  Temsirolimus has antiproliferative activity in three MCL cell lines in a dose- and time-dependent manner. Mechanistically, temsirolimus inhibited mTOR, as evidenced by inhibition of ribosomal S6 phosphorylation, and induced cell-cycle arrest in the G(0)/G(1) phase and a decrease in p21 expression without altering p27 or cyclin D1 levels. Furthermore, temsirolimus increased the number of acidic vesicular organelles and the amount of microtubule-associated protein 1 light-chain 3 processing, which are characteristic of autophagy, without induction of apoptosis. These changes were not associated with alteration in phosphorylated extracellular signal-regulated kinase (ERK), beclin-1, Bax, or Bak levels. In contrast, treatment of these cell lines with the histone deacetylase inhibitor vorinostat decreased ERK phosphorylation, activated caspase 3, and induced apoptosis. Moreover, temsirolimus synergized with submaximal concentrations of vorinostat in all MCL cell lines.
  
  
  CONCLUSIONS
  This is the first report of temsirolimus-induced autophagy in MCL, and of vorinostat inhibition of ERK phosphorylation in MCL. Collectively, these data suggest that the combination of temsirolimus and vorinostat have synergistic antiproliferative activity in MCL cells by distinctively targeting apoptosis and autophagy.
authors.affiliation: Department of Lymphoma/Myeloma, The University of Texas M. D. Anderson Cancer Center, Houston, Tex. 77030, USA.
authors.forename: Victor Y
authors.initials: VY
authors.lastname: Yazbeck
authors.forename: Daniela
authors.initials: D
authors.lastname: Buglio
authors.forename: Georgios V
authors.initials: GV
authors.lastname: Georgakis
authors.forename: Yang
authors.initials: Y
authors.lastname: Li
authors.forename: Eiji
authors.initials: E
authors.lastname: Iwado
authors.forename: Jorge E
authors.initials: JE
authors.lastname: Romaguera
authors.forename: Seiji
authors.initials: S
authors.lastname: Kondo
authors.forename: Anas
authors.initials: A
authors.lastname: Younes
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D001343:Autophagy / Q000187:drug effects*; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D019938:Cyclin D1 / Q000378:metabolism*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects*; D004357:Drug Synergism; D016193:G1 Phase / Q000187:drug effects; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology*; D020522:Lymphoma, Mantle-Cell / Q000188:drug therapy / Q000378:metabolism*; D020123:Sirolimus / Q000031:analogs & derivatives* / Q000494:pharmacology; D000077337:Vorinostat
chemical_list: D000970:Antineoplastic Agents; D050759:Cyclin-Dependent Kinase Inhibitor p21; D006877:Hydroxamic Acids; D019938:Cyclin D1; D000077337:Vorinostat; C401859:temsirolimus; D020123:Sirolimus