title: Vorinostat and bortezomib synergistically cause ubiquitinated protein accumulation in prostate cancer cells.
abstract: OBJECTIVE
  Protein ubiquitination is a novel strategy used to treat malignancies. We investigated whether the histone deacetylase inhibitor vorinostat (Cayman Chemical, Ann Arbor, Michigan) and the proteasome inhibitor bortezomib (LC Laboratories, Woburn, Massachusetts) would synergistically cause the accumulation of ubiquitinated proteins in prostate cancer cells.
  
  
  METHODS
  LNCaP, PC-3 and DU 145 cells (ATCC™) were treated with vorinostat and/or bortezomib. Cell viability and induction of apoptosis were assessed. In vivo efficacy was evaluated in a murine subcutaneous tumor model using PC-3 cells. The influence of androgen receptor expression on bortezomib efficacy was examined using RNA interference. Changes in the expression of ubiquitinated proteins, cell cycle associated proteins and acetylated histone were evaluated.
  
  
  RESULTS
  Androgen receptor expression seemed to decrease bortezomib activity. PC-3 and DU 145 cells were more susceptible to bortezomib than LNCaP cells and the silencing of androgen receptor expression in LNCaP cells enhanced bortezomib activity. Vorinostat and bortezomib synergistically induced apoptosis, inhibited prostate cancer cell growth and suppressed tumor growth in a murine xenograft model. The combination decreased cyclin D1 and cyclin-dependent kinase 4 expression, and increased p21 expression. The combination synergistically caused the accumulation of ubiquitinated proteins and histone acetylation. This histone acetylation was a consequence of the accumulation of ubiquitinated proteins.
  
  
  CONCLUSIONS
  Vorinostat and bortezomib inhibit the growth of prostate cancer cells synergistically by causing ubiquitinated proteins to accumulate in cells. The current study provides a framework for testing the combination in patients with advanced prostate cancer.
authors.affiliation: Department of Urology, National Defense Medical College, Tokorozawa, Saitama, Japan. zenpaku@ndmc.ac.jp
authors.forename: Akinori
authors.initials: A
authors.lastname: Sato
authors.forename: Takako
authors.initials: T
authors.lastname: Asano
authors.forename: Keiichi
authors.initials: K
authors.lastname: Ito
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Asano
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D045744:Cell Line, Tumor / Q000187:drug effects*; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004195:Disease Models, Animal; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008819:Mice, Nude; D058990:Molecular Targeted Therapy; D011471:Prostatic Neoplasms / Q000188:drug therapy* / Q000473:pathology; D011719:Pyrazines / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000032:analysis; D011897:Random Allocation; D012680:Sensitivity and Specificity; D057149:Ubiquitinated Proteins / Q000187:drug effects* / Q000378:metabolism; D000077337:Vorinostat; D023041:Xenograft Model Antitumor Assays
chemical_list: D001897:Boronic Acids; D006877:Hydroxamic Acids; D011719:Pyrazines; D034741:RNA, Small Interfering; D057149:Ubiquitinated Proteins; D000077337:Vorinostat; D000069286:Bortezomib