title: Ritonavir interacts with bortezomib to enhance protein ubiquitination and histone acetylation synergistically in renal cancer cells.
abstract: OBJECTIVE
  To investigate the combined effects of the HIV protease inhibitor ritonavir and proteasome inhibitor bortezomib on renal cancer cells. Ritonavir induces endoplasmic reticulum (ER) stress and we hypothesized that inhibiting proteasome activity under ER stress would further inhibit cancer cell growth by enhancing protein ubiquitination.
  
  
  METHODS
  The effectiveness of the combination of ritonavir and bortezomib on renal cancer cells (Caki-1, ACHN, 786-O, 769-P) was assessed by MTS assay, colony formation assay, cell cycle analysis, and annexin-V assay. In vivo efficacy was evaluated using mice subcutaneous tumor models. Induction of ER stress, protein ubiquitination, histone acetylation, and changes in the expression of histone deacetylase (HDAC) were evaluated by Western blotting.
  
  
  RESULTS
  Ritonavir in combination with bortezomib induced apoptosis and inhibited renal cancer growth synergistically at clinically feasible concentrations. In subcutaneous tumor models using Caki-1 cells, 10-day treatment with the combination was well tolerated and inhibited tumor growth significantly. Ritonavir induced ER stress and the combination enhanced protein ubiquitination synergistically. The combination was also found to induce histone acetylation by suppressing the HDAC expression.
  
  
  CONCLUSIONS
  The combination of ritonavir and bortezomib inhibits renal cancer growth synergistically. The effectiveness of the combination is caused by protein ubiquitination and histone acetylation. Our results provide a rationale for investigating the combination in patients with renal 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: D000107:Acetylation / Q000187:drug effects; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004721:Endoplasmic Reticulum / Q000187:drug effects; D017320:HIV Protease Inhibitors / Q000494:pharmacology*; D006657:Histones / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D011719:Pyrazines / Q000494:pharmacology*; D019438:Ritonavir / Q000494:pharmacology*; D057149:Ubiquitinated Proteins / Q000187:drug effects*; D054875:Ubiquitination / Q000187:drug effects*; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D001897:Boronic Acids; D017320:HIV Protease Inhibitors; D006657:Histones; D011719:Pyrazines; D057149:Ubiquitinated Proteins; D000069286:Bortezomib; D019438:Ritonavir