title: Panobinostat synergizes with bortezomib to induce endoplasmic reticulum stress and ubiquitinated protein accumulation in renal cancer cells.
abstract: BACKGROUND
  Inducing endoplasmic reticulum (ER) stress is a novel strategy used to treat malignancies. Inhibition of histone deacetylase (HDAC) 6 by the HDAC inhibitor panobinostat hinders the refolding of unfolded proteins by increasing the acetylation of heat shock protein 90. We investigated whether combining panobinostat with the proteasome inhibitor bortezomib would kill cancer cells effectively by inhibiting the degradation of these unfolded proteins, thereby causing ubiquitinated proteins to accumulate and induce ER stress.
  
  
  METHODS
  Caki-1, ACHN, and 769-P cells were treated with panobinostat and/or bortezomib. Cell viability, clonogenicity, and induction of apoptosis were evaluated. The in vivo efficacy of the combination was evaluated using a murine subcutaneous xenograft model. The combination-induced ER stress and ubiquitinated protein accumulation were assessed.
  
  
  RESULTS
  The combination of panobinostat and bortezomib induced apoptosis and inhibited renal cancer growth synergistically (combination indexes <1). It also suppressed colony formation significantly (p <0.05). In a murine subcutaneous tumor model, a 10-day treatment was well tolerated and inhibited tumor growth significantly (p <0.05). Enhanced acetylation of the HDAC6 substrate alpha-tubulin was consistent with the suppression of HDAC6 activity by panobinostat, and the combination was shown to induce ER stress and ubiquitinated protein accumulation synergistically.
  
  
  CONCLUSIONS
  Panobinostat inhibits renal cancer growth by synergizing with bortezomib to induce ER stress and ubiquitinated protein accumulation. The current study provides a basis for testing the combination in patients with advanced renal cancer.
authors.affiliation: Department of Urology, National Defense Medical College, 3-2 Namiki, Tokorozawa, Saitama 359-8513, 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: Makoto
authors.initials: M
authors.lastname: Isono
authors.forename: Keiichi
authors.initials: K
authors.lastname: Ito
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Asano
mesh_terms: D000107:Acetylation; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D001897:Boronic Acids / Q000494:pharmacology* / Q000627:therapeutic use; D000069286:Bortezomib; D045744:Cell Line, Tumor; D004195:Disease Models, Animal; D004357:Drug Synergism; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D006657:Histones / Q000378:metabolism; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology* / Q000627:therapeutic use; D007211:Indoles / Q000494:pharmacology* / Q000627:therapeutic use; D007680:Kidney Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D008807:Mice, Inbred BALB C; D000077767:Panobinostat; D011719:Pyrazines / Q000494:pharmacology* / Q000627:therapeutic use; D057149:Ubiquitinated Proteins / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D001897:Boronic Acids; D056572:Histone Deacetylase Inhibitors; D006657:Histones; D006877:Hydroxamic Acids; D007211:Indoles; D011719:Pyrazines; D057149:Ubiquitinated Proteins; D000069286:Bortezomib; D000077767:Panobinostat