title: Interactions between bortezomib and romidepsin and belinostat in chronic lymphocytic leukemia cells.
abstract: OBJECTIVE
  The goal of this study was to characterize interactions between the proteasome inhibitor bortezomib and the histone deacetylase (HDAC) inhibitors (HDACI) romidepsin or belinostat in chronic lymphocytic leukemia (CLL) cells.
  
  
  METHODS
  Primary and cultured (JVM-3 and MEC-2) CLL cells were exposed to agents alone or in combination, after which cell death was determined by 7-aminoactinomycin D staining/flow cytometry. Acetylation of target proteins, activation of caspase cascades, and expression of apoptosis-regulatory proteins were monitored by Western blot analysis. Nuclear factor-kappaB (NF-kappaB) activity was determined by luciferase reporter assay. Cells were transiently transfected with wild-type and acetylation site-mutated (inactive) RelA(p65) (e.g., K221R, K310R, or K281/221/310R) and assessed for HDACI sensitivity.
  
  
  RESULTS
  Combined exposure to very low concentrations of romidepsin or belinostat (i.e., low nanomolar and submicromolar, respectively) in combination with low nanomolar concentrations of bortezomib synergistically induced cell death in primary and cultured CLL cells. These events were likely associated with prevention of HDACI-mediated RelA acetylation and NF-kappaB activation by bortezomib, down-regulation of antiapoptotic proteins (i.e., Bcl-xL, Mcl-1, and XIAP), as well as up-regulation of the proapoptotic protein Bim, resulting in activation of caspase cascade. Finally, CLL cells transfected with inactive RelA displayed a significant increase in HDACI lethality.
  
  
  CONCLUSIONS
  Coadministration of the clinically relevant HDACIs romidepsin or belinostat with bortezomib synergistically induces cell death in CLL cells, likely through mechanisms involving, among other factors, NF-kappaB inactivation and perturbation in the expression of proapoptotic and antiapoptotic proteins. A strategy combining HDAC with proteasome inhibition warrants further attention in CLL.
authors.affiliation: Department of Medicine, Virginia Commonwealth University/Massey Cancer Center, Richmond, VA 23298, USA.
authors.forename: Yun
authors.initials: Y
authors.lastname: Dai
authors.forename: Shuang
authors.initials: S
authors.lastname: Chen
authors.forename: Lora B
authors.initials: LB
authors.lastname: Kramer
authors.forename: Vanessa L
authors.initials: VL
authors.lastname: Funk
authors.forename: Paul
authors.initials: P
authors.lastname: Dent
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
mesh_terms: D000107:Acetylation / Q000187:drug effects; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D047630:Depsipeptides / Q000494:pharmacology*; D004357:Drug Synergism; D006655:Histone Deacetylases / Q000378:metabolism*; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology*; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000378:metabolism* / Q000473:pathology*; D016328:NF-kappa B / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D011719:Pyrazines / Q000494:pharmacology*; D013449:Sulfonamides
chemical_list: D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; D001897:Boronic Acids; D047630:Depsipeptides; D006877:Hydroxamic Acids; D016328:NF-kappa B; D011480:Protease Inhibitors; D011719:Pyrazines; D013449:Sulfonamides; D000069286:Bortezomib; C087123:romidepsin; D020169:Caspases; D006655:Histone Deacetylases; C487081:belinostat