title: Combination of retinoid and histone deacetylase inhibitor produced an anti-tumor effect in cutaneous T-cell lymphoma by restoring tumor suppressor gene, retinoic acid receptorβ2, via histone acetylation.
abstract: BACKGROUND
  Retinoids exert anti-proliferative, differentiative, and apoptosis-inducing effects through their receptors. Retinoic acid receptor (RAR) β2 behaves as a tumor suppressor gene, and its expression is suppressible by DNA methylation in many malignancies.
  
  
  OBJECTIVE
  We aimed to determine whether combining a retinoid, Am 80, with a histone deacetylase inhibitor, MS-275, could suppress tumor growth in a RARβ2-negative human cutaneous T cell lymphoma (CTCL) cell lines and freshly isolated primary CTCL cells, and to elucidate the epigenetic mechanism behind the phenomena.
  
  
  METHODS
  SeAx cells were implanted subcutaneously in NOD-SCID mice which were randomly divided into four groups and treated with either Am80, MS-275 by oral gavage (five days/week), or a combination of the two agents. Cell proliferation assay, methylation-specific PCR, flow cytometric analysis of cell cycle and apoptosis and chromatin immunoprecipitation assay were employed.
  
  
  RESULTS
  Quantitative PCR analysis revealed that RARβ2 gene expression was restored only by this combination rather than by either of the agents singly. Restored retinoid sensitivity was observed in combining retinoid with a histone deacetylase inhibitor significantly inhibited cell growth in vitro, suppressed subcutaneously transplanted tumor growth, and prolonged survival of tumor-bearing mice in vivo by more strongly inducing apoptosis and p21 expression in CTCL cells than either agent alone. In the combination treatment, the histone H4 acetylation level at lysine 12 and 16 in the promoter region increased after restoration of RARβ2 expression although the DNA methylation of RARβ2 remained unchanged.
  
  
  CONCLUSIONS
  This is the first report of histone acetylation as the primary event in the restoration of RARβ2. Inducible RARβ2 expression may serve as a reliable predictor for tumor response in patients undergoing 'epigenetic & differentiation' therapy.
authors.affiliation: Department of Dermatology, Tokyo Medical University, Tokyo Japan; Department of Dermatology, Tokyo Metropolitan Tama Medical Center, Tokyo, Japan. Electronic address: y-kato@tokyo-med.ac.jp.
authors.forename: Yukihiko
authors.initials: Y
authors.lastname: Kato
authors.affiliation: Department of Dermatology, Tokyo Medical University, Tokyo Japan.
authors.forename: Chizu
authors.initials: C
authors.lastname: Egusa
authors.affiliation: Department of Dermatology, Tokyo Medical University, Tokyo Japan.
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Maeda
authors.affiliation: Department of Dermatology, Tokyo Medical University, Tokyo Japan.
authors.forename: Ryoji
authors.initials: R
authors.lastname: Tsuboi
mesh_terms: D000107:Acetylation / Q000187:drug effects; D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000008:administration & dosage*; D017209:Apoptosis / Q000187:drug effects; D001549:Benzamides / Q000008:administration & dosage*; D001565:Benzoates / Q000008:administration & dosage*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D005260:Female; D016147:Genes, Tumor Suppressor / Q000187:drug effects; D056572:Histone Deacetylase Inhibitors / Q000008:administration & dosage*; D006657:Histones / Q000378:metabolism; D006801:Humans; D016410:Lymphoma, T-Cell, Cutaneous / Q000188:drug therapy* / Q000235:genetics* / Q000473:pathology; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D011401:Promoter Regions, Genetic / Q000187:drug effects; D011725:Pyridines / Q000008:administration & dosage*; D018168:Receptors, Retinoic Acid / Q000235:genetics*; D012176:Retinoids / Q000008:administration & dosage*; D012878:Skin Neoplasms / Q000188:drug therapy* / Q000235:genetics* / Q000473:pathology; D013764:Tetrahydronaphthalenes / Q000008:administration & dosage*; D023041:Xenograft Model Antitumor Assays
chemical_list: D001549:Benzamides; D001565:Benzoates; D056572:Histone Deacetylase Inhibitors; D006657:Histones; D011725:Pyridines; D018168:Receptors, Retinoic Acid; D012176:Retinoids; D013764:Tetrahydronaphthalenes; C540966:retinoic acid receptor, beta2, human; C061133:tamibarotene; C118739:entinostat
keywords: Cutaneous T cell lymphoma; DNA methylation; Histone acetylation; Retinoic acid receptor