title: [Arsenic trioxide restores ERα expression in ERα-negative human breast cancer cells and its treatment efficacy in combination with tamoxifen in xenografts in nude mice].
abstract: OBJECTIVE
  To study the demethylation effect of arsenic trioxide (As2O3) on ERα-negative human breast cancer MDA-MB-435s cells and its possible mechanisms, and to observe its treatment efficacy in combination with tamoxifen (TAM) after ERα re-expression.
  
  
  METHODS
  MTT assay was used to examine the inhibitory effect of As2O3 treatment alone or in combination with TAM on cell proliferation. A nude mouse xenograft model was used to further examine the treatment efficacy in vivo. MSP was used to detect the methylation status of ERα gene after treated with As2O3 in MDA-MB-435s cells and the transplanted tumor tissues. RT-PCR was used to detect the mRNA expression of DNMT1 and Erα. Western bolt was used to detect the DNMT1 and ERα protein expression. The diameter of xenograft tumors was measured weekly, and the tumor growth curve was drawn.
  
  
  RESULTS
  The level of proliferation of the MDA-MB-435s cells was significantly suppressed after treatment with different concentration of As2O3 alone or As2O3 combined with TAM, and the 4 µmol/L As2O3 + TAM treatment for 72 h showed the highest inhibition rate (62.6%). 1, 2, 4 µmol/L As2O3 had demethylation effect on MDA-MB-435s cells, and the DNMT1 mRNA and protein expression was inhibited and accompanied by ERα mRNA and protein re-expression. The unmethylation specific bands of ERα gene were enhanced after treated by As2O3 alone or As2O3 combined with TAM in the xenograft tumors. The expression of DNMT1 mRNA and protein was inhibited, and accompanied by ERα mRNA and protein re-expression. An significant decrease of volume and weight of the xenograft tumors in the As2O3 treated alone or combined with TAM groups was observed compared with those of the normal saline group or TAM alone group (P < 0.05), and the 4 mg/kg As2O3 + TAM group had the highest inhibition rate of tumor weight (79.5%) and volume (76.4%).
  
  
  CONCLUSIONS
  ERα can be re-expressed in ERα-negative breast cancer MDA-MB-435s cells after treated with As2O3 by inhibiting the DNMT1 activity. MDA-MB-435s cells are re-sensitized to endocrine therapy after ERα re-expression. As2O3 combined with TAM may provide a new therapeutic approach for patients with ERα-negative breast cancer in the clinic.
authors.affiliation: Department of Oncology, First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, China.
authors.forename: Wei-jie
authors.initials: WJ
authors.lastname: Zhang
authors.forename: Deng-fei
authors.initials: DF
authors.lastname: Xu
authors.forename: Qing-xia
authors.initials: QX
authors.lastname: Fan
authors.forename: Xin-ai
authors.initials: XA
authors.lastname: Wu
authors.forename: Feng
authors.initials: F
authors.lastname: Wang
authors.forename: Rui
authors.initials: R
authors.lastname: Wang
authors.forename: Liu-xing
authors.initials: LX
authors.lastname: Wang
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D018931:Antineoplastic Agents, Hormonal / Q000008:administration & dosage; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D000077237:Arsenic Trioxide; D001152:Arsenicals / Q000008:administration & dosage / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; D019175:DNA Methylation; D004305:Dose-Response Relationship, Drug; D047628:Estrogen Receptor alpha / Q000235:genetics / Q000378:metabolism*; D005260:Female; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D010087:Oxides / Q000008:administration & dosage / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D013629:Tamoxifen / Q000008:administration & dosage*; D047368:Tumor Burden / Q000187:drug effects*; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D018931:Antineoplastic Agents, Hormonal; D001152:Arsenicals; D047628:Estrogen Receptor alpha; D010087:Oxides; D012333:RNA, Messenger; D013629:Tamoxifen; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; C000619380:DNMT1 protein, human; C000619381:Dnmt1 protein, mouse; D000077237:Arsenic Trioxide