title: Hyperglycemia-induced thioredoxin-interacting protein expression differs in breast cancer-derived cells and regulates paclitaxel IC50.
abstract: OBJECTIVE
  We studied the hyperglycemia-induced expression of thioredoxin-interacting protein (TXNIP) expression and its relevance on the cytotoxic activity of paclitaxel in mammary epithelial-derived cell lines.
  
  
  METHODS
  Nontumorigenic cells (MCF10A); tumorigenic, nonmetastatic cells (MCF-7/T47D); and tumorigenic, metastatic cells (MDA-MB-231/MDA-MB-435s) were grown either in 5 or 20 mmol/L glucose chronically. Semiquantitative reverse transcription-PCR was used to assess TXNIP RNA expression in response to glucose. Reactive oxygen species were detected by CM-H2DCFDA (5-6-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate) and measured for mean fluorescence intensity with flow cytometry. Thioredoxin activity was assayed by the insulin disulfide-reducing assay. Proliferation was evaluated using CellTiter96 reagent with 490-nm absorption. Obtained absorbance values were used to calculate the paclitaxel IC(50) in 5 or 20 mmol/L glucose using the Chou's dose-effect equation.
  
  
  RESULTS
  We show that hyperglycemia by itself affects the level of TXNIP RNA in breast cancer-derived cells. TXNIP RNA level differs between nontumorigenic/nonmetastatic, tumorigenic cells (low TXNIP level), and metastatic cells (high TXNIP level). The differences in TXNIP RNA level, in reactive oxygen species level, and in thioredoxin activity are all related. We further show that hyperglycemia is a favorable condition in increasing the paclitaxel cytotoxicity by causing IC(50) 3-fold decrease in metastatic breast cancer-derived MDA-MB-231 cells. The increased paclitaxel cytotoxicity is associated with an additive effect on the hyperglycemia-mediated TXNIP expression more evident in conditions of hyperglycemia than normoglycemia.
  
  
  CONCLUSIONS
  Our study opens a new perspective on the relevance of metabolic conditions of hyperglycemia in the biology and treatment of cancer, particularly in view of the epidemic of diabetes.
authors.affiliation: Department of Medicine, Feist-Weiller Cancer Center, Louisiana State University Health Science Center, Shreveport, Louisiana 71103, USA. fturtu@lsuhsc.edu
authors.forename: Francesco
authors.initials: F
authors.lastname: Turturro
authors.forename: Gary
authors.initials: G
authors.lastname: Von Burton
authors.forename: Ellen
authors.initials: E
authors.lastname: Friday
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D005260:Female; D005434:Flow Cytometry; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D006943:Hyperglycemia / Q000503:physiopathology*; D020128:Inhibitory Concentration 50; D017239:Paclitaxel / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis; D017382:Reactive Oxygen Species / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013879:Thioredoxins / Q000378:metabolism
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D002352:Carrier Proteins; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; C486715:TXNIP protein, human; D013879:Thioredoxins; D017239:Paclitaxel