title: Global DNA hypermethylation-associated cancer chemotherapy resistance and its reversion with the demethylating agent hydralazine.
abstract: BACKGROUND
  The development of resistance to cytotoxic chemotherapy continues to be a major obstacle for successful anticancer therapy. It has been shown that cells exposed to toxic concentrations of commonly used cancer chemotherapy agents develop DNA hypermethylation. Hence, demethylating agents could play a role in overcoming drug resistance.
  
  
  METHODS
  MCF-7 cells were rendered adriamycin-resistant by weekly treatment with adriamycin. Wild-type and the resulting MCF-7/Adr cells were analyzed for global DNA methylation. DNA methyltransferase activity and DNA methyltransferase (dnmt) gene expression were also determined. MCF-7/Adr cells were then subjected to antisense targeting of dnmt1, -3a, and -b genes and to treatment with the DNA methylation inhibitor hydralazine to investigate whether DNA demethylation restores sensitivity to adriamycin.
  
  
  RESULTS
  MCF-7/Adr cells exhibited the multi-drug resistant phenotype as demonstrated by adriamycin resistance, mdr1 gene over-expression, decreased intracellular accumulation of adriamycin, and cross-resistance to paclitaxel. The mdr phenotype was accompanied by global DNA hypermethylation, over-expression of dnmt genes, and increased DNA methyltransferase activity as compared with wild-type MCF-7 cells. DNA demethylation through antisense targeting of dnmts or hydralazine restored adriamycin sensitivity of MCF-7/Adr cells to a greater extent than verapamil, a known inhibitor of mdr protein, suggesting that DNA demethylation interferes with the epigenetic reprogramming that participates in the drug-resistant phenotype.
  
  
  CONCLUSIONS
  We provide evidence that DNA hypermethylation is at least partly responsible for development of the multidrug-resistant phenotype in the MCF-7/Adr model and that hydralazine, a known DNA demethylating agent, can revert the resistant phenotype.
authors.affiliation: Unidad de Investigación Biomédica en Cáncer, Instituto de Investigaciones Biomédicas, Universidad Nacional Autonóma de Mexico, Instituto Nacional de Cancerología, Mexico. bba0512@prodigy.net.mx
authors.forename: Blanca
authors.initials: B
authors.lastname: Segura-Pacheco
authors.forename: Enrique
authors.initials: E
authors.lastname: Perez-Cardenas
authors.forename: Lucia
authors.initials: L
authors.lastname: Taja-Chayeb
authors.forename: Alma
authors.initials: A
authors.lastname: Chavez-Blanco
authors.forename: Alma
authors.initials: A
authors.lastname: Revilla-Vazquez
authors.forename: Luis
authors.initials: L
authors.lastname: Benitez-Bribiesca
authors.forename: Alfonso
authors.initials: A
authors.lastname: Duenas-González