Research

Global DNA hypermethylation-associated cancer chemotherapy resistance and its reversion with the demethylating agent hydralazine

Blanca Segura-Pacheco¹ , Enrique Perez-Cardenas¹ , Lucia Taja-Chayeb¹ , Alma Chavez-Blanco¹ , Alma Revilla-Vazquez² , Luis Benitez-Bribiesca³ and Alfonso Duenas-González¹

¹  Unidad de Investigación Biomédica en Cáncer, Instituto de Investigaciones Biomédicas, Universidad Nacional Autonóma de Mexico, Instituto Nacional de Cancerología, Mexico

²  Lab. de Desarrollo de Metodos Analiticos, FES-Cuautitlan, UNAM, Cuautitlan Izcalli, Estado de Mexico, Mexico

³  Unidad de Investigacion Medica en Enfermedades Oncologicas, Hospital de Oncologia, CMN-SXXI, IMSS, DF, Mexico

author email corresponding author email

Journal of Translational Medicine 2006, 4:32doi:10.1186/1479-5876-4-32

Published:	7 August 2006

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 hypermetylation. 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 hypermetylation, 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.

Conclusion

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.