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The temporal relationship between ABCB1 promoter hypomethylation, ABCB1 expression and acquisition of drug resistance

K Reed1, S L Hembruff, J A Sprowl

  • 1Program in Biomolecular Sciences, Laurentian University, Sudbury, ON, Canada.

The Pharmacogenomics Journal
|February 4, 2010
PubMed

Insights

Epigenetic changes, specifically ABCB1 promoter hypomethylation, drive chemotherapy resistance in breast cancer cells. This study links ABCB1 promoter methylation changes to drug resistance, offering new therapeutic targets.

Area of Science:

  • Molecular Biology
  • Epigenetics
  • Cancer Research

Background:

  • The Abcb1 drug transporter is often upregulated in tumors during chemotherapy.
  • The precise role of epigenetic modifications in the ABCB1 promoter in regulating Abcb1 expression is not fully understood.

Purpose of the Study:

  • To investigate the relationship between epigenetic modifications in the ABCB1 promoter and Abcb1 expression during the development of chemotherapy resistance.
  • To determine if changes in ABCB1 promoter methylation are causally linked to drug resistance in breast cancer cells.

Main Methods:

  • MCF-7 cells were selected for survival under increasing doses of chemotherapy drugs (epirubicin, paclitaxel).
  • The methylation status of 66 CpG sites within the ABCB1 promoter was assessed.
  • Abcb1 transcript expression and gene amplification were analyzed.
  • Demethylating and acetylating agents were used to treat control cells.

Main Results:

  • Increased ABCB1 transcript expression correlated with hypomethylation of the downstream ABCB1 promoter during acquisition of resistance.
  • No gene amplifications or changes in mRNA stability were observed.
  • Demethylating/acetylating agents increased ABCB1 transcript expression in control cells.
  • Specific CpG site hypomethylation and allele-specific methylation changes were noted, suggesting a role in transcriptional activation and promoter usage.

Conclusions:

  • Changes in ABCB1 promoter methylation are temporally and causally associated with the acquisition of drug resistance in breast tumor cells.
  • Promoter hypomethylation, particularly at specific CpG sites, plays a key role in activating ABCB1 expression.
  • Allele-specific methylation may regulate ABCB1 promoter usage in resistant cells.

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