Glutathione S-transferases in wild-type and doxorubicin-resistant MCF-7 human breast cancer cell lines

Abstract

1. Overexpression of glutathione S -transferases (GST) in breast cancer cells is hypothesized to be a component of the multifactorial doxorubicin-resistant phenotype. 2. We have characterized the expression of GST enzymes at the catalytic activity, protein and mRNA levels in wild-type MCF-7 (MCF-7 WT) human breast cancer cells and a line selected for resistance to doxorubicin (MCF-7 ADR), with the goal of modulating GST activity to overcome resistance. 3. The MCF-7 ADR cells were 30-65-fold more resistant to doxorubicin than the MCF-7 WT cells. 4. Totalcytosolic GST catalytic activity waselevated23-fold in the MCF-7 ADR cells as compared with the MCF-7 WT cells, and the MCF-7 ADR cells also showed 3-fold increases in catalytic activity toward GST pi and alpha class-selective substrates. Neither cell line showed detectable catalytic activity with a GST mu class-selective substrate. 5. MCF-7 ADR cells showed pronounced overexpression of GST pi protein and GST P1 mRNA in comparison with the wild-type cellline. Neither cell-line displayed detectable GST alpha or mu at the protein level. 6. Aglutathioneanalogue that functions as a selective GST pi inhibitor was more potent at inhibiting total cytosolic GST catalytic activity in the MCF-7 ADR cell line than GST alpha and mu class-selective inhibitory glutathione analogues and the non-selective GST inhibitor ethacrynic acid. 7. The multidrug resistance-associated protein, which can function as a glutathioneconjugate transporter, appeared weakly overexpressed in the MCF-7 ADR cells in comparison with the MCF-7 WT cells.