Glutathione S-transferases in wild-type and doxorubicin-resistant MCF-7 human breast cancer cell lines.
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. Total cytosolic GST catalytic activity was elevated 23-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 mu 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 mu protein and GST P1 mRNA in comparison with the wild-type cell line. Neither cell line displayed detectable GST alpha or mu at the protein level. 6. A glutathione analogue that functions as a selective GST alpha 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 glutathione-conjugate transporter, appeared weakly overexpressed in the MCF-7/ADR cells in comparison with the MCF-7/WT cells.
Wang
K
K
Department of Pharmacology, University of Toronto, Ontario, Canada.
Ramji
S
S
Bhathena
A
A
Lee
C
C
Riddick
D S
DS
D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000230:Adenocarcinoma / Q000201:enzymology; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000201:enzymology*; D002384:Catalysis; D003600:Cytosol / Q000201:enzymology; D004317:Doxorubicin / Q000627:therapeutic use*; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D005260:Female; D005982:Glutathione Transferase / Q000378:metabolism*; D006801:Humans; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009363:Neoplasm Proteins / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D014407:Tumor Cells, Cultured
D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D004317:Doxorubicin; D005982:Glutathione Transferase; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009363:Neoplasm Proteins; D012333:RNA, Messenger