title: Role of glutathione S-transferases in the resistance of human colon cancer cell lines to doxorubicin.
abstract: The anthracycline doxorubicin has little activity against colorectal cancers. It is hypothesized that this is attributable to a multifactorial resistance mechanism in which the glutathione S-transferases (GST) may play a role. We studied the relationship between GST expression and doxorubicin resistance in four human colon adenocarcinoma cell lines (HT-29, LoVo, SW620, and Caco-2), with the goal of modulating GST activity to overcome resistance. Caco-2 cells were the most resistant to doxorubicin, showing an IC50 value approximately 80- to 90-fold higher than HT-29 or LoVo and 600-fold higher than SW620. Total GST catalytic activity was significantly higher in Caco-2 cells compared with the other lines. All four cell lines expressed GST-pi at the catalytic activity, protein, and mRNA levels; however, no significant differences were observed among the cell lines. GST-mu expression was not detectable at the protein and mRNA levels, and the four cell lines displayed very low catalytic activity toward a GST-mu-selective substrate. Caco-2 cells showed a unique, highly expressed GST-alpha-immunoreactive band that was not detected in the other lines; however, the glutathione peroxidase activity of Caco-2 cells was the lowest among the four cell lines. Neither ethacrynic acid nor glutathione analogues that function as GST class-selective inhibitors were able to potentiate the cytotoxic effects of doxorubicin in these colon cancer cell lines, as demonstrated in both microplate colorimetric and clonogenic assays. The multidrug resistance-associated protein and P-glycoprotein were either not detectable or expressed at such low levels that they are not likely to contribute to the differences in doxorubicin sensitivity observed among these cell lines.
authors.affiliation: Department of Pharmacology, University of Toronto, Ontario, Canada.
authors.forename: P O
authors.initials: PO
authors.lastname: Beaumont
authors.forename: M J
authors.initials: MJ
authors.lastname: Moore
authors.forename: K
authors.initials: K
authors.lastname: Ahmad
authors.forename: M M
authors.initials: MM
authors.lastname: Payne
authors.forename: C
authors.initials: C
authors.lastname: Lee
authors.forename: D S
authors.initials: DS
authors.lastname: Riddick
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology* / Q000627:therapeutic use; D018938:Caco-2 Cells; D004317:Doxorubicin / Q000494:pharmacology* / Q000627:therapeutic use; D004352:Drug Resistance, Microbial; D019008:Drug Resistance, Neoplasm; D005982:Glutathione Transferase / Q000096:biosynthesis*; D006801:Humans
chemical_list: D000903:Antibiotics, Antineoplastic; D004317:Doxorubicin; D005982:Glutathione Transferase