Expression of the GST pi gene and response to tamoxifen therapy in locally advanced breast carcinomas.
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Breast Neoplasms↗
Biomedical subjects
J A Moscow
Publications and source records attributed to J A Moscow.
Glutathione-related enzymes, glutathione and multidrug resistance.
This review examines the hypothesis that glutathione and its associated enzymes contribute to the overall drug-resistance seen in multidrug resistant cell lines. Reports of 34 cell lines independently selected for resistance to MDR drugs are compared for evidence of consistent changes in activity of glutathione-related enzymes as well as for changes in glutathione content. The role of glutathione S-transferases in MDR is further analyzed by comparing changes in sensitivity to MDR drugs in cell lines selected for resistance to non-MDR drugs that have resulting increases in glutathione S-transferase activity. In addition, results of studies in which genes for glutathione S-transferase isozymes were transfected into drug-sensitive cells are reviewed. The role of the glutathione redox cycle is examined by comparing changes in elements of this cycle in MDR cell lines as well as by analyzing reports of the effects of glutathione depletion on MDR drug sensitivity. Overall, there is no consistent or compelling evidence that glutathione and its associated enzymes augment resistance in multidrug resistant cell lines.
ATP Binding Cassette Transporter, Subfamily B, Mem↗
Decreased melphalan accumulation in a human breast cancer cell line selected for resistance to melphalan.
An in vitro model of acquired melphalan resistance was developed by serial incubation of an MCF-7 human breast cancer cell line in increasing concentrations of melphalan. The resulting derivative cell line, Me1R MCF-7, was 30-fold resistant to melphalan. Uptake studies demonstrated decreased initial melphalan accumulation in Me1R MCF-7 cells. Inverse-reciprocal plots of initial melphalan uptake revealed a 4-fold decrease in the apparent Vmax of Me1R MCF-7 compared with WT MCF-7 (516 amol cell-1 min-1 vs 2110 amol cell-1 min-1 respectively) as well as a decrease in the apparent Kt (36 microM vs 70 microM respectively). Two amino acid transporters have previously been identified as melphalan transporters: system L, which is sodium-independent and inhibited by 2-amino-bicyclo[2,2,1]heptane-2-carboxylic acid (BCH), and system ASC which is sodium dependent and unaffected by BCH. At low concentrations of melphalan (3-30 microM), 1mM BCH competition eliminated the differences between the two cell lines, thus implicating an alteration of the system L transporter in the transport defect in the resistant cells. Me1R MCF-7 cells were also evaluated for glutathione-mediated detoxification mechanisms associated with melphalan resistance. There was no difference between Me1R MCF-7 and WT MCF-7 in glutathione content, glutathione-S-transferase activity and expression of pi class glutathione S-transferase RNA. In addition, buthionine sulfoximine did not reverse melphalan resistance in Me1R MCF-7 cells. Therefore, Me1R MCF-7 cells provide an in vitro model of transport-mediated melphalan resistance in human breast cancer cells.
Amino Acid Transport Systems↗
Glutathione transferase GST pi in breast tumors evaluated by three techniques.
The glutathione transferases are involved in intracellular detoxification reactions. One of these, GST pi, is elevated in some breast cancer cells, particularly cells selected for resistance to anticancer agents. We evaluated GST pi expression in 60 human breast tumors by three techniques, immunohistochemistry. Northern hybridization, and Western blot analysis. There was a significant positive correlation between the three methods, with complete concordance seen in 64% of the tumors. There was strong, inverse relationship between GST pi expression and steroid receptor status with all of the techniques utilized. In addition, there was a trend toward higher GST pi expression in poorly differentiated tumors, but no correlation was found between tumor GST pi content and DNA ploidy or %S-phase. GST pi expression was also detected in adjacent benign breast tissue as well as infiltrating lymphocytes; this expression may contribute to GST pi measurements using either Northern hybridization or Western blot analysis. These results suggest that immunohistochemistry is the method of choice for measuring GST pi in breast tumors.
Blotting, Northern↗
A pilot study of pi-class glutathione S-transferase expression in breast cancer: correlation with estrogen receptor expression and prognosis in node-negative breast cancer.
PURPOSE AND METHODS: Previous studies have indicated that RNA levels for pi-class glutathione S-transferase (GST pi), a phase II, drug-metabolizing enzyme, were inversely related to estrogen receptor (ER) and progesterone receptor (PR) levels in human breast tumors. Because GST pi also is expressed in normal breast epithelium, an immunohistochemical assay that uses affinity-purified polyclonal antibodies to GST pi was developed to examine the possible relationship between GST pi expression in breast cancer cells and hormone receptor expression, as well as prognosis, in patients with primary breast cancer. RESULTS: A strong inverse correlation between GST pi expression and ER (two-sided P [P2] = .002) and PR status (P2 = .023) was found in our study of 189 patients with primary breast cancer. GST pi expression was not related to tumor size, nodal metastasis, nuclear grade, histology, or age of the patient. In node-negative breast cancer (n = 72), increased GST pi expression was associated with decreased disease-free survival (DFS) and overall survival (OS). When GST pi expression was divided into categories of negative (no GST pi-positive tumor cells), intermediate (1% to 70% GST pi-positive tumor cells), and high (> 70% GST pi-positive tumor cells), the relative risk of tumor recurrence in patients with node-negative breast cancer was increased 3.39-fold for each successive category of expression (P2 = .0045; 95% confidence interval, 1.46 to 7.87) and the relative risk of death was increased 4.49-fold for each successive category (P2 = .0003; 95% confidence interval, 2.02 to 10.42). The actuarial 5-year OS was 100%, 79%, and 51%, and the DFS was 94%, 77%, and 44%, for the negative, intermediate, and high tumor groups, respectively. Among the factors studied in multivariate analysis (ER status, PR status, nuclear grade, and tumor size), GST pi expression was the factor that most accurately predicted shorter DFS and OS in node-negative patients. CONCLUSION: GST pi expression is inversely related to hormone receptor status in breast cancer. This pilot study also suggests that increased GST pi expression may be an important predictor of early recurrence and death in node-negative breast cancer patients that merits additional investigation.
Breast Neoplasms↗
Multidrug resistance.
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ATP Binding Cassette Transporter, Subfamily B, Mem↗
Structure and function of the 5'-flanking sequence of the human cytosolic selenium-dependent glutathione peroxidase gene (hgpx1).
Human selenium-dependent glutathione peroxidase (hGPx1) (EC 1.11.1.9) is thought to be involved in many critical cellular functions as a result of its role in glutathione-mediated reduction of toxic peroxides, and it is implicated as a mechanism of resistance against oxygen free radicals. Previous studies have demonstrated that the gene encoding hGPx1 (hgpx1) is more highly expressed in multidrug-resistant AdrR MCF-7 human breast cancer cells than in the parental WT MCF-7 cell line. In order to further study the transcriptional regulation of hgpx1, we have cloned the genomic hgpx1 gene and determined its nucleotide sequence. The 2550-base pair (bp) 5'-flanking sequence of hgpx1 contained the terminal 511 bp of the 3' end of a previously reported rhoH12 cDNA (Yeramian, P., Chardin, P., Madaule, P., and Tavitian, A. (1987) Nucleic Acids Res. 15, 1989), a ras-related oncogene. Further downstream from rhoH12, but before the start of transcription of hgpx1, RNase protection analysis revealed a transcribed sequence of at least 270 bp which we have called mid. RNA transcripts homologous to both rhoH12 (1.8 and 1.5 kilobase pairs (kb)) and mid (1.8 kb) are also more highly expressed in AdrR MCF-7 cells than in WT MCF-7 cells. We screened an AdrR MCF-7 cDNA library with the mid sequence and isolated a partial cDNA clone which contains both mid and rhoH12 sequences and is colinear with the genomic sequence which extends from 10 bp 3' to the rhoH12 stop codon to 810 bp 5' to the start of transcription of hgpx1. The start of transcription of hgpx1 in AdrR MCF-7 cells was determined by primer extension analysis. The promoter and 2 kb of the 5'-flanking sequence of hgpx1 was fused to the bacterial chloramphenicol acetyltransferase gene (hGPx1-CAT1). Analysis of deletion constructs of hGPx1-CAT1 revealed three possible cis-acting regulatory regions. The transcriptional regulation of hgpx1 was examined using the hGPx1-CAT hybrid genes and nuclear run-on studies. We found no evidence that increased mRNA transcript formation could account for different levels of hgpx1 RNA either in different breast cancer cell lines or in response to selenium.
Amino Acid Sequence↗
Multidrug resistance.
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ATP Binding Cassette Transporter, Subfamily B, Mem↗
Contribution of glutathione and glutathione-dependent enzymes in the reversal of adriamycin resistance in colon carcinoma cell lines.
Four human colon cancer cell lines (SW620, LS 180, DLD-I, and HCT-15) and sub-lines isolated in vitro by selection with Adriamycin were studied for reversal of intrinsic and acquired Adriamycin resistance, using buthionine sulfoximine (BSO) to deplete cellular glutathione alone and in combination with the P-glycoprotein antagonist verapamil. GSH levels varied among the parental cell lines but did not increase with resistance. In the parental SW620, DLD-I and HCT-15 and their drug-resistant derivatives, there was no relation between the effect of the glutathione-depleting agent BSO, the mRNA expression of both selenium-dependent glutathione peroxidase (GPx) and glutathione S-transferase pi (GST pi), bulk glutathione S-transferase (GST) activity, and the degree of resistance. However, in LS 180 and its derivative sub-lines, which do not principally rely on P-glycoprotein (Pgp) for Adriamycin resistance, treatment with BSO demonstrated a relatively diminished GSH depletion and enhanced recovery. In comparison with the other acquired cell lines, BSO specifically reversed acquired resistance in the LS 180 Adriamycin-resistant subline (LS 180 Ad150) after short-term drug exposure. Furthermore, the LS 180 Ad150 cells demonstrated an increase in both GPx and GST pi mRNA expression. These observations suggest that glutathione-mediated detoxification of Adriamycin may play a role in the resistance of this sub-line. Verapamil enhanced Adriamycin cytotoxicity 1.2- to 12-fold in the intrinsically resistant cells and as much as 15-fold in cell lines with acquired resistance. Combination of BSO with verapamil resulted in additive, but not synergistic, reversal of resistance. The results underscore the complex nature of Adriamycin resistance, and suggest a role for drug-resistance-modulating agents in the treatment of colon carcinoma.
ATP Binding Cassette Transporter, Subfamily B, Mem↗
Multidrug resistance.
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ATP Binding Cassette Transporter, Subfamily B, Mem↗
Multidrug resistance in cells transfected with human genes encoding a variant P-glycoprotein and glutathione S-transferase-pi.
The nucleotide sequence of the mdr1 gene encoding a putative drug efflux pump (P-glycoprotein) is homologous to a class of bacterial membrane-associated transport proteins. These bacterial proteins are part of a multicomponent system that includes soluble periplasmic proteins that bind substrates, channeling them through the membrane in an energy-dependent manner. We have investigated the possibility that a similar multicomponent transport system exists in a multidrug-resistant human MCF-7 breast cancer cell line that was initially selected for resistance to doxorubicin (AdrR MCF-7). AdrR MCF-7 cells overexpress both the mdr1 gene and the pi class isozyme of glutathione S-transferase (GST-pi) (EC 2.5.1.18). The latter is one of several isozymes known to have a ligand-binding function in addition to drug-metabolizing capabilities. Although we have recently shown that transfection of a functional GST-pi expression vector is insufficient to confer resistance to doxorubicin in cells that lack P-glycoprotein expression [Mol. Pharmacol. 36:22-28 (1989)], we examined the possibility that GST-pi interacts with P-glycoprotein to alter multidrug resistance. To do this, we have cloned cDNAs encoding these proteins from AdrR MCF-7 cells, constructed expression vectors containing these two genes, and transfected these vectors sequentially into drug-sensitive MCF-7 cells. The human mdr1 cDNA isolated from AdrR MCF-7 is a variant gene whose sequence differs from that isolated previously from vinblastine-resistant KB cells [Cell 53:519-529 (1989)], resulting in an amino acid substitution of alanine to serine at position 893 (mdr1/893ala). Transfection of eukaryotic expression vectors containing the mdr1 gene isolated from AdrR MCF-7 cells produced a multidrug-resistant phenotype in recipient cells, with a cross-resistance pattern similar to that in the AdrR MCF-7 cells. To determine whether GST-pi expression could augment resistance provided by mdr1, two clones transfected with mdr1, one with high levels (153% of mdr1 RNA in AdR MCF-7 cells) and one with low levels (10% of mdr1 RNA in AdrR MCF-7 cells), were subsequently cotransfected with a GST-pi expression vector and pSVNeo and selected for resistance to G418. Six of these clones contained levels of GST-pi that were 8- to 18-fold greater than GST levels found in mdr1-expressing clones transfected with nonspecific DNA. We found no difference in the degree of resistance to doxorubicin, actinomycin D, and vinblastine between the clones expressing mdr1 only and the clones expressing both mdr1 and GST-pi.(ABSTRACT TRUNCATED AT 400 WORDS)
ATP Binding Cassette Transporter, Subfamily B, Mem↗
Multidrug resistance.
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ATP Binding Cassette Transporter, Subfamily B, Mem↗
Expression of anionic glutathione-S-transferase and P-glycoprotein genes in human tissues and tumors.
The development of multidrug resistance in MCF-7 human breast cancer cells and the acquisition of broad resistance to xenobiotics in rat hyperplastic nodules are both associated with increased P-glycoprotein (mdr) gene expression as well as changes in activities of intracellular detoxication enzymes; among these changes is a significant increase in the activity of the anionic isozyme of glutathione-S-transferase (GST). We have isolated a cDNA encoding the human anionic glutathione-S-transferase, GST pi-1, from a cDNA library constructed from multidrug-resistant MCF-7 cells. The deduced amino acid sequence of GST pi-1 shows that while the human anionic GST displays 85% nucleotide and amino acid sequence homology to the rat anionic isozyme, it is markedly less related to human basic GST isozymes. We have examined the expression of GST pi and P-glycoprotein in 170 specimens of human tissues and tumors. P-Glycoprotein RNA expression was positive in eight of 23 lymphomas and two of 12 colon tumors; however, many other normal and malignant tissues, including lung, bladder, and breast tumors, had low or undetectable levels of P-glycoprotein RNA expression. In contrast, GST pi was readily detected in a wide variety of normal and malignant tissues. The level of GST pi mRNA expression in normal tissues was heterogeneous, with lowest levels found in liver and the highest levels found in lung, esophagus, and placenta. GST pi was also variably expressed in human tumors, with the lowest relative levels occurring in lymphoma and breast cancer and the highest levels found in lung cancer and head and neck tumors. In addition, comparison of paired specimens from the same patient indicated that GST pi expression was increased in many tumors relative to matched normal tissue.
ATP Binding Cassette Transporter, Subfamily B, Mem↗
Glutathione S-transferase and drug resistance.
GST isozymes are an important part of the normal cellular defense against toxic xenobiotics and carcinogens. These multifunctional proteins can interact with a broad range of substrates in a variety of ways. In particular, GSTs have been implicated in the detoxication of many antineoplastic agents. Elevated levels of certain GST isozymes have been associated with malignant transformation and with experimental drug resistance. Although the role of GST in antineoplastic drug resistance is unclear, recent studies have shown increased activity of GST in many human tumors relative to normal tissues. These findings raise the possibility that the presence of certain GST isozymes may be a marker for malignant transformation in some human tumors, and that GSTs may play a role in de novo and acquired drug resistance. Identifying the factors which regulate the expression of these drug-metabolizing enzymes as well as agents which inhibit their activities may provide new insights into the therapy of tumors clinically refractory to chemotherapy.
Animals↗
Elevation of pi class glutathione S-transferase activity in human breast cancer cells by transfection of the GST pi gene and its effect on sensitivity to toxins.
Increased expression of the glutathione S-transferase (GST; E.C.2.5.1.18) pi class isozyme is associated with both malignant transformation and drug resistance, as well as with decreased estrogen receptor content in breast cancer. In order to further characterize the role of this enzyme in drug resistance, we cloned the cDNA encoding the human isozyme GST pi and developed two eukaryotic expression vectors using this cDNA and either the human metallothionein IIa or cytomegalovirus immediate-early promoters. These GST pi expression vectors were cotransfected with pSV2neo into drug-sensitive MCF-7 human breast cancer cells, which have low amounts of GST activity and which do not express GST pi. The transfected cells were selected for G418 resistance and individual clones were screened for GST activity. Three clones that demonstrated increased GST activity were selected for further study. Immunoprecipitation studies demonstrated that the increase in GST activity in these clones was due to expression of GST pi. Although the total GST activity of the positive clones was increased as much as 15-fold over that in wild-type MCF-7 cells, there was no change in glutathione peroxidase activity, as measured using cumene hydroperoxide as a substrate. Immunoblot studies revealed that the increased GST enzyme produced in the transfected cells was identical in size to endogenous GST pi. Southern blot analysis demonstrated the incorporation of the GST pi expression vector into the genome of the positive clones and Northern blot analysis showed that the transfected genes made a hybrid GST pi RNA that was slightly larger than the endogenous GST pi RNA. Primer extension studies demonstrated that this increase in length corresponded to the added length of the 5' leader sequence of the expression vector. The effect of increased GST pi activity on the sensitivity of the transfected clones to several cytotoxic agents was assessed by colony-forming assay. The transfected clones were slightly more resistant (1.3-4.1-fold) to benzo(a)pyrene and its toxic metabolite benzo(a)pyrene-(anti)-7,8-dihydrodiol-9,10-epoxide, as well as to ethacrynic acid (3.1-to 4.4-fold). Although increased GST pi expression is found in MCF-7 cells selected for doxorubicin resistance, the transfected clones were not consistently more resistant to doxorubicin than control cells. In addition, the transfected cells were not resistant to either melphalan or (cis)-platinum, even though conjugation with glutathione is known to play a role in the detoxification of both of these drugs.(ABSTRACT TRUNCATED AT 400 WORDS)
Breast Neoplasms↗
Multidrug resistance.
The ability of malignant cells to develop resistance to cytotoxic drugs poses a major obstacle to the ultimate success of cancer therapy. While some mechanisms of resistance allow cells to survive exposure to a single agent, the phenomenon of multidrug resistance (MDR) confers upon cells the ability to withstand exposure to lethal doses of many structurally unrelated antineoplastic agents. MDR has been strongly linked to the overexpression of a membrane-associated glycoprotein, P-glycoprotein, which appears to play a role in drug efflux. However, several lines of evidence suggest that other mechanisms of resistance are involved in MDR; biochemical similarities observed in a human breast cancer cell line after the acquisition of MDR and in carcinogen-induced rat preneoplastic hepatic nodules indicate that changes in regulation of phase I and phase II drug-metabolizing enzymes may also play a role in MDR. An atypical pattern of MDR has been characterized and related to altered topoisomerase activity. Improvement in current cancer chemotherapy may be achieved by interfering with the regulation and expression of mechanisms of MDR.
ATP Binding Cassette Transporter, Subfamily B, Mem↗
Altered phenytoin clearance during intensive chemotherapy for acute lymphoblastic leukemia.
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Antineoplastic Combined Chemotherapy Protocols↗
Isolation of the human anionic glutathione S-transferase cDNA and the relation of its gene expression to estrogen-receptor content in primary breast cancer.
The development of multidrug resistance in MCF7 human breast cancer cells is associated with overexpression of P-glycoprotein, changes in activities of several detoxication enzymes, and loss of hormone sensitivity and estrogen receptors (ERs). We have cloned the cDNA for one of the drug-detoxifying enzymes overexpressed in multidrug-resistant MCF7 cells (AdrR MCF7), the anionic isozyme of glutathione S-transferase (GST pi). Hybridization with this GST pi cDNA, GST pi-1, demonstrated that increased GST pi activity in AdrR MCF7 cells is associated with overexpression but not with amplification of the gene. We mapped the GST pi gene to human chromosome 11q13 by in situ hybridization. Since multidrug resistance and GST pi overexpression are associated with the loss of ERs in AdrR MCF7 cells, we examined several other breast cancer cell lines that were not selected for drug resistance. In each of these cell lines we found an inverse association between GST pi expression and ER content. We also examined RNA from 21 primary breast cancers and found a similar association between GST pi expression and ER content in vivo. GST pi mRNA content in 11 ER-positive tumors (less than or equal to 10 fmol/mg of protein) was significantly different from the GST pi content of 10 ER-negative tumors (P = 0.002; Mann-Whitney Wilcoxon test for two independent samples). The finding of similar patterns of expression of a drug-detoxifying enzyme and of ERs in vitro as well as in vivo suggests that ER-negative breast cancer cells may have greater protection against antineoplastic agents conferred by GST pi than ER-positive tumors.
Breast Neoplasms↗