Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:5.99.1.2 (topoisomerase)
 9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The cyanomorpholino derivative of doxorubicin (MRA-CN) is a DNA intercalator and alkylator that is a highly potent cytotoxin, non-cross-resistant in multidrug-resistant cells, and noncardiotoxic in comparison with doxorubicin. To further examine mechanisms of action and resistance to MRA-CN, a cell line resistant to MRA-CN, ES-2R, was established by growing a human ovarian carcinoma cell line, ES-2, in increasing concentrations of the drug. The resistant subline was 4-fold resistant to MRA-CN and cross-resistant to other DNA cross-linking agents, cisplatin (7-fold) and carmustine (3-fold), as well as to the DNA strand-breaking agents etoposide (6-fold), doxorubicin (2-fold), bleomycin (5-fold), and ionizing radiation (2-fold). In contrast, ES-2R cells were not cross-resistant to vinblastine. Several months of additional growth of ES-2R cells in MRA-CN did not yield higher, stable levels of drug resistance. A low level of P-glycoprotein was detectable in the ES-2R cells. However, the extent of intracellular accumulation of [3H]MRA-CN by this resistant cell line was identical to that of the sensitive line. The number of DNA cross-links formed by cisplatin in ES-2R was only 50% of that of the ES-2 cells and was associated with a 50% increase in the rate of repair of these cross-links in the resistant cells. Ionizing radiation induced similar amounts of single- and double-strand breaks in the ES-2 line as well as in the ES-2R cells. There was no apparent difference between the two cell lines in the rate and extent of repair of these DNA breaks. Thus, enhanced DNA repair cannot explain the phenomenon of cross-resistance to radiation. Comparisons of glutathione (GSH) content and the enzymes involved in GSH homeostasis showed significant differences. Resistant cells contained 1.5-fold more GSH, a 2.2-fold increase in gamma-glutamyltranspeptidase activity, and a 2.4-fold increase in GSH reductase compared with ES-2 cells (all P less than 0.05). Total glutathione-S-transferase (GST) activity was 2.6-fold higher (P less than 0.01) in the ES-2R line. The pi-class GST subunit by Western blotting and GST activity toward ethacrynic acid were increased 2-fold in the resistant cells. Depletion of GSH levels in ES-2R cells by buthionine sulfoximine restored the sensitivity of ES-2R to MRA-CN. These findings implicate a role for GSH metabolism in the resistance phenotype of ES-2R cells. We have previously reported that these cells have an increased generation time and decreased topoisomerase II content. Thus, the ES-2R cell line exhibits a complex phenotype of broad cross-resistance, which is likely to involve multiple mechanisms, and includes enhanced DNA repair and increased GSH content and GST activity.
 ...
PMID:Multifactorial mechanisms associated with broad cross-resistance of ovarian carcinoma cells selected by cyanomorpholino doxorubicin. 171 40

Resistance may limit the clinical usefulness of a variety of chemotherapeutic drugs including mitomycin C (MMC). The MMC-sensitive HT-29 colon cancer cell line and its MMC-resistant subline, HT-29R13, were studied in vitro under aerobic conditions to help characterize the mechanisms associated with MMC resistance. HT-29R13 cells exhibit approximately 2-fold resistance to MMC compared with HT-29 cells and lack the typical multidrug-resistance pattern; resistance is stable in the absence of drug exposure. Levels of glutathione (GSH) and total glutathione-S-transferase (GST) activity were not different between the two cell lines; however, levels of GSH reductase and GSH peroxidase were increased significantly in HT-29R13. Although total GST activity was unchanged, GST-pi and GST-alpha isoenzyme expression as measured using western blot were increased significantly in HT-29R13 compared with HT-29. DT-diaphorase levels and topoisomerase II activity were decreased significantly in HT-29R13. Both cell lines had equal P-glycoprotein expression. Multiple drug resistance mechanisms are present in HT-29R13 including decreased drug activation (decreased DT-diaphorase), increased drug detoxification (increased GST-pi and GST-alpha, GSH reductase, GSH peroxidase), and decreased accessibility of DNA targets (decreased topoisomerase II). Further work will be necessary to determine the degree to which each of these mechanisms contribute to MMC resistance in this model.
 ...
PMID:Biochemical characterization of a mitomycin C resistant colon cancer cell line variant. 790 34

Although they are known to be effective antidiabetic agents, little is published about the toxic effects of carnitine palmitoyltransferase-1 (CPT-1) inhibitors, such as etomoxir (ET). These compounds inhibit mitochondrial fatty acid beta-oxidation by irreversibly binding to CPT-1 and preventing entry of long chain fatty acids into the mitochondrial matrix. Treatment of HepG2 cells with 1 mM etomoxir for 6 h caused significant modulations in the expression of several redox-related and cell cycle mRNAs as measured by microarray analysis. Upregulated mRNAs included heme oxygenase 1 (HO1), 8-oxoguanine DNA glycosylase 1 (OGG1), glutathione reductase (GSR), cyclin-dependent kinase inhibitor 1A (CDKN1 [p21(waf1)]) and Mn+ superoxide dismutase precursor (SOD2); while cytochrome P450 1A1 (CYP1A1) and heat shock 70kD protein 1 (HSPA1A) were downregulated. Real time quantitative PCR (RT-PCR) confirmed the significant changes in 4 of 4 mRNAs assayed (CYP1A1, HO1, GSR, CDKN1), and identified 3 additional mRNA changes; 2 redox-related genes, gamma-glutamate-cysteine ligase modifier subunit (GCLM) and thioredoxin reductase (TXNRD1) and 1 DNA replication gene, topoisomerase IIalpha (TOP2A). Temporal changes in selected mRNA levels were examined by RT-PCR over 11 time points from 15 min to 24 h postdosing. CYP1A1 exhibited a 38-fold decrease by 4 h, which rebounded to a 39-fold increase by 20 h. GCLM and TXNRD1 exhibited 13- and 9-fold increases, respectively at 24 h. Etomoxir-induced oxidative stress and impaired mitochondrial energy metabolism were confirmed by a significant decrease in reduced glutathione (GSH), reduced/oxidized glutathione ratio (GSH/GSSG), mitochondrial membrane potential (MMP), and ATP levels, and by concurrent increase in oxidized glutathione (GSSG) and superoxide generation. This is the first report of oxidative stress caused by etomoxir.
 ...
PMID:Etomoxir-induced oxidative stress in HepG2 cells detected by differential gene expression is confirmed biochemically. 1207 14