Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.6.5.2 (NQO1)
6,196 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The flavoenzyme DT-diaphorase has the potential either to bioactivate or to detoxify different bioreductive cytotoxins. Elucidation of structural features governing the ability to act as a substrate for DT-diaphorase should facilitate rational optimization or elimination of this reductive pathway for a particular class of bioreductive drug. We have examined structure-activity relationships governing both the cytotoxicity and the DT-diaphorase mediated reduction of two groups of bioreductive alkylating agents: (1) Indoloquinones related to EO9 [3-hydroxy-methyl-5-aziridinyl-1-methyl-2-(1H-indole-4,7-dione)prop-beta - en-alpha-ol]; and (2) derivatives of diaziridinyl benzoquinone or diaziquone [2,5-bis(carboethoxyamino)-3,6-diaziridinyl-1,4-benzoquinone]. The rat U.K. 256 Walker tumor cell line and the human HT29 colon carcinoma line were studied because of their high DT-diaphorase content. Enzyme activity was measured spectrophotometrically by dicoumarol inhibitable cytochrome c reduction in the presence of drug, and aerobic cytotoxicity was assessed by the MTT assay. EO9 acted as a good substrate for both enzyme preparations and was highly potent in each cell line, especially in Walker tumor cells (ID50 0.039 nM). AZQ was also reduced efficiently and gave an ID50 of 6 nM in the Walker tumor line. Slight modifications in structure resulted in large variations in both DT-diaphorase metabolism and toxicity for both types of agent. There was a clear tendency for the most efficiently reduced analogues to exhibit greater cytotoxic potency. Inclusion of an aziridine moiety in the structure appears to be desirable, but not essential, for both rapid reduction and cytotoxicity. There was no evidence of active site-directed enzyme inhibition.
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PMID:Structure-activity relationships for DT-diaphorase reduction of hypoxic cell directed agents: indoloquinones and diaziridinyl benzoquinones. 154 32

NAD(P)H:quinone oxidoreductase (NQO1) is a flavoprotein which catalyzes the two-electron reduction of quinones and azo-dyes and thus prevents the formation of free radicals and toxic oxygen metabolites that may be generated by the one-electron reductions catalyzed by cytochrome P450 reductase. Analysis of RNA indicated 20- to 50-fold higher levels of NQO1 gene expression in the liver tumors and in the tissue surrounding the tumors of patients with hepatocarcinoma than in normal individuals. An approximately 50-fold higher level of NQO1 mRNA was also observed in human hepatoblastoma (Hep-G2) cells than in normal liver. By deletion mutagenesis in the human NQO1 gene promoter and subsequent transfection into hepatic and nonhepatic cell lines, a 1.42 kb DNA segment has been identified to contain cis-acting elements responsible for high levels of expression of the NQO1 gene in tumor cells.
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PMID:High levels of expression of the NAD(P)H:quinone oxidoreductase (NQO1) gene in tumor cells compared to normal cells of the same origin. 165 29

Quinone metabolites of catechol estrogens have been postulated to mediate estradiol-induced carcinogenesis. In this study, this postulate was examined by investigating the effect of modulators of quinone metabolism on estradiol-induced tumor incidence in male Syrian hamsters. 2(3)-t-Butyl-4-hydroxyanisol (BHA) and dicumarol which are known to stimulate or inhibit respectively, the activity of quinone reductase, lowered tumor incidence by 33 and 42% respectively (3/9 and 5/12 tumor-free animals/total respectively), from 100% (13/13) observed with 17 beta-estradiol (E2) treatment only. Ebselen, a substance with glutathione peroxidase-like activity, and sodium 2-mercaptoethanesulfonate (Mesna), a cytoprotective thiol-containing agent, were only marginally effective in decreasing the estradiol-induced kidney tumor incidence (3/11 and 4/19 tumor-free animals/total respectively). The lowering of tumor incidence by BHA and dicumarol correlated well with a 40-45% decrease in renal peroxidatic activity of cytochrome P450 in hamsters treated with these substances plus estradiol for 1 month. In addition, these compounds also inhibited the oxidation of diethylstilbestrol to its corresponding quinone in vitro. An influence on quinone reductase or other detoxifying enzymes in chronically treated male Syrian hamsters could not be detected. These data support a mediation of estradiol-induced carcinogenesis by quinones formed by metabolic oxidation of catechol estrogens.
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PMID:Inhibition of estrogen-induced kidney carcinogenesis in Syrian hamsters by modulators of estrogen metabolism. 169 Oct 52

Inducibility of oxidative stress in rat liver in vivo by menadione-associated redox cycling activation under redox enzyme modulating conditions was examined by monitoring hepatocyte injury and 8-hydroxydeoxyguanosine (8-OHdG) levels of liver DNA. In addition, the treatment-associated liver tumor initiating activity was assessed in terms of development of gamma-glutamyl-transpeptidase (GGT)- and glutathione S-transferase placental form (GST-P)-positive foci and hyperplastic nodules. With or without following menadione treatment (50 mg/kg, i.g.), redox enzyme modulations of increased cytochrome P450 reductase activity induced by phenobarbital (PB)-Na (100 mg/kg, i.p. for 5 days), inhibition of DT-diaphorase by dicumarol (25 mg/kg, i.p.) and depletion of glutathione by phorone (200 mg/kg, i.p.), with or without further supplement of iron EDTA-Na-Fe(III) (70 mg/kg, i.p.), caused both substantial hepatocyte necrosis and 8-OHdG production in Fischer 344 male rats. Subsequent feeding with a 0.05% PB diet for 64 weeks resulted in slightly increased development of GGT-positive foci but not GST-P positive lesions or hyperplastic nodules, suggesting a lack of tumor-initiating activity of the oxidative DNA damage associated with redox enzyme modulations with or without menadione.
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PMID:Induction of 8-hydroxydeoxyguanosine but not initiation of carcinogenesis by redox enzyme modulations with or without menadione in rat liver. 170 52

EO9 [3-hydroxymethyl-5-aziridinyl-1-methyl-2-(H-indole-4, 7-indione)-propenol] is a novel indoloquinone structurally related to mitomycin C, a quinone anticancer drug that requires reductive bioactivation. NAD(P)H: (quinone-acceptor) oxidoreductase (quinone reductase, DT-diaphorase, EC 1.6.99.2) is an obligate 2-electron donating enzyme that can reduce a variety of quinones resulting either in bioactivation or bioprotection. Using quinone reductase (QR) preparations from rat Walker 256 mammary tumor cells and human HT29 colon carcinoma cells, we have characterized the role of this enzyme in EO9 reductive metabolism. QR activity was assayed under optimal conditions by following cytochrome c reduction at 550 nm in the presence of enzyme, quinone substrate, NADH, and bovine albumin, and confirmed by loss of EO9 absorbance at 550 nm. Both the rat and human tumor cell enzymes catalyzed reduction of the benchmark quinone menadione with a similar Km of 1.4-3.1 microM, although the Vmax was 7 to 8-fold lower for the human preparation. EO9 was readily reduced by the rat Walker QR. The mean Km was about 5-fold higher than for menadione at around 15 microM and the Vmax was 6-fold lower at around 2.5 mumol of cytochrome c reduced mg-1 of protein. EO9 was also metabolized by QR from HT29 human colon carcinoma cells but rather less efficiently than by the rat tumor enzyme. For example, the rate was 6-fold lower than that for the Walker tumor enzyme at 100 microM substrate concentration after correcting for the 7- to 8-fold difference in specific activity for the two preparations.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The role of NAD(P)H: quinone reductase (EC 1.6.99.2, DT-diaphorase) in the reductive bioactivation of the novel indoloquinone antitumor agent EO9. 171 84

A polymerase chain reaction (PCR)-based method was used to quantitate the expression levels of low abundance genes relevant to cancer drug activity. RNA from tumor samples as small as 20 mg was isolated and converted to cDNA using random hexamers. The 5' primers for the PCR contained a T7 polymerase promoter sequence, allowing the PCR-amplified DNA to be transcribed to RNA fragments. In each sample, the linear ranges of amplification of each cDNA of interest were established. Relative gene expressions were calculated by extrapolating the amounts of PCR products generated within the linear amplification regions of each gene to equal volumes of the cDNA solution. The method was accurate to less than a 2-fold difference in expression levels. Using beta 2-microglobulin and beta-actin gene expressions as internal reference standards and cDNA from HT-29 cells as an external linearity standard, we measured the relative expressions of thymidylate synthase, dihydrofolate reductase, and DT-diaphorase in a number of clinical tumor samples. The expressions of these genes varied from 50- to 100-fold among different tumors, although most of the values were grouped within about a 10-fold range. The amount of thymidylate synthase gene expression in tumor tissues was directly proportional to the content of thymidylate synthase protein. Those tumors with the lowest thymidylate synthase expression had the best response to both the 5-fluorouracil-leucovorin and 5-fluorouracil-cisplatin combinations.
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PMID:Quantitation of thymidylate synthase, dihydrofolate reductase, and DT-diaphorase gene expression in human tumors using the polymerase chain reaction. 172 69

DT-diaphorase (DTD) is a flavoprotein which catalyzes obligate two-electron reduction of a diverse group of substrates. We have reported previously that non-tumorigenic mouse lung alveolar type-II pneumocytes have high DTD activity, while cell lines derived from lung tumors do not. In contrast, other investigators, using human lung tissue, reported increased DTD activity in tumors compared with normal tissue. We therefore investigated DTD associated with mouse lung neoplasia in vivo as well as in vitro. Pulmonary tumors had far less DTD activity compared with normal mouse lung. Correspondingly, a tumorigenic mouse lung cell line which arose as a spontaneous transformant of a normal cell line had very low DTD activity compared with non-tumorigenic lung cells. DTD-specific mRNA levels were also much higher in normal cell lines than in neoplastic ones. DTD was localized histochemically in type-II pneumocytes in situ, but was not observed by this technique in normal bronchiolar epithelia or in tumor cells. These data show that, unlike what has been observed in human lung cancer, a marked decrease in DTD content and activity accompanied mouse lung tumorigenesis in vivo and neoplastic transformation in vitro.
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PMID:NAD(P)H:quinone oxidoreductase (DT-diaphorase) activity and mRNA content in normal and neoplastic mouse lung epithelia. 190 40

In the present study, we investigated Phase I (cytochrome P450; DT-diaphorase, DTD) and Phase II (epoxide hydrolase, EH; glutathione-S-transferases, GSTs) enzymes in normal colon from patients without colorectal adenocarcinoma and in peritumoral and tumoral tissues from patients with colorectal adenocarcinoma. No significant changes in levels of cytochrome P450IIIA4 (the only P450 detectable in this tissue), EH, GSTs and DTD activity were found between normal and peritumoral tissues. In tumoral tissue, compared with peritumoral tissues, we observed significant decreases in cytochrome P450IIIA4 (-50%, P less than 0.002) and EH (-60%, P less than 0.03), no change in DTD activity and significant increases in GST pi (+40%, P less than 0.03) and total GST activity (+30%, P less than 0.01). The numerous changes observed in tumoral tissues suggest that variations in drug-metabolizing enzyme expression in colorectal adenomatous polyps could represent pretumoral markers. Moreover, a better understanding of the expression of these enzymes in tumoral tissues would help us to choose the most appropriate colon tumor cell lines for the testing of new anti-cancer drugs.
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PMID:Drug-metabolizing enzyme expression in human normal, peritumoral and tumoral colorectal tissue samples. 202 56

Most chemical carcinogens require activation to reactive electrophilic forms by Phase 1 enzymes (cytochromes P-450) in order to exert their toxic and neoplastic effects. The resultant electrophiles are susceptible to metabolic conjugation and other types of detoxications by Phase 2 enzymes (glutathione transferases, NAD(P)H: quinone reductase, glucuronosyltransferases). The balance between Phase 1 and Phase 2 enzymes is an important determinant of whether exposure to carcinogens will result in toxicity and neoplasia. Measurements of the activity of quinone reductase (QR) provide an efficient method for studying the potency and mechanism of Phase 2 enzyme induction. QR can be measured easily in murine hepatoma cells (Hepa lclc7) grown in microtiter plate wells, and the inductive response of these cells closely parallels the behavior of rodent tissues in vivo. Some inducers (such as large planar aromatics) are bifunctional; they induce both Phase 1 and Phase 2 enzymes and require binding to the Ah receptor and enhanced transcription of the cytochrome P1-450 system. Other inducers (e.g., phenolic antioxidants, 1, 2-dithiole-3-thiones, coumarins, thiocarbamates) are monofunctional and are independent of Ah receptor function. Monofunctional enzyme induction protects against carcinogens. The induction of Phase 2 enzymes by monofunctional inducers depends on the presence, or acquisition by metabolism, of electrophilic centers, and many of these inducers are Michael reaction acceptors. Our search for chemoprotective enzyme inducers for potential use as chemoprotectors in man is currently focused on fumarate derivatives, as well as on the identification of other monofunctional inducers in extracts of vegetables.
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PMID:Regulation of enzymes that detoxify the electrophilic forms of chemical carcinogens. 213 77

NAD(P)H:(quinone-acceptor)oxidoreductase (QAO), previously known as DT-diaphorase, catalyzes the reduction of quinones to hydroquinones. Enhanced activity of the enzyme has been suggested to protect cells against the cellular toxicity and carcinogenicity of quinones, but may activate some cytotoxic anti-tumor quinones. Cytosolic levels of QAO, carbonyl reductase (CR) and total quinone reductase activity have been measured in normal and tumorous human tissues. QAO was the major component of the total cytosolic quinone reductase activity in all the tissues investigated. CR represented 10 to 28% of the total cytosolic quinone reductase activity in normal tissue. Normal tissue QAO was high in the stomach and kidney, and lower in the lung, liver, colon and breast. Primary tumor from lung, liver, colon and breast had elevated levels of QAO compared to normal tissue, while tumor from kidney and stomach had lower levels. CR was not significantly altered in tumor tissue, except in the case of lung and colon tumor which showed an increase compared to normal tissue. A major determinant of the variability of human lung tumor QAO was the cigarette-smoking history of the donor. Non-smokers and past smokers had high levels of tumor QAO compared to normal tissue. Smokers had levels of tumor QAO that were not significantly different from those of normal tissue QAO. Smokers had a small increase in normal lung QAO compared to non-smokers. Alcohol use was associated with an increase in lung tumor QAO but had no effect on QAO in normal lung. The function of QAO in tumors is not known but the elevated activity of QAO in some tumors and the apparent depressant effect of smoking could influence the response of these tumors to quinone drugs or toxic agents that are metabolized by QAO.
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PMID:Cytosolic NAD(P)H:(quinone-acceptor)oxidoreductase in human normal and tumor tissue: effects of cigarette smoking and alcohol. 230 29


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