Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0596263 (carcinogenesis)
 64,820 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The role of human sulfotransferase(s) in the bioactivation of the N-hydroxy (N-OH) metabolite of the human bladder carcinogen 4-aminobiphenyl (ABP) was investigated in vitro with human tissue cytosols. Using an enzymatic assay consisting of a PAPS-regenerating system, [3H]N-OH-ABP, calf thymus DNA and tissue cytosols, the sulfotransferase-mediated metabolic activation of N-OH-ABP was determined as the PAPS-dependent covalent binding of the N-OH substrate to DNA. With cytosols prepared from various tissues, we found that the sulfotransferase(s) in human liver, and to a lesser extent colon, can readily metabolize N-OH-ABP. No PAPS-dependent metabolic activation was detected with cytosols prepared from human pancreas or from the carcinogen target tissue, the urinary bladder epithelium. The N-OH-ABP sulfotransferase activities of liver and colon cytosols from different individuals were highly correlated with their thermostable phenol sulfotransferase (TS-PST) activity (liver, r = 0.99, P < 0.01; colon, r = 0.88, P < 0.01), but not with activities for the thermolabile phenol sulfotransferase (TL-PST; liver, r = 0.29; colon, r = 0.53), or for the dehydroepiandrosterone sulfotransferase (DHEA-ST; liver, r = 0.32; colon, negligible activity). N-OH-ABP sulfotransferase activity was highly sensitive to inhibition by a selective TS-PST inhibitor, 2,6-dichloro-4-nitrophenol (IC50 = 0.7 microM), and by p-nitrophenol, but was unaffected by competitive inhibitors of TL-PST (dopamine) or DHEA-ST (DHEA, DHEA-sulfate). The N-OH-ABP sulfotransferase activity also exhibited thermostability properties similar to that of the TS-PST. From these data, we conclude that human liver TS-PST but not TL-PST or DHEA-ST can metabolically activate the proximate human carcinogen N-OH-ABP to a reactive sulfuric acid ester intermediate that binds covalently to DNA. In addition, in view of the putative role of N-OH-ABP as a major transport form of the carcinogen to the urinary bladder and of the absence of sulfotransferase activity in this tissue, we hypothesize that sulfotransferase activation in the liver may actually decrease the bioavailability of N-OH-ABP toward extrahepatic tissues and thus serve as an important overall detoxification mechanism for the urinary bladder.
Carcinogenesis 1995 Feb
PMID:Metabolic activation of the N-hydroxy derivative of the carcinogen 4-aminobiphenyl by human tissue sulfotransferases. 785 74

Exposure to pentachlorophenol (PCP) strongly intensifies the formation of mouse hepatic DNA adducts elicited by oral administration of tamoxifen (TAM), as previously shown by 32P-postlabeling. To explain this effect, PCP was proposed to interfere with the detoxication by sulfate conjugation of an as yet unidentified hydroxylated proximate TAM metabolite. A comparison of the present and earlier results shows that the hepatic TAM adduct pattern in female ICR mice depended on the route of administration of TAM (120 mumol/kg), with oral administration primarily eliciting formation of more polar adducts (termed group I adducts), while after i.p. administration less polar adducts (group II) predominated over group I adducts by a factor of 17.5. All these adducts were also formed in female Sprague-Dawley rats after i.p. dosing with TAM, but total adduct levels were 3.5- to 5-fold higher than in mice. After four daily i.p. treatments, TAM adducts accumulated in mouse liver DNA in a non-linear fashion. Adduct levels were 30-50 times lower in mouse kidney and lung than in liver. The phenolic metabolite 4-hydroxy TAM (120 mumol/kg) exclusively led to formation of polar (group I) hepatic adducts, and this process was stimulated 8-fold by co-administration of PCP (75 mumol/kg). Co-administration of PCP with the parent compound led to an 11-fold enhancement of group I adduct formation; simultaneously, levels of group II adducts were suppressed 6-fold. Another inhibitor of sulfate conjugation, 2,6-dichloro-4-nitrophenol, unlike PCP, had no effect on group I adducts, but it reduced group II adduct formation 2.2-fold. The PCP metabolite 2,3,5,6-tetrachlorohydroquinone (75 mumol/kg) did not significantly affect any major TAM adduct, suggesting that PCP itself was the active compound. Similar to group II TAM adducts, the formation of hepatic safrole-DNA adducts was inhibited in female ICR mice by both sulfotransferase inhibitors, consistent with the proposal that metabolic alpha-hydroxylation of the ethyl group of TAM followed by sulfate conjugation represented a mechanism of TAM activation. On the other hand, the strong intensification of group I adducts by PCP and the lack of this effect by 2,6-dichloro-4-nitrophenol suggested that inhibition of sulfate conjugation may not have been the primary mechanism underlying the intensification of group I adducts formed from TAM or 4-hydroxy TAM. The results presented herein demonstrate conclusively that TAM was activated to DNA-reactive compounds along two distinct pathways which contrasted in their responses to metabolic inhibitors.
Carcinogenesis 1994 Oct
PMID:Tamoxifen: evidence by 32P-postlabeling and use of metabolic inhibitors for two distinct pathways leading to mouse hepatic DNA adduct formation and identification of 4-hydroxytamoxifen as a proximate metabolite. 795 37

DNA adduct formation was examined in rat peritoneal serosa, a tumor target for i.p. administered aqueous suspensions of N-hydroxy-N-2-fluorenylbenzamide (N-OH-2-FBA) and N-hydroxy-N-2-fluorenylacetamide (N-OH-2-FAA), and compared to that in the liver, which is a tumor target for N-OH-2-FAA in the male rat. 32P-Postlabeling analyses showed the presence of a single adduct, N-(deoxyguanosin-8-yl)-2-fluorenamine (dG-C8-FA), from activation of both hydroxamic acids by the serosa and liver in vitro and in vivo. The relatively low levels of dG-C8-FA (60-80 fmol/micrograms DNA) from N-OH-2-FBA in vitro were increased 2.7- and 35-fold upon the addition of acetyl coenzyme A (AcCoA) to the serosal cytosol and hepatic cytosol or microsomes respectively. By contrast, addition of AcCoA led to a decrease (approximately 34%) in the high level of dG-C8-FA (4330 fmol/micrograms DNA) from activation of N-OH-2-FAA by hepatic cytosol and did not alter the levels from activation by hepatic microsomes and serosal cytosols (530 and 78.3 fmol/micrograms DNA respectively). These data and the previously reported hydroxamic acid activation enzyme activities in the serosa and liver indicated that the precursor of dG-C8-FA, N-acetoxy-N-2-fluorenamine, was formed from N-OH-2-FAA chiefly via an intramolecular N,O-acetyltransfer and from N-OH-2-FBA via a two-step sequence of N-debenzoylation and AcCoA-dependent O-acetylation. The levels of dG-C8-FA were approximately 2- to 3-fold higher in the serosal DNA (up to 515 and 1012 fmol/micrograms DNA) after one (30 mumol/rat) and ten or eleven (cumulative dose of approximately 275 mumol/rat) injections of N-OH-2-FBA or N-OH-2-FAA than in the hepatic DNA. This correlated with the carcinogenicities of the hydroxamic acids, but was inversely proportional to the rates and extents of their activation in vitro. Multiple injections affected hepatic enzyme activities related to the activation of the hydroxamic acids in that the cytosolic N-debenzoylation of N-OH-2-FBA increased (approximately 1.7-fold) whereas N-OH-2-FAA acetyltransferase and sulfotransferase activities decreased. The effect of treatment with N-OH-2-FBA was greater than that with N-OH-2-FAA and was greater on the sulfotransferase activity (approximately 88% decrease). The latter suggested that N-OH-2-FBA, although a poor acceptor for an enzymatic sulfate transfer, may be carcinogenic for the rat liver.(ABSTRACT TRUNCATED AT 400 WORDS)
Carcinogenesis 1994 Dec
PMID:Detection of N-(deoxyguanosin-8-yl)-2-fluorenamine in DNA of peritoneal serosa and liver after intraperitoneal exposure of rats to N-hydroxy-N-2-fluorenylbenzamide or N-hydroxy-N-2-fluorenylacetamide. 800 Dec 51

Although negative in assays for mutagenicity, the clinically important antiestrogen tamoxifen induces hepatic DNA adduct formation in mice, rats and hamsters, as indicated by 32P-postlabeling, and is a potent hepatocarcinogen in rats. Both phenolic and alcoholic metabolites of tamoxifen have been reported. As these metabolites are potential candidates for sulfate conjugation, we examined whether the sulfotransferase inhibitor pentachlorophenol, a ubiquitous environmental contaminant, modulates hepatic tamoxifen adduct formation in vivo. Female ICR mice were given tamoxifen (45 mg/kg) daily per os for up to 4 days, with and without i.p. pretreatment with pentachlorophenol (20 mg/kg) 1 h before dosing with tamoxifen. At days 1, 2 and 4, liver DNA was analyzed 5 h after tamoxifen administration by a modified monophosphate version of the 32P-postlabeling assay. At day 4, pentachlorophenol pretreatment led to a large increase (13- to 17-fold) of the levels of four tamoxifen adduct fractions, while two adducts appeared unaffected, resulting in an approximately 7-fold enhancement of overall adduct formation. Significant pentachlorophenol related increases were also observed at day 1 and day 2. The mechanism of this effect has not yet been determined, but may involve the inhibition of sulfation of a tamoxifen metabolite(s) involved in the detoxication of the drug to nonelectrophilic derivatives. It was also apparent that there are two pathways of metabolic activation of tamoxifen, one being sensitive and the other resistant to pentachlorophenol.
Carcinogenesis 1994 May
PMID:Strong intensification of mouse hepatic tamoxifen DNA adduct formation by pretreatment with the sulfotransferase inhibitor and ubiquitous environmental pollutant pentachlorophenol. 820 78

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) are mutagenic and carcinogenic heterocyclic amines produced during the ordinary cooking of meat. These compounds undergo metabolic activation via both cytochrome P450-mediated N-oxidation and phase II esterification in order to exert their genotoxicity. In the current study, we examined the in vitro phase II activation of N-hydroxy-IQ, N-hydroxy-PhIP and N-hydroxy-MeIQx by cytosolic acetyltransferase, sulfotransferase, aminoacyl-tRNA synthetase and phosphatase from a number of tissues including liver, kidney, colon and heart. These tissues were chosen for study because each is either a target organ for carcinogenicity or has displayed high levels of DNA adducts in in vivo studies with the heterocyclic amines. Cytosol from various tissues of both monkeys and rats was incubated with and without the respective cofactors, and carcinogen binding to calf thymus DNA was measured by 32P-postlabeling analysis. Our results show that all four phase II enzymes may participate in the activation of the N-hydroxylamines. However, the degree of activation depends on the substrate, tissue and animal species. For example, in both monkeys and rats, the highest acetyl CoA-enhanced binding was observed with N-hydroxy-IQ and the lowest acetyl CoA-enhanced binding was observed with N-hydroxy-MeIQx. In contrast, no significant adenosine 3'-phosphate 5'-phosphosulfate-dependent activation of N-hydroxy-IQ was observed with monkey cytosol from liver, kidney, heart or colon but the sulfotransferase-mediated activation of N-hydroxy-PhIP was at least 10 times higher in all four tissues of monkeys than in rats. Prolylation appears important in the activation of all three N-hydroxylamines by rat liver and heart cytosol, whereas in monkeys, prolylation appears important in kidney cytosol. The differences observed in the phase II activation of heterocyclic amines may have implications for DNA adduct formation, toxicity and carcinogenicity.
Carcinogenesis 1993 Oct
PMID:Enzymatic phase II activation of the N-hydroxylamines of IQ, MeIQx and PhIP by various organs of monkeys and rats. 822 59

Sulfation activity towards various heterocyclic and homocyclic aromatic hydroxamic acids and hydroxylamines was determined in adult human liver cytosol and with partially purified human liver sulfotransferases (STs). In adult human liver cytosols comparable ST activities towards N-hydroxy-2-acetyl-amino-5-phenylpyridine (N-OH-2AAPP), N-hydroxy-4-acetylaminobiphenyl (N-OH-4AABP) and N-hydroxy-4'fluoro-4-acetylaminobiphenyl (N-OH-4FAABP) were found, while the sulfation rates towards N-hydroxy-2-acetylaminofluorene (N-OH-2AAF), N-hydroxy-2-acetylaminonaphthalene (N-OH-2AAN), N-hydroxy-2-acetylaminophenanthrene (N-OH-2AAP) and N-hydroxy-4-acetylaminostilbene (N-OH-4AAS) were two- to five-fold lower. In adult liver cytosol ST activity was found towards all hydroxylamines tested. No significant differences were found for the various hydroxylamines. In general, the ST activities towards the various hydroxamic acids and hydroxylamines were comparable to phenol ST activity using adult liver cytosols. Partial purification of adult human liver STs was achieved by DEAE-Sepharose chromatography followed by anion exchange FPLC. Two separated protein peaks showing both N-OH-2AAPP and N-OH-2APP ST activities were observed and were designated human hydroxylamine/hydroxamic acid sulfotransferase (hHST) 1 and 2. Immunoblot analysis using an anti-rat estrogen ST antibody demonstrated cross reactivity with both hHSTs at a subunit mol. wt of 32 kDa corresponding to the phenol-sulfating form of phenol ST (P-PST). ST activity towards dopamine was low with both hHSTs, but hHST1 also contained significant capacity to sulfate dehydroepiandrosterone. The highest ST activity towards N-OH-2AAPP and N-OH-2APP was measured at pH 5.5 with both hHSTs. The Km values of the two hHSTs for sulfation of N-OH-2AAPP and N-OH-2APP were comparable, while the Vmax values for sulfation of N-OH-2APP were higher than for N-OH-2AAP with both hHSTs. FPLC anion exchange analysis of human platelet STs demonstrated that sulfation of N-OH-4ABP and N-OH-4AABP was associated with P-PST rather than M-PST (platelets do not possess any significant DHEA ST activity). Our results show that the various hydroxamic acids and hydroxylamines are converted by at least two hHSTs. The results presented here for the human liver hydroxamic acid and hydroxylamine ST activities are discussed in relation to those observed in the rat.
Carcinogenesis 1994 Jan
PMID:Sulfation of aromatic hydroxamic acids and hydroxylamines by multiple forms of human liver sulfotransferases. 829 46

To better understand drug and carcinogen metabolism pathways in head and neck squamous cell carcinoma we assayed the principal drug- and carcinogen-metabolizing enzyme systems in both tumors and their corresponding adjacent non-tumoral tissues. Cytochromes P450 (1A1/A2, 2B1/B2, 2C8-10, 2E1, 3A4), epoxide hydrolase and glutathione S-transferases (GST-alpha, GST-mu, GST-pi) were assayed by immunoblotting. GST activity, total glutathione, UDP-glucuronosyltransferase, beta-glucuronidase, sulfotransferase and sulfatase, were determined by spectral assays. Results showed the absence of all probed cytochromes P450 in tumors and non-tumoral tissues, including P450 1A1/1A2 known to be involved in tobacco-related carcinogenesis. No statistical difference was noted between tumors and adjacent non-tumoral tissues for most enzymes studied (GST-alpha, GST-mu, GST-pi, GST activity, UDP-glucuronosyltransferase, beta-glucuronidase, sulfotransferase and sulfatase). However, total glutathione concentrations were significantly higher (P < 0.05) in tumors (47 +/- 20 nmol/mg protein) than in non-tumoral tissues (19 +/- 9). On the contrary, epoxide hydrolase was significantly less expressed in tumors (18 +/- 9 micrograms/mg protein) compared to corresponding non-tumoral tissues (37 +/- 9). These data provide new information concerning human head and neck cancer biology that could possibly have clinical implications.
Carcinogenesis 1993 Jul
PMID:Principal xenobiotic-metabolizing enzyme systems in human head and neck squamous cell carcinoma. 833 Mar 40

To better understand the importance of drug-metabolizing enzymes in carcinogenesis and anticancer drug sensitivity of human non-small cell lung cancer, we studied the main drug-metabolizing enzyme systems in both lung tumors and their corresponding nontumoral lung tissues in 12 patients. The following enzymes were assayed by Western blot analysis: cytochromes P-450 (1A1/A2, 2B1/B2, 2C8-10, 2E1, 3A4); epoxide hydrolase; and glutathione S-transferase isoenzymes (GST-alpha, -mu, and -pi). The activity of the following enzymes or cofactor were determined by spectrophotometric or fluorometric assays: glutathione S-transferase (GST); total glutathione; UDP-glucuronosyltransferase; beta-glucuronidase; sulfotransferase; and sulfatase. Results showed the presence of cytochrome P-450 1A1/1A2 in both tumoral and nontumoral tissues. P-450 1A1/1A2 levels were 3-fold lower in tumors compared to corresponding nontumoral tissues (P < 0.05). None of the other probed cytochromes P-450 were detected in either tumoral or nontumoral lung tissues. For the glutathione system, no significant difference between tumoral and nontumoral tissues was observed (GST activity, glutathione content, GST-alpha, -mu, and -pi). A positive linear correlation was observed between GST activity and GST-alpha or GST-pi. No significant difference was observed for the glucuronide and the sulfate pathways and their corresponding hydrolytic enzymes. Epoxide hydrolase was significantly decreased in tumors compared to nontumoral lung tissues (P < 0.05). In conclusion, these results showed differences between non-small cell lung tumors and nontumoral tissues for cytochrome P-450 1A1/1A2 and epoxide hydrolase. These differences between tumors and peritumoral tissues with regard to these drug-metabolizing enzymes could reflect differences occurring after malignant transformation and may play a role in drug sensitivity to anticancer drugs.
 ...
PMID:Main drug- and carcinogen-metabolizing enzyme systems in human non-small cell lung cancer and peritumoral tissues. 840 35

Studies on drug metabolism have opened new fields in the evaluation of drug efficacy and drug safety in experimental animals and humans, especially in the development of new drugs. The author described the history of discoveries of induction and inhibition of drug-metabolizing enzymes as a key point in the development of drug interaction studies. Studies on the sex-related differences in drug-metabolism have been important fields for understanding the sex-related toxicity and efficacy of drugs and their species differences under normal and pathological conditions. Rats are unique animals among experimental animals and humans. The activities of hepatic drug-metabolizing enzymes, especially cytochrome P450 and sulfotransferase, are regulated through the sex-related secretion pattern of growth hormone. The drug-metabolizing enzymes convert drugs into not only inactive metabolites, but produce toxic intermediates which cause mutagenesis, carcinogenesis and drug-caused allergic reactions. The author carried out extensive studies on the metabolic activation of mutagenic-carcinogenic arylamines and demonstrated important roles of O-acetylation and O-sulfation to cause DNA damages by N-hydroxyarylamines. Pharmacogenetic studies on hamster acetyltransferase were described to understand the individual differences in polymorphic acetylation of arylamines and N-hydroxyarylamines in relation to DNA damages. Finally, the author emphasizes important roles of drug metabolism studies for the development of new drugs by showing a prototype, which has multiple metabolic pathways by multiple enzymes and this shows reduced-extents of individual differences, for increasing efficacy and safety in a future clinical drug therapy.
 ...
PMID:[Molecular pharmacological and toxicological studies of drug-metabolizing enzymes]. 852 65

Exposure to perfluorocarboxylic acids, pthalate esters, and some hypolipidemic agents results in the proliferation of peroxisomes in the rodent liver. The structural diversity of these compounds suggests mechanistic diversity in their toxicity as well. To establish reliable biomarkers of peroxisome proliferation (PP) in compounds with distinct chemical toxicities, this study investigated the effect of in vivo exposure to perfluoro-n-octanoic acid, perfluoro-n-decanoic acid, di(2-ethylhexyl)phthalate (DEHP) and clofibrate on two-dimensional electrophoretic protein patterns of rat hepatic sulfotransferases, ST1A1, ST1C1 and ST2A1. After exposure to peroxisome proliferative doses, both ST1A1 and ST1C1 abundance in whole liver homogenates was significantly reduced, but only as a result of perfluorocarboxylic and exposure. The well-established PPs, DEHP and clofibrate had no effect on sulfotransferase expression whatsoever. The observed down-regulation of these STs is significant with respect to their normal detoxication activities and its potential correlation to carcinogenesis warrants further study. The present investigation supports previous studies that demonstrate the unique features of perfluorocarboxylic acid toxicity, relative to classic peroxisome proliferators and endorses the continued use of 2D protein-mapping of Sts and other proteins as biomarkers of chemical toxicity.
 ...
PMID:Effect of structurally diverse peroxisome proliferators on rat hepatic sulfotransferase. 862 May 80


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>