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PubMed1989

DNA binding by 1-nitropyrene and dinitropyrenes in vitro and in vivo: effects of nitroreductase induction.

1-Nitropyrene, the predominant nitropolycyclic aromatic hydrocarbon found in diesel exhaust, is both a mutagen and a tumorigen. 1,6-Dinitropyrene is present in diesel exhaust in much smaller quantities than is 1-nitropyrene, but is much more mutagenic and carcinogenic. In an attempt to understand this difference in biological potencies, we have compared the extents to which these two nitropyrenes bind DNA in vivo. We have also determined the effect of 1-nitropyrene pretreatment upon the induction of nitroreductases and the subsequent DNA binding by both 1-nitropyrene and 1,6-dinitropyrene. In subsequent experiments, we have examined the importance of acetylation phenotype in the formation of DNA adducts from dinitropyrene in vivo. After a single intraperitoneal injection of 1-nitropyrene, covalent DNA binding could not be detected in vivo; however, 1,6-dinitropyrene formed N-(deoxyguanosin-8-yl)-1-amino-6-nitropyrene as the major DNA adduct in rat liver, kidney, urinary bladder, and mammary gland, with the highest levels being found in the bladder. The capability of liver microsomes to catalyze the oxidative metabolism of 1-nitropyrene was unchanged after treating rats with a single dose of 8 mg of 1-nitropyrene per kilogram of body weight. Cytochrome P-450, reduced nicotinamide adenine dinucleotide phosphate (NADPH2)-cytochrome P-450 reductase, and cytochrome b5 levels were also unchanged, while slight increases were detected in reduced nicotinamide adenine dinucleotide (NADH)-cytochrome b5 reductase and epoxide hydrase activities. Liver cytosolic and microsomal nitroreductase activities toward both 1-nitropyrene and 1,6-dinitropyrene were increased twofold, and cytosolic nitrosoreductase activity toward 1-nitrosopyrene and 1-nitro-6-nitrosopyrene was elevated by about 20 percent. DNA binding of both 1-nitropyrene and 1,6-dinitropyrene in vitro was twofold higher when cytosol from rats pretreated with 1-nitropyrene was used. However, pretreatment of rats with 1-nitropyrene only slightly increased the amount of in vivo DNA binding by 1,6-dinitropyrene except in the kidney, where there was a 60 percent increase. In the presence of S-acetylcoenzyme A, liver cytosol from slow-acetylator phenotype hamster strains Bio. 1.5 and 82.73 catalyzed the binding of two-to-three times more 1,8-dinitropyrene to DNA than was observed with the fast-acetylator phenotype strain Bio. 87.20. Similarly, when 1,8-dinitropyrene was administered in vivo and the extent of binding was assayed in liver, bladder, and intestinal DNA, there was more binding in strain Bio. 1.5 than in strain Bio. 87.20.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMedDate not supplied

Effect of multiple doses of clonazepam on the nitroreductase activity in hepatic microsomal preparation from rat.

The hepatic microsomal nitroreductase activity and urinary excretion of the sum of the main metabolites of clonazepam (CNZ) were investigated in rats that had received 7 daily injections of 2 mg/kg of the compound. Despite the significant decrease in CNZ nitroreductase activity, there was only poor correlation between the enzyme activity and excretion of the assayed metabolites.

Animals↗
PubMed1980

Relative importance of bacterial and mammalian nitroreductases for niridazole mutagenesis.

Niridazole is a nitrothiazole anthelmintic agent used to treat schistosomiasis. Its antibacterial activity was found to require the presence of the nitro group; a synthetic desnitro analog was completely inactive. Niridazole was mutagenic for Salmonella tester strains TA1538, TA98, and TA100, suggesting that it was both a frame-shift- and a base substitution-type mutagen. It was effective under both aerobic and anaerobic conditions, while similar testing of the desnitro niridazole produced consistently negative results. Addition of rat liver S-9 fraction under either aerobic or anaerobic conditions did not enhance mutagenicity. However, since bacterial killing limited the dose of niridazole to 0.33 microgram/plate in standard tester strains (1/20 Km for the mammalian liver enzymes), further studies were performed using niridazole-resistant, histidine-dependent mutants derived from strains TA98 and TA100. These mutants were found to be nitroreductase deficient and to resist the mutagenic effects of niridazole, in the presence or absence of S-9, up to concentrations of 10 microgram/plate. In addition, even at niridazole concentrations of up to 100 microgram/plate, rat liver S-9 was ineffective in enhancing the mutagenicity of niridazole. These results suggest that the mutagenicity of niridazole is dependent on its aromatic nitro group and a specific bacterial nitroreductase.

Aerobiosis↗
PubMed2002

Two-electron reduction of quinones by Enterobacter cloacae NAD(P)H:nitroreductase: quantitative structure-activity relationships.

Enterobacter cloacae NAD(P)H:nitroreductase (NR; EC 1.6.99.7) catalyzes two-electron reduction of a series of quinoidal compounds according to a "ping-pong" scheme, with marked substrate inhibition by quinones. The steady-state catalytic constants (k(cat)) range from 0.1 to 1600s(-1), and bimolecular rate constants (k(cat)/K(m)) range from 10(3) to 10(8)M(-1)s(-1). Quinones, nitroaromatic compounds and competitive to NADH inhibitor dicumarol, quench the flavin mononucleotide (FMN) fluorescence of nitroreductase. The reactivity of NR with single-electron acceptors is consistent with an "outer-sphere" electron transfer model, taking into account high potential of FMN semiquinone/FMNH(-) couple and good solvent accessibility of FMN. However, the single-electron acceptor 1,1(')-dibenzyl-4,4(')-bipyridinium was far less reactive than quinones possessing similar single-electron reduction potentials (E(1)(7)). For all quinoidal compounds except 2-hydroxy-1,4-naphthoquinones, there existed parabolic correlations between the log of rate constants of quinone reduction and their E(1)(7) or hydride-transfer potential (E(7)(Q/QH(-))). Based on pH dependence of rate constants, a single-step hydride transfer seems to be a more feasible quinone reduction mechanism. The reactivities of 2-hydroxy-1,4-naphthoquinones were much higher than expected from their reduction potential. Most probably, their enhanced reactivity was determined by their binding at or close to the binding site of NADH and dicumarol, whereas other quinones used the alternative, currently unidentified binding site.

Electrons↗
PubMed2000

Two-electron reduction of nitroaromatic compounds by Enterobacter cloacae NAD(P)H nitroreductase: description of quantitative structure-activity relationships.

Enterobacter cloacae NAD(P)H:nitroreductase catalyzes the reduction of a series of nitroaromatic compounds with steady-state bimolecular rate constants (kcat/Km) ranging from 10(4) M(-1) s(-1) to 10(7) M(-1) s(-1), and oxidizing 2 moles NADH per mole mononitrocompound. Oxidation of excess NADH by polynitrobenzenes including explosives 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenyl-N-methylnitramine (tetryl), has been observed as a slower secondary process, accompanied by O2 consumption. This type of 'redox cycling' was not related to reactions of nitroaromatic anion-radicals, but was caused by the autoxidation of relatively stable reaction products. The logs kcat/Km of all the compounds examined exhibited parabolic dependence on their enthalpies of single-electron- or two-electron (hydride) reduction, obtained by quantum mechanical calculations. This type of quantitative structure-activity relationships shows that the reactivity of nitroaromatics towards E. cloacae nitroreductase depends mainly on their hydride accepting properties, but not on their particular structure, and does not exclude the possibility of multistep hydride transfer.

Electrons↗
PubMed1984

Reduction of nifurtimox and nitrofurantoin to free radical metabolites by rat liver mitochondria. Evidence of an outer membrane-located nitroreductase.

Nifurtimox and nitrofurantoin are reduced by intact rat liver mitochondria to nitro anion radicals whose autoxidation generates superoxide anion as detected by direct electron spin resonance spectroscopy and by spin-trapping experiments, respectively. Although nitroreduction occurred in the presence of respiratory substrates such as beta-hydroxybutyrate, malate-glutamate, succinate, or endogenous substrates, nitro anion radical formation activity was much greater on addition of exogenous reduced pyridine nucleotides. NAD(P)H generated from endogenous mitochondrial NAD(P)+ by intramitochondrial reactions could not be used for the NAD(P)H nitroreductase reactions unless the mitochondria were solubilized by detergent. In addition, NAD(P)H nitroreductase activity was detected in the crude mitochondrial outer membrane fraction, with a higher activity than in mitoplasts and intact mitochondria. These results provide direct evidence of a nitrofuran reductase activity associated with the mitochondrial outer membrane that is far more important than that of respiratory chain enzymes.

Animals↗
PubMed1981

Effect of genotype on mutagenicity of niridazole in nitroreductase-deficient bacteria.

The mutagenicity of niridazole for Salmonella typhimurium depends upon the enzymic reduction of the nitro function. The response of niridazole nitroreductase-deficient bacteria to niridazole is reduced to 4.4 and 0.19% that exhibited by the enzyme-proficient parent strain when the deficiency is the result of a base substitution and frame-shift mutation, respectively. The results are taken to indicate that the residual activity (4.4%) seen in the strain with a base substitution mutation reflects the activity of an enzyme with an amino acid substitution, while the basal level (0.19%) of activity indicates the action of a different nitroreductase with a low specificity for niridazole.

Genotype↗
PubMed1993

Highly sensitive umu test system for the detection of mutagenic nitroarenes in Salmonella typhimurium NM3009 having high O-acetyltransferase and nitroreductase activities.

A highly sensitive umu test system for the detection of genotoxic activities of a variety of mutagenic nitroarenes has been developed using a new tester strain, Salmonella typhimurium NM3009 having high O-acetyltransferase (O-AT) and nitroreductase (NR) activities. The NM3009 was constructed by subcloning both the O-AT and NR genes into plasmid vector pACYC184, and the resulting plasmid was introduced into the parent tester strain S. typhimurium TA1535/pSK1002 harboring an umuC'-'lacZ fusion gene. The induction of umuC gene expression could be monitored by measuring the cellular beta-galactosidase activity produced by fusion gene. The purpose of the study was to evaluate whether the newly developed strain NM3009 is highly sensitive toward nitroarene compounds. The sensitivity of the strain NM3009 was compared with those of the parent TA1535/pSK1002 strain, the NR-overexpressing strain NM1011, the NR-deficient strain NM1000, the O-AT-overexpression strain NM2009, and the O-AT-defective strain NM2000. The newly developed NM3009 strain had about 13-fold and 3-fold higher activities for N-AT and NR, respectively, than the original S. typhimurium TA1535/pSK1002 strain. Among six strains tested, NM3009 showed the highest sensitivity toward such chemicals as 1-nitronaphthalene, 2-nitrofluorene, 3,7-dinitrofluoranthene, 3-nitrofluoranthene, 5-nitroacenaphthene, 2-nitronaphthalene, 1-nitropyrene, 1,6-dinitropyrene, 3,9-dinitrofluoranthene, 4,4'-dinitrobiphenyl, 1,8-dinitropyrene, m-dinitrobenzene, 2,4-dinitrotoluene, and 1,3-dinitropyrene. We have also found that the order of sensitivities to induce umuC gene expression toward a variety of nitroarenes was NM3009 > NM2009 > NM1011 > TA1535/pSK1002 > NM2000 > NM1000. These results suggest that the newly developed tester strain NM3009 is of great use for the detection of genotoxic activities of numerous carcinogenic and mutagenic chemicals including nitroarenes, which require NR and/or O-AT for the activation.

Acetyltransferases↗
PubMed1981

Evidence for the existence of a family of bacterial nitroreductases capable of activating nitrated polycyclics to mutagens.

A derivative of Salmonella typhimurium TA98 which does not respond to the potent mutagenicity of 1,8-dinitropyrene is described. This novel strain also shows a lack of response to the mutagenic action of 1,3-dinitropyrene and a greatly reduced response to 1,6-dinitropyrene and 1-nitropyrene. The responses to 1,3,6-trinitropyrene and 1,3,6,8-tetranitropyrene are affected to a much lesser extent. This strain (TA98/1,8DNP6) is fully sensitive to the mutagenicity of 4-nitroquinoline-1-oxide, niridazole, nitroacridine, and nonnitrated frameshift mutagens. This strain appears to be deficient in a nitroreductase which reduces nitrated pyrenes and possibly other nitrated polycyclic aromatic hydrocarbons to corresponding hydroxylamines, the penultimate mutagens.

Animals↗
PubMed2003

Immune enhancement of nitroreductase-induced cytotoxicity: studies using a bicistronic adenovirus vector.

The nitroreductase (NR)/CB1954 enzyme prodrug system has given promising results in preclinical studies and is currently being assessed in phase I clinical trials. It is well established that there is an immune component to the bystander effect observed with other systems such as thymidine kinase and cytosine deaminase; however, such an effect has not previously been described using NR. We have preliminary data suggesting an immune bystander effect with NR to further examine these effects and their potential enhancement by cytokines, an adenoviral vector containing CMV-NR, an internal ribosome entry site (IRES) and the gene for murine GM-CSF (mGM-CSF) was constructed. The NR-GM-CSF virus was validated in 2 experimental models and demonstrated increased therapeutic efficacy in the MC26 murine colorectal tumour model. These data illustrate that the combination of suicide gene therapy using NR and CB1954 with immune stimulation via GM-CSF gives an improved response compared to either modality alone and suggests that the immune component of this response may be beneficial in combating unresectable, metastatic disease and preventing tumour recurrence.

Adenocarcinoma↗
PubMed1994

Aromatic nitroreductase from the basidiomycete Phanerochaete chrysosporium.

A membrane-associated aromatic nitroreductase activity was identified in cell-free extracts of the lignin-degrading fungus Phanerochaete chrysosporium. The enzyme catalyzed the nitro group reduction of 1,3-dinitrobenzene, 2,4-dinitrotoluene, 2,4,6-trinitrotoluene, 1-chloro-2,4-dinitrobenzene, and 2,4-dichloro-1-nitrobenzene. The corresponding hydroxylamines and/or amines were identified as reaction products by HPLC and/or GC-MS. 1-Nitroso-3-nitrobenzene and 1-hydroxylamino-3-nitrobenzene also were reduced by the enzyme, suggesting they were intermediates in the reaction. The enzyme required NAD(P)H as a cosubstrate and the optimal pH and temperature for the reaction were 6.5 and 50 degrees C, respectively. Enzyme activity was not observed in the presence of molecular oxygen. The membrane-associated enzyme could be solubilized with the nonionic detergent Triton X-100.

Basidiomycota↗
PubMed1994

Crystallization and preliminary crystallographic data for an FMN-dependent nitroreductase from Escherichia coli B.

An FMN-dependent nitroreductase enzyme isolated from Escherichia coli B has been crystallized in a form suitable for high-resolution structural analysis. The crystals belong to the tetragonal space group P4(1)2(1)2 or its enantiomorph P4(3)2(1)2 with cell parameters a = b = 57.74 A, c = 275.51 A and two molecules per asymmetric unit. Diffraction extends to beyond 1.9 A.

Crystallization↗
PubMed2001

The structure of Escherichia coli nitroreductase complexed with nicotinic acid: three crystal forms at 1.7 A, 1.8 A and 2.4 A resolution.

Escherichia coli nitroreductase is a flavoprotein that reduces a variety of quinone and nitroaromatic substrates. Its ability to convert relatively non-toxic prodrugs such as CB1954 (5-[aziridin-1-yl]-2,4-dinitrobenzamide) into highly cytotoxic derivatives has led to interest in its potential for cancer gene therapy. We have determined the structure of the enzyme bound to a substrate analogue, nicotinic acid, from three crystal forms at resolutions of 1.7 A, 1.8 A and 2.4 A, representing ten non-crystallographically related monomers. The enzyme is dimeric, and has a large hydrophobic core; each half of the molecule consists of a five-stranded beta-sheet surrounded by alpha-helices. Helices F and F protrude from the core region of each monomer. There is an extensive dimer interface, and the 15 C-terminal residues extend around the opposing monomer, contributing the fifth beta-strand. The active sites lie on opposite sides of the molecule, in solvent-exposed clefts at the dimer interface. The FMN forms hydrogen bonds to one monomer and hydrophobic contacts to both; its si face is buried. The nicotinic acid stacks between the re face of the FMN and Phe124 in helix F, with only one hydrogen bond to the protein. If the nicotinamide ring of the coenzyme NAD(P)H were in the same position as that of the nicotinic acid ligand, its C4 atom would be optimally positioned for direct hydride transfer to flavin N5. Comparison of the structure with unliganded flavin reductase and NTR suggests reduced mobility of helices E and F upon ligand binding. Analysis of the structure explains the broad substrate specificity of the enzyme, and provides the basis for rational design of novel prodrugs and for site-directed mutagenesis for improved enzyme activity.

Amino Acid Sequence↗
PubMed2001

Combined adenovirus-mediated nitroreductase gene delivery and CB1954 treatment: a well-tolerated therapy for established solid tumors.

Gene-directed enzyme prodrug therapy (GDEPT) is a refinement of cancer chemotherapy that generates a potent cell-killing drug specifically in tumor cells by enzymatic activation of an inert prodrug. We describe in vivo studies that evaluate the efficacy and safety of intratumoral (i.t.) injection of an adenovirus vector (CTL102) expressing Escherichia coli nitroreductase (NTR) combined with systemic prodrug (CB1954) treatment. A single i.t. injection of CTL102 (7.5 x 10(9) to -2 x 10(10) particles) followed by CB1954 treatment produced clear anti-tumor effects in subcutaneous (s.c.) xenograft models of four cancers that are likely candidates for GDEPT (i.e., primary liver, head and neck, colorectal and prostate). Virus dose-response studies (s.c. liver model) revealed a steep increase and subsequent rapid plateauing of both NTR gene delivery and anti-tumor efficacy. Evidence of minor virus spread (toxicity) was observed in a s.c. head and neck xenograft model. This was eliminated by passive immunization with neutralizing anti-Ad5 antibodies prior to virus injection without reducing the magnitude of the anti-tumor effect. Preexisting anti-Ad5 neutralizing antibodies may therefore be an advantage rather than an issue in the clinical use of this new therapy.

Adenoviridae↗
PubMed2005

Nitroreductase-based therapy of prostate cancer, enhanced by raising expression of heat shock protein 70, acts through increased anti-tumour immunity.

Gene-directed enzyme-prodrug therapy (GDEPT) using nitroreductase (NTR), with efficient adenoviral delivery, and CB1954 (CB), is an effective means of directly killing tumours. However, an immune-mediated bystander effect remains an important product of GDEPT since it is often critical to the elimination of untransduced tumour cells both locally and at distal metastatic sites through generation of tumour-specific immunity without the need for tumour antigen identification or the generation of a personalised vaccine. The mode of induced tumour cell death is thought to contribute to the immunisation process, together with the induction and release of stress proteins. Here, RM-9 murine prostate tumour cells were efficiently killed by adenovirally delivered NTR/CB treatment both in vitro and in vivo, and bystander effects were observed. Cells appeared to die by pathways that suggest necrosis more than that of classical apoptosis. NTR/CB-induced expression of a range of stress proteins was determined by proteomic analysis, revealing chiefly heat shock protein (HSP)25 and HSP70 upregulation, whilst immune responses in vivo were weak. In an attempt to enhance the anti-tumour effect, an adenoviral vector was constructed that co-expressed NTR and HSP70, the latter being a known immune stimulator and chaperone of antigen. This combination elicited significantly enhanced protection over NTR alone for both the treated tumour and a subsequent re-challenge. Protection was CD4+ and CD8+ T cell-dependent and was associated with tumour-specific CTL, IFNgamma and IL-5 responses. The use of such a cytotoxic and immunomodulatory gene combination in cancer therapy warrants further pursuit.

Adenoviridae↗
PubMed1988

The nitroreductase enzyme in Walker cells that activates 5-(aziridin-1-yl)-2,4-dinitrobenzamide (CB 1954) to 5-(aziridin-1-yl)-4-hydroxylamino-2-nitrobenzamide is a form of NAD(P)H dehydrogenase (quinone) (EC 1.6.99.2).

A nitroreductase enzyme has been isolated from Walker 256 rat carcinoma cells which can convert 5-(aziridin-1-yl)-2,4-dinitrobenzamide (CB 1954) to a cytotoxic DNA interstrand crosslinking agent by reduction of its 4-nitro group to the corresponding hydroxylamino species (Roberts JJ et al., Biochem Biophys Res Commun 140: 1073-1078, 1986; Knox RJ et al., Biochem Pharmacol 37: 4661-4669, 1988). The enzyme has now been identified as a form of NAD(P)H dehydrogenase (quinone) (DT diaphorase, menadione reductase (NMOR), phylloquinone reductase, quinone reductase, EC 1.6.99.2) by comparison of partial protein sequences, coenzymes, substrate and inhibitor specificities, and spectroscopic data. 2-Phenyl-5(4)-aminoimidazole-4(5)-carboxamide and 5(4)-aminoimidazole-4(5)-carboxamide were shown to be inhibitors of the isolated Walker cell enzyme. This observation could explain the reported antagonistic action of the aminoimidazole carboxamides to the antitumour effects of CB 1954.

Amino Acid Sequence↗
PubMed1986

Oxygen and nitroreductase-dependent binding of AF-2 in spheroids and murine tumors.

Fluorescent nitroheterocycles such as AF-2 may be useful in identifying hypoxic cells in tumors. Since binding is dependent on rate of drug metabolism (nitroreduction) as well as cellular oxygen content, flow cytometric analysis of cells from tumors and spheroids was used to quantify AF-2 binding, and differential pulse polarography was used to measure reduction of AF-2 by several mammalian cell lines, spheroids and tumor cells. Hypoxic V79 spheroid cells and Lewis lung tumor cells bound 20 times more AF-2 than oxic cells, and binding proceeded with first order kinetics. Nitroreductase activity varied about tenfold among different tumor cells. As expected, the rate of binding of AF-2 correlated well with the rate of nitroreduction. Oral injection of AF-2 (5 mg) was the most successful method of administration to tumor-bearing mice. In mice injected with both AF-2 and Hoechst 33342 (which stains well-perfused cells), SCCVII tumor cells which contained the most Hoechst contained the least AF-2. Although minimal toxicity by AF-2 was observed in these tumors, binding of AF-2 was barely sufficient for detection using flow cytometry.

Animals↗