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Mutagenesis by 9,10-anthraquinone derivatives and related compounds in Salmonella typhimurium.

Ninety 9,10-anthraquinone (AQ) derivatives and related anthracene derivatives were screened for mutagenicity with five Salmonella typhimurium tester strains with and without mammalian microsomal activation. About 35% of the compounds tested are considered to be mutagenic. Three patterns of mutagenesis were apparent. (1)Direct frameshift mutagenesis by certain AQ compounds bearing free hydroxyl groups. The most potent were anthragallol (1,2,3-trihydroxy-AQ), purpurin (1,2,4-trihydroxy-AQ) and anthraufin (1,5-dihydroxy-AQ). Some hydroxy-AQ compounds exhibited activation by mammalian microsomal preparations, particularly at lower concentrations, and the majority of mutagenic hydroxy-AQs appeared to revert strain TA1537 (his 3076) specifically.(2)Frameshift mutagenesis by certain AQ compounds with primary amino and, in a few cases, with secondary amino groups. Mammalian microsomes invariably potentiated frameshift mutagenesis, and activity with strain TA100 (sensitive to base pair substitution) is seen in a few cases, e.g. 1,2-diamino-AQ. (3)AQ compounds with one or more nitro groups. These derivatives exhibit the least specificity with regard to tester strain reverted and to microsomal activation. All seven nitro-AQ's tested were mutagenic. In those compounds with mixed "mutagenic" functional groups, the type of mutagenesis observed is usually N02 greater than 0H greater than NH2. AQs bearing halogens, sulfonate or alkyl groups were non-mutagenic, as were AQs substituted solely with secondary amines.

Anthraquinones

Mutagenesis in the strains E. coli K-12 with different ability to genetic recombination.

Data on the role of recombination in spontaneous mutagenesis in E. coli K-12 are presented. On the basis of these data it can be presumed that such mutagenesis results from errors in spontaneous recombination. The study of the dependence of mutagenesis induced by mitomycin C, nitrosoguanidine and ethylmethanesulphonate has revealed that only mutagenesis induced by mitomycin C depends on the recombination ability of the cells. Mutagenesis induced by mitomyin C results from errors in the recombinative restoration of damages to DNA induced by this mutagen.

Alleles

Extensive and differential platinum chemotherapy mutagenesis in livers of children.

Childhood cancer survivors often experience late adverse effects that may be linked to chemotherapy mutagenesis. We studied chemotherapy mutagenesis in normal pediatric tissues using duplex sequencing (NanoSeq) to enable the detection of mutations from single DNA molecules. We found that platinum chemotherapeutics increased the mutation burdens of normal pediatric tissues to levels seen in adults. In the liver, platinum agents imparted a tissue-specific mutational signature that was absent from other tissues. Gene-focused duplex sequencing revealed that chemotherapy mutagenesis generates a great diversity of nonsynonymous variants, some of which may have functional potential, such as leukemogenic variants in blood. Our findings demonstrate extensive chemotherapy mutagenesis in normal tissues of children, which may provide a plausible link between chemotherapy exposure and adverse effects in later life.

Child

Cell-mediated mutagenesis in cultured Chinese hamster cells by carcinogenic polycyclic hydrocarbons: nature and extent of the associated hydrocarbon-DNA reaction.

A system of cell-mediated mutagenesis is described for the study of compounds which require metabolic activation to exert their cytotoxic and mutagenic effects. This system combines BHK21 cells for metabolism of the compounds and V79 cells as targets for mutagenesis. Using the two polycyclic hydrocarbon carcinogens benzo(a)pyrene and 7-methylbenz(a)anthracene we have shown that the hydrocarbon-DNA reaction which accompanies mutagenesis in the target cell is indistinguishable from that reported to occur in vivo and in primary cell cultures. Our results also support the view that a diol epoxide metabolite is responsible for the biological activity of benzo(a)pyrene. The application of cell-mediated mutagenesis to the routine testing of suspect environmental chemicals for biological activity is discussed.

Azaguanine

In vitro mutagenesis assays as predictors of chemical carcinogenesis in mammals.

In vitro microbial mutagenesis assays coupled with mammalian activation systems offer promising technique to screen chemicals for their potential carcinogenic activity. The correlation between mutagenic and carcinogenic properties for a large array of chemicals is approximately 0.9. The best correlation exists for those carcinogens which are themselves highly electrophilic or produce electrophilic metabolites. Correlation between mutagenicity and carcinogenicity for hormonal, metallic, or physical carcinogens has been disappointing but not unexpected based on their proposed mechanisms of action. In addition to the application of in vitro mutagenesis techniques to screening chemicals for the identification of potential carcinogens, they are useful tools for investigating genetic, biochemical, and pharmacologic properties of different animal species. Studies with the chemical carcinogen dimethylnitrosamine have been conducted and show a functional relationship between mutagenesis and carcinogenesis. The assays can also be conducted using activation systems prepared from the tissues of any mammalian species. This permits a direct assessment of phylogenic extrapolation by comparing the metabolic activation capabilities of tissues from several mammalian species, including human samples. The advantages of mutagenicity testing are the short period of time required for results, the high sensitivity of the assay (microgram of nanogram quantities of chemicals can be used), and the fact that the ultimate agent can be detected biologically without first necessitating chemical identification and isolation. It appears from current studies that in vitro mutagenesis techniques may well open new avenues of investigation into some old toxicologic problems.

Aging

Mechanisms of inhibition by ascorbate of microbial mutagenesis induced by N-nitroso compounds.

Mutagenesis induced by N-methyl-N-nitrosoguanidine (MNNG) and dimethylnitrosamine (DMN) in Salmonella TA 1530 was inhibited by ascorbate. Inhibition of MNNG-induced mutagenesis resulted from a reaction between ascorbate and MNNG that led to consumption of MNNG. The rate of this reaction was considerably enhanced by catalytic amounts of Cu(II) and Fe(III). No direct reaction between DMN and ascorbate was detectable, but relatively high concentrations of Cu(II) enchanced inhibition of DMN-induced mutagenesis by ascorbate. Added protein reduced the effectiveness of Cu(II) as a catalyst of the reaction between ascorbate and MNNG, which suggested that the microsomal protein necessary to activate DMN, may reduce the concentration of free Cu(II) and thereby lower its catalytic efficiency. Mutagenesis by N-methyl-N-nitrosourea was not inhibited by ascorbate.

Animals

Mutagenesis of certain activated carcinogens in vitro associated with genetically mediated increases in monooxygenase activity and cytochrome P 1-450.

A bacterial mutagenesis assay and genetic differences in microsomal CO-binding cytochromes were combined in vitro to evaluate the metabolic activation of several known carcinogens to frameshift mutagens. With the use of liver fractions from C57BL/6N and DBA/2N control mice and mice treated in vivo with 3-methylcholanthrene, beta-naphthoglavone, phenobarbital, or 2,3,7,,-tetrachlorodibenzo-p-dioxin, the in vitro mutagenicity of 3-methylcholanthrene, 6-aminochrysene, and 2-acetylaminofluorene --but not benzo[a]pyrene==is closely associated with the genetically mediated difference in both aromatic hydrocarbon-inducible aryl hydrocarbon (benzo[a]pyrene) hydroxylase activity and new cytochrome P1-450 formation; such an association between 7,12-dimethylbenz[a]anthracene or benz[a]anthracene activation to mutagens in vitro and these genetic differences between C57BL/6N and DBA/2N mouse strains in uncertain. The Salmonella typhimurium histidine mutant TA1538 is more effective than tester strains TA1537 and TA1535 in the determination of 3-methylcholanthrene mutagenesis in vitro. The relationships between the histidine revertant rate as a function of both liver protein concentration per plate and mutagen concentration per plate are illustrated for 3-methylcholanthrene, benzo[a]pyrene, 6-aminochrysene, and 2-acetylaminofluorene. With the use of offspring from the appropriate genetic crosses, the aromatic hydrocarbon-inducible hydroxylase activity appears to be expressed as an autosomal dominant trait, whereas the mutagenesis of 3-methylcholanthrene in vitro appears to be expressed additively; this apparent discrepancy probably reflects different proportional amounts of phenolic benzo[a]pyrene, compared with mutagenic 3-methylcholanthrene metabolites, formed by the monooxygenase(s). 3-Methylcholanthrene, 6-aminochrysene, and 2-acetylaminofluorene--but not benzo[a]pyrene--are each more mutagenic in vitro per molecule of cytochrome P1-450 than per molecule of CO-binding cytochrome other than P1450. Diethylmaleate, a compound which depletes flutathione content in liver, and 1,1,1-trichloropropene-2,3-epoxide, an inhibitor of epoxide hydrase (EC 4.2.1.63), were also studied in vitro. Diethylmaleate, and especially 1,1,1-trichloropropene-2,3-epoxide, increases the mutagenicity of benzo[a]pyrene, whereas no increases occur with 3-methylcholanthrene, 6-aminochrysene, or 2-acetylaminofluorene activation to mutagens in vitro. Both diethylmaleate and 1,1,1-trichloropropene-2,3-epoxide cause decreases in 2-acetylaminofluorene mutagenesis in vitro when liver fractions from phenobarbital-treated mice are used.

2-Acetylaminofluorene

Genomic Evolution of Myeloproliferative Neoplasms and Therapy-Associated Mutagenesis.

UNLABELLED: Philadelphia-negative myeloproliferative neoplasms are chronic blood neoplasms. Treatments control blood counts, but disease can progress to myelofibrosis or acute myeloid leukemia. We performed longitudinal whole-genome and targeted sequencing in 30 patients, integrating clonal dynamics with 7,986 blood counts and clinical histories. Distinct evolutionary patterns distinguished stable from progressive disease, with leukemic transformation arising via TP53 loss, stepwise driver mutation acquisition within complex clones, or emergence of independent leukemic clones. In contrast, stable disease showed long-term clonal equilibrium without new drivers. Phylogenetic analysis using 203 whole-genomes of hematopoietic colonies revealed age-appropriate polyclonal hematopoiesis in triple-negative essential thrombocythemia and germline predisposition to thrombocytosis, supporting non-neoplastic origins. Therapy-associated mutagenesis was observed, including C > G mutations following azacitidine and characteristic T > A/T > G after hydroxycarbamide exposure in blood cells, although not in skin where UV damage predominated. These findings demonstrate that progression is genomically encoded years in advance and support serial monitoring and further study of treatment-related mutagenesis. SIGNIFICANCE: Longitudinal whole-genome sequencing shows MPN progression is genomically encoded years before clinical transformation, with distinct evolutionary routes to leukemia and MF. It identifies DNA mutagenesis associated with HC and 5-azacitidine, suggests some triple-negative cases are nonclonal, and supports serial clinical genomic monitoring for improved risk stratification and long-term management. See related commentary by Agarwal and Sankaran, p. 1724.

Humans

Identifying sites of simultaneous DNA replication in eukaryotes by N-methyl-N'-nitro-N-nitrosoguanidine multiple mutagenesis.

N-methyl-N'-nitro-N-nitrosoguanidine (NG) induces certain classes of multiple mutations in yeast at high frequency. By selecting for mutation at one locus (his4 or leu1) one frequently obtains double mutants where another mutation to temperature sensitivity has also been induced. This multiple mutagenesis exhibits a considerable specificity: for mutation at one particular locus there is a high chance that another mutation will be found in the same cell at one of a restricted number of other loci. For any given locus (e.g. his4) there is a spectrum of sites at which temperature-sensitivity mutations are co-induced. This spectrum differs for different loci, such that the spectrum of sites co-mutating with leu1 differs completely from that for sites co-mutating with his4. This NG'induced co-mutation is interpreted in terms of NG acting to enhance mutagenesis at sites of simultaneous DNA replication within the cell. The results so obtained indicate a very strict control over the order and timing of gene replication in Saccharomyces cerevisiae, and it is suggested that it is now possible to use NG double mutagenesis to try and locate origins of replication in yeast.

DNA Replication

Plasmid (pKM101)-mediated enhancement of repair and mutagenesis: dependence on chromosomal genes in Escherichia coli K-12.

The drug resistance plasmid pKM101 plays a mojor role in the Ames Salmonella/microsome carcinogen detecting system by enhancing chemical mutagenesis. It is shown that in Escherichia coli K-12 the plasmid pKM101 enhances both spontaneous and methyl methanesulfonate-caused reversion of an ochre mutation, bacterial survival after ultraviolet irradiation, and reactivation of ultraviolet-irradiated lambda in unirradiated cells. All these effects are shown to be dependent on the recA+ lexA+ genotype but not on the recB+ recC+ or recF+ genotypes. The recA lexA-dependence of the plasmid-mediated repair and mutagenesis suggests an interaction with the cell's inducible error-prone repair system. The presence of pKM101 is shown to cause an additional increase in methyl methanesulfonate mutagenesis in a tif mutant beyond that caused by growth at 42 degrees. The presence of the plasmid raises the level of the Weigle-reactivation curve for the raactivation of ultraviolet-irradiated lambda in E. coli and causes a shif of the maximum to a higher UV fluence. These observations suggest that pKM101 does not exert its effects by altering the regulation of the cell's error-prone repair system but rather by supplying a mechanistic component or components.

Chromosomes, Bacterial

Persistence and decay of thermoinducible error-prone repair activity in nonfilamentous derivatives of tif-1, Escherichia coli B/r: the timing of some critical events in ultraviolet mutagenesis.

Ultraviolet (UV) mutagenesis in E. coli is associated with a UV-inducible type of error-prone postreplication repair ("SOS" repair) which, in tif-1 strains, is thermo-inducible in coordination with other recA+ lexA+-dependent inducible functions, including filamentous growth. Mutants of E. coli B/r tif-1 strains have been isolated which retain thermoinducibility of SOS repair activity, but lack the thermosensitivity caused by filamentous growth at 42 degrees C. These strains have been used to determine: the kinetics of decay at 30 degrees C of thermally induced ability to enhance UV mutagenesis; the kinetics of thermal enhancement of spontaneous and UV-induced mutability at 42 degrees C, and the kinetics of decay at 30 degrees C of susceptibility to thermal enhancement of spontaneous and UV-induced mutability. Mutations from tryptophane requirement to prototrophy (Trp- to Trp+) were scored. UV doses were 0.2 J/M2 for excision repair-deficient (Uvr-) and 2J/m2 for Uvr+ strains. The results support the following conclusions. 1) thermally induced SOS repair activity decays at 30 degrees C to about 25% of its maximum level in 45 min, and is no longer detectable after 90 min. 2) Thermal enhancement of UV mutability occurs at sites produced primarily (perhaps exclusively) before completion of the first post-irradiation cell division. 3) UV-induced sites susceptible to thermally induced SOS repair are stable at 30 degrees C in cells not containing the error-prone repair system, and are refractory to constitutive error-free repair for at least 2-3 hours. 4) UV produces a potentially mutagenic type of photoproduct in DNA which can, without interacting with another UV lesion, provide a site susceptible to SOS repair, but which is not a sufficient signal for SOS induction. 5) 50-70% of the SOS-mutable SOS-noninducing UV photoproducts are photoreversible pyrimidine dimers. The results are discussed in relation to current models of UV mutagenesis and induction of UV-inducible functions.

Animals

Mutagenesis and repair deficiencies of Escherichia coli umuC mutants are suppressed by the plasmid pKM101.

The presence of the drug resistance plasmid pKM101 restored the ability of Escherichia coli umuC mutant strains to be mutated by methyl methanesulfonate. Inducible (Weigle) reactivation of ultraviolet-irradiated bacteriophage lambda was not observed in uvrA6 umuC mutant strains lacking pKM101 but was observed if the plasmid was present in the strains. In a uvrA+ umuC36 strain pKM101 increased the efficiency of the Weigle reactivation process. Plasmid-mediated UV-resistance and plasmid-mediated phage reactivation were observed in umuC(pKM101) strains both in uvrA+ and uvrA6 backgrounds. No restoration of methyl methanesulfonate mutability by pKM101 was observed in umuC36 recA56 strains. pKM101 mutants unable to enhance mutagenesis in umuC+ backgrounds also had no effect on methyl methanesulfonate mutagenesis in umuC mutant strains. Neither a umuC mutation nor the presence of pKM101 affected the UV induction of protein X, the recA protein. Hypotheses relating the mode of action of pKM101 to the process of mutagenesis and inducible phage reactivation are discussed.

DNA Repair

Transversion mutagenesis in bacteriophage T4.

Transversion mutations can be distinguished from transition mutations by the use of special tauII mutants of bacteriophage T4. Methyl methanesulfonate did not induce reversion of the tester mutants along transversion or transition pathways from A:T1 base pair sites, nor along transversion pathways from G:C base pair sites. Ethyl methanesulfonate and N-methyl-N-nitrosourea, however, induced both transversions and transitions at an A:T base pair site; no transversions were detected at G:C-sites. Mn++ induced transversions and transitions at both A:T-and G:C-sites. The influence of temperature-sensitive gene-43 DNA polymerase mutator and antimutator mutations on the reversion of the tauII tester mutants was measured: some gene-43 mutants differentially influenced different pathways of reversion. Studies of thymineless mutagenesis demonstrated A:T-site transversion mutations. A synergistic interaction between thymineless mutagenesis and the gene-43 mutator, tsL56, was used to demonstrate thymineless mutagenesis at one site where it was not detected in the presence of the wild type polymerase.

Base Sequence

Resistance to bromodeoxyuridine mutagenesis and toxicity in mammalian cells selected for resistance to hydroxyurea.

Mutant cell lines resistant to hydroxyurea (HU), an inhibitor of the enzyme ribonucleotide reductase, were selected from a line of Syrian hamster melanoma cells. Mutant lines were selected for resistance to 0.3 mM HU, and from these lines, second-step mutants were selected for resistance to 1.9 mM HU. The HUr lines were tested ffor their responses to 5-bromodeoxyuridine (brdU), in terms of toxicity, mutagenesis, and incorporation of BrdU into DNA. All of the HUr lines showed increased resistance to the toxic effects of BrdU. in addition, the HUr lines all were resistant to BrdU mutagenesis. Overall, there was good correlation among the levels of resistance to HU toxicity, BrdU toxicity, and BrdU mutagenesis in the HUr lines. These tests were carried out under conditions such that the parental and HUr cells incorporated equal amounts of BrdU into nuclear DNA. Therefore, the resistance of the HUr cells to the effects of BrdU cannot be attributed to decreased incorporation of BrdU into DNA. These results suggest that the HUr cells have an lateration in ribonucleotide reductase activity that simultaneously confers resistance to HU and BrdU. The properties of the HUr cells suggest that the perturbation of deoxcytidine metabolism by BrdU. The properties of the HUr cells suggest that the perturbation of deoxcytidine metabolism by BrdU triphosphate inhibition of ribonucleotide reductase activity plays a key role in the toxic and mutagenic effects of BrdU in mammalian cells.

Animals

Mutagenesis by N-acetoxy-2-acetyl aminofluorene of chinese hamster V79 cells is unaffected by caffeine.

8-Azaguanine (AZG)- and 6-thioguanine (TG)-resistant cells (mutants) were induced in Chinese hamster V79-4 cells by 0.1--2.5 microgram/ml N-acetoxy-2-acetyle aminofluorine (AcAAF) treatments in the presence of 5% fetal bovine serum (FBS). The frequency of resistant colonies increased from 1 to 47 per 10(5) survivors. The effect of caffeine (50--200 microgram/ml) during the mutagenesis expression period was determined by adding caffeine 1--24 h after AcAAF. The medium was replaced after 48 h exposures so that caffeine was absent during subsequent selection with AZG or TG. No significant change in the AcAAF-induced mutant frequency occurred with any treatment combination although caffeine greatly enhanced the lethality associated with AcAAF treatments. Thus, caffeine interferes with postreplication repair in V79-4 cells without affecting the probability of error of the repair process. These results were obtained with a quantitative mutagenesis assay in which the cells were reseeded prior to selection to achieve maximum expression without interference from metabolic crossfeeding. In contrast, the commonly used in situ assay is subject to serious interference from crossfeeding and yields an artifactual enhancement of AcAAF mutagenesis by caffeine.

Acetoxyacetylaminofluorene

Frameshift mutagenesis in bacteria by 8-methoxypsoralen (methoxalen) in the dark.

We confirm that 8-methoxypsoralen (8-MOP) in the dark induces frameshift mutations in both Escherichia coli and Salmonella typhimurium when present in adequate concentration under growth conditions. The dose response is sigmoidal with a threshold or quasi-threshold at concentrations below about 10 microgram/ml. Frameshift mutagenesis by 8-MOP in the dark is unaffected by mutations at the uvrA or uvrB genes, in contrast to base pair substitution mutagenesis by 8-MOP plus near UV light. RecA (but not recB) bacteria are hypersensitive to the growth-inhibiting action of 8-MOP in the dark and are not detectably mutagenized. The characteristics of 8-MOP dark mutagenesis are consistent with the chemical interacting in a non-covalent manner with DNA and affecting the rate of occurrence of base deletions or insertions during DNA replication. The question of extrapolation of the genetic effect of 8-MOP to man is discussed.

Darkness

Nitrous acid mutagenesis of duplex DNA as a three-component system.

Purified native Hemophilus influenzae DNA is relatively insusceptible to nitrous acid (NA) mutagenesis in vitro, but is readily mutated following denaturation. NA mutagenicity for duplex DNA is significantly increased in the presence of various alcohols, glycols, phenols or primary amines. Phenol-extracted DNA contains dissociable contaminants of low molecular weight that enhance NA mutagenesis. Enhancement of NA mutagenesis by phenol and by spermine is due to the formation of unstable molecular species. We propose that reactive organic nitroso compounds are formed which then serve as delivery vehicles to promote mutagenicity of native DNA, perhaps via transnitrosation reactions. Similar reactions probably occur in vivo to promote NA-induced base substitution (but not frameshift) mutations in Salmonella typhimurium and in Escherichia coli. The possible significance of these observations to carcinogenesis is discussed.

DNA, Bacterial

Local mutagenesis: a method for generating viral mutants with base substitutions in preselected regions of the viral genome.

DNA from simian virus 40 (SV40) was prepared for local mutagenesis by nicking the molecule at a specific site with a restriction endonuclease that recognizes one site in SV40 DNA and then extending the nick enzymatically to expose a short, single-stranded segment of DNA. The "gapped" DNA was treated with a single-strand-specific mutagen, sodium bisulfite, which converts cytosine to uracil. After mutagenesis, the gap was repaired with DNA polymerase, generating molecules resistant to the restriction enzyme used to make the initial nick. From cells infected with DNA thus modified, SV40 mutants were isolated that had enzyme-resistant genomes. In some cases, precise positions of G.C to A.T transitions could be inferred from the patterns of susceptibility of mutant DNA to other restriction endonucleases whose recognition sequences were altered by the mutagenesis procedure. One of the restriction endonuclease sites mutagenized (Bgl I) maps at the origin of SV40 DNA replication and near sequences corresponding to the 5' ends of viral mRNAs. Many of the resulting Bgl I-resistant mutants yielded small plaques, suggesting partial defectiveness in DNA replication or transcription.

DNA Polymerase I