Frameshift mutations induced by three classes of acridines in the lacZ reversion assay in Escherichia coli: potency of responses and relationship to slipped mispairing models

Unboxing the molecular modalities of mutagens in cancer

The etiology of the majority of human cancers is associated with a myriad of environmental causes, including physical, chemical, and biological factors. DNA damage induced by such mutagens is the initial step in the process of carcinogenesis resulting in the accumulation of mutations. Mutational events are considered the major triggers for introducing genetic and epigenetic insults such as DNA crosslinks, single- and double-strand DNA breaks, formation of DNA adducts, mismatched bases, modification in histones, DNA methylation, and microRNA alterations. However, DNA repair mechanisms are devoted to protect the DNA to ensure genetic stability, any aberrations in these calibrated mechanisms provoke cancer occurrence. Comprehensive knowledge of the type of mutagens and carcinogens and the influence of these agents in DNA damage and cancer induction is crucial to develop rational anticancer strategies. This review delineated the molecular mechanism of DNA damage and the repair pathways to provide a deep understanding of the molecular basis of mutagenicity and carcinogenicity. A relationship between DNA adduct formation and cancer incidence has also been summarized. The mechanistic basis of inflammatory response and oxidative damage triggered by mutagens in tumorigenesis has also been highlighted. We elucidated the interesting interplay between DNA damage response and immune system mechanisms. We addressed the current understanding of DNA repair targeted therapies and DNA damaging chemotherapeutic agents for cancer treatment and discussed how antiviral agents, anti-inflammatory drugs, and immunotherapeutic agents combined with traditional approaches lay the foundations for future cancer therapies.

A perspective review on medicinal plant resources for their antimutagenic potentials

Mutagens present in the environment manifest toxic effects and are considered as serious threat for human health and healthcare. Recent reports reveal that medicinal plant resources are being explored for identifying potent antimutagenic as well as cancer preventing agents. There is mounting evidence that cancer and other mutation-related diseases can be prevented with the use of medicinal pant resources including crude extracts, active fractions, phytochemicals, and pure phytomolecules. These medicinal plant resources possessing antimutagenic potentials have been shown to target molecular mechanisms underlying the mutagenic impacts. Technological advents and high-throughput screening/activity methods have revolutionized this field, though several potent plants and their active principles have been reported as effective antimutagens. The translational success rate needs to be improved, but the trends are encouraging. In this review, we present the current understandings and updates on various mutagens in the environment, toxicities related/attributed to them, the resultant mutations (and cancer), and how medicinal plants come to the rescue. A perspective review has been presented on whether and how medicinal plant resources can be an effective approach for addressing mutagens in the environment. An account of medicinal plant resources used as antimutagenic agents has been given along with the underlying mechanism of action and their therapeutic potential in various models of cancer. Recent success stories, current challenges, and future prospects are discussed.

Natural and artificial sources of genetic variation used in crop breeding: A baseline comparator for genome editing

Traditional breeding has successfully selected beneficial traits for food, feed, and fibre crops over the last several thousand years. The last century has seen significant technological advancements particularly in marker assisted selection and the generation of induced genetic variation, including over the last few decades, through mutation breeding, genetic modification, and genome editing. While regulatory frameworks for traditional varietal development and for genetic modification with transgenes are broadly established, those for genome editing are lacking or are still evolving in many regions. In particular, the lack of "foreign" recombinant DNA in genome edited plants and that the resulting SNPs or INDELs are indistinguishable from those seen in traditional breeding has challenged development of new legislation. Where products of genome editing and other novel breeding technologies possess no transgenes and could have been generated via traditional methods, we argue that it is logical and proportionate to apply equivalent legislative oversight that already exists for traditional breeding and novel foods. This review analyses the types and the scale of spontaneous and induced genetic variation that can be selected during traditional plant breeding activities. It provides a base line from which to judge whether genetic changes brought about by techniques of genome editing or other reverse genetic methods are indeed comparable to those routinely found using traditional methods of plant breeding.

Tracing brain genotoxic stress in Parkinson's disease with a novel single-cell genetic sensor

To develop an in vivo tool to probe brain genotoxic stress, we designed a viral proxy as a single-cell genetic sensor termed PRISM that harnesses the instability of recombinant adeno-associated virus genome processing and a hypermutable repeat sequence-dependent reporter. PRISM exploits the virus-host interaction to probe persistent neuronal DNA damage and overactive DNA damage response. A Parkinson's disease (PD)-associated environmental toxicant, paraquat (PQ), inflicted neuronal genotoxic stress sensitively detected by PRISM. The most affected cell type in PD, dopaminergic (DA) neurons in substantia nigra, was distinguished by a high level of genotoxic stress following PQ exposure. Human alpha-synuclein proteotoxicity and propagation also triggered genotoxic stress in nigral DA neurons in a transgenic mouse model. Genotoxic stress is a prominent feature in PD patient brains. Our results reveal that PD-associated etiological factors precipitated brain genotoxic stress and detail a useful tool for probing the pathogenic significance in aging and neurodegenerative disorders.

Half-Intercalation Stabilizes Slipped Mispairing and Explains Genome Vulnerability to Frameshift Mutagenesis by Endogenous "Molecular Bookmarks"

Some 60 years ago chemicals that intercalate between base pairs of duplex DNA were found to amplify frameshift mutagenesis. Surprisingly, the robust induction of frameshifts by intercalators still lacks a mechanistic model, leaving this classic phenomenon annoyingly intractable. A promising idea of asymmetric half-intercalation-stabilizing frameshift intermediates during DNA synthesis has never been developed into a model. Instead, researchers of frameshift mutagenesis embraced the powerful slipped-mispairing concept that unexpectedly struggled with the role of intercalators in frameshifting. It is proposed that the slipped mispairing and the half-intercalation ideas are two sides of the same coin. Further, existing findings are reviewed to test predictions of the combined "half-intercalation into the slipped-mispairing intermediate" model against accumulated knowledge. The existence of potential endogenous intercalators and the phenomenon of "DNA bookmarks" reveal ample possibilities for natural frameshift mutagenisis in the cell. From this alarming perspective, it is discussed how the cell could prevent genome deterioration from frameshift mutagenesis.

Two antigenotoxic chalcone glycosides from Mentha longifolia subsp. longifolia

CONTEXT

Mentha L. (Labiatae) species (mint) with their flavoring properties have been used in food industries for centuries. Besides they have a great importance in drug development and medicinal applications due to various bioactive compounds of several members of the genus.

OBJECTIVE

The aim of this study was to isolate bioactive compounds with antimutagenic potential by bio-guided fractionation and determine their structures by spectroscopic methods.

MATERIALS AND METHODS

The structural elucidation of the isolated compounds was done based on spectroscopic methods, including MALDI-MS, UV, IR, and 2D NMR experiments, and the bio-guided fractionation process was done by using the Ames/Salmonella test system. Henceforth, solely genotoxic and antigenotoxic potential of the new compounds were also confirmed up to 2 µM/plate by using the same test system.

RESULTS

Two new chalcone glycosides: (βR)-β,3,2',6'-tetrahydroxy-4-methoxy-4'-O-rutinosyldihydrochalcone and (βR)-β,4,2',6'-tetrahydroxy-4'-O-rutinosyldihydrochalcone, were isolated from Mentha longifolia (L.) Hudson subsp. longifolia, together with known six flavonoid glycosides and one phenolic acid: apigenin-7-O-glucoside, luteolin-7-O-glucoside, apigenin-7-O-rutinoside, luteolin-7-O-rutinoside, apigenin-7-O-glucuronide, luteolin-7-O-glucuronide, rosmarinic acid. According to the antimutagenicity results, both new test compounds significantly inhibited the mutagenic activity of 9-aminoacridine in a dose-dependent manner at the tested concentrations from 0.8 to 2 µM/plate. (βR)-β,4,2',6'-Tetrahydroxy-4'-O-rutinosyldihydrochalcone showed the maximum inhibition rate as 75.94% at 2 µM/plate concentration.

CONCLUSIONS

This is the first report that two new chalcone glycosides were isolated from Mentha longifolia subsp. longifolia and their antimutagenic potentials by using mutant bacterial tester strains. In conclusion, the two new chalcone glycosides showed a significant antigenotoxic effect on 9-aminoacridine-induced mutagenesis at tested concentrations.

Antimutagenic compounds and their possible mechanisms of action

Mutagenicity refers to the induction of permanent changes in the DNA sequence of an organism, which may result in a heritable change in the characteristics of living systems. Antimutagenic agents are able to counteract the effects of mutagens. This group of agents includes both natural and synthetic compounds. Based on their mechanism of action among antimutagens, several classes of compounds may be distinguished. These are compounds with antioxidant activity; compounds that inhibit the activation of mutagens; blocking agents; as well as compounds characterized with several modes of action. It was reported previously that several antitumor compounds act through the antimutagenic mechanism. Hence, searching for antimutagenic compounds represents a rapidly expanding field of cancer research. It may be observed that, in recent years, many publications were focused on the screening of both natural and synthetic compounds for their beneficial muta/antimutagenicity profile. Thus, the present review attempts to give a brief outline on substances presenting antimutagenic potency and their possible mechanism of action. Additionally, in the present paper, a screening strategy for mutagenicity testing was presented and the characteristics of the most widely used antimutagenicity assays were described.

The synthesis, characterization, antimicrobial and antimutagenic activities of hydroxyphenylimino ligands and their metal complexes of usnic acid isolated from Usnea longissima

Novel Schiff base ligands of usnic acid isolated from Usnea longissima and their metal complexes were synthesized and characterized. Investigated their antimicrobial and antimutagenic activities.

The antioxidant and antigenotoxic potential of methanol extract of Cladonia foliacea (Huds.) Willd

In this article, the genotoxic and antigenotoxic effects of methanol extract of of Cladonia foliacea (Huds.) Willd. (CME) were studied using WP2, Ames (TA1535 and TA1537), and sister chromatid exchange (SCE) test systems. The results of our studies showed that 5 µM concentration of aflatoxin B1(AFB1) changed the frequencies of SCE and malondialdehyde (MDA) levels, superoxide dismutase (SOD), glutathione (GSH), and glutathione peroxidase (GPx) activities. When 5 and 10 µg/mL concentrations of CME was added to AFB1, the frequencies of SCE and MDA level were decreased and SOD, GSH, and GPx levels were increased. The extract CME did not show any mutagenicity on Ames (Salmonella typhimurium TA1535, TA1537) and WP2 (Escherichia coli) test systems. On the other hand, CME has antimutagenicity on the mentioned test systems. The results of this experiment have clearly shown that CME has a significant antioxidative and antigenotoxic effect, which is thought to be due to the antigenotoxic activities of antioxidant enzymes.

Genotoxic, antigenotoxic and antioxidant properties of methanol extracts obtained from Peltigera horizontalis and Peltigera praetextata

Now-a-days, there is a big need to reduce genotoxic effects of mutagenic and carcinogenic agents in environment, which are increased by the technological development. Lichens produce a wide variety of unique metabolites due to being in various extreme areas and being symbiotic organisms of fungi and algae. Therefore, this study was planned to search new sources having antimutagenic activity by researching two different lichen species and to determine whether their usage is safe. With this respect, the mutagenic and antimutagenic properties of methanol extracts of the lichens were determined by the bacterial reverse mutation and sister chromatid exchange assays. Furthermore, the malondialdehyde level, superoxide dismutase, glutathione and glutathione peroxidase activities against aflatoxin B1 were determined for understanding the ways in which the lichens showed their genotoxic properties.

Antigenotoxic potencies of a lichen species, Evernia prunastri

In this article, the genotoxic and antigenotoxic effects of methanol extract of Evernia prunastri (Huds.) Willd. (MEP) were studied using WP2, Ames (TA1535 and TA1537) and sister chromatid exchange (SCE) test systems. The results obtained from bacterial test systems demonstrated that MEP has strong antimutagenic potencies on TA1537 and WP2 strains. The highest inhibition rates for MEP on TA1537 and WP2 strains were 37.70% and 69.70%, respectively. According to the SCE test system, MEP reduced the genotoxic effects of aflatoxin. In order to clarify the mechanism underlying the antigenotoxic effects of MEP, the antioxidants were determined. Cotreatments of 5, 10 and 20 µg/mL concentrations of MEP with aflatoxin B1 decreased the frequencies of SCE and the malondialdehyde level and increased amount of superoxide dismutase, glutathione and glutathione peroxidase which were decreased by aflatoxin. The data obtained from this work have clearly shown that MEP has significant antigenotoxic effects which are thought to be partly due to the antioxidant activities and antioxidant inducing capability of MEP. This is the first report indicating the antigenotoxic activities of MEP against several mutagen agents such as N-methyl-N'-nitro-N-nitrosoguanidine, acridin and aflatoxin.

Determination of genotoxic and antigenotoxic properties of essential oil from Ferula orientalis L. using Ames/Salmonella and E. coli WP2 bacterial test systems

The essential oils having many application fields such as medicine, flavoring, cosmetics are natural products obtained from aromatic plants. As the natural products of Ferula species have a wide range of use in folk medicine, this study was planned to evaluate the mutagenic and antimutagenic activities of essential oils of leaves and flowers of Ferula orientalis grown in Erzurum, through the bacterial reverse mutation assay. Furthermore, the chemical compositions of essential oils isolated by the hyrodistillation method were analysed by gas chromatography (GC) and gas chromatography-mass spectroscopy (GC-MS), as their biological activities were connected to their contents. According to our results, any tested essential oil at any used concentration on Salmonella typhimurium TA1535 and TA1537 strains and in Escherichia coli WP2 uvrA strain showed no mutagenic activity. However, the tested materials at different concentrations showed antimutagenic activities against the used mutagens. The inhibition rates ranged against sodium azide (NaN3) on S. typhimurium TA1535 from 29% to 36%, against 9-aminoacridine (9-AA) on S. typhimurium TA1537 from 40% to 68% and against N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) on E. coli WP2 uvrA from 23% to 52%, respectively. Also, it is revealed by GC and GC/MS analysis of the essential oils isolated from the leaves and flowers, respectively. The major compounds in these oils were determined as α-cadinol, δ-cadinene and germacrene D-4-ol. The results of this study indicate that as the essential oils of F. orientalis have many constituents, they show no mutagenic activity but significant antimutagenic activity, and these materials can be safely used in medicinal applications after further investigations.

Genotoxic and antigenotoxic assessment of four newly synthesized dihydropyridine derivatives

The current study aims to determine the genotoxic and antigenotoxic potential of four newly synthesized dihydropyridine derivatives using Escherichia coli WP2 and Ames/ Salmonella bacterial reversion assay systems. The bacterial mutant tester strains, E. coli WP2 uvrA with a point mutation and Salmonella typhimurium TA1537 with a frameshift mutation, were used to determine genotoxic potentials of the test compounds. To determine antigenotoxic potentials of the test compounds, the same strains were also used together with positive mutagens N-methyl- N′-nitro- N-nitrosoguanidine (MNNG) for E. coli WP2 uvrA and 9-aminoacridine (9-AA) for S. typhimurium TA1537. According to the results, neither of the test compounds showed significant genotoxic activity on both tester strains at the tested concentrations. However, except compound 4, all the test compounds showed significant antigenotoxic activity on MNNG- or/and 9-AA-induced mutations. The inhibition rates of mutagenesis ranged from 27.0% (compound 2: 2.5 mM/plate) to 65.0% (compound 2: 0.5 mM/plate) for MNNG and from 30.6% (compound 2: 2 mM/plate) to 58.5% (compound 1: 1 mM/plate) for 9-AA genotoxicity. According to these results, it is concluded that all the test compounds do not have a mutagenic potential on the bacterial strains at the tested concentrations, and some of them have antigenotoxic potentials against MNNG- and 9-AA-induced mutagenesis.

Antigenotoxic properties of two newly synthesized β-aminoketones against N-methyl-N'-nitro-N-nitrosoguanidine and 9-aminoacridine-induced mutagenesis

The aim of this study was to determine the antigenotoxic potential of two newly synthesized β-aminoketones against N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and 9-aminoacridine (9-AA)-induced mutagenesis. The mutant bacterial tester strains were MNNG-sensitive Escherichia coli WP2 uvrA and 9-AA-sensitive Salmonella typhimurium TA1537. Both test compounds showed significant antimutagenic activity at various tested concentrations. The inhibition rates ranged from 29.5% (compound 1: 2 mM/plate) to 47.5% (compound 2: 1.5 mM/plate) for MNNG and from 25.0% (compound 2: 1 mM/plate) to 52.1% (compound 2: 2.5 mM/plate) for 9-AA genotoxicity. Moreover, the mutagenicity of the test compounds was investigated by using the same strains. Neither test compound has mutagenic properties on the bacterial strains at the tested concentrations. Thus, the findings of the present study give valuable information about chemical prevention from MNNG and 9-AA genotoxicity by using synthetic β-aminoketones.

A deletion mutation in the spacing within the psaA core promoter enhances transcription in a cyanobacterium Synechocystis sp. PCC 6803

Transcriptional regulation of PSI reaction center psaA is one of the important physiological responses to changing environments. We previously reported that the Rrf2-type transcriptional regulator Slr0846 activates transcription of psaA in Synechocystis sp. PCC 6803. In the Δslr0846 mutant, transcripts from two promoters, P1 and P2, were downshifted and, as a result, a lower Chl content and slower growth were observed. Here, we report spontaneous suppressors which recovered Chl accumulation and photoautotrophic growth. Sequencing of the whole promoter region revealed in some suppressors the same single nucleotide deletion in a 9 bp G stretch (-21 to -29 from the transcriptional start point of P1), which is located between the -35 and -10 elements of the P1 core promoter (hereafter the -G mutation). The transcripts from P1 were higher in abundance in this pseudorevertant than in the Δslr0846 mutant. When the promoter was fused to a reporter gene, the -G mutation conferred ~4 times higher expression than the wild-type promoter. It has been shown that the P1 promoter activity of psaA is regulated by a high light regulatory element 1 just upstream of -35. The -G mutated P1 promoter still retained the high light response. Thus, the -G mutation enhanced the expression level of psaA without a loss of the response to the high light conditions. This is the first study of the spontaneous mutation of a spacer length of a promoter for expression in cyanobacteria.

Protective effects of methanol extracts from Cladonia rangiformis and Umbilicaria vellea against known mutagens sodium azide and 9-aminoacridine

Lichens and their various extracts have been occasionally used in the treatment of many diseases. Cladonia rangiformis and Umbilicaria vellea are two important species of these lichens and they have several biological activities. In the present study, methanol extracts of these lichens, which are grown in the Eastern Anatolia Region of Turkey, were isolated, and their mutagenic and antimutagenic properties were investigated by using AMES-Salmonella and Zea mays Root Tip Mitotic Index mutagenicity and antimutagenicity assay systems. Known mutagens sodium azide (NaN3) and 9-Aminoacridine (9-AA) were used to determine antimutagenic properties of methanol extracts. The results showed that all methanol extracts, investigated in the present study, can be considered genotoxically safe because they do not have mutagenic activity at the tested concentrations. Besides, all of them have antimutagenic activity against 9-AA known as a model intercalator agent in the AMES-Salmonella test system. The inhibition rates obtained from the antimutagenicity assays ranged from 37.07% (C. rangiformis—5 µg/plate) to 54.39% (C. rangiformis—5 µg/plate). Furthermore, all the methanol extracts have significant antimutagenic activity against NaN3 mutagenicity in Z. mays Root Tip Mitotic Index assay system. These activities are valuable towards an extension of the employ of these drugs as new phytotherapeutic or preservative ingredients.

Potentiation of the mutagenicity and recombinagenicity of bleomycin in yeast by unconventional intercalating agents

Interactions between bleomycin (BLM) and conventional or unconventional intercalating agents were analyzed in an assay for mitotic gene conversion at the trp5 locus and reversion of the ilv1-92 allele in Saccharomyces cerevisiae strain D7. BLM is a potent recombinagen and mutagen in the assay. Various chemicals modulate the genetic activity of BLM, producing either antimutagenic effects or enhanced genotoxicity. Effects of cationic amino compounds include enhancement of BLM activity by aminoacridines and protection against BLM by aliphatic amines. The potentiation of BLM is similar to findings in a micronucleus-based BLM amplification assay in Chinese hamster V79 cells. In this study, the amplification of BLM activity was explored in yeast using known intercalators, compounds structurally related to known intercalators, and unconventional intercalators that were identified on the basis of computer modeling or results in the Chinese hamster BLM amplification assay. As shown in previous studies, the classical intercalator 9-aminoacridine (9AA) caused dose-dependent enhancement of BLM activity. Other compounds found to enhance the induction of mitotic recombination and point mutations in strain D7 were chlorpromazine, chloroquine, mefloquine, tamoxifen, diphenhydramine, benzophenone, and 3-hydroxybenzophenone. The increased activity was detectable by cotreatment of yeast with BLM and the modulator compound in growth medium or by separate interaction of the intercalator with DNA followed by BLM treatment of nongrowing cells in buffer. The data support the interpretation drawn from micronucleus assays in mammalian cells that BLM enhancement results from DNA intercalation and may be useful in detecting noncovalent interactions with DNA. Environ.

Mutagenic and antimutagenic effects of hexane extract of some Astragalus species grown in the eastern Anatolia region of Turkey

Medical plants and their various extracts have been occasionally used in the treatment of many diseases. Astragalus is one of those medical plants and it has several biological activities. In the present study, the hexane extracts of six Astragalus species, which are grown in the eastern Anatolia region of Turkey, were isolated, and their mutagenic and antimutagenic properties were investigated by using Salmonella typhimurium TA1535, TA1537 and Escherichia coli WP2uvrA tester strains at 0.05, 0.5 and 5 microg/plate concentrations. Known mutagens sodium azide (NaN(3)), 9-Aminoacridine (9-AA) and N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG) were used to determine antimutagenic properties of hexane extracts. The results showed that all hexane extracts, investigated in the present study, can be considered genotoxically safe because they do not have mutagenic activity at the tested concentrations. But, a great many of them have antimutagenic activity against 9-Aminoacridine known as a model intercalator agent. The inhibition rates obtained from the antimutagenicity assays ranged from 27.51% (A. macrocephalus--0.05 microg/plate) to 54.39% (A. galegiformis--5 microg/plate). These activities are valuable toward an extension of the employ of these drugs as new phytotherapeutic or preservative ingredients.

Enhancement of the recombinagenic and mutagenic activities of bleomycin in yeast by intercalation of acridine compounds into DNA

Strain D7 of Saccharomyces cerevisiae was used to measure the induction by bleomycin (BLM) of mitotic recombination at the trp5 locus and point mutations at ilv1 in the presence and absence of acridine compounds. BLM is a potent mutagen and recombinagen in the D7 assay. The acridines vary, some being mutagenic or recombinagenic and others not. Combined treatments were used to distinguish whether a genetically inactive acridine has no effect on the genetic activity of BLM or modulates its action. When an acridine is itself genetically active, combined treatments were used to determine whether its effects are additive with those of BLM or whether there is interaction between the two compounds. Acridine compounds that share the ability to intercalate between the base pairs of DNA but differ in their mutagenic specificity owing to the presence of different substituent groups were analysed. Clear potentiation and synergistic interactions were detected in combined treatments with BLM and aminoacridines, nitroacridines or an acridine mustard. Potentiation and synergy were also observed in sequential exposures in which the yeast were grown in the presence of acridine compounds and then treated with BLM in the absence of free acridine. The results are consistent with an increase in BLM susceptibility conferred by acridine intercalation. It is likely that the intercalating agents increase the access of BLM to the minor groove of DNA, where it abstracts a hydrogen from the 4' position of deoxyribose, creating a free radical that is processed into strand breaks.

DNA-damaging activity and mutagenicity of 16 newly synthesized thiazolo[5,4-a]acridine derivatives with high photo-inducible cytotoxicity

The discovery of the potent anticancer properties of natural alkaloids in the pyrido-thiazolo-acridine series has suggested that thiazolo-acridine derivatives could be of great interest. In a continuous attempt to develop DNA-binding molecules and DNA photo-cleavers, 16 new thiazolo[5,4-a]acridines were synthesized and studied for their photo-inducible DNA-intercalative, cytotoxic and mutagenic activities, by use of the DNA methyl-green bioassay, the Alamar Blue viability assay and the Salmonella mutagenicity test using strains TA97a and TA98 with and without metabolic activation and photo-activation. Without photo-activation, one compound showed a DNA-intercalative activity in the DNA major groove while three compounds displayed intercalating properties after photo-activation. In the dark, four molecules possessed cytotoxic activities against a THP1 acute monocytic leukemia cell line while 15 derivatives displayed photo-inducible cytotoxic activity against this cell line. All compounds were mutagenic in strain TA97a with metabolic activation (+S9mix) and 15 molecules were mutagenic in strain TA98 without activation (-S9mix). Study of the quantitative structure-activity relationships (QSAR) from the Salmonella mutagenicity data revealed that several descriptors could describe cytotoxic and mutagenic activities after photo-activation. From the results of the mutagenicity test, four compounds with elevated mutagenic activities were selected for additional experiments. Their capacities to induce single-strand breaks (SSB) and chromosome-damaging effects were monitored by the comet and the micronucleus assays in normal human keratinocytes. Comparison of the minimal genotoxic concentrations showed that two compounds possessed higher capacities to induce SSB after photo-activation. In the micronucleus assay, three molecules were able to induce high numbers of micronuclei following photo-activation. Overall, the results of this study confirm that acridines are predominantly genotoxic via a DNA-intercalating mechanism in the dark, while DNA-adducts were probably induced following photo-activation.

Tackling the intractable - approaching the genetics of Chlamydiales

Chlamydia trachomatis and Chlamydia (Chlamydophila) pneumoniae are important human pathogens with significant socio-economic and medical impact. The development of an improved therapy or vaccine would represent a major break-through in the battle against these infections. Despite intense research on Chlamydiaceae, the molecular genetic analysis of these pathogens remains difficult as genetic manipulation still remains impossible. Even though several options for generating a universal genetic system are currently being pursued, the anticipated success of these approaches is uncertain. As an alternative approach, random chemical mutagenesis is currently pursued which could allow spotlighting critical chlamydial pathogenesis features in the near future. Another research track lies in the identification of immunogenic peptides which could serve two goals: Immunogenic peptides could provide a basis for generating an efficient antichlamydial vaccine. Further, they also might offer an efficient tool to diagnose acute and chronic chlamydial infections. Both are currently pursued by applying the autodisplay approach that facilitates the exposure of whole peptide libraries on the Escherichia coli cell surface, thus allowing immediate detection and gene tracking through antibody binding. Finally, global transcriptome analysis is an approach to circumvent the genetic intractability of Chlamydiaceae. Current analysis indicates that gene expression takes place in an ordered manner throughout the course of the developmental cycle and, as expected, gene expression appears to be directly linked to host cell responses. Moreover, recent microarray analysis in C. pneumoniae corroborated the notion that distinct mRNA species are being carried-over by the infectious elementary bodies (EBs). These and other recent observations on the chlamydial gene expression patterns offer unique opportunities to interfere with the onset, the course, and the persistency of chlamydial infections by paving the ways towards the development of novel diagnostic and therapeutic treatment regimens.

Genotoxicity of non-covalent interactions: DNA intercalators

This review provides an update on the mutagenicity of intercalating chemicals, as carried out over the last 17 years. The most extensively studied DNA intercalating agents are acridine and its derivatives, that bind reversibly but non-covalently to DNA. These are frameshift mutagens, especially in bacteria and bacteriophage, but do not otherwise show a wide range of mutagenic properties. Di-acridines or di-quinolines may be either mono- or bis-intercalators, depending upon the length of the alkyl chain separating the chromophores. Those which monointercalate appear as either weak frameshift mutagens in bacteria, or as non-mutagens. However, some of the bisintercalators act as "petite" mutagens in Saccharomyces cerevisiae, suggesting that they may be more likely to target mitochondrial as compared with nuclear DNA. Some of the new methodologies for detecting intercalation suggest this may be a property of a wider range of chemicals than previously recognised. For example, quite a number of flavonoids appear to intercalate into DNA. However, their mutagenic properties may be dominated by the fact that many of them are also able to inhibit topoisomerase II enzymes, and this property implies that they will be potent recombinogens and clastogens. DNA intercalation may serve to position other, chemically reactive molecules, in specific ways on the DNA, leading to a distinctive (and wider) range of mutagenic properties, and possible carcinogenic potential.

Modulation of the genotoxicity of bleomycin by amines through noncovalent DNA interactions and alteration of physiological conditions in yeast

The effects of amines on the induction of mitotic gene conversion by bleomycin (BLM) were studied at the trp5 locus in Saccharomyces cerevisiae strain D7. BLM induces double-strand breaks in DNA and is a potent recombinagen in this assay. The polyamine spermidine causes concentration-dependent protection against the genotoxicity of BLM, reducing the convertant frequency by over 90% under the most protective conditions. Spermine, diethylenetriamine, ethylenediamine, putrescine, and ethylamine were also antigenotoxic in combined treatments with BLM. There was a general correspondence between the protective effect and the number of amino groups, suggesting that more strongly cationic amines tend to be stronger antirecombinagens. Electrostatic association of the amines with DNA probably hinders BLM access to the 4' position of deoxyribose where it generates a free radical. Other amines interact with BLM differently from these unbranched aliphatic amines. The aminothiol cysteamine inhibits the genotoxicity of BLM under hypoxic conditions but increases it under euoxic conditions. In contrast, pargyline potentiates the genotoxicity of BLM under hypoxic conditions but not under euoxic conditions. The antirecombinagenic effect of cysteamine apparently involves DNA binding and depletion of oxygen needed for BLM activity, whereas its potentiation of BLM entails its serving as an electron source for the activation of BLM. Pargyline may enhance BLM indirectly by preventing the depletion of oxygen by monoamine and polyamine oxidase. The planar 9-aminoacridine weakly induces gene conversion in strain D7, but it is strongly synergistic with BLM. Enhancement of BLM activity by this compound and by the related nitroacridine Entozon is apparently mediated by intercalation of the acridine ring system into DNA. Thus, the influence of amines on the genotoxicity of BLM in yeast encompasses antigenotoxic, potentiating, and synergistic interactions. The underlying mechanisms involve noncovalent association with DNA, altered BLM access to DNA, and modulation of physiological conditions.

Flow cytometric detection of tandem repeat mutations induced by various chemical classes

To facilitate detection of genotoxicity from environmental mutagen exposure, we generated an in vitro enhanced green fluorescence protein (EGFP) reactivation assay that quickly and effectively detects frameshift mutations in tandem repeat sequences (TRS). Two murine cell lines, C3H10T1/2 and mismatch repair deficient MC2a, were stably transfected with EGFP reporter plasmids in which the EGFP constructs contain TRS that put the EGFP sequence out of frame. These included several 2, 3, 4, 5 and 6 bp repeat sequences, a control non-repetitive sequence and a human gene sequence containing a 4 bp repeat motif. Transfected cultures were exposed to five model mutagens and carcinogens: hydrogen peroxide (H(2)O(2)), 12-O-tetradecanoyl-phorbol-13-acetate (TPA), benzo-a-pyrene-diol-epoxide (BPDE), ethyl nitrosourea (ENU), 9-aminoacridine (9AA) and two controls: acetone and ethanol. Frameshift mutations resulted in green fluorescent revertants, as determined by flow cytometry, and were confirmed, for 9AA treatments, by sequencing. All five treatments with model agents induced statistically significant sequence- and exposure-dependent responses in MC2a cells and a negative response with the two negative control treatments, acetone and ethanol. Similar responses were seen in a smaller panel of treatments and plasmids in C3H10T1/2 cells. The mutation frequencies were higher in cells transfected with the plasmids containing TRS than those harbouring the control construct lacking repeats. The highest mutation frequencies were observed with H(2)O(2) and 9AA treatments, yielding up to a 50-fold difference between vehicle and highest concentration treatment. ENU, BPDE, and to a lesser extent TPA treatments, also showed a statistically significant exposure response. Results from these experiments reveal that the assay responds robustly to various classes of mutagenic substances, as well as to rodent carcinogens that are inactive in conventional mutation assays, and that responses are not linked to cytotoxicity. This assay is a promising approach for detecting chemically induced frameshifts within certain DNA sequences of interest, but further characterization and validation are required prior to general use in genotoxicity screening.

Frameshift mutations induced by four isomeric nitroacridines and their des-nitro counterpart in the lacZ reversion assay in Escherichia coli

Acridines are well-known as compounds that intercalate noncovalently between DNA base pairs and induce +/-1 frameshift mutations at sites of monotonous repeats of a single base. Reactive derivatives of acridines, including acridine mustards and nitroacridines, form covalent adducts in DNA and exhibit mutagenic properties different from the simple intercalators. We compared the frameshift mutagenicity of the cancer chemotherapy drug nitracrine (1-nitro-9-(3'-dimethylaminopropylamino)-acridine), its des-nitro counterpart 9-(3'-dimethylaminopropylamino)-acridine (DAPA), and its 2-, 3-, and 4-nitro isomers (2-, 3-, and 4-nitro-DAPA) in the lacZ reversion assay in Escherichia coli. DAPA is a simple intercalator, much like the widely studied 9-aminoacridine. It most strongly induced +/-1 frameshift mutations in runs of guanine residues and more weakly induced -1 frameshifts in a run of adenine residues. A nitro group in the 1, 3, or 4 position of DAPA reduced the yield of +/-1 frameshift mutations. DAPA weakly induced -2 frameshifts in an alternating CG sequence. In contrast, nitracrine and its 3-nitro isomer resembled the 3-nitroacridine Entozon in effectively inducing -2 frameshift mutations. The 2- and 4-nitro isomers were less effective than the 1- and 3-nitro compounds in -2 frameshift mutagenesis. The results are interpreted with respect to intercalation, steric interactions, effects of base strength on DNA binding, enzymatic processing, and a slipped mispairing model of frameshift mutagenesis.

Comparative analysis of mutagenic potency of 1-nitro-acridine derivatives

The anticancer effect of 1-nitro-9-hydroxyethylamino acridine (C-857), a compound belonging to the 1-nitroacridine class, has been well documented. Despite its therapeutic efficacy, the clinical development of C-857 has been impeded partly due to its high systemic toxicity. In an effort to enhance antitumor efficacy and lower toxicity, derivatives of C-857 have been synthesized with substitutions made at position C-4 and/or an esterified hydroxyl group in side chain at the C-9 position. The introduction of a methyl group at C-4 resulted in C-1748, which has a significantly higher therapeutic efficacy and is being clinically developed as an anticancer agent for solid tumors. The present study was undertaken to correlate the mutagenicity of C-857, C-1748, C-1790, C-1872 and C-1873 with their cytotoxicity and their anti-tumor efficacy. The mutagenicity of these drugs was determined using three Ames Salmonella typhimurium strains TA1537, TA98 and TA102. The bacteria were treated with different molar concentrations, ranging from 10(-3) to 10(-12) M, of the drugs and drug-induced histidine revertants were then counted after a 48 h incubation. C-1748 did not induce any revertants in both TA1537 and TA98 at a dose of 10(-6) M, whereas, C-857 at the same dose induced approximately 842 and approximately 1034 revertants respectively. In TA102, mutagenicity was lower than observed with TA98 and TA1537 with highest revertants observed at 10(-5) M with C-857 (approximately 606) and C-1748 (approximately 108). Higher mutagenicity was observed in the derivatives C-1790, C-1872 and C-1873 compared to C-1748, but lower than C-857. These studies demonstrate that C-1748 has the least mutagenic potential, with a much higher antitumor effect in prostate cancer and is a promising chemotherapeutic agent for clinical development.