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Wu Y, Adeel MM, Sancar A, Li W. Nucleotide Excision Repair of Aflatoxin-induced DNA Damage within the 3D Human Genome Organization. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.27.559858. [PMID: 37808841 PMCID: PMC10557652 DOI: 10.1101/2023.09.27.559858] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/10/2023]
Abstract
Aflatoxin B1 (AFB1), a potent mycotoxin, is one of the two primary risk factors that cause liver cancer. In the liver, the bioactivated AFB1 intercalates into the DNA double helix to form a bulky DNA adduct which will lead to mutation if left unrepaired. We have adapted the tXR-seq method to measure the nucleotide excision repair of AFB1-induced DNA adducts. We have found that transcription-coupled repair plays a major role in the damage removal process and the released excision products have a distinctive length distribution pattern. We further analyzed the impact of 3D genome organization on the repair of AFB1-induced DNA adducts. We have revealed that chromosomes close to the nuclear center and A compartments undergo expedited repair processes. Notably, we observed an accelerated repair around both TAD boundaries and loop anchors. These findings provide insights into the complex interplay between repair, transcription, and 3D genome organization, shedding light on the mechanisms underlying AFB1-induced liver cancer.
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Affiliation(s)
- Yiran Wu
- Department of Environmental Health Science, College of Public Health, University of Georgia, Athens, GA 30602
| | - Muhammad Muzammal Adeel
- Department of Environmental Health Science, College of Public Health, University of Georgia, Athens, GA 30602
| | - Aziz Sancar
- Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599
| | - Wentao Li
- Department of Environmental Health Science, College of Public Health, University of Georgia, Athens, GA 30602
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Tomar R, Minko IG, Kellum AH, Voehler MW, Stone MP, McCullough AK, Lloyd RS. DNA Sequence Modulates the Efficiency of NEIL1-Catalyzed Excision of the Aflatoxin B 1-Induced Formamidopyrimidine Guanine Adduct. Chem Res Toxicol 2021; 34:901-911. [PMID: 33595290 DOI: 10.1021/acs.chemrestox.0c00517] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Dietary exposure to aflatoxins is a significant risk factor in the development of hepatocellular carcinomas. Following bioactivation by microsomal P450s, the reaction of aflatoxin B1 (AFB1) with guanine (Gua) in DNA leads to the formation of stable, imidazole ring-opened 8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl-formamido)-9-hydroxyaflatoxin B1 (AFB1-FapyGua) adducts. In contrast to most base modifications that result in destabilization of the DNA duplex, the AFB1-FapyGua adduct increases the thermal stability of DNA via 5'-interface intercalation and base-stacking interactions. Although it was anticipated that this stabilization might make these lesions difficult to repair relative to helix distorting modifications, prior studies have shown that both the nucleotide and base excision repair pathways participate in the removal of the AFB1-FapyGua adduct. Specifically for base excision repair, we previously showed that the DNA glycosylase NEIL1 excises AFB1-FapyGua and catalyzes strand scission in both synthetic oligodeoxynucleotides and liver DNA of exposed mice. Since it is anticipated that error-prone replication bypass of unrepaired AFB1-FapyGua adducts contributes to cellular transformation and carcinogenesis, the structural and thermodynamic parameters that modulate the efficiencies of these repair pathways are of considerable interest. We hypothesized that the DNA sequence context in which the AFB1-FapyGua adduct is formed might modulate duplex stability and consequently alter the efficiencies of NEIL1-initiated repair. To address this hypothesis, site-specific AFB1-FapyGua adducts were synthesized in three sequence contexts, with the 5' neighbor nucleotide being varied. DNA structural stability analyses were conducted using UV absorbance- and NMR-based melting experiments. These data revealed differentials in thermal stabilities associated with the 5'-neighbor base pair. Single turnover kinetic analyses using the NEIL1 glycosylase demonstrated corresponding sequence-dependent differences in the repair of this adduct, such that there was an inverse correlation between the stabilization of the duplex and the efficiency of NEIL1-mediated catalysis.
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Affiliation(s)
- Rachana Tomar
- Department of Chemistry and the Vanderbilt-Ingram Cancer Center, Vanderbilt University, VU Station B, Box 351822, Nashville, Tennessee 37235, United States
| | - Irina G Minko
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, United States
| | - Andrew H Kellum
- Department of Chemistry and the Vanderbilt-Ingram Cancer Center, Vanderbilt University, VU Station B, Box 351822, Nashville, Tennessee 37235, United States
| | - Markus W Voehler
- Department of Chemistry and the Vanderbilt-Ingram Cancer Center, Vanderbilt University, VU Station B, Box 351822, Nashville, Tennessee 37235, United States
| | - Michael P Stone
- Department of Chemistry and the Vanderbilt-Ingram Cancer Center, Vanderbilt University, VU Station B, Box 351822, Nashville, Tennessee 37235, United States
| | - Amanda K McCullough
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, United States.,Department of Molecular and Medical Genetics, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, United States
| | - R Stephen Lloyd
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, United States.,Department of Molecular and Medical Genetics, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, United States
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Benkerroum N. Chronic and Acute Toxicities of Aflatoxins: Mechanisms of Action. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2020; 17:E423. [PMID: 31936320 PMCID: PMC7013914 DOI: 10.3390/ijerph17020423] [Citation(s) in RCA: 191] [Impact Index Per Article: 47.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Revised: 12/23/2019] [Accepted: 12/29/2019] [Indexed: 01/01/2023]
Abstract
There are presently more than 18 known aflatoxins most of which have been insufficiently studied for their incidence, health-risk, and mechanisms of toxicity to allow effective intervention and control means that would significantly and sustainably reduce their incidence and adverse effects on health and economy. Among these, aflatoxin B1 (AFB1) has been by far the most studied; yet, many aspects of the range and mechanisms of the diseases it causes remain to be elucidated. Its mutagenicity, tumorigenicity, and carcinogenicity-which are the best known-still suffer from limitations regarding the relative contribution of the oxidative stress and the reactive epoxide derivative (Aflatoxin-exo 8,9-epoxide) in the induction of the diseases, as well as its metabolic and synthesis pathways. Additionally, despite the well-established additive effects for carcinogenicity between AFB1 and other risk factors, e.g., hepatitis viruses B and C, and the hepatotoxic algal microcystins, the mechanisms of this synergy remain unclear. This study reviews the most recent advances in the field of the mechanisms of toxicity of aflatoxins and the adverse health effects that they cause in humans and animals.
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Affiliation(s)
- Noreddine Benkerroum
- Department of Food Science and Agricultural Chemistry MacDonald Campus, McGill University, 21111 Lakeshore, Ste Anne de Bellevue, QC H9X 3V9, Canada
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Aflatoxin B₁⁻Formamidopyrimidine DNA Adducts: Relationships between Structures, Free Energies, and Melting Temperatures. Molecules 2019; 24:molecules24010150. [PMID: 30609733 PMCID: PMC6337653 DOI: 10.3390/molecules24010150] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Revised: 12/21/2018] [Accepted: 12/26/2018] [Indexed: 12/02/2022] Open
Abstract
Thermal stabilities of DNA duplexes containing Gua (g), α- (a) or β-anomer of formamidopyrimidine-N7-9-hydroxy-aflatoxin B1 (b) differ markedly (Tm: a<g<b), but the underlying molecular origin of this experimentally observed phenomenon is yet to be identified and determined. Here, by employing explicit-solvent molecular dynamics simulations coupled with free-energy calculations using a combined linear-interaction-energy/linear-response-approximation approach, we explain the quantitative differences in Tm in terms of three structural features (bulkiness, order, and compactness) and three energetical contributions (non-polar, electrostatic, and preorganized-electrostatic), and thus advance the current understanding of the relationships between structures, free energies, and thermal stabilities of DNA double helices.
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Abstract
The eukaryotic global genomic nucleotide excision repair (GG-NER) pathway is the major mechanism that removes most bulky and some nonbulky lesions from cellular DNA. There is growing evidence that certain DNA lesions are repaired slowly or are entirely resistant to repair in cells, tissues, and in cell extract model assay systems. It is well established that the eukaryotic DNA lesion-sensing proteins do not detect the damaged nucleotide, but recognize the distortions/destabilizations in the native DNA structure caused by the damaged nucleotides. In this article, the nature of the structural features of certain bulky DNA lesions that render them resistant to NER, or cause them to be repaired slowly, is compared to that of those that are good-to-excellent NER substrates. Understanding the structural features that distinguish NER-resistant DNA lesions from good NER substrates may be useful for interpreting the biological significance of biomarkers of exposure of human populations to genotoxic environmental chemicals. NER-resistant lesions can survive to replication and cause mutations that can initiate cancer and other diseases. Furthermore, NER diminishes the efficacy of certain chemotherapeutic drugs, and the design of more potent pharmaceuticals that resist repair can be advanced through a better understanding of the structural properties of DNA lesions that engender repair-resistance.
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Affiliation(s)
- Nicholas E. Geacintov
- Chemistry and Biology Departments, New York University, New York, New York 10003-5180, United States
| | - Suse Broyde
- Chemistry and Biology Departments, New York University, New York, New York 10003-5180, United States
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6
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Li L, Brown KL, Ma R, Stone MP. DNA Sequence Modulates Geometrical Isomerism of the trans-8,9- Dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl-formamido)- 9-hydroxy Aflatoxin B1 Adduct. Chem Res Toxicol 2016; 28:225-37. [PMID: 25587868 PMCID: PMC4332041 DOI: 10.1021/tx5003832] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
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Aflatoxin
B1 (AFB1), a mycotoxin produced
by Aspergillus flavus, is oxidized
by cytochrome P450 enzymes to aflatoxin B1-8,9-epoxide,
which alkylates DNA at N7-dG. Under basic conditions,
this N7-dG adduct rearranges to yield the trans-8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl-formamido)-9-hydroxy
aflatoxin B1 (AFB1–FAPY) adduct. The
AFB1–FAPY adduct exhibits geometrical isomerism
involving the formamide moiety. NMR analyses of duplex oligodeoxynucleotides
containing the 5′-XA-3′, 5′-XC-3′, 5′-XT-3′,
and 5′-XY-3′ sequences (X = AFB1–FAPY;
Y = 7-deaza-dG) demonstrate that the equilibrium between E and Z isomers is controlled by major groove hydrogen
bonding interactions. Structural analysis of the adduct in the 5′-XA-3′
sequence indicates the preference of the E isomer
of the formamide group, attributed to formation of a hydrogen bond
between the formyl oxygen and the N6 exocyclic amino group
of the 3′-neighbor adenine. While the 5′-XA-3′
sequence exhibits the E isomer, the 5′-XC-3′
sequence exhibits a 7:3 E:Z ratio
at equilibrium at 283 K. The E isomer is favored
by a hydrogen bond between the formyl oxygen and the N4-dC exocyclic amino group of the 3′-neighbor cytosine. The
5′-XT-3′ and 5′-XY-3′ sequences cannot
form such a hydrogen bond between the formyl oxygen and the 3′-neighbor
T or Y, respectively, and in these sequence contexts the Z isomer is favored. Additional equilibria between α and β
anomers and the potential to exhibit atropisomers about the C5–N5 bond do not depend upon sequence. In each
of the four DNA sequences, the AFB1–FAPY adduct
maintains the β deoxyribose configuration. Each of these four
sequences feature the atropisomer of the AFB1 moiety that
is intercalated above the 5′-face of the damaged guanine. This
enforces the Ra axial conformation for
the C5–N5 bond.
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Toxicology of DNA Adducts Formed Upon Human Exposure to Carcinogens. ADVANCES IN MOLECULAR TOXICOLOGY 2016. [DOI: 10.1016/b978-0-12-804700-2.00007-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Lin YC, Li L, Makarova AV, Burgers PM, Stone MP, Lloyd RS. Molecular basis of aflatoxin-induced mutagenesis-role of the aflatoxin B1-formamidopyrimidine adduct. Carcinogenesis 2014; 35:1461-8. [PMID: 24398669 DOI: 10.1093/carcin/bgu003] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Aflatoxin B1 (AFB1) is a known carcinogen associated with early-onset hepatocellular carcinoma (HCC) and is thought to contribute to over half a million new HCCs per year. Although some of the fundamental risk factors are established, the molecular basis of AFB1-induced mutagenesis in primate cells has not been rigorously investigated. To gain insights into genome instability that is produced as a result of replicating DNAs containing AFB1 adducts, site-specific mutagenesis assays were used to establish the mutagenic potential of the persistent ring-opened AFB1 adduct, AFB1-formamidopyrimidine (AFB1-FAPY). This lesion was highly mutagenic, yielding replication error frequencies of 97%, with the predominant base substitution being a G to T transversion. This transversion is consistent with previous mutational data derived from aflatoxin-associated HCCs. In vitro translesion synthesis assays demonstrated that polymerase (pol) ζ was the most likely candidate polymerase that is responsible for the G to T mutations induced by this adduct.
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Affiliation(s)
- Ying-Chih Lin
- Oregon Institute of Occupational Health Sciences and Cancer Biology Program, Oregon Health & Science University, Portland, OR 97239, USA
| | - Liang Li
- Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA
| | - Alena V Makarova
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA and
| | - Peter M Burgers
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA and
| | - Michael P Stone
- Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA
| | - R Stephen Lloyd
- Oregon Institute of Occupational Health Sciences and Department of Molecular and Medical Genetics, Oregon Health & Science University, Portland, OR 97239, USA
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9
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Banerjee S, Brown KL, Egli M, Stone MP. Bypass of aflatoxin B1 adducts by the Sulfolobus solfataricus DNA polymerase IV. J Am Chem Soc 2011; 133:12556-68. [PMID: 21790157 PMCID: PMC3154525 DOI: 10.1021/ja2015668] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Aflatoxin B(1) (AFB(1)) is oxidized to an epoxide in vivo, which forms an N7-dG DNA adduct (AFB(1)-N7-dG). The AFB(1)-N7-dG can rearrange to a formamidopyrimidine (AFB(1)-FAPY) derivative. Both AFB(1)-N7-dG and the β-anomer of the AFB(1)-FAPY adduct yield G→T transversions in Escherichia coli, but the latter is more mutagenic. We show that the Sulfolobus solfataricus P2 DNA polymerase IV (Dpo4) bypasses AFB(1)-N7-dG in an error-free manner but conducts error-prone replication past the AFB(1)-FAPY adduct, including misinsertion of dATP, consistent with the G→T mutations observed in E. coli. Three ternary (Dpo4-DNA-dNTP) structures with AFB(1)-N7-dG adducted template:primers have been solved. These demonstrate insertion of dCTP opposite the AFB(1)-N7-dG adduct, and correct vs incorrect insertion of dATP vs dTTP opposite the 5'-template neighbor dT from a primed AFB(1)-N7-dG:dC pair. The insertion of dTTP reveals hydrogen bonding between the template N3 imino proton and the O(2) oxygen of dTTP, and between the template T O(4) oxygen and the N3 imino proton of dTTP, perhaps explaining why this polymerase does not efficiently catalyze phosphodiester bond formation from this mispair. The AFB(1)-N7-dG maintains the 5'-intercalation of the AFB(1) moiety observed in DNA. The bond between N7-dG and C8 of the AFB(1) moiety remains in plane with the alkylated guanine, creating a 16° inclination of the AFB(1) moiety with respect to the guanine. A binary (Dpo4-DNA) structure with an AFB(1)-FAPY adducted template:primer also maintains 5'-intercalation of the AFB(1) moiety. The β-deoxyribose anomer is observed. Rotation about the FAPY C5-N(5) bond orients the bond between N(5) and C8 of the AFB(1) moiety out of plane in the 5'-direction, with respect to the FAPY base. The formamide group extends in the 3'-direction. This improves stacking of the AFB(1) moiety above the 5'-face of the FAPY base, as compared to the AFB(1)-N7-dG adduct. Ternary structures with AFB(1)-β-FAPY adducted template:primers show correct vs incorrect insertion of dATP vs dTTP opposite the 5'-template neighbor dT from a primed AFB(1)-β-FAPY:dC pair. For dATP, the oxygen atom of the FAPY formamide group participates in a water-mediated hydrogen bond with Arg332. The insertion of dTTP yields a structure similar to that observed for the AFB(1)-N7-dG adduct. The differential accommodation of these AFB(1) adducts within the active site may, in part, modulate lesion bypass.
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Affiliation(s)
- Surajit Banerjee
- Department of Chemistry, Center in Molecular Toxicology, Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, Tennessee 37235, United States
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Brown KL, Voehler MW, Magee SM, Harris CM, Harris TM, Stone MP. Structural perturbations induced by the alpha-anomer of the aflatoxin B(1) formamidopyrimidine adduct in duplex and single-strand DNA. J Am Chem Soc 2010; 131:16096-107. [PMID: 19831353 PMCID: PMC2773149 DOI: 10.1021/ja902052v] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
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The guanine N7 adduct of aflatoxin B1exo-8,9-epoxide hydrolyzes to form the formamidopyrimidine (AFB-FAPY) adduct, which interconverts between α and β anomers. The β anomer is highly mutagenic in Escherichia coli, producing G → T transversions; it thermally stabilizes the DNA duplex. The AFB-α-FAPY adduct blocks replication; it destabilizes the DNA duplex. Herein, the structure of the AFB-α-FAPY adduct has been elucidated in 5′-d(C1T2A3T4X5A6T7T8C9A10)-3′·5′-d(T11G12A13A14T15C16A17T18A19G20)-3′ (X = AFB-α-FAPY) using molecular dynamics calculations restrained by NMR-derived distances and torsion angles. The AFB moiety intercalates on the 5′ face of the pyrimidine moiety at the damaged nucleotide between base pairs T4·A17 and X5·C16, placing the FAPY C5−N5 bond in the Ra axial conformation. Large perturbations of the ε and ζ backbone torsion angles are observed, and the base stacking register of the duplex is perturbed. The deoxyribose orientation shifts to become parallel to the FAPY base and displaced toward the minor groove. Intrastrand stacking between the AFB moiety and the 5′ neighbor thymine remains, but strong interstrand stacking is not observed. A hydrogen bond between the formyl group and the exocyclic amine of the 3′-neighbor adenine stabilizes the E conformation of the formamide moiety. NMR studies reveal a similar 5′-intercalation of the AFB moiety for the AFB-α-FAPY adduct in the tetramer 5′-d(C1T2X3A4)-3′, involving the Ra axial conformation of the FAPY C5−N5 bond and the E conformation of the formamide moiety. Since in duplex DNA the AFB moiety of the AFB-β-FAPY adduct also intercalates on the 5′ side of the pyrimidine moiety at the damaged nucleotide, we conclude that favorable 5′-stacking leads to the Ra conformational preference about the C5−N5 bond; the same conformational preference about this bond is also observed at the nucleoside and base levels. The structural distortions and the less favorable stacking interactions induced by the AFB-α-FAPY adduct explain its lower stability as compared to the AFB-β-FAPY adduct in duplex DNA. In this DNA sequence, hydrogen bonding between the formyl oxygen and the exocyclic amine of the 3′-neighboring adenine stabilizing the E configuration of the formamide moiety is also observed for the AFB-β-FAPY adduct, and suggests that the identity of the 3′-neighbor nucleotide modulates the stability and biological processing of AFB adducts.
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Affiliation(s)
- Kyle L Brown
- Department of Chemistry, Center in Molecular Toxicology, and the Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37235, USA
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Ferguson LR, Denny WA. Genotoxicity of non-covalent interactions: DNA intercalators. Mutat Res 2007; 623:14-23. [PMID: 17498749 DOI: 10.1016/j.mrfmmm.2007.03.014] [Citation(s) in RCA: 160] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2006] [Revised: 03/27/2007] [Accepted: 03/31/2007] [Indexed: 11/18/2022]
Abstract
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.
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Affiliation(s)
- Lynnette R Ferguson
- Auckland Cancer Society Research Centre, Faculty of Medical & Health Science, The University of Auckland, New Zealand.
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Brown KL, Deng JZ, Iyer RS, Iyer LG, Voehler MW, Stone MP, Harris CM, Harris TM. Unraveling the aflatoxin-FAPY conundrum: structural basis for differential replicative processing of isomeric forms of the formamidopyrimidine-type DNA adduct of aflatoxin B1. J Am Chem Soc 2007; 128:15188-99. [PMID: 17117870 PMCID: PMC2693076 DOI: 10.1021/ja063781y] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Aflatoxin B1 (AFB) epoxide forms an unstable N7 guanine adduct in DNA. The adduct undergoes base-catalyzed ring opening to give a highly persistent formamidopyrimidine (FAPY) adduct which exists as a mixture of forms. Acid hydrolysis of the FAPY adduct gives the FAPY base which exists in two separable but interconvertible forms that have been assigned by various workers as functional, positional, or conformational isomers. Recently, this structural question became important when one of the two major FAPY species in DNA was found to be potently mutagenic and the other a block to replication [Smela, M. E.; Hamm, M. L.; Henderson, P. T.; Harris, C. M.; Harris, T. M.; Essigmann, J. M. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 6655-6660]. NMR studies carried out on the AFB-FAPY bases and deoxynucleoside 3',5'-dibutyrates now establish that the separable FAPY bases and nucleosides are diastereomeric N5 formyl derivatives involving axial asymmetry around the congested pyrimidine C5-N5 bond. Anomerization of the protected beta-deoxyriboside was not observed, but in the absence of acyl protection, both anomerization and furanosyl --> pyranosyl ring expansion occurred. In oligodeoxynucleotides, two equilibrating FAPY species, separable by HPLC, are assigned as anomers. The form normally present in duplex DNA is the mutagenic species. It has previously been assigned as the beta anomer by NMR (Mao, H.; Deng, Z. W.; Wang, F.; Harris, T. M.; Stone, M. P. Biochemistry 1998, 37, 4374-4387). In single-stranded environments the dominant species is the beta anomer; it is a block to replication.
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Affiliation(s)
- Kyle L Brown
- Department of Chemistry, Center in Molecular Toxicology, Vanderbilt University, Nashville, Tennessee 37235, USA
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