1
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Bellamri M, Yao L, Tomar R, Vartanian V, Rizzo CJ, Stone MP, Groopman JD, Lloyd RS, Turesky RJ. Mass Spectrometry-Based Method to Measure Aflatoxin B 1 DNA Adducts in Formalin-Fixed Paraffin-Embedded Tissues. Chem Res Toxicol 2024; 37:633-642. [PMID: 38498000 DOI: 10.1021/acs.chemrestox.4c00005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/19/2024]
Abstract
Aflatoxin B1 (AFB1) is a potent human liver carcinogen produced by certain molds, particularly Aspergillus flavus and Aspergillus parasiticus, which contaminate peanuts, corn, rice, cottonseed, and ground and tree nuts, principally in warm and humid climates. AFB1 undergoes bioactivation in the liver to produce AFB1-exo-8,9-epoxide, which forms the covalently bound cationic AFB1-N7-guanine (AFB1-N7-Gua) DNA adduct. This adduct is unstable and undergoes base-catalyzed opening of the guanine imidazolium ring to form two ring-opened diastereomeric 8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl-formamido)-9-hydroxy-aflatoxin B1 (AFB1-FapyGua) adducts. The AFB1 formamidopyrimidine (Fapy) adducts induce G → T transversion mutations and are likely responsible for the carcinogenic effects of AFB1. Quantitative liquid chromatography-mass spectrometry (LC-MS) methods have shown that AFB1-N7-Gua is eliminated in rodent and human urine, whereas ring-opened AFB1-FapyGua adducts persist in rodent liver. However, fresh frozen biopsy tissues are seldom available for biomonitoring AFB1 DNA adducts in humans, impeding research advances in this potent liver carcinogen. In contrast, formalin-fixed paraffin-embedded (FFPE) specimens used for histopathological analysis are often accessible for molecular studies. However, ensuring nucleic acid quality presents a challenge due to incomplete reversal of formalin-mediated DNA cross-links, which can preclude accurate quantitative measurements of DNA adducts. In this study, employing ion trap or high-resolution accurate Orbitrap mass spectrometry, we demonstrate that ring-opened AFB1-FapyGua adducts formed in AFB1-exposed newborn mice are stable to the formalin fixation and DNA de-cross-linking retrieval processes. The AFB1-FapyGua adducts can be detected at levels comparable to those in a match of fresh frozen liver. Orbitrap MS2 measurements can detect AFB1-FapyGua at a quantification limit of 4.0 adducts per 108 bases when only 0.8 μg of DNA is assayed on the column. Thus, our breakthrough DNA retrieval technology can be adapted to screen for AFB1 DNA adducts in FFPE human liver specimens from cohorts at risk of this potent liver carcinogen.
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Affiliation(s)
| | | | - Rachana Tomar
- Department of Chemistry, Vanderbilt Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Vladimir Vartanian
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, Oregon 97239, United States
| | - Carmelo J Rizzo
- Department of Chemistry, Vanderbilt Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Michael P Stone
- Department of Chemistry, Vanderbilt Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - John D Groopman
- Department of Environmental Health and Engineering, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland 21205, United States
| | - R Stephen Lloyd
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, Oregon 97239, United States
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2
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Minko I, Luzadder M, Vartanian V, Rice SM, Nguyen M, Sanchez-Contreras M, Van P, Kennedy S, McCullough A, Lloyd R. Frequencies and spectra of aflatoxin B 1-induced mutations in liver genomes of NEIL1-deficient mice as revealed by duplex sequencing. NAR MOLECULAR MEDICINE 2024; 1:ugae006. [PMID: 38779538 PMCID: PMC11105970 DOI: 10.1093/narmme/ugae006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/22/2024] [Revised: 04/18/2024] [Accepted: 05/16/2024] [Indexed: 05/25/2024]
Abstract
Increased risk for the development of hepatocellular carcinoma (HCC) is driven by a number of etiological factors including hepatitis viral infection and dietary exposures to foods contaminated with aflatoxin-producing molds. Intracellular metabolic activation of aflatoxin B1 (AFB1) to a reactive epoxide generates highly mutagenic AFB1-Fapy-dG adducts. Previously, we demonstrated that repair of AFB1-Fapy-dG adducts can be initiated by the DNA glycosylase NEIL1 and that male Neil1-/- mice were significantly more susceptible to AFB1-induced HCC relative to wild-type mice. To investigate the mechanisms underlying this enhanced carcinogenesis, WT and Neil1-/- mice were challenged with a single, 4 mg/kg dose of AFB1 and frequencies and spectra of mutations were analyzed in liver DNAs 2.5 months post-injection using duplex sequencing. The analyses of DNAs from AFB1-challenged mice revealed highly elevated mutation frequencies in the nuclear genomes of both males and females, but not the mitochondrial genomes. In both WT and Neil1-/- mice, mutation spectra were highly similar to the AFB1-specific COSMIC signature SBS24. Relative to wild-type, the NEIL1 deficiency increased AFB1-induced mutagenesis with concomitant elevated HCCs in male Neil1-/- mice. Our data establish a critical role of NEIL1 in limiting AFB1-induced mutagenesis and ultimately carcinogenesis.
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Affiliation(s)
- Irina G Minko
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR, USA
| | - Michael M Luzadder
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR, USA
| | - Vladimir L Vartanian
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR, USA
| | - Sean P M Rice
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR, USA
- School of Public Health, Oregon Health & Science University - Portland State University, Portland, OR, USA
| | - Megan M Nguyen
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA, USA
| | | | - Phu Van
- TwinStrand Biosciences, Inc., Seattle, WA, USA
| | - Scott R Kennedy
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA, USA
| | - Amanda K McCullough
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR, USA
- Department of Molecular and Medical Genetics, Oregon Health & Science University, Portland, OR, USA
| | - R Stephen Lloyd
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR, USA
- Department of Molecular and Medical Genetics, Oregon Health & Science University, Portland, OR, USA
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3
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McCarty KD, Liu L, Tateishi Y, Wapshott-Stehli HL, Guengerich FP. The multistep oxidation of cholesterol to pregnenolone by human cytochrome P450 11A1 is highly processive. J Biol Chem 2024; 300:105495. [PMID: 38006947 PMCID: PMC10716780 DOI: 10.1016/j.jbc.2023.105495] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Revised: 11/17/2023] [Accepted: 11/20/2023] [Indexed: 11/27/2023] Open
Abstract
Cytochrome P450 (P450, CYP) 11A1 is the classical cholesterol side chain cleavage enzyme (P450scc) that removes six carbons of the side chain, the first and rate-limiting step in the synthesis of all mammalian steroids. The reaction is a 3-step, 6-electron oxidation that proceeds via formation of 22R-hydroxy (OH) and 20R,22R-(OH)2 cholesterol, yielding pregnenolone. We expressed human P450 11A1 in bacteria, purified the enzyme in the absence of nonionic detergents, and assayed pregnenolone formation by HPLC-mass spectrometry of the dansyl hydrazone. The reaction was inhibited by the nonionic detergent Tween 20, and several lipids did not enhance enzymatic activity. The 22R-OH and 20R,22R-(OH)2 cholesterol intermediates were bound to P450 11A1 relatively tightly, as judged by steady-state optical titrations and koff rates. The electron donor adrenodoxin had little effect on binding; the substrate cholesterol showed a ∼5-fold stimulatory effect on the binding of adrenodoxin to P450 11A1. Presteady-state single-turnover kinetic analysis was consistent with a highly processive reaction with rates of intermediate oxidation steps far exceeding dissociation rates for products and substrates. The presteady-state kinetic analysis revealed a second di-OH cholesterol product, separable by HPLC, in addition to 20R,22R-(OH)2 cholesterol, which we characterized as a rotamer that was also converted to pregnenolone at a similar rate. The first oxidation step (at C-22) is the slowest, limiting the overall rate of cleavage. d3-Cholesterol showed no kinetic deuterium isotope effect on C-22, indicating that C-H bond cleavage is not rate-limiting in the first hydroxylation step.
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Affiliation(s)
- Kevin D McCarty
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - Lu Liu
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - Yasuhiro Tateishi
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | | | - F Peter Guengerich
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
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4
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Latham RL, Boyle JT, Barbano A, Loveman WG, Brown NA. Diverse mycotoxin threats to safe food and feed cereals. Essays Biochem 2023; 67:797-809. [PMID: 37313591 PMCID: PMC10500202 DOI: 10.1042/ebc20220221] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2023] [Revised: 05/15/2023] [Accepted: 05/18/2023] [Indexed: 06/15/2023]
Abstract
Toxigenic fungi, including Aspergillus and Fusarium species, contaminate our major cereal crops with an array of harmful mycotoxins, which threaten the health of humans and farmed animals. Despite our best efforts to prevent crop diseases, or postharvest spoilage, our cereals are consistently contaminated with aflatoxins and deoxynivalenol, and while established monitoring systems effectively prevent acute exposure, Aspergillus and Fusarium mycotoxins still threaten our food security. This is through the understudied impacts of: (i) our chronic exposure to these mycotoxins, (ii) the underestimated dietary intake of masked mycotoxins, and (iii) the synergistic threat of cocontaminations by multiple mycotoxins. Mycotoxins also have profound economic consequences for cereal and farmed-animal producers, plus their associated food and feed industries, which results in higher food prices for consumers. Climate change and altering agronomic practices are predicted to exacerbate the extent and intensity of mycotoxin contaminations of cereals. Collectively, this review of the diverse threats from Aspergillus and Fusarium mycotoxins highlights the need for renewed and concerted efforts to understand, and mitigate, the increased risks they pose to our food and feed cereals.
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Affiliation(s)
- Rosie L Latham
- Milner Centre for Evolution, Department of Life Sciences, University of Bath, Bath, U.K
- Department of Life Sciences, University of Bath, Bath, U.K
| | - Jeremy T Boyle
- Department of Life Sciences, University of Bath, Bath, U.K
| | - Anna Barbano
- Department of Life Sciences, University of Bath, Bath, U.K
| | | | - Neil A Brown
- Milner Centre for Evolution, Department of Life Sciences, University of Bath, Bath, U.K
- Department of Life Sciences, University of Bath, Bath, U.K
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5
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Akagi JI, Yokoi M, Miyake Y, Shirai T, Baba T, Cho YM, Hanaoka F, Sugasawa K, Iwai S, Ogawa K. A formamidopyrimidine derivative from the deoxyguanosine adduct produced by food contaminant acrylamide induces DNA replication block and mutagenesis. J Biol Chem 2023; 299:105002. [PMID: 37394003 PMCID: PMC10406624 DOI: 10.1016/j.jbc.2023.105002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2023] [Revised: 06/23/2023] [Accepted: 06/26/2023] [Indexed: 07/04/2023] Open
Abstract
Acrylamide, a common food contaminant, is metabolically activated to glycidamide, which reacts with DNA at the N7 position of dG, forming N7-(2-carbamoyl-2-hydroxyethyl)-dG (GA7dG). Owing to its chemical lability, the mutagenic potency of GA7dG has not yet been clarified. We found that GA7dG undergoes ring-opening hydrolysis to form N6-(2-deoxy-d-erythro-pentofuranosyl)-2,6-diamino-3,4-dihydro-4-oxo-5-[N-(2-carbamoyl-2-hydroxyethyl)formamido]pyrimidine (GA-FAPy-dG), even at neutral pH. Therefore, we aimed to examine the effects of GA-FAPy-dG on the efficiency and fidelity of DNA replication using an oligonucleotide carrying GA-FAPy-9-(2-deoxy-2-fluoro-β-d-arabinofuranosyl)guanine (dfG), a 2'-fluorine substituted analog of GA-FAPy-dG. GA-FAPy-dfG inhibited primer extension by both human replicative DNA polymerase ε and the translesion DNA synthesis polymerases (Polη, Polι, Polκ, and Polζ) and reduced the replication efficiency by less than half in human cells, with single base substitution at the site of GA-FAPy-dfG. Unlike other formamidopyrimidine derivatives, the most abundant mutation was G:C > A:T transition, which was decreased in Polκ- or REV1-KO cells. Molecular modeling suggested that a 2-carbamoyl-2-hydroxyethyl group at the N5 position of GA-FAPy-dfG can form an additional H-bond with thymidine, thereby contributing to the mutation. Collectively, our results provide further insight into the mechanisms underlying the mutagenic effects of acrylamide.
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Affiliation(s)
- Jun-Ichi Akagi
- Division of Pathology, National Institute of Health Sciences, Kawasaki, Kanagawa, Japan.
| | - Masayuki Yokoi
- Biosignal Research Center, Kobe University, Kobe, Hyogo, Japan
| | - Yumi Miyake
- Forefront Research Center, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan
| | - Tsuyoshi Shirai
- Department of Bioscience, Nagahama Institute of Bio-Science and Technology, Nagahama, Shiga, Japan
| | - Tomohiro Baba
- Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan
| | - Young-Man Cho
- Division of Pathology, National Institute of Health Sciences, Kawasaki, Kanagawa, Japan
| | - Fumio Hanaoka
- Biosignal Research Center, Kobe University, Kobe, Hyogo, Japan; National Institute of Genetics, Mishima, Shizuoka, Japan
| | - Kaoru Sugasawa
- Biosignal Research Center, Kobe University, Kobe, Hyogo, Japan
| | - Shigenori Iwai
- Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan
| | - Kumiko Ogawa
- Division of Pathology, National Institute of Health Sciences, Kawasaki, Kanagawa, Japan
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6
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Schmaltz LF, Koag MC, Kou Y, Zhang L, Lee S. Genotoxic effects of the major alkylation damage N7-methylguanine and methyl formamidopyrimidine. Biochem J 2023; 480:573-585. [PMID: 37078496 PMCID: PMC11061863 DOI: 10.1042/bcj20220460] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Revised: 03/29/2023] [Accepted: 04/19/2023] [Indexed: 04/21/2023]
Abstract
Various alkylating agents are known to preferentially modify guanine in DNA, resulting in the formation of N7-alkylguanine (N7-alkylG) and the imidazole ring opened alkyl-formamidopyrimidine (alkyl-FapyG) lesions. Evaluating the mutagenic effects of N7-alkylG has been challenging due to the instability of the positively charged N7-alkylG. To address this issue, we developed a 2'-fluorine-mediated transition-state destabilization approach, which stabilizes N7-alkylG and prevents spontaneous depurination. We also developed a postsynthetic conversion of 2'-F-N7-alkylG DNA into 2'-F-alkyl-FapyG DNA. Using these methods, we incorporated site-specific N7-methylG and methyl-FapyG into pSP189 plasmid and determined their mutagenic properties in bacterial cells using the supF-based colony screening assay. The mutation frequency of N7-methylG was found to be less than 0.5%. Our crystal structure analysis revealed that N7-methylation did not significantly alter base pairing properties, as evidenced by a correct base pairing between 2'-F-N7-methylG and dCTP in Dpo4 polymerase catalytic site. In contrast, the mutation frequency of methyl-FapyG was 6.3%, highlighting the mutagenic nature of this secondary lesion. Interestingly, all mutations arising from methyl-FapyG in the 5'-GGT(methyl-FapyG)G-3' context were single nucleotide deletions at the 5'-G of the lesion. Overall, our results demonstrate that 2'-fluorination technology is a useful tool for studying the chemically labile N7-alkylG and alkyl-FapyG lesions.
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Affiliation(s)
- Lillian F Schmaltz
- From the Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, U.S.A
| | - Myong-Chul Koag
- From the Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, U.S.A
| | - Yi Kou
- From the Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, U.S.A
| | - Louis Zhang
- From the Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, U.S.A
| | - Seongmin Lee
- From the Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712, U.S.A
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7
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Jaruga P, Tomar R, Kant M, Vartanian V, Sexton B, Rizzo CJ, Turesky RJ, Stone MP, Lloyd RS, Dizdaroglu M. Synthesis and Characterization of 15N 5-Labeled Aflatoxin B 1-Formamidopyrimidines and Aflatoxin B 1-N7-Guanine from a Partial Double-Stranded Oligodeoxynucleotide as Internal Standards for Mass Spectrometric Measurements. ACS OMEGA 2023; 8:14841-14854. [PMID: 37125130 PMCID: PMC10134230 DOI: 10.1021/acsomega.3c01328] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Accepted: 03/20/2023] [Indexed: 05/03/2023]
Abstract
Aflatoxin B1 (AFB1) exposure through contaminated food is a primary contributor to hepatocellular carcinogenesis worldwide. Hepatitis B viral infections in livers dramatically increase the carcinogenic potency of AFB1 exposures. Liver cytochrome P450 oxidizes AFB1 to the epoxide, which in turn reacts with N7-guanine in DNA, producing the cationic trans-8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 adduct (AFB1-N7-Gua). The opening of the imidazole ring of AFB1-N7-Gua under physiological conditions causes the formation of the cis- and trans-diastereomers of 8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl-formamido)-9-hydroxyaflatoxin B1 (AFB1-FapyGua). These adducts primarily lead to G → T mutations, with AFB1-FapyGua being significantly more mutagenic than AFB1-N7-Gua. The unequivocal identification and accurate quantification of these AFB1-Gua adducts as biomarkers are essential for a fundamental understanding and prevention of AFB1-induced hepatocellular carcinogenesis. Among a variety of analytical techniques used for this purpose, liquid chromatography-tandem mass spectrometry, with the use of the stable isotope-labeled analogues of AFB1-FapyGua and AFB1-N7-Gua as internal standards, provides the greatest accuracy and sensitivity. cis-AFB1-FapyGua-15N5, trans-AFB1-FapyGua-15N5, and AFB1-N7-Gua-15N5 have been synthesized and used successfully as internal standards. However, the availability of these standards from either academic institutions or commercial sources ceased to exist. Thus, quantitative genomic data regarding AFB1-induced DNA damage in animal models and humans remain challenging to obtain. Previously, AFB1-N7-Gua-15N5 was prepared by reacting AFB1-exo-8,9-epoxide with the uniformly 15N5-labeled DNA isolated from algae grown in a pure 15N-environment, followed by alkali treatment, resulting in the conversion of AFB1-N7-Gua-15N5 to AFB1-FapyGua-15N5. In the present work, we used a different and simpler approach to synthesize cis-AFB1-FapyGua-15N5, trans-AFB1-FapyGua-15N5, and AFB1-N7-Gua-15N5 from a partial double-stranded 11-mer Gua-15N5-labeled oligodeoxynucleotide, followed by isolation and purification. We also show the validation of these 15N5-labeled standards for the measurement of cis-AFB1-FapyGua, trans-AFB1-FapyGua, and AFB1-N7-Gua in DNA of livers of AFB1-treated mice.
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Affiliation(s)
- Pawel Jaruga
- Biomolecular
Measurement Division, National Institute
of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Rachana Tomar
- Department
of Chemistry, Vanderbilt Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Melis Kant
- Biomolecular
Measurement Division, National Institute
of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Vladimir Vartanian
- Oregon
Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, Oregon 97239, United States
| | - Benjamin Sexton
- Department
of Chemistry, Vanderbilt Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Carmelo J. Rizzo
- Department
of Chemistry, Vanderbilt Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Robert J. Turesky
- Masonic
Cancer Center, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Michael P. Stone
- Department
of Chemistry, Vanderbilt Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - R. Stephen Lloyd
- Oregon
Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, Oregon 97239, United States
| | - Miral Dizdaroglu
- Biomolecular
Measurement Division, National Institute
of Standards and Technology, Gaithersburg, Maryland 20899, United States
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8
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Pujari SS, Jokipii Krueger CC, Chao C, Hutchins S, Hurben AK, Boysen G, Tretyakova N. DEB-FAPy-dG Adducts of 1,3-Butadiene: Synthesis, Structural Characterization, and Formation in 1,2,3,4-Diepoxybutane Treated DNA. Chemistry 2022; 28:e202103245. [PMID: 34767297 PMCID: PMC10603587 DOI: 10.1002/chem.202103245] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Indexed: 11/10/2022]
Abstract
Metabolic activation of the human carcinogen 1,3-butadiene (BD) by cytochrome 450 monooxygenases gives rise to a genotoxic diepoxide, 1,2,3,4-diepoxybutane (DEB). This reactive electrophile alkylates guanine bases in DNA to produce N7-(2-hydroxy-3,4-epoxy-1-yl)-dG (N7-DE-dG) adducts. Because of the positive charge at the N7 position of the purine heterocycle, N7-DEB-dG adducts are inherently unstable and can undergo spontaneous depurination or base-catalyzed imidazole ring opening to give N6 -[2-deoxy-D-erythro-pentofuranosyl]-2,6-diamino-3,4-dihydro-4-oxo-5-N-1-(oxiran-2-yl)propan-1-ol-formamidopyrimidine (DEB-FAPy-dG) adducts. Here we report the first synthesis and structural characterization of DEB-FAPy-dG adducts. Authentic standards of DEB-FAPy-dG and its 15 N3 -labeled analogue were used for the development of a quantitative nanoLC-ESI+ -HRMS/MS method, allowing for adduct detection in DEB-treated calf thymus DNA. DEB-FAPy-dG formation in DNA was dependent on DEB concentration and pH, with higher numbers observed under alkaline conditions.
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Affiliation(s)
- Suresh S Pujari
- Department of Medicinal Chemistry, College of Pharmacy, Cancer and Cardiovascular Research Building, University of Minnesota, 2231 6th Street SE, Minneapolis, MN, 55455, USA
| | - Caitlin C Jokipii Krueger
- Department of Medicinal Chemistry, College of Pharmacy, Cancer and Cardiovascular Research Building, University of Minnesota, 2231 6th Street SE, Minneapolis, MN, 55455, USA
| | - Christopher Chao
- Department of Medicinal Chemistry, College of Pharmacy, Cancer and Cardiovascular Research Building, University of Minnesota, 2231 6th Street SE, Minneapolis, MN, 55455, USA
| | - Spencer Hutchins
- Department of Medicinal Chemistry, College of Pharmacy, Cancer and Cardiovascular Research Building, University of Minnesota, 2231 6th Street SE, Minneapolis, MN, 55455, USA
| | - Alexander K Hurben
- Department of Medicinal Chemistry, College of Pharmacy, Cancer and Cardiovascular Research Building, University of Minnesota, 2231 6th Street SE, Minneapolis, MN, 55455, USA
| | - Gunnar Boysen
- Department of Environmental and Occupational Health and the Winthrop P Rockefeller Cancer Institute, University of Arkansas for Medical Sciences, 4301 West Markham St., Slot 820, Little Rock, AR, 72205, USA
| | - Natalia Tretyakova
- Department of Medicinal Chemistry, College of Pharmacy, Cancer and Cardiovascular Research Building, University of Minnesota, 2231 6th Street SE, Minneapolis, MN, 55455, USA
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9
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Leškovskis K, Zaķis JM, Novosjolova I, Turks M. Applications of Purine Ring Opening in the Synthesis of Imidazole, Pyrimidine, and New Purine Derivatives. European J Org Chem 2021. [DOI: 10.1002/ejoc.202100755] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Kristaps Leškovskis
- Institute of Technology of Organic Chemistry, Faculty of Materials Science and Applied Chemistry Riga Technical University P. Valdena Str. 3 Riga LV-1048 Latvia
| | - Jānis Miķelis Zaķis
- Institute of Technology of Organic Chemistry, Faculty of Materials Science and Applied Chemistry Riga Technical University P. Valdena Str. 3 Riga LV-1048 Latvia
| | - Irina Novosjolova
- Institute of Technology of Organic Chemistry, Faculty of Materials Science and Applied Chemistry Riga Technical University P. Valdena Str. 3 Riga LV-1048 Latvia
| | - Māris Turks
- Institute of Technology of Organic Chemistry, Faculty of Materials Science and Applied Chemistry Riga Technical University P. Valdena Str. 3 Riga LV-1048 Latvia
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10
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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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11
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Genome Profiling for Aflatoxin B 1 Resistance in Saccharomyces cerevisiae Reveals a Role for the CSM2/SHU Complex in Tolerance of Aflatoxin B 1-Associated DNA Damage. G3-GENES GENOMES GENETICS 2020; 10:3929-3947. [PMID: 32994210 PMCID: PMC7642924 DOI: 10.1534/g3.120.401723] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Exposure to the mycotoxin aflatoxin B1 (AFB1) strongly correlates with hepatocellular carcinoma (HCC). P450 enzymes convert AFB1 into a highly reactive epoxide that forms unstable 8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 (AFB1-N 7-Gua) DNA adducts, which convert to stable mutagenic AFB1 formamidopyrimidine (FAPY) DNA adducts. In CYP1A2-expressing budding yeast, AFB1 is a weak mutagen but a potent recombinagen. However, few genes have been identified that confer AFB1 resistance. Here, we profiled the yeast genome for AFB1 resistance. We introduced the human CYP1A2 into ∼90% of the diploid deletion library, and pooled samples from CYP1A2-expressing libraries and the original library were exposed to 50 μM AFB1 for 20 hs. By using next generation sequencing (NGS) to count molecular barcodes, we initially identified 86 genes from the CYP1A2-expressing libraries, of which 79 were confirmed to confer AFB1 resistance. While functionally diverse genes, including those that function in proteolysis, actin reorganization, and tRNA modification, were identified, those that function in postreplication DNA repair and encode proteins that bind to DNA damage were over-represented, compared to the yeast genome, at large. DNA metabolism genes also included those functioning in checkpoint recovery and replication fork maintenance, emphasizing the potency of the mycotoxin to trigger replication stress. Among genes involved in postreplication repair, we observed that CSM2, a member of the CSM2 (SHU) complex, functioned in AFB1-associated sister chromatid recombination while suppressing AFB1-associated mutations. These studies thus broaden the number of AFB1 resistance genes and have elucidated a mechanism of error-free bypass of AFB1-associated DNA adducts.
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12
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Zhang H. Mechanisms of mutagenesis induced by DNA lesions: multiple factors affect mutations in translesion DNA synthesis. Crit Rev Biochem Mol Biol 2020; 55:219-251. [PMID: 32448001 DOI: 10.1080/10409238.2020.1768205] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Environmental mutagens lead to mutagenesis. However, the mechanisms are very complicated and not fully understood. Environmental mutagens produce various DNA lesions, including base-damaged or sugar-modified DNA lesions, as well as epigenetically modified DNA. DNA polymerases produce mutation spectra in translesion DNA synthesis (TLS) through misincorporation of incorrect nucleotides, frameshift deletions, blockage of DNA replication, imbalance of leading- and lagging-strand DNA synthesis, and genome instability. Motif or subunit in DNA polymerases further affects the mutations in TLS. Moreover, protein interactions and accessory proteins in DNA replisome also alter mutations in TLS, demonstrated by several representative DNA replisomes. Finally, in cells, multiple DNA polymerases or cellular proteins collaborate in TLS and reduce in vivo mutagenesis. Summaries and perspectives were listed. This review shows mechanisms of mutagenesis induced by DNA lesions and the effects of multiple factors on mutations in TLS in vitro and in vivo.
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Affiliation(s)
- Huidong Zhang
- Key Laboratory of Environment and Female Reproductive Health, West China School of Public Health and West China Fourth Hospital, Sichuan University, Chengdu, China
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13
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Hernandez-Castillo C, Termini J, Shuck S. DNA Adducts as Biomarkers To Predict, Prevent, and Diagnose Disease-Application of Analytical Chemistry to Clinical Investigations. Chem Res Toxicol 2020; 33:286-307. [PMID: 31638384 DOI: 10.1021/acs.chemrestox.9b00295] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Characterization of the chemistry, structure, formation, and metabolism of DNA adducts has been one of the most significant contributions to the field of chemical toxicology. This work provides the foundation to develop analytical methods to measure DNA adducts, define their relationship to disease, and establish clinical tests. Monitoring exposure to environmental and endogenous toxicants can predict, diagnose, and track disease as well as guide therapeutic treatment. DNA adducts are one of the most promising biomarkers of toxicant exposure owing to their stability, appearance in numerous biological matrices, and characteristic analytical properties. In addition, DNA adducts can induce mutations to drive disease onset and progression and can serve as surrogate markers of chemical exposure. In this perspective, we highlight significant advances made within the past decade regarding DNA adduct quantitation using mass spectrometry. We hope to expose a broader audience to this field and encourage analytical chemistry laboratories to explore how specific adducts may be related to various pathologies. One of the limiting factors in developing clinical tests to measure DNA adducts is cohort size; ideally, the cohort would allow for model development and then testing of the model to the remaining cohort. The goals of this perspective article are to (1) provide a summary of analyte levels measured using state-of-the-art analytical methods, (2) foster collaboration, and (3) highlight areas in need of further investigation.
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Affiliation(s)
- Carlos Hernandez-Castillo
- Department of Molecular Medicine , Beckman Research Institute at City of Hope Duarte , California 91010 , United States
| | - John Termini
- Department of Molecular Medicine , Beckman Research Institute at City of Hope Duarte , California 91010 , United States
| | - Sarah Shuck
- Department of Molecular Medicine , Beckman Research Institute at City of Hope Duarte , California 91010 , United States
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McCullough AK, Lloyd RS. Mechanisms underlying aflatoxin-associated mutagenesis - Implications in carcinogenesis. DNA Repair (Amst) 2019; 77:76-86. [PMID: 30897375 PMCID: PMC6959417 DOI: 10.1016/j.dnarep.2019.03.004] [Citation(s) in RCA: 53] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Revised: 03/01/2019] [Accepted: 03/05/2019] [Indexed: 01/07/2023]
Abstract
Chronic dietary exposure to aflatoxin B1 (AFB1), concomitant with hepatitis B infection is associated with a significant increased risk for hepatocellular carcinomas (HCCs) in people living in Southeast Asia and sub-Saharan Africa. Human exposures to AFB1 occur through the consumption of foods that are contaminated with pervasive molds, including Aspergillus flavus. Even though dietary exposures to aflatoxins constitute the second largest global environmental risk factor for cancer development, there are still significant questions concerning the molecular mechanisms driving carcinogenesis and what factors may modulate an individual's risk for HCC. The objective of this review is to summarize key discoveries that established the association of chronic inflammation (most commonly associated with hepatitis B viral (HBV) infection) and environmental exposures to aflatoxin with increased HCC risk. Special emphasis will be given to recent investigations that have: 1) refined the aflatoxin-associated mutagenic signature, 2) expanded the DNA repair mechanisms that limit mutagenesis via adduct removal prior to replication-induced mutagenesis, 3) implicated a specific DNA polymerase in the error-prone bypass and resulting mutagenesis, and 4) identified human polymorphic variants that may modulate individual susceptibility to aflatoxin-induced cancers. Collectively, these investigations revealed that specific sequence contexts are differentially resistant against, or prone to, aflatoxin-induced mutagenesis and that these associations are remarkably similar between in vitro and in vivo analyses. These recent investigations also established DNA polymerase ζ as the major polymerase that confers the G to T transversion signature. Additionally, although the nucleotide excision repair (NER) pathway has been previously shown to repair aflatoxin-induced DNA adducts, recent murine data demonstrated that NEIL1-initiated base excision repair was significantly more important than NER relative to the removal of the highly mutagenic AFB1-Fapy-dG adducts. These data suggest that inactivating polymorphic variants of NEIL1 could be a potential driver of HCCs in aflatoxin-exposed populations.
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Affiliation(s)
- Amanda K McCullough
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR 97239, United States; Department of Molecular and Medical Genetics, Oregon Health & Science University, Portland, OR 97239, United States
| | - R Stephen Lloyd
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR 97239, United States; Department of Molecular and Medical Genetics, Oregon Health & Science University, Portland, OR 97239, United States; Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, OR 97239, United States.
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15
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Pottenger LH, Boysen G, Brown K, Cadet J, Fuchs RP, Johnson GE, Swenberg JA. Understanding the importance of low-molecular weight (ethylene oxide- and propylene oxide-induced) DNA adducts and mutations in risk assessment: Insights from 15 years of research and collaborative discussions. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2019; 60:100-121. [PMID: 30536466 PMCID: PMC6590209 DOI: 10.1002/em.22248] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Revised: 08/10/2018] [Accepted: 08/23/2018] [Indexed: 05/11/2023]
Abstract
The interpretation and significance of DNA adduct data, their causal relationship to mutations, and their role in risk assessment have been debated for many years. An extended effort to identify key questions and collect relevant data to address them was focused on the ubiquitous low MW N7-alkyl/hydroxyalkylguanine adducts. Several academic, governmental, and industrial laboratories collaborated to gather new data aimed at better understanding the role and potential impact of these adducts in quantifiable genotoxic events (gene mutations/micronucleus). This review summarizes and evaluates the status of dose-response data for DNA adducts and mutations from recent experimental work with standard mutagenic agents and ethylene oxide and propylene oxide, and the importance for risk assessment. This body of evidence demonstrates that small N7-alkyl/hydroxyalkylguanine adducts are not pro-mutagenic and, therefore, adduct formation alone is not adequate evidence to support a mutagenic mode of action. Quantitative methods for dose-response analysis and derivation of thresholds, benchmark dose (BMD), or other points-of-departure (POD) for genotoxic events are now available. Integration of such analyses of genetox data is necessary to properly assess any role for DNA adducts in risk assessment. Regulatory acceptance and application of these insights remain key challenges that only the regulatory community can address by applying the many learnings from recent research. The necessary tools, such as BMDs and PODs, and the example datasets, are now available and sufficiently mature for use by the regulatory community. Environ. Mol. Mutagen. 60: 100-121, 2019. © 2018 The Authors. Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.
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Affiliation(s)
- L. H. Pottenger
- Olin Corporation/Blue Cube Operations, LLC, retired, LHP TOX CONSULT, LLCMidlandMIUSA
| | - G. Boysen
- Department of Environmental and Occupational Health and The Winthrop P Rockefeller Cancer Institute University of Arkansas for Medical SciencesLittle RockArkansasUSA
| | - K. Brown
- Leicester Cancer Research CentreUniversity of LeicesterLeicesterUnited Kingdom
| | - J. Cadet
- Institut Nanosciences et Cryogénie, CEA‐GrenobleGrenobleFrance
- Université de SherbrookeSherbrookeCanada
| | - R. P. Fuchs
- Centre de Recherche en Cancérologie de Marseille (CRCM), Inserm, U1068Marseille, 13009France
- CNRS, UMR7258Marseille, 13009France
- Institut Paoli‐CalmettesMarseille, 13009France
- Aix‐Marseille UniversityUM 105, 13284, MarseilleFrance
| | - G. E. Johnson
- Swansea University, Institute of Life SciencesSwanseaUnited Kingdom
| | - J. A. Swenberg
- University of North CarolinaChapel HillNorth CarolinaUSA
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16
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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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17
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Engin AB, Engin A. DNA damage checkpoint response to aflatoxin B1. ENVIRONMENTAL TOXICOLOGY AND PHARMACOLOGY 2019; 65:90-96. [PMID: 30594067 DOI: 10.1016/j.etap.2018.12.006] [Citation(s) in RCA: 52] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2018] [Revised: 11/20/2018] [Accepted: 12/07/2018] [Indexed: 05/28/2023]
Abstract
Although most countries regulate the aflatoxin levels in food by legislations, high amounts of aflatoxin B1 (AFB1)-DNA adducts can still be detected in normal and tumorous tissue obtained from cancer patients. AFB1 cannot directly interact with DNA unless it is biotransformed to AFB1-8, 9-epoxide via cytochrome p450 enzymes. This metabolite spontaneously and irreversibly attaches to guanine residues to generate highly mutagenic DNA adducts. AFB1-induced mutation of ATM kinase results in the deterioration of the cell cycle checkpoint activation at the G2/M checkpoint site. Genomic instability and increased cancer risk due to A-T mutation is the result of diminished repair of DNA double strand breaks. The major point mutation caused by AFB1 is G-to-T transversion that is related with the high frequency of p53 mutation. Majority of AFB1 associated hepatocellular cancer cases carry TP53 mutant DNA, which is an indicator of AFB1 exposure, as well as hepatocellular cancer risk.
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Affiliation(s)
- Ayse Basak Engin
- Gazi University, Faculty of Pharmacy, Department of Toxicology, Ankara, Turkey.
| | - Atilla Engin
- Gazi University, Faculty of Medicine, Department of General Surgery, Ankara, Turkey
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18
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Coskun E, Jaruga P, Vartanian V, Erdem O, Egner PA, Groopman JD, Lloyd RS, Dizdaroglu M. Aflatoxin-Guanine DNA Adducts and Oxidatively Induced DNA Damage in Aflatoxin-Treated Mice in Vivo as Measured by Liquid Chromatography-Tandem Mass Spectrometry with Isotope Dilution. Chem Res Toxicol 2018; 32:80-89. [PMID: 30525498 DOI: 10.1021/acs.chemrestox.8b00202] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Dietary exposure to aflatoxin B1 (AFB1) is a significant contributor to the incidence of hepatocellular carcinomas globally. AFB1 exposure leads to the formation of AFB1-N7-guanine (AFB1-N7-Gua) and two diastereomers of the imidazole ring-opened 8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl-formamido)-9-hydroxyaflatoxin B1 (AFB1-FapyGua) in DNA. These adducts lead to G → T transversion mutations with the ring-opened adduct being more mutagenic than the cationic species. Accurate measurement of these three adducts as biomarkers in DNA and urine will help identify dietary exposure to AFB1 as a risk factor in the development of hepatocellular carcinoma worldwide. Herein, we report an improved methodology for the measurement of AFB1-N7-Gua and the two diastereomers of AFB1-FapyGua using liquid chromatography-tandem mass spectrometry with isotope dilution. We measured the levels of these compounds in liver DNA of six control mice and six AFB1-treated mice. Levels varying from 1.5 to 45 lesions/106 DNA bases in AFB1-treated mice were detected depending on the compound and animal. No background levels of these adducts were detected in control mice. We also tested whether the AFB1 treatment caused oxidatively induced DNA base damage using gas chromatography-tandem mass spectrometry with isotope dilution. Although background levels of several pyrimidine- and purine-derived lesions were detected, no increases in these levels were found upon AFB1 treatment of mice. On the other hand, significantly increased levels of (5' R)- and (5' S)-8,5'-cyclo-2'-deoxyadenosines were observed in liver DNA of AFB1-treated mice. The impact of this work is expected to achieve the accurate measurement of three AFB1-DNA adducts and oxidatively induced DNA lesions as biomarkers of AFB1 exposure as germane to investigations designed for the prevention of aflatoxin-related hepatocellular carcinomas and for determining the effects of genetic deficiencies in human populations.
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Affiliation(s)
- Erdem Coskun
- Biomolecular Measurement Division , National Institute of Standards and Technology , Gaithersburg , Maryland 20899 , United States
| | - Pawel Jaruga
- Biomolecular Measurement Division , National Institute of Standards and Technology , Gaithersburg , Maryland 20899 , United States
| | - Vladimir Vartanian
- Oregon Institute of Occupational Health Sciences , Oregon Health & Science University , Portland , Oregon 97239 , United States
| | - Onur Erdem
- Biomolecular Measurement Division , National Institute of Standards and Technology , Gaithersburg , Maryland 20899 , United States.,Department of Toxicology, Gülhane Faculty of Pharmacy , University of Health Sciences , Ankara 06010 , Turkey
| | - Patricia A Egner
- Department of Environmental Health and Engineering , Johns Hopkins University Bloomberg School of Public Health , Baltimore , Maryland 21205 , United States
| | - John D Groopman
- Department of Environmental Health and Engineering , Johns Hopkins University Bloomberg School of Public Health , Baltimore , Maryland 21205 , United States
| | - R Stephen Lloyd
- Department of Toxicology, Gülhane Faculty of Pharmacy , University of Health Sciences , Ankara 06010 , Turkey
| | - Miral Dizdaroglu
- Biomolecular Measurement Division , National Institute of Standards and Technology , Gaithersburg , Maryland 20899 , United States
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Minko IG, Christov PP, Li L, Stone MP, McCullough AK, Lloyd RS. Processing of N 5-substituted formamidopyrimidine DNA adducts by DNA glycosylases NEIL1 and NEIL3. DNA Repair (Amst) 2018; 73:49-54. [PMID: 30448017 DOI: 10.1016/j.dnarep.2018.11.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2018] [Revised: 11/02/2018] [Accepted: 11/02/2018] [Indexed: 12/29/2022]
Abstract
A variety of agents cause DNA base alkylation damage, including the known hepatocarcinogen aflatoxin B1 (AFB1) and chemotherapeutic drugs derived from nitrogen mustard (NM). The N7 site of guanine is the primary site of alkylation, with some N7-deoxyguanosine adducts undergoing imidazole ring-opening to stable mutagenic N5-alkyl formamidopyrimidine (Fapy-dG) adducts. These adducts exist as a mixture of canonical β- and unnatural α-anomeric forms. The β species are predominant in double-stranded (ds) DNA. Recently, we have demonstrated that the DNA glycosylase NEIL1 can initiate repair of AFB1-Fapy-dG adducts both in vitro and in vivo, with Neil1-/- mice showing an increased susceptibility to AFB1-induced hepatocellular carcinoma. Here, we hypothesized that NEIL1 could excise NM-Fapy-dG and that NEIL3, a closely related DNA glycosylase, could excise both NM-Fapy-dG and AFB1-Fapy-dG. Product formation from the reaction of human NEIL1 with ds oligodeoxynucleotides containing a unique NM-Fapy-dG followed a bi-component exponential function under single turnover conditions. Thus, two adduct conformations were differentially recognized by hNEIL1. The excision rate of the major form (∼13.0 min-1), presumed to be the β-anomer, was significantly higher than that previously reported for 5-hydroxycytosine, 5-hydroxyuracil, thymine glycol (Tg), and AFB1-Fapy-dG. Product generation from the minor form was much slower (∼0.4 min-1), likely reflecting the rate of conversion of the α anomer into the β anomer. Mus musculus NEIL3 (MmuNEIL3Δ324) excised NM-Fapy-dG from single-stranded (ss) DNA (turnover rate of ∼0.4 min-1), but not from ds DNA. Product formation from ss substrate was incomplete, presumably because of a substantial presence of the α anomer. MmuNEIL3Δ324 could not initiate repair of AFB1-Fapy-dG in either ds or ss DNA. Overall, the data suggest that both NEIL1 and NEIL3 may protect cells against cytotoxic and mutagenic effects of NM-Fapy-dG, but NEIL1 may have a unique role in initiation of base excision repair of AFB1-Fapy-dG.
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Affiliation(s)
- Irina G Minko
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR 97239, United States
| | - Plamen P Christov
- Vanderbilt Institute of Chemical Biology, Vanderbilt University School of Medicine, Vanderbilt University, Nashville, TN 37235, United States
| | - Liang Li
- Department of Chemistry and Biochemistry, Vanderbilt-Ingram Cancer Center, Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, TN 37235, United States
| | - Michael P Stone
- Department of Chemistry and Biochemistry, Vanderbilt-Ingram Cancer Center, Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, TN 37235, United States
| | - Amanda K McCullough
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR 97239, United States; Department of Molecular and Medical Genetics, Oregon Health & Science University, Portland, OR 97239, United States
| | - R Stephen Lloyd
- Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR 97239, United States; Department of Molecular and Medical Genetics, Oregon Health & Science University, Portland, OR 97239, United States; Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, OR 97239, United States.
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20
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Groehler AS, Najjar D, Pujari SS, Sangaraju D, Tretyakova NY. N 6-(2-Deoxy-d- erythro-pentofuranosyl)-2,6-diamino-3,4-dihydro-4-oxo-5- N-(2-hydroxy-3-buten-1-yl)-formamidopyrimidine Adducts of 1,3-Butadiene: Synthesis, Structural Identification, and Detection in Human Cells. Chem Res Toxicol 2018; 31:885-897. [PMID: 30016111 DOI: 10.1021/acs.chemrestox.8b00123] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
1,3-Butadiene (BD) is an environmental and occupational toxicant classified as a human carcinogen. BD is metabolically activated by cytochrome P450 monooxygenases to 3,4-epoxy-1-butene (EB), which alkylates DNA to form a range of nucleobase adducts. Among these, the most abundant are the hydrolytically labile N7-guanine adducts such as N7-(2-hydroxy-3-buten-1-yl)-guanine (N7-EB-dG). We now report that N7-EB-dG can be converted to the corresponding ring open N6-(2-deoxy-d- erythro-pentofuranosyl)-2,6-diamino-3,4-dihydro-4-oxo-5- N-(2-hydroxy-3-buten-1-yl)-formamidopyrimidine (EB-Fapy-dG) adducts. EB-Fapy-dG lesions were detected in EB-treated calf thymus DNA and in EB-treated mammalian cells using quantitative isotope dilution nanoLC-ESI+-MS/MS. EB-Fapy-dG adduct formation in EB-treated calf thymus DNA was concentration dependent and was greatly accelerated at an increased pH. EB-FAPy-dG adduct amounts were 2-fold higher in base excision repair-deficient NEIL1-/- mouse embryonic fibroblasts (MEF) as compared to isogenic controls (NEIL1+/+), suggesting that this lesion may be a substrate for NEIL1. Furthermore, NEIL1-/- cells were sensitized to EB treatment as compared to NEIL1+/+ fibroblasts. Overall, our results indicate that ring-opened EB-FAPy-dG adducts form under physiological conditions, prompting future studies to determine their contributions to genotoxicity and mutagenicity of BD.
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Affiliation(s)
- Arnold S Groehler
- Department of Medicinal Chemistry and Masonic Cancer Center , University of Minnesota , Minneapolis , Minnesota 55455 , United States
| | - Dominic Najjar
- Department of Medicinal Chemistry and Masonic Cancer Center , University of Minnesota , Minneapolis , Minnesota 55455 , United States
| | - Suresh S Pujari
- Department of Medicinal Chemistry and Masonic Cancer Center , University of Minnesota , Minneapolis , Minnesota 55455 , United States
| | - Dewakar Sangaraju
- Department of Medicinal Chemistry and Masonic Cancer Center , University of Minnesota , Minneapolis , Minnesota 55455 , United States
| | - Natalia Y Tretyakova
- Department of Medicinal Chemistry and Masonic Cancer Center , University of Minnesota , Minneapolis , Minnesota 55455 , United States
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Bamberger SN, Malik CK, Voehler MW, Brown SK, Pan H, Johnson-Salyard TL, Rizzo CJ, Stone MP. Configurational and Conformational Equilibria of N 6-(2-Deoxy-d-erythro-pentofuranosyl)-2,6-diamino-3,4-dihydro-4-oxo-5- N-methylformamidopyrimidine (MeFapy-dG) Lesion in DNA. Chem Res Toxicol 2018; 31:924-935. [PMID: 30169026 DOI: 10.1021/acs.chemrestox.8b00135] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The most common lesion in DNA occurring due to clinical treatment with Temozolomide or cellular exposures to other methylating agents is 7-methylguanine (N7-Me-dG). It can undergo a secondary reaction to form N6-(2-deoxy-d-erythro-pentofuranosyl)-2,6-diamino-3,4-dihydro-4-oxo-5- N-methylformamidopyrimidine (MeFapy-dG). MeFapy-dG undergoes epimerization in DNA to produce either α or β deoxyribose anomers. Additionally, conformational rotation around the formyl bond, C5- N5 bond, and glycosidic bond may occur. To characterize and quantitate the mixture of these isomers in DNA, a 13C-MeFapy-dG lesion, in which the CH3 group of the MeFapy-dG was isotopically labeled, was incorporated into the trimer 5'-TXT-3' and the dodecamer 5'-CATXATGACGCT-3' (X = 13C-MeFapy-dG). NMR spectroscopy of both the trimer and dodecamer revealed that the MeFapy-dG lesion exists in single strand DNA as ten configurationally and conformationally discrete species, eight of which may be unequivocally assigned. In the duplex dodecamer, the MeFapy-dG lesion exists as six configurationally and conformationally discrete species. Analyses of NMR data in the single strand trimer confirm that for each deoxyribose anomer, atropisomerism occurs around the C5- N5 bond to produce R a and S a atropisomers. Each atropisomer exhibits geometrical isomerism about the formyl bond yielding E and Z conformations. 1H NMR experiments allow the relative abundances of the species to be determined. For the single strand trimer, the α and β anomers exist in a 3:7 ratio, favoring the β anomer. For the β anomer, with respect to the C5- N5 bond, the R a and S a atropisomers are equally populated. However, the Z geometrical isomer of the formyl moiety is preferred. For the α anomer, the E- S a isomer is present at 12%, whereas all other isomers are present at 5-7%. DNA processing enzymes may differentially recognize different isomers of the MeFapy-dG lesion. Moreover, DNA sequence-specific differences in the populations of configurational and conformational species may modulate biological responses to the MeFapy-dG lesion.
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Affiliation(s)
- Stephanie N Bamberger
- Department of Chemistry , Vanderbilt University Center for Structural Biology, Vanderbilt Center in Molecular Toxicology, and the Vanderbilt-Ingram Cancer Center, Vanderbilt University , Nashville , Tennessee 37235 , United States
| | - Chanchal K Malik
- Department of Chemistry , Vanderbilt University Center for Structural Biology, Vanderbilt Center in Molecular Toxicology, and the Vanderbilt-Ingram Cancer Center, Vanderbilt University , Nashville , Tennessee 37235 , United States
| | - Markus W Voehler
- Department of Chemistry , Vanderbilt University Center for Structural Biology, Vanderbilt Center in Molecular Toxicology, and the Vanderbilt-Ingram Cancer Center, Vanderbilt University , Nashville , Tennessee 37235 , United States
| | - Summer K Brown
- Department of Chemistry , Vanderbilt University Center for Structural Biology, Vanderbilt Center in Molecular Toxicology, and the Vanderbilt-Ingram Cancer Center, Vanderbilt University , Nashville , Tennessee 37235 , United States
| | - Hope Pan
- Department of Chemistry , Vanderbilt University Center for Structural Biology, Vanderbilt Center in Molecular Toxicology, and the Vanderbilt-Ingram Cancer Center, Vanderbilt University , Nashville , Tennessee 37235 , United States
| | - Tracy L Johnson-Salyard
- Department of Chemistry , Vanderbilt University Center for Structural Biology, Vanderbilt Center in Molecular Toxicology, and the Vanderbilt-Ingram Cancer Center, Vanderbilt University , Nashville , Tennessee 37235 , United States
| | - Carmelo J Rizzo
- Department of Chemistry , Vanderbilt University Center for Structural Biology, Vanderbilt Center in Molecular Toxicology, and the Vanderbilt-Ingram Cancer Center, Vanderbilt University , Nashville , Tennessee 37235 , United States
| | - Michael P Stone
- Department of Chemistry , Vanderbilt University Center for Structural Biology, Vanderbilt Center in Molecular Toxicology, and the Vanderbilt-Ingram Cancer Center, Vanderbilt University , Nashville , Tennessee 37235 , United States
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Kou Y, Koag MC, Lee S. Structural and Kinetic Studies of the Effect of Guanine N7 Alkylation and Metal Cofactors on DNA Replication. Biochemistry 2018; 57:5105-5116. [PMID: 29957995 DOI: 10.1021/acs.biochem.8b00331] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
A wide variety of endogenous and exogenous alkylating agents attack DNA to preferentially generate N7-alkylguanine (N7-alkylG) adducts. Studies of the effect of N7-alkylG lesions on biological processes have been difficult in part because of complications arising from the chemical lability of the positively charged N7-alkylG, which can readily produce secondary lesions. To assess the effect of bulky N7-alkylG on DNA replication, we prepared chemically stable N7-benzylguanine (N7bnG)-containing DNA and evaluated nucleotide incorporation opposite the lesion by human DNA polymerase β (polβ), a model enzyme for high-fidelity DNA polymerases. Kinetic studies showed that the N7-benzyl-G lesion greatly inhibited dCTP incorporation by polβ. The crystal structure of polβ incorporating dCTP opposite N7bnG showed a Watson-Crick N7bnG:dCTP structure. The polβ-N7bnG:dCTP structure showed an open protein conformation, a relatively disordered dCTP, and a lack of catalytic metal, which explained the inefficient nucleotide incorporation opposite N7bnG. This indicates that polβ is sensitive to major groove adducts in the templating base side and deters nucleotide incorporation opposite bulky N7-alkylG adducts by adopting a catalytically incompetent conformation. Substituting Mg2+ for Mn2+ induced an open-to-closed conformational change due to the presence of catalytic metal and stably bound dCTP and increased the catalytic efficiency by ∼10-fold, highlighting the effect of binding of the incoming nucleotide and catalytic metal on protein conformation and nucleotidyl transfer reaction. Overall, these results suggest that, although bulky alkyl groups at guanine-N7 may not alter base pairing properties of guanine, the major groove-positioned lesions in the template could impede nucleotidyl transfer by some DNA polymerases.
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Affiliation(s)
- Yi Kou
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy , The University of Texas at Austin , Austin , Texas 78712 , United States
| | - Myong-Chul Koag
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy , The University of Texas at Austin , Austin , Texas 78712 , United States
| | - Seongmin Lee
- Division of Chemical Biology and Medicinal Chemistry, College of Pharmacy , The University of Texas at Austin , Austin , Texas 78712 , United States
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Moore MM, Schoeny RS, Becker RA, White K, Pottenger LH. Development of an adverse outcome pathway for chemically induced hepatocellular carcinoma: case study of AFB1, a human carcinogen with a mutagenic mode of action. Crit Rev Toxicol 2018; 48:312-337. [PMID: 29431554 DOI: 10.1080/10408444.2017.1423462] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Adverse outcome pathways (AOPs) are frameworks starting with a molecular initiating event (MIE), followed by key events (KEs) linked by KE relationships (KERs), ultimately resulting in a specific adverse outcome. Relevant data for the pathway and each KE/KER are evaluated to assess biological plausibility, weight-of-evidence, and confidence. We aimed to describe an AOP relevant to chemicals directly inducing mutation in cancer critical gene(s), via the formation of chemical-specific pro-mutagenic DNA adduct(s), as an early critical step in tumor etiology. Such chemicals have mutagenic modes-of-action (MOA) for tumor induction. To assist with developing this AOP, Aflatoxin B1 (AFB1) was selected as a case study because it has a rich database and is considered to have a mutagenic MOA. AFB1 information was used to define specific KEs, KERs, and to inform development of a generic AOP for mutagen-induced hepatocellular carcinoma (HCC). In assessing the AFB1 information, it became clear that existing data are, in fact, not optimal and for some KEs/KERs, the definitive data are not available. In particular, while there is substantial information that AFB1 can induce mutations (based on a number of mutation assays), the definitive evidence - the ability to induce mutation in the cancer critical gene(s) in the tumor target tissue - is not available. Thus, it is necessary to consider the patterns of results in the weight-of-evidence for KEs and KERs. It was important to determine whether there was sufficient evidence that AFB1 can induce the necessary critical mutations early in the carcinogenic process, which was the case.
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Affiliation(s)
- Martha M Moore
- a Ramboll Environ US Corporation , Little Rock , AR , USA
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24
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NEIL1 protects against aflatoxin-induced hepatocellular carcinoma in mice. Proc Natl Acad Sci U S A 2017; 114:4207-4212. [PMID: 28373545 PMCID: PMC5402411 DOI: 10.1073/pnas.1620932114] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Global distribution of hepatocellular carcinomas (HCCs) is dominated by its incidence in developing countries, accounting for >700,000 estimated deaths per year, with dietary exposures to aflatoxin (AFB1) and subsequent DNA adduct formation being a significant driver. Genetic variants that increase individual susceptibility to AFB1-induced HCCs are poorly understood. Herein, it is shown that the DNA base excision repair (BER) enzyme, DNA glycosylase NEIL1, efficiently recognizes and excises the highly mutagenic imidazole ring-opened AFB1-deoxyguanosine adduct (AFB1-Fapy-dG). Consistent with this in vitro result, newborn mice injected with AFB1 show significant increases in the levels of AFB1-Fapy-dG in Neil1-/- vs. wild-type liver DNA. Further, Neil1-/- mice are highly susceptible to AFB1-induced HCCs relative to WT controls, with both the frequency and average size of hepatocellular carcinomas being elevated in Neil1-/- The magnitude of this effect in Neil1-/- mice is greater than that previously measured in Xeroderma pigmentosum complementation group A (XPA) mice that are deficient in nucleotide excision repair (NER). Given that several human polymorphic variants of NEIL1 are catalytically inactive for their DNA glycosylase activity, these deficiencies may increase susceptibility to AFB1-associated HCCs.
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Abstract
DNA nucleobases are the prime targets for chemical modifications by endogenous and exogenous electrophiles. Alkylation of the N7 position of guanine and adenine in DNA triggers base-catalyzed imidazole ring opening and the formation of N5-substituted formamidopyrimidine (N5-R-FAPy) lesions. Me-FAPy-dG adducts induced by exposure to methylating agents and AFB-FAPy-dG lesions formed by aflatoxin B1 have been shown to persist in cells and to contribute to toxicity and mutagenicity. In contrast, the biological outcomes of other N5-substituted FAPy lesions have not been fully elucidated. To enable their structural and biological evaluation, N5-R-FAPy adducts must be site-specifically incorporated into synthetic DNA strands using phosphoramidite building blocks, which can be complicated by their unusual structural complexity. N5-R-FAPy exist as a mixture of rotamers and can undergo isomerization between α, β anomers and furanose-pyranose forms. In this Perspective, we will discuss the main types of N5-R-FAPy adducts and summarize the strategies for their synthesis and structural elucidation. We will also summarize the chemical biology studies conducted with N5-R-FAPy-containing DNA to elucidate their effects on DNA replication and to identify the mechanisms of N5-R-FAPy repair.
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Affiliation(s)
- Suresh S. Pujari
- Department of Medicinal Chemistry and Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Natalia Tretyakova
- Department of Medicinal Chemistry and Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota 55455, USA
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DNA polymerase ζ limits chromosomal damage and promotes cell survival following aflatoxin exposure. Proc Natl Acad Sci U S A 2016; 113:13774-13779. [PMID: 27849610 PMCID: PMC5137696 DOI: 10.1073/pnas.1609024113] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Routine dietary consumption of foods that contain aflatoxins is the second leading cause of environmental carcinogenesis worldwide. Aflatoxin-driven mutagenesis is initiated through metabolic activation of aflatoxin B1 (AFB1) to its epoxide form that reacts with N7 guanine in DNA. The resulting AFB1-N7-dG adduct undergoes either spontaneous depurination or imidazole-ring opening yielding formamidopyrimidine AFB1 (AFB1-Fapy-dG). Because this latter adduct is known to persist in human tissues and contributes to the high frequency G-to-T mutation signature associated with many hepatocellular carcinomas, we sought to establish the identity of the polymerase(s) involved in processing this lesion. Although our previous biochemical analyses demonstrated the ability of polymerase ζ (pol ζ) to incorporate an A opposite AFB1-Fapy-dG and extend from this mismatch, biological evidence supporting a unique role for this polymerase in cellular tolerance following aflatoxin exposure has not been established. Following challenge with AFB1, survival of mouse cells deficient in pol ζ (Rev3L-/-) was significantly reduced relative to Rev3L+/- cells or Rev3L-/- cells complemented through expression of the wild-type human REV3L. Furthermore, cell-cycle progression of Rev3L-/- mouse embryo fibroblasts was arrested in late S/G2 following AFB1 exposure. These Rev3L-/- cells showed an increase in replication-dependent formation of γ-H2AX foci, micronuclei, and chromosomal aberrations (chromatid breaks and radials) relative to Rev3L+/- cells. These data suggest that pol ζ is essential for processing AFB1-induced DNA adducts and that, in its absence, cells do not have an efficient backup polymerase or a repair/tolerance mechanism facilitating survival.
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Dracínský M, Pohl R. Determination of the Nucleic Acid Adducts Structure at the Nucleoside/Nucleotide Level by NMR Spectroscopy. Chem Res Toxicol 2016; 28:155-65. [PMID: 25584790 DOI: 10.1021/tx5004535] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
All living organisms are exposed to xenobiotics from the environment. The exposure can lead to the formation of covalent adducts of xenobiotics or their metabolites with nucleic acids (NAs).The knowledge of NA adduct structure provides valuable information n the mechanism of carcinogenesis on a molecular level. While NMR spectroscopy is extremely successful in structural analysis of many classes of molecules ranging from small inorganic and organic molecules to large biomacromolecules, the structural analysis of NA adducts by NMR spectroscopy is accompanied by some challenges. First, the structural diversity of the adducts is very large; the electrophilic species generated from the metabolism of xenobiotics can attack various atoms of the nucleobases, and new rings are frequently formed. The second challenge in the DNA adducts structure determination is the low sensitivity of NMR spectroscopy and low amount of the adducts isolated from in vivo experiments. Recent developments of NMR hardware and experimental methods have led, however, to unprecedented sensitivity. This contribution reviews NMR techniques that are commonly applied in the determination of nucleic acid adducts structure at the nucleoside/nucleotide level. These NMR techniques and the large structural heterogeneity of NA adducts are demonstrated on recent examples (mostly published after 2000) of NA adducts structure determined by NMR. Most of the examples report 2′-deoxyribonucles(t)ide derivatives, but RNA adducts are also briefly discussed. The influence of the formation of NA adducts on nucleoside conformation (particularly syn/anti orientation of the base) is also demonstrated on recent examples.
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28
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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
![]()
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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Shang J, Rambo BM, Hao X, Xiang JF, Gong HY, Sessler JL. Post-synthetic modification of a macrocyclic receptor via regioselective imidazolium ring-opening. Chem Sci 2016; 7:4148-4157. [PMID: 30155059 PMCID: PMC6014093 DOI: 10.1039/c5sc04860e] [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] [Received: 12/16/2015] [Accepted: 03/03/2016] [Indexed: 11/22/2022] Open
Abstract
A facile post-synthetic modification of a tetracationic tetraimidazolium macrocycle, 14+ (i.e., the "Texas-sized" molecular box (cyclo[2](2,6-di(1H-imidazol-1-yl)pyridine)[2](1,4-dimethylenebenzene)), is described. Under mild basic conditions, ring-opening of the imidazolium moieties occurs. This results in two new isomeric dicationic macrocycles. This simple yet efficient modification serves to alter the size of the molecular cavity, the charge of the macromolecular receptor, and the manner whereby it interacts with dianionic guest molecules. The isomeric mixture of imidazolium ring opened macrocycles can be synthesized in relatively high overall yield (86-93%). The reaction shows regioselectivity and the ratio of major to minor (i.e., trans : cis ring-opened products) was determined to be ca. 3 : 1 via1H NMR spectroscopy. The major isomer, trans-cyclo[2]((Z)-N-(2-((6-(1H-imidazol-1-yl)pyridin-2-yl)amino)vinyl)formamide)[2](1,4-bismethylbenzene) hexafluorophosphate (22+·2PF6-), was isolated in its pure form in 42% yield via recrystallization. The molecular recognition properties of 22+ were investigated using a series of dianionic guests (i.e., 2,6-naphthalenedicarboxylate (4), 2,6-naphthalenedisulfonate (5), and 1,5-naphthalenedisulfonate (6)) whose binding interactions with 14+ have been previously reported. This allowed us to evaluate how imidazolium ring-opening affects the inherent host/guest interactions of 14+. On the basis of solution spectroscopic studies (e.g., 1H NMR, 1H-1H COSY NMR, DOSY NMR, and NOESY NMR), in tandem with mass spectrometric analyses (ESI-MS) and single-crystal X-ray diffraction studies, we conclude that opening up the macrocyclic structure (i.e., converting 14+ to 22+) leads to considerable changes in the recognition behavior, with so-called outside binding or weak ion pair interactions, rather than pseudorotaxane formation, being favored both in solution and the solid-state. We postulate that methodologies such as those described herein could provide a means to control the molecular interactions of both free-standing macrocycles and those used to construct mechanically-interlocked molecules. Indeed, the application of hydroxide anion under the present conditions not only serves to effect the ring-opening of 14+, but also pseudorotaxane structures, such as, e.g., [14+·4] or [14+·5] derived there from.
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Affiliation(s)
- Jia Shang
- College of Chemistry , Beijing Normal University , Xinjiekouwaidajie 19 , Beijing 100875 , P. R. China .
| | - Brett M Rambo
- Department of Chemistry , The University of Texas at Austin , 105 East 24th Street, Stop A5300 , Austin , Texas 78712-1224 , USA .
| | - Xiang Hao
- Institute of Chemistry , Chinese Academy of Sciences , Zhongguancunbeiyijie 2 , Beijing 100190 , P. R. China
| | - Jun-Feng Xiang
- Institute of Chemistry , Chinese Academy of Sciences , Zhongguancunbeiyijie 2 , Beijing 100190 , P. R. China
| | - Han-Yuan Gong
- College of Chemistry , Beijing Normal University , Xinjiekouwaidajie 19 , Beijing 100875 , P. R. China .
| | - Jonathan L Sessler
- Department of Chemistry , The University of Texas at Austin , 105 East 24th Street, Stop A5300 , Austin , Texas 78712-1224 , USA .
- Department of Chemistry , Shanghai University , Shanghai 200444 , China
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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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Kou Y, Koag MC, Lee S. N7 methylation alters hydrogen-bonding patterns of guanine in duplex DNA. J Am Chem Soc 2015; 137:14067-70. [PMID: 26517568 DOI: 10.1021/jacs.5b10172] [Citation(s) in RCA: 76] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
N7-Alkyl-2'-deoxyguanosines are major adducts in DNA that are generated by various alkylating mutagens and drugs. However, the effect of the N7 alkylation on the hydrogen-bonding patterns of the guanine remains poorly understood. We prepared N7-methyl-2'-deoxyguanosine (N7mdG)-containing DNA using a transition-state destabilization strategy, developed a novel polβ-host-guest complex system, and determined eight crystal structures of N7mdG or dG paired with dC, dT, dG, and dA. The structures of N7mdG:dC and N7mdG:dG are very similar to those of dG:dC and dG:dG, respectively, indicating the involvement of the keto tautomeric form of N7mdG in the base pairings with dC and dG. On the other hand, the structure of N7mdG:dT shows that the mispair forms three hydrogen bonds and adopts a Watson-Crick-like geometry rather than a wobble geometry, suggesting that the enol tautomeric form of N7mdG involves in its base pairing with dT. In addition, N7mdG:dA adopts a novel shifted anti:syn base pair presumably via the enol tautomeric form of N7mdG. The polβ-host-guest complex structures reveal that guanine-N7 methylation changes the hydrogen-bonding patterns of the guanine when paired with dT or dA and suggest that N7 alkylation may alter the base pairing patterns of guanine by promoting the formation of the rare enol tautomeric form of guanine.
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Affiliation(s)
- Yi Kou
- Division of Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin , Austin, Texas 78712, United States
| | - Myong-Chul Koag
- Division of Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin , Austin, Texas 78712, United States
| | - Seongmin Lee
- Division of Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin , Austin, Texas 78712, United States
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Gruppi F, Hejazi L, Christov PP, Krishnamachari S, Turesky RJ, Rizzo CJ. Characterization of nitrogen mustard formamidopyrimidine adduct formation of bis(2-chloroethyl)ethylamine with calf thymus DNA and a human mammary cancer cell line. Chem Res Toxicol 2015; 28:1850-60. [PMID: 26285869 DOI: 10.1021/acs.chemrestox.5b00297] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A robust, quantitative ultraperformance liquid chromatography ion trap multistage scanning mass spectrometric (UPLC/MS(3)) method was established to characterize and measure five guanine adducts formed by reaction of the chemotherapeutic nitrogen mustard (NM) bis(2-chloroethyl)ethylamine with calf thymus (CT) DNA. In addition to the known N7-guanine (NM-G) adduct and its cross-link (G-NM-G), the ring-opened formamidopyrimidine (FapyG) monoadduct (NM-FapyG) and cross-links in which one (FapyG-NM-G) or both (FapyG-NM-FapyG) guanines underwent ring-opening to FapyG units were identified. Authentic standards of all adducts were synthesized and characterized by NMR and mass spectrometry. These adducts were quantified in CT DNA treated with NM (1 μM) as their deglycosylated bases. A two-stage neutral thermal hydrolysis was developed to mitigate the artifactual formation of ring-opened FapyG adducts involving hydrolysis of the cationic adduct at 37 °C, followed by hydrolysis of the FapyG adducts at 95 °C. The limit of quantification values ranged between 0.3 and 1.6 adducts per 10(7) DNA bases when the equivalent of 5 μg of DNA hydrolysate was assayed on column. The principal adduct formed was the G-NM-G cross-link, followed by the NM-G monoadduct; the FapyG-NM-G cross-link adduct; and the FapyG-NM-FapyG was below the limit of detection. The NM-FapyG adducts were formed in CT DNA at a level ∼20% that of the NM-G adduct. NM-FapyG has not been previously quanitified, and the FapyG-NM-G and FapyG-NM-FapyG adducts have not been previously characterized. Our validated analytical method was then applied to measure DNA adduct formation in the MDA-MB-231 mammary tumor cell line exposed to NM (100 μM) for 24 h. The major adduct formed was NM-G (970 adducts per 10(7) bases), followed by G-NM-G (240 adducts per 10(7) bases), NM-FapyG (180 adducts per 10(7) bases), and, last, the FapyG-NM-G cross-link adduct (6.0 adducts per 10(7) bases). These lesions are expected to contribute to NM-mediated toxicity and genotoxicity in vivo.
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Affiliation(s)
- Francesca Gruppi
- Departments of Chemistry and Biochemistry, Center in Molecular Toxicology, Vanderbilt-Ingram Cancer Center, Vanderbilt University , Nashville, Tennessee 37235, United States
| | - Leila Hejazi
- Masonic Cancer Center and Department of Medicinal Chemistry, College of Pharmacy, University of Minnesota , 2231 Sixth Street South East, Minneapolis, Minnesota 55455, United States
| | - Plamen P Christov
- Departments of Chemistry and Biochemistry, Center in Molecular Toxicology, Vanderbilt-Ingram Cancer Center, Vanderbilt University , Nashville, Tennessee 37235, United States
| | - Sesha Krishnamachari
- Masonic Cancer Center and Department of Medicinal Chemistry, College of Pharmacy, University of Minnesota , 2231 Sixth Street South East, Minneapolis, Minnesota 55455, United States
| | - Robert J Turesky
- Masonic Cancer Center and Department of Medicinal Chemistry, College of Pharmacy, University of Minnesota , 2231 Sixth Street South East, Minneapolis, Minnesota 55455, United States
| | - Carmelo J Rizzo
- Departments of Chemistry and Biochemistry, Center in Molecular Toxicology, Vanderbilt-Ingram Cancer Center, Vanderbilt University , Nashville, Tennessee 37235, United States
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Christov PP, Son KJ, Rizzo CJ. Synthesis and characterization of oligonucleotides containing a nitrogen mustard formamidopyrimidine monoadduct of deoxyguanosine. Chem Res Toxicol 2014; 27:1610-8. [PMID: 25136769 PMCID: PMC4164228 DOI: 10.1021/tx5002354] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
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N5-Substituted formamidopyrimidine
adducts have been observed from the reaction of dGuo or DNA with aziridine
containing electrophiles, including nitrogen mustards. However, the
role of substituted Fapy-dGuo adducts in the biological response to
nitrogen mustards and related species has not been extensively explored.
We have developed chemistry for the site-specific synthesis of oligonucleotides
containing an N5-nitrogen mustard Fapy-dGuo
using the phosphoramidite approach. The lesion was found to be a good
substrate for Escherichia coli endonuclease
IV and formamidopyrimidine glycosylase.
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Affiliation(s)
- Plamen P Christov
- Departments of Chemistry and Biochemistry, Center in Molecular Toxicology, and Vanderbilt-Ingram Cancer Center, Vanderbilt University , Nashville, Tennessee 37235, United States
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Lin YC, Li L, Makarova AV, Burgers PM, Stone MP, Lloyd RS. Error-prone replication bypass of the primary aflatoxin B1 DNA adduct, AFB1-N7-Gua. J Biol Chem 2014; 289:18497-506. [PMID: 24838242 DOI: 10.1074/jbc.m114.561563] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Hepatocellular carcinomas (HCCs) are the third leading cause of cancer deaths worldwide. The highest rates of early onset HCCs occur in geographical regions with high aflatoxin B1 (AFB1) exposure, concomitant with hepatitis B infection. Although the carcinogenic basis of AFB1 has been ascribed to its mutagenic effects, the mutagenic property of the primary AFB1-DNA adduct, AFB1-N7-Gua, in mammalian cells has not been studied extensively. Taking advantage of the ability to create vectors containing a site-specific DNA adduct, the mutagenic potential was determined in primate cells. This adduct was highly mutagenic following replication in COS-7 cells, with a mutation frequency of 45%. The spectrum of mutations was predominantly G to T base substitutions, a result that is consistent with previous mutation data derived from aflatoxin-associated HCCs. To assess which DNA polymerases (pol) might contribute to the mutational outcome, in vitro replication studies were performed. Unexpectedly, replicative pol δ and the error-prone translesion synthesis pol ζ were able to accurately bypass AFB1-N7-Gua. In contrast, replication bypass using pol κ was shown to occur with low fidelity and could account for the commonly detected G to T transversions.
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Affiliation(s)
- Ying-Chih Lin
- From the Cancer Biology Program, Oregon Institute of Occupational Health Sciences, and
| | - Liang Li
- the Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, and
| | - Alena V Makarova
- the Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Peter M Burgers
- the Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Michael P Stone
- the Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, and
| | - R Stephen Lloyd
- Oregon Institute of Occupational Health Sciences, and Department of Molecular and Medical Genetics, Oregon Health & Science University, Portland, Oregon 97239,
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35
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Pottenger LH, Andrews LS, Bachman AN, Boogaard PJ, Cadet J, Embry MR, Farmer PB, Himmelstein MW, Jarabek AM, Martin EA, Mauthe RJ, Persaud R, Preston RJ, Schoeny R, Skare J, Swenberg JA, Williams GM, Zeiger E, Zhang F, Kim JH. An organizational approach for the assessment of DNA adduct data in risk assessment: case studies for aflatoxin B1, tamoxifen and vinyl chloride. Crit Rev Toxicol 2014; 44:348-91. [DOI: 10.3109/10408444.2013.873768] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
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36
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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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37
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Carvajal M, Berumen J, Guardado-Estrada M. The presence of aflatoxin B1-FAPY adduct and human papilloma virus in cervical smears from cancer patients in Mexico. Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2012; 29:258-68. [DOI: 10.1080/19440049.2011.647098] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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38
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Fekry MI, Szekely J, Dutta S, Breydo L, Zang H, Gates KS. Noncovalent DNA binding drives DNA alkylation by leinamycin: evidence that the Z,E-5-(thiazol-4-yl)-penta-2,4-dienone moiety of the natural product serves as an atypical DNA intercalator. J Am Chem Soc 2011; 133:17641-51. [PMID: 21954957 PMCID: PMC3268133 DOI: 10.1021/ja2046149] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Molecular recognition and chemical modification of DNA are important in medicinal chemistry, toxicology, and biotechnology. Historically, natural products have revealed many interesting and unexpected mechanisms for noncovalent DNA binding and covalent DNA modification. The studies reported here characterize the molecular mechanisms underlying the efficient alkylation of duplex DNA by the Streptomyces-derived natural product leinamycin. Previous studies suggested that alkylation of duplex DNA by activated leinamycin (2) is driven by noncovalent association of the natural product with the double helix. This is striking because leinamycin does not contain a classical noncovalent DNA-binding motif, such as an intercalating unit, a groove binder, or a polycation. The experiments described here provide evidence that leinamycin is an atypical DNA-intercalating agent. A competition binding assay involving daunomycin-mediated inhibition of DNA alkylation by leinamycin provided evidence that activated leinamycin binds to duplex DNA with an apparent binding constant of approximately 4.3 ± 0.4 × 10(3) M(-1). Activated leinamycin caused duplex unwinding and hydrodynamic changes in DNA-containing solutions that are indicative of DNA intercalation. Characterization of the reaction of activated leinamycin with palindromic duplexes containing 5'-CG and 5'-GC target sites, bulge-containing duplexes, and 5-methylcytosine-containing duplexes provided evidence regarding the orientation of leinamycin with respect to target guanine residues. The data allow construction of a model for the leinamycin-DNA complex suggesting how a modest DNA-binding constant combines with proper positioning of the natural product to drive efficient alkylation of guanine residues in the major groove of duplex DNA.
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Affiliation(s)
- Mostafa I. Fekry
- University of Missouri–Columbia Departments of Chemistry and Biochemistry 125 Chemistry Building Columbia, MO 65211
- Cairo University Pharmacognosy Department Faculty of Pharmacy Kasr El-Aini, Cairo, Egypt 11562
| | - Jozsef Szekely
- University of Missouri–Columbia Departments of Chemistry and Biochemistry 125 Chemistry Building Columbia, MO 65211
| | - Sanjay Dutta
- University of Missouri–Columbia Departments of Chemistry and Biochemistry 125 Chemistry Building Columbia, MO 65211
| | - Leonid Breydo
- University of Missouri–Columbia Departments of Chemistry and Biochemistry 125 Chemistry Building Columbia, MO 65211
| | - Hong Zang
- University of Missouri–Columbia Departments of Chemistry and Biochemistry 125 Chemistry Building Columbia, MO 65211
| | - Kent S. Gates
- University of Missouri–Columbia Departments of Chemistry and Biochemistry 125 Chemistry Building Columbia, MO 65211
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39
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Stone MP, Huang H, Brown KL, Shanmugam G. Chemistry and structural biology of DNA damage and biological consequences. Chem Biodivers 2011; 8:1571-615. [PMID: 21922653 PMCID: PMC3714022 DOI: 10.1002/cbdv.201100033] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The formation of adducts by the reaction of chemicals with DNA is a critical step for the initiation of carcinogenesis. The structural analysis of various DNA adducts reveals that conformational and chemical rearrangements and interconversions are a common theme. Conformational changes are modulated both by the nature of adduct and the base sequences neighboring the lesion sites. Equilibria between conformational states may modulate both DNA repair and error-prone replication past these adducts. Likewise, chemical rearrangements of initially formed DNA adducts are also modulated both by the nature of adducts and the base sequences neighboring the lesion sites. In this review, we focus on DNA damage caused by a number of environmental and endogenous agents, and biological consequences.
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Affiliation(s)
- Michael P Stone
- Department of Chemistry, Center in Molecular Toxicology, Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, TN 37235, USA.
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40
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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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41
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Woo LL, Egner PA, Belanger CL, Wattanawaraporn R, Trudel LJ, Croy RG, Groopman JD, Essigmann JM, Wogan GN, Bouhenguel JT. Aflatoxin B1-DNA adduct formation and mutagenicity in livers of neonatal male and female B6C3F1 mice. Toxicol Sci 2011; 122:38-44. [PMID: 21507988 DOI: 10.1093/toxsci/kfr087] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Exposure to genotoxic chemicals at a young age increases cancer incidence later in life. Aflatoxin B(1) (AFB(1)) is a potent genotoxin that induces hepatocellular carcinoma (HCC) in many animal species and in humans. Whereas adult mice are insensitive to aflatoxin-induced carcinogenesis, mice treated with AFB(1) shortly after birth develop a high incidence of HCC in adulthood. Furthermore, the incidence of HCC in adult male mice treated as infants is much greater than in females, reasons for which are unclear. In this study, treatment with AFB(1) produced similar levels of DNA damage and mutations in the liver of newborn male and female gpt delta B6C3F1 mice. Twenty-four hours after dosing with AFB(1) (6 mg/kg), the highly mutagenic AFB(1)-FAPY adduct was present at twice the level of AFB(1)-N(7)-guanine in liver DNA of males and females. A multiple dose regimen (3 × 2 mg/kg), while delivering the same total dose, resulted in lower AFB(1) adduct levels. Mutation frequencies in the gpt transgene in liver were increased by 20- to 30-fold. The most prominent mutations in AFB(1)-treated mice were G:C to T:A transversions and G:C to A:T transitions. At this 21-day time point, no significant differences were found in mutation frequency or types of mutations between males and females. These results show that infant male and female B6C3F1 mice experience similar amounts of DNA damage and mutation from AFB(1) that may initiate the neoplastic process. The gender difference in the subsequent development of HCC highlights the importance of elucidating additional factors that modulate HCC development.
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Affiliation(s)
- Leslie L Woo
- Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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42
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Christov PP, Banerjee S, Stone MP, Rizzo CJ. Selective Incision of the alpha-N-Methyl-Formamidopyrimidine Anomer by Escherichia coli Endonuclease IV. J Nucleic Acids 2010; 2010. [PMID: 20798848 PMCID: PMC2925382 DOI: 10.4061/2010/850234] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2010] [Accepted: 06/04/2010] [Indexed: 01/09/2023] Open
Abstract
Formamidopyrimidines (Fapy) lesions result from ring opening of the imidazole portion of purines. Fapy lesions can isomerize from the natural β-anomeric stereochemistry to the α-configuration. We have unambiguously demonstrated that the α-methyl-Fapy-dG (MeFapy-dG) lesion is a substrate for Escherichia coli Endonuclease IV (Endo IV). Treatment of a MeFapy-dG-containing 24 mer duplex with Endo IV resulted in 36–40% incision. The catalytic efficiency of the incision was comparable to that of α-dG in the same duplex sequence. The α- and β-MeFapy-dG anomers equilibrate to ~21 : 79 ratio over ~3 days. Related studies with a duplex containing the α-Fapy-dG lesion derived from aflatoxin B1 epoxide (α-AFB-Fapy-dG) showed only low levels of incision. It is hypothesized that the steric bulk of the aflatoxin moiety interferes with the binding of the substrate to Endo IV and the incision chemistry.
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Affiliation(s)
- Plamen P Christov
- Departments of Chemistry and Biochemistry, Center in Molecular Toxicology, Vanderbilt University, VU Station B 351822, Nashville, N 37235-1822, USA
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43
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Gates KS. An overview of chemical processes that damage cellular DNA: spontaneous hydrolysis, alkylation, and reactions with radicals. Chem Res Toxicol 2010; 22:1747-60. [PMID: 19757819 DOI: 10.1021/tx900242k] [Citation(s) in RCA: 348] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The sequence of heterocyclic bases on the interior of the DNA double helix constitutes the genetic code that drives the operation of all living organisms. With this said, it is not surprising that chemical modification of cellular DNA can have profound biological consequences. Therefore, the organic chemistry of DNA damage is fundamentally important to diverse fields including medicinal chemistry, toxicology, and biotechnology. This review is designed to provide a brief overview of the common types of chemical reactions that lead to DNA damage under physiological conditions.
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Affiliation(s)
- Kent S Gates
- Departments of Chemistry and Biochemistry, University of Missouri-Columbia, 125 Chemistry Building, Columbia, Missouri 65211.
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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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45
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Wild CP, Gong YY. Mycotoxins and human disease: a largely ignored global health issue. Carcinogenesis 2010; 31:71-82. [PMID: 19875698 PMCID: PMC2802673 DOI: 10.1093/carcin/bgp264] [Citation(s) in RCA: 535] [Impact Index Per Article: 38.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2009] [Revised: 10/18/2009] [Accepted: 10/22/2009] [Indexed: 11/12/2022] Open
Abstract
Aflatoxins and fumonisins (FB) are mycotoxins contaminating a large fraction of the world's food, including maize, cereals, groundnuts and tree nuts. The toxins frequently co-occur in maize. Where these commodities are dietary staples, for example, in parts of Africa, Asia and Latin America, the contamination translates to high-level chronic exposure. This is particularly true in subsistence farming communities where regulations to control exposure are either non-existent or practically unenforceable. Aflatoxins are hepatocarcinogenic in humans, particularly in conjunction with chronic hepatitis B virus infection, and cause aflatoxicosis in episodic poisoning outbreaks. In animals, these toxins also impair growth and are immunosuppressive; the latter effects are of increasing interest in human populations. FB have been reported to induce liver and kidney tumours in rodents and are classified as Group 2B 'possibly carcinogenic to humans', with ecological studies implying a possible link to increased oesophageal cancer. Recent studies also suggest that the FB may cause neural tube defects in some maize-consuming populations. There is a plausible mechanism for this effect via a disruption of ceramide synthase and sphingolipid biosynthesis. Notwithstanding the need for a better evidence-base on mycotoxins and human health, supported by better biomarkers of exposure and effect in epidemiological studies, the existing data are sufficient to prioritize exposure reduction in vulnerable populations. For both toxins, there are a number of practical primary and secondary prevention strategies which could be beneficial if the political will and financial investment can be applied to what remains a largely and rather shamefully ignored global health issue.
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Affiliation(s)
- Christopher P Wild
- International Agency for Research on Cancer, 69372 Lyon Cedex 08, France.
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46
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Christov PP, Brown KL, Kozekov ID, Stone MP, Harris TM, Rizzo CJ. Site-specific synthesis and characterization of oligonucleotides containing an N6-(2-deoxy-D-erythro-pentofuranosyl)-2,6-diamino-3,4-dihydro-4-oxo-5-N-methylformamidopyrimidine lesion, the ring-opened product from N7-methylation of deoxyguanosine. Chem Res Toxicol 2009; 21:2324-33. [PMID: 19053322 DOI: 10.1021/tx800352a] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
A phosphoramidite reagent of N6-(2-deoxy-D-erythro-pentofuranosyl)-2,6-diamino-1,4-dihydro-4-oxo-5-N-methylformamidopyrimidine (MeFapy-dGuo) lesions was synthesized in four steps from 2'-deoxyguanosine. Fapy nucleosides can rearrange to the pyranose form when the 5'-hydroxyl group is unprotected. The phosphoramidite was incorporated into oligonucleotides using solid-phase synthesis by adjusting the deprotection time for removal of the 5'-dimethoxytrityl group of the MeFapy-dGuo nucleotide, thereby minimizing its rearrangement to the ribopyranose. The furanose and pyranose forms were differentiated by a series of two-dimensional NMR experiments.
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Affiliation(s)
- Plamen P Christov
- Department of Chemistr, Center in Molecular Toxicology, Vanderbilt University, Nashville, Tennessee 37235-1822, USA
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47
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Christov PP, Kozekov ID, Rizzo CJ, Harris TM. The formamidopyrimidine derivative of 7-(2-oxoethyl)-2'-deoxyguanosine. Chem Res Toxicol 2008; 21:1777-86. [PMID: 18690723 DOI: 10.1021/tx800142m] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Vinyl chloride induces hepatic angiosarcomas, which are otherwise rare malignancies. The biochemical basis involves the formation of the epoxide, which reacts with DNA to give approximately 98% of the 7-(2-oxoethyl) adduct (4) of dGuo plus small amounts of the etheno derivatives of dGuo, dCyd, and dAdo. The carcinogenicity is generally ascribed to the etheno adducts, not 4, because 4 has been shown to disappear from cells rapidly and to have negligible mutagenicity, which argues against its biological importance, whereas etheno adducts are both persistent and mutagenic. It has also been shown that apurinic sites derived from 4 are unlikely to be crucial lesions. A confounding factor with regard to the etheno hypothesis is that etheno adducts arise in unexposed cells by reactions of various lipid peroxidation products. The present study explores the possibility that a major contributor to the carcinogenicity of vinyl chloride may be formamidopyrimidine (FAPy) 12, N-[2-amino-6-[(2-deoxy-beta-D-erythro-pentofuranosyl)amino]-3,4-dihydro-4-oxo-5-pyrimidinyl]-N-(2-oxoethyl)-formamide, which can arise by ring opening of 4, although its formation has not been observed until the present study. N7 adduct 4 undergoes deglycosylation to give 7-(2-oxoethyl)-Gua (13) in acid and imidazolium ring-opening to 12 in base. At pH 7.4, both processes occur with the formation of 12 representing approximately 10% of the product mixture. FAPy 12 spontaneously cyclizes to 22, which upon mild acid treatment yields the deglycosylation product 2-amino-3,4,7,8-tetrahydro-7-hydroxy-4-oxopteridine-5(6H)-carbaldehyde (14). The structure of 14 has been established by NMR and mass spectroscopy and by independent synthesis. Reaction of the epoxide of crotonaldehyde with dGuo failed to give either 13 or 14, indicating that both compounds are unique products of the reactions of dGuo with the epoxides of vinyl monomers. Although FAPy 12 was found to be unstable, carbinolamine 22 arising from cyclization of 12 may be an important contributor to the carcinogenicity of vinyl chloride.
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Affiliation(s)
- Plamen P Christov
- Department of Chemistry, Vanderbilt University, NashVille, Tennessee 37235-1822, USA
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Coste F, Ober M, Le Bihan YV, Izquierdo MA, Hervouet N, Mueller H, Carell T, Castaing B. Bacterial Base Excision Repair Enzyme Fpg Recognizes Bulky N7-Substituted-FapydG Lesion via Unproductive Binding Mode. ACTA ACUST UNITED AC 2008; 15:706-17. [DOI: 10.1016/j.chembiol.2008.05.014] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2008] [Revised: 05/14/2008] [Accepted: 05/19/2008] [Indexed: 01/18/2023]
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Delaney JC, Essigmann JM. Biological properties of single chemical-DNA adducts: a twenty year perspective. Chem Res Toxicol 2008; 21:232-52. [PMID: 18072751 PMCID: PMC2821157 DOI: 10.1021/tx700292a] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The genome and its nucleotide precursor pool are under sustained attack by radiation, reactive oxygen and nitrogen species, chemical carcinogens, hydrolytic reactions, and certain drugs. As a result, a large and heterogeneous population of damaged nucleotides forms in all cells. Some of the lesions are repaired, but for those that remain, there can be serious biological consequences. For example, lesions that form in DNA can lead to altered gene expression, mutation, and death. This perspective examines systems developed over the past 20 years to study the biological properties of single DNA lesions.
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Affiliation(s)
- James C. Delaney
- Departments of Chemistry and Biological Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139
| | - John M. Essigmann
- Departments of Chemistry and Biological Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139
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Sturla SJ. DNA adduct profiles: chemical approaches to addressing the biological impact of DNA damage from small molecules. Curr Opin Chem Biol 2007; 11:293-9. [PMID: 17574899 DOI: 10.1016/j.cbpa.2007.05.021] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2007] [Accepted: 05/29/2007] [Indexed: 10/23/2022]
Abstract
Diverse small molecules alkylate DNA and form covalently linked adducts that can influence crucial biological processes, contributing to toxicity and mutation. Understanding the chemical reactivity dictating DNA alkylation and interactions of adducts with biological pathways can impact disease prevention and treatment. The ambident reactivity of DNA-alkylating small molecules, and of DNA itself, often results in formation of multiple adducts. Determining which structures impart biological responses is important for understanding the underlying relationships between small-molecule structure and biology. With application of sensitive and structure-specific experimental and analytical methodology, such as heteronuclear NMR spectroscopy and mass spectrometry, there are increasing numbers of studies that evaluate DNA alkylation from the perspective of resulting adduct profiles. DNA adduct profiles have been examined for both exogenous and endogenous reactive small molecules. Examples of recent findings are in the areas of tobacco-specific carcinogens, lipid peroxidation products, environmental and dietary chlorophenols, and natural-product-derived antitumor therapies. As more profile data are obtained, correlations with biological impact are being observed that would not be identified by a simplified single agent/single adduct approach.
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Affiliation(s)
- Shana J Sturla
- Department of Medicinal Chemistry and The Cancer Center, University of Minnesota, 308 Harvard Street SE, Minneapolis, MN 55455, USA.
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