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DNA Repair Apr 2007Cytotoxic and mutagenic methylated bases in DNA can be generated by endogenous and environmental alkylating agents. Such damaged bases are removed by three distinct... (Review)
Review
Cytotoxic and mutagenic methylated bases in DNA can be generated by endogenous and environmental alkylating agents. Such damaged bases are removed by three distinct strategies. The abundant toxic lesion 3-methyladenine (3-alkyladenine) is excised by a specific DNA glycosylase that initiates a base excision-repair process. The toxic lesions 1-methyladenine and 3-methylcytosine are corrected by oxidative DNA demethylation catalyzed by DNA dioxygenases. These enzymes release the methyl moiety as formaldehyde, directly reversing the base damage. The third strategy involves the mutagenic and cytotoxic lesion O(6)-methylguanine which is also repaired by direct reversal but uses a different mechanism. Here, the methyl group is transferred from the lesion to a specific cysteine residue within the methyltransferase itself. In this review, we briefly describe endogenous alkylating agents and the extensively investigated DNA repair enzymes, mammalian 3-methyladenine-DNA glycosylase and O(6)-methylguanine-DNA methyltransferase. We provide a more detailed description of the structures and biochemical properties of the recently discovered DNA dioxygenases.
Topics: Alkylating Agents; Alkylation; Amino Acid Sequence; Animals; Crystallography, X-Ray; DNA; DNA Methylation; DNA Repair; DNA Repair Enzymes; Humans; Mice; Molecular Sequence Data; Protein Conformation; S-Adenosylmethionine
PubMed: 17112791
DOI: 10.1016/j.dnarep.2006.10.005 -
Mutation Research Apr 2010Approximately one-third of IVF cases in the UK are attributed to male factor infertility and in the majority of cases the origin of male infertility is unknown. The...
Approximately one-third of IVF cases in the UK are attributed to male factor infertility and in the majority of cases the origin of male infertility is unknown. The integrity of sperm DNA is important both for the success of assisted reproduction and the implications for the off-spring. One type of DNA damage that has not been investigated with respect to fertility outcomes is the adduct N7-methyldeoxyguanosine (N7-MedG), a biomarker for exposure to alkylating agents. A prospective cohort of couples attending for IVF had their N7-MedG levels in sperm measured using an immunoslot blot technique to examine whether sperm N7-MedG levels are associated with male factor infertility, semen quality measures or assisted reproduction outcomes. Sufficient DNA for analysis was obtained from 67/97 couples and N7-MedG was detected in 94% of sperm samples analysed. Men diagnosed with male factor infertility had significantly higher mean levels of N7-MedG in their sperm DNA (P=0.03). Logistic regression analysis showed that N7-MedG levels were significantly negatively associated with the proportion of oocytes successfully fertilised irrespective of the method of fertilisation used (IVF or intra-cytoplasmic sperm injection; ICSI, P<0.001). Therefore exposure to DNA alkylating agents is significantly associated with male infertility and the proportion of oocytes fertilised during assisted reproduction. Reducing such exposure may improve male fertility but further work is required to determine the relative importance of exogenous and endogenous sources of exposure.
Topics: Adult; Alkylating Agents; DNA Adducts; DNA Methylation; Deoxyguanosine; Female; Guanine; Humans; Infertility, Male; Male; Middle Aged; Reproductive Techniques, Assisted; Spermatozoa
PubMed: 20307685
DOI: 10.1016/j.mrgentox.2010.02.019 -
Journal of the American Chemical Society Mar 2006Metabolism of food- and tobacco-borne procarcinogens results in the exposure of DNA to toxic alkylating agents. These assaults can bring about DNA alkylation damage,...
Metabolism of food- and tobacco-borne procarcinogens results in the exposure of DNA to toxic alkylating agents. These assaults can bring about DNA alkylation damage, mutations, and cancer. Dietary inorganic compounds such as selenium and vanadium are known to prevent cancer, possibly by reacting directly with alkylating agents, thereby preventing DNA damage. To understand potential interactions between oxo species and alkylating toxins, we reacted a series of alkylating agents with varied classes of oxo compounds (i.e., vanadates, selenate, phosphate, sulfate, acetate, nitrate, and nitrite). A new organic-soluble selenate, [(C6H5)4P]3(O3SeOCH2OSeO3)(HSeO4), was synthesized and characterized for these studies. Vanadates were found to convert ethylating agents into ethanol, whereas other anions formed esters upon alkylation. General trends show that oxo anions of the greatest charge density were the most reactive. These studies suggest that the design of new compounds for cancer prevention should incorporate reactive oxo groups with high anionic charge density.
Topics: Acetates; Alkylating Agents; Alkylation; DNA; DNA Damage; Nitrates; Nitrites; Phosphates; Selenic Acid; Selenium Compounds; Structure-Activity Relationship; Sulfates; Vanadates
PubMed: 16522120
DOI: 10.1021/ja056568v -
Chemical Research in Toxicology Dec 2003Reaction with thiol converts the antitumor natural product leinamycin to an episulfonium ion that alkylates the N(7)-position of guanine residues in double-stranded DNA....
Reaction with thiol converts the antitumor natural product leinamycin to an episulfonium ion that alkylates the N(7)-position of guanine residues in double-stranded DNA. The sequence specificity for DNA alkylation by this structurally novel compound has not previously been examined. It is reported here that leinamycin shows significant (>10-fold) preferences for alkylation at the 5'-G in 5'-GG and 5'-GT sequences. The sequence preferences for activated leinamycin are significantly different from that observed for the structurally simple episulfonium ion generated from 2-chloroethyl ethyl sulfide. DNA alkylation by activated leinamycin is inhibited by addition of salt (100 mM NaClO(4)), although the degree of inhibition is somewhat less than that seen for 2-chloroethyl ethyl sulfide. This result suggests that electrostatic interactions between the activated leinamycin and the N(7)-position of guanine residues facilitate efficient DNA alkylation. However, the observed sequence preferences for DNA alkylation by activated leinamycin do not correlate strongly with calculated sequence-dependent variations in the molecular electrostatic potential at the N(7)-atom of guanine residues in duplex DNA. Thus, electrostatic interactions between activated leinamycin and DNA do not appear to be the primary determinant for sequence specificity. Rather, the results suggest that sequence-specific noncovalent interactions of leinamycin with the DNA double helix on the 3'-side of the alkylated guanine residue play a major role in determining the preferred alkylation sites. Consistent with the notion that noncovalent binding plays an important role in DNA alkylation by leinamycin, experiments with 2'-deoxyoligonucleotide substrates confirm that the natural product does not alkylate single-stranded DNA under conditions where duplex DNA is efficiently alkylated.
Topics: Alkylation; Animals; Antineoplastic Agents, Alkylating; Base Sequence; Binding Sites; Cattle; DNA; DNA, Single-Stranded; Fishes; Guanine; Lactams; Macrolides; Male; Molecular Sequence Data; Mustard Gas; Oligonucleotides; Perchlorates; Phosphoric Monoester Hydrolases; Plasmids; Sodium Compounds; Spermatozoa; Substrate Specificity; Sulfuric Acid Esters; Thiazoles; Thiones
PubMed: 14680367
DOI: 10.1021/tx0341658 -
Biochemistry Aug 1993A series of sulfonate esters that are attached to a noncationic minor-groove-binding N-methylpyrrole dipeptide (Lex) related to netrospin have been synthesized. The...
A series of sulfonate esters that are attached to a noncationic minor-groove-binding N-methylpyrrole dipeptide (Lex) related to netrospin have been synthesized. The compounds prepared differ in two respects: (1) the length [(CH2)2 vs (CH2)8] of the tether between the DNA affinity binding portion of the molecule and the sulfonate ester and (2) whether a methyl group [MeOSO2(CH2)n-Lex] or the dipeptide including the aliphatic tether [MeSO2O(CH2)n-Lex] is covalently transferred to the DNA. The DNA-cleavage patterns of these bimolecular alkylating compounds have been mapped in 32P-end-labeled restriction fragments using neutral thermal hydrolysis and alkali treatment to expose single-strand breaks at bases with thermally labile modifications. In contrast to the alkylation of DNA by simple alkyl alkanesulfonate esters, that predominantly yield major-groove alkylation at N7-guanine, the modification of DNA by MeOSO2(CH2)n-Lex and MeSO2O(CH2)n-Lex occurs primarily at N3-adenine residues associated with previously footprinted Lex DNA affinity binding regions. The ratio for the formation of N3-methyladenine (minor groove) to N7-methylguanine (major groove) in calf thymus DNA is 1:7 for dimethyl sulfate, while only the former adenine product is observed with MeSO2O(CH2)n-Lex indicating the change in groove specificity. DNA cleavage by MeOSO2(CH2)n-Lex and MeSO2O(CH2)n-Lex is efficiently inhibited by the coaddition of distamycin; however, only the DNA damage generated by the latter is blocked by NaCl. As expected, increasing the length of the (CH2)n tether from n = 2 to n = 8 moves the alkylation site by 1-2 base pairs further from the affinity binding domain. Finally, a comparison of the methylation patterns of MeOSO2(CH2)n-Lex as a function of tether length provides an insight into Lex sequence and orientational preferences.
Topics: Alkanesulfonates; Alkylating Agents; Base Sequence; DNA; Models, Molecular; Molecular Sequence Data; Netropsin
PubMed: 8394120
DOI: 10.1021/bi00082a017 -
Journal of Biological Inorganic... Oct 2004Human exposure to alkylating agents metabolized from tobacco- and food-borne carcinogens occurs regularly. Dietary inorganic compounds such as selenium and vanadium have...
Human exposure to alkylating agents metabolized from tobacco- and food-borne carcinogens occurs regularly. Dietary inorganic compounds such as selenium and vanadium have been shown previously to provide chemoprotective benefits in rat and human trials. Here, we present biochemical data on the ability of inorganic compounds to protect DNA from alkylation damage. An enzyme cleavage assay is used to observe alkylated DNA. Simple salts (e.g., NaCl or NiCl(2)) did not prevent DNA alkylation, whereas anionic oxo species (e.g., Na(2)SeO(4) or Na(3)VO(4)) did inhibit alkylation. We propose that these oxo species behave as nucleophilic targets for the electrophilic alkylating agents, thereby preventing DNA damage.
Topics: Alkylation; DNA; DNA Damage; Dose-Response Relationship, Drug; Salts; Selenic Acid; Selenium Compounds; Vanadates
PubMed: 15378408
DOI: 10.1007/s00775-004-0597-1 -
Journal of Chromatography. B,... Feb 2003Nitrogen mustards are among the oldest cancer chemotherapeutic agents and remain the drugs of choice for treatment of many human cancers. A serious complication of...
Alkylation of DNA by melphalan: investigation of capillary liquid chromatography-electrospray ionization tandem mass spectrometry in the study of the adducts at the nucleoside level.
Nitrogen mustards are among the oldest cancer chemotherapeutic agents and remain the drugs of choice for treatment of many human cancers. A serious complication of treatment with nitrogen mustards is the increased risk of a secondary leukaemia in long-term survivors because not all alkylating agent interactions with DNA result in cell death. In an earlier study 2'-deoxy-5'-mononucleotide/melphalan adducts have been analysed by us by LC-ES MSMS. In this work we want to present the first results of the analysis of the corresponding 2'-deoxynucleoside/melphalan adducts from DNA hydrolysates by column switching/capillary LC-ES tandem mass spectrometry. Nucleosides, compared to nucleotides, give better chromatographic results and show a good sensitivity under electrospray (+) [ES(+)] ionisation. Several adducts were identified under ES(+) conditions. Mono-alkylated nucleoside adducts alkylated at the base moiety were identified for dGuo, dCyd and dAdo. Structures were identified by recording the low-energy CAD product ion scans. Also a mono-alkylated nucleotide pdA with alkylation position at the phosphate moiety could be detected. This proves that in the case of phosphate alkylation the enzymatic dephosphorylation reaction was inhibited. A Jurkat cell suspension was treated with melphalan (1 mM) and incubated at 37 degrees C (5% CO(2)). After 6 and 48 h, the DNA was isolated and enzymatically hydrolysed. The corresponding nucleoside pool was evaluated with the developed LC-MS method. In the 48-h experiment, one adduct could be identified as a N-7 alkylated dGuo. In the 6-h experiment, no adducts could be found. Additional experiments were done wherein Jurkat-DNA, isolated from a non-treated cell culture, was treated with melphalan. These results were analogous with the data found in melphalan-treated calf thymus DNA. Additionally, we tried to determine the exact alkylation position by interpreting high-resolution fragmentation spectra.
Topics: Alkylation; Animals; Antineoplastic Agents, Alkylating; Cattle; Chromatography, Liquid; DNA; DNA Adducts; Humans; Jurkat Cells; Melphalan; Sensitivity and Specificity; Spectrometry, Mass, Electrospray Ionization
PubMed: 12535835
DOI: 10.1016/s1570-0232(02)00851-6 -
Current Medicinal Chemistry.... Mar 2004Acronycine, a natural alkaloid originally extracted from the bark of the Australian ash scrub Acronychia baueri, has shown a significant antitumor activity in animal... (Review)
Review
Acronycine, a natural alkaloid originally extracted from the bark of the Australian ash scrub Acronychia baueri, has shown a significant antitumor activity in animal models. Acronycine has been tested against human cancers in the early 1980s, but the clinical trials showed modest therapeutic effects and its development was rapidly discontinued. In order to optimize the antineoplastic effect, different benzoacronycine derivatives were synthesized. Among those, the di-acetate compound S23906-1 was recently identified as a promising anticancer drug candidate and a novel alkylating agent specifically reacting with the exocylic 2-NH2 group of guanines in DNA. The study of DNA bonding capacity of acronycine derivatives leads to the identification of the structural requirements for DNA alkylation. In nearly all cases, the potent alkylating agents, such as S23906-1, were found to be much more cytotoxic than the unreactive analogs such as acronycine itself or diol derivatives. Alkylation of DNA by the monoacetate derivative S28687-1, which is a highly reactive hydrolysis metabolite of S23906-1, occurs with a marked preference for the N2 position of guanine. Other bionucleophiles can react with S23906-1. The benzacronycine derivatives, which efficiently alkylate DNA, also covalently bind to the tripeptide glutathione (GSH) but not to the oxidized product glutathione disulfide. Here we review the reactivity of S23906-1 and some derivatives toward DNA and GSH. The structure-activity relationships in the benzacronycine series validate the reaction mechanism implicating DNA as the main molecular target. S23906-1 stands as the most promising lead of a medicinal chemistry program aimed at discovering novel antitumor drugs based on the acronycine skeleton.
Topics: Acronine; Alkylation; Animals; Antineoplastic Agents, Alkylating; DNA; Glutathione; Guanine; Humans; Structure-Activity Relationship
PubMed: 15032716
DOI: 10.2174/1568011043482115 -
Environmental and Molecular Mutagenesis 1988Treatment of cells with low levels of alkylating agents for extended periods of time causes them to become resistant to the lethal and mutagenic effects of subsequent... (Review)
Review
Treatment of cells with low levels of alkylating agents for extended periods of time causes them to become resistant to the lethal and mutagenic effects of subsequent high-level challenge treatments with alkylating agents. This increased resistance has been called the adaptive response to alkylation damage and results from the induction of an alkylation-specific DNA repair response. The adaptive response is most efficiently induced by methylating agents and is most effective against the lethal and mutagenic effects of methylation damage to DNA. Four genes have been identified as components of this response, ada, alkA, alkB and aidB. The functions of two of these genes are known. AlkA protein functions as a glycosylase that repairs N3-meA, N3-meG, O2-meT, and O2-meC residues in DNA, and Ada protein functions as an alkyltransferase that removes alkyl groups from O6-meG, O4-meT residues as well as methylphosphotriesters. After it interacts with methylated DNA, Ada protein functions as a positive regulatory element that controls the expression of the adaptive response by stimulating the expression of the ada-alkB operon, and the alkA and aidB genes.
Topics: Alkylating Agents; Alkylation; Bacterial Proteins; DNA Damage; DNA Repair; DNA, Bacterial; Drug Resistance, Microbial; Escherichia coli; Genes, Bacterial; Methylation; SOS Response, Genetics
PubMed: 3278898
DOI: 10.1002/em.2850110210 -
Acta Oncologica (Stockholm, Sweden) 1988An examination of the DNA sequence specificity of guanine-N7 alkylation for nitrogen mustards and chlorethylnitrosoureas revealed that large variations in alkylation... (Review)
Review
An examination of the DNA sequence specificity of guanine-N7 alkylation for nitrogen mustards and chlorethylnitrosoureas revealed that large variations in alkylation intensities existed among different guanines in the DNA sequence. The most striking finding was that most agents reacted preferentially at runs of G's, the degree of preference being much greater than would be expected from the number of G's alone. This correlated with the molecular electrostatic potential induced at the guanine-N7 position by the nearest neighbor base pairs. Uracil and quinacrine mustards, however, showed distinctly different reaction patterns from other mustards and a detailed examination has led to structural hypotheses to account for the differences. Certain regions of the genome including regions in some oncogenes and the Epstein-Barr virus have unusually high GC contents (greater than 80% GC) which suggests that the antitumor effectiveness of alkylating agents may in part be due to selective reaction at certain regions in the genome. In fact certain mustards have been shown to exhibit enhanced reactivities with such regions in DNA fragments derived from the c-H-ras oncogene. The above findings point to the possibility of design of alkylating agents to optimise the selectivity of reaction with critical DNA regions. An alternative approach presently under investigation has emerged from an understanding of the characteristics of the sequence specific interaction of the natural oligopeptide antibiotics netropsin and distamycin in the minor groove of DNA. This has led to the synthesis of novel agents (lexitropsins) in which the binding specificity can be shifted from (AT)n in (GC)n in a predictable fashion. Thus the rational design of DNA sequence specific vectors linked to DNA reactive groups, such as alkylating or cleaving agents, could enable DNA damage to be delivered selectively to predetermined critical sites on the genome.
Topics: Alkylating Agents; Antineoplastic Agents; Base Sequence; DNA; Distamycins; Humans; Netropsin; Nitrogen Mustard Compounds; Oncogenes
PubMed: 2849464
DOI: 10.3109/02841868809093578