Reactivity of the antibodies to DNA modified by the carcinogen N-acetoxy-N-acetyl-2-aminofluorene

In situ detection of acetylaminofluorene-DNA adducts in human cells using monoclonal antibodies

The present study was performed to generate monoclonal antibodies capable of detecting N-acetoxy-2-acetylaminofluorene (NA-AAF)-derived DNA adducts in human cells in situ. As an immunogen, we employed NA-AAF-modified single-stranded DNA coupled electrostatically to methylated protein and we produced five different monoclonal antibodies. All of them showed strong binding to NA-AAF-modified DNA, but had undetectable or minimal binding to undamaged DNA. Competitive inhibition experiments revealed that the epitope recognized by these antibodies is N-(deoxyguanosin-8-yl)-2-acetylaminofluorene (dG-C8-AAF) in DNA, although deacetylated N-(deoxyguanosin-8-yl)-2-aminofluorene in DNA is also recognized with slightly less efficiency. In contrast, these antibodies did not bind to 3-(deoxyguanosin-N(2)-yl)-2-acetylaminofluorene in DNA or to UV-induced lesions in DNA. Interestingly, they showed only minimal binding to small AAF-nucleoside adducts (dG-C8-AAF), indicating that DNA regions flanking a DNA-bound adduct, in addition to the adduct itself, are essential for the stable binding of the antibodies. Using an enzyme-linked immunosorbent assay with the most promising antibody (AAF-1), we detected the concentration-dependent induction of NA-AAF-modified adducts in DNA from repair deficient xeroderma pigmentosum (XP) cells treated with physiological concentrations of NA-AAF. Moreover, the assay enabled to confirm that normal human cells efficiently repaired NA-AAF-induced DNA adducts but not XP-A cells. Most importantly, the formation of NA-AAF-induced DNA adducts in individual nuclei of XP cells could be clearly visualized using indirect immunofluorescence. Thus, we succeeded in establishing novel monoclonal antibodies capable of the in situ detection of NA-AAF-induced DNA adducts in human cells.

Observing Translesion Synthesis of an Aromatic Amine DNA Adduct by a High-fidelity DNA Polymerase

Aromatic amines have been studied for more than a half-century as model carcinogens representing a class of chemicals that form bulky adducts to the C8 position of guanine in DNA. Among these guanine adducts, the N-(2'-deoxyguanosin-8-yl)-aminofluorene (G-AF) and N-2-(2'-deoxyguanosin-8-yl)-acetylaminofluorene (G-AAF) derivatives are the best studied. Although G-AF and G-AAF differ by only an acetyl group, they exert different effects on DNA replication by replicative and high-fidelity DNA polymerases. Translesion synthesis of G-AF is achieved with high-fidelity polymerases, whereas replication of G-AAF requires specialized bypass polymerases. Here we have presented structures of G-AF as it undergoes one round of accurate replication by a high-fidelity DNA polymerase. Nucleotide incorporation opposite G-AF is achieved in solution and in the crystal, revealing how the polymerase accommodates and replicates past G-AF, but not G-AAF. Like an unmodified guanine, G-AF adopts a conformation that allows it to form Watson-Crick hydrogen bonds with an opposing cytosine that results in protrusion of the bulky fluorene moiety into the major groove. Although incorporation opposite G-AF is observed, the C:G-AF base pair induces distortions to the polymerase active site that slow translesion synthesis.

Use of drug-specific antibodies to identify ethidium adducts produced in Trypanosoma brucei by photoaffinity labeling

A photoreactive azido analog of the trypanocide ethidium bromide, 3-amino-8-azido-5-ethyl-6-phenylphenanthridinium chloride, attached covalently to calf thymus DNA (CT DNA) by photoaffinity labeling, was used to generate antibodies for the drug analog. The specificity of the antiserum was tested using enzyme-linked immunoadsorbant assays (ELISA) against immobilized antigen (photoaffinity labeled DNA) and by both the avidin-biotin peroxidase reaction and indirect immunofluorescence performed on smears of drug treated trypanosomes. The reaction of the antiserum with the covalently bound drug adduct was diminished effectively by prior incubation with an excess of ethidium monoazide, ethidium diazide, and ethidium bromide, and to a lesser extent by the DNA-ethidium complex, the diazide-DNA or RNA adduct, and the monoazide-RNA adduct. DNA which had been photoaffinity labeled with either the propidium or the acridine moiety did not react. The antiserum recognition of DNA photoaffinity labeled with ethidium monoazide was based on the substituted phenanthridinium ring system of the parent ethidium, as evidenced by competition binding studies involving the free monoazido analog (EA1), the diazido analog (EA2), and the parent compound, ethidium bromide (EB). This approach and the sensitivity it provides should prove useful for identifying the distribution and fate of covalently bound drugs resulting from antiparasitic drug treatment, and for studying their roles in antiparasitic action.

Spectrophotometrical and immunochemical studies on the conformational changes in poly(dG-dC).poly(dG-dC) after modification by 4-hydroxyaminoquinoline 1-oxide

Poly(dG-dC).poly(dG-dC) was modified by the reaction with 4-hydroxyaminoquinoline 1-oxide (4HAQO) in the presence of seryl-AMP. The conformations of 4HAQO-modified poly(dG-dC).poly(dG-dC) and of poly(dG-dC).poly(dG-dC) were studied by circular dichroism spectra under various salt concentration conditions. 4HAQO residues to guanine bases are inefficient in inducing the transition of poly(dG-dC).poly(dG-dC) from B-form to Z-form conformation. We have elicited monoclonal antibodies against 4HAQO-poly(dG-dC).poly(dG-dC). They were characterized using enzyme-linked immunosorbent assay (ELISA), radioimmunoassay (RIA) and binding to supercoiled DNA. These antibodies reacted with 4HAQO-poly(dG-dC).poly(dG-dC) specifically but not with 4HAQO-modified DNA or poly(dG).poly(dC). However, they cross-reacted with N-acetoxy-2-acetylaminofluorene-modified poly(dG-dC).poly(dG-dC) in Z-form conformation. These monoclonal antibodies may recognize a unique conformation in poly(dG-dC).poly(dG-dC) after 4HAQO modification.

Application of new techniques for the detection of carcinogen adducts to human population monitoring

Several techniques have recently been developed for the detection and quantitation of carcinogen-DNA or -protein adducts without the requirement for radioactive carcinogens. These assays can be used to detect adducts in animals or cultured cells exposed to test compounds or in humans exposed to environmental carcinogens. Immunologic, 32P-postlabeling and fluorescence techniques, used on human samples for DNA adduct measurement, are reviewed here. Methods for the detection of carcinogen-protein adducts on human samples are also summarized.

Polyclonal antibodies to DNA modified with 4-nitroquinoline 1-oxide: application for the detection of 4-nitroquinoline 1-oxide-DNA adducts in vivo

Antibodies against 4-nitroquinoline 1-oxide (4NQO) adducts were elicited in rabbits immunized with 4NQO-modified DNA complexed with methylated bovine serum albumin. In enzyme-linked immunosorbent assay (ELISA), the antibodies could recognize either denatured or native 4NQO-modified DNA, but not unmodified DNA, DNA modified with other carcinogens or free 4NQO derivative. Modification levels as low as 5 mumol of adduct per one mole DNA nucleotide (5 adducts/10(6) nucleotides) can be easily detected by the competitive ELISA. Indirect immunofluorescence staining by anti 4NQO-DNA antibody indicated that the antibodies bound specifically to the nuclei of normal human skin fibroblast cells treated with 4NQO. The intensity of fluorescence was proportional to the dose of 4NQO used to treat the cells, and the fluorescence-positive cells could be detected after treatment with 0.25 microM 4NQO (which resulted in the formation of 10(4) adducts per cell). Applying the competitive ELISA to the quantitation of DNA-adducts in rats treated with 4NQO, it was confirmed that the sensitivity of immunochemical assays was equivalent to that of isotopic assays. These methods should be helpful in studies on the formation of adducts and their removal in cells and tissues.

Time-resolved fluorometry: a sensitive method to quantify DNA-hybrids

Europium and other lanthanides can be excitated with UV-radiation, whereafter the energy is released as fluorescence, delayed in time up to 1 ms after the excitation. Eu can be used as a sensitive label in biological assays. Here we report on the application of time-resolved fluorometry to detect nucleic acid hybrids. The probe DNA was tagged with a hapten, either a fluorene or a sulfone group. After hybridization the probe DNA was detected by a two-step immunological assay with the second antibody labelled with Eu. The method is quantitative with a detection limit of 0.3 pg of actual target regions of immobilized adenovirus genomic DNA. The label was also used in sandwich hybridization, which allowed analyzing nasopharyngeal mucus for the presence of adenovirus.

Immunologic quantification of carcinogen-DNA adducts

Sensitive immunological methods for the detection of carcinogen-DNA adducts have recently been developed. These techniques are particularly useful for screening human populations for exposure to environmental carcinogens. Measurement of the biologically effective dose in humans may be useful in detecting carcinogenic hazards and carrying out risk estimates. We have developed monoclonal antibodies to several carcinogen-DNA adducts. These have included DNA modified by a benzo[a]pyrene diol epoxide (BPDE-I), 1-aminopyrene (1-AP) and 8-methoxypsoralen (8-MOP). BALB/cCr mice were immunized with the modified DNAs complexed electrostatically to methylated bovine serum albumin. Several stable clones have been isolated for each of the modified DNAs and characterized by enzyme-linked immunosorbent assay (ELISA). All antibodies are highly specific for the appropriate modified DNA and do not cross-react with nonmodified DNA. The antibodies to BPDE-I-DNA have significant cross-reactivity with DNAs modified by similar antitrans diol epoxides of benz[a]anthracene and chrysene. These DNAs all contain N-2 of guanine adducts. The antibody probably recognizes a shared determinant encompassing the guanine base and the hydrocarbon ring containing the hydroxide groups. The antibodies cross-react with BPDE-I-dG, the monoadduct isolated from DNA, but with lower sensitivity than for the intact modified DNA. They do not react with acetylaminofluorene (AAF) or 1-AP modified DNA, both of which contain C-8 of guanosine adducts. The antibodies to 1-AP-modified DNA demonstrate cross-reactivity with 8-nitro-1-aminopyrene- and 6-nitro-1-aminopyrene-modified DNA, as well as some slight cross-reactivity with BPDE-I-DNA and AAF-DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunological detection of lesions in DNA

The purpose of this paper is to show that the antibodies to nucleic acids, to nucleosides or to DNA damaged by a physical or a chemical agent, are useful tools in the study of DNA damage and repair. The results obtained with antibodies to nucleosides, antibodies to nucleosides and DNA modified by chemical carcinogens emphasize the potential of immunological methods in three main areas, a) the sensitive detection and quantitation of adducts; b) the visualization of adducts in tissues, individual cells, and along the DNA double helix; c) the study of conformational changes of DNA induced by adducts.

Chemically modified nucleic acids as immunodetectable probes in hybridization experiments

Guanine residues in nucleic acids can be modified by treatment with N-acetoxy-N-2-acetylaminofluorene and its 7-iodo derivative in an in vitro nonenzymatic reaction. The modified nucleic acids (ribo or deoxyribo, single or double stranded) are recognized by specific antibodies. They can be immunoprecipitated or used as probes in hybridization experiments and detected by immunochemical techniques.

Mutagenicity and genotoxicity of nitroarenes. All nitro-containing chemicals were not created equal

The nitrated polycyclic aromatic hydrocarbons constitute a group of chemicals of environmental concern which display a broad spectrum of mutagenic, genotoxic and carcinogenic properties. Some members of the group are the most potent direct-acting bacterial mutagens while others exhibit low levels of potencies which require metabolic activation mixtures. Bacterial mutagenicity is dependent upon reduction of the nitro function. In mammalian cell systems the genetic and genotoxic effects of these nitrated chemicals include the induction of unscheduled DNA synthesis, sister-chromatid exchanges, chromosomal aberrations, gene mutations and cell transformation. The qualitative as well as quantitative expression of these effects is dependent upon the species and tissue of origin as well as culture history of the cell which in turn determine their enzymic capabilities and the conversion of these nitroarenes to ultimate mutagens and genotoxicants. In eukaryotic cells the following bioactivation pathways have been recognized: (a) reduction of the nitro moiety, (b) ring oxidation (the nature of which is influenced by the nitro function) followed by reduction of the nitro group, and (c) ring oxidation without concomitant reduction of the nitro moiety.

Non-random binding of N-acetoxy-N-2-acetylamino-fluorene to chromatin subunits as visualized by immunoelectron microscopy

The influence of chromatin structure on the accessibility of DNA to the model ultimate carcinogen N-acetoxy-N-2-acetylaminofluorene (N-Aco-AAF) was investigated by means of an immunoelectron microscopic technique developed recently. An homogeneous population of core particles or trinucleosomes from chicken erythrocytes, was submitted to electrophilic attack by N-Aco-AAF. After DNA isolation, N-2-acetylaminofluorene (AAF) binding sites were mapped upon the DNA fragments using specific antibodies as a probe. Our results indicate a non-random binding of AAF along the DNA. Our data support the results of previous studies showing a preferential binding on the linker region.

Immunocytological detection of AAF-DNA adducts in HeLa cell nuclei

Acetylaminofluorene-DNA adducts (AAF-DNA) were detected in the nuclei of HeLa cells exposed to N-acetoxy-2-acetylaminofluorene (N-Ac-AAF), using an immunocytological technique and specific antibodies directed against AAF modified DNA. The proportion of cells exhibiting specific nuclear immunoreactivity was dose-dependent. The time course of disappearance of adduct specific nuclear immunoreactivity was compared with removal of N-(deoxyguanosin-8-yl)-2-acetylaminofluorene (dG-C8-AAF) and other adducts.

Conformation of poly(dG-dC) . poly(dG-dC) modified by the carcinogens N-acetoxy-N-acetyl-2-aminofluorene and N-hydroxy-N-2-aminofluorene

Poly(dG-dC) . poly(dG-dC) was modified by reaction with N-acetoxy-N-acetyl-2-aminofluorene (N-AcO-AAF). Two samples with 6.6% and 8.5% modified bases were prepared. The modified bases are randomly distributed along the polymer chain, as deduced from competition experiments between antibodies against N-2-(guanosin-8-yl)-acetylaminofluorene, modified poly(dG-dC) . poly(dG-dC), and modified DNAs. Circular dichroism studies show that poly(dG-dC) . poly(dG-dC) modified by N-AcO-AAF is much more sensitive to the addition of alcohol than poly(dG-dC) . poly(dG-dC). In about 50% (vol/vol) alcohol, both polynucleotides have the same conformation, which is the Z form or a Z-like form. Moreover, in low salt and in the absence of alcohol, poly(dG-dC) . poly(dG-dC) modified by N-AcO-AAF is partially in the Z form. Poly(dG-dC) . poly(dG-dC) modified by N-hydroxy-N-2-aminofluorene can also adopt the Z form, but the transition is induced at a higher percentage than that of poly(dG-dC) . poly(dG-dC) modified by N-AcO-AAF. In low salt and in the absence of alcohol, no Z form was detected in poly(dG-dC) . poly(dG-dC) modified by N-hydroxy-N-2-aminofluorene.

Antibodies to N-(guanosin-8-yl)-2-aminofluorene

Antibodies to Guo-AF were elicited in rabbits by immunization with bovine serum albumin -Guo-AF conjugate. The antibodies were purified by affinity chromatography. The affinity of the antibodies towards several ligands was studied by radioimmunoassays. The antibodies recognize Gua-AAF and Guo-AF (K(Guo-AF)/K(Guo-AAF) congruent to 25). The circular dichroism of Guo-AF as a function of pH is reported.