Identification and quantitation of hepatic DNA adducts formed in B6C3F1 mice from 1'-hydroxy-2',3'-dehydroestragole: comparison of the adducts detected with the 1'-3H-labelled carcinogen and by 32P-postlabelling

Adduct detection by acylation with [35S]methionine: analysis of DNA adducts of 4-aminobiphenyl

Reaction of synthetic N-(2'-deoxyguanosin-8-yl)-4-aminobiphenyl (dGuo-8-ABP) with t-butoxycarbonyl-L-[35S]methionine, N-hydroxysuccinimidyl ester (35S-labeled TBM-NHS), under optimized conditions produced mono-, bis-, and tris-TBM-acylated nucleosides that were separable by HPLC. Reaction of different amounts of N-(2'-deoxy-1',2'-[3H]guanosin-8-yl)-4-aminobiphenyl ([3H]dGuo-8-ABP) with 35S-labeled TBM-NHS established that total 35S content of acylated products was linearly related to adduct concentration (r = 0.992) over the range of 10 fmol to 30.6 pmol. Additionally, the N-(deoxyguanosin-8-yl)-4-[3H]aminobiphenyl (dGuo-8-[3H]ABP) adduct was isolated from calf thymus DNA adducted in vitro and from rat liver DNA adducted in vivo and similarly reacted with 35S-labeled TBM-NHS. Acylation products of dGuo-8-ABP from all three sources showed HPLC retention times identical to those of authentic TBM-dGuo-8-ABP, and 35S incorporation into acylated products was linearly related to amount of adduct reacted. These results indicate that the procedure, to which we have referred as adduct detection by acylation with methionine (ADAM), has potential applicability as an analytical procedure for detection and quantification of DNA adducts in human tissues in the molecular epidemiology of cancer.

Application of HPLC in the 32P-postlabeling assay

The postlabeling procedure for the detection of DNA modifications entails enzyme-catalyzed incorporation of 32P into nucleotides and chromatographic separation of radiolabeled products for quantification. Alternate versions of this procedure have been developed which vary in sensitivity and in applicability for the detection of different DNA adducts. Methods that utilize HPLC in either of two steps in the procedure (i.e., the separation of modified and unmodified nucleotides before the labeling reaction or the resolution of 32P-labeled adducts) are applicable for the detection of alkyl adducts as well as bulky, hydrophobic adducts and are discussed in this review. In some cases, postlabeling assays have been tailored for the quantitative detection of specific adducts. Use of multiple optimized postlabeling methods to analyze one DNA sample may enable identification of multiple specific adducts in human DNA. The widest and most promising applications for adduct detection with the postlabeling assay are for previously characterized adducts, where adduct standards are available for optimization and characterization of recovery in the assay. 32P-Postlabeling is a powerful way to measure DNA adducts as it is very sensitive. However, caution should be applied in drawing conclusions from postlabeling studies without appropriate corroborative data using another adduct detection method or without appropriate method development preceding the study. Examples of applications in human, laboratory animal, and environmental studies are available.

Simple chromatographic systems permitting both DNA purification and separation of 2'-deoxyribonucleoside 3'-monophosphates as substrates for 32P-postlabelling studies

The 32P-postlabelling method has recently been applied to the measurement of oxidative DNA damage. The assay requires the isolation of 2'-deoxyribonucleoside 3'-monophosphates subsequent to the extraction of DNA followed by its enzymatic digestion. As an alternative to the use of toxic and oxidizing solvents such as phenol, a simple purification method is proposed, based mainly on size-exclusion chromatography carried out either with ready-made columns (NAP-10, SEC-2000) or, more conveniently, with stainless-steel laboratory-packed columns (Fractogel HW 65 F). This method was applied to the purification of the DNA extracted from seeds of Lactuca sativa. After enzymatic digestion of DNA, the 2'-deoxyribonucleoside 3'-monophosphates may be further separated in less than 30 min by high-performance liquid chromatography on a Hypersil octadecylsilylsilica gel column in the ion-suppression mode by using either ammonium formate (0.05 M, pH 6.5) or sodium succinate (0.02 M, pH 6.0). The use of these eluent systems is compatible with straightforward 32P-labelling of the 2'-deoxyribonucleoside 3'-monophosphates without any concentration and desalting steps.

Advantages and limitations of laboratory methods for measurement of carcinogen-DNA adducts for epidemiological studies

In molecular epidemiological studies, the measurement of carcinogen-DNA adducts in human tissues can provide direct evidence of current exposure to chemical carcinogens. Moreover, data on steady state DNA adduct levels and the rate of cell proliferation can be related not only to carcinogen-target tissue dosimetry but may also be useful in assessment of human cancer risk. Thus far, laboratory methods for adduct detection have primarily utilized 32P-postlabelling, immunoassays, and mass spectrometry. However, accurate quantitation of DNA adducts requires knowledge of the structural identity and chemical properties of carcinogen-base adducts, the availability of synthetic standards for recovery determinations, and the development of complementary methods to corroborate analytical findings.

32P-post-labeling analysis of DNA adduct formation by antitumor drug nitracrine (Ledakrin) and other nitroacridines in different biological systems

A 32P-post-labeling method has been employed to detect DNA adducts formed by derivatives of nitro-9-aminoacridine in both cellular and non-cellular systems. The treatment of HeLa S3 cells in culture or Ehrlich ascites tumor cells in vivo with nitracrine and two other antitumor 1-nitro-9-aminoacridines, denoted C-857 and C-1006, resulted in covalent binding of these compounds to cellular DNA. Each derivative studied gave rise to a distinct pattern of adduct spots and the similarity of the respective adduct profiles was noted for the both cellular models. Calf thymus DNA samples modified in vitro with nitracrine and C-857 in the presence of either rat hepatic microsomal fraction or dithiothreitol yielded chromatographic profiles resembling those obtained in the cellular systems, suggesting similarity in the DNA adduct structures. There were also neither qualitative nor quantitative differences in calf thymus DNA modification by these two 1-nitro derivatives between aerobic and anaerobic conditions, thus the reduction of a nitro group seems not to be the only determinant of covalent binding to DNA in vitro. No DNA adduct formation was detected in the cellular systems used with 2-nitro and 4-nitro isomers of nitracrine that are devoid of cytotoxic activity, which provides further evidence that both covalent binding and DNA crosslinking, but not intercalation, are responsible for cytotoxic and antitumor properties of 1-nitro-9-aminoacridines.

32P-postlabeling analysis of DNA adducts from non-alternant PAH using thin-layer and high performance liquid chromatography

DNA adduct formation in vivo in mouse skin following a single topical application of benzo[a]fluoranthene (BbF), benzo[j]fluoranthene (BjF), benzo[k]fluoranthene (BkF), or indeno[1,2,3-cd]pyrene (IP) was investigated in female CD-1 mice using 32P-postlabeling analysis. Distinct adduct profiles were detected for each of the non-alternant hydrocarbons examined. Two adducts, one major and one minor, were detected using polyethyleneiminecellulose (PEI-cellulose) thin-layer chromatography (TLC) for BbF and BjF while a single major adduct was detected for BkF and IP. The relative extent of binding to mouse skin DNA was in the order BbF greater than BjF greater than BkF greater than IP. 32P-Postlabeled DNA adducts separated by PEI-cellulose TLC were further analyzed by high performance liquid chromatography (HPLC). A single radioactive peak was detected for 32P-labeled DNA adducts of BjF and BkF. Three general areas of radioactivity were detected when 32P-labeled DNA adducts of BbF were separated on HPLC.