Heterogeneity of DNA repair: implications for human disease and oncology

32P-postlabelling and mass spectrometric methods for analysis of bulky, polyaromatic carcinogen-DNA adducts in humans

There has been significant recent progress toward the development of human carcinogen-DNA adduct biomonitoring methods. 32P-Postlabelling is a technique which has found wide application in human studies. 32P-Postlabelling involves enzymatic preparation and labelling of DNA samples, followed by chromatographic separation of carcinogen-nucleotide adducts from unadducted nucleotides. Thin-layer ion-exchange and high-performance liquid chromatography (HPLC) have been utilized. This paper critically reviews 32P-postlabelling methods for analysis of bulky, polyaromatic carcinogen-DNA adducts and details a strategy to optimize this technique for monitoring human samples. Development of a human carcinogen biomonitoring method requires that the biomarker meet certain criteria: that the biomarker be responsive to exposures known to increase human cancer risk, to reductions in those exposures, and to the influence of metabolic differences. In addition, reliable samples must be available by non-invasive means. The ability of 32P-postlabelling to meet these criteria is traced in the literature and discussed. Identification of specific carcinogen-DNA adducts is a difficult task due to the low (femtomole) levels in human target tissues. Because co-chromatography in thin-layer chromatography (TLC) is generally not considered to be proof of chemical identity, both synchronous fluorescence and HPLC in conjunction with 32P-postlabelling and TLC are used to confirm the identity of specific carcinogen-DNA adducts in human samples. Mass spectrometry is a highly specific method, the sensitivity of which has been improved to the point which may allow its use to confirm the identity of carcinogen-DNA adducts isolated by 32P-postlabelling and other methods. The literature relating to the use of mass spectral techniques in carcinogen-DNA adduct analysis is reviewed.