High-affinity monoclonal antibodies for the specific recognition and quantification of deoxynucleosides structurally modified by N-nitroso compounds.

The applicability of conventional radiochromatographic procedures to the detection and quantification of specific, carcinogen-induced structural modifications in the DNA of mammalian cells is limited by the necessity of using radioactively labelled agents and by the relatively large amounts of DNA required for analysis of low levels of DNA modification. Recently developed immunoanalytical methods have improved this situation considerably. High-affinity monoclonal antibodies (MAB), in combination with radio- and enzyme-immunoassays, now permit the sensitive detection of alkyldeoxynucleosides in small samples of hydrolysed DNA from tissues and cultured cells exposed previously to non-radioactive (e.g., environmental) alkylating N-nitroso carcinogens. Furthermore, MAB can be used to quantify by direct immunofluorescence (and with the aid of computer-based image analysis of electronically intensified fluorescence signals) specific alkylation products in the DNA of individual cells. With this method, the present detection limit for, e.g. O6-ethyl-2'-deoxyguanosine (O6-EtdGuo) is of the order of 7 X 10(2) O6-EtdGuo molecules per diploid genome. Therefore, cells (e.g. from biopsy material) can now be monitored directly for the presence of specific carcinogen-DNA adducts, or with respect to their capacity to remove enzymatically such modified structures from DNA. In combination with transmission electron microscopy, MAB also permit the direct visualization of specific carcinogen-modified sites in DNA. Thus, O6-EtdGuo can be localized in double-stranded DNA molecules by the binding of a MAB specifically directed against this ethylation product.