Oxidation of the sugar moiety of DNA by ionizing radiation or bleomycin could induce the formation of a cluster DNA lesion

International audienceBleomycin, a radiomimetic drug currently used in human cancer therapy, is a well known carcinogen. Its toxicity is mostly attributed to its potentiality to induce DNA double strand breaks likely arising from the formation of two vicinal DNA strand breaks, initiated by C4-hydrogen abstraction on the 2-deoxyribose moiety. In this work we demonstrate that such a hydrogen abstraction reaction is able to induce the formation of a clustered DNA lesion, involving a 3' strand break together with a modified sugar residue exhibiting a reactive $\alpha , \beta-unsaturated aldehyde that further reacts with a proximate cytosine base. The lesion thus produced was detected as a mixture of four isomers by HPLC coupled to tandem mass spectrometry subsequent to DNA extraction and enzymatic digestion. The modified nucleosides that constitute new types of cytosine adducts were identified as the likely two pairs of diastereomers of 6-(2-deoxy--Derythro-pentofuranosyl)-2-hydroxy-3(3-hydroxy-2-oxopropyl)-2,6- dihydroimidazo[1,2-c]-pyrimidin-5(3H)-one as inferred from mass spectrometry and NMR analyses of the chemically synthesized nucleosides. We demonstrate that bleomycin, and to a minorextent ionizing radiation, are able to induce significant amounts of the cytosine damage in cellular DNA. In addition, the repair kineticof the lesion in a human lymphocyte cell line is rather slow, with a half-life of 10 h. The 2'-deoxycytidine adducts thus characterizedthat represent the first example of complex DNA lesions isolated and identified in cellular DNA upon one radical hit are likely to playan important role in the toxicity of bleomyci