Modification of deoxyribonucleic acid with reductively activated mitomycin C. Structures of modified nucleotides.

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Abstract
Mitomycin C [an antitumor agent] (MMC) binds to DNA after its reductive activation by catalytic hydrogenation with Pd on charcoal. Three modified nucleotides, named MG-1, MG-2 and MA, were isolated and purified by high performance liquid chromatography (HPLC) from the modified DNA after enzymatic hydrolysis to 5''-nucleotides with nuclease P1. Analysis of the 1H-NMR and UV spectra, and studies of the acid and enzymatic hydrolysates of these modified nucleotides suggested that MG-1 and MG-2 are deoxyguanylic acid-MMC adducts bound at position 1 of mitosene and a heteroatom of the guanine moiety. Analogous binding to an adenine moiety is proposed for the adduct, MA. Chemical transformations (methylation, diazotization and thioketonization) were used to unambiguously determine the binding sites of the purine bases. The binding sites were identified as the N2 atom of guanine for MG-1, the O6 atom of guanine for MG-2 and the N6 atom of adenine for MA. These 3 modified nucleotides were 1,2-trans-2,7-diamino-1-(N2-deoxyguanylyl)mitosene (MG-1), 2,7-diamino-1-(O6-deoxyguanylyl)mitosene (MG-2) and 2,7-diamino-1-(N6-deoxyadenylyl)mitosene (MA). These same modified nucleotides were identified in DNA extracted from the livers of rats treated with MMC.