Nuclease digestion and mass spectrometric characterization of oligodeoxyribonucleotides containing 1,2-GpG, 1,2-ApG, and 1,3-GpXpG cisplatin intrastrand cross-links

BackgroundThe primary mode of action for cis-diamminedichloroplatinum (II), referred to as cisplatin, toward the treatment of solid malignancies is through formation of cross-links with DNA at purine sites, especially guanines.MethodsWe prepared oligodeoxyribonucleotides (ODNs) containing a 1,2-GpG, 1,2-ApG, or 1,3-GpXpG cisplatin intrastrand cross-link and the corresponding ODNs modified with 15N2-labeled cisplatin, and characterized these ODNs with electrospray ionization mass spectrometry (ESI-MS) and tandem MS (MS/MS). We also employed LC–MS/MS to characterize the digestion products of these ODNs after treatment with a cocktail of 4 enzymes (nuclease P1, phosphodiesterases I and II, and alkaline phosphatase).Results1,2-GpG was released from the ODNs as a dinucleoside monophosphate or a dinucleotide. Analyses of the digestion products of ODNs containing a 1,2-GpG cross-link on the 5′ or 3′ terminus revealed that the dinucleotide carries a terminal 5′ phosphate. On the other hand, digestion of the 1,3-GpXpG intrastrand cross-link yielded 3 dinucleoside products with 0, 1, or 2 phosphate groups.ConclusionThe availability of the ODNs carrying the stable isotope-labeled lesions, MS/MS analyses of the cisplatin-modified ODNs, and the characterization of the enzymatic digestion products of these ODNs set the stage for the future LC–MS/MS quantification of the 1,2-GpG, 1,2-ApG, and 1,3-GpXpG lesions in cellular DNA.

► Oligodeoxyribonucleotides with unlabeled and 15N2-labeled cisplatin were prepared.
► These modified DNA were characterized in detail by ESI-MS and MS/MS.
► The enzymatic digestion products for the modified DNA were identified.
► This study will facilitate the future LC–MS/MS quantification of cisplatin DNA adducts.