Tandem mass spectrometry for the determination of the sites of DNA interstrand cross-link.

Formation of DNA interstrand cross-link is implicated in the mechanism of anticancer activity of some drugs. Here we examined the fragmentation of deprotonated ions of double-stranded oligodeoxynucleotides (ODNs) that are covalently held together with either a mitomycin C or a 4,5',8-trimethylpsoralen. Our results showed that, upon collisional activation, the covalently-bound duplex ODNs cleaved to give a series of wn and [an-base] ions; the sites of interstrand cross-linking could be determined from the mass shifts of some product ions. In addition, compared with the product-ion spectra acquired on an ion trap, those obtained from sustained off-resonance irradiation-collisionally activated dissociation (SORI-CAD) on a Fourier transform mass spectrometer offered high mass-resolving power, which facilitated unambiguous assignment of product ions and made it an effective method for locating the cross-linking sites.