DNA Crosslinkomics

DNA-DNA crosslinks, especially interstrand crosslinks (ICLs), cause cytotoxicity via blocking replication and transcription. Most measurements of ICLs lack sensitivity and structural information. Here, a high resolution, accurate mass spectrometry (HRMS) method was developed to comprehensively determine the untargeted, totality of DNA crosslinks, a.k.a. DNA crosslinkomics. Two novel features were introduced into this method: the accurate mass neutral losses of both two 2-deoxyribose (dR) and one dR groups will screen for ICLs as modified dinucleosides; the accurate mass neutral losses of both of the two nucleobases and one nucleobase will detect unstable DNA crosslinks, that could undergo depurination. Our crosslinkomics approach was tested by screening for crosslinks in formaldehyde- and chlorambucil-treated calf thymus DNA. The results showed that all expected drug-bridged crosslinks were detected successfully, along with various unexpected crosslinks. Using HRMS, the molecular formula and chemical structures of these unexpected crosslinks were determined. The formation of apurinic/apyrimidinic (AP) site-derived crosslinks, at levels comparable to those for drug-bridged crosslinks, highlighted their novel, potential role in cytotoxicity. Our new crosslinkomics approach can detect expected and unexpected environmental and drug-induced crosslinks in biological samples. This broadens the existing cellular DNA adductome and offers the potential to become a powerful tool in precision medicine.