Low-energy electron-induced DNA damage : product analysis and mechanistic studies of damage in short oligonucleotides
SubjectÉlectrons de basse énergie
The major objective of our group is to understand the mechanism of DNA damage induced by secondary low-energy electrons (LEE) arising from ionizing radiation and its relationship to radiosensitization and radiotherapy. Prof. Sanche has developed a novel low-energy electron irradiation system in which a relatively large area of thin films of DNA constituents can be irradiated with mono-energetic electrons under ultra high vacuum. This permits the irradiation of target DNA and the formation of sufficient degraded material to allow for chemical analysis (HPLC, GC/MS, and LC/MS/MS) of products remaining on the target surface, so as to elucidate the mechanism of LEE-induced DNA damage. My project focuses on simple systems, in which small DNA components nucleosides (dThd), nucleotides (pT, Tp, pTp), oligonucleotides (TT and TTT) and modified oligonucleotides (T5BrUT) are exposed to low-energy electrons, and the subsequent reactions are studied by chemical analysis of the products. My studies revealed three mechanisms of LEE-induced fragmentation reactions in DNA: 1) the terminal phosphate group has a larger cross-section in LEE-induced DNA damage; 2) initial LEE capture and subsequent bond breaking within the intermediate anion depend on the sequence and electron affinity of the bases; and 3) at 10 eV, one electron might induce double events. This study provides a chemical basis for the formation of DNA strand breaks by the interaction of LEE with DNA.