Effects and applications of ultrashort-lived prehydrated electrons in radiation biology and radiotherapy of cancer

The subpicosecond-lived prehydrated electron (epre−) is a fascinating species in radiation biology and radiotherapy of cancer. Using femtosecond time-resolved laser spectroscopy, we have recently resolved that epre− states are electronically excited states and have lifetimes of ∼180 fs and ∼550 fs, after the identification and removal of a coherence spike, respectively. Notably, the weakly bound epre− (<0 eV) has the highest yield among all the radicals generated in the cell during ionizing radiation. Recently, it has been demonstrated that dissociative electron transfer (DET) reactions of epre− can lead to important biological effects. By direct observation of the transition states of the DET reactions, we have showed that DET reactions of epre− play key roles in bond breakage of nucleotides and in activations of halopyrimidines as potential hypoxic radiosensitizers and of the chemotherapeutic drug cisplatin in combination with radiotherapy. This review discusses all of these findings, which may lead to improved strategies in radiotherapy of cancer, radioprotection of humans and in discovery of new anticancer drugs.