Role of Secondary Low-Energy Electrons in the Concomitant Chemoradiation Therapy of Cancer

Solid films of DNA with and without the chemotherapeutic agent cisplatin bonded to guanine were bombarded with electrons of 1, 10, 100, and 60 000 eV causing single and double strand breaks. In the presence of cisplatin this damage was increased by factors varying from 1.3 to 4.4 owing to an increase in bond dissociation triggered by the formation of transient anions. This mechanism may lie at the basis of the efficiency of concomitant cisplatin-radiation therapy.

Figure 1

Enhancement of damage arising from the bonding of 2 and 8 cisplatin molecules to DNA as a function of electron energy. The exposure response curve for production of SSB by 100 eV electrons is shown in the upper inset.

Figure 2

Comparison of the yield of SSB (A) and DSB (B) as a function of different cisplatin to plasmid ratios. The yields were obtained from exposure curves of 5 ML cisplatin/plasmid mixture deposited on a tantalum substrate and bombarded with $100\pm 0.5\mathrm{eV}$ electrons.