Fast He2+ and C6+ Ion Irradiation of DNA Loaded With Platinum Containing Molecules.

Complexes of plasmid-DNA and dichloroterpyridine platinum (PtTC) molecules are irradiated with fast He2+ and C6+ ions. The results show a significant increase in DNA strand breaks when platinum is present, suggesting a radio-sensitization. The increase in DNA damages is attributed to inner-shell ionization of a platinum atom by secondary electrons, emitted along the He2+ tracks and followed by an Auger effect. Additional experiments, performed in presence of dimethyl sulfoxide (DMSO), a free radical scavenger, indicate that a large part of the DNA damages are mediated by a free radical attack. These findings suggest that the Auger effect, following the ionization of the platinum atom by secondary electrons, leads significantly to radiolysis of the surrounding water; OH free radical clusters are created close to the platinum atom and therefore close to the DNA, inducing efficiently DNA strand breaks. The respective contribution of scavengeable and non-scavengeable effects is quantitatively evaluated. A discussion of the contribution of the Auger effect to scavengeable and non-scavengeable effects is also presented. Considerations of Auger effects in the other atoms constituing the DNA (P, O, C, N) are made. The role of the K shell ionisation in these atoms is investigated in the light of the results obtained when platinum atoms are present. The present results are qualitatively similar to those obtained when soft X-rays photons are used to irradiate such DNA complexes. They suggest a possible application to protocols associating protontherapy (hadrontherapy) and chemotherapy with molecules containing high-Z atoms like cis-dichloro-diamino platin (cis DDP).Research and Applications in Radiobiology with Swift Ion