Mammalian cells loaded with platinum-containing molecules are sensitized to fast atomic ions

Purpose: This work investigates whether a synergy in cell death induction exists in combining atomic ions irradiation and addition of platinum salts. Such a synergy could be of interest in view of new cancer therapy protocol based on atomic ions - hadrontherapy - with the addition of radiosensitizing agents containing high-Z atoms. The experiment consists in irradiating by fast ions cultured cells previously exposed to dichloroterpyridine Platinum (PtTC) and analyzing cell survival by a colony-forming assay. Materials and methods: Chinese Hamster Ovary (CHO) cells were incubated for six hours in medium containing 350 mu M PtTC, and then irradiated by fast ions C6+ and He2+, with Linear Energy Transfer (LET) within range 2-70 keV/mu m. In some experiments, dimethyl sulfoxide (DMSO) was added to investigate the role of free radicals. The intracellular localization of platinum was determined by Nano Secondary Ion Mass Spectroscopy (Nano-SIMS). Results: For all LET examined, cell death rate is largely enhanced when irradiating in presence of PtTC. At fixed irradiation dose, cell death rate increases with increasing LET, while the platinum relative effect is larger at low LET. Conclusion: This finding suggests that hadrontherapy or protontherapy therapeutic index could be improved by combining irradiation procedure with concomitant chemotherapy protocols using platinum salts.