Pouget, J-P., Frelon, S., Ravanat, J-L., Testard, I., Odin, F. and Cadet, J. Formation of Modified DNA Bases in Cells Exposed either to Gamma Radiation or to High-LET Particles. Radiat. Res. 157, 589–595 (2002).The aim of the present study was to measure the formation of eight base modifications in the DNA of cells exposed to either low-LET (60Co γ rays) or high-LET (12C6 particles) radiation. For this purpose, a recently optimized HPLC-MS/MS method was used subsequent to DNA extraction and hydrolysis. The background level of the measured modified bases and nucleosides was shown to vary between 0.2 and 2 lesions/106 bases. Interestingly, thymidine glycols constitute the main radiation-induced base modifications, with an overall yield of 0.097 and 0.062 lesion/106 bases per gray for γ rays and carbon heavy ions, respectively. Both types of radiations generate four other major degradation products, in the following order of decreasing importance: FapyGua > 5-HmdUrd > 5-FordUrd > 8-oxodGuo. The yields of formation of FapyAde and 8-oxoAde are one order of magnitude lower than those of the related guanine modifications, whereas the radiation-induced generation of 5-OHdUrd was below the limit of detection of the assay. The efficiency for both types of radiation to generate base damage in cellular DNA is low because the highest yield per gray was 0.097 thymine glycols per 106 DNA bases. As a striking observation, the yield of formation of the measured DNA lesions was found to be, on average, twofold lower after exposure to high-LET radiation (12C6 ) than after exposure to low-LET γ radiation. These studies show that the HPLC-MS/MS assay provides an accurate, reliable and sensitive method for measuring cellular DNA base damage.

During the last decades, new radionuclide-based targeted therapies have emerged as efficient tools for cancer treatment. Targeted radionuclide therapies (TRT) are based on a multidisciplinary approach that involves the cooperation of specialists in several research fields. Among them, radiobiologists investigate the biological effects of ionizing radiation, specifically the molecular and cellular mechanisms involved in the radiation response. Most of the knowledge about radiation effects concerns external beam radiation therapy (EBRT) and radiobiology has then strongly contributed to the development of this therapeutic approach. Similarly, radiobiology and dosimetry are also assumed to be ways for improving TRT, in particular in the therapy of solid tumors which are radioresistant. However, extrapolation of EBRT radiobiology to TRT is not straightforward. Indeed, the specific physical characteristics of TRT (heterogeneous and mixed irradiation, protracted exposure and low absorbed dose rate) differ from those of conventional EBRT (homogeneous irradiation, short exposure and high absorbed dose rate), and consequently the response of irradiated tissues might be different. Therefore, specific TRT radiobiology needs to be explored. Determining dose-effect correlation is also a prerequisite for rigorous preclinical radiobiology studies because dosimetry provides the necessary referential to all TRT situations. It is required too for developing patient-tailored TRT in the clinic in order to estimate the best dose for tumor control, while protecting the healthy tissues, thereby improving therapeutic efficacy. Finally, it will allow to determine the relative contribution of targeted effects (assumed to be dose-related) and non-targeted effects (assumed to be non-dose-related) of ionizing radiation. However, conversely to EBRT where it is routinely used, dosimetry is still challenging in TRT. Therefore, it constitutes with radiobiology, one of the main challenges of TRT.