PO-129 In vitro radiosensitivity and repair kinetics of pbmcs from prostate cancer patients and healthy donors evaluated by comet assay

Introduction A high cellular radiosensitivity is connected with a risk for development of severe side effects after radiotherapy. In this study we have attempted to find a correlation between the initial radiosensitivity of in vitro irradiated peripheral blood mononuclear cells (PBMC) of prostate cancer patients and the adverse side effects of radiotherapy. Material and methods PBMCs isolated from 7 prostate cancer patients, before the onset of radiotherapy and 3 healthy men were exposed in vitro to 2 Gy of x-ray radiation (Varian, 6 MeV). Following irradiation cell death was measured using the Annexin V/PI assay. DNA repair kinetics (0 and 24 hour after irradiation) was performed using the comet assay, and the results were expressed as% of tail DNA. Acute toxicity were graded according to the EORTC radiation morbidity scoring scale. Results and discussions Our data show that the in vitro irradiation of PBMCs in prostate cancer patients initially caused a significantly higher DNA damage than in the control group of healthy donors. After a repair time of 24 hour, samples from all healthy donors showed no residual DNA damage (average 2.6%) in PBMCs. If all patients are observed for 0 hour and 24 hour after in vitro PBMCs irradiation then there is a significant reduction in the degree of DNA damage, from 35.5 to 30.4 tail% DNA. What is also important is that 4 patients had a very low level of DNA damage, which can be considered as normal cellular reaction to irradiation, while 3 patients had a very high level of damage. Also, in 5 out of 7 examined prostate cancer patients, there was an increase in the percentage of PBMCs in the early and late stages of apoptosis 24 hour after in vitro irradiation of their PBMCs. Most patients had mild side reactions to radiotherapy and were graded as grade 1 (per EORTC scale). Only in 1 of 7 patients observed side effects are classified as grade 2 and this is in correlation with a very high level of DNA damage (82.25% initial, versus 64.77% 24 hour after in vitro irradiation). Conclusion Our study was insufficient to reveal the relationship between the risk of developing side effects to radiotherapy and the sensitivity of PBMCs irradiated in vitro , measured by comet assay. A larger number of patients and further studies are necessary to confirm the potential application of the comet assay.