Relation between DNA repair, apoptosis and chromosomal aberrations in presence of pifithrin-α, an inhibitor of p53

The aim of this study was to investigate the impact of inhibition of p53 in X-irradiated human peripheral blood lymphocytes (HPBL) in the G0 phase of the cell cycle in the presence or absence of pifithrin-α (PFT-α), a specific inhibitor of p53, on repair of DNA damage or induced apoptosis.Lymphocyte (HPBL) cultures were X-irradiated with 3 Gy in the absence or presence of PFT-α. In order to distinguish the effects of PFT-α either on DNA repair or on apoptosis, PFT-α was added to the cultures employing different protocols namely, a) “continuous treatment”, where PFT-α was added four hours before X-irradiation and left until the end of the experiment, b) “pre-treatment”, where PFT-α was added four hours before X-irradiation and removed by washing the cells with phosphate buffered saline (PBS) four hours after irradiation and c) “post-treatment”, where PFT-α was added four hours after irradiation and left in the medium until the harvest. At various times after irradiation of lymphocytes, Single Cell Gel Electrophoresis was performed to detect DNA damage in individual cells. Apoptosis and chromosomal aberrations were quantified at later sampling times following irradiation. The results presented here strengthen the known role of p53 protein in priming apoptotic cell death in HPBL following X-irradiation. Furthermore, our data suggest that the inhibition of p53 by PFT-α affects the repair kinetics of X-ray induced DNA lesions leading to mis-repair events and consequently to an enhancement of cytogenetic damage in HPBL.