Effects of Cisplatin on the Radiation Response and DNA Damage Markers in Peripheral Blood Lymphocytes <i>Ex Vivo</i>

Platinum-based radiochemotherapy is associated with hematologic side effects, impacting patient outcomes. However, the mechanisms of action of cisplatin and its interaction with ionizing radiation (IR) are still not fully understood clinically and for biodosimetry in radiotherapy. For this purpose, healthy donors’ peripheral blood lymphocytes (PBLs) were pretreated with cisplatin in a pulse (1-4h) or continuous (24h) regime followed by X-rays. DNA damage was assessed as DNA double-strand breaks using repair foci of yH2AX and 53BP1 after 0.5h and 24h in G1 PBLs, and the proliferation-based cytokinesis-block micronucleus assay. Additionally, cell death and proliferation activity were measured. Unlike a 1h pulse, a 24h cisplatin pretreatment caused a concentration-dependent increase in cisplatin-induced foci while decreasing IR-induced foci, especially 24h after irradiation. This was accompanied by increased apoptosis, with cisplatin and IR having additive effects. Both genotoxins alone caused a dose-dependent increase in micronuclei, while cisplatin significantly reduced binuclear cells, especially after 24h treatment, leading to lower micronuclei frequencies post-irradiation. Our results show that prolonged cisplatin exposure, even at low concentrations, impacts the vitality and division activity of PBLs, with significantly stronger effects post-irradiation. This has major implications and must be considered for the detection of DNA damage-associated biomarkers in PBLs used in clinical prediction or biodosimetry during radiotherapy.