APOPTOSIS OF PERIPHERAL BLOOD LYMPHOCYTES OF PROSTATE CANCER PATIENTS INDUCED BY IN VITRO IRRADIATION

Philchenkov A.A., Zavelevich M.P., Domina E.A., Glavin А.А.

• R.E. Kavetsky Institute of Experimental Pathology, Oncology and Radiobiology, NAS of Ukraine, Kyiv, Ukraine

High-dose radiation therapy required for treating radioresistant tumors such as prostate cancer (PC) could entail the increased risk of postradiation complications. The individual radiation sensitivity (IRS) should be taken into account for predicting side effects of radiation therapy. The assessment of apoptosis in peripheral blood lymphocytes (PBL) of patients may be considered as one of the methods for IRS estimation. Aim: to study the level of apoptosis induced by in vitro test-irradiation of PBL isolated from PC patients throughout the course of radiation therapy and its probable correlation with content of reactive oxygen species (ROS), the frequency of postradiation chromosomal abnormalities and several clinical indices. Object and methods: 16 PC patients, predominantly stages II–III were included in the study. Apoptosis level was estimated in PBL isolated prior to the treatment, after the first fraction of therapeutic irradiation and after the completion of the treatment. Apoptotic fraction in PBL was determined by flow cytometry following 48-h culture of isolated cells without mitogen stimulation both in untreated samples and in samples subjected to in vitro X-ray test-exposure prior to the initiation of culture. Fe²⁺ induced ROS generation in blood plasma was measured with N,N-diethyl-paraphenylenediamine. Metaphase analysis of chromosomal aberrations was provided following the «provocative» X-ray exposure of PBL culture at the end of the G₂-phase of the mito­tic cycle (1.5 Gy). Results: The correlation between the values of the apoptotic fraction in PBL samples with/without in vitro test-irradiation has been found both in PBL isolated prior to the beginning (r = 0.88) and after the first fraction of the therapeutic irradiation (r = 0.77). The wide range of the apoptotic index in PBL from PC patients suggests the substantial variability of IRS. The apoptotic fraction in PBL correlated with ROS level in blood plasma in the samples obtained following the first fraction of the radiotherapy (r = 0.77) but not in the samples obtained prior to the beginning of the treatment. According to G₂-assay, the frequency of radiation-­induced chromatid aberrations was within the range of 11.0–19.0 aberrations per 100 metaphases. Conclusions: The apoptotic indices in in vitro test-irradiated PBL isolated from PC patients subjected to radiotherapy correlated with those in PBL cultured without test-irradiation. Only weak correlation is revealed between the level of spontaneous apoptosis and ROS level in blood plasma. The level of spontaneous apoptosis does not correlate with clinical indices.