A Comparison of the Biological Effects of (125)I Seeds Continuous Low-Dose-Rate Radiation and (60)Co High-Dose-Rate Gamma Radiation on Non-Small Cell Lung Cancer Cells

OBJECTIVES: To compare the biological effects of (125)I seeds continuous low-dose-rate (CLDR) radiation and (60)Co γ-ray high-dose-rate (HDR) radiation on non-small cell lung cancer (NSCLC) cells. MATERIALS AND METHODS: A549, H1299 and BEAS-2B cells were exposed to (125)I seeds CLDR radiation or (60)Co γ-ray HDR radiation. The survival fraction was determined using a colony-forming assay. The cell cycle progression and apoptosis were detected by flow cytometry (FCM). The expression of the apoptosis-related proteins caspase-3, cleaved-caspase-3, PARP, cleaved-PARP, BAX and Bcl-2 were detected by western blot assay. RESULTS: After irradiation with (125)I seeds CLDR radiation, there was a lower survival fraction, more pronounced cell cycle arrest (G(1) arrest and G(2)/M arrest in A549 and H1299 cells, respectively) and a higher apoptotic ratio for A549 and H1299 cells than after (60)Co γ-ray HDR radiation. Moreover, western blot assays revealed that (125)I seeds CLDR radiation remarkably up-regulated the expression of Bax, cleaved-caspase-3 and cleaved-PARP proteins and down-regulated the expression of Bcl-2 proteins in A549 and H1299 cells compared with (60)Co γ-ray HDR radiation. However, there was little change in the apoptotic ratio and expression of apoptosis-related proteins in normal BEAS-2B cells receiving the same treatment. CONCLUSIONS: (125)I seeds CLDR radiation led to remarkable growth inhibition of A549 and H1299 cells compared with (60)Co HDR γ-ray radiation; A549 cells were the most sensitive to radiation, followed by H1299 cells. In contrast, normal BEAS-2B cells were relatively radio-resistant. The imbalance of the Bcl-2/Bax ratio and the activation of caspase-3 and PARP proteins might play a key role in the anti-proliferative effects induced by (125)I seeds CLDR radiation, although other possibilities have not been excluded and will be investigated in future studies.