A comparison of the biological effects of 125I seeds continuous low-dose-rate radiation and 60Co high-dose-rate gamma radiation on non-small cell lung cancer cells

Abstract

Objectives: To compare the biological effects of 125I seeds continuous low-dose-rate (CLDR) radiation and 60Co 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 125I seeds CLDR radiation or 60Co 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 125I seeds CLDR radiation, there was a lower survival fraction, more pronounced cell cycle arrest (G1 arrest and G2/M arrest in A549 and H1299 cells, respectively) and a higher apoptotic ratio for A549 and H1299 cells than after 60Co γ-ray HDR radiation. Moreover, western blot assays revealed that 125I 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 60Co 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: 125I seeds CLDR radiation led to remarkable growth inhibition of A549 and H1299 cells compared with 60Co 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 125I seeds CLDR radiation, although other possibilities have not been excluded and will be investigated in future studies.

Fig 1. Clonogenic survival fraction of A549, H1299 and BEAS-2B cells irradiated with ¹²⁵I seeds and ⁶⁰Co γ-rays.

A-C: the difference in the survival fraction of A549, H1299 and BEAS-2B cells between ¹²⁵I seeds CLDR radiation and ⁶⁰Co γ-ray HDR radiation. * indicates a significant difference (P<0.05) when comparing the two radiation treatments and control treatment, and # indicates a significant difference (P<0.05) when comparing ¹²⁵I seeds CLDR radiation and ⁶⁰Co γ-ray HDR radiation of the same doses. D, E: The difference in the survival fraction of the three cell lines receiving the same treatment. * indicates a significant difference (P<0.05). Bars, standard error (SE).

Fig 2. Cell cycle analysis by flow cytometry.

A: G₁ arrest of A549 cells irradiated with the two radiation sources; B, C: G₂/M arrest of H1299 and BEAS-2B cells after irradiation with the two radiation sources. * indicates a significant difference (P<0.05) when comparing 2, 4, 6 and 8 Gy irradiation by the two radiation sources and control (0 Gy) treatment, and # indicates a significant difference (P<0.05) when comparing the two radiation treatments of the same dose. Bars, standard error (SE).

Fig 3. Apoptotic ratio of A549, H1299 and BEAS-2B cells irradiated with ¹²⁵I seeds CLDR radiation and ⁶⁰Co γ-ray HDR radiation.

A-C: the difference in the apoptotic ratio of A549, H1299 and BEAS-2B cells receiving ¹²⁵I seeds CLDR radiation and ⁶⁰Co γ-ray HDR radiation. * indicates a significant difference (P<0.05) when comparing 2, 4, 6 and 8 Gy irradiation by the two radiation sources and control (0 Gy) treatment, and # indicates a significant difference (P<0.05) when comparing the two radiation treatments of the same doses. D, E: the difference in the apoptotic ratios of the three cell lines irradiated with ¹²⁵I seeds and ⁶⁰Co γ-rays. * indicates a significant difference (P<0.05). Bars, standard error (SE).

Fig 4. The expression of Bcl-2 and BAX proteins in A549, H1299 and BEAS-2B cells after exposure to ¹²⁵I seeds CLDR radiation and ⁶⁰Co γ-ray HDR radiation of 4 and 8 Gy.

One representative result of three independent experiments with identical results is shown. Con: control.

Fig 5. The expression of cleaved-caspase-3 and cleaved-PARP proteins in A549, H1299 and BEAS-2B cells after exposure to ¹²⁵I seeds CLDR radiation and ⁶⁰Co γ-ray HDR radiation of 4 and 8 Gy.

One representative result of three independent experiments with identical results is shown.