Radiosensitivity of human ovarian carcinoma and melanoma cells to γ-rays and protons

Abstract

Introduction: Proton radiation offers physical advantages over conventional radiation. Radiosensitivity of human 59M ovarian cancer and HTB140 melanoma cells was investigated after exposure to γ-rays and protons.

Material and methods: Irradiations were performed in the middle of a 62 MeV therapeutic proton spread out Bragg peak with doses ranging from 2 to 16 Gy. The mean energy of protons was 34.88 ±2.15 MeV, corresponding to the linear energy transfer of 4.7 ±0.2 keV/µm. Irradiations with γ-rays were performed using the same doses. Viability, proliferation and survival were assessed 7 days after both types of irradiation while analyses of cell cycle and apoptosis were performed 48 h after irradiation.

Results: Results showed that γ-rays and protons reduced the number of viable cells for both cell lines, with stronger inactivation achieved after irradiation with protons. Surviving fractions for 59M were 0.91 ±0.01 for γ-rays and 0.81 ±0.01 for protons, while those for HTB140 cells were 0.93 ±0.01 for γ-rays and 0.86 ±0.01 for protons. Relative biological effectiveness of protons, being 2.47 ±0.22 for 59M and 2.08 ±0.36 for HTB140, indicated that protons provoked better cell elimination than γ-rays. After proton irradiation proliferation capacity of the two cell lines was slightly higher as compared to γ-rays. Proliferation was higher for 59M than for HTB140 cells after both types of irradiation. Induction of apoptosis and G2 arrest detected after proton irradiation were more prominent in 59M cells.

Conclusions: The obtained results suggest that protons exert better antitumour effects on ovarian carcinoma and melanoma cells than γ-rays. The dissimilar response of these cells to radiation is related to their different features.

Keywords: apoptosis; cell cycle; melanoma; ovarian carcinoma; protons; γ-rays.

Figure 1

Effects of γ-rays and protons on 59M cell viability 7 days after irradiation, estimated by MTT (A) and SRB assays (B). Data obtained from 4 experiments are presented as means ± SD. Irradiation doses were 2–16 Gy *Statistical significance compared to the control, ^#statistical significance compared to γ-rays; *^,#0.01 < p < 0.05, *^,##0.001 < p < 0.01, ***^,###p < 0.001

Figure 2

Effects of γ-rays and protons on HTB140 cell viability 7 days after irradiation, estimated by MTT (A) and SRB assays (B). Data obtained from 4 experiments are presented as means ± SD. Irradiation doses were 2–16 Gy *Statistical significance compared to the control, ^#statistical significance compared to γ-rays, *^,#0.01 < p < 0.05, **^,##0.001 < p < 0.01, ***^,###p < 0.001

Figure 3

Dose-response curves of 59M cells (A) and HTB140 cells (B) exposed to γ-rays and protons, obtained by clonogenic assay. Irradiation doses were 2–16 Gy. Data obtained from 4 experiments are presented as means ± SD

Figure 4

Dose-dependent cell proliferation of 59M cells (A) and HTB140 cells (B) estimated by BrdU assay. Data obtained from 4 experiments are presented as means ± SD. Irradiation doses were 2–16 Gy *Statistical significance compared to the control, ^#statistical significance compared to γ-rays, *^,#0.01 < p < 0.05, **^,##0.001 < p < 0.01, ***^,###p < 0.001

Figure 5

The effects of γ-rays and proton radiation on cell cycle distribution in 59M (A) and HTB140 (B) cell line, estimated by flow cytometry 48 h after irradiation. Irradiation dose was 8 Gy. Data obtained from 4 experiments are presented as means ± SD *Statistical significance compared to the control, ^#statistical significance compared to γ-rays, *^,#0.01 < p < 0.05, **^,##0.001 < p < 0.01, ***^,###p < 0.001

Figure 6

The effects of γ-rays and proton radiation on apoptosis in 59M and HTB140 cell line, estimated by flow cytometry 48 h after irradiation. Irradiation dose was 8 Gy. Data obtained from 4 experiments are presented as means ± SD *Statistical significance compared to the control, ^#statistical significance compared to γ-rays, *^,#0.01 < p < 0.05, **^,##0.001 < p < 0.01, ***^,###p < 0.001