| Objective: To explore the effect of arsenic trioxide (Arsenic trioxide, As2O3) and As2O3 combined with radiation for the growth inhibition of esophageal cancer cell line -Eca109 and to analysis the impact of As2O3 joined with radiation for the cell cycle and apoptosis of Eca109 in order to provide a theoretical basis for As2O3 applied the treatment of esophageal cancer.Methods: (1) As2O3 on the inhibition of proliferation: The inhibitory effect on proliferation was measured by MTT assay when Eca109 was treated by 0.05μmol/L, 0.10μmol/L, 0.15μmol/L, 0.20μmol/L, 0.25μmol/L, 0.30μmol/L, 0.35μmol/L, 0.40μmol/L, 0.45μmol/L, 0.50μmol/L As2O3 for four different treatment times (12h, 24h, 48h, 72h); (2) Radiation on the inhibition of proliferation: The inhibitory effect on proliferation Eca109 was measured by MTT assay when Eca109 was treated by 0.5Gy, 1Gy, 2Gy, 4Gy, 6Gy, 8Gy radiation for four different treatment times (12h, 24h, 48h, 72h); (3) As2O3 combined with radiation on the inhibition of proliferation: The inhibitory effect on proliferation was measured by MTT assay when Eca109 was treated by two concentrations of As2O3 (0.20μmol/L, 0.25μmol/L) combined with radiation (2Gy, 4Gy) for four different treatment times (12h, 24h, 48h, 72h); (4) As2O3 combined with radiation on the cell cycle and apoptosis of Eca109 cell: The effect on the cell cycle and apoptosis was detected by flow cytometry when Eca109 was treated by 0.20μmol/L As2O3 combined with 2Gy radiation for two different treatment times (48h, 72h); (5) The description changes of cyt-c and MnSOD were detected by Western blotting when Eca109 was treated by 0.20μmol/L As2O3 combined with 2Gy radiation for 48h.Results: (1) As2O3 whose concentration range between 0.05 and 0.50μmol / L was able to a certain degree to inhibit the proliferation of esophageal cancer cells-Eca109. With the concentration increasing and the time prolonging, inhibition of cell proliferation enhanced. When the concentration between 0.05 and 0.20μmol/L, inhibition rate increased more moderate, but when exceeds 0.25μmol/L, it increased rapidly. 0.20～0.25μmol/L was a buffer area for inhibition rate from low to high. (2) Radiation whose dose range between 0.5 and 8Gy was able to a certain degree to inhibit the proliferation of esophageal cancer cells-Eca109. When the dose between 0.5 and 2Gy, inhibition rate either decreased or had no change, but when the dose exceeded 4Gy, inhibition rate increased rapidly. 2～4Gy was a buffer area for inhibition rate from low to high. (3) Compared with drug group or irradiation group, the inhibition rate of joined group was higher in the corresponding period times. What was more, it exceeded to the sum of inhibition rate of drug group and irradiation group. With the time prolonging, inhibition rate of every joint group increased. The largest of cell inhibitory rate was 83.56%, which occurred in the joint group after 72 hours. It had significant difference when compared with other joined group in the corresponding period(P=0.000～0.001). However, the comparison of the two joint group which was As2O3 (0.25μmol/L) combined with radiation (2Gy) and As2O3 (0.20μmol/L) combined with radiation (4Gy) had no significant difference in the corresponding period times ( P=0.057～0.298). (4) Flow cytometry results showed that the highest apoptosis rate occurred at 72 hours in the joint group which was 12.26%. Compared with single drug group or single radiation group, it had significant difference (P=0.008～0.046). The most obvious change of cell cycle happened in the joint Group after 72 hours, where G2/M phase arrest occurred, and the proportion of this period was 27.5% (P=0.000). (5) Western blotting analysis revealed that cyt-c in each group did not change significantly (P=0.27～0.86), while MnSOD expression in the treatment group had reduced, and the joint group which reduced the most obviously was As2O3 (0.20μmol/L) combined with radiation (2Gy). The comparison of any two group had significant difference (P=0.000～0.028).Conclusion: (1) With a clear dose and time effect, As2O3 could inhibit the proliferation of esophageal cell line-Eca109. (2) As2O3 had a synergistic effect to improve radiation's inhibition on Eca109 cells. (3) Via influencing cell cycle and inducing apoptosis, As2O3 could enhance radiation's killing effect on Eca109 cells; (4) Radiation could reduce the expression of MnSOD protein, and this effect could be significantly enhanced when combined with As2O3. Neither individual nor joints had effect on the expression of cyt-c.
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