Study On Biological Effect Of Prolonged Irradiation On Nasopharyngeal Carcinoma

Part I Effect of prolonged irradiation on killing mouse nasopharyngeal carcinoma CNE-2Z cellsPurpose:To examine the effects of the prolonged irradiation on mouse nasopharyngeal carcinoma CNE-2Z cells as well as changes in expressions of the related proteins Bcl-2and Bax by simulating accurate radiotherapy. Methods Male mice with nasopharyngeal carcinoma were randomly divided into4groups with10in each:sham-irradiated, regularly-irradiated, simulative IMRT, and simulative IGRT.(1) The sham-irradiated group was irradiated triply for1min each time for a total time of6min.(2) The regularly-irradiated group was irradiated15min in total.(3) The IGRT simulated group was irradiated30min in total. The doses delivered for the simulative groups were equivalent to that in the regularly-irradiated group. For each dose level, the plans were made by physicists as in practical treatments and applied separately. The total dose delivery includes7fractions with a total time of15min for the simulative IMRT group and30min for the simulative IGRT group. All the mice were executed at24hours after irradiation respectively. By using the methods of TUNEL and immunohistochemical staining, the changes of apoptosis index(AI) and level of Bcl-2, Bax protein expression in tumor tissues were examined. Results:1. The difference in the apoptosis index between the groups is statistically significant (P<0.01). The lowest index was found in the sham-irradiated group while the highest was observed in the regularly-irradiated group. Compared to the regularly-irradiated group, the IMRT and IGRT simulated groups have lower apoptosis indices, which were statistically significant (P<0.01). No difference was seen between the simulative IMRT and the simulative IGRT groups (p=0.05). Compared to the sham-irradiated group, the apoptosis index increased significantly for other groups (P<0.01).2. Differences were observed between the groups in the quasi-quantitative measurement of the Bcl-2proteins. Among them, the sham-irradiated group had the highest Bcl-2concentration while the regularly-irradiated group had the lowest. Compared to the sham-irradiated group, all other groups had significantly lower values in the concentration of Bcl-2(P<0.01). Although the simulative IMRT and IGRT groups had seemingly higher Bcl-2concentrations than the regularly-irradiated group, the differences were not statistically significant (P=0.22).3. Differences were also observed between the groups for the concentration of the Bax protein measured quasi-quantitatively. The highest concentration belonged to the sham-irradiated group. The concentration increased for all remaining groups. In contrast to the regularly-irradiated group, the simulative IMRT and IGRT groups had lower Bax concentrations while the latter had the lowest (P<0.01). Conclusion:Prolonged irradiation with high energy X-rays negates the killing of the nasopharygeal carcinoma CNE-2Z cells in the mouse. It has been reflected in the decrease in the apoptosis index as well as the reduction in the BAX concentration increase and Bcl-2decrease. This suggests the total dose should be appropriately escalated to make up for the loss due to the radiobiological effect.Part II Effect of prolonged irradiation on expression of MMP-9and E-cadherin in mouse nasopharyngeal carcinoma CNE-2Z cellsPurpose:To investigate the effect of the prolonged irradiation on the expression of the matrix metalloproteinase (MMP-9) and E-cadherin in the mouse nasopharyngeal carcinoma CNE-2Z cells by simulating accurate irradiation. Methods:Male mice with nasopharyngeal carcinoma were randomly divided into4groups with10in each: sham-irradiated, regularly-irradiated, simulative IMRT, and simulative IGRT.(1) The sham-irradiated group was irradiated triply for1min each time for a total time of6min.(2) The regularly-irradiated group was irradiated15min in total.(3) The IGRT simulated group was irradiated30min in total. The doses delivered for the simulative groups were equivalent to that in the regularly-irradiated group. For each dose level, the plans were made by physicists as in practical treatments and applied separately. The total dose delivery includes7fractions with a total time of15min for the simulative IMRT group and30min for the simulative IGRT group. All the mice were executed at24hours after irradiation respectively the changes of MMP-9E-cadherin expression in tumor tissues were examined. Results:Compared to the sham-irradiated group, the decrease of MMP-9and increase of E-cadherin were significant for the remaining groups (P<0.01). Both simulative IMRT and IGRT groups yielded higher MMP-9expresions and lower E-cadherin expressions than the regularly-irradiated group (P<0.01). The expressions of MMP-9and E-cadherin showed no significant difference between the two simulative groups. Conclusion:At the same dose level and to a certain extent, prolonged irradiation with high energy X-rays leads to an increase in the expression of MMP-9and a decrease in the expression of E-cadherin. Therefore it weakens the ability of radiotherapy to depress the metastasis and migration of nasopharyngeal carcinoma CNE-2Z cells, and eventually affects the treatment outcome.