The Biological Effect Of¹²⁵I Seeds Low Dose Rate Irradiation On Pancreatic Cancer Cell PANC-1and SW1990

Objective:Pancreatic cancer is a high mortality malignant tumor. Recent years125I seeds implantation has achieved satisfactory curative effect in the treatment pancreatic cancer, it is one of the important means in treatment of pancreatic cancer patients, prevention of postoperative recurrence and prolonging survival and improving quality of life. The relative biological effect of125I seeds is1.0～1.5, close to1.3. Because of its low dose rate,125I is not suitable for the rapid growth of the tumor. Within the scope of the low dose rate, tumor killing effect increases with the increase of dose rate, but the relative biological effect has no obvious change. Inverse dose rate effect exists in the low dose rate range. The purpose of this study is to find the biological effect of125I seeds on pancreatic cell by comparing the growth inhibition, cell cycle, cell apoptosis rate after irradiation of125I seeds and60Co-γ ray.Methods:Growth inhibition of the cells was assessed by MTT assay. Cell viability was evaluated by clone formation assay. Cell cycle distribution and apoptosis rate were analyzed by flow cytometry.Results:(1) Cell growth inhibitory rate of PANC-1and SW1990after2、4、6Gy irradiated by60Co-γ ray for2,4,6Gy were23%,39%,53%and20%,42%,50%, irradiated by125I seeds were30%,51%,62%and29%,53%,60%.(2) Dose-survival curve was drawn according to the result of clone formation test. The curve of125I group had a narrower’shoulder’portion than that of60Co-y ray. SF2of PANC-1after irradiation of60Co-γ ray was0.48, and that of125I seeds was0.32which was lower than the former (P<0.05). SF2of SW1990after irradiation of60Co-y ray and125I seeds were0.53and0.36, and the former was higher than the latter (P<0.05). The difference of SF2among different cells was not significant (P>0.05).(3) Cell cycle analysis showed that:125I and60Co-y ray irradiation change cell cycle distribution. They both lead to increasing of cell population in G2/M. The percentage of the cell proportion in G2/M increased with the increasing of dose. G2/M phase cells reached the highest proportion when irradiation dose was6Gy:20.2and23.5of PANC-1cell,22.2and25.0of SW1990cell, the difference of cell proportion in G2/M among different cells or different irradiation was not significant (P>0.05).(4) Cell apoptosis analysis showed that:125I and60Co-γ ray irradiation change apoptosis rate, and apoptosis rate increased with dose increasing of both irradiation. The apoptosis rate reached the highest number when irradiation dose was6Gy:PANC-121.7and47.0, SW199022.1and47.6.Conclusion:(1)125I low dose rate irradiation lead a more significant growth inhibition of Pancreatic cancer cell than60Co-γ ray irradiation.(2)125I decreased pancreatic cancer cell clone formation rate, reducing cell proliferative capacity, and the effect is better than60Co-y ray irradiation.(3)125I blocked cell cycle in G2phase with a dose-dependent manner almost the same with60Co-γ ray irradiation.(4)125I more significantly promoted the apoptosis of pancreatic cancer cell than60Co-γ ray irradiation.125I seeds continuous low dose rate irradiation lead to pancreatic cancer cell growth inhibition, of which the reason is related to promote cell apoptosis.