| Latest 50 years, the incidence of lung cancer increased significantly in worldwide. According to statistics, the incidence rate of lung cancer has been on the top of various tumors in male in some European, American countries and big cities of China. In recent years, the incidence rate of lung cancer in women has increased significantly. Lung cancer is a kind of malignant tumor which has the fastest growing in morbidity and mortality, is the biggest threat to human health and lives. While the effective treatment of lung cancer is not satisfactory, the overall cure rate and the 5-year survival rate are still lower than 15%.The method of 125I particles interstitial brachytherapy to tumor is a low-dose-rate but continuing ionizing radiation treatment. As an independent treatment, it has been widely used in the treatment of prostate cancer and other kinds of tumor in foreign countries, and has been able to reach a satisfactory local control rate in long-term. The treatment of radioactive seed brachytherapy for tumor is applied more and more extensively in clinics, and the scope of its application is gradually expanding, however, the mechanism of treatment has not been clear yet.The effects of 125I seeds on tumor treatment has a close correlation with particle activity, total dose and irradiation time. It has a high clinical value to study the ability of controlling lung cancer with 125I seeds of different activity in different time. This study discussed the effects and mechanism of curing tumor by radioactive particle.Objective: Take the mice transplantation of tumor Lewis lung cancer as the model, we observe the anti-tumor effect of radioactive particles and the damage to the surrounding normal tissues, and the change of tumor pathology, rate of tumor cell apoptosis and expression of apoptosis associated protein to approach tumor-killing mechanism of 125I particles, providing the basis for clinical treatment of cancer.Methods: Build up the model of transplantation of tumor Lewis lung cancer in 48 mice, which were randomly divided into two groups: 1.0mCi group and 0.5mCi group; each group was divided into control group and experiment group, 8 in control group, 16 in experiment group. One empty particle was implanted into control group, one 1.0mCi particle was implanted into 1.0mCi group, and one 0.5mCi particle was implanted into 0.5mCi group. After that, the maximum tumor diameter (a) and the shortest track (b) were measured by vernier caliper every two days. According to the formula v=ab2/2, tumor volume (mm3) was calculated, tumor growth curve was mapped. The inhibition rate (IR) of tumor in accordance with the following formula, IR=(1-average tumor size of survived mice in experiment group after being radiated/average tumor size of survived mice in control group after being radiated)×100%. Drawing the materials from the position of 0.5cm away from the site of particles, then we observed the change of tumor histomorphology by microtome section of pathology; apoptosis rate was analyzed by flow cytometry; the expression of Bcl-2, Bax, Caspase-9, Caspase-3 protein levels in tumor tissue were detected by immunohistochemical staining for comparison.Results: 1 Change of tumor size 1.1 Tumor of mice in control group grew progressively, tumor increased significantly on the fourth day; tumor volume were increased more on 10±2 days, the tumor became quaggy, the ulcer existed in the skin on the tumor for 15±2 days, the tumor packaged the nearly leg of the mouse for 19±3 days, the mice were difficult in walking; tendency of growth curve presented upward. 1.2 The experiment group of 1.0mCi radioactive particles group: anti-role of radioactive particles on mice was obvious, tumor shrank when 5Gy(4days) irradiation was reached, 10Gy(9days) tumor reduced nearly a half; 1.0mCi group much more decreased compared with control group; tendency of growth curve presented downward. 1.3 The experiment group of 0.5mCi radioactive particles group: when 5Gy(9days) irradiation was reached, the change of tumor volume was not significant, 10Gy(19days) tumor volume increased a bit than before; 0.5mCi group much more decreased compared with control group; tendency of growth curve presented steady, upward a bit. 2 Inhibition rate: inhibitory rate of 5Gy, 10Gy in 1.0mCi group was: 48.7%, 97.8%, respectively,inhibition rate has significant difference(P<0.01); inhibitory rate of 5Gy, 10Gy in 0.5mCi group was: 60.8%, 94.1%, respectively, inhibition rate has significant difference(P<0.01); In two experiment groups under the same radiation dose, inhibition rate had no significant difference in statistics (P> 0.05). 3 Expression on morphology (light microscope) Experiment group: in the center of tumor, necrosis was not obvious, there was no difference with surrounding organization; At position of particle implanted and its ambitus, necrosis was obvious, lots of phlegmasia cells infiltrated at the edge of necrosis. We can saw large area's apoptosis at the edge of necrosis, showing off that nucleolemma crenulated, cellular nucleus concentrated, chromatic agglutinated and crescent formated, partis were broken to pieces to form apoptotic body, vacuole increased in intracytoplasm.Control group: In the center of tumor, necrosis was severe (considered that volume of tumor increased too fast which caused tissue ischemia and necrosis), extensive phlegmonosis cells could be found around the necrosis; At the position of empty particle and its ambitus, few phlegmonosis cells infiltrated. As time prolonged, there was no significant change; it was rarely to see apoptosis phenomenon. 4 Flow cytometry detected apoptosis rate of tumor 1.0mCi group: 5Gy, 10Gy, control group apoptosis rate of tumor were: 52.39%, 31.97±4.84%, 9.55±2.51%,respectively;The apoptosis rate of tumor in experiment group were higher than control group, have significant difference (P <0.01). 0.5mCi group: 5Gy, 10Gy, control group apoptosis rate of tumor were: 20.66±1.92%, 34.52±3.46%, 9.55±2.51%,respectively;The apoptosis rate of tumor in experiment group were higher than control group, have significant difference (P<0.01). Typical subdiploid"apoptotic peak"emerged in DNA histogram of experiment group's sample by flow cytometry. 5 Bcl-2, Bax, caspase-3, caspase-9 protein expression 5.1 Bcl-2 1.0mCi group: 5Gy, 10Gy, control group expression rate of Bcl-2 protein in tumor were: 17.87±1.78%, 15.67±0.99%, 24.46±7.04%,respectively;The expression rate of Bcl-2 protein in tumor of experiment group were lower than control group compared with control group, have significant difference (P <0.01). 0.5mCi group: 5Gy, 10Gy, control group expression rate of Bcl-2 protein in tumor were: 21.29±1.73%, 20.56±2.11%, 27.09±6.53%,respectively;The expression rate of Bcl-2 protein in tumor of experiment group were lower than control group, have significant difference (P <0.01). 5.2 Bax 1.0mCi group: 5Gy, 10Gy, control group expression rate of Bax protein in tumor were: 18.37±2.39%, 30.18±1.03%, 16.11±0.78%,respectively; The expression rate of Bax protein in tumor of experiment group were higher than control group, have significant difference, 5Gy(P<0.05), 10Gy(P<0.01). 0.5mCi group: 5Gy, 10Gy, control group expression rate of Bcl-2 protein in tumor were: 17.86±1.58%, 23.01±2.80%, 16.33±1.46% , respectively; The expression rate of Bcl-2 protein in tumor of experiment group were higher than control group, have significant difference (P<0.01). 5.3 Caspase-9 1.0mCi group: 5Gy, 10Gy, control group expression rate of Caspase-9 protein in tumor were: 15.64±2.08%, 30.71±2.15%, 13.15±1.74%, respectively; The expression rate of Caspase-9 protein in tumor of experiment group were higher than control group, have significant difference, 5Gy(P<0.05), 10Gy(P<0.01). 0.5mCi group: 5Gy, 10Gy, control group expression rate of Caspase-9 protein in tumor were: 15.23±1.89%, 21.13±1.37%, 13.33±1.09%, respectively; The expression rate of Caspase-9 protein in tumor of experiment group were higher than control group, have significant difference, 5Gy(P<0.05), 10Gy(P<0.01). 5.4 Caspase-3 1.0mCi group: 5Gy, 10Gy, control group expression rate of Caspase-3 protein in tumor were: 25.10±5.97%, 26.45±5.19%, 12.20±2.01%, respectively; The expression rate of Caspase-3 protein in tumor of experiment group were higher than control group compared with control group, have significant difference (P<0.05). 0.5mCi group: 5Gy, 10Gy, control group expression rate of Caspase-9 protein in tumor were: 24.51±5.33%, 24.18±4.97%, 12.54±1.66 %, respectively; The expression rate of Caspase-3 protein in tumor of experiment group were higher than control group, have significant difference (P<0.05). Conclusion: 1 Mice with implanted tumor were treated by 125I brachytherapy, tumor growth could be controlled effectively; as time prolonged, inhibit rate of tumor increased. 2 Pathology results: necrosis existed at the sites of tumor, apoptosis could be found around necrosis. Apoptosis and necrosis might be a way of particles to kill and wound tumor. 3 Flow cytometry analysis found that being irradiated by particles, apoptosis rate increased obviously. Apoptosis might be a mechanicsm of tumor cell destruction. In small-dose range of irradiation, the rate of apoptosis was increased with increased cumulative radiation dose. 4 Low-dose irradiation treatment could decrease the protein expression of apoptosis inhibiting gene Bcl-2 was decreased, protein expression of apoptosis inducing gene Bax was increased, apoptosis procedure was switched on. 5 Low-dose irradiation treatment could heighten protein expression of Caspase-9, Caspas-3, inducing tumor apoptosis, killing tumor at last. This might be one of the ways that low-dose radiation induced apoptosis to killing tumor.
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