| Research on Radiosensitivity of Lung Adenocarcinoma in Vitro to RecombinantHuman Adenovirus-p53 InjectionPrefaceLung cancer was divided mainly into two types: SCLC and NSCLC. 80％of lung cancer is NSCLC which includes adenocarcinoma(25％), squamous-carcinoma(35％), undifferentiated carcinoma of megacell (15％) and others. Operation is a preferred therapeutic method, but 70％～80％of patients who are diagnosed as lung carcinoma exactly, have been in advanced stage. Radical operation has been impossible. So radiotherapy is one of the most important methods for unresectable carcinoma, and radiosensitivity is a key point for the effect. It's important for enhancing the radiosensitivity to combine with various kinds of antineoplastic drugs and biology instruments when using ionizing radiation to treat tumor.In the recent years, with the development of oncomolecularbiology, clinicians have paid closed attention to utilize the gene drugs for enhancing the radiosensitivity.Now we have found that many genes, such as p53 RB and ras et al, are concerned with the occurrence and development of oncoma and sensitivity of radiotherapy. Among them, the p53 gene is studied and researched abundantly, and it has powerful function against tumor. The p53 gene reside in normal cells of human body, 50％of mankind tumor is according with p53 gene mutation including 50％of small cell lung cancer and 70-80％of non small cell lung cancer.PurposeTo evaluate the radiosensitivity caused by rAd-p53 on culutured human lung adenocarcinoma cell line A2 and investigate the possible sensitization mechanism of rAd-p53.Materials and methodsAfter exposed to rAd-p53, viability of cultured human lung adenocarcinoma cells is assessed by MTT assay. MTT was used to analyze the cytotoxics of rAd-p53 in A2 cell line and calculate the ID50 and ID20 value. ID20 was used for the radiosensitivity experiment.The experiment was divided into control(C)group, simple drug(D) group, simple radiation(R)group and radiation plus drug (R+D)group. The cell survival curves were determined by cloning assay and cell clone technique for evaluating the cell lethal effects. The cell cycles and cell apoptosis rates were analyzed by using FCM (Flow cytometry) in the different groups which were given single dose 2Gy radiation.Statistical analysis was done with SPSS 11.5 and Origin 6.0 software. The data was expressed as mean+SD, comparison among groups was performed by One-Way ANOVA, t-test and pearson linear correlation. Significance was accepted when P＜0.05.ResultsDetection of MTT colorimetric assay: the inhibitory action on A2 cells by rAd-p53 appear to be dose-dependent. With the increasing of drug concentration, survival rate of cell decreased. 24h later, ID50 and ID20 of rAd-p53 for A2 cell line were 8.9×109VP/ml and 1.0×109VP/ml. When the concentration less than 1.0×109VP/ml, Cyto- inhibition was not obvious.Experiment result of radiosensitivity indicated that the ability of A2 cell forming colony in the testing group degraded contrasting with C group. With the increasing of radiation does, forming colony ability decreased obviously. With the same radiation does, colony rate in the R+D group was much less than that in the R group. The D0 and Dq values were 1.26Gy and 3.37Gy in R group, and in R+D group, the D0 and Dq values were 0.45Gy and 1.05Gy. The SERD0 and SERDq were 2.8and 3.21, respectively.The measure result of cell cycles by using FCM displayed that the percentage in G2/M phase increased after A2 cell was given by rAd-p53 as well as single dose 2Gy radiation. The cell cycles in G2/M phase were blocked significantly(P＜0.05). Apoptosis rates in the D group was higher than that in the R group, which was 2.37 times and 2.02 times than that in the C group. Apoptosis rates in the R+D group was the highest and was 3.25 times than that in the C group (P＜0.05). Statistical analysis demonstrated that the percentage in G2/M phase had good relationship with apoptosis rates(rs=0.989, P＜0.05)ConclusionrAd-p53 is a potential radiosensitizer for pulmonary adenocarcinoma cell line A2 in vitro. The mechanism of radiosensitization is associated with restraining the repair of sublethal damage to cell, inducing apoptosis and influencing redistributing of cell cycle.
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