辐射基因治疗黑色素瘤的实验研究

Experimental research of radiogenic therapy on human melanoma

研究低剂量辐射结合腺病毒(AdCMV)载体介导的p53基因转导对人黑色素瘤A375细胞系基因转移效率和辐射敏感性的影响。用复制缺陷的重组腺病毒载体(AdCMV-p53)介导人p53基因转染1GyX-射线预辐照的A375细胞系,RT-PCR检测mRNA水平,流式细胞仪测定细胞周期阻滞及外源性P53蛋白表达情况,克隆形成率测定辐射后细胞存活率。用携带报道基因的复制缺陷重组腺病毒载体AdCMV-GFP作为对照。实验结果表明,1GyX-射线辐照可较高地增加AdCMV-p53对A375细胞的基因转导效率,转导的外源性野生型p53可在A375(wtp53)细胞中高效表达,并诱导细胞周期G1期阻滞;单纯转导p53对A375细胞无明显诱导凋亡和生长抑制效应;而转导p53后给予X-射线辐射,当剂量达到4Gy及其以上时,48h后AdCMV-p53感染组细胞开始出现明显形态改变,克隆存活率明显低于AdCMV-GFP感染组和未感染组,显示存活曲线下移,4Gy时细胞存活率就减少了1个量级。小剂量辐射既可有效增加AdCMV-p53介导的p53转导,又不会对患者产生明显副作用;转导野生型p53的人黑色素瘤A375细胞系显示P53过表达;过表达的P53蛋白虽然对A375细胞无明显生长抑制及凋亡诱导作用,但可明显增加其辐射敏感性。这表明p53是基因治疗黑色素瘤较好的侯选基因,也为临床上放疗联合基因治疗黑色素瘤提供了实验室依据,即减轻临床上对于辐射敏感性差的肿瘤单纯大剂量照射或单纯基因疗法中rAd-p53制品用量过大而给病人造成的毒副作用。

To investigate the effect of low dose irradiation on gene transfer efficiency and the effect of adenoviral-mediated exogenous P53 overexpression on radiosensitivity of radioresistant human melanoma cell line A375 with wild type p53, control vector, a replication deficient recombinant adenoviral vector containing a CMV promoter and green fluorescent protein （AdCMV-GFP）, was used to transfect the A375 cells preirradiated with or without 1 Gy X-ray radiation. The transduction efficiency of GFP gene was determined with fluorescence microscope directly. A375 cells radiated by 1 Gy X-ray were transfected with a replication deficient recombinant adenoviral vector carrying human wild p53 （AdCMV-P53）, and mRAN level was detected by RT-PCR. The cell cycle delay and the expression of exogenous P53 were detected using flow cytometry （FCM） at different time after transfection. The radiosensivity of A375 cells after p53 transduction was assayed by clonoy formation. We found that 1Gy exposure increased the gene transfer efficiency of A375 cells. The expression of exogenous P53 was found to be 60% to 80% of transfected cells during the first three days after transduction and then declined continuously down to the control level on the day 10. The G1 cell cycle arrest was also observed after p53 gene transfer. A375 cells that were transfected with p53 showed higher sensitivity to X-ray -induced cell killing than those cells that either were transfected with the viral vector carrying a green fluorescent protein gene or were not transfected at all. Low dose ionizing radiation can improve gene transfer efficiency of A375 cells mediated by adenovirus vector. Althrough the overexpresion of exogenous P53 may not inhibit cell growth and induce apoptosis of melanoma cell line A375 in vitro, it made the tumor cells much sensitive to death by irradiation. The data suggested that p53 gene might be a potential gene for melanoma therapy and provide the experimental evidences to clinically using the combination of radiation with gene therapy on melanoma. Namely, there may be a reduction of side effects resulting from high dose radiation on radioresistant tumors or rAd-P53 administration alone in clinical applications.