Urano M, Kuroda M, Reynolds R, Oberley T D, St Clair D K
Department of Radiation Medicine, University of Kentucky Medical Center, Lexington 40536-0084, USA.
Cancer Res. 1995 Jun 15;55(12):2490-3.
This study investigated the in vitro and in vivo radiation response of tumor cells transfected with human manganese superoxide dismutase (MnSOD) cDNA. A major objective was to test the potential tumor suppressive effect of MnSOD in vivo. Tumor cells studied were an in vitro line derived from a murine spontaneous fibrosarcoma, FSa-II, which expressed an undetectable MnSOD activity. These cells were transfected with pSV2-NEO plasmid (NEO line) or cotransfected with MnSOD plasmid plus pSV2-NEO plasmid (SOD lines) as described previously. The cell lines used were SOD-L and SOD-H, which expressed, respectively, low and high MnSOD activities after transfection, and NEO and parental FSa-II controls. Both SOD-L and SOD-H cell lines were slightly more resistant to ionizing radiation than were the two control cell lines when irradiated in vitro in the presence of oxygen. The dose-modifying factors calculated at the survival level of 0.01 were 1.13 and 1.15 for the SOD-L and SOD-H cells, respectively. To investigate potential tumor suppressive effects, animal tumors of 4 mm diameter were irradiated in vivo under hypoxic conditions, and the radiation dose to control one-half of the irradiated tumors (TCD50) was determined for each tumor. The TCD50S obtained on the basis of the tumor control rate in 120 days after irradiation were substantially lower for the SOD-H and SOD-L tumors compared to the NEO tumors. They were 22.9, 28.6, and 47.5 Gy for SOD-H, SOD-L and NEO tumors, respectively. To analyze these data, survival curves were obtained for hypoxic cells by irradiating NEO and SOD-H tumors under hypoxic conditions in vivo and assaying in vitro. Analysis of these curves suggests that the decrease in the TCD50S of SOD tumors is attributable to the reduced tumorigenicity in these tumors. The hypoxic cell survival curves also showed that SOD did not protect cells from radiation in the absence of oxygen. Electron microscopy showed no morphological differences between these cells. These results suggest that the fraction of tumorigenic cells could be reduced by expression of MnSOD, resulting in a substantial decrease in the TCD50.
本研究调查了转染人锰超氧化物歧化酶（MnSOD）cDNA的肿瘤细胞的体外和体内辐射反应。一个主要目标是测试MnSOD在体内的潜在肿瘤抑制作用。所研究的肿瘤细胞是源自小鼠自发性纤维肉瘤FSa-II的体外细胞系，其MnSOD活性检测不到。如前所述，这些细胞用pSV2-NEO质粒转染（NEO系）或与MnSOD质粒加pSV2-NEO质粒共转染（SOD系）。所用的细胞系为SOD-L和SOD-H，转染后分别表达低和高MnSOD活性，以及NEO和亲本FSa-II对照。当在有氧条件下进行体外照射时，SOD-L和SOD-H细胞系对电离辐射的抗性均略高于两个对照细胞系。在存活水平为0.01时计算的剂量修正因子，SOD-L和SOD-H细胞分别为1.13和1.15。为了研究潜在的肿瘤抑制作用，对直径4mm的动物肿瘤在缺氧条件下进行体内照射，并确定每个肿瘤使受照射肿瘤的一半得到控制（TCD50）的辐射剂量。根据照射后120天的肿瘤控制率获得的TCD50，SOD-H和SOD-L肿瘤相比NEO肿瘤显著更低。SOD-H、SOD-L和NEO肿瘤的TCD50分别为22.9、28.6和47.5 Gy。为了分析这些数据，通过在体内缺氧条件下照射NEO和SOD-H肿瘤并进行体外测定，获得了缺氧细胞的存活曲线。对这些曲线的分析表明，SOD肿瘤TCD50的降低归因于这些肿瘤中致瘤性的降低。缺氧细胞存活曲线还表明，在无氧情况下SOD不能保护细胞免受辐射。电子显微镜显示这些细胞之间无形态学差异。这些结果表明，MnSOD的表达可降低致瘤细胞的比例，导致TCD50大幅降低。
