CONTROL MECHANISM OF RADIORESISTANT HYPOXIC CELLS IN MUTICELLULAR TUMOR SPHEROIDS

本研究建立了含人胰岛素样生长因子-IR基因(A7(R))的人胶质母细胞瘤细胞(A-7)，或与仅含有嘌呤霉素抗性基因的A7(Puro)共转染的人胶质母细胞瘤细胞(A-7)。IGF-IR过表达导致A7(R)球体坏死区消失，而A7(Puro)细胞球体呈中央坏死。结合A7(R)细胞球体内较快的生长速度，提示IGF-IR高表达细胞构成的肿瘤生长较快，坏死率较低。然而，球体中的A7(R)细胞表现出比A7(Puro)细胞更高的放射敏感性，并且这种辐射敏感性依赖于剂量分数的大小。用IGF-IR(R-)基因敲除小鼠的成纤维细胞和转染人IGF-IR基因的细胞(R+)研究了严重缺氧细胞中IGF-IR的作用。在氧分压低于3 mm Hg的低氧条件下，(R+)细胞比(R-)细胞存活时间更长，在低氧条件下比(R-)细胞更耐受辐射。(R+)生长在融合状态的细胞在短时间内从培养皿表面脱落，这表明在严重缺氧条件下，这些细胞倾向于迅速死亡，这取决于细胞密度。

Human glioblastoma cells(A-7)transfected with plasmid containing human IGF-IR cDNA(A7(R)), or co-transfected with that containing only puromycin-resistant gene(A7(puro))were established in this study. Overexpression of IGF-IR resulted in the loss of necrotic zone in A7(R)spheroids, whereas spheroids of A7(puro)cells showed a central necrosis. Together with faster growth rate in the spheroids of A7(R)cells, it was suggested that tumors consisting cells with overexpression of IGF-IR grow faster with reduced formation of necrosis. A7(R)cells in spheroids, however, showed a higher radiosensitivity than A7(puro)cells and the radiosensitivity was dependent on a size of dose fraction.Role of IGF-IR in severely hypoxic cells was studied using fibroblasts derived from knockout mouse of IGF-IR(R-), or cells transfected with human IGF-IR cDNA(R+). (R+)cells survived longer than(R-)cells in a hypoxic condition of less than 3 mm Hg of partial oxygen pressure, and were more radioresistant than(R-)cells in the hypoxic condition. (R+)cells grown in confluent state exfoliated in a short time from the surface of petri dish, indicating that these cells tend to die rapidly depending on the cell density in a severely hypoxic condition.