FACTORS AFFECTING BCNU CYTOTOXICITY IN VITRO

因为我们实验室研究的7个脑瘤细胞系中有6个显示出 在低氧条件下对BCNU的敏感性增加，这似乎是 这是脑瘤细胞的共同特征，但不是普遍特征。此外，还有 是否有一篇已发表的报告显示缺氧时BCNU细胞毒性增加 KHT-IV细胞，但也有报告表明，BCNU产生的 缺氧和缺氧对CHO和EMT6细胞的细胞毒性。目前尚不清楚 这些不同的发现是否仅仅是由于特定于 单个细胞系，或者是由于 遵循实验方案，或两者都遵循，但显然是不正确的 简单根据氧合作用对BCNU细胞毒性进行普遍分类 单元的状态。在脑瘤细胞中表现出增加 低氧条件下对BCNU的敏感性及其依赖关系 关于时间上的现象尚不清楚，需要的缺氧程度 发生的现象未知(只有放射生物学上的低氧细胞 已经研究过)，而这种现象背后的机制尚不清楚。 进一步了解-BCNU在低氧条件下的细胞毒作用 条件下，我们建议使用9L大鼠脑进行时间和机制研究 肿瘤细胞和选定的人脑肿瘤细胞系表现出不同的 对BCNU的敏感性。这些研究的结果应该有助于确定 脑肿瘤中BCNU细胞毒作用增强的决定因素 细胞在低氧条件下，并可能表明它是否有用 探讨改变脑内氧分压的方法和参数 可能应用的原位肿瘤(或可能的其他实体肿瘤) 到临床使用BCNU治疗。也许更有可能的是，这样的数据 在规划药物组合时会很有用，每种药物都可能是 以不同亚群的细胞为目标，如缺氧和缺氧 肿瘤。具体地说，我们建议：1)定义缺氧程度 以及产生增强的BCNU细胞毒性所需的时间 指数级增长的单层培养，并确定类似的 BCNU对其他选定化合物也有增强作用；2)调查 BCNU的细胞毒性是否增强取决于细胞的生长状态 细胞周期与非周期、细胞周期时相、细胞-细胞接触； 以及，3)确定可能的增强机制。

Because 6 of 7 brain tumor cell lines studied in our laboratory show an increased sensitivity to BCNU under hypoxic conditions, this appears to be a common, but not universal, trait of brain tumor cells. Moreover, there is one published report showing increased BCNU cytotoxicity in hypoxic KHT-iv cells, but there are also reports showing that BCNU produces equal cytotoxicity in oxic and hypoxic CHO and EMT6 cells. It is not known whether these different findings are due solely to differences specific to individual cell lines, or to the considerable differences in the experimental protocol followed, or to both, but clearly it is incorrect to universally classify BCNU cytotoxicity simply according to oxygenation status of the cells. In brain tumor cells that exhibit increased sensitivity to BCNU under hypoxic conditions, the dependence of this phenomenon on timing is not known, the degree of hypoxia needed for the phenomenon to occur is not known (only radiobiologically hypoxic cells have been studied), and the mechanisms underlying this phenomenon are not known. To further understand the cytotoxic effects of -BCNU under hypoxic conditions, we propose timing and mechanistic studies using 9L rat brain tumor cells and selected human brain tumor cell lines that exhibit varying sensitivity to BCNU. Results of these studies should help identify the determinants underlying the increased cytotoxicity of BCNU in brain tumor cells under hypoxic conditions, and may suggest whether it would be useful to investigate means and parameters for altering oxygen tension in brain tumors (or possibly other solid tumors) in situ for possible applications to clinical treatment with BCNU. Perhaps more likely is that such data would be useful in planning combinations of drugs, each of which might be targeted towards a separate subpopulation of cells, eg oxic and hypoxic, in the tumor. Specifically, we propose to: 1) define the degree of hypoxia and the timing required to produce enhanced BCNU cytotoxicity in exponentially-growing monolayer cultures, and determine whether similar enhancement of BCNU occurs for other selected compounds; 2) investigate whether the enhancement of BCNU cytotoxicity depends on the growth status of the cells (cycling vs noncycling, cell cycle phase, cell-cell contact); and, 3) identify possible mechanisms of the enhancement.