Miyagi Y, Zhang H, Wheeler K T
Department of Radiation Oncology, Bowman Gray School of Medicine of Wake Forest University, Winston-Salem, North Carolina 27157, USA.
Radiat Res. 1997 Jul;148(1):29-34.
Using a variety of techniques, several laboratories have recently demonstrated the feasibility of using radiation-induced DNA strand breaks and/or DNA-protein crosslinks (DPCs) to detect and/or quantify hypoxic cells in tumors and normal tissues. However, if strand breaks and/or DPCs are to be used to estimate the hypoxic fraction or the fractional hypoxic volume of tumors and normal tissues, their formation as a function of the oxygen concentration near the DNA must be relatively independent of the biological properties of these cells. In the present study, the shape of the oxygen dependence curves and the K(m) values for radiation-induced strand breaks and DPCs were measured by alkaline elution for proliferative (P) and quiescent (Q) cells of the mouse mammary adenocarcinoma, line 66. The sigmoidal shape of the oxygen dependence curves, the K(m) for strand breaks (approximately 0.027 mM) and the K(m) for the formation of DPCs (approximately 0.020 mM) were identical for the P and Q cells of line 66. Consequently, the proliferative status of these tumor cells had no measurable influence on the oxygen-dependent formation of radiation-induced strand breaks and DPCs. In addition, the percentage of the DNA retained on the filters after approximately 24 ml of elution without proteinase K in the lysis solution, a parameter equal to the sum of the strand breaks and DPCs that has been shown to be proportional to the percentage of hypoxic cells in the sample, was not significantly different for fully oxygenated or fully hypoxic populations from five tumor cell lines that varied in species, site of origin, proliferative status and/or properties of the proteins which are intimately associated with their DNA. These data indicate that the formation of radiation-induced strand breaks and DPCs depends predominantly on the oxygen concentration in the microenvironment around the DNA, and only minimally on the biological properties of the cells.
最近，几个实验室运用多种技术证明了利用辐射诱导的DNA链断裂和/或DNA-蛋白质交联（DPC）来检测和/或定量肿瘤及正常组织中缺氧细胞的可行性。然而，如果要利用链断裂和/或DPC来估计肿瘤及正常组织的缺氧分数或缺氧体积分数，那么它们作为DNA附近氧浓度函数的形成过程必须相对独立于这些细胞的生物学特性。在本研究中，通过碱性洗脱法测量了小鼠乳腺腺癌66号线增殖（P）细胞和静止（Q）细胞辐射诱导的链断裂和DPC的氧依赖性曲线形状及K(m)值。66号线P细胞和Q细胞的氧依赖性曲线呈S形，链断裂的K(m)（约0.027 mM）和DPC形成的K(m)（约0.020 mM）相同。因此，这些肿瘤细胞的增殖状态对辐射诱导的链断裂和DPC的氧依赖性形成没有可测量的影响。此外，在裂解液中不添加蛋白酶K、洗脱约24毫升后保留在滤膜上的DNA百分比，这个等于链断裂和DPC总和且已被证明与样品中缺氧细胞百分比成正比的参数，对于来自五个肿瘤细胞系的完全氧合或完全缺氧群体而言并无显著差异，这五个肿瘤细胞系在物种、起源部位、增殖状态和/或与DNA紧密相关的蛋白质特性方面各不相同。这些数据表明，辐射诱导的链断裂和DPC的形成主要取决于DNA周围微环境中的氧浓度，而对细胞生物学特性的依赖极小。
