O'Hara M D, Pollard M D, Wheatley G, Regine W F, Mohiuddin M, Leeper D B
Department of Radiation Oncology and Nuclear Medicine, Thomas Jefferson University, Philadelphia, PA 19107-5097.
Int J Radiat Oncol Biol Phys. 1995 Feb 15;31(4):905-10. doi: 10.1016/0360-3016(94)00435-8.
Scid mice are severely immunodeficient as a result of a defective recombinase system. Mice with the scid mutation have been shown to have an increased sensitivity to ionizing radiation, presumably as a result of an inability to repair DNA damage. Little is known of the impact of this mutation on the thermal response and on hyperthermic radiosensitization. This investigation established the thermal response (42-44 degrees C), patterns of thermotolerance development, and the impact of hyperthermia (60 min at 40 degrees C or 42 degrees C) on the radiation response of bone marrow colony forming unit-culture cells (CFU-C) in scid mice.
Anesthetized scid mice (pentobarbital, 90 mg/kg) were killed by cervical dislocation and the nucleated marrow obtained from both tibia and femora by passing 2 ml of cold McCoy's 5A medium supplemented with 15% fetal bovine serum through each bone. Single cell suspensions of nucleated marrow were heated in 12 x 75 mm sterile tissue culture tubes at a concentration of approximately 5 x 10(6) cells/ml. Radiation, when used, was delivered immediately prior to hyperthermia by a 137Cs irradiator (dose rate of 1.20 Gy/min). Colony forming unit-culture were cultured in semisolid agar in the presence of colony stimulating factor (conditioned medium from L929 cells) for 7 days.
The slope of the radiation dose-response curve for CFU-C in scid mice was biphasic, the Dos (+/- SE) were 0.29 +/- 0.03 Gy and 1.09 +/- 0.20 Gy, respectively. The Dos of the radiation dose-response curve for wild type marrow from CB-17 and Balb/c mice were 1.28 +/- 0.05 Gy and 1.47 +/- 0.15 Gy, respectively. The Dos of the hyperthermia dose-response curves for scid mice were 75 +/- 5, 10 +/- 1.4, and 4 +/- 0.2 min, respectively, for temperatures of 42 degrees, 43 degrees, and 44 degrees C. Thermotolerance development at 37 degrees C increased to a maximum at approximately 240 min after acute hyperthermia (15 min at 44 degrees C) and thereafter, decreased to control levels within 15 h. Thermotolerance did not develop in scid CFU-C during chronic hyperthermia at temperatures < 42.5 degrees C. Hyperthermia (60 min at 40 degrees or 42 degrees C) immediately after ionizing radiation did not significantly alter the terminal slope of the radiation dose-response curve of scid CFU-C (Do = 1.28 +/- 0.08 Gy). By contrast, hyperthermia following radiation of wild type CFU-C resulted in a decrease in the Do from 1.47 +/- 0.05 Gy (Balb/c, rad only) to 1.31 +/- 0.08 or 1.06 +/- 0.18 Gy for 60 min at 40 degrees or 42 degrees C, respectively.
These results show that the thermal response and the pattern of thermotolerance development of scid CFU-C were similar to that of wild type Balb/c CFU-C, but that hyperthermia given immediately after ionizing radiation did not alter the radiation response of scid CFU-C. The scid mutation does not increase hyperthermic sensitivity or change the pattern of thermotolerance development of scid mouse CFU-C, implying that the scid mutation is not involved with thermal response, but does render the already radiation-sensitive scid cells incapable of thermal radiosensitization.
由于重组酶系统存在缺陷，严重联合免疫缺陷（Scid）小鼠存在严重免疫缺陷。已证明携带Scid突变的小鼠对电离辐射的敏感性增加，这可能是由于其无法修复DNA损伤所致。关于这种突变对热反应和热增敏放疗的影响，目前所知甚少。本研究确定了Scid小鼠骨髓集落形成单位培养细胞（CFU-C）的热反应（42 - 44摄氏度）、热耐受发展模式以及热疗（40摄氏度或42摄氏度下60分钟）对其辐射反应的影响。
将麻醉后的Scid小鼠（戊巴比妥，90 mg/kg）通过颈椎脱臼处死，通过向每根骨头注入2 ml添加15%胎牛血清的冷 McCoy's 5A培养基，从双侧胫骨和股骨获取有核骨髓。有核骨髓的单细胞悬液在12×75 mm无菌组织培养管中加热，浓度约为5×10⁶细胞/ml。如需进行辐射，在热疗前立即通过¹³⁷Cs辐照器进行（剂量率为1.20 Gy/min）。集落形成单位培养细胞在含有集落刺激因子（L929细胞条件培养基）的半固体琼脂中培养7天。
Scid小鼠CFU-C的辐射剂量反应曲线斜率呈双相，剂量（±标准误）分别为0.29±0.03 Gy和1.09±0.20 Gy。CB - 17和Balb/c小鼠野生型骨髓的辐射剂量反应曲线的剂量分别为1.28±0.05 Gy和1.47±0.15 Gy。Scid小鼠在42摄氏度、43摄氏度和44摄氏度下的热疗剂量反应曲线的剂量分别为75±5、10±1.4和4±0.2分钟。在37摄氏度下，急性热疗（44摄氏度下15分钟）后约240分钟热耐受发展达到最大值，此后在15小时内降至对照水平。在温度低于42.5摄氏度的慢性热疗过程中，Scid CFU-C未形成热耐受。电离辐射后立即进行热疗（40摄氏度或42摄氏度下60分钟）并未显著改变Scid CFU-C辐射剂量反应曲线的终末斜率（Do = 1.28±0.08 Gy）。相比之下，野生型CFU-C辐射后进行热疗导致Do从1.47±0.05 Gy（Balb/c，仅辐射）分别降至40摄氏度或42摄氏度下60分钟时的1.31±0.08 Gy或1.06±0.18 Gy。
这些结果表明，Scid CFU-C的热反应和热耐受发展模式与野生型Balb/c CFU-C相似，但电离辐射后立即进行热疗并未改变Scid CFU-C的辐射反应。Scid突变不会增加热敏感性，也不会改变Scid小鼠CFU-C的热耐受发展模式，这意味着Scid突变与热反应无关，但确实使本就对辐射敏感的Scid细胞无法实现热增敏。
