Radionuclide imaging of apoptosis in irradiated tumors

本研究的目的是建立一种非侵入性的成像技术，利用125I标记的Annexin V来测量和监测辐射引起的肿瘤细胞的凋亡。肿瘤照射剂量分别为2、5、10Gy.~(125)I-AnnexinV于照射后6小时静脉注射。5Gy照射组在照射后不同时间(3、6、12h)注射同位素。注射3小时后，处死小鼠，迅速切除肿瘤，并使用冷冻显微切割机制备厚度为6-40μm的冰冻切片。在放射自显影成像中，比较不同照射组的肿瘤与肌肉的比率。用ISEL(Klenow)法对同一切片进行细胞凋亡检测。放射自显影和免疫组织化学染色显示，所有照射组肿瘤细胞凋亡率均显著高于对照组(p&lt；0.05)。虽然免疫组织化学染色显示5Gy射线照射组的细胞凋亡频率最高，但放射自显影显示峰值出现在低于5Gy射线照射组。改变照射至安奈辛注射的时间，两种显像均显示照射后6h注射组的细胞凋亡率最高，为在体细胞凋亡显像无创性预测肿瘤放疗后的治疗效果提供了可能性。

The purpose of this study was to develop a non-invasive imaging technique to measure and monitor apoptosis in tumor cells caused by irradiation, using 125I radiolabeled Annexin V.The tumors used were human ependymoblastomas that were transplanted into nude mice. The tumors were irradiated at 2,5 or 10 Gy. ^<125>I-annexinV was administered intravenously 6 hours after the irradiation. In the 5-Gy irradiation group, the isotope was injected after various time-intervals (3,6 and 12 hours) from the irradiation. Three hours after the injection, the mice were sacrificed and the tumors quickly removed, and frozen sections were prepared at 6- to 40-μm thickness using a cryomicrotome. In autoradiography imaging, the tumor-to-muscle ratios were compared in the respective irradiated groups. In addition, apoptosis detection by the ISEL (Klenow) assay was couducted on the same sections. The number of Klenow-positive cells was counted in x100 fields for each section.Both autoradiography and immunohistochemical staining showed a significantly higher frequency of apoptosis in the neoplasm in all the irradiated groups as compared with that in the control group (p<0.05). Although immunohistochemical staining revealed the peak apoptosis frequency in the 5-Gy-irradiated group, autoradiography revealed the peak in the group receiving a lower dose than 5 Gy. When time from irradiation to Annexin injection was changed, both imaging showed the peak apoptosis frequency in the group receiving the injection 6 hours after the irradiation.The possibility of noninvasive prediction of the treatment effect in cases of cancer by apoptosis imaging in vivo after radiotherapy was shown in this study.