Chitneni Satish K, Bida Gerald T, Zalutsky Michael R, Dewhirst Mark W
Department of Radiology, Duke University Medical Center, Durham, North Carolina; and
Department of Radiology, Duke University Medical Center, Durham, North Carolina; and.
J Nucl Med. 2014 Jul;55(7):1192-7. doi: 10.2967/jnumed.114.137448. Epub 2014 May 22.
The availability of (18)F-labeled and unlabeled 2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)-acetamide (EF5) allows for a comparative assessment of tumor hypoxia by PET and immunohistochemistry; however, the combined use of these 2 approaches has not been fully assessed in vivo. The aim of this study was to evaluate (18)F-EF5 tumor uptake versus EF5 binding and hypoxia as determined from immunohistochemistry at both macroscopic and microregional levels.
Three tumor models-PC3, HCT116, and H460-were evaluated. Tumor-bearing animals were coinjected with (18)F-EF5 and EF5 (30 mg/kg), and PET imaging was performed at 2.5 h after injection. After PET imaging and 2 min after Hoechst 33342 injection, the tumors were excised and evaluated for (18)F-EF5 distribution by autoradiography and EF5 binding by immunohistochemistry. Additionally, the effects of nonradioactive EF5 (30 mg/kg) on the hypoxia-imaging characteristics of (18)F-EF5 were evaluated by comparing the PET data for H460 tumors with those from animals injected with (18)F-EF5 alone.
The uptake of (18)F-EF5 in hypoxic tumor regions and the spatial relationship between (18)F-EF5 uptake and EF5 binding varied among tumors. H460 tumors showed higher tumor-to-muscle contrast in PET imaging; however, the distribution and uptake of the tracer was less specific for hypoxia in H460 than in HCT116 and PC3 tumors. Correlation analyses revealed that the highest spatial correlation between (18)F-EF5 uptake and EF5 binding was in PC3 tumors (r = 0.73 ± 0.02) followed by HCT116 (r = 0.60 ± 0.06) and H460 (r = 0.53 ± 0.10). Uptake and binding of (18)F-EF5 and EF5 correlated negatively with Hoechst 33342 perfusion marker distribution in the 3 tumor models. Image contrast and heterogeneous uptake of (18)F-EF5 in H460 tumors was significantly higher when the radiotracer was used alone versus in combination with unlabeled EF5 (tumor-to-muscle ratio of 2.51 ± 0.33 vs. 1.71 ± 0.17, P < 0.001).
The uptake and hypoxia selectivity of (18)F-EF5 varied among tumor models when animals also received nonradioactive EF5. Combined use of radioactive and nonradioactive EF5 for independent assessment of tumor hypoxia by PET and immunohistochemistry methods is promising; however, the EF5 drug concentrations that are required for immunohistochemistry assays may affect the uptake of (18)F-EF5 in hypoxic cells in certain tumor types as observed in H460 in this study.
有（18）F标记和未标记的2-（2-硝基-1H-咪唑-1-基）-N-（2,2,3,3,3-五氟丙基）-乙酰胺（EF5），可通过PET和免疫组织化学对肿瘤缺氧情况进行对比评估；然而，这两种方法的联合应用在体内尚未得到充分评估。本研究的目的是在宏观和微观区域水平上，评估（18）F-EF5在肿瘤中的摄取情况与EF5结合及缺氧情况之间的关系，后者通过免疫组织化学确定。
评估了三种肿瘤模型——PC3、HCT116和H460。给荷瘤动物同时注射（18）F-EF5和EF5（30mg/kg），并在注射后2.5小时进行PET成像。在PET成像后以及注射Hoechst 33342两分钟后，切除肿瘤，通过放射自显影评估（18）F-EF5的分布，通过免疫组织化学评估EF5的结合情况。此外，通过比较H460肿瘤的PET数据与单独注射（18）F-EF5的动物的数据，评估非放射性EF5（30mg/kg）对（18）F-EF5缺氧成像特征的影响。
缺氧肿瘤区域中（18）F-EF5的摄取以及（18）F-EF5摄取与EF5结合之间的空间关系在不同肿瘤中有所不同。H460肿瘤在PET成像中显示出更高的肿瘤与肌肉对比度；然而，与HCT116和PC3肿瘤相比，H460中示踪剂的分布和摄取对缺氧的特异性较低。相关性分析显示，（18）F-EF5摄取与EF5结合之间的空间相关性在PC3肿瘤中最高（r = 0.73±0.02），其次是HCT116（r = 0.60±0.06）和H460（r = 0.53±0.10）。在这三种肿瘤模型中，（18）F-EF5和EF5的摄取及结合与Hoechst 33342灌注标记物分布呈负相关。当单独使用放射性示踪剂时，H460肿瘤中（18）F-EF5的图像对比度和异质性摄取显著高于与未标记的EF5联合使用时（肿瘤与肌肉比值为2.51±0.33对1.71±0.17，P < 0.001）。
当动物同时接受非放射性EF5时，（18）F-EF5的摄取和缺氧选择性在不同肿瘤模型中有所不同。联合使用放射性和非放射性EF5通过PET和免疫组织化学方法独立评估肿瘤缺氧情况是有前景的；然而，正如本研究在H460中所观察到的，免疫组织化学检测所需的EF5药物浓度可能会影响某些肿瘤类型中缺氧细胞对（18）F-EF5的摄取。
