Department of Nuclear Medicine, Peking University First Hospital, Beijing, China.
PLoS One. 2013;8(4):e61043. doi: 10.1371/journal.pone.0061043. Epub 2013 Apr 3.
Visualization of tumor angiogenesis using radionuclide targeting provides important diagnostic information. In previous study, we proved that an arginine-arginine-leucine (RRL) peptide should be a tumor endothelial cell specific binding sequence. The overall aim of this study was to evaluate whether (99m)Tc-radiolabeled RRL could be noninvasively used for imaging of malignant tumors in vivo, and act as a new molecular probe targeting tumor angiogenesis.
The RRL peptide was designed and radiosynthesized with (99m)Tc by a one-step method. The radiolabeling efficiency and radiochemical purity were then characterized in vitro. (99m)Tc-RRL was injected intravenously in HepG2 xenograft-bearing BALB/c nude mice. Biodistribution and in vivo imaging were performed periodically. The relationship between tumor size and %ID uptake of (99m)Tc-RRL was also explored.
The labeling efficiencies of (99m)Tc-RRL reached 76.9% ± 4.5% (n = 6) within 30-60 min at room temperature, and the radiochemical purity exceeded 96% after purification. In vitro stability experiment revealed the radiolabeled peptide was stable. Biodistribution data showed that (99m)Tc-RRL rapidly cleared from the blood and predominantly accumulated in the kidneys and tumor. The specific uptake of (99m)Tc-RRL in tumor was significantly higher than that of unlabeled RRL blocking and free pertechnetate control test after injection (p<0.05). The ratio of the tumor-to-muscle exceeded 6.5, tumor-to-liver reached 1.98 and tumor-to-blood reached 1.95. In planar gamma imaging study, the tumors were imaged clearly at 2-6 h after injection of (99m)Tc-RRL, whereas the tumor was not imaged clearly in blocking group. The tumor-to-muscle ratio of images with (99m)Tc-RRL was comparable with that of (18)F-FDG PET images. Immunohistochemical analysis verified the excessive vasculature of tumor. There was a linear relationship between the tumor size and uptake of (99m)Tc-RRL with R(2) = 0.821.
(99m)Tc-RRL can be used as a potential candidate for visualization of tumor angiogenesis in malignant carcinomas.
利用放射性核素靶向肿瘤血管生成的可视化提供了重要的诊断信息。在之前的研究中，我们证明精氨酸-精氨酸-亮氨酸（RRL）肽应该是肿瘤内皮细胞特异性结合序列。本研究的总体目标是评估（99m）Tc 标记的 RRL 是否可用于体内恶性肿瘤的无创成像，并作为一种新的靶向肿瘤血管生成的分子探针。
通过一步法设计并放射性合成 RRL 肽。然后在体外对放射性标记效率和放射化学纯度进行了表征。（99m）Tc-RRL 静脉注射到 HepG2 异种移植裸鼠中。定期进行生物分布和体内成像。还探索了肿瘤大小与（99m）Tc-RRL 的摄取百分比（%ID）之间的关系。
（99m）Tc-RRL 的标记效率在室温下 30-60 分钟内达到 76.9%±4.5%（n=6），纯化后放射化学纯度超过 96%。体外稳定性实验表明放射性标记的肽很稳定。生物分布数据表明，（99m）Tc-RRL 从血液中迅速清除，主要在肾脏和肿瘤中积累。与未标记的 RRL 阻断和游离高锝酸盐对照试验相比，（99m）Tc-RRL 在肿瘤中的特异性摄取明显更高（p<0.05）。肿瘤与肌肉的比值超过 6.5，肿瘤与肝脏的比值达到 1.98，肿瘤与血液的比值达到 1.95。在平面伽马成像研究中，（99m）Tc-RRL 注射后 2-6 小时肿瘤清晰成像，而阻断组肿瘤未清晰成像。（99m）Tc-RRL 图像的肿瘤与肌肉比值与（18）F-FDG PET 图像相当。免疫组织化学分析证实了肿瘤过度血管生成。（99m）Tc-RRL 的摄取与肿瘤大小之间存在线性关系，R2=0.821。
（99m）Tc-RRL 可作为恶性癌肿肿瘤血管生成可视化的潜在候选物。
