99mTc标记BmK CT及其胶质瘤荷瘤裸鼠的SPECT成像研究

目的:通过放射性核素~(99m)Tc标记BmK CT多肽制备靶向胶质瘤的显像剂,探讨~(99m)?Tc-BmK CT用于胶质瘤显像的可行性。方法:采用BmK CT多肽游离的氨基与DTPA酸酐反应得到BmK CT-DTPA,经99m Tc标记后通过柱层析分离纯化制备~(99m)?Tc-BmK CT。测定标记物在PBS溶液和血清中不同时间点放射性化学纯度,评价BmK CT-~(99m)?Tc体外稳定性。新西兰白兔耳缘静脉注射~(99m)Tc-BmK CT进行SPECT显像,观察不同时间点体内的放射性分布。皮下胶质瘤裸鼠经尾静脉注射~(99m)Tc-BmK CT,观察不同时间点肿瘤的摄取情况;注射后4 h处死裸鼠,分离肿瘤和主要器官进行离体SPECT显像,并用勾画感兴趣区法分析相对放射性计数。结果:~(99m)Tc标记BmK CT多肽标记率大于80%,经柱层析分离纯化后放射性化学纯度大于99%。标记物在PBS和血清稳定性良好,6 h内放射性化学纯度均大于95%,12 h内放射性化学纯度大于90%。正常白兔SPECT显像表明~(99m)Tc-BmK CT主要浓聚在肝脏、脾脏和肾脏,软组织持续显影微弱,甲状腺区及胃肠未见核素浓聚;显像剂主要通过泌尿系统排泄,24 h肾脏与肝脏显影接近。胶质瘤裸鼠SPECT显像表明,注射后4 h肿瘤显像清楚,ROI分析结果显示肿瘤/肌肉比4.26±0.25,标记物在肿瘤内代谢缓慢,8 h肿瘤部位仍有较高摄取。结论:本研究成功制备了~(99m)Tc标记BmK CT多肽,标记物主要被肝、脾和肾摄取,经泌尿系统排泄;~(99m)Tc-BmK CT能够在皮下胶质瘤中浓聚,注射后4 h肿瘤显影清晰,瘤内代谢缓慢,有潜力成为一种新型胶质瘤分子探针。

Preparation of 99mTc Labeled BmK CT and the Application for SPECT Imaging in Tumor-bearing Nude Mice

ABSTRACT Objective: ^99mTc labeled BmK CT was prepared and its potential as a tumor-specific agent for SPECT imaging of glioma was performed via a xenografted nude mouse model. Methods: BmK CT was linked with DTPA to form BmK CT-DTPA, followed by radiolabeling with ^99mTc. After purification from PD-10 column, the stability of ^99mTc-BmK CT in vitro was studied. SPECT imaging at different time points was performed both in normal rabbits and tumor bearing nude mice after intravenous injection of ^99mTc-BmK CT. At 4 h post-injection, one tumor bearing mouse was sacrificed to remove the tumor and major organs. Their relative radioactivity ratios were recorded by analyzing the regions of interest. Results: The radiochemical yield of ^99mTc-BmK CT was above 80% and its mean radiochemical purity was more than 99%. The radiochemical purity of purified ^99mTc-BmK CT was greater than 90% within 24 h both in PBS and FBS. SPECT images of ^99mTc-BmK CT in normal rabbits showed that the major radioactivity was accumulated in the liver, kidney and spleen, while other tissues including thyroid had very low level. ^99mTc-BmK CT could be slowly cleared from the body through urinary system. The SPECT imaging in tumor bearing nude mice suggested that mildly increased SPECT signal intensity was found in the tumor site at 0.5 h post-injection and much higher was displayed at 1 h and 2 h, followed by the highest at 4 h. After that, the tumor SPECT signal descended steadily and could still be detected at 8 h post-injection. Conclusion: ^99mTc-BmK CT was successfully prepared with a high radiochemical purity and stability and could be used as a tumor-specific ligand for SPECT imaging of xenografted glioma model in vivo.