肺癌特异性靶向小分子多肽的^(131)I标记及其在兔体内的动态显像

Radiolabelling of a lung cancer- targeting small molecule polypeptide with ^(131)I and its radioactivity distribution in normal rabbits

目的建立肺癌特异性靶向小分子多肽cNGQGEQc的131I标记方法,并通过SPECT动态显像以研究131I-cNGQGEQc在兔体内的放射分布特性。方法采用氯胺-T法对N-端连接有酪氨酸的小分子多肽cNGQGEQc进行131I标记,利用纸层析法测定131I-cNGQGEQc的标记率与放化纯度,并观察131I-cNGQGEQc在生理盐水(NS)和正常人血清中于37℃孵育24 h后的体外稳定性及其脂水分配系数。应用SPECT对经耳缘静脉注入131I-cNGQGEQc的新西兰白兔进行显像,结合感兴趣区时间-放射性曲线分析,观察家兔体内放射性动态分布变化。结果131I-cNGQGEQc的标记率为90%,经HPLC纯化后放化纯度为95%;131IcNGQGEQc在NS和正常人血清中其放化纯度分别为(93.12±1.18)%和(88.34±5.43)%。131I-cNGQGEQc的脂水分配系数lg P(正辛醇∕生理盐水)为-1.75,提示所制备的标记多肽是水溶性的。兔SPECT动态显像示:l min双肾即显影,5 min心、肝影开始减弱,膀胱显影,随后膀胱影持续增强,30 min后软组织影逐渐减弱;胆囊未显影,腹部呈持续低放射分布;甲状腺区及胃未见明显核素浓聚;各组织器官T-A曲线均随时间逐渐下降。结论131I-cNGQGEQc的制备方法简便,标记率高(>90%),在体外具有良好的稳定性;131I-cNGQGEQc为水溶性,主要经泌尿系统排泄,具有比较理想的体内分布特性。本实验结果为进一步的肺癌荷瘤裸鼠放射性标记多肽的靶向定位诊断与治疗提供实验基础。

Objective To establish a labeling method for a specific lung cancer-targeting small molecule peptide cNGQGEQc with 131I and observe the radioactivity distribution of the labeled peptide in rabbits using single-photon emission computed tomography （SPECT）. Methods Chloramine-T method was used for 131I labeling of the tyrosine amino group on cNGQGEQc, and the labeling efficiency and radiochemical purity of 131I-cNGQGEQc were determined with paper chromatography. The stability of 131I-cNGQGEQc in saline and human serum was assessed after incubation in water bath at 37 ℃ for 24 h. The octanol-water partition coefficient lg P （the radioactivity counting ratio of 131I-cNGQGEQc dissolved in 100 μl octanol or in 100 μl saline） was calculated. SPECT was performed in 3 male New Zealand white rabbits after intravenous injection of 131I-cNGQGEQc to observe the dynamic distribution of the peptide with the time-radioactivity curve （T-A curve） of the region of interest （ROI）. Results With a labeling efficiency of 90%, 131I-cNGQGEQc showed a radiochemical purity of was 95% after purification with HPLC. The radiochemical purity of 131I-cNGQGEQc was （93.12±1.18）% and （88.34±5.43）% after intubation in saline and human serum for 24 h, respectively. The octanol-water partition coefficient lg P of 131I-cNGQGEQc was-1,75, suggesting its hydrosolubility. In rabbits with intravenous injection of 131I-cNGQGEQc, SPECT visualized the kidneys at 1 min after the injection; the imaging of the heart and liver became attenuated at 5 min when the bladder was visualized with an increasing radioactivity. The radioactivity of the soft tissues began to fade at 30 min. No gallbladder visualization was detected, and the radioactivity of the abdomen remained low. No obvious radioactivity concentration was observed in the thyroid and stomach. The T-A curves of the ROI of all the tissues and organs descended over time. Conclusion Radiolabeling of cNGQGEQc with 131I is simple and highly efficient. 131I-cNGQGEQc has good stability in vitro and good distribution characteristics for in vivo imaging, and is cleared mainly by renal excretion due to its hydrosolubility. These results provide experimental basis for further studies of diagnosis and therapy of lung cancer with targeting polypeptide.