摘要目的:设计合成 68Ga-1，4，7，10-四氮杂环十二烷-1，4，7，10-四乙酸(DOTA)-半胱氨酸-天冬氨酸-缬氨酸(CDV)-Nb109，探讨其用于检测不同肿瘤中程序性细胞死亡蛋白配体1(PD-L1)表达水平的潜力。 方法:采用基因工程技术将CDV引入单域抗体Nb109序列的尾部，通过马来酰亚胺-半胱氨酸定点偶联策略，将马来酰亚胺-DOTA与CDV-Nb109(物质的量比1∶1)反应制备前体DOTA-CDV-Nb109，随后进行 68Ga标记并用PD-10脱盐柱纯化。建立人黑色素瘤A375、人源性PD-L1转染的A375-hPD-L1及人胶质瘤U87荷瘤裸鼠模型，通过稳定性分析、细胞摄取和microPET显像评价 68Ga-DOTA-CDV-Nb109的诊断价值。采用单因素方差分析和最小显著差异 t检验分析数据。 结果:68Ga-DOTA-CDV-Nb109放射化学产率为(69.79±4.69)%，放化纯大于97%，摩尔活度为(12.85±1.51) GBq/μmol。 68Ga-DOTA-CDV-Nb109与A375-hPD-L1细胞具有较强的亲和力，解离常数( Kd)为(66.43±17.89) nmol/L。 68Ga-DOTA-CDV-Nb109在A375-hPD-L1细胞[(3.17±0.15)百分加入放射性剂量(%AD)]、U87细胞[(2.08±0.03) %AD]中的摄取明显高于A375细胞[(1.21±0.14) %AD； F＝82.87， t值：15.23、9.98， P值：<0.001、0.003]。 68Ga-DOTA-CDV-Nb109在A375-hPD-L1[(5.21±0.35)每毫升百分注射剂量率(%ID/ml)]和U87[(3.44±0.69) %ID/ml]荷瘤裸鼠肿瘤中的摄取显著高于A375荷瘤裸鼠[(2.17±0.36) %ID/ml； F＝249.72， t值：35.70、3.43，均 P<0.001]。 结论:成功制得定点标记的PET探针 68Ga-DOTA-CDV-Nb109，可无创、动态监测不同肿瘤中PD-L1表达水平的变化，在PD-L1免疫检查点阻断治疗潜在受益患者筛选方面具有应用潜力。

abstractsObjective:To synthesize a novel site-specifically labelled probe 68Ga-1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetic acid (DOTA)-Cys-Asp-Val (CDV)-Nb109 and explore its potential for detection of the programmed cell death ligand 1 (PD-L1) expression level in different tumors. Methods:Firstly, CDV was inserted into the tail of the sequence of Nb109 by genetic engineering. Then the precursor DOTA-CDV-Nb109 was prepared by mixing the maleimide-DOTA and the single-domain antibody CDV-Nb109 (amount of substance ratio 1∶1) via the maleimide-cysteine site-specific coupling strategy. Subsequently, the DOTA-CDV-Nb109 was labeled with 68Ga and purified by PD-10 column. Human melanoma A375, human PD-L1 transfected melanoma A375-hPD-L1 and human glioma U87 tumor-bearing mice models were established, and the diagnostic value of 68Ga-DOTA-CDV-Nb109 was evaluated by stability assay, cellular uptake, and microPET imaging. One-way analysis of variance and the least significant difference t test were used to analyze the data. Results:The probe 68Ga-DOTA-CDV-Nb109 was obtained with the radiochemical yield of (69.79±4.69)%, radiochemical purity more than 97%, and molar activity of (12.85±1.51) GBq/μmol. 68Ga-DOTA-CDV-Nb109 had strong binding affinity for A375-hPD-L1 with the dissociation constant ( Kd) of (66.43±17.89) nmol/L. The uptake of 68Ga-DOTA-CDV-Nb109 in A375-hPD-L1 and U87 cells were (3.17±0.15) percentage of the added radioactivity dose (%AD) and (2.08±0.03) %AD respectively, which were significantly higher than that in A375 cells ((1.21±0.14) %AD; F=82.87, t values: 15.23, 9.98, P values: <0.001, 0.003). The tumor uptake of the probe in A375-hPD-L1 ((5.21±0.35) percentage of injected dose per ml (%ID/ml)) and U87 tumor-bearing mice ((3.44±0.69) %ID/ml) were significantly higher than that in A375 tumor-bearing mice ((2.17±0.36) %ID/ml; F=249.72, t values: 35.70, 3.43, both P<0.001). Conclusion:The site-specifically labelled probe 68Ga-DOTA-CDV-Nb109, which can non-invasively and dynamically monitor the change of PD-L1 expression level in different tumors and help screen patients who can benefit from PD-L1 immune checkpoint blocking therapy, is successfully synthesized with high radiochemical purity.