^(99)Tc^m标记VPAC1配体TP1724及其在动物体内分布与显像研究

Distribution and imaging of a ^(99)Tc^m-labeled linear peptide derived from vasoactive intestinal peptide receptor in vivo

目的制备同位素^(99)Tc^m标记血管活性肠肽受体(vasoactive intestinal peptide receptor,VIPR)结合肽TP1724(标记率>90%),鉴定其理化性质,并探讨其在正常动物体内的生物分布特点、示踪动力学及显像表现。方法制备G(D)AGG-Aba-VP2(TP1724);^(99)Tc^m间接标记TP1724(Sn Cl2·2H2O还原法),纸层析法测定标记率和比活度;稳定性实验(体外)、人血浆蛋白结合实验、半胱氨酸置换实验及脂/水分配实验等鉴定标记多肽的理化性质;35只正常小鼠分成7组,每只尾静脉注射3.7 MBq^(99)Tc^m-TP1724后于不同时间处死,收集9种组织器官并称取质量、分别测定各种组织器官的放射性,换算为%ID/g(每克组织百分注射剂量);9只健康家兔各静脉注射37 MBq^(99)Tc^m-TP1724后不同时间取血,测定血液放射性并换算为k Bq/L,经DAS 3.1.6软件处理判断最佳房室模型,并得出动力学参数;5只健康家兔分别静脉注射37 MBq^(99)Tc^m-TP1724,SPECT动态显像观察体内放射性分布变化。结果^(99)Tc^m-TP1724的标记率(96.57±0.71)%,比活度(25.52±0.29)TBq/mmol。室温下隔绝空气放置4 h,放化纯度为(93.64±2.25)%;Sephadex G-50柱层析示,^(99)Tc^m-TP1724血浆蛋白结合率约为6.61%;^(99)Tc^mTP1724与不同浓度半胱氨酸37℃温育1 h后,未结合^(99)Tc^m含量无明显变化;脂/水分配系数lg P为-(1.99±0.02)。^(99)Tc^m-TP1724在健康家兔体内的动力学符合权重为1的二室模型,分布半衰期t1/2α为(2.64±1.32)min,消除半衰期t1/2β为(78.36±13.38)min。体内生物分布和/或动态显像示:血液放射性清除迅速;颈部及胃区未见异常放射性聚集,脑部显示低放射性分布;放射性大部分通过肾脏排泄,少量经肝胆分泌。结论^(99)Tc^m-TP1724标记方法简便、标记率和比活度高、稳定性好、体内动力学性质优良。

Objective To prepare a 99Tcm-labeled linear peptide [ GFRFGALHEYNS, derived from vasoactive intestinal peptide （VIP） receptor type 1, and named TP1724 ], identify its physiochemical properties, and investigate its biodistribution features, tracer kinetics and imaging manifestations in normal animals. Methods Using stannous chloride as the reductive agent, G （D）AGG-Aba-VP2 （TP1724） prepared by chemosynthesis was labeled with 99Tcm. The labeling rate of 99Tcm-TP1724 was determined by 3MM paper chromatogramphy and its specific activity was calculated by directive method. Physicochemical properties of 99Tem-TP1724 were identified by stability test in vitro, human plasma protein binding test, cysteine challenge test and oil-water distribution test. Thirty-five mice were divided into 7 groups with 5 in each group. After intravenous injection of 3.7 MBq 99Tcm-TP1724, the mice were executed at different time points, the main organ tissues were collected, weighted and determined by γ counter, and then the results was expressed as % ID/g. Tracer kinetics was carried out after injection of 37 MBq 99Tcm-TP1724 via auris vein in 9 rabbits, the blood samples were harvested at different time points and measured by scintillation counter, then the results were expressed as kBq/L. The best compartment model and its kinetic parameters were obtained by DAS 3. 1.6 software processing. The scintigraphy was performed respectively at different time points after intravenous injection of 37 MBq 99Tcm-TP1724 in another 5 rabbits, and the dynamic distribution manifestation of radioactivity in vivo was observed. Results The labeling rate and specific activity of 99Tcm-TP1724 were （96.57 ± 0.71 ）% and 25.52 ±0.29 TBq/mmol respectively. The radiochemical purity was （93.64 ± 2.25 ）% after being placed for 4 h at room temperature. Sephadex G-50 chromatography indicated that the combination ratio of 99Tcm-TP1724 with human plasma protein was about 6.61%. The free 99Tom had no obvious change after incubation of 99Tcm-TP1724 with different concentrations of cysteine for 1 h at 37 ℃. The oil-water distribution coefficient （lg P） of 99Tcm-TP1724 was - （1.99 ± 0.02）. Dynamics of 99Tcm-TP1724 in the health rabbits fitted for two-compartment model with a weight coefficient of 1, and the main kinetic parameters, t1/2β and t1/2β, were 2.64 ± 1.32 and 78.36 ± 13.38 min, respectively. Biodistribution test and/ or SPECT imaging showed that the blood radioactivity disappeared rapidly, and radioactivity in vivo was mainly eliminated through the kidneys and partly secreted via hepatobiliary system. There was no abnormal radioactivity accumulation in the neck and stomach region during the whole imaging, and low radioactive background was presented in the brain. Conclusion 99 Tcm_TP1724 can be easily prepared with a high labeling rate and specific activity, and has favorable stability and dynamics properties.