靶向肽介导的131I-PAMAM(G5.0)纳米探针在甲状腺髓样癌鼠模型中的实验研究

Targeting peptide-mediated 131I-polyamidoamine in medullary thyroid carcinoma bearing mice

目的制备新型分子靶向探针131I-第五代聚酰胺-胺[PAMAM(G5.0)]-多肽[靶向甲状腺髓样癌(MTC)细胞的丝氨酸-精氨酸-谷氨酸-丝氨酸-脯氨酸-组氨酸-脯氨酸(SRESPHP,简称SR)、靶向肿瘤新生血管的甘氨酸-脯氨酸-亮氨酸-脯氨酸-亮氨酸-精氨酸(GPLPLR,简称GP)及双靶向肽(SR/GP)],探讨其对MTC模型的靶向性。方法用氯胺T法对修饰后的前体药物PAMAM(G5.0)、PAMAM(G5.0)-SR、PAMAM(G5.0)-GP及PAMAM(G5.0)-SR/GP进行131I标记,合成阳性对照组131I-PAMAM(G5.0)及实验组131I-PAMAM(G5.0)-SR、131I-PAMAM(G5.0)-GP、131I-PAMAM(G5.0)-SR/GP 4种探针,用薄层色谱法测定放化纯和稳定性。予MTC荷瘤裸鼠腹腔注射探针后,检测24 h各器官及组织的放射性摄取值[每克组织百分注射剂量率(%ID/g)];分别于4、8和24 h进行SPECT/CT显像,利用感兴趣区(ROI)技术获得肿瘤与对侧肌肉组织的肿瘤/正常组织放射性比值(T/NT),并对实验组与阳性对照组及阴性对照组(Na131I)进行比较。采用单因素方差分析、重复测量方差分析和Dunnet-t检验处理数据,24 h肿瘤%ID/g与T/NT之间的相关性采用Pearson相关分析。结果对照组和实验组探针131I标记率均>75%,放化纯均>90%。各组间24 h肿瘤%ID/g差异有统计学意义(F=14.400,P<0.001),其中注射131I-PAMAM(G5.0)-SR的肿瘤摄取最高[(1.80±0.18)%ID/g]。5组探针SPECT/CT显像的T/NT差异有统计学意义(F=4.776,P<0.05),不同时间的T/NT差异也有统计学意义(F=8.630,P<0.05)。与阴性对照组比较,131I-PAMAM(G5.0)-SR在4、8和24 h T/NT明显升高(t=4.169、7.123和4.032,均P<0.05),131I-PAMAM(G5.0)-GP在4 h T/NT明显升高(t=5.893,P<0.05);131I-PAMAM(G5.0)-SR在24 h T/NT明显高于131I-PAMAM(G5.0)-SR/GP(t=2.871,P<0.05)。结论实验组3种多肽探针对MTC均具有一定靶向性,其中131I-PAMAM(G5.0)-SR靶向性最好,有望应用于MTC的靶向诊治及预后评估。

Objective To construct 131I-the fifth generation polyamidoamine (PAMAM(G5.0)) with targeting peptide Ser-Arg-Glu-Ser-Pro-His-Pro (SRESPHP;SR) or Gly-Pro-Leu-Pro-Leu-Arg (GPLPLR;GP) and double targeting peptide SR/GP, and evaluate the targeting ability in medullary thyroid carcinoma (MTC) model. Methods PAMAM(G5.0), PAMAM(G5.0)-SR, PAMAM(G5.0)-GP and PAMAM(G5.0)-SR/GP were radiolabeled with 131I by chloramine T method. The radiolabeled yield and radiochemical purity were determined by thin layer chromatography. MTC xenografts were developed and the percentage radio-activity of injection dose per gram of tissue (%ID/g) in tumor and organs was measured at 24 h post-injection. Region of interest (ROI) was drawn and the tumor/non-tumor (T/NT) ratios at 4, 8 and 24 h post-injection were calculated and compared among different groups. One-way analysis of variance, repetitive measurement analysis of variance and Dunnett-t test were used to compare the data of different groups. The relationship between %ID/g and T/NT was analyzed with Pearson correlation. Results The radiolabeled yield was more than 75% and radiochemistry purity was more than 90%. The difference of %ID/g at 24 h post-injection was significant (F=14.400, P<0.001) in tumors of all groups. The radioactive uptake in tumor of 131I-PAMAM(G5.0)-SR group was the highest at 24 h post-injection((1.80±0.18)%ID/g). There were significant differences of T/NT ratios among different groups(F=4.776, P<0.05)and between different time points(F=8.630, P<0.05). Compared with negative control group (Na131I), the T/NT ratios significantly increased in 131I-PAMAM(G5.0)-SR group at 4, 8 and 24 h post-injection (t=4.169, 7.123 and 4.032, all P<0.05) and in 131I-PAMAM(G5.0)-GP group at 4 h post-injection (t=5.893, P<0.05). The T/NT ratio in 131I-PAMAM(G5.0)-SR group was higher than that in 131I-PAMAM(G5.0)-GP group at 24 h post-injection (t=2.871, P<0.05). Conclusions PAMAM(G5.0)-SR, PAMAM(G5.0)-GP and PAMAM(G5.0)-SR/GP can target the MTC models. 131I-PAMAM(G5.0)-SR has the best biological properties and may provide a new precision method for MTC diagnosis, treatment and prognosis evaluation.