放射性碘标记反义寡核苷酸在荷人淋巴瘤裸鼠中的分布及显像研究

目的:探讨用放射性碘标记的框架区(framework region mRNA,FR)mRNA反义寡核苷酸(antisense oligonucleotide,ASON)作为B细胞淋巴瘤反义显像剂及反义治疗药物的可能性.方法:通过氯胺-T法用碘125Ⅰ]与碘131Ⅰ]标记含酪胺的18聚体寡核苷酸获得125Ⅰ-或131Ⅰ-FR-ASON,建立荷人淋巴瘤裸鼠动物模型.将148 kBq125Ⅰ-FR-ASON(2～3μg)经尾静脉注入正常小鼠,于不同时间处死小鼠,测定不同组织及标准源的放射性计数.荷瘤裸鼠瘤内注入脂质体包裹的3.33 MBq131Ⅰ-FR-ASON(7～9μg),分别于注射后不同时间进行单光子发射计算机断层(single photon emission computer tomography,SPECT)显像,以脂质体包裹的正义寡核苷酸作为对照,24 h显像后处死裸鼠,取出血液、重要器官和肿瘤组织,测定各组织的放射性计数,并计算每克组织摄取率及肿瘤与非肿瘤组织放射性摄取比值(T/NT).结果:125Ⅰ-FR-ASON注入正常小鼠体内后1 h,各脏器的放射性摄取达高峰,24 h基本清除.肝、胃和肠放射性分布最高,骨、肌肉、脑中放射性分布较少.荷瘤裸鼠瘤内注入脂质体包裹的131Ⅰ标记ASON后立即用SPECT成像仅见肿瘤部位,1和2 h成像可见示踪剂从肿瘤到腹腔,24 h仍可见肿瘤显像.比较24 h反义组与正义组肿瘤的每克组织摄取率、T/NT均有显著性差异.结论:放射性碘标记ASON对淋巴瘤组织有很强的特异性,有望用于淋巴瘤反义显像和反义治疗的研究.

Study on biodistribution and imaging of radioiodinated antisense oligonucleotides in nude mice bearing human lymphoma

OBJECTIVE: To investigate the possibility of using radioiodine labeled framework region (FR) antisense oligonucleotides (ASONs) as an imaging agent or antisense therapeutic radiopharmaceutical in lymphoma. METHODS: A 18-mer partial phosphorothioate oligonucleotide sequence was synthesized and grafted in 5' with a tyramine group which was further radioiodinated. Radioiodination of the tyramine derivatized oligonucleotides was performed using the chloramine T method. (1) Normal CD-1 mice were injected via a tail vein with 148 kBq (125)I-FR-ASON (2-3 microg). Animals were sacrificed at the end of 1, 2, 4 and 24 h, and tissue samples were studied.(2) Liposome-mediated 3.33 MBq (131)I-FR-ASON (7-9 microg) were injected intratumorally into tumor-bearing BALB/c mice (6 weeks after inoculation of 107 Namalwa cells) meanwhile liposome-mediated (131)I labeled sense oligonucleotides served as controls. Biodistribution was monitored by sequential scintigraphy and organ radioactivity measurement 24 h after injection. Percentage of the injected dose per gram of tumor and tumor/non-tumor tissue ratios (T/NT) were calculated for each group of mice and the difference between two groups was assessed. RESULTS: The 5' tyramine group allowed specific and stable radiolabeling of the ASON with radioiodine. The radioactivity reached its peak 1 h after injection, and then decreased rapidly in normal mice after intravenous administration of (125)I-FR-ASON.The liver, stomach and intestine played an important role in biodistribution and radioactivity counts were low in bone, brain and blood. When (131)I-FR-ASON was injected intratumorally into mice grafted with Namalwa cell line, images showed the tracer accumulated in the tumor. Immediately after intratumoral administration, only the tumor was visible. Scintiscans performed at the end of 1 and 2 h showed elimination of the tracer from the tumor to the abdomen and at the end of 24 h the tumor was clearly seen. Percentage of the injected dose per gram of tumor and T/NT ratios for the sense group (control) were significantly lower than those of the antisense group. CONCLUSION: Radiolabeled Ig FR ASON showed high specificity in V1 family B-cell lymphoma, which should be further investigated for nuclear medicine imaging application and radionuclide antisense therapy.