用于体内DNA合成成像的4'-[甲基-14C]硫代胸苷的评估。

Evaluation of 4'-[methyl-14C]thiothymidine for in vivo DNA synthesis imaging.

作者信息

Toyohara Jun, Kumata Katsutoshi, Fukushi Kiyoshi, Irie Toshiaki, Suzuki Kazutoshi

机构信息

Department of Molecular Probes, Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan.

出版信息

J Nucl Med. 2006 Oct;47(10):1717-22.

PMID:17015909

Abstract

UNLABELLED

We evaluated 4'-[methyl-11C]thiothymidine ([methyl-11C]S-dThd) to obtain a thymidine analog that might prove simpler to use for imaging DNA synthesis and that might follow the same biochemistry as its surrogate.

METHODS

[Methyl-14C]S-dThd was synthesized by rapid methylation of 5-trimethylstannyl-4'-thio-2'-deoxyuridine via a palladium-mediated Stille coupling reaction with 14C-methyl iodide. Degradation of [methyl-14C]S-dThd, when incubated in human blood, was analyzed by high-performance liquid chromatography (HPLC). The in vivo potential of [methyl-14C]S-dThd was evaluated by studying its distribution in EMT-6 mammary carcinoma-bearing mice. 2-Fluoro-2'-deoxycytidine, a potent inhibitor of DNA synthesis, was used to modulate cell proliferation. Tissue extraction was also performed to investigate the incorporation of [methyl-14C]S-dThd into DNA.

RESULTS

[Methyl-14C]S-dThd was obtained in a 31%-41% radiochemical yield (calculated from 14C-methyl iodide) at 130 degrees C, 5-min reaction in N,N-dimethylformamide followed by semipreparative HPLC purification. The radiochemical purity of [methyl-14C]S-dThd was >99% and the specific activity was 2.04 GBq/mmol (according to the specific activity of 14C-methyl iodide). [2-14C]Thymidine, when incubated with human blood, demonstrated rapid degradation. In contrast, [methyl-14C]S-dThd was stable with <3% degradation at 60 min. An in vivo distribution study showed the accumulation of radioactivity in proliferating tissues (spleen, thymus, duodenum, and tumor). On the other hand, the radioactivity of nonproliferating tissues (lung, liver, kidney, and muscle) was rapidly cleared in parallel with the clearance of blood radioactivity. The tumor uptake of [methyl-14C]S-dThd was high (8.8 percentage injected dose per gram at 60 min) and selective (tumor-to-blood ratio, 12.2 at 60 min). 2-Fluoro-2'-deoxycytidine pretreatment significantly reduced the tumor uptake of [methyl-14C]S-dThd. Relative blood flow as measured by the uptake of 4-[N-methyl-14C]iodoantipyrine was similar between the treated and untreated groups. Tissue extraction studies showed that most of the total tissue radioactivity of rapidly proliferating tissues was recovered in the DNA fraction at 60 min after [methyl-14C]S-dThd injection.

CONCLUSION

The labeling procedure is rapid and suitable for 11C labeling. Positron-labeled 4'-thiothymidine should be useful for imaging DNA synthesis by PET.

摘要

未标记

我们评估了4'-[甲基-¹¹C]硫代胸腺嘧啶核苷（[甲基-¹¹C]S-dThd），以获得一种可能被证明在用于DNA合成成像时更易于使用且可能遵循与其替代物相同生物化学过程的胸腺嘧啶类似物。

方法

通过5-三甲基锡基-4'-硫代-2'-脱氧尿苷与¹⁴C-甲基碘经钯介导的Stille偶联反应进行快速甲基化反应合成[甲基-¹⁴C]S-dThd。将[甲基-¹⁴C]S-dThd与人血一起孵育时的降解情况通过高效液相色谱（HPLC）进行分析。通过研究[甲基-¹⁴C]S-dThd在携带EMT-6乳腺癌的小鼠体内的分布来评估其体内潜力。使用DNA合成的强效抑制剂2-氟-2'-脱氧胞苷来调节细胞增殖。还进行了组织提取以研究[甲基-¹⁴C]S-dThd掺入DNA的情况。

结果

在130℃下，于N，N-二甲基甲酰胺中反应5分钟，然后通过半制备HPLC纯化，以31%-41%的放射化学产率（根据¹⁴C-甲基碘计算）获得[甲基-¹⁴C]S-dThd。[甲基-¹⁴C]S-dThd的放射化学纯度>99%，比活度为2.04 GBq/mmol（根据¹⁴C-甲基碘的比活度）。[2-¹⁴C]胸腺嘧啶与人血一起孵育时显示出快速降解。相比之下，[甲基-¹⁴C]S-dThd在60分钟时稳定，降解<3%。体内分布研究表明放射性在增殖组织（脾脏、胸腺十二指肠和肿瘤）中积累。另一方面，非增殖组织（肺、肝、肾和肌肉）中的放射性与血液放射性的清除同时迅速清除。[甲基-¹⁴C]S-dThd的肿瘤摄取率高（60分钟时为每克注射剂量的8.8%）且具有选择性（肿瘤与血液的比率，60分钟时为12.2）。2-氟-2'-脱氧胞苷预处理显著降低了[甲基-¹⁴C]S-dThd的肿瘤摄取。通过4-[N-甲基-¹⁴C]碘安替比林摄取测量的相对血流在治疗组和未治疗组之间相似。组织提取研究表明，在注射[甲基-¹⁴C]S-dThd后60分钟，快速增殖组织的总组织放射性大部分在DNA部分中回收。