Department of Chemistry, University of Iowa, IA 52242, USA.
Nucl Med Biol. 2012 Jul;39(5):697-701. doi: 10.1016/j.nucmedbio.2011.12.003. Epub 2012 Feb 1.
Thymidylate synthase and folate receptors are well-developed targets of cancer therapy. Discovery of a simple and fast method for the conversion of 11CH3Ito[11C]-formaldehyde (11CH2O) encouraged us to label the co-factor of this enzyme. Preliminary studies conducted on cell lines have demonstrated a preferential uptake of [11-14C]-(R)-N5,N10-methylene-5,6,7,8-tetrahydrofolate (14CH2H4folate) by cancerous cell vs. normal cells from the same organ (Saeed M., Sheff D. and Kohen A. Novel positron emission tomography tracer distinguishes normal from cancerous cells. J Biol Chem 2011;286:33872-33878), pointing out 11CH2H4folate as a positron emission tomography (PET) tracer for cancer imaging. Herein we report the synthesis of 11CH2H4folate, which may serve as a potential PET tracer.
In a remotely controlled module, methyl iodide (11CH3I) was bubbled into a reaction vial containing trimethylamine N-oxide in N,N-Dimethylformamide (DMF) and heated to 70°C for 2 min. Formaldehyde (11CH2O) formed after the completion of reaction was then mixed with a solution of freshly prepared tetrahydrofolate (H4folate) by using a fast chemoenzymatic approach to accomplish synthesis of 11CH2H4folate. Purification of the product was carried out by loading the crude reaction mixture on a SAX cartridge, washing with water to remove unbound impurities and finally eluting with a saline solution.
The synthesis and purification of 11CH2H4folate were completed within 5 min. High-performance liquid chromatography analysis of the product after SAX purification indicates that more than 90% of the radioactivity that was retained on the SAX cartridge was in 11CH2H4folate, with minor (<10%) radioactivity due to unreacted 11CH2O.
We present a fast (∼5 min) synthesis and purification of 11CH2H4folate as a potential PET tracer. The final product is received in physiologically compatible buffer (100 mM sodium phosphate, pH 7.0 containing 500 mM NaCl) and ready for use in vivo.
胸苷酸合成酶和叶酸受体是癌症治疗中成熟的靶点。发现一种简单、快速的方法将 11CH3I 转化为[11C]-甲醛（11CH2O），这鼓励我们标记这种酶的辅因子。我们在细胞系上进行的初步研究表明，与来自同一器官的正常细胞相比，癌细胞优先摄取[11-14C]-(R)-N5，N10-亚甲基-5,6,7,8-四氢叶酸（14CH2H4folate）（Saeed M.，Sheff D.和 Kohen A. Novel positron emission tomography tracer distinguishes normal from cancerous cells. J Biol Chem 2011;286:33872-33878），指出 11CH2H4folate 是癌症成像的正电子发射断层扫描（PET）示踪剂。本文报道了 11CH2H4folate 的合成，它可能作为一种潜在的 PET 示踪剂。
在远程控制模块中，将甲基碘（11CH3I）鼓泡入含有三甲胺 N-氧化物的反应小瓶中，在 N,N-二甲基甲酰胺（DMF）中加热至 70°C 2 分钟。反应完成后形成的甲醛（11CH2O）然后与新鲜制备的四氢叶酸（H4folate）溶液混合，通过快速化学酶法完成 11CH2H4folate 的合成。通过将粗反应混合物加载到 SAX 柱上，用去离子水洗涤以去除未结合的杂质，最后用生理盐水洗脱来进行产物的纯化。
11CH2H4folate 的合成和纯化在 5 分钟内完成。SAX 纯化后产物的高效液相色谱分析表明，保留在 SAX 柱上的放射性的 90%以上是 11CH2H4folate，只有不到 10%的放射性是由于未反应的 11CH2O。
我们提出了一种快速（约 5 分钟）合成和纯化 11CH2H4folate 的方法，作为一种潜在的 PET 示踪剂。最终产物在生理相容的缓冲液（100 mM 磷酸钠，pH 7.0 含 500 mM NaCl）中接收，可立即用于体内。
