A fast chemoenzymatic synthesis of [C-11]-N-5,N-10-methylenetetrahydrofolate as a potential PET tracer for proliferating cells

作者：Saeed Muhammad; Tewson Timothy J; Erdahl Colbin E; Kohen Amnon^*

来源：Nuclear Medicine and Biology, 2012, 39(5): 697-701.

DOI：10.1016/j.nucmedbio.2011.12.003

• Cancer
• PET imaging
• Radiotracer
• Folate receptors
• Thymidylate synthase
• Carbon 11

Introduction: Thymidylate synthase and folate receptors are well-developed targets of cancer therapy. Discovery of a simple and fast method for the conversion of (11)CH(3)Ito[C-11]-formaldehyde ((CH2O)-C-11) encouraged us to label the co-factor of this enzyme. Preliminary studies conducted on cell lines have demonstrated a preferential uptake of [11-C-14]-(R)-N-5,N-10-methylene-5,6,7,8-tetrahydrofolate ((14)CH(2)H(4)folate) 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 (11)CH(2)H(4)folate as a positron emission tomography (PET) tracer for cancer imaging. Herein we report the synthesis of (11)CH(2)H(4)folate, which may serve as a potential PET tracer. %26lt;br%26gt;Methods: In a remotely controlled module; methyl iodide ((CH3I)-C-11) was bubbled into a reaction vial containing trimethylamine N-oxide in N,N-Dimethylformamide (DMF) and heated to 70 degrees C for 2 min. Formaldehyde ((CH2O)-C-11) formed after the completion of reaction was then mixed with a solution of freshly prepared tetrahydrofolate (H(4)folate) by using a fast chemoenzymatic approach to accomplish synthesis of (11)CH(2)H(4)folate. 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. %26lt;br%26gt;Results: The synthesis and purification of (11)CH(2)H(4)folate 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 (11)CH(2)H(4)folate, with minor (%26lt;10%) radioactivity due to unreacted (CH2O)-C-11. %26lt;br%26gt;Conclusion: We present a fast (similar to 5 min) synthesis and purification of (11)CH(2)H(4)folate 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.

• 出版日期2012-7