Introduction
Thymidylate synthase (TSase) and folate receptors (FRs) are well developed targets of cancer therapy. Discovery of a simple and fast method for the conversion of 11CH3I to [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 [1] pointing out 11CH2H4folate as a PET tracer for cancer imaging. Herein we report the synthesis of 11CH2H4folate, which may serve as a potential positron emission tomography (PET) tracer.
Methods
In a remotely controlled module, 11CH3I was bubbled into a reaction vial containing trimethylamine N-oxide (TMAO) in DMF and heated to 70 °C for 2 min. 11CH2O formed after the completion of reaction was then mixed with a solution of freshly prepared tetrahydrofolate (H4folate) by using a fast chemo-enzymatic 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.
Results
The synthesis and purification of 11CH2H4folate was completed within 5 min. HPLC analysis of the product after SAX purification indicate more than 90% of the radioactivity that was retained on the SAX cartridge was in 11CH2H4folate with minor (<10%) radioactivity due to unreacted 11CH2O.
Conclusion
We present a fast (~5 min) synthesis and purification of 11CH2H4folate, as a potential PET tracer. The final product is received in physiological compatible buffer (100 mM sodium phosphate, pH 7.0 containing 500 mM NaCl) and ready for use in vivo.
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