The Preparation Of ¹⁸F-labeled P-fluoroacetophenone Ester Folic Acid Derivative

Positron emission computed tomography (PET) is an imaging technique that can show the metabolism of biological molecule, the activity of receptor and neurotransmitter. PET demonstrates the capability to obtain the three-dimendional image with best sensitivity and resolution among the nuclear medicine imaging modalities. The half-life of 18F isotope is 110 min, which is longer than the other clinically used nuclides such as 11C,13N and 15O. Therefore, it allows the preparation of complicated radiotracers labeled with 18F isotope.Folate is a vitamin which is necessary for human, but it can't be synthesized in human body. Previous work find that folate and folate conjugates were transported into the cell through a process called folate receptor-mediated endocytosis. Folate receptor(FR) exhibits limited expression on normal cells, but over-expressed on several kinds of tumor cells. Therefore, the folate receptor-positive tumor cells usually uptake more folate and folate conjugates than the normal cells. Considering this principle, we synthesized a 18F-labeled p-fluoroacetophenone ester folic acid derivative (18F-FAP-FA) that shows the potential for targeted tumor imaging by using PET. Firstly, we synthesized a FITC-labeled folic acid derivative [FA-EA-(FITC)2] and it was evaluated through in vivo fluorescence imaging study in KB tumor-bearing nude mice. Next, we prepared 18F-FAP-FA and the initial biodistribution study was performed. The results revealed that FA-EA-(FITC)2 showed good tumor targeting specificity, the initial biodistribution of 18F-FAP-FA revealed the %ID/g of tumor is 0.37 (2 h after injection), which was much higher than other main organs and tissues. In conclusion, the optical imaging studies as well as the initial biodistribution studies demonstrated the potential appliction of 18F-FAP-FA as a PET tracer in tumor targeted imaging.