Preparation of the novel fluorine-18-labeled VIP analog for PET imaging studies using two different synthesis methods

Vasoactive intestinal peptide (VIP) receptors are expressed on various tumor cells in much higher density than somatostatin receptors, which provides the basis for radiolabeling VIP as tumor diagnostic agent. However, fast proteolytic degradation of VIP in vivo limits its clinical application. With the aim to develop and evaluate new ligands for depicting the VIP receptors with positron emission tomography (PET), the structure modified [R8,15,21, L17]-VIP analog was radiolabeled with 18F using two different methods. With the first method, N-4-[18F]fluorobenzoyl-[R8,15,21, L17]-VIP ([18F]FB-[R8,15,21, L17]-VIP 7) was produced in a decay-corrected radiochemical yield (RCY) of 33.6 ± 3%, a specific radioactivity of 255 GBq/μmol (n = 5) within 100 min in four steps. Similarly, N-4-[18F](fluoromethyl)-benzoyl-[R8,15,21, L17]-VIP ([18F]FMB-[R8,15,21, L17]-VIP 8) was synthesized in a RCY of 34.85 ± 5%, a specific radioactivity of 180 GBq/μmol (n = 5) within 60 min in only one step. The two products 7 and 8 were both shown good stability in HSA. Moreover, the low bone uptakes of 7 and 8 in vivo of mice showed good defluorination stability.

In an effort to develop 18F-labeled vasoactive intestinal peptide (VIP) analog as a positron emission tomography (PET) imaging agent for tumors, two methods of synthesis have been discussed in this study and we have obtained 18F-labeled products in a convenient way.Figure optionsDownload as PowerPoint slide