Radiosynthesis and evaluation of 18F-labeled methylsulfonylpyrimidin-4-amine derivates as COX-2 PET ligands

1046 Objectives: Upregulation of cyclooxigenase-2 (COX-2) is involved in neuroinflammation associated with many neurological diseases and malignancies of the brain. Outside the brain, inflammation and COX-2 induction contribute to the pathogenesis of pain, arthritis, and acute allograft rejection, and to responses to infections, tumors, autoimmune disorders and injuries. Therefore, targeting COX-2 may be a potential neuroprotective treatment strategy aiming to reduce the progression of neurodegenerative and other diseases. Herein, we report the radiochemical synthesis and evaluation of two 18F- labeled thiophene and phenyl analogues of 4-(methylsulfonyl)phenyl-N-pyrimidin-4-amine (18F-FMTP and 18F-FMPP) using cell uptake and PET imaging. Methods: Synthesis of nonradioactive FMTP and FMPP were achieved in five steps from 4-(methylthio)- benzimidamide. The radiolabeling precursors were obtained from 4-(methylthio)benzimidamide in four steps. The radiochemical synthesis of [18F]FMTP and [18F]FMPP were optimized by reacting [18F]fluoride/K222/K2CO3 using a chlorine to fluorine displacement reaction with the corresponding precursor molecules. The cell uptake of radioligands were performed in COX-2 negative PANC-1 and COX-2 positive BxPC3 cells with unlabeled ligands and celecoxib as nonspecific binding agents. Dynamic 60 min microPET (Inveon) image acquisition of radiotracers were performed in anesthetized B6 mice using lipopolysaccharide (LPS) induced brain inflammation model and vehicle (PBS) treated mice. Results: Synthesis of FMTP, FMPP and its chloro-precursor were accomplished with 65% and 75% yields respectively. [18F]FMTP and [18F]FMPP were produced in high radiochemical purity (>98%) and specific activity (2.5+0.5 Ci/μmol) in 30+5% and 20+5% radiochemical yield, decay corrected to EOS. Both tracers did not exhibit significant specific binding to COX-2 negative PANC-1 cells. Whereas, specific binding (>50%) of the radioligands were found in COX-2 positive BxPC3 cells . PET studies in normal mice indicated blood-brain barrier (BBB) penetration of [18F]FMPT and [18F]FMPP and a faster washout of radioactivity in brain was observed presumably due to the lack of sufficient COX-2 in normal brain. [18F]FMTP shows ~2-fold higher binding in LPS treated mice vs Phosphate-Buffered Saline (PBS) treated control mice group. Conclusions: We report a novel radiolabeling of 4-18F-pyrimidine analogues [18F]FMTP and [18F]FMPP, as COX-2 PET tracers in excellent purity and molar activity. [18F]FMTP exhibit higher binding in LPS induced brain inflammation mice. Details of in vitro and in vivo evaluations of [18F]FMTP and [18F]FMPP will be presented. Research Support: Diane Goldberg Foundation (NYSPI/CUMC), American Cancer Society Mentored Research Scholar grant 124443-MRSG-13-121-01-CDD (CUMC), and NCATS UL1TR001873 (Reilly) Irving Institute/CTSA Translational Therapeutics Accelerator