Design, Synthesis and Radiolabeling of Peptide GPRPILE with 18FDG as Fibrin Imaging Agent for Thrombosis Detection

The radionuclide of choice for routine clinical PET imaging is 18-F. As direct fluorination of peptides with 18-F is not possible, indirect methods using fluorinated prosthetic groups have been developed. Due to the availability of 18FDG in most PET centers, there is potential for 18FDG as a fluorinated prosthetic group. In this study, the linear peptide GPRPILE with an aminooxy group was designed, synthesized and radiolabeled with 18FDG as fibrin imaging agent.
Material and Docking studies were conducted done using AutoDock 4.1 and HEX software programs. Aoe-GPRPILE peptide was designed, synthesized through Fmoc method and radiolabeled with 18FDG. The radiochemical purity, stability of radiolabeled and cold peptide in PBS and human plasma was determined using chromatographic methods. The solubility ratio of the radiolabeled peptide in lipid to water (LogP) was determined.
Docking and pharmacophore studies using HEX software revealed high affinity of designed peptide to fibrin (E Total=-0.01). The identity and structure of peptide were determined by LC-Mass. Peptide was stable over 24 hr in human plasma and PBS buffer. The optimum conditions of radiolabeling were 0.2 mg peptide, 1 mCi 18FDG, 90°C for 30 min, pH=5. The radiochemical purity was over 95%. The stability of radiolabeled peptide in human plasma for 2 hr was over 95%. The partition coefficient (LogP) was 1.5.
18FDG has a high potential to be used as a prosthetic group for radiolabeling of peptides with 18-F. In this study, peptide Aoe-GPRPILE with aminooxy was synthesized and labeled with 18FDG with high yield and radiochemical purity. Aminooxy is conjugated to peptide sequence as a prosthetic group in the last step with minimal effect on peptide properties and selectively forms stable oxime bond with the aldehyde group of 18FDG.