Radiolabeling Of Peptide¹⁸F Probes Via Click Chemistry For PET Imaging

Due to their favorable pharmacokinetics and biological activities, small peptides labeled with positron emitting radionuclides have shown great potential in PET imaging. In this thesis, I designed a novel aromatic18F prosthetic group [F]FNPB, and developed a new method for radio-labeling peptides via click chemistry with high radiochemical yield. Different azido-peptides were successfully labeled with [18F]FNPB. The biological activities of [18F]FNPB and [18F]Fluoro-Triazole-peptides were evaluated in vivo using Micro PET/CT. The thesis consists of four major sections.I. The feasibility of the novel Click-labeling method was first investigated. We developed an one-step procedure for synthesis [19F]FNPB, and modified the peptides with two different methods. Seven azido-peptides were labeled with [19F]FNPB, and the yield was above80%in20min under the optimized conditions.II.[18F]FNPB was synthesized using one-step procedure under90℃, after HPLC purification, the uncorrected radiochemical yield was above45%, the specific activity was above350GBq/μmol and radiochemical purity exceeded98%in30min. The click labeling yield of four different peptides with [18F]FNPB were all above90%in15min. After HPLC purification, the uncorrected radiochemical yield was all above79%, the specific activity was above90GBq/μmol and radiochemical purity exceeded98%with a total synthesis time of approximately75min.III. The in vitro stability studies of [18F]FNPB showed no detectable radiodefluorination. The biodistribution of [18F]Fluoro-Triazole-peptide1,[18F]Fluoro-Triazole-peptide3, and [18F]Fluoro-Triazole-peptide5in vivo were evaluated by Micro PET/CT.[18F]Fluoro-Triazole-peptide5showed significant activity accumulation in tumor, but [18F]Fluoro-Triazole-peptide1and [18F]Fluoro-Triazole-peptide3revealed no specific tumor accumulation. Besides, high radioactivity concentration in bone indicated that all three [18F]Fluoro-Triazole-peptides were unstable against defluorination in vivo. Then the biodistribution of [18F]FNPB in vivo were studied.IV. The biodistribution study showed that [18F]FNPB can cross the Blood-Brain Barrier, and the brain-to-muscle ratio was3.5±0.4, but a strong defluorination of the [18F]FNPB was identified in vivo. To decrease defluorination, we selected three Cytochrome P450inhibitors:tetraethylthiuram disulfide, cimetidine and miconazole nitrate. Tetraethylthiuram disulfide and cimetidine had relatively small effect on inhibiting the radiodefluorination of [18F]FNPB, while miconazole nitrate could dramatically reduce the radioactivity concentration in skull by82%, ex vivo biodistribution (%ID/g) showed that bone uptake was reduced50%.In conclusion, We have developed an one-step procedure for radiosynthesis of [18F]FNPB which can be a useful prosthetic group for radio-labeling of peptides via click chemistry with high radiochemical yield, although a significant degree of in vivo defluorination was observed, we can inhibit the radiodefluorination with miconazole nitrate.[18F]FNPB is suitable for click-labeling a large number of peptides with a broad range of applications.