Click Chemistry For ¹⁸F-labeling Of Transferrin Receptor Targeting T7 Peptide And Its Preliminary Evaluation

ObjectiveA unique targeting peptides under investigation currently is HAIYPRH, designated as T7, which is screened by phage display system on the cells expressing human transferrin receptor. T7 could target to transferrin receptor high expression tumor cells specificity, such as glioma, hepatocellular carcinoma. So far T7 has studied for cellular affinity and medicine loading research, and radio labeled fluorine derivatives has not been founded. According to T7 peptide s Chemical structure characteristics, we conjugateA azido on T7 peptide s amino terminal. Selecting triethylene glycol as the initial reactants as 18F-labeling intermediate. Finally,18F-labeling T7 peptide preparation as a new tumor targeting imaging probe in "One pot of two step" click chemistry. We evaluated the preliminary physical properties and biological assessment of 18F-TEG-T7. Lay the foundation for exploiting a new tumor specificity positive electron radionuclide labeling molecular probe in the future.MethodsThe preparation of the peptide probe could be divided into two parts, including the non-radioactivity and the radioactivity chemosynthesis. In the non-radioactivity part, we synthesis the acetylene toluene sulfonate (TsOTEGay) step-by-step in conventional organic chemistry using triethylene glycol as the industrial chemicals. And identify the chemical structure with H NMR Spectroscopy. In the radioactivity part,18F-anion product by cyclotron, eluted in a micro-reaction vial with K222/K2CO3 solution. Nucleophilic substitution reaction was performed with 18F-anion and TsOTEGay in ACN to form 18F-TEGay. And then without farther purification, mix the catalyst (including CuSO4·5H2O, ASC and THPTA) and T7 peptide with azido group. Synthesis the tumor targeting positron probe 18F-TEG-T7 by click chemistry. Meanwhile, synthesis the standard substance 19F-TEG-T7, and identify with mass spectrometer. And the radioactivity probe 18F-TEG-T7 was corresponded to standard substance 19F-TEG-T7 in Radio-HPLC to confirm. And farther separation and purification before used for other experiments. Octanol-Water Partition Coefficient study was proceeded to test the physical property of the probe. Furthermore, injected the radio probe into KM mice through tail veins, and observe the radioactivity distribution in vivo of the normal mice.ResultsThe LC-MS result of standard substance 19F-TEG-T7 demonstrated the molecular mass was correspond to the expected value. The imaging agent 18F-TEG-T7 was acquisition in two step reactions. The whole labeling process cost about 120 minutes. The Radio-HPLC result reveals that the decay-corrected yield of the labeling intermediate 18F-TEGay was about 78%±7.43%. And decay-corrected yield of the final product 18F-TEG-T7 was about 28.26±7.43%. The total radiochemistry yield of two steps was about 24.56%±15.59%(n=3).ConclusionThis study product a new kind of polypeptide tumor probe 18F-TEG-T7 through the "One pot of two step" click chemistry. We improved the entire labeling experimental procedure, and reduced the experiment time notably and optimized the radiochemistry yield the probe. The radioactivity distribution experiment in vivo of the normal mice shows the positron-labelled tracer excreting mainly by the kidney. The research result is expected apply to develop new polypeptide positron-labelled imaging probe, and provide the new methods for clinical application in tumor diagnosis.