Basic Research Of Positron Radionuclide Labelled RGD Peptides

The integrins, which act as an important role in regulating cell adhesion , proliferation, differentiation, metastasis and apoptosis, are closely involved with tumor invasion and angiogenesis. In particular,α_vβ₃ integrin, which is specifically expressed on proliferating endothelial cells and tumor cells, and RGD peptide sequence is the specific ligand of integrins. So RGD antagonistic peptides radiolabelled by positron isotope could be used to assessα_vβ₃ Integrin by imaging. It is of significance to locate and quantitate tumors high special for early diagnosis and therapy.In this paper, the ¹⁸F^- was binded to the monomer RGDyK or the dimer RGDyK peptides by a indirect way. By optimizing the reaction conditions, monomer RGD peptide and dimer RGD peptide were labelled well. The reaction of Prepareing ¹⁸F^- labelled RGD peptides can be divided five steps: ¹⁸F-F^-production, the nucleophilic reaction, the hydrolization reaction of protected groups, the reaction of [¹⁸F] FBA with TSTU, and reaction of [¹⁸F] SFB with RGD. And, the synthesis of the second labelled precursor called the ¹⁸F labelled group ([ ¹⁸F] SFB) was one of the key steps for labelling RGD peptide. Therefore, we studied the efficiency factors on preparing [¹⁸F] SFB. The most important steps were nucleophilic reaction and the reaction of [ ¹⁸] FBA with the TSTU. During nucleophilic reaction, using anhydrous DMSO as resolver of labelled precursor (TMA·OTS) setting 115℃heating 10min, the efficiency of nucleophilic is higher. During studying reaction of [¹⁸F] FBA with TSTU, setting 100°C heating 10min to obtain [¹⁸F] SFB. As a reasult, the efficiency was higher. Intermediat products were separated by the solid phase separation extraction (SPE) method using C18 column. As a result, the radiochemistry purity had achieved more than 90%. After dried [¹⁸F]SFB be abtained, RGD peptides, which were dissolved in the anhydrous DMSO solution, were gethered into the dried [¹⁸F] SFB. Setting temprature at 60℃, reacted for 30min in water bath. The RGD peptide tracers were separated by the gradient HPLC. We obtained high radiochemistry purity and yield. The two tracers had good stability in the physiological saline and in the embryo cow blood serum (FBS) system for 12 hours.Do distribution experiments with C57BL/6N mices planted with Lewis lung cancer. The results appeared the two tracers had rapid, high tumor uptaking and rapid blood washout. Compared to [¹⁸F] FB-RGD, [¹⁸F] FB-RGD2 had the higher tumor uptaking, prolonging tumor uptaking times and decreasing uptaking in small intestine and liver. However, [¹⁸F] FB-RGD2 had higher uptaking in kidney. After injected using the monomer RGD peptides in advance, mices were injected to this two tracers respectively. One hour later, the blocking experiments had been done. Results indicated that the two tracers could combindα_vβ₃ integrins well and [¹⁸F] FB-RGD2 had the stronger affinity withα_vβ₃ integrins. Do PET imaging using [¹⁸F] FB-RGD2 and [¹⁸F] FDG. [¹⁸F]FB-RGD2 could target to the function location of tumor organization better. It could get a better PET image using [¹⁸F] FB-RGD2 as tracer. Compared to [¹⁸F] FDG, [¹⁸F] FB-RGD2 was more sensitively, specificly targetting to tumor tissue than [¹⁸F] FDG. And it was binded to the intergrinα_vβ₃ better.This experiment was useful for automatic praparing of [¹⁸F]SFB and labelling peptide fast. It was base step for making ¹⁸F labelled RGD to clinic diagnosis peptides. Therefore, it can provide important references to research on diagnosis methods of high sensitive and specificity localization of the tumor, selecting specific tumor treatment medicine and drug pharmacology of the anti-tumor blood vessel drug.