Synthesis and Labeling of Two Fibrin-Targeted Peptides (HYNIC-GPRPILE, HYNIC-GPKGAAD) Using Technetium-99m and In Vitro Evaluation of Fibrin Binding and Platelet Aggregation

Early detection of thrombus and its location in the body are critical factors for the treatment of thrombosis related diseases. Fibrin is the main component of thrombus, abundant in all thrombi, and is not found in non-pathological conditions. The presenceof fibrin in all types of thrombi and its low concentration in blood makes it a sensitive and specific target for imaging studies of thrombus. Fibrin also accumulates in malignant tumors. Thus, fibrin imaging can be used in oncology, atherosclerosis, and thrombosis-related pathologies such as pulmonary emboli and deep vein thrombosis. Different compounds such as antibodies, nanoparticles, and peptides have been studied for fibrin imaging. Among them, peptides are more attractive because of better pharmacokinetics, simple and cheap preparation, and better radiolabeling methods. In this study, two peptides (HYNIC-GPRPILE, HYNIC-GPKGAAD) designed to target fibrin were synthesized. The peptides were identified by LC-MS. The stability and platelet aggregation of peptides were determined. Peptides were radiolabeled with 99mTc using HYNIC as chelating agent. The release of 99mTc and fibrin binding of radiopeptideswere evaluated. Based on the results, peptides were stable in human plasma for at least 6 h and had no effect on platelet aggregation. Peptides were radiolabeled with pertechnetate at 80°C in 30 min. Radiochemical purity was over 95%. Radiopeptides were stable in human plasma and there was less than 5% release of 99mTc. The fibrin binding of radiopeptides was 70%>. Since peptides had no platelet binding activity, it can be concluded that binding of radiopeptides to fibrin is specific.