Synthesis of Fibrin=Binding Peptide ¹³¹I-YSSCREKA for Targeting Early Thrombosis

To develop the radiotracer for imaging vein thrombosis, the ¹³¹I labeled octapeptide containing CREKA(Cys-Arg-Glu-Lys-Ala) sequence had been proved to bind to fibrin-fibronectin complexes in clotted plasma and was injected into animals models to investigate the targeting effect on early thrombosis. The octapeptide YSSCREKA(Tyr-(D)Ser-(D)Ser-Cys-Arg-Glu-Lys-Ala) was constructed and labeled with ¹³¹I by Ch-T method. The ¹³¹I radiolabeling yield and radiochemical purity are (77.2±1.1)% and (90.0±3.1)%（n=3） respectively. ¹³¹I-YSSCREKA performs high stability in vitro at room temperature within 72 h. The fresh vein thrombus is clearly visible at 20 h on inferior vena cava of rabbits. The count ratio of thrombus/blood by region of interest(ROI) method is 1.36. The thrombus uptake of radiolabeled peptide at 20 h post-injection is (0.19±0.06)ID%/g（n=5）. The count ratios of thrombus/muscle and thrombus/blood are 3.80 and 1.90, respectively. ¹³¹I-YSSCREKA is a promising tracer for early thrombosis and is worthy to be further studied to improve the thrombus uptake.