In Vitro And In Vivo Evaluation Of ¹⁸f-sfb-annexin B1 In Detecting Apoptosis

Part One 18F-SFB-Annexin B1 binding assay with apoptotic Jurkat cellsObject Phosphatidylserine(PS) is transferred from the inner layer to the outer layer of the cell membrane in the early stage of apoptosis,which is one of the representative events. Annexin B1(MW=37584 Da), a novel Ca2+-dependent PS-binding protein, has been shown to have a high affinity for PS exposed on the surface of apoptotic cells.18F-SFB-Annexin B1:a molecular probe targeting apoptosis developed by labeling Annexin B1 with 18F via N-succinimidyl-4-fluorobenzoate (SFB).Binding assay with apoptotic Jurkat cells was carried out to evaluate the in vitro biological activity of 18F-SFB-Annexin B1.Methods Anti-Fas monoclone antibody was used to induce apoptosis in Jurkat cells(10,30,60,90,120 min).γcounter was used to measure the radioactivity of the samples,which reflected the uptake of 18F-SFB-Annexin B1. Flow cytometer (FCM) was utilized to detect apoptosis in the cells,confirming that anti-Fas apoptosis in Jurkat cells exist.Results Uptake of 18F-SFB-Annexin B1 in treated cells was obviously greater than untreated,and the uptake increased gradually as the action time increased. FCM proved that there were more apoptotic cells in treated samples than control sample.Conclusion These data suggested that 18F-SFB-Annexin B1 retain its in vitro biological activities. 18F-SFB-Annexin B1 therefore represents a novel class of detectors for apoptosis. Part Two Detecting apoptosis in vivo in a rabbit model using 18F-SFB-Annexin B1Object Apoptosis plays a critical role in the pathogenesis of cerebral and myocardial ischemia-reperfusion injury, transplant rejection, tumor response to chemotherapy and radiotherapy,and autoimmune and neurodegenerative diseases. Thus, the detection and quantification of apoptosis in vivo could provide insight into the disease status of a patient and/or the efficacy of a particular treatment. Annexin B1, a member of a novel Annexin subfamily, has high PS-binding activity equivalent to that of Annexin V, radiolabeled Annexin B1 may also be applied as an in vivo marker of apoptosis. The aim of this study was to evaluate the potentiality and feasibility of 18F-SFB-Annexin B1 in detecting apoptosis in vivo.Methods Unilateral renal ischemia/reperfusion injury was produced by transient (45 min) ligation of the right renal artery followed by 24-h reperfusion in the rabbit. Then,18F-SFB-Annexin B1 was injected via ear vein.PET/CT static imaging were performed 10,30,60,90,120,240 min postinjection,respectively.Apoptosis in kidneys was confirmed by TUNEL and HE staining.Results Marked accumulation of the radiotracer in the damaged ischemic kidney, but not in the control intact kidney was observed in the PET/CT images 4 h postinjection.Analysis by ROI technique indicated that the right kidney is 2.4 times as much as the left kidney in the terms of SUVmax. The TUNEL staining confirmed that there were a lot of cells undergoing apoptosis in the treated kidney.HE staining also confirmed that the existence of apoptosis in the right kidney morphologically.Conclusion These data suggested that 18F-SFB-Annexin B1 may be useful as a novel radioligand for the noninvasive detecting of apoptosis in in vivo.