Starmans Lucas W E, van Duijnhoven Sander M J, Rossin Raffaella, Berben Monique, Aime Silvio, Daemen Mat J A P, Nicolay Klaas, Grüll Holger
Department of Biomedical Engineering, Eindhoven University of Technology , Eindhoven, The Netherlands.
Mol Pharm. 2013 Nov 4;10(11):4309-21. doi: 10.1021/mp400406x. Epub 2013 Oct 23.
Fibrin targeting is an attractive strategy for nuclear imaging of thrombosis, atherosclerosis and cancer. Recently, FibPep, an (111)In-labeled fibrin-binding peptide, was established as a tracer for fibrin SPECT imaging and was reported to allow sensitive detection of minute thrombi in mice using SPECT. In this study, we developed EPep, a novel (111)In-labeled fibrin-binding peptide containing the fibrin-binding domain of the clinically verified EP-2104R peptide, and sought to compare the potential of EPep and FibPep as tracers for fibrin SPECT imaging. In vitro, both EPep and FibPep showed high stability in serum, but were less stable in liver and kidney homogenate assays. Both peptide probes displayed comparable affinities toward human and mouse derived fibrin (Kd ≈ 1 μM), and similarly to FibPep, EPep showed fast blood clearance, low nontarget uptake and high thrombus uptake (6.8 ± 1.2% ID g(-1)) in a mouse carotid artery thrombosis model. Furthermore, EPep showed a similar affinity toward rat derived fibrin (Kd ≈ 1 μM), displayed high thrombus uptake in a rat carotid artery thrombosis model (0.74 ± 0.39% ID g(-1)), and allowed sensitive detection of thrombosis in rats using SPECT. In contrast, FibPep displayed a significantly lower affinity toward rat derived fibrin (Kd ≈ 14 μM) and low uptake in rat thrombi (0.06 ± 0.02% ID g(-1)) and did not allow clear visualization of carotid artery thrombosis in rats using SPECT. These results were confirmed ex vivo by autoradiography, which showed a 7-fold higher ratio of activity in the thrombus over the contralateral carotid artery for EPep in comparison to FibPep. These findings suggest that the FibPep binding fibrin epitope is not fully homologous between humans and rats, and that preclinical rat models of disease should not be employed to gauge the clinical potential of FibPep. In conclusion, both peptides showed approximately similar metabolic stability and affinity toward human and mouse derived fibrin, and displayed high thrombus uptake in a mouse carotid artery thrombosis model. Therefore, both EPep and FibPep are promising fibrin targeted tracers for translation into clinical settings to serve as novel tools for molecular imaging of fibrin.
纤维蛋白靶向是用于血栓形成、动脉粥样硬化和癌症核成像的一种有吸引力的策略。最近，FibPep，一种（111）铟标记的纤维蛋白结合肽，被确立为纤维蛋白SPECT成像的示踪剂，据报道它能够使用SPECT在小鼠中灵敏地检测微小血栓。在本研究中，我们开发了EPep，一种新型的（111）铟标记的纤维蛋白结合肽，其包含经临床验证的EP - 2104R肽的纤维蛋白结合结构域，并试图比较EPep和FibPep作为纤维蛋白SPECT成像示踪剂的潜力。在体外，EPep和FibPep在血清中均表现出高稳定性，但在肝脏和肾脏匀浆试验中稳定性较差。两种肽探针对人和小鼠来源的纤维蛋白均表现出相当的亲和力（解离常数Kd≈1 μM），并且与FibPep类似，EPep在小鼠颈动脉血栓形成模型中显示出快速的血液清除、低非靶摄取和高血栓摄取（6.8±1.2%注射剂量每克）。此外，EPep对大鼠来源的纤维蛋白表现出相似的亲和力（Kd≈1 μM），在大鼠颈动脉血栓形成模型中显示出高血栓摄取（0.74±0.39%注射剂量每克），并能够使用SPECT灵敏地检测大鼠中的血栓形成。相比之下，FibPep对大鼠来源的纤维蛋白表现出显著更低的亲和力（Kd≈14 μM），在大鼠血栓中的摄取较低（0.06±0.02%注射剂量每克），并且不能使用SPECT清晰地显示大鼠颈动脉血栓形成。这些结果通过放射自显影在体外得到证实，其显示与FibPep相比，EPep在血栓中的活性与对侧颈动脉的活性比值高7倍。这些发现表明FibPep结合的纤维蛋白表位在人和大鼠之间并非完全同源，并且疾病的临床前大鼠模型不应被用于评估FibPep 的临床潜力。总之，两种肽在代谢稳定性以及对人和小鼠来源纤维蛋白的亲和力方面表现出大致相似性，并在小鼠颈动脉血栓形成模型中显示出高血栓摄取。因此，EPep和FibPep都是有前景的纤维蛋白靶向示踪剂，有望转化为临床应用，作为纤维蛋白分子成像的新型工具。
