Synthesis and characterization of pH-sensitive, biotinylated MRI contrast agents and their conjugates with avidin
作者:Sandip M. Vibhute、Jörn Engelmann、Tatjana Verbić、Martin E. Maier、Nikos K. Logothetis、Goran Angelovski
DOI:10.1039/c2ob26555a
日期:——
Responsive or smart contrast agents (SCAs) provide new opportunities in magnetic resonance imaging (MRI) to examine a number of physiological and pathological events. However, their application in vivo remains challenging. Therefore, much research is focused on the optimization of their properties, to enable their use in additional imaging modalities, pre-targeted delivery, or to increase the local concentration of the agent. The key feature in the SCA synthetic modification is the retention of their physicochemical properties related to the specific MR response. Here, we report the preparation and characterization of pH sensitive SCAs appended with a phosphonate pendant arm and either an aliphatic (GdL1) or aromatic linker (GdL2). The longitudinal relaxivity of GdL1 and GdL2 increases by 146% and 31%, respectively, while the pH decreases from 9 to 5. These two SCAs were converted to the biotinylated systems GdL3 and GdL4 and their interaction with avidin was investigated. The binding affinity with avidin was assessed with a fluorescence displacement assay and with MRI phantom experiments in a 3T MRI scanner. The fluorometric assay and MRI E-titrations revealed a 3 : 1 binding mode of GdL3–4 to avidin with the binding affinity as high as that of the parent avidin–biotin complex. The high binding affinity was confirmed with MRI by a competitive assay. The avidin–GdL3–4 complexes thus obtained exhibit changes in both r1 and r2 that are pH dependent. The results reveal a new pathway for the modification and improvement of SCAs to make them more suitable for in vivo application.
响应性或智能对比剂(SCAs)为磁共振成像(MRI)提供了新的机遇,以检测一系列生理和病理事件。然而,它们在体内的应用仍然面临挑战。因此,大量研究集中在优化其性能,以使其能够用于更多成像模式、前体定位递送或增加局部的对比剂浓度。SCAs合成修饰的关键特征是保持特定的MR响应相关的物理化学性质。在此,我们报告了制备和表征带有膦酸酯侧臂和对脂族(GdL1)或芳香族连接臂(GdL2)的pH敏感型SCAs。当pH从9降至5时,GdL1和GdL2的纵向弛豫率分别增加146%和31%。这两种SCAs被转化为生物素化的系统GdL3和GdL4,并研究了它们与亲和素的相互作用。结合亲和力通过荧光置换分析和3T MRI扫描仪中的MRI幻影实验进行评估。荧光分析法和MRI E滴定揭示了GdL3-4与亲和素之间存在3∶1的结合模式,其结合亲和力与亲和素-生物素复合物相当。通过竞争性分析,使用MRI确认了高结合亲和力。由此得到的亲和素-GdL3-4复合物在r1和r2上均呈pH依赖性变化。结果揭示了一条新的SCAs修饰和改进途径,使其更适合体内应用。