The detection limit of a Gd3+-based T1 agent is substantially reduced when targeted to a protein microdomain
The detection limit of a Gd3+-based T1 agent is substantially reduced when targeted to a protein microdomain
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DOI：
10.1016/j.mri.2007.11.002
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发表时间：
2008-06-01
影响因子：
2.5
通讯作者：
Sherry, A. Dean
中科院分区：
文献类型：
--
作者：
Hanaoka, Kenjiro;Lubag, Angelo Josue M.;Sherry, A. Dean
钆（Gd³⁺）的简单低分子量螯合物，例如目前临床磁共振成像（MRI）中使用的那些，对于大多数分子成像应用来说被认为灵敏度太低。在此，我们在受体浓度精确已知的模型中评估了一种基于低分子量Gd³⁺的分子靶向T₁造影剂的检测限（DL）。数据表明，即使受体的总体浓度相当低，聚集在一起形成高局部浓度微区的受体也能成功成像。通过噬菌体展示鉴定出一种靶向抗FLAG抗体的GdDO₃A - 肽，对其进行了合成、纯化和表征。将T₁加权磁共振图像与在大量溶液中结合抗体的造影剂以及结合在琼脂糖珠上的抗体的造影剂进行了比较。荧光竞争结合试验表明，该造影剂对抗体具有高结合亲和力（K₍D₎ = 150 nM），而溶液中GdDO₃A - 肽/抗FLAG抗体完全结合时的弛豫率相对适中，为17 mM⁻¹ s⁻¹。在浓度低于约9 μM时，造影剂/抗体复合物在磁共振成像中无信号，但当呈现给聚集在琼脂糖珠表面的抗体时，在总体浓度低至4 μM时仍可检测到。这些结果为其他具有更高完全结合弛豫率或与聚集受体分子结合的多聚体结构的T₁造影剂的检测限提供了估计。结果表明，分子靶向造影剂的灵敏度取决于目标蛋白的局部微区浓度和结合复合物的分子弛豫率。提出了一个模型，该模型预测对于由单个Gd³⁺复合物组成且结合弛豫率为100 mM⁻¹ s⁻¹，或者更合理地，由四个连接的Gd³⁺复合物组成且每个复合物结合弛豫率为25 mM⁻¹ s⁻¹的分子靶向造影剂，在9.4 T时蛋白质微区的检测限约为690 nM。这些实验和外推的检测限均远低于当前文献估计值，这表明检测低分子量分子靶向T₁造影剂并非不切实际的目标。（C）2008爱思唯尔公司。保留所有权利。
Simple low molecular weight (MW) chelates of Gd3+ such as those currently used in clinical MRI are considered too insensitive for most molecular imaging applications. Here, we evaluated the detection limit (DL) of a molecularly targeted low MW Gd3+-based T-1 agent in a model where the receptor concentration was precisely known. The data demonstrate that receptors clustered together to form a microdomain of high local concentration can be imaged successfully even when the bulk concentration of the receptor is quite low. A GdDO3A-peptide identified by phage display to target the anti-FLAG antibody was synthesized, purified and characterized. T-1-weighted MR images were compared with the agent bound to antibody in bulk solution and with the agent bound to the antibody localized on agarose beads. Fluorescence competition binding assays show that the agent has a high binding affinity (K-D=150 nM) for the antibody, while the fully bound relaxivity of the GdDO3A-peptide/anti-FLAG antibody in solution was a relatively modest 17 mM(-1) s(-1). The agent/antibody complex was MR silent at concentrations below similar to 9 mu M but was detectable down to 4 mu M bulk concentrations when presented to antibody clustered together on the surface of agarose beads. These results provided an estimate of the DLs for other T-1-based agents with higher fully bound relaxivities or multimeric structures bound to clustered receptor molecules. The results demonstrate that the sensitivity of molecularly targeted contrast agents depends on the local microdomain concentration of the target protein and the molecular relaxivity of the bound complex. A model is presented, which predicts that for a molecularly targeted agent consisting of a single Gd3+ complex with bound relaxivity of 100 mM(-1) s(-1) or, more reasonably, four tethered Gd3+ complexes each having a bound relaxivity of 25 mM(-1) s(-1), the DL of a protein microdomain is similar to 690 nM at 9.4 T. These experimental and extrapolated DLs are both well below current literature estimates and suggests that detection of low MW molecularly targeted T-1 agents is not an unrealistic goal. (C) 2008 Elsevier Inc. All rights reserved.