Nwe Kido, Xu Heng, Regino Celeste Aida S, Bernardo Marcelino, Ileva Lilia, Riffle Lisa, Wong Karen J, Brechbiel Martin W
Radioimmune and Inorganic Chemistry Section, Radiation Oncology Branch, and Molecular Imaging Program, National Cancer Institute, 10 Center Drive, Bethesda, Maryland 20892, USA.
Bioconjug Chem. 2009 Jul;20(7):1412-8. doi: 10.1021/bc900057z.
In this paper, we report a new method to prepare and characterize a contrast agent based on a fourth-generation (G4) polyamidoamine (PAMAM) dendrimer conjugated to the gadolinium complex of the bifunctional diethylenetriamine pentaacetic acid derivative (1B4M-DTPA). The method involves preforming the metal-ligand chelate in alcohol prior to conjugation to the dendrimer. The dendrimer-based agent was purified by a Sephadex G-25 column and characterized by elemental analysis. The analysis and SE-HPLC data gave a chelate to dendrimer ratio of 30:1 suggesting conjugation at approximately every other amine terminal on the dendrimer. Molar relaxivity of the agent measured at pH 7.4 displayed a higher value than that of the analogous G4 dendrimer based agent prepared by the postmetal incorporation method (r(1) = 26.9 vs 13.9 mM(-1) s(-1) at 3 T and 22 degrees C). This is hypothesized to be due to the higher hydrophobicity of this conjugate and the lack of available charged carboxylate groups from noncomplexed free ligands that might coordinate to the metal and thus also reduce water exchange sites. Additionally, the distribution populations of compounds that result from the postmetal incorporation route are eliminated from the current product simplifying characterization as quality control issues pertaining to the production of such agents for clinical use as MR contrast agents. In vivo imaging in mice showed a reasonably fast clearance (t(1/2) = 24 min) suggesting a viable agent for use in clinical application.
在本文中，我们报告了一种制备和表征基于第四代（G4）聚酰胺-胺（PAMAM）树枝状大分子的造影剂的新方法，该树枝状大分子与双功能二乙烯三胺五乙酸衍生物（1B4M-DTPA）的钆配合物共轭。该方法包括在与树枝状大分子共轭之前，先在醇中形成金属-配体螯合物。基于树枝状大分子的试剂通过Sephadex G-25柱纯化，并通过元素分析进行表征。分析和SE-HPLC数据给出螯合物与树枝状大分子的比例为30:1，表明在树枝状大分子上大约每隔一个胺末端进行共轭。在pH 7.4下测量的该试剂的摩尔弛豫率显示出比通过金属后掺入法制备的类似G4树枝状大分子试剂更高的值（在3 T和22℃下，r(1)=26.9 vs 13.9 mM(-1)s(-1)）。据推测，这是由于该共轭物具有更高的疏水性，并且不存在未络合的游离配体中可能与金属配位从而也减少水交换位点的带电荷羧基。此外，当前产品中消除了由金属后掺入途径产生的化合物的分布群体，简化了表征，因为与作为磁共振造影剂的此类试剂的生产相关的质量控制问题。在小鼠体内成像显示清除速度相当快（t(1/2)=24分钟），表明该试剂可用于临床应用。
