Wilbur D S, Hamlin D K, Pathare P M, Heusser S, Vessella R L, Buhler K R, Stray J E, Daniel J, Quadros E V, McLoughlin P, Morgan A C
Department of Radiation Oncology, University of Washington, Seattle 98195, USA.
Bioconjug Chem. 1996 Jul-Aug;7(4):461-74. doi: 10.1021/bc960033x.
A new method of preparing radiolabeled cobalamin derivatives has been developed. The method involves the use of cobalamin-tri-n-butylstannyl hippurate conjugates as intermediates to obtain radioiodinated cobalamin-iodohippurate conjugates. The arylstannyl functionality was used as an exchangeable group to obtain high specific activity radioiodinations and to circumvent some deleterious side reactions common to cobalamins under electrophilic iodination conditions. The first step in the synthesis of tri-n--butylstannyl hippurate conjugates was to obtain free carboxylate groups on the cobalamin moiety. This was accomplished by mild acid hydrolysis of the b-, d-, or e-propionamide side chains on the corrin ring, followed by careful separation of the isomeric products. The second step was to couple a linking molecule (diaminododecane) to the carboxylate. The final step was to conjugate p-tri-n-butylstannyl hippurate to the cobalamin-diaminododecane adduct. All three isomeric cobalamin-p-tri-n-butylstannyl hippurate conjugates were prepared, as were the corresponding cobalamin-p-iodohippurate conjugates (HPLC standards). Radioiodination reactions were conducted with N-chlorosuccinimide and Na[*I]I in Me OH using conditions previously developed for arylstannylations. However, unlike the previous reactions, a key factor in obtaining the desired radioiodinated cobalamins was that the reaction be conducted under neutral conditions. Isolated yields of 40-65% were obtained for all three cobalamin isomers. Specific activities of 10-33% theoretical were obtained for the radioiodinated cobalamins. Evaluation of competitive binding of (nonradioactive) cobalamin-iodohippurate conjugates with recombinant human transcobalamin II showed that the e-isomer bound nearly as well as [57Co]cyanocobalamin (50%), whereas the b-isomer had decreased binding (6%) and the d-isomer was significantly decreased in its binding (0.7%). Two biodistributions of the radioiodinated e-isomer were conducted in athymic mice. One biodistribution investigated tissue localization in mice bearing a renal cell carcinoma xenograft, and the other biodistribution investigated tissue localization when the radioiodinated cyanocobalamin was mixed with 1% BSA prior to injection. A comparison of the results of the two biodistributions and a discussion of how they relate to previous [57/60Co]cyanocobalamin biodistributions are provided.
已开发出一种制备放射性标记钴胺素衍生物的新方法。该方法涉及使用钴胺素 - 三正丁基锡马尿酸酯共轭物作为中间体来获得放射性碘化钴胺素 - 碘马尿酸酯共轭物。芳基锡官能团用作可交换基团，以获得高比活度的放射性碘化产物，并规避在亲电碘化条件下钴胺素常见的一些有害副反应。合成三正丁基锡马尿酸酯共轭物的第一步是在钴胺素部分获得游离羧基。这通过对咕啉环上的β -、δ - 或ε - 丙酰胺侧链进行温和酸水解，然后仔细分离异构体产物来实现。第二步是将连接分子（二氨基十二烷）与羧基偶联。最后一步是将对 - 三正丁基锡马尿酸酯与钴胺素 - 二氨基十二烷加合物共轭。制备了所有三种异构体钴胺素 - 对 - 三正丁基锡马尿酸酯共轭物，以及相应的钴胺素 - 对 - 碘马尿酸酯共轭物（HPLC标准品）。放射性碘化反应使用先前为芳基锡化反应开发的条件，在甲醇中用N - 氯代琥珀酰亚胺和Na[*I]I进行。然而，与先前的反应不同，获得所需放射性碘化钴胺素的一个关键因素是反应要在中性条件下进行。所有三种钴胺素异构体的分离产率为40 - 65%。放射性碘化钴胺素的比活度为理论值的10 - 33%。对（非放射性）钴胺素 - 碘马尿酸酯共轭物与重组人转钴胺素II的竞争结合评估表明，ε - 异构体的结合能力几乎与[57Co]氰钴胺（50%）相同，而β - 异构体的结合能力下降（6%），δ - 异构体的结合能力显著下降（0.7%）。在无胸腺小鼠中进行了放射性碘化ε - 异构体的两次生物分布研究。一次生物分布研究了荷肾细胞癌异种移植瘤小鼠的组织定位，另一次生物分布研究了在注射前将放射性碘化氰钴胺与1%牛血清白蛋白混合时的组织定位。提供了两次生物分布结果的比较以及它们与先前[57/60Co]氰钴胺生物分布的关系讨论。
