Both in clinical routine and in preclinical research, the established standard procedure for the final purification of radiometal-labeled peptide radiopharmaceuticals is cartridge-based reversed-phase (RP) solid phase extraction (SPE). It allows the rapid and quantitative separation of the radiolabeled peptide from hydrophilic impurities and easy integration into automated synthesis procedures. However, product elution from RP cartridges necessitates the use of organic solvents and product recovery is sometimes limited. Thus, an alternative purification method based on commercially available size exclusion cartridges was investigated. Since most peptide radiopharmaceuticals have a molecular weight > 1 kDa, Sephadex G10 cartridges with a molecular size cut-off of 700 Da were used for the final purification of a broad palette of 68Ga-, 64Cu- and 99mTc-labeled experimental peptide radiotracers as well as the clinically relevant ligand PSMA-617. Results (radiochemical purity (RCP, determined by ITLC), recovery from the solid support) were compared to the respective standard RP-SPE method. Generally, retention of unreacted 68Ga, 64Cu and 99mTc salts on the G10 cartridges was quantitative up to the specified elution volume (1.2 mL) for 68Ga and 99mTc and 99.6% for 64Cu. Even at increased elution volumes of 1.5-2 mL, RCPs of the eluted 68Ga- and 99mTc -radiopeptides were > 99%. For all peptides with a molecular weight ≥ 2 kDa, product recovery from the G10 cartridges was consistently > 85% upon respective adjustment of the elution volume. Product recovery was lowest for [68Ga]Ga-PSMA-617 (67%, 1.2 mL to 84%, 2 mL). The pH of the final product solution was found to be volume-dependent (1.2 mL: pH 6.3; 1.5 mL: pH 5.9; 2 mL: pH 5.5). Notably, the G10 cartridges were reused up to 20 times without compromising performance, and implementation of the method in an automated radiosynthesis procedure was successful. Overall, size exclusion purification yielded all peptide radiopharmaceuticals in excellent radiochemical purities (> 99%) in saline within 10–12 min. Although product recovery is marginally inferior to classical SPE purifications, this method has the advantage of completely avoiding organic solvents and representing a cost-effective, easy-to-implement purification approach for automated radiotracer synthesis.

中文翻译：

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肽放射性药物伴随纯化和配制的尺寸排阻方法的验证

在临床常规和临床前研究中，放射性金属标记肽放射性药物最终纯化的既定标准程序是基于柱的反相 (RP) 固相萃取 (SPE)。它可以快速定量地从亲水性杂质中分离放射性标记的肽，并轻松集成到自动合成程序中。然而，从反相柱中洗脱产品需要使用有机溶剂，并且产品回收有时受到限制。因此，研究了基于市售尺寸排阻柱的替代纯化方法。由于大多数肽放射性药物的分子量 > 1 kDa，因此分子大小截止值为 700 Da 的 Sephadex G10 柱也用于最终纯化 68Ga、64Cu 和 99mTc 标记的实验性肽放射性示踪剂。作为临床相关配体 PSMA-617。将结果（放射化学纯度（RCP，通过 ITLC 测定）、固相支持物的回收率）与相应的标准 RP-SPE 方法进行比较。一般来说，G10 柱上未反应的 68Ga、64Cu 和 99mTc 盐的保留量是定量的，68Ga 和 99mTc 为指定洗脱体积 (1.2 mL)，64Cu 为 99.6%。即使洗脱体积增加到 1.5-2 mL，洗脱的 68Ga- 和 99mTc-放射性肽的 RCP 仍 > 99%。对于分子量 ≥ 2 kDa 的所有肽，在分别调整洗脱体积后，G10 柱的产物回收率始终 > 85%。 [68Ga]Ga-PSMA-617 的产物回收率最低（67%，1.2 mL 至 84%，2 mL）。发现最终产品溶液的 pH 值与体积有关（1.2 mL：pH 6.3；1.5 mL：pH 5.9；2 mL：pH 5.5）。值得注意的是，G10 试剂盒可重复使用多达 20 次而不会影响性能，并且该方法在自动放射合成程序中的实施是成功的。总体而言，尺寸排阻纯化可在 10-12 分钟内在盐水中产生具有优异放射化学纯度 (> 99%) 的所有肽放射性药物。尽管产物回收率略低于经典 SPE 纯化，但该方法的优点是完全避免使用有机溶剂，并且代表了一种经济有效、易于实施的自动放射性示踪剂合成纯化方法。