Martin Sebastian, Wendlinger Lennard, Litvinenko Alexandra, Faizova Radmila, Schottelius Margret
Translational Radiopharmaceutical Sciences, Department of Nuclear Medicine and Department of Oncology, Centre Hospitalier Universitaire Vaudois (CHUV) and University of Lausanne (UNIL), Rue du Bugnon 25A, Agora, Lausanne, CH-1011, Switzerland.
AGORA, Pôle de recherche sur le cancer, Lausanne, 1011, Switzerland.
EJNMMI Radiopharm Chem. 2024 Mar 21;9(1):23. doi: 10.1186/s41181-024-00254-2.
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 Ga-, Cu- and Tc-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 Ga, Cu and Tc salts on the G10 cartridges was quantitative up to the specified elution volume (1.2 mL) for Ga and Tc and 99.6% for Cu. Even at increased elution volumes of 1.5-2 mL, RCPs of the eluted Ga- and Tc -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 [Ga]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.
在临床常规和临床前研究中，放射性金属标记的肽类放射性药物最终纯化的既定标准程序是基于柱式的反相（RP）固相萃取（SPE）。它能快速、定量地从亲水性杂质中分离出放射性标记的肽，并且易于整合到自动化合成程序中。然而，从RP柱上洗脱产物需要使用有机溶剂，且产物回收率有时有限。因此，研究了一种基于市售尺寸排阻柱的替代纯化方法。
由于大多数肽类放射性药物的分子量>1 kDa，因此使用截留分子量为700 Da的Sephadex G10柱对多种Ga、Cu和Tc标记的实验性肽类放射性示踪剂以及临床相关配体PSMA-617进行最终纯化。将结果（放射化学纯度（RCP，通过ITLC测定）、从固相载体上的回收率）与相应的标准RP-SPE方法进行比较。一般来说，未反应的Ga、Cu和Tc盐在G10柱上的保留量在Ga和Tc的指定洗脱体积（1.2 mL）以及Cu的99.6%以内是定量的。即使在洗脱体积增加到1.5 - 2 mL时，洗脱的Ga和Tc放射性肽的RCP仍>99%。对于所有分子量≥2 kDa的肽，在相应调整洗脱体积后，从G10柱上的产物回收率始终>85%。[Ga]Ga-PSMA-617的产物回收率最低（67%，1.2 mL至84%，2 mL）。发现最终产物溶液的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柱可重复使用多达20次而不影响性能，并成功地将该方法应用于自动化放射性合成程序中。
总体而言，尺寸排阻纯化在10 - 12分钟内可在生理盐水中以优异的放射化学纯度（>99%）得到所有肽类放射性药物。尽管产物回收率略低于经典的SPE纯化，但该方法的优点是完全避免了有机溶剂，是一种经济高效、易于实施的放射性示踪剂自动化合成纯化方法。
