Trachsel Belinda, Valpreda Giulia, Lutz Alexandra, Schibli Roger, Mu Linjing, Béhé Martin
Center for Radiopharmaceutical Sciences, ETH-PSI-USZ, Paul Scherrer Institute (PSI), 5232, Villigen, Switzerland.
Department of Chemistry and Applied Biosciences, Institute of Pharmaceutical Sciences, ETH Zurich, 8093, Zurich, Switzerland.
EJNMMI Radiopharm Chem. 2023 Sep 4;8(1):21. doi: 10.1186/s41181-023-00206-2.
Peptidic radiotracers are preferentially excreted through the kidneys, which often results in high persistent renal retention of radioactivity, limiting or even preventing therapeutic clinical translation of these radiotracers. Exendin-4, which targets the glucagon-like-peptide 1 receptor (GLP-1R) overexpressed in insulinomas and in congenital hyperinsulinism, is an example thereof. The use of the tripeptide MVK, which is readily cleaved between methionine and valine by neprilysin at the renal brush border membrane, already showed promising results in reducing kidney uptake as reported in the literature. Based on our previous findings we were interested how linker variants with multiple copies of the MV-motive influence renal washout of radiolabelled exendin-4.
Three exendin-4 derivatives, carrying either one MVK, a MV-MVK or a MVK-MVK linker were synthesized and compared to a reference compound lacking a cleavable linker. In vivo results of a biodistribution in GLP-1R overexpressing tumour bearing mice at 24 h post-injection demonstrated a significant reduction (at least 57%) of renal retention of all In-labeled exendin-4 compounds equipped with a cleavable linker compared to the reference compound. While the insertion of the single linker MVK led to a reduction in kidney uptake of 70%, the dual approach with the linker MV-MVK slightly, but not significantly enhanced this effect, with 77% reduction in kidney uptake compared to the reference. In vitro IC and cell uptake studies were conducted and demonstrated that though the cleavable linkers negatively influenced the affinity towards the GLP-1R, cell uptake remained largely unaffected, except for the MV-MVK cleavable linker conjugate, which displayed lower cell uptake than the other compounds. Importantly, the tumour uptake in the biodistribution study was not significantly affected with 2.9, 2.5, 3.2 and 1.5% iA/g for radiolabelled Ex4, MVK-Ex4, MV-MVK-Ex4 and MVK-MVK-Ex4, respectively.
Cleavable linkers are highly efficient in reducing the radioactivity burden in the kidney. Though the dual linker approach using the instillation of MV-MVK or MVK-MVK between exendin-4 and the radiometal chelator did not significantly outperform the single cleavable linker MVK, further structural optimization or the combination of different cleavable linkers could be a stepping stone in reducing radiation-induced nephrotoxicity.
肽类放射性示踪剂主要通过肾脏排泄，这常常导致放射性在肾脏中长期大量滞留，限制甚至阻碍了这些放射性示踪剂在治疗中的临床应用。以Exendin-4为例，它作用于胰岛素瘤和先天性高胰岛素血症中过表达的胰高血糖素样肽-1受体（GLP-1R）。文献报道，使用三肽MVK，其在肾刷状缘膜处易被中性内肽酶在甲硫氨酸和缬氨酸之间裂解，在减少肾脏摄取方面已显示出有前景的结果。基于我们之前的研究结果，我们感兴趣的是带有多个MV基序拷贝的连接体变体如何影响放射性标记的Exendin-4的肾脏清除。
合成了三种Exendin-4衍生物，分别带有一个MVK、一个MV-MVK或一个MVK-MVK连接体，并与一种缺乏可裂解连接体的参考化合物进行比较。在注射后24小时对过表达GLP-1R的荷瘤小鼠进行生物分布的体内结果表明，与参考化合物相比，所有配备可裂解连接体的In标记的Exendin-4化合物的肾脏滞留率均显著降低（至少57%）。虽然单个连接体MVK的插入导致肾脏摄取减少70%，但使用连接体MV-MVK的双重方法略微但不显著地增强了这种效果，与参考相比肾脏摄取减少了77%。进行了体外IC和细胞摄取研究，结果表明，尽管可裂解连接体对与GLP-1R的亲和力有负面影响，但细胞摄取在很大程度上不受影响，除了MV-MVK可裂解连接体缀合物，其细胞摄取低于其他化合物。重要的是，生物分布研究中的肿瘤摄取没有受到显著影响，放射性标记的Ex4、MVK-Ex4、MV-MVK-Ex4和MVK-MVK-Ex4的肿瘤摄取分别为2.9%、2.5%、3.2%和1.5% iA/g。
可裂解连接体在减少肾脏放射性负担方面非常有效。虽然在Exendin-4和放射性金属螯合剂之间使用MV-MVK或MVK-MVK滴注的双重连接体方法没有显著优于单个可裂解连接体MVK，但进一步的结构优化或不同可裂解连接体的组合可能是减少辐射诱导的肾毒性的一个跳板。
