Institut de Chimie Moléculaire de l'Université de Bourgogne, UMR 6302, CNRS, Université de Bourgogne, Dijon 21000, France.
Bioconjug Chem. 2024 May 15;35(5):633-637. doi: 10.1021/acs.bioconjchem.4c00105. Epub 2024 Apr 24.
Zirconium-89 is the most widely used radioisotope for immunoPET because its physical half-life (78.2 h) suits the one of antibodies. Desferrioxamine B (DFO) is the standard chelator for the complexation of zirconium(IV), and its bifunctional version, containing a phenylisothiocyanate function, is the most commonly used for the conjugation of DFO to proteins. However, preliminary results have shown that the thiourea link obtained from the conjugation of isothiocyanate and lysines is sensitive to the ionizing radiation generated by the radioisotope, leading to the rupture of the link and the release of the chelator/radiometal complex. This radiolysis phenomenon could produce nonspecific signal and prevent the detection of bone metastasis, as free zirconium accumulates into the bones. The aim of this work was to study the stability of a selection of conjugation linkers in Zr-labeled immunoconjugates. We have synthesized several DFO-based bifunctional chelators appended with an isothiocyanate moiety, a bicyclononyne, or a squaramate ester. Two antibodies (trastuzumab and rituximab) were conjugated and radiolabeled with zirconium-89. The effect of increasing activities of zirconium-89 on the integrity of the bioconjugate bearing thiourea links was evaluated as well as the impact of the presence of a radioprotectant. The stability of the radiolabeled antibodies was studied over 7 days in PBS and human plasma. Radioconjugates' integrity was evaluated using iTLC and size-exclusion chromatography. This study shows that the nature of the linker between the chelator and biomolecule can have a strong impact on the stability of the Zr-labeled conjugates, as well as on the aggregation of the conjugates.
锆-89 是免疫 PET 中最常用的放射性同位素，因为其物理半衰期（78.2 h）适合于抗体。去铁胺 B（DFO）是用于配合锆（IV）的标准螯合剂，其双功能版本，含有苯异硫氰酸酯功能，是最常用于将 DFO 与蛋白质结合的。然而，初步结果表明，从异硫氰酸酯和赖氨酸的缀合获得的硫脲键对放射性同位素产生的电离辐射敏感，导致键的断裂和螯合剂/放射性金属配合物的释放。这种放射分解现象可能会产生非特异性信号，并阻止骨转移的检测，因为游离的锆会积聚到骨头中。这项工作的目的是研究 Zr 标记免疫缀合物中选择的连接键的稳定性。我们合成了几种基于 DFO 的双功能螯合剂，带有异硫氰酸酯部分、二环壬烯或 squaramate 酯。两种抗体（曲妥珠单抗和利妥昔单抗）被缀合并用锆-89 标记。评估了增加锆-89 活性对带有硫脲键的生物缀合物完整性的影响，以及存在放射保护剂的影响。在 PBS 和人血浆中研究了放射性抗体在 7 天内的稳定性。使用 iTLC 和分子筛层析法评估放射性缀合物的完整性。这项研究表明，螯合剂和生物分子之间的连接体的性质会强烈影响 Zr 标记缀合物的稳定性，以及缀合物的聚集。
