Trommer Johanna, Ullrich Martin, Reissig Falco, Brühlmann Santiago Andres, Nitt-Weber Anne-Kathrin, Novy Zbynek, Hajduova Katarina, Kurfurstova Daniela, Hendrychova Romana, Bouchal Jan, Petrik Milos, Neuber Christin, Sihver Wiebke, Stadlbauer Sven, Pietzsch Jens, Kreller Martin, Kopka Klaus, Mamat Constantin, Zarschler Kristof
Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiopharmaceutical Cancer Research, Dresden, Germany.
Institute of Molecular and Translational Medicine, Faculty of Medicine and Dentistry, Palacký University, Olomouc, Czech Republic.
EJNMMI Radiopharm Chem. 2025 Jun 19;10(1):31. doi: 10.1186/s41181-025-00354-7.
Targeted alpha therapy represents an advanced and rapidly evolving form of precision cancer treatment with increasing importance in recent years. The alpha-emitter Ac plays a key role in this clinical development due to its attractive physical and chemical properties. In this context, the macropa chelator has favorable characteristics in terms of labeling conditions and complex stability, making its derivatives exceptionally appealing for Ac-labeling of heat-sensitive biomolecules. However, preclinical evaluation of such Ac-containing molecules and comprehensive assessment of their pharmacokinetics, dosimetry and radiobiology necessitate a suitable diagnostic counterpart. Due to its attractive radiation properties, La represents an adequate positron-emitting radionuclide to form a matched pair with Ac for macropa-based radiopharmaceuticals. Herein, we describe the preparation and radiopharmacological characterization of macropa-functionalized, La/Ac-labeled single-domain antibodies (sdAbs) targeting the epidermal growth factor receptor (EGFR) to demonstrate the general suitability of this theranostic pair of radionuclides.
The synthesis of a clickable, bicyclononyne-modified macropa chelator and its site-specific conjugation to azide-modified, monovalent and biparatopic sdAbs is presented. Subsequent labeling at room temperature (rt) for 15 min resulted in molar activities of 30 MBq/nmol for La and 0.5 MBq/nmol for Ac, respectively. In vitro studies using the La-labeled sdAbs revealed comparable binding characteristics, but an enhanced cellular internalization of the biparatopic variant compared to its monovalent counterparts. This increased uptake consequently resulted in higher cytotoxicity of the Ac-labeled biparatopic conjugate. In vivo PET imaging of the La-labeled conjugates indicated comparable uptake and retention of the mono- and biparatopic variants in liver and kidneys, with the former showing slightly higher tumor accumulation. Ex vivo biodistribution studies conducted with Ac-labeled conjugates largely confirmed the findings obtained by PET imaging, albeit with a marginally higher tumor accumulation of the biparatopic Ac-radioimmunoconjugate. Final histological examinations of tumor and kidney tissues showed DNA damage in the renal cortex of the Ac-radioimmunoconjugate-treated mice, but no differences in the number of γ-H2AX-positive cells in the corresponding tumor tissues could be detected.
We present a comprehensive study on the theranostic application of La and Ac for antibody-based biomolecules and lay the foundation for the future application of this matched pair of radionuclides towards labeling of heat-sensitive, macropa-functionalized radiopharmaceuticals in general.
The online version contains supplementary material available at 10.1186/s41181-025-00354-7.
靶向α治疗是一种先进且快速发展的精准癌症治疗形式，近年来愈发重要。α发射体锕（Ac）因其具有吸引力的物理和化学性质，在这一临床发展中发挥着关键作用。在此背景下，大环螯合剂在标记条件和配合物稳定性方面具有良好特性，使其衍生物对于热敏生物分子的Ac标记格外具有吸引力。然而，对这类含Ac分子进行临床前评估以及对其药代动力学、剂量学和放射生物学进行全面评估，需要合适的诊断对应物。由于其具有吸引力的辐射特性，镧（La）是一种合适的正电子发射放射性核素，可与Ac形成基于大环的放射性药物的匹配对。在此，我们描述了靶向表皮生长因子受体（EGFR）的大环功能化、La/Ac标记的单域抗体（sdAb）的制备及放射药理学特性，以证明这一治疗诊断用放射性核素对的总体适用性。
展示了一种可点击的、双环壬炔修饰的大环螯合剂的合成及其与叠氮修饰的单价和双特异性sdAb的位点特异性共轭。随后在室温下标记15分钟，得到的La的摩尔活度为30 MBq/nmol，Ac的摩尔活度为0.5 MBq/nmol。使用La标记的sdAb进行的体外研究显示出可比的结合特性，但与单价对应物相比，双特异性变体的细胞内化增强。这种摄取增加因此导致Ac标记的双特异性缀合物具有更高的细胞毒性。La标记的缀合物的体内PET成像表明，单价和双特异性变体在肝脏和肾脏中的摄取和滞留相当，前者在肿瘤中的积累略高。用Ac标记的缀合物进行的离体生物分布研究在很大程度上证实了PET成像获得的结果，尽管双特异性Ac放射性免疫缀合物在肿瘤中的积累略高。对肿瘤和肾脏组织的最终组织学检查显示，Ac放射性免疫缀合物处理的小鼠肾皮质有DNA损伤，但在相应肿瘤组织中未检测到γ-H2AX阳性细胞数量的差异。
我们对La和Ac在基于抗体的生物分子的治疗诊断应用方面进行了全面研究，为这一放射性核素匹配对未来用于标记一般热敏、大环功能化放射性药物奠定了基础。
在线版本包含可在10.1186/s41181-025-00354-7获取的补充材料。
