Floresta Giuseppe, Keeling George P, Memdouh Siham, Meszaros Levente K, de Rosales Rafael T M, Abbate Vincenzo
Department of Analytical, Environmental and Forensic Sciences, King's College London, London SE1 9NH, UK.
School of Biomedical Engineering & Imaging Sciences, King's College London, St Thomas' Hospital, London SE1 7EH, UK.
Biomedicines. 2021 Apr 1;9(4):367. doi: 10.3390/biomedicines9040367.
Hexadentate tris(3,4-hydroxypyridinone) ligands (THP) complex Fe at very low iron concentrations and their high affinities for oxophilic trivalent metal ions have led to their development for new applications as bifunctional chelators for the radiometal gallium-68 (Ga). THP-peptide bioconjugates rapidly and quantitatively complex Ga at room temperature, neutral pH, and micromolar ligand concentrations, making them amenable to kit-based radiosynthesis of Ga PET radiopharmaceuticals. With the aim to produce an -hydroxysuccinimide-(NHS)-THP reagent for kit-based Ga-labeling and PET imaging, THP-derivatives were designed and synthesized to exploit the advantages of NHS chemistry for coupling with peptides, proteins, and antibodies. The more stable five-carbon atoms linker product was selected for a proof-of-concept conjugation and radiolabeling study with an anti-programmed death ligand 1 (PD-L1) camelid single domain antibody (sdAb) under mild conditions and further evaluated for site-specific amide bond formation with a synthesized glucagon-like peptide-1 (GLP-1) targeting peptide using solid-phase synthesis. The obtained THP-GLP-1 conjugate was tested for its Ga chelating ability, demonstrating to be a promising candidate for the detection and monitoring of GLP-1 aberrant malignancies. The obtained sdAb-THP conjugate was radiolabeled with Ga under mild conditions, providing sufficient labeling yields after 5 min, demonstrating that the novel NHS-THP bifunctional chelator can be widely used to easily conjugate the THP moiety to different targeting molecules (e.g., antibodies, anticalins, or peptides) under mild conditions, paving the way to the synthesis of different imaging probes with all the advantages of THP radiochemistry.
六齿三（3,4-羟基吡啶酮）配体（THP）在极低铁浓度下就能与铁络合，且它们对亲氧三价金属离子具有高亲和力，这促使它们被开发用于作为放射性金属镓-68（Ga）的双功能螯合剂的新应用。THP-肽生物共轭物在室温、中性pH值和微摩尔配体浓度下能快速且定量地与Ga络合，使其适用于基于试剂盒的Ga PET放射性药物的放射性合成。为了生产用于基于试剂盒的Ga标记和PET成像的N-羟基琥珀酰亚胺（NHS）-THP试剂，设计并合成了THP衍生物，以利用NHS化学在与肽、蛋白质和抗体偶联方面的优势。选择了更稳定的五碳原子连接体产物，在温和条件下与抗程序性死亡配体1（PD-L1）骆驼单域抗体（sdAb）进行概念验证共轭和放射性标记研究，并使用固相合成法进一步评估其与合成的胰高血糖素样肽-1（GLP-1）靶向肽形成位点特异性酰胺键的情况。对获得的THP-GLP-1共轭物的Ga螯合能力进行了测试，证明它是检测和监测GLP-1异常恶性肿瘤的有前景的候选物。在温和条件下用Ga对获得的sdAb-THP共轭物进行放射性标记，5分钟后提供了足够的标记产率，表明新型NHS-THP双功能螯合剂可广泛用于在温和条件下轻松地将THP部分与不同的靶向分子（如抗体、抗钙素或肽）偶联，为合成具有THP放射化学所有优势的不同成像探针铺平了道路。
