Ishizaki Atsushi, Mishiro Kenji, Shiba Kazuhiro, Hanaoka Hirofumi, Kinuya Seigo, Odani Akira, Ogawa Kazuma
Graduate School of Medical Sciences, Kanazawa University, Kanazawa, Japan.
Institute for Frontier Science Initiative, Kanazawa University, Kakuma-machi, Kanazawa, Japan.
Ann Nucl Med. 2019 Apr;33(4):244-251. doi: 10.1007/s12149-018-01326-5. Epub 2019 Jan 3.
Somatostatin receptors are highly expressed in neuroendocrine tumors, and many radiolabeled somatostatin analogs for diagnosis and treatment have been developed. To simultaneously detect not only primary cancer but also bone metastases, this study aimed to develop a positron emission tomography probe using generator-produced nuclide Gallium-68 (T = 68 min), in which a carrier for primary cancer, a carrier for bone metastases lesions, and a stable gallium complex are introduced into the one molecule. Based on this strategy, the somatostatin receptor-targeted peptide, [Tyr]-octreotate (TATE), aspartic acid peptide (D) with high binding affinity for hydroxyapatite, and Ga-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) as a stable gallium complex were selected. The novel complexes, Ga-DOTA-D-TATE (n = 0, 2, 5, 8, or 11), were designed, synthesized, and evaluated. The radiogallium complexes were prepared using the easy-to-handle radioisotope Ga due to relatively long half-life.
The radiogallium complex precursor DOTA-D-TATE was synthesized by the Fmoc-based solid-phase method and by the air oxidation method to form the disulfide bond. [Ga]Ga-DOTA-D-TATE was synthesized by reacting DOTA-D-TATE and Ga. Hydroxyapatite binding assays, in vitro cellular uptake experiments in AR42J tumor cells, in biodistribution experiments in AR42J tumor-bearing mice, were performed using [Ga]Ga-DOTA-D-TATE.
The radiochemical purities of [Ga]Ga-DOTA-D-TATE were > 96.0%. In in vitro and in vivo experiments, [Ga]Ga-DOTA-D-TATE had a high affinity for hydroxyapatite and highly accumulated in bone. However, the uptake of [Ga]Ga-DOTA-D-TATE into somatostatin receptor-positive AR42J cells was lower than that of [Ga]Ga-DOTA-TATE, and the accumulation of [Ga]Ga-DOTA-D-TATE in tumor was significantly low.
Ga-DOTA-D-TATE may not be recognized by somatostatin receptor by the introduction of D, and the charge adjustment may be important for somatostatin receptor-positive cell uptake.
生长抑素受体在神经内分泌肿瘤中高度表达，许多用于诊断和治疗的放射性标记生长抑素类似物已被开发出来。为了同时检测原发性癌症和骨转移灶，本研究旨在开发一种使用发生器产生的核素镓 - 68（半衰期T = 68分钟）的正电子发射断层扫描探针，将原发性癌症载体、骨转移灶载体和稳定的镓配合物引入到一个分子中。基于此策略，选择了生长抑素受体靶向肽[酪氨酸] - 奥曲肽（TATE）、对羟基磷灰石具有高结合亲和力的天冬氨酸肽（D）以及作为稳定镓配合物的镓 - 1,4,7,10 - 四氮杂环十二烷 - 1,4,7,10 - 四乙酸（DOTA）。设计、合成并评估了新型配合物Ga - DOTA - D - TATE（n = 0、2、5、8或11）。由于半衰期相对较长，使用易于操作的放射性同位素镓制备了放射性镓配合物。
通过基于Fmoc的固相方法并采用空气氧化法形成二硫键，合成放射性镓配合物前体DOTA - D - TATE。通过使DOTA - D - TATE与镓反应合成[镓]Ga - DOTA - D - TATE。使用[镓]Ga - DOTA - D - TATE进行羟基磷灰石结合试验、AR42J肿瘤细胞的体外细胞摄取实验以及荷AR42J肿瘤小鼠的生物分布实验。
[镓]Ga - DOTA - D - TATE的放射化学纯度> 96.0%。在体外和体内实验中，[镓]Ga - DOTA - D - TATE对羟基磷灰石具有高亲和力且在骨中高度蓄积。然而，[镓]Ga - DOTA - D - TATE进入生长抑素受体阳性AR42J细胞的摄取低于[镓]Ga - DOTA - TATE，并且[镓]Ga - DOTA - D - TATE在肿瘤中的蓄积显著较低。
引入D后，Ga - DOTA - D - TATE可能不被生长抑素受体识别，电荷调节对于生长抑素受体阳性细胞摄取可能很重要。
