Läppchen Tilman, Rossin Raffaella, van Mourik Tiemen R, Gruntz Guillaume, Hoeben Freek J M, Versteegen Ron M, Janssen Henk M, Lub Johan, Robillard Marc S
Philips Research, High Tech Campus 11, 5656 AE Eindhoven, The Netherlands; Department of Nuclear Medicine, Medical Center- University of Freiburg, Faculty of Medicine, University of Freiburg, Hugstetterstrasse 55, 79106 Freiburg, Germany; Department of Nuclear Medicine, Inselspital, Bern University Hospital and University of Bern, Freiburgstrasse, 3010 Bern, Switzerland.
Philips Research, High Tech Campus 11, 5656 AE Eindhoven, The Netherlands; Tagworks Pharmaceuticals BV, c/o Department of Nuclear Medicine and Radiology, Radboud University Medical Center, 6500 HB Nijmegen, The Netherlands.
Nucl Med Biol. 2017 Dec;55:19-26. doi: 10.1016/j.nucmedbio.2017.09.001. Epub 2017 Sep 14.
Pretargeted radioimmunoimaging and -therapy approaches building on the bioorthogonal inverse-electron-demand Diels-Alder (IEDDA) reaction between strained trans-cyclooctenes (TCO) and electron-deficient tetrazines (Tz) have yielded impressive results in recent years and have proven a vital alternative to biological pretargeting systems. After improvement of the TCO-antibody conjugates, we here report on our evaluation of a new series of radiolabeled Tz-probes.
Four new Tz-probes were synthesized, radiolabeled with lutetium-177, and characterized in vitro in terms of lipophilicity, reactivity, and stability in PBS and mouse serum. The in vivo biodistribution profile and tumor-targeting potential of the probes were evaluated in LS174T tumor-bearing mice pretargeted with TCO-antibody conjugates using non-pretargeted mice as control.
Radiolabeling of all probes proceeded in high yields providing the Lu-labeled tetrazines in >95% radiochemical purity without any further purification. In mouse serum, half-lives of the probes varied between 8 and 13 h, with the exception of the most lipophilic probe, [Lu]1b, with a serum half-life of less than 1 h. This probe also showed the fastest blood clearance (t = 5.4 min), more than 2-fold faster than PEG-linked probes [Lu]3 and [Lu]4, and even 3-fold faster than the other small probes without the PEG-linker, [Lu]1a and [Lu]2. In the pretargeting experiments, tumor uptake of the lead probe [Lu]4 (~6 %ID/g) was most closely approached by [Lu]2, followed by [Lu]3 and [Lu]1a. While all the smaller and more lipophilic probes suffered from increased liver uptake, the PEG-linked probe [Lu]3 with its additional negative charge surprisingly showed the highest kidney uptake among all of the probes.
The in vitro performance of some of the new tetrazine probes turned out to be comparable to the established lead probe [Lu]Lu-DOTA-PEG-Tz ([Lu]4). However, tumor pretargeting studies in vivo showed lower tumor uptake and increased uptake in non-target organs.
基于张力反式环辛烯（TCO）与缺电子四嗪（Tz）之间的生物正交逆电子需求狄尔斯-阿尔德（IEDDA）反应的预靶向放射免疫成像和治疗方法近年来取得了令人瞩目的成果，并已被证明是生物预靶向系统的重要替代方案。在改进了TCO-抗体偶联物后，我们在此报告对一系列新的放射性标记Tz探针的评估。
合成了四种新的Tz探针，用镥-177进行放射性标记，并在体外对其亲脂性、反应性以及在磷酸盐缓冲盐水（PBS）和小鼠血清中的稳定性进行了表征。使用未进行预靶向的小鼠作为对照，在预先用TCO-抗体偶联物进行预靶向的荷LS174T肿瘤小鼠中评估了探针的体内生物分布情况和肿瘤靶向潜力。
所有探针的放射性标记产率都很高，得到的镥标记四嗪的放射化学纯度>95%，无需进一步纯化。在小鼠血清中，除了亲脂性最强的探针[Lu]1b（血清半衰期小于1小时）外，其他探针的半衰期在8到13小时之间。该探针的血液清除速度也最快（t = 5.4分钟），比聚乙二醇连接的探针[Lu]3和[Lu]4快2倍以上，甚至比其他没有聚乙二醇连接基团的小探针[Lu]1a和[Lu]2快3倍。在预靶向实验中，先导探针[Lu]4（~6 %ID/g）的肿瘤摄取量与[Lu]2最为接近，其次是[Lu]3和[Lu]1a。虽然所有较小且亲脂性更强得探针的肝脏摄取量都增加了，但带有额外负电荷的聚乙二醇连接探针[Lu]3在所有探针中显示出最高的肾脏摄取量。
一些新的四嗪探针的体外性能被证明与已确立的先导探针[Lu]Lu-DOTA-PEG-Tz（[Lu]4）相当。然而，体内肿瘤预靶向研究显示肿瘤摄取量较低，非靶器官摄取量增加。
