Department for Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark.
Life Sciences Division, TRIUMF, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada.
Nucl Med Biol. 2022 Jan-Feb;104-105:11-21. doi: 10.1016/j.nucmedbio.2021.11.001. Epub 2021 Nov 10.
Radiotherapy of cancer requires both alpha- and beta-particle emitting radionuclides, as these radionuclide types are efficient at destroying different types of tumors. Both classes of radionuclides require a vehicle, such as an antibody or a polymer, to be delivered and retained within the tumor. Polyglutamic acid (pGlu) is a polymer that has proven itself effective as a basis of drug-polymer conjugates in the clinic, while its derivatives have been used for pretargeted tumor imaging in a research setup. trans-Cyclooctene (TCO) modified pGlu is suitable for pretargeted imaging or therapy, as well as for intratumoral radionuclide therapy. In all cases, it becomes indirectly radiolabeled via the bioorthogonal click reaction with the tetrazine (Tz) molecule carrying the radionuclide. In this study, we report the radiolabeling of TCO-modified pGlu with either lutetium-177 (Lu), a beta-particle emitter, or actinium-225 (Ac), an alpha-particle emitter, using the click reaction between TCO and Tz.
A panel of Tz derivatives containing a metal ion binding chelator (DOTA or macropa) connected to the Tz moiety directly or through a polyethylene glycol (PEG) linker was synthesized and tested for their ability to chelate Lu and Ac, and click to pGlu-TCO. Radiolabeled Lu-pGlu and Ac-pGlu were isolated by size exclusion chromatography. The retention of Lu or Ac by the obtained conjugates was investigated in vitro in human serum.
All DOTA-modified Tzs efficiently chelated Lu resulting in average radiochemical conversions (RCC) of >75%. Isolated radiochemical yields (RCY) for Lu-pGlu prepared from Lu-Tzs ranged from 31% to 55%. TLC analyses detected <5% unchelated Lu for all Lu-pGlu preparations over six days in human serum. For Ac chelation, optimized RCCs ranged from 61 ± 34% to quantitative for DOTA-Tzs and were quantitative for the macropa-modified Tz (>98%). Isolated radiochemical yields (RCY) for Ac-pGlu prepared from Ac-Tzs ranged from 28% to 51%. For 3 out of 5 Ac-pGlu conjugates prepared from DOTA-Tzs, the amount of unchelated Ac stayed below 10% over six days in human serum, while Ac-pGlu prepared from macropa-Tz showed a steady release of up to 37% Ac.
We labeled TCO-modified pGlu polymers with alpha- and beta-emitting radionuclides in acceptable RCYs. All Lu-pGlu preparations and some Ac-pGlu preparations showed excellent stability in human plasma. Our work shows the potential of pGlu as a vehicle for alpha- and beta-radiotherapy of tumors and demonstrated the usefulness of Tz ligation for indirect radiolabeling.
癌症放射疗法需要同时使用发射阿尔法粒子和贝塔粒子的放射性核素，因为这些放射性核素类型在破坏不同类型的肿瘤方面非常有效。这两类放射性核素都需要一种载体，如抗体或聚合物，以便将其输送并保留在肿瘤内。聚谷氨酸（pGlu）是一种已被证明在临床中作为药物-聚合物缀合物基础有效的聚合物，而其衍生物已被用于研究中基于靶标的肿瘤成像。反式环辛烯（TCO）修饰的 pGlu 适用于基于靶标的成像或治疗，以及肿瘤内放射性核素治疗。在所有情况下，它都通过与携带放射性核素的四嗪（Tz）分子的生物正交点击反应间接放射性标记。在这项研究中，我们报告了使用 TCO 与 Tz 之间的点击反应，用镥-177（Lu），一种贝塔粒子发射体，或锕-225（Ac），一种阿尔法粒子发射体，对 TCO 修饰的 pGlu 进行放射性标记。
合成了一组含有金属离子结合螯合剂（DOTA 或大环）的 Tz 衍生物，直接或通过聚乙二醇（PEG）接头连接到 Tz 部分，并测试了它们与 Lu 和 Ac 螯合以及与 pGlu-TCO 点击的能力。通过尺寸排阻色谱法分离放射性标记的 Lu-pGlu 和 Ac-pGlu。在人血清中研究了获得的缀合物对 Lu 或 Ac 的保留情况。
所有 DOTA 修饰的 Tz 都能有效地与 Lu 螯合，导致平均放射化学转化率（RCC）>75%。从 Lu-Tzs 制备的 Lu-pGlu 的分离放射化学产率（RCY）范围为 31%至 55%。在人血清中，所有 Lu-pGlu 制剂在六天内检测到<5%未螯合的 Lu 的 TLC 分析。对于 Ac 螯合，优化的 RCC 范围为 61±34%至定量（DOTA-Tzs），并且大环修饰的 Tz（>98%）为定量。从 Ac-Tzs 制备的 Ac-pGlu 的分离放射化学产率（RCY）范围为 28%至 51%。对于从 DOTA-Tzs 制备的 5 个 Ac-pGlu 缀合物中的 3 个，在人血清中六天内未螯合的 Ac 的量保持在 10%以下，而从大环-Tz 制备的 Ac-pGlu 则显示出高达 37%的 Ac 稳定释放。
我们以可接受的 RCY 用发射阿尔法粒子和贝塔粒子的放射性核素标记 TCO 修饰的 pGlu 聚合物。所有 Lu-pGlu 制剂和一些 Ac-pGlu 制剂在人血浆中表现出极好的稳定性。我们的工作表明 pGlu 作为肿瘤阿尔法和贝塔放射疗法的载体具有潜力，并证明了 Tz 连接在间接放射性标记中的有用性。
