Radiochemistry Division, Department of Radiation Oncology, University of Washington, Seattle, WA 98105, United States of America.
GU Cancer Research Lab, Department of Urology, University of Washington, Seattle, WA 98195, United States of America.
Nucl Med Biol. 2021 Jan;92:217-227. doi: 10.1016/j.nucmedbio.2020.04.005. Epub 2020 May 3.
The use of lysine-urea-glutamate (LuG) for targeting the PSMA antigen on prostate cancer (PCa) is a promising method for delivering the alpha particle-emitting radionuclide astatine-211 (At) to metastatic PCa. High kidney localization has been a problem with radiolabeled LuG derivatives, but has been adequately addressed in radiometal-labeled DOTA-LuG derivatives by linker optimization. Herein, we report an investigation of an alternate approach to diminishing the kidney concentrations of radiolabeled LuG-containing compounds.
Our approach involves PEGylated LuG moieties and closo-decaborate (2-) moieties conjugated to streptavidin (SAv) or human serum albumin (HSA). After preparing the LuG conjugates, SAv and HSA conjugates were succinylated to decrease their kidney localization and radioiodinated for evaluation in athymic mice bearing C4-2B osseous PCa tumor xenografts.
Covalently attaching LuG to succinylated SAv and HSA significantly reduced kidney localization, but unfortunately succinylation resulted in decreased tumor concentrations. In contrast, a potential metabolite [I]16b, an unconjugated LuG derivative containing a dPEG® linker, provided tumor concentrations of ~15% ID/g at 4 h pi. A second unconjugated LuG derivative with a similar structure, but containing a dPEG® linker, [I]16a had tumor concentrations of ~4%ID/g at 4 h pi. Those results suggest that long PEG linkers also affect tumor localization in a negative manner.
Conjugation of PEGylated LuG derivatives to proteins can be an effective approach to diminishing kidney localization of radiolabeled LuG reagents, but the protein, linker and the method of linkage need to be further studied. Additionally, modification of the unconjugated 16b to decrease kidney localization may provide PCa targeting agents for use with radiohalogens, including At. Advances in knowledge and implications for patient care: This study is the first to evaluate PEGylated LuG and closo-decaborate (2-) moieties conjugated to proteins as potential methods for diminishing the kidney concentrations of radiolabeled LuG-containing compounds.
利用赖氨酸-尿素-谷氨酸（LuG）靶向前列腺癌（PCa）上的 PSMA 抗原，是将发射α粒子的放射性核素锕-211（At）递送至转移性 PCa 的一种很有前途的方法。含放射性标记 LuG 衍生物的化合物存在肾区高定位的问题，但通过连接子优化，已在放射性标记的 DOTA-LuG 衍生物中得到充分解决。在此，我们报告了一种降低含放射性标记 LuG 化合物肾区浓度的替代方法的研究结果。
我们的方法涉及聚乙二醇化 LuG 部分和 closo-癸硼酸盐（2-）部分与链霉亲和素（SAv）或人血清白蛋白（HSA）的偶联。制备 LuG 缀合物后，对 SAv 和 HSA 缀合物进行琥珀酰化，以降低其肾区定位，并对其进行放射性碘标记，以评估其在携带 C4-2B 骨源性 PCa 肿瘤异种移植物的无胸腺小鼠中的应用。
LuG 与琥珀酰化 SAv 和 HSA 的共价偶联显著降低了肾区定位，但不幸的是，琥珀酰化导致肿瘤浓度降低。相比之下，一种潜在的代谢产物[I]16b，即含有 dPEG®连接子的未偶联 LuG 衍生物，在 4 hpi 时提供了约 15% ID/g 的肿瘤浓度。另一种具有类似结构但含有 dPEG®连接子的未偶联 LuG 衍生物[I]16a 在 4 hpi 时的肿瘤浓度约为 4% ID/g。这些结果表明，长 PEG 连接子也会以负性方式影响肿瘤定位。
将聚乙二醇化 LuG 衍生物与蛋白质偶联可能是降低放射性标记 LuG 试剂肾区定位的有效方法，但蛋白质、连接子和连接方式需要进一步研究。此外，修饰未偶联的 16b 以降低肾区定位可能会为使用放射性卤化物（包括 At）提供针对 PCa 的靶向试剂。
本研究首次评估了与蛋白质偶联的聚乙二醇化 LuG 和 closo-癸硼酸盐（2-）部分作为降低含放射性标记 LuG 化合物肾区浓度的潜在方法。
