Radiopharmaceutical Laboratory, Division of Nuclear Medicine, Department of Radiology and Imaging Sciences, NIH Clinical Center, Bethesda, MD 20892, USA.
Nucl Med Biol. 2011 Nov;38(8):1119-27. doi: 10.1016/j.nucmedbio.2011.05.003. Epub 2011 Jul 7.
Radiolabeling of a monoclonal antibody (mAb) with a metallic radionuclide requires the conjugation of a bifunctional chelator to the mAb. The conjugation, however, can alter the physical and immunological properties of the mAb, consequently affecting its tumor-targeting pharmacokinetics. In this study, we investigated the effect of the amount of 2-(p-isothiocyanatobenzyl)-cyclohexyl-diethylenetriamine-pentaacetic acid (CHX-A″) conjugated to MORAb-009, a mAb directed against mesothelin, and the effect of MORAb dose on the biodistribution of (111)In-labeled MORAb-009.
We used nude mice bearing the A431/K5 tumor as a mesothelin-positive tumor model and the A431 tumor as a mesothelin-negative control. To find the optimal level of CHX-A″ conjugation, CHX-A″-MORAb-009 conjugates with 2.4, 3.5 and 5.5 CHX-A″ molecules were investigated. To investigate the effect of injected MORAb-009 dose on neutralizing the shed mesothelin in the circulation, biodistribution studies were performed after the intravenous co-injection of (111)In-labeled MORAb-009 (2.4 CHX-A″/MORAb-009) with three different doses: 0.2, 2 and 30 μg of MORAb-009.
The tumor uptake in A431/K5 tumor was four times higher than that in A431 tumor, indicating that the tumor uptake in A431/K5 was mesothelin mediated. The conjugate with 5.5 CHX-A″ showed a lower isoelectric point (pI) and lower immunoreactivity (IR) than the 2.4 CHX-A″ conjugate. These differences were reflected in the biodistribution of the (111)In label. The (111)In-labeled MORAb-009 conjugated with 2.4 CHX-A″ produced higher tumor uptake and lower liver and spleen uptakes than the 5.5 CHX-A″ conjugate. The biodistribution studies also revealed that the tumor uptake was significantly affected by the injected MORAb-009 dose and tumor size. The 30-μg dose produced higher tumor uptake than the 0.2- and 2-μg doses, whereas the 30-μg dose produced lower liver and spleen uptakes than the 0.2-μg dose.
This study demonstrates that the number of chelate conjugation and the injected dose are two important parameters to achieve high tumor and low non-target organ uptake of (111)In-labeled MORAb-009. This study also suggests that the injected dose of mAb could be individualized based on the tumor size or the blood level of shed antigen in a patient to achieve the ideal tumor-to-organ radioactivity ratios.
将单克隆抗体 (mAb) 用放射性核素放射性标记需要将双功能螯合剂与 mAb 偶联。然而，偶联会改变 mAb 的物理和免疫学特性，从而影响其肿瘤靶向药代动力学。在这项研究中，我们研究了与 MORAb-009 偶联的 2-(p-异硫氰酸苄基)-环己基-二乙撑三胺五乙酸 (CHX-A″) 的量对 mAb 针对间皮素的影响，以及 MORAb 剂量对 (111)In 标记的 MORAb-009 生物分布的影响。
我们使用携带 A431/K5 肿瘤的裸鼠作为间皮素阳性肿瘤模型，使用 A431 肿瘤作为间皮素阴性对照。为了找到最佳的 CHX-A″偶联水平，我们研究了与 2.4、3.5 和 5.5 个 CHX-A″分子偶联的 CHX-A″-MORAb-009 缀合物。为了研究注射的 MORAb-009 剂量对中和循环中脱落的间皮素的影响，在静脉注射 (111)In 标记的 MORAb-009(2.4 CHX-A″/MORAb-009) 后进行了生物分布研究，使用三种不同剂量：0.2、2 和 30 μg 的 MORAb-009。
A431/K5 肿瘤的肿瘤摄取量是 A431 肿瘤的四倍，表明 A431/K5 肿瘤的摄取量与间皮素有关。与 2.4 CHX-A″ 缀合物相比，具有 5.5 CHX-A″ 的缀合物具有更低的等电点 (pI) 和更低的免疫反应性 (IR)。这些差异反映在 (111)In 标记的生物分布中。与 5.5 CHX-A″ 缀合物相比，与 2.4 CHX-A″ 缀合的 (111)In 标记的 MORAb-009 产生更高的肿瘤摄取量和更低的肝脏和脾脏摄取量。生物分布研究还表明，肿瘤摄取量受注射的 MORAb-009 剂量和肿瘤大小的显著影响。30 μg 剂量产生的肿瘤摄取量高于 0.2 和 2 μg 剂量，而 30 μg 剂量产生的肝脏和脾脏摄取量低于 0.2 μg 剂量。
这项研究表明，螯合剂偶联的数量和注射剂量是实现 (111)In 标记的 MORAb-009 高肿瘤和低非靶器官摄取的两个重要参数。这项研究还表明，根据患者的肿瘤大小或脱落抗原的血液水平，可以对 mAb 的注射剂量进行个体化，以实现理想的肿瘤与器官放射性比值。
