Shankar Sriram, Vaidyanathan Ganesan, Kuan Chien-Tsun, Bigner Darell D, Zalutsky Michael R
Department of Radiology, Duke University Medical Center, Durham, NC 27710, USA.
Nucl Med Biol. 2006 Jan;33(1):101-10. doi: 10.1016/j.nucmedbio.2005.08.004.
MR1-1 is a single-chain Fv (scFv) fragment that binds with high affinity to epidermal growth factor receptor variant III, which is overexpressed on gliomas and other tumors but is not present on normal tissues. The objective of this study was to evaluate four different methods for labeling MR1-1 scFv that had been previously investigated for the radioiodinating of an intact anti-epidermal growth factor receptor variant III (anti-EGFRvIII) monoclonal antibody (mAb) L8A4.
The MR1-1 scFv was labeled with (125)I/(131)I using the Iodogen method, and was also radiohalogenated with acylation agents bearing substituents that were positively charged--N-succinimidyl-3-[*I]iodo-5-pyridine carboxylate and N-succinimidyl-4-guanidinomethyl-3-[*I]iodobenzoate ([*I]SGMIB)--and negatively charged--N-succinimidyl-3-[*I]iodo-4-phosphonomethylbenzoate ([*I]SIPMB). In vitro internalization assays were performed with the U87MGDeltaEGFR cell line, and the tissue distribution of the radioiodinated scFv fragments was evaluated in athymic mice bearing subcutaneous U87MGDeltaEGFR xenografts.
As seen previously with the anti-EGFRvIII IgG mAb, retention of radioiodine activity in U87MGDeltaEGFR cells in the internalization assay was labeling method dependent, with SGMIB and SIPMB yielding the most prolonged retention. However, unlike the case with the intact mAb, the results of the internalization assays were not predictive of in vivo tumor localization capacity of the labeled scFv. Renal activity was dependent on the nature of the labeling method. With MR1-1 labeled using SIPMB, kidney uptake was highest and most prolonged; catabolism studies indicated that this uptake primarily was in the form of epsilon-N-3-[*I]iodo-4-phosphonomethylbenzoyl lysine.
MR1-1是一种单链Fv（scFv）片段，它与表皮生长因子受体变体III具有高亲和力结合，该变体在胶质瘤和其他肿瘤中过表达，但在正常组织中不存在。本研究的目的是评估四种不同的标记MR1-1 scFv的方法，这些方法先前已被研究用于完整的抗表皮生长因子受体变体III（抗EGFRvIII）单克隆抗体（mAb）L8A4的放射性碘化。
使用碘甘醚法用（125）I/（131）I标记MR1-1 scFv，并用带有带正电荷取代基的酰化剂——N-琥珀酰亚胺基-3-[*I]碘-5-吡啶羧酸盐和N-琥珀酰亚胺基-4-胍基甲基-3-[*I]碘苯甲酸酯（[*I]SGMIB）——以及带负电荷的——N-琥珀酰亚胺基-3-[*I]碘-4-膦酰甲基苯甲酸酯（[*I]SIPMB）进行放射性卤化。用U87MGDeltaEGFR细胞系进行体外内化试验，并在携带皮下U87MGDeltaEGFR异种移植物的无胸腺小鼠中评估放射性碘化scFv片段的组织分布。
如先前在抗EGFRvIII IgG mAb中所见，内化试验中U87MGDeltaEGFR细胞中放射性碘活性的保留取决于标记方法，SGMIB和SIPMB产生的保留时间最长。然而，与完整mAb的情况不同，内化试验的结果不能预测标记scFv的体内肿瘤定位能力。肾脏活性取决于标记方法的性质。用SIPMB标记的MR1-1，肾脏摄取最高且持续时间最长；分解代谢研究表明，这种摄取主要是以ε-N-3-[*I]碘-4-膦酰甲基苯甲酰赖氨酸的形式。
