Department of Nuclear Medicine, Shanghai Ruijin Hospital, Shanghai Jiaotong University, 2nd Ruijin Rd, Shanghai, 200025, People's Republic of China.
Eur J Nucl Med Mol Imaging. 2011 Apr;38(4):613-22. doi: 10.1007/s00259-010-1684-x. Epub 2010 Dec 10.
Cystine knot peptides (knottins) 2.5D and 2.5F were recently engineered to bind integrin receptors with high affinity and specificity. These receptors are overexpressed on the surface of a variety of malignant human tumor cells and tumor neovasculature. In this study, 2.5D and 2.5F were labeled with a therapeutic radionuclide, (177)Lu, and the resulting radiopeptides were then evaluated as potential radiotherapeutic agents in a murine model of human glioma xenografts.
Knottins 2.5D and 2.5F were synthesized using solid phase peptide synthesis, folded in vitro, and site-specifically coupled with 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid (DOTA) at their N terminus for (177)Lu radiolabeling. The stability of the radiopeptides (177)Lu-DOTA-2.5D and (177)Lu-DOTA-2.5F was tested in both phosphate-buffered saline (PBS) and mouse serum. Cell uptake assays of the radiolabeled peptides were performed in U87MG integrin-expressing human glioma cells. The biodistribution studies of both (177)Lu-DOTA-2.5D and (177)Lu-DOTA-2.5F were examined in U87MG tumor-bearing athymic nu/nu mice. Radiation absorbed doses for the major tissues of a human adult male were calculated based on the mouse biodistribution results.
DOTA-2.5D and DOTA-2.5F were labeled with (177)Lu at over 55% efficiency. High radiochemical purity for both radiocomplexes (> 95%) could be achieved after high performance liquid chromatography (HPLC) purification. Both radiopeptides were stable in PBS and mouse serum. Compared to (177)Lu-DOTA-2.5D (0.39 and 0.26 %ID/g at 2 and 24 h, respectively), (177)Lu-DOTA-2.5F showed much higher tumor uptake (2.16 and 0.78 %ID/g at 2 and 24 h, respectively). It also displayed higher tumor to blood ratios than that of (177)Lu-DOTA-2.5D (31.8 vs 18.7 at 24 h and 52.6 vs 20.6 at 72 h). Calculation of radiodosimetry for (177)Lu-DOTA-2.5D and (177)Lu-DOTA-2.5F suggested that tumor and kidney were tissues with the highest radiation absorbed doses. Moreover, (177)Lu-DOTA-2.5F had a higher tumor to kidney radiation absorbed dose ratio than that of (177)Lu-DOTA-2.5D.
Cystine knot peptides can be successfully radiolabeled with (177)Lu for potential therapeutic applications. Knottin 2.5F labeled with (177)Lu exhibits favorable distribution in murine U87MG xenograft model; thus, it is a promising agent for radionuclide therapy of integrin-positive tumors.
半胱氨酸结肽（knottins）2.5D 和 2.5F 最近被设计用于与整合素受体高亲和力和特异性结合。这些受体在多种恶性人类肿瘤细胞和肿瘤新生血管表面过度表达。在这项研究中，2.5D 和 2.5F 用治疗放射性核素（177）Lu 标记，然后将所得放射性肽作为潜在的放射治疗剂在人神经胶质瘤异种移植的小鼠模型中进行评估。
使用固相肽合成合成 knottins 2.5D 和 2.5F，在体外折叠，并在其 N 末端特异性地与 1,4,7,10-四氮杂环十二烷-N，N'，N“，N”'-四乙酸（DOTA）偶联用于（177）Lu 放射性标记。在磷酸盐缓冲盐水（PBS）和小鼠血清中测试放射性肽（177）Lu-DOTA-2.5D 和（177）Lu-DOTA-2.5F 的稳定性。在表达整合素的 U87MG 人神经胶质瘤细胞中进行放射性标记肽的细胞摄取测定。在 U87MG 荷瘤无胸腺 nu/nu 小鼠中检查了（177）Lu-DOTA-2.5D 和（177）Lu-DOTA-2.5F 的生物分布研究。根据小鼠的生物分布结果，计算了成人男性主要组织的辐射吸收剂量。
DOTA-2.5D 和 DOTA-2.5F 以超过 55%的效率用（177）Lu 标记。通过高效液相色谱（HPLC）纯化后，两种放射性络合物的高放射化学纯度（均>95%）都可以达到。两种放射性肽在 PBS 和小鼠血清中均稳定。与（177）Lu-DOTA-2.5D 相比（分别为 2 小时和 24 小时时的 0.39 和 0.26%ID/g），（177）Lu-DOTA-2.5F 的肿瘤摄取率更高（分别为 2 小时和 24 小时时的 2.16 和 0.78%ID/g）。它还显示出比（177）Lu-DOTA-2.5D 更高的肿瘤与血液比（24 小时时为 31.8 比 18.7，72 小时时为 52.6 比 20.6）。（177）Lu-DOTA-2.5D 和（177）Lu-DOTA-2.5F 的放射剂量学计算表明，肿瘤和肾脏是吸收辐射剂量最高的组织。此外，（177）Lu-DOTA-2.5F 比（177）Lu-DOTA-2.5D 具有更高的肿瘤与肾脏辐射吸收剂量比。
半胱氨酸结肽可以成功地用（177）Lu 放射性标记，用于潜在的治疗应用。用（177）Lu 标记的 knottin 2.5F 在小鼠 U87MG 异种移植模型中表现出良好的分布; 因此，它是一种有前途的整合素阳性肿瘤的放射性核素治疗剂。
