School of Health Sciences, Purdue University, West Lafayette, IN 47907, USA.
Amino Acids. 2011 Nov;41(5):1059-70. doi: 10.1007/s00726-009-0439-0. Epub 2010 Jan 6.
The present study describes the synthesis and biological evaluation of (111)In(DOTA-3P-RGD(2)) (DOTA = 1,4,7,10-tetraazacyclo-dodecane-1,4,7,10-tetraacetic acid; 3P-RGD(2) = PEG(4)-EPEG(4)-c(RGDfK); PEG(4) = 15-amino-4,7,10,13-tetraoxapentadecanoic acid), (111)In(DTPA-3P-RGD(2)) (DTPA = diethylenetriaminepentaacetic acid) and (111)In(DTPA-Bn-3P-RGD(2)) (DTPA-Bn = 2-(p-thioureidobenzyl)-diethylenetriaminepentaacetic acid) as potential radiotracers for imaging tumor integrin α(v)β(3) expression in athymic nude mice bearing U87MG glioma xenografts. The aim of the study is to assess the impact of the bifunctional chelator (BFC) (DOTA vs. DTPA or DTPA-Bn) on the biodistribution characteristics of the (111)In-labeled 3P-RGD(2). IC(50) values of DOTA-3P-RGD(2), DTPA-3P-RGD(2) and DTPA-Bn-3P-RGD(2) were determined to be 1.3 ± 0.2, 1.4 ± 0.3, 1.3 ± 0.3 nM, respectively, against (125)I-c(RGDyK) bound to U87MG human glioma cells. Radiotracers were prepared by reacting (111)InCl(3) with the RGD peptide conjugates in NH(4)OAc buffer (100 mM, pH 5.5). For DOTA-3P-RGD(2), successful radiolabeling could be completed by heating the reaction mixture at 100°C for 15-20 min. For DTPA-3P-RGD(2) and DTPA-Bn-3P-RGD(2), the radiolabeling was almost instantaneous at room temperature. The specific activity was ~50 mCi/mg (or ~100 mCi/μmol) for (111)In(DOTA-3P-RGD(2)) and ~200 mCi/mg (or ~400 mCi/μmol) for (111)In(DTPA-3P-RGD(2)). The results from biodistribution studies showed that all the three radiotracers have high tumor uptake and excellent tumor-to-background (T/B) ratios up to 4-h postinjection. After that time point, both (111)In(DTPA-3P-RGD(2)) and (111)In(DTPA-Bn-3P-RGD(2)) showed a much faster tumor washout and poorer T/B ratios than (111)In(DOTA-3P-RGD(2)). The tumor uptake of (111)In(DOTA-3P-RGD(2)) is integrin α(v)β(3)- and RGD-specific. (111)In(DOTA-3P-RGD(2)) is metabolically stable while only ~25% of (111)In(DTPA-Bn-3P-RGD(2)) remains intact in the feces during 2-h period. On the basis of results from this study, it was concluded that (111)In(DTPA-3P-RGD(2)) can be an effective integrin α(v)β(3)-targeted radiotracer if the high-specific activity is required. However, DOTA remains to be the BFC of choice for the development of therapeutic lanthanide radiotracers.
本研究描述了 (111)In(DOTA-3P-RGD(2))（DOTA = 1,4,7,10-四氮杂环十二烷-1,4,7,10-四乙酸；3P-RGD(2) = PEG(4)-EPEG(4)-c(RGDfK)；PEG(4) = 15-氨基-4,7,10,13-四氧杂十五烷酸）、(111)In(DTPA-3P-RGD(2))（DTPA = 二乙三胺五乙酸）和 (111)In(DTPA-Bn-3P-RGD(2))（DTPA-Bn = 2-(对硫代脲基苄基）-二乙三胺五乙酸）作为潜在的放射性示踪剂，用于成像荷瘤裸鼠中 U87MG 神经胶质瘤异种移植瘤的肿瘤整合素 α(v)β(3)表达。该研究的目的是评估双功能螯合剂（BFC）（DOTA 与 DTPA 或 DTPA-Bn）对 (111)In 标记的 3P-RGD(2)的生物分布特征的影响。DOTA-3P-RGD(2)、DTPA-3P-RGD(2)和 DTPA-Bn-3P-RGD(2)的 IC(50)值分别为 1.3±0.2、1.4±0.3 和 1.3±0.3 nM，与 U87MG 人神经胶质瘤细胞结合的 (125)I-c(RGDyK)。放射性示踪剂通过在 NH(4)OAc 缓冲液（100 mM，pH 5.5）中反应 (111)InCl(3)与 RGD 肽缀合物来制备。对于 DOTA-3P-RGD(2)，通过将反应混合物在 100°C 加热 15-20 分钟可以完成成功的放射性标记。对于 DTPA-3P-RGD(2)和 DTPA-Bn-3P-RGD(2)，室温下的放射性标记几乎是瞬时的。(111)In(DOTA-3P-RGD(2))的比活度约为 50 mCi/mg（或 100 mCi/μmol），(111)In(DTPA-3P-RGD(2))的比活度约为 200 mCi/mg（或 400 mCi/μmol）。来自生物分布研究的结果表明，所有三种放射性示踪剂在注射后 4 小时内具有高肿瘤摄取和极好的肿瘤与背景（T/B）比值。在此时间点之后，(111)In(DTPA-3P-RGD(2))和 (111)In(DTPA-Bn-3P-RGD(2))都显示出比 (111)In(DOTA-3P-RGD(2))更快的肿瘤清除和更差的 T/B 比值。(111)In(DOTA-3P-RGD(2))的肿瘤摄取是整合素 α(v)β(3)-和 RGD 特异性的。(111)In(DOTA-3P-RGD(2))代谢稳定，而在 2 小时期间，只有约 25%的 (111)In(DTPA-Bn-3P-RGD(2))以完整形式存在于粪便中。基于这项研究的结果，得出结论，如果需要高比活度，则 (111)In(DTPA-3P-RGD(2))可以作为有效的整合素 α(v)β(3)-靶向放射性示踪剂。然而，DOTA 仍然是开发治疗性镧系元素放射性示踪剂的首选 BFC。
