Liu Zhibo, Radtke Mark Alex, Wong May Q, Lin Kuo-Shyan, Yapp Donald T, Perrin David M
Chemistry Department University of British Columbia 2036 Main Mall, Vancouver, British Columbia V6T-1Z1, Canada.
Bioconjug Chem. 2014 Nov 19;25(11):1951-62. doi: 10.1021/bc5003357. Epub 2014 Sep 29.
The design of dual mode fluorescent-PET peptidic tracers that can be labeled with [(18)F]fluoride at high specific activity and high yield has been challenged by the short half-life of (18)F and its aqueous indolence toward nucleophilic displacement, that often necessitates multistep reactions that start with punctiliously dry conditions. Here we present a modular approach to constructing a fluorescent dimeric peptide with a pendant radioprosthesis that is labeled in water with [(18)F]fluoride ion in a single, user-friendly step. The modular approach starts with grafting a new zwitterionic organotrifluoroborate radioprosthesis onto a pentaerythritol core with three pendent alkynes that enable successive grafting of a bright fluorophore (rhodamine) followed by two peptides (cylcoRGD). The construct is labeled with [(18)F]fluoride via isotope exchange within 20 min in a single step at high specific activity (>3 Ci/μmol) and in good yield to provide 275 mCi and high radiochemical purity. Neither drying of the [(18)F]fluoride ion solution nor HPLC purification of the labeled tracer is required. Facile chemical synthesis of this dual mode tracer along with a user-friendly one-step radiolabeling method affords very high specific activity. In vivo PET images of the dual mode tracer are acquired at both high and low specific activities. At very high specific activity, i.e., 3.5 Ci/μmol, tumor uptake is relatively high (5.5%ID/g), yet the associated mass is below the limits of fluorescent detection. At low specific activity, i.e., 0.01 Ci/μmol, tumor uptake in the PET image is reduced by approximately 50% (2.9%ID/g), but the greater associated mass enables fluorescence detection in the tumor. These data highlight a facile production of a dual mode fluorescent-PET tracer which is validated with in vivo and ex vivo images. These data also define critical limitations for the use of dual mode tracers in small animals.
设计能够以高比活度和高收率用[¹⁸F]氟化物标记的双模式荧光 - PET肽类示踪剂，一直受到¹⁸F半衰期短及其对亲核取代反应在水溶液中惰性的挑战，这常常需要从严格干燥的条件开始进行多步反应。在此，我们提出一种模块化方法来构建带有侧链放射性假体的荧光二聚体肽，该肽可以在水中通过一个用户友好的步骤用[¹⁸F]氟离子进行标记。这种模块化方法首先将一种新的两性离子有机三氟硼酸盐放射性假体接枝到具有三个侧链炔烃的季戊四醇核心上，这使得能够依次接枝一个明亮的荧光团（罗丹明），然后是两个肽（环RGD）。该构建体通过同位素交换在20分钟内一步用[¹⁸F]氟化物进行标记，比活度高（>3 Ci/μmol）且收率良好，可提供275 mCi和高放射化学纯度。既不需要干燥[¹⁸F]氟离子溶液，也不需要对标记的示踪剂进行HPLC纯化。这种双模式示踪剂的简便化学合成以及用户友好的一步放射性标记方法可提供非常高的比活度。在高比活度和低比活度下均采集了双模式示踪剂的体内PET图像。在非常高的比活度下，即3.5 Ci/μmol，肿瘤摄取相对较高（5.5%ID/g），但相关质量低于荧光检测限。在低比活度下，即0.01 Ci/μmol，PET图像中的肿瘤摄取降低约50%（2.9%ID/g），但更大的相关质量使得能够在肿瘤中进行荧光检测。这些数据突出了一种双模式荧光 - PET示踪剂的简便生产方法，并通过体内和体外图像进行了验证。这些数据还确定了在小动物中使用双模式示踪剂的关键限制。
