Scavenging strategy for specific activity improvement: application to a new CXCR4-specific cyclopentapeptide positron emission tomography tracer
作者:Guillaume P. C. George、Federica Pisaneschi、Elizabeth Stevens、Quang-Dé Nguyen、Ola Åberg、Alan C. Spivey、Eric O. Aboagye
DOI:10.1002/jlcr.3095
日期:2013.11
Huisgen cycloaddition is attractive to label peptide because of its rapidity and bioorthogonality. However, for larger tracers, the physico-chemical differences between the precursor and the tracer are usually insufficient to allow their separation by HPLC, reducing the specific activity. This is of importance for peptidic tracers because the combination of their high-affinity receptor with low specific activity results in the precursor saturating the receptors, causing non-specific tracer binding. Here, we report a fast, one-pot, general strategy to circumvent this issue, yielding a tracer of improved specific activity. It consists in adding a lipophilic azide after the labeling step to scavenge unreacted precursor into a more lipophilic species that does not co-elute with the tracer. We applied this strategy to a new fluorinated cyclopentapeptidic CXCR4 antagonist for the PET imaging of cancer, CCIC15, for which we managed to reduce the apparent peptide concentration by a factor of 34 in 10 min. This tracer was radiolabeled by click chemistry with 2-[18F]fluoroethylazide, yielding the tracer in 18 ± 6% (n = 5) end-of-synthesis radiochemical yields (EOS-RCY) in 1.5 h from [18F]fluoride with a specific activity of 19.4 GBq µmol−1. Preliminary biological evaluation of the probe confirmed potency and specificity for CXCR4; further biological evaluation is underway.
Huisgen环加成因其快速性和生物正交性而成为标记肽的有吸引力的方法。然而,对于较大的示踪剂,前体和示踪剂之间的物化差异通常不足以通过HPLC分离它们,从而降低了比活性。这对于肽示踪剂很重要,因为它们与高亲和力受体和低比活性的结合导致前体饱和受体,引起非特异性示踪剂结合。在这里,我们报告了一种快速、一步、通用的策略来规避这个问题,产生了比活性提高的示踪剂。它包括在标记步骤之后添加一个亲脂性叠氮化物,以将未反应的前体捕获成更亲脂的物种,该物种不与示踪剂共洗脱。我们将这种策略应用于一种新的氟化环戊肽CXCR4拮抗剂,用于癌症的PET成像,CCIC15,我们设法在10分钟内将明显肽浓度降低了34倍。通过点击化学与2-[18F]氟乙基叠氮化物放射性标记该示踪剂,产生了18±6%(n=5)的最终合成放射化学产率(EOS-RCY),从[18F]氟化物开始在1.5小时内比活性为19.4 GBq µmol−1。探针的初步生物学评估证实了CXCR4的效力和特异性;进一步的生物学评估正在进行中。