⁶⁸Ga-labeling and in vivo evaluation of a uPAR binding DOTA- and NODAGA-conjugated peptide for PET imaging of invasive cancers

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• 作者：Morten Persson^a ; ^b ; ^c ; Jacob Madsen^b ; S&oslash ; ren &Oslash ; stergaard^d ; Michael Ploug^a ; ^e ; Andreas Kjaer^a ; ^b ; ^c ; ^{akjaer@sund.ku.dk}
• 关键词：uPAR ; MicroPET ; NODAGA ; DOTA ; AE105 ; Gallium-68 ; Cancer xenograft
• 刊名：Nuclear Medicine and Biology
• 出版年：2012
• 期刊代码：43_09698051
• 类别：ph
• 出版时间：May, 2012
• 卷：39
• 期：4
• 页码：560-569
• 文件大小：1021 K

摘要

Introduction

The urokinase-type plasminogen activator receptor (uPAR) is a well-established biomarker for tumor aggressiveness and metastatic potential. DOTA-AE105 and DOTA-AE105-NH₂ labeled with ⁶⁴Cu have previously been demonstrated to be able to noninvasively monitor uPAR expression using positron emission tomography (PET) in human cancer xenograft mice models. Here we introduce ⁶⁸Ga-DOTA-AE105-NH₂ and ⁶⁸Ga-NODAGA-AE105-NH₂ and evaluate their imaging properties using small-animal PET.

Methods

Synthesis of DOTA-AE105-NH₂ and NODAGA-AE105-NH₂ was based on solid-phase peptide synthesis protocols using the Fmoc strategy. ⁶⁸GaCl₃ was eluted from a ⁶⁸Ge/⁶⁸Ga generator. The eluate was either concentrated on a cation-exchange column or fractionated and used directly for labeling. For in vitro characterization of both tracers, partition coefficient, buffer and plasma stability, uPAR binding affinity and cell uptake were determined. To characterize the in vivo properties, dynamic microPET imaging was carried out in nude mice bearing human glioma U87MG tumor xenograft.

Results

In vitro experiments revealed uPAR binding affinities in the lower nM range for both conjugated peptides and identical to AE105. Labeling of DOTA-AE105-NH₂ and NODAGA-AE105-NH₂ with ⁶⁸Ga was done at 95掳C and room temperature, respectively. The highest radiochemical yield and purity were obtained using fractionated elution, whereas a negative effect of acetone on labeling efficiency for NODAGA-AE105-NH₂ was observed. Good stability in phosphate-buffered saline and mouse plasma was observed. High cell uptake was found for both tracers in U87MG tumor cells. Dynamic microPET imaging demonstrated good tumor-to-background ratio for both tracers. Tumor uptake was 2.1%ID/g and 1.3%ID/g 30 min postinjection and 2.0%ID/g and 1.1%ID/g 60 min postinjection for ⁶⁸Ga-NODAGA-AE105-NH₂ and ⁶⁸Ga-DOTA-AE105-NH₂, respectively. A significantly higher tumor-to-muscle ratio (P<.05) was found for ⁶⁸Ga-NODAGA-AE105-NH₂ 60 min postinjection.

Conclusions

The use of ⁶⁸Ga-DOTA-AE105-NH₂ and ⁶⁸Ga-NODAGA-AE105-NH₂ as the first gallium-68 labeled uPAR radiotracers for noninvasive PET imaging is reported, which combine versatility with good imaging properties. These new tracers thus constitute an interesting alternative to the ⁶⁴Cu-labeled version (⁶⁴Cu-DOTA-AE105 and 64Cu-DOTA-AE105-NH₂) for detecting uPAR expression in tumor tissue. In our hands, the fractionated elution approach was superior for labeling of peptides, and ⁶⁸Ga-NODAGA-AE105-NH₂ is the favored tracer as it provides the highest tumor-to-background ratio.