Department of Nuclear Medicine, Innsbruck Medical University, Innsbruck, Austria.
Eur J Nucl Med Mol Imaging. 2011 Jul;38(7):1303-12. doi: 10.1007/s00259-011-1778-0. Epub 2011 Apr 13.
A molecular target involved in the angiogenic process is the α(v)β(3) integrin. It has been demonstrated in preclinical as well as in clinical studies that radiolabelled RGD peptides and positron emission tomography (PET) allow noninvasive monitoring of α(v)β(3) expression. Here we introduce a (68)Ga-labelled NOTA-conjugated RGD peptide ([(68)Ga]NODAGA-RGD) and compare its imaging properties with [(68)Ga]DOTA-RGD using small animal PET.
Synthesis of c(RGDfK(NODAGA)) was based on solid phase peptide synthesis protocols using the Fmoc strategy. The (68)Ga labelling protocol was optimized concerning temperature, peptide concentration and reaction time. For in vitro characterization, partition coefficient, protein binding properties, serum stability, α(v)β(3) binding affinity and cell uptake were determined. To characterize the in vivo properties, biodistribution studies and microPET imaging were carried out. For both in vitro and in vivo evaluation, α(v)β(3)-positive human melanoma M21 and α(v)β(3)-negative M21-L cells were used.
[(68)Ga]NODAGA-RGD can be produced within 5 min at room temperature with high radiochemical yield and purity (> 96%). In vitro evaluation showed high α(v)β(3) binding affinity (IC(50) = 4.7 ± 1.6 nM) and receptor-specific uptake. The radiotracer was stable in phosphate-buffered saline, pH 7.4, FeCl(3) solution, and human serum. Protein-bound activity after 180 min incubation was found to be 12-fold lower than for [(68)Ga]DOTA-RGD. Biodistribution data 60 min post-injection confirmed receptor-specific tumour accumulation. The activity concentration of [(68)Ga]NODAGA-RGD was lower than [(68)Ga]DOTA-RGD in all organs and tissues investigated, leading to an improved tumour to blood ratio ([(68)Ga]NODAGA-RGD: 11, [(68)Ga]DOTA-RGD: 4). MicroPET imaging confirmed the improved imaging properties of [(68)Ga]NODAGA-RGD compared to [(68)Ga]DOTA-RGD.
The introduced [(68)Ga]NODAGA-RGD combines easy accessibility with high stability and good imaging properties making it an interesting alternative to the (18)F-labelled RGD peptides currently used for imaging α(v)β(3) expression.
参与血管生成过程的一个分子靶标是α(v)β(3)整联蛋白。临床前和临床研究表明，放射性标记的 RGD 肽和正电子发射断层扫描（PET）允许非侵入性监测α(v)β(3)的表达。在这里，我们介绍了一种（68）Ga 标记的 NOTA 缀合的 RGD 肽（[(68)Ga]NODAGA-RGD），并使用小动物 PET 比较了其与 [(68)Ga]DOTA-RGD 的成像特性。
使用 Fmoc 策略，基于固相肽合成方案合成 c(RGDfK（NODAGA）)。优化了（68）Ga 标记方案，考虑了温度、肽浓度和反应时间。为了进行体外特性表征，测定了分配系数、蛋白结合特性、血清稳定性、α(v)β(3)结合亲和力和细胞摄取。为了表征体内特性，进行了生物分布研究和 microPET 成像。对于体外和体内评估，均使用了α(v)β(3)阳性人黑色素瘤 M21 和α(v)β(3)阴性 M21-L 细胞。
（68）Ga]NODAGA-RGD 可以在室温下在 5 分钟内以高放射化学产率和纯度（>96%）生成。体外评估显示出高α(v)β(3)结合亲和力（IC50=4.7±1.6 nM）和受体特异性摄取。放射性示踪剂在磷酸盐缓冲盐水、pH7.4、FeCl3溶液和人血清中稳定。孵育 180 分钟后，发现蛋白结合活性比 [(68)Ga]DOTA-RGD 低 12 倍。60 分钟注射后，生物分布数据证实了受体特异性肿瘤积累。与所有研究的器官和组织相比，[(68)Ga]NODAGA-RGD 的放射性浓度较低，导致肿瘤与血液的比值提高[（68）Ga]NODAGA-RGD：11，（68）Ga]DOTA-RGD：4）。microPET 成像证实了与 [(68)Ga]DOTA-RGD 相比，[(68)Ga]NODAGA-RGD 的成像特性得到了改善。
所介绍的[(68)Ga]NODAGA-RGD 结合了易于获得性、高稳定性和良好的成像特性，使其成为目前用于成像α(v)β(3)表达的（18）F 标记 RGD 肽的一种有趣替代品。
