Preclinical PET Platform, Department of Medicinal Chemistry, Faculty of Pharmacy, Uppsala University, Uppsala, Sweden.
PLoS One. 2013 Dec 3;8(12):e81932. doi: 10.1371/journal.pone.0081932. eCollection 2013.
Expression of the gastrin-releasing peptide receptor (GRPR) in prostate cancer suggests that this receptor can be used as a potential molecular target to visualize and treat these tumors. We have previously investigated an antagonist analog of bombesin (D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2, RM26) conjugated to 1,4,7-triazacyclononane-N,N',N''-triacetic acid (NOTA) via a diethylene glycol (PEG2) spacer (NOTA-P2-RM26) labeled with (68)Ga and (111)In. We found that this conjugate has favorable properties for in vivo imaging of GRPR-expression. The focus of this study was to develop a (18)F-labelled PET agent to visualize GRPR. NOTA-P2-RM26 was labeled with (18)F using aluminum-fluoride chelation. Stability, in vitro binding specificity and cellular processing tests were performed. The inhibition efficiency (IC50) of the [(nat)F]AlF-NOTA-P2-RM26 was compared to that of the (nat)Ga-loaded peptide using (125)I-Tyr(4)-BBN as the displacement radioligand. The pharmacokinetics and in vivo binding specificity of the compound were studied. NOTA-P2-RM26 was labeled with (18)F within 1 h (60-65% decay corrected radiochemical yield, 55 GBq/µmol). The radiopeptide was stable in murine serum and showed high specific binding to PC-3 cells. [(nat)F]AlF-NOTA-P2-RM26 showed a low nanomolar inhibition efficiency (IC50=4.4±0.8 nM). The internalization rate of the tracer was low. Less than 14% of the cell-bound radioactivity was internalized after 4 h. The biodistribution of [(18)F]AlF-NOTA-P2-RM26 demonstrated rapid blood clearance, low liver uptake and low kidney retention. The tumor uptake at 3 h p.i. was 5.5±0.7 %ID/g, and the tumor-to-blood, -muscle and -bone ratios were 87±42, 159±47, 38±16, respectively. The uptake in tumors, pancreas and other GRPR-expressing organs was significantly reduced when excess amount of non-labeled peptide was co-injected. The low uptake in bone suggests a high in vivo stability of the Al-F bond. High contrast PET image was obtained 3 h p.i. The initial biological results suggest that [(18)F]AlF-NOTA-P2-RM26 is a promising candidate for PET imaging of GRPR in vivo.
胃泌素释放肽受体（GRPR）在前列腺癌中的表达表明，该受体可以作为一种潜在的分子靶点，用于可视化和治疗这些肿瘤。我们之前研究了一种通过二甘醇（PEG2）间隔臂连接到 1,4,7-三氮杂环壬烷-N,N',N''-三乙酸（NOTA）的蛙皮素（D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2，RM26）的拮抗剂类似物（68）Ga 和（111）In 标记的 NOTA-P2-RM26。我们发现，这种缀合物具有用于 GRPR 表达的体内成像的良好特性。本研究的重点是开发一种用于可视化 GRPR 的（18）F 标记的 PET 试剂。NOTA-P2-RM26 用铝-氟化物螯合标记（18）F。进行了稳定性、体外结合特异性和细胞处理测试。使用（125）I-Tyr（4）-BBN 作为置换放射性配体比较了 [（nat）F]AlF-NOTA-P2-RM26 的抑制效率（IC50）与（nat）Ga 负载肽的抑制效率。研究了化合物的药代动力学和体内结合特异性。NOTA-P2-RM26 在 1 小时内用（18）F 标记（60-65% 衰减校正放射性化学产率，55GBq/µmol）。放射性肽在鼠血清中稳定，对 PC-3 细胞表现出高特异性结合。[（nat）F]AlF-NOTA-P2-RM26 表现出低纳摩尔抑制效率（IC50=4.4±0.8 nM）。示踪剂的内化率低。4 小时后，细胞结合的放射性不到 14%被内化。[18F]AlF-NOTA-P2-RM26 的生物分布显示快速清除血液，肝脏摄取低，肾脏保留低。3 小时时肿瘤摄取率为 5.5±0.7%ID/g，肿瘤与血液、肌肉和骨骼的比值分别为 87±42、159±47、38±16。当共注射过量未标记的肽时，肿瘤、胰腺和其他 GRPR 表达器官的摄取明显减少。骨中的低摄取表明 Al-F 键具有高体内稳定性。3 小时时获得高对比度的 PET 图像。初步生物学结果表明，[18F]AlF-NOTA-P2-RM26 是一种有前途的用于体内 GRPR PET 成像的候选物。
