Division of Radiological Chemistry, University Hospital Basel, Basel, Switzerland.
Eur J Nucl Med Mol Imaging. 2011 Jan;38(1):97-107. doi: 10.1007/s00259-010-1596-9. Epub 2010 Aug 18.
Radiolabelled somatostatin-based antagonists show a higher uptake in tumour-bearing mouse models than agonists of similar or even distinctly higher receptor affinity. Very similar results were obtained with another family of G protein-coupled receptor ligands, the bombesin family. We describe a new conjugate, RM2, with the chelator DOTA coupled to D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH(2) via the cationic spacer 4-amino-1-carboxymethyl-piperidine for labelling with radiometals such as (111)In and (68)Ga.
RM2 was synthesized on a solid support and evaluated in vitro in PC-3 cells. IC(50) and K(d) values were determined. The antagonist potency was evaluated by immunofluorescence-based internalization and Ca(2+) mobilization assays. Biodistribution studies were performed in PC-3 and LNCaP tumour-bearing mice with (111)In-RM2 and (68)Ga-RM2, respectively. PET/CT studies were performed on PC-3 and LNCaP tumour-bearing nude mice with (68)Ga-RM2.
RM2 and (111)In-RM2 are high-affinity and selective ligands for the GRP receptor (7.7 ± 3.3 nmol/l for RM2; 9.3 ± 3.3 nmol/l for (nat)In-RM2). The potent antagonistic properties were confirmed by an immunofluorescence-based internalization and Ca(2+) mobilization assays. (68)Ga- and (111)In-RM2 showed high and specific uptake in both the tumour and the pancreas. Uptake in the tumour remained high (15.2 ± 4.8%IA/g at 1 h; 11.7 ± 2.4%IA/g at 4 h), whereas a relatively fast washout from the pancreas and the other abdominal organs was observed. Uptake in the pancreas decreased rapidly from 22.6 ± 4.7%IA/g at 1 h to 1.5 ± 0.5%IA/g at 4 h.
RM2 was shown to be a potent GRPr antagonist. Pharmacokinetics and imaging studies indicate that (111)In-RM2 and (68)Ga-RM2 are ideal candidates for clinical SPECT and PET studies.
放射性标记的生长抑素拮抗剂在荷瘤小鼠模型中的摄取率高于类似甚至受体亲和力明显更高的激动剂。另一种 G 蛋白偶联受体配体家族——蛙皮素家族也得到了非常相似的结果。我们描述了一种新的化合物 RM2，它通过带正电荷的间隔物 4-氨基-1-羧甲基-哌啶将螯合剂 DOTA 与 D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH（2）偶联，用于标记放射性金属如（111）In 和（68）Ga。
RM2 在固相上合成，并在 PC-3 细胞中进行体外评估。测定 IC（50）和 K（d）值。通过免疫荧光内化和 Ca（2+）动员测定评估拮抗剂的效力。用（111）In-RM2 和（68）Ga-RM2 分别在荷 PC-3 和 LNCaP 肿瘤的小鼠中进行生物分布研究。用（68）Ga-RM2 在荷 PC-3 和 LNCaP 肿瘤的裸鼠中进行 PET/CT 研究。
RM2 和（111）In-RM2 是 GRP 受体的高亲和力和选择性配体（RM2 为 7.7±3.3 nmol/L；（nat）In-RM2 为 9.3±3.3 nmol/L）。通过免疫荧光内化和 Ca（2+）动员测定证实了其有效的拮抗作用。（68）Ga-和（111）In-RM2 在肿瘤和胰腺中均有高特异性摄取。肿瘤摄取仍很高（1 h 时为 15.2±4.8%IA/g；4 h 时为 11.7±2.4%IA/g），而胰腺和其他腹部器官的快速清除。胰腺摄取从 1 h 时的 22.6±4.7%IA/g 迅速下降到 4 h 时的 1.5±0.5%IA/g。
RM2 被证明是一种有效的 GRPr 拮抗剂。药代动力学和成像研究表明，（111）In-RM2 和（68）Ga-RM2 是临床 SPECT 和 PET 研究的理想候选物。
