Lipiński Piotr F J, Garnuszek Piotr, Maurin Michał, Stoll Raphael, Metzler-Nolte Nils, Wodyński Artur, Dobrowolski Jan Cz, Dudek Marta K, Orzełowska Monika, Mikołajczak Renata
Neuropeptides Department, Mossakowski Medical Research Centre Polish Academy of Sciences, Pawińskiego 5 Str., 02-106, Warszawa, Poland.
Radioisotope Centre POLATOM, National Centre for Nuclear Research, A. Sołtana 7 Str, 05-400, Otwock, Poland.
EJNMMI Res. 2018 Apr 16;8(1):33. doi: 10.1186/s13550-018-0387-3.
The cholecystokinin receptor subtype 2 (CCK-2R) is an important target for diagnostic imaging and targeted radionuclide therapy (TRNT) due to its overexpression in certain cancers (e.g., medullary thyroid carcinoma (MTC)), thus matching with a theranostic principle. Several peptide conjugates suitable for the TRNT of MTC have been synthesized, including a very promising minigastrin analogue DOTA-(DGlu)-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH (CP04). In this contribution, we wanted to see whether CP04 binding affinity for CCK-2R is sensitive to the type of the complexed radiometal, as well as to get insights into the structure of CP04-CCK2R complex by molecular modeling.
In vitro studies demonstrated that there is no significant difference in CCK-2R binding affinity and specific cellular uptake between the CP04 conjugates complexed with [Ga]Ga or [Lu]Lu. In order to investigate the background of this observation, we proposed a binding model of CP04 with CCK-2R based on homology modeling and molecular docking. In this model, the C-terminal part of the molecule enters the cavity formed between the receptor helices, while the N-terminus (including DOTA and the metal) is located at the binding site outlet, exposed in large extent to the solvent. The radiometals do not influence the conformation of the molecule except for the direct neighborhood of the chelating moiety.
The model seems to be in agreement with much of structure-activity relationship (SAR) studies reported for cholecystokinin and for CCK-2R-targeting radiopharmaceuticals. It also explains relative insensitivity of CCK-2R affinity for the change of the metal. The proposed model partially fits the reported site-directed mutagenesis data.
胆囊收缩素2型受体（CCK-2R）是诊断成像和靶向放射性核素治疗（TRNT）的重要靶点，因为它在某些癌症（如甲状腺髓样癌（MTC））中过度表达，符合诊疗一体化原则。已经合成了几种适用于MTC的TRNT的肽缀合物，包括一种非常有前景的小胃泌素类似物DOTA-(DGlu)-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH（CP04）。在本研究中，我们想了解CP04对CCK-2R的结合亲和力是否对络合放射性金属的类型敏感，以及通过分子建模深入了解CP04-CCK2R复合物的结构。
体外研究表明，与[Ga]Ga或[Lu]Lu络合的CP04缀合物之间，CCK-2R结合亲和力和特异性细胞摄取没有显著差异。为了研究这一观察结果的背景，我们基于同源建模和分子对接提出了CP04与CCK-2R的结合模型。在该模型中，分子的C末端部分进入受体螺旋之间形成的腔中，而N末端（包括DOTA和金属）位于结合位点出口处，在很大程度上暴露于溶剂中。除了螯合部分的直接邻域外，放射性金属不会影响分子的构象。
该模型似乎与许多关于胆囊收缩素和靶向CCK-2R的放射性药物的构效关系（SAR）研究一致。它还解释了CCK-2R亲和力对金属变化相对不敏感的原因。所提出的模型部分符合报道的定点诱变数据。
