Bolik Kim-Viktoria, Hellmann Jan, Maschauer Simone, Neu Eduard, Einsiedel Jürgen, Riss Patrick, Vogg Nora, König Jörg, Fromm Martin F, Hübner Harald, Gmeiner Peter, Prante Olaf
Department of Nuclear Medicine, Molecular Imaging and Radiochemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Kussmaulallee 10/12, 91054, Erlangen, Germany.
Department of Chemistry and Pharmacy, Medicinal Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Nikolaus-Fiebiger-Str. 10, 91058, Erlangen, Germany.
EJNMMI Res. 2024 Sep 4;14(1):80. doi: 10.1186/s13550-024-01141-2.
The orexin receptor (OXR) plays a role in drug addiction and is aberrantly expressed in colorectal tumors. Subtype-selective OXR PET ligands suitable for in vivo use have not yet been reported. This work reports the development of F-labeled OXR PET ligand candidates derived from the OXR antagonist suvorexant and the OX1R-selective antagonist JH112.
Computational analysis predicted that fluorine substitution (1e) and introduction of the fluorobenzothiazole scaffold (1f) would be suitable for maintaining high OX1R affinity. After multi-step synthesis of 1a-1f, in vitro OXR binding studies confirmed the molecular dynamics calculations and revealed single-digit nanomolar OX1R affinities for 1a-f, ranging from 0.69 to 2.5 nM. The benzothiazole 1f showed high OX1R affinity (K = 0.69 nM), along with 77-fold subtype selectivity over OX2R. Cu-mediated F-fluorination of boroxine precursors allowed for a shortened reaction time of 5 min to provide the non-selective OXR ligand [F]1c and its selective OX1R congener [F]1f in activity yields of 14% and 22%, respectively, within a total synthesis time of 52-76 min. [F]1c and [F]1f were stable in plasma and serum in vitro, with logD of 2.28 ([F]1c) and 2.37 ([F]1f), and high plasma protein binding of 66% and 77%, respectively. Dynamic PET imaging in rats showed similar brain uptake of [F]1c (0.17%ID/g) and [F]1f (0.15%ID/g). However, preinjection of suvorexant did not significantly block [F]1c or [F]1f uptake in the rat brain. Pretreatment with cyclosporine A to study the role of P-glycoprotein (P-gp) in limiting brain accumulation moderately increased brain uptake of [F]1c and [F]1f. Accordingly, in vitro experiments demonstrated that the P-gp inhibitor zosuquidar only moderately inhibited polarized, basal to apical transport of 1c (p < 0.05) and had no effect on the transport of 1f, indicating that P-gp does not play a relevant role in brain accumulation of [F]1c and [F]1f in vivo.
The in vitro and in vivo results of [F]1c and [F]1f provide a solid basis for further development of suitable OXR PET ligands for brain imaging.
食欲素受体（OXR）在药物成瘾中起作用，且在结直肠癌中异常表达。尚未有适用于体内使用的亚型选择性OXR PET配体的报道。本研究报道了源自OXR拮抗剂苏沃雷生和OX1R选择性拮抗剂JH112的F标记OXR PET配体候选物的研发情况。
计算分析预测，氟取代（1e）和引入氟苯并噻唑支架（1f）将适合维持高OX1R亲和力。经过1a - 1f的多步合成，体外OXR结合研究证实了分子动力学计算，并揭示了1a - f对OX1R的亲和力为个位数纳摩尔，范围为0.69至2.5 nM。苯并噻唑1f表现出高OX1R亲和力（K = 0.69 nM），对OX2R的亚型选择性为77倍。硼氧六环前体的铜介导F - 氟化反应时间缩短至5分钟，可分别以14%和22%的活性产率提供非选择性OXR配体[F]1c及其选择性OX1R类似物[F]1f，总合成时间为52 - 76分钟。[F]1c和[F]1f在体外血浆和血清中稳定，logD分别为2.28（[F]1c）和2.37（[F]1f），血浆蛋白结合率分别为66%和77%。大鼠动态PET成像显示[F]1c（0.17%ID/g）和[F]1f（0.15%ID/g）在脑中的摄取相似。然而，预先注射苏沃雷生并未显著阻断大鼠脑中[F]1c或[F]1f的摄取。用环孢素A预处理以研究P - 糖蛋白（P - gp）在限制脑内蓄积中的作用，适度增加了[F]1c和[F]1f的脑摄取。因此，体外实验表明，P - gp抑制剂唑尼沙胺仅适度抑制1c从基底到顶端的极化转运（p < 0.05），对1f的转运无影响，表示P - gp在体内[F]1c和[F]1f的脑内蓄积中不起相关作用。
[F]1c和[F]1f的体外和体内结果为进一步研发适用于脑成像的OXR PET配体提供了坚实基础。
