The adenosine A2B receptor has been proposed as a novel therapeutic target in cancer, as its expression is drastically elevated in several tumors and cancer cells. Noninvasive molecular imaging via positron emission tomography (PET) would allow the in vivo quantification of this receptor in pathological processes and most likely enable the identification and clinical monitoring of respective cancer therapies. On the basis of a bicyclic pyridopyrimidine-2,4-dione core structure, the new adenosine A2B receptor ligand 9 was synthesized, containing a 2-fluoropyridine moiety suitable for labeling with the short-lived PET radionuclide fluorine-18. Compound 9 showed a high binding affinity for the human A2B receptor (Ki(A2B) = 2.51 nM), along with high selectivities versus the A1, A2A, and A3 receptor subtypes. Therefore, it was radiofluorinated via nucleophilic aromatic substitution of the corresponding nitro precursor using [18F]F-/K2.2.2./K2CO3 in DMSO at 120 °C. Metabolic studies of [18F]9 in mice revealed about 60% of radiotracer intact in plasma at 30 minutes p.i. A preliminary PET study in healthy mice showed an overall biodistribution of [18F]9, corresponding to the known ubiquitous but low expression of the A2B receptor. Consequently, [18F]9 represents a novel PET radiotracer with high affinity and selectivity toward the adenosine A2B receptor and a suitable in vivo profile. Subsequent studies are envisaged to investigate the applicability of [18F]9 to detect alterations in the receptor density in certain cancer-related disease models.
腺苷A2B受体已被提议作为癌症的新型治疗靶点,因为其在多种肿瘤和癌细胞中表达显著升高。通过正电子发射断层扫描(PET)的非侵入性分子成像将允许体内定量评估病理过程中的该受体,并很可能实现相应癌症治疗的识别和临床监测。基于双环吡啶嘧啶-2,4-二酮核心结构,合成了新的腺苷A2B受体配体9,其中包含适用于标记短寿命PET放射性核素氟-18的2-氟吡啶基团。化合物9表现出高亲和力与人类A2B受体(Ki(A2B)= 2.51 nM),以及高选择性对A1、A2A和A3受体亚型。因此,它通过相应的硝基前体的亲核芳香取代在DMSO中以120℃下使用[18F]F-/K2.2.2./K2CO3进行放射性氟标记。小鼠[18F]9的代谢研究显示,放射性示踪剂在30分钟p.i.时血浆中保持约60%的完整性。在健康小鼠中进行的初步PET研究显示,[18F]9的整体生物分布与已知的A2B受体普遍但低表达相一致。因此,[18F]9代表一种具有高亲和力和选择性的新型PET放射性示踪剂,具有适合的体内特性。随后的研究将探讨[18F]9在某些与癌症相关的疾病模型中检测受体密度变化的适用性。