Janssen Research and Development LLC, San Diego, California; and.
MNI, a Division of Invicro, New Haven, Connecticut.
J Nucl Med. 2019 Aug;60(8):1154-1159. doi: 10.2967/jnumed.118.212696. Epub 2019 Feb 7.
The P2X7 receptor is an adenosine triphosphate-gated ion channel, which is abundantly expressed in glial cells within the central nervous system and in the periphery. P2X7 receptor activation leads to the release of the proinflammatory cytokine IL-1β in the brain, and antagonism of the P2X7 receptor is a novel therapeutic strategy to dampen adenosine triphosphate-dependent IL-1β signaling. PET ligands for the P2X7 receptor will not only be valuable to assess central target engagement of drug candidates but also hold promise as surrogate markers of central neuroinflammation. Herein we describe the in vitro and in vivo evaluation of F-JNJ-64413739, an F-labeled PET ligand for imaging the P2X7 receptor in the brain. P2X7 receptor affinity and specificity, pharmacokinetics, metabolic stability, blood-brain barrier permeability, and off-target binding of JNJ-64413739 were evaluated in a series of in vitro, ex vivo, and in vivo assays. F-JNJ-64413739 was radiolabeled via a one-step nucleophilic aromatic substitution. The tracer was also studied in rhesus macaques, and PET images were analyzed with an arterial plasma input function-based Logan graphical analysis. The potency (half-maximal inhibitory concentration) of the P2X7 receptor antagonist JNJ-64413739 is 1.0 ± 0.2 nM and 2.0 ± 0.6 nM at the recombinant human and rat P2X7 receptor, respectively, and the binding affinity is 2.7 nM (rat cortex binding assay) and 15.9 nM (human P2X7 receptor). In nonhuman primate PET imaging studies, dose-dependent receptor occupancy of JNJ-54175446 was observed in 2 rhesus monkeys. At a 0.1 mg/kg dose (intravenous) of JNJ-54175446, the receptor occupancy was calculated to be 17% by Logan graphical analysis, whereas a dose of 2.5 mg/kg yielded a receptor occupancy of 60%. The preclinical evaluation of F-JNJ-64413739 demonstrates that the tracer engages the P2X7 receptor. Reproducible and dose-dependent receptor occupancy studies with the P2X7 receptor antagonist JNJ-54175446 were obtained in rhesus monkeys. This novel PET tracer exhibits in vitro and in vivo characteristics suitable for imaging the P2X7 receptor in the brain and warrants further studies in humans.
P2X7 受体是一种三磷酸腺苷门控离子通道，在中枢神经系统和外周的神经胶质细胞中大量表达。P2X7 受体的激活导致大脑中促炎细胞因子 IL-1β的释放，而 P2X7 受体的拮抗作用是一种新的治疗策略，可以抑制三磷酸腺苷依赖性 IL-1β信号传导。用于 P2X7 受体的 PET 配体不仅对评估候选药物的中枢靶标结合具有重要意义，而且作为中枢神经炎症的替代标志物也具有很大的潜力。本文描述了 F-JNJ-64413739 的体外和体内评估，F-JNJ-64413739 是一种用于脑内 P2X7 受体成像的 F 标记 PET 配体。 在一系列体外、离体和体内测定中，评估了 JNJ-64413739 的 P2X7 受体亲和力和特异性、药代动力学、代谢稳定性、血脑屏障通透性和脱靶结合。通过一步亲核芳香取代反应对 F-JNJ-64413739 进行放射性标记。该示踪剂还在恒河猴中进行了研究，并通过动脉血浆输入函数的 Logan 图形分析对 PET 图像进行了分析。 P2X7 受体拮抗剂 JNJ-64413739 的效力（半最大抑制浓度）分别为 1.0±0.2 nM 和 2.0±0.6 nM，在重组人 P2X7 受体和大鼠 P2X7 受体上的结合亲和力分别为 2.7 nM（大鼠皮质结合测定）和 15.9 nM（人 P2X7 受体）。在非人类灵长类动物的 PET 成像研究中，在 2 只恒河猴中观察到 JNJ-54175446 的剂量依赖性受体占有率。在 0.1mg/kg（静脉内）剂量的 JNJ-54175446 下，通过 Logan 图形分析计算出受体占有率为 17%，而 2.5mg/kg 的剂量产生的受体占有率为 60%。 F-JNJ-64413739 的临床前评估表明，该示踪剂与 P2X7 受体结合。用 P2X7 受体拮抗剂 JNJ-54175446 在恒河猴中进行了可重复和剂量依赖性的受体占有率研究。这种新型的 PET 示踪剂在体外和体内均表现出适合脑内 P2X7 受体成像的特征，值得在人类中进一步研究。
