Background. Inducible nitric oxide synthase (iNOS) plays a crucial role in neuroinflammation, especially microglial activity, and may potentially represent a useful biomarker of neuroinflammation. In this study, we carefully defined a strategic plan to develop iNOS-targeted molecular PET imaging using (4-amino-5,8-difluoro-1H-spiro[piperidine-4,2-quinazolin]-1-yl)(4-fluorophenyl)methanone ([¹⁸F]FBAT) as a tracer in a mouse model of lipopolysaccharide- (LPS-) induced brain inflammation. Methods. An in vitro model, murine microglial BV2 cell line, was used to assess the uptake of [¹⁸F]FBAT in response to iNOS induction at the cellular level. In vivo whole-body dynamic PET/MR imaging was acquired in LPS-treated (5 mg/kg) and control mice. Standard uptake value (SUV), total volume of distribution (), and area under the curve (AUC) based on the [¹⁸F]FBAT PET signals were determined. The expression of iNOS was confirmed by immunohistochemistry (IHC) of brain tissues. Results. At the end of synthesis, the yield of [¹⁸F]FBAT was 2.2–3.1% (EOS), radiochemical purity was >99%, and molar radioactivity was 125–137 GBq/μmol. In vitro, [¹⁸F]FBAT rapidly and progressively accumulated in murine microglial BV2 cells exposed to LPS; however, [¹⁸F]FBAT accumulation was inhibited by aminoguanidine, a selective iNOS inhibitor. In vivo biodistribution studies of [¹⁸F]FBAT showed a significant increase in the liver and kidney on LPS-treated mice. At 3 h postinjection of LPS, in vivo, the [¹⁸F]FBAT accumulation ratios at 30 min post intravenous (i.v.) radiotracer injection for the whole brain, cortex, cerebellum, and brainstem were , , , and , respectively, compared to those of mice not injected with LPS. The mean area under the curve (AUC_0-30min), total volume of distribution (, mL/cm³), and (influx rate) of [¹⁸F]FBAT were - and -fold higher in the 3 h LPS group, respectively, than in the control group. In the pharmacokinetic two-compartment model, the whole brain of [¹⁸F]FBAT was significantly higher in mice injected with LPS compared to the control group. Aminoguanidine, selective iNOS inhibitor, pretreatment significantly reduced the AUC_0-30min and values in LPS-induced mice. Quantitative analysis of immunohistochemically stained brain sections confirmed iNOS was preferentially upregulated in the cerebellum and cortex of mice injected with LPS. Conclusion. An automated robotic method was established for radiosynthesis of [¹⁸F]FBAT, and the preliminary in vitro and in vivo results demonstrated the feasibility of detecting iNOS activity/expression in LPS-treated neuroinflammation by noninvasive imaging with [¹⁸F]FBAT PET/MRI.

中文翻译：

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(4-Amino-5,8-difluoro-1H-spiro[piperidine-4,2-quinazolin]-1-yl)(4-[18F]fluorophenyl)methanone 用于诱导型 PET/MR 成像的自动合成和初步评估一氧化氮合酶

背景。诱导型一氧化氮合酶 (iNOS) 在神经炎症，尤其是小胶质细胞活性中起着至关重要的作用，并可能代表一种有用的神经炎症生物标志物。在这项研究中，我们仔细制定了一项战略计划，以使用 (4 - amino-5 , 8 - difluoro-1 H-spiro[piperidine-4,2 - quinazolin]-1-yl) (4)开发 iNOS 靶向分子 PET 成像-氟苯基）甲酮（[ ¹⁸ F]FBAT）作为脂多糖（LPS-）诱导的脑炎症小鼠模型中的示踪剂。方法。体外模型，鼠小胶质细胞 BV2 细胞系，用于评估 [ ¹⁸F]FBAT 在细胞水平上响应 iNOS 诱导。在 LPS 处理 (5 mg/kg) 和对照小鼠中获得了体内全身动态 PET/MR 成像。测定基于[ ¹⁸ F]FBAT PET信号的标准摄取值（SUV）、总分布容积（）和曲线下面积（AUC）。通过脑组织的免疫组织化学（IHC）证实了iNOS的表达。结果。合成结束时，[ ¹⁸ F]FBAT的收率为2.2-3.1%（EOS），放射化学纯度>99%，摩尔放射性为125-137 GBq/ μmol。体外, [ ¹⁸F]FBAT 在暴露于 LPS 的小鼠小胶质细胞 BV2 细胞中迅速且渐进地积累；然而，[ ¹⁸ F]FBAT 的积累被一种选择性 iNOS 抑制剂氨基胍抑制。[ ^{18 F]FBAT的}体内生物分布研究显示LPS处理的小鼠的肝脏和肾脏显着增加。在体内注射 LPS 后 3 小时，静脉内 (iv) 放射性示踪剂注射后 30 分钟对整个大脑、皮层、小脑和脑干的 [ ^{18 F]FBAT 积累比率为}, , ,和，分别与未注射 LPS 的小鼠相比。^{[ 18} F]FBAT的平均曲线下面积 (AUC _0-30min )、总分布容积 ( , mL/cm ³ ) 和(流入率)-和- 3 小时 LPS 组中的倍数分别高于对照组。在药代动力学二室模型中，的[ ¹⁸ F]FBAT全脑显着升高。氨基胍，选择性 iNOS 抑制剂，预处理显着降低了LPS 诱导小鼠_{的 AUC 0-30min}和免疫组织化学染色脑切片的定量分析证实，在注射 LPS 的小鼠的小脑和皮质中 iNOS 优先上调。结论。^{建立了[ 18} F]FBAT 放射合成的自动化机器人方法，以及初步的体外和体内结果证明了通过 [ ¹⁸ F]FBAT PET/MRI 的无创成像检测 LPS 治疗的神经炎症中 iNOS 活性/表达的可行性。