Inducible isozyme cyclooxygenase-2 (COX-2) is upregulated under acute and chronic inflammatory conditions, including cancer, wherein it promotes angiogenesis, tissue invasion, and resistance to apoptosis. Due to its high expression in various cancers, COX-2 has become an important biomarker for molecular imaging and therapy of cancer. Recently, our group applied in situ click chemistry for the identification of the highly potent and selective COX-2 inhibitor triacoxib. In this study, we present the radiosynthesis in vitro and in vivo radiopharmacological validation of [18F]triacoxib, a novel radiotracer for PET imaging of COX-2. Radiosynthesis of [18F]triacoxib was accomplished using copper-mediated late-stage radiofluorination chemistry. The radiosynthesis, including radio-HPLC purification, of [18F]triacoxib was accomplished within 90 min in decay-corrected radiochemical yields of 72% (n = 7) at molar activities exceeding 90 GBq/μmol. Cellular uptake and inhibition studies with [18F]triacoxib were carried out in COX-2 expressing HCA-7 cells. Cellular uptake of [18F]triacoxib in HCA-7 cells reached 25% radioactivity/mg protein after 60 min. Cellular uptake was reduced by 63% upon pretreatment with 0.1 mM celecoxib, and 90% of the radiotracer remained intact in vivo after 60 min p.i. in mice. [18F]Triacoxib was further evaluated in HCA-7 tumor-bearing mice using dynamic PET imaging, radiometabolite analysis, autoradiography, and immunohistochemistry. PET imaging revealed a favorable baseline radiotracer uptake in HCA-7 tumors (SUV60min = 0.76 ± 0.02 (n = 4)), which could be blocked by 20% through i.p. pretreatment with 2 mg of celecoxib. Autoradiography and immunohistochemistry experiments further the confirmed blocking of COX-2 in vivo. [18F]Triacoxib, whose nonradioactive analogue was identified through in situ click chemistry, is a novel radiotracer for PET imaging of COX-2 in cancer. Despite a substantial amount of nonspecific uptake in vivo, [18F]triacoxib displayed specific binding to COX-2 in vivo and reinforced the feasibility of optimal structure selection by in situ click chemistry. It remains to be elucidated how this novel radiotracer would perform in first-in-human studies to detect COX-2 with PET.

中文翻译：

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[18F] Triacoxib的放射合成和生物学评估：用于COX-2 PET成像的新型放射性示踪剂。

诱导型同工酶环氧合酶2（COX-2）在包括癌症在内的急性和慢性炎症条件下均被上调，其中它促进血管生成，组织浸润和对细胞凋亡的抵抗力。由于其在各种癌症中的高表达，COX-2已成为癌症分子成像和治疗的重要生物标志物。最近，我们小组将原位点击化学应用于鉴定高效和选择性的COX-2抑制剂triacoxib。在这项研究中，我们提出[18F] triacoxib的放射合成的体外和体内放射药理学验证，这是一种用于PET成像COX-2的新型放射性示踪剂。[18F] triacoxib的放射性合成是通过铜介导的后期放射性氟化化学完成的。放射合成，包括放射HPLC纯化，在摩尔活性超过90 GBq /μmol的情况下，[18F] triacoxib的分离在90分钟内完成了72％（n = 7）的衰变校正放射化学产率。[18F] triacoxib的细胞摄取和抑制研究是在表达COX-2的HCA-7细胞中进行的。60分钟后，HCA-7细胞中[18F] triacoxib的细胞摄取达到25％放射性/ mg蛋白。用0.1 mM塞来昔布进行预处理后，细胞摄取降低了63％，在pi注射60分钟后，体内90％的放射性示踪剂保持完整。[18F]使用动态PET成像，放射性代谢物分析，放射自显影和免疫组织化学技术在HCA-7荷瘤小鼠中进一步评估了Triacoxib。PET成像显示HCA-7肿瘤基线放射性示踪剂摄取良好（SUV60min = 0.76±0.02（n = 4）），可通过ip阻断20％用2毫克塞来昔布进行预处理。放射自显影和免疫组织化学实验进一步证实了体内对COX-2的阻断。[18F] Triacoxib是通过放射原位化学鉴定的非放射性类似物，是一种用于癌症中COX-2的PET成像的新型放射性示踪剂。尽管体内有大量的非特异性摄取，[18F] triacoxib在体内显示出与COX-2的特异性结合，并增强了通过原位点击化学选择最佳结构的可行性。尚需阐明这种新型放射性示踪剂在首次人类研究中如何用PET检测COX-2的性能。是用于癌症中COX-2的PET成像的新型放射性示踪剂。尽管体内有大量的非特异性摄取，[18F] triacoxib在体内显示出与COX-2的特异性结合，并增强了通过原位点击化学选择最佳结构的可行性。尚需阐明这种新型放射性示踪剂在人类首次研究中如何用PET检测COX-2的性能。是用于癌症中COX-2的PET成像的新型放射性示踪剂。尽管体内有大量的非特异性摄取，[18F] triacoxib在体内显示出与COX-2的特异性结合，并增强了通过原位点击化学选择最佳结构的可行性。尚需阐明这种新型放射性示踪剂在人类首次研究中如何用PET检测COX-2的性能。