Carbon-11-labelling of the histone deacetylase 6 radioligand EKZ-001

IF 3.6 4区医学 Q1 RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING

Nuclear medicine and biology Pub Date : 2025-05-23 DOI:10.1016/j.nucmedbio.2025.109030

Tetsuro Tago , Jun Toyohara

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引用次数: 0

Abstract

Purpose

Histone deacetylase 6 (HDAC6) is involved in microtubule stabilisation and protein degradation, and is attracting attention as a therapeutic target molecule for neurodegenerative diseases. [¹⁸F]EKZ-001 is a positron emission tomography (PET) radioligand that can visualise HDAC6 in the brain and allows exploration of the relationship between diseases and HDAC6 expression levels and distribution. The present study reports the radiosynthesis of a carbon-11-labelled version of EKZ-001 that is chemically identical to [¹⁸F]EKZ-001. This radiosynthesis adopted a conventional ¹¹C-labelling method with [¹¹C]methyl triflate instead of the originally reported ruthenium-mediated ¹⁸F-deoxyfluorination. Preliminary biological evaluations using [¹¹C]EKZ-001 were also performed.

Methods

Carbon-11-labelling was conducted with a desmethyl precursor and [¹¹C]methyl triflate in acetone, which was selected after solvent optimisation. After the ¹¹C-labelling reaction at room temperature for 5 min, [¹¹C]EKZ-001 was purified using semipreparative high-performance liquid chromatography. The solvent of the fraction containing the product was removed by evaporation, and the resulting residue was formulated in physiological saline containing ethanol and ascorbic acid. The radioligand kinetics in the brain were assessed in normal mice by small-animal PET with and without coadministration of unlabelled EKZ-001. Metabolite analysis was also performed in the brain and plasma at 15 and 30 min after radioligand administration in normal mice. Radioligand binding in the mouse brain was evaluated by in vitro autoradiography and compared with HDAC6 immunostaining.

Results

[¹¹C]EKZ-001 was obtained in a radiochemical yield of 35.5 ± 4.2 % (decay corrected to [¹¹C]CO₂; n = 3), with a radiochemical purity and molar activity at the end of the synthesis of 96.0 ± 1.1 % and 111.2 ± 32.3 MBq/nmol, respectively. PET imaging in normal mice demonstrated an excellent brain uptake of [¹¹C]EKZ-001 that was reduced by coadministration of unlabelled EKZ-001. [¹¹C]EKZ-001 was stable in the mouse brain, and the proportion of [¹¹C]EKZ-001 radioactivity remained intact at 85 % even 30 min after administration. In autoradiography using mouse brain sections, [¹¹C]EKZ-001 showed specific binding in regions generally consistent with HDAC6 immunostaining.

Conclusions

[¹¹C]EKZ-001 can be synthesised in a conventional way with [¹¹C]methyl triflate and used as a radioligand for HDAC6 imaging in the brain.

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组蛋白去乙酰化酶6放射性配体EKZ-001的碳-11标记

目的组蛋白去乙酰化酶6 （HDAC6）参与微管稳定和蛋白质降解，作为神经退行性疾病的治疗靶点分子受到关注。[18F]EKZ-001是一种正电子发射断层扫描（PET）放射配体，可以可视化HDAC6在大脑中的表达，并允许探索疾病与HDAC6表达水平和分布之间的关系。本研究报告了一种碳11标记版本的EKZ-001的放射性合成，其化学性质与[18F]EKZ-001相同。该放射性合成采用了传统的11C标记方法，用[11C]三氟化甲基代替了最初报道的钌介导的18f脱氧氟化。使用[11C]EKZ-001进行初步生物学评价。方法用去甲基前体和丙酮中的[11C]三氟化甲酯进行碳-11标记，丙酮经溶剂优化后选定。室温下11C标记反应5 min后，采用半制备高效液相色谱法纯化[11C]EKZ-001。通过蒸发除去含有该产物的馏分的溶剂，得到的残渣在含有乙醇和抗坏血酸的生理盐水中配制。用小动物PET评估正常小鼠脑内放射性配体动力学，并与未标记的EKZ-001共给药和不给药。在给药后15和30分钟，对正常小鼠的脑和血浆进行代谢物分析。采用体外放射自显影技术评价放射配体在小鼠脑内的结合，并与HDAC6免疫染色进行比较。结果[11C]EKZ-001的放射化学产率为35.5±4.2%(衰变校正为[11C]CO2；n = 3)，其放射化学纯度为96.0±1.1%，合成结束时的摩尔活性为111.2±32.3 MBq/nmol。正常小鼠的PET成像显示，[11C]EKZ-001的大脑摄取良好，而未标记的EKZ-001共同给药则会减少。[11C]EKZ-001在小鼠脑内稳定，即使给药30 min后，[11C]EKZ-001的放射性比例仍保持在85%。在使用小鼠脑切片的放射自显影中，[11C]EKZ-001在与HDAC6免疫染色基本一致的区域显示特异性结合。结论[11C]EKZ-001可与[11C]三氟酸甲酯用常规方法合成，并作为HDAC6脑成像的放射配体。

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来源期刊

Nuclear medicine and biology 医学-核医学

CiteScore

6.00

自引率

9.70%

发文量

479

审稿时长

51 days

期刊介绍： Nuclear Medicine and Biology publishes original research addressing all aspects of radiopharmaceutical science: synthesis, in vitro and ex vivo studies, in vivo biodistribution by dissection or imaging, radiopharmacology, radiopharmacy, and translational clinical studies of new targeted radiotracers. The importance of the target to an unmet clinical need should be the first consideration. If the synthesis of a new radiopharmaceutical is submitted without in vitro or in vivo data, then the uniqueness of the chemistry must be emphasized. These multidisciplinary studies should validate the mechanism of localization whether the probe is based on binding to a receptor, enzyme, tumor antigen, or another well-defined target. The studies should be aimed at evaluating how the chemical and radiopharmaceutical properties affect pharmacokinetics, pharmacodynamics, or therapeutic efficacy. Ideally, the study would address the sensitivity of the probe to changes in disease or treatment, although studies validating mechanism alone are acceptable. Radiopharmacy practice, addressing the issues of preparation, automation, quality control, dispensing, and regulations applicable to qualification and administration of radiopharmaceuticals to humans, is an important aspect of the developmental process, but only if the study has a significant impact on the field. Contributions on the subject of therapeutic radiopharmaceuticals also are appropriate provided that the specificity of labeled compound localization and therapeutic effect have been addressed.