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内容記述 |
Objectives: Leucine-rich repeat kinase 2(LRRK2) is a large protein (280 kDa) and includes GTPase and kinase domains. Mutation in the LRRK2 gene upregulates the activity of LRRK2 protein and is a main factor for the genetic development of Parkinson's disease (PD) [1]. In the last decade, several LRRK2 inhibitors, such as [18F]FIPM, [11C]GNE-1023 and [18F]PF-064555943, have been synthesized, but no PET tracer was used for clinical study [2-4]. In this study, we synthesized [11C]GNE-7915 ([11C]2), a compound with high activity for LRRK2 (IC50 = 9 nM) [5], and evaluated its potential as a PET tracer for brain imaging.Methods: The phenol precursor 1 and standard compound 2 (GNE-7915) were synthesized in house within 3–4 steps each from 4-amino-3-methoxybenzoic acid (chemical yield: 1, 11%; 2: 9%). Compound 2 was radiolabeled with [11C]CH3I. The [11C]CH3I gas was prepared by the reaction of [11C]CO2 with LiAlH4, followed by treatment with HI, and trapped into a solution of precursor 1 (1.0 mg) and 0.5 M NaOH (4.7 μL) in DMF (300 μL). The reaction mixture was heated at 80 °C for 5 min (Scheme 1). This radioactive mixture was diluted by the preparative HPLC solvent and applied to semi-preparative HPLC column. The brain uptake, binding specificity and selectivity of [11C]2 for LRRK2 were evaluated by in vitro autoradiography and small animal PET on rat brains.Results: Starting from 22–24 GBq of [11C]CO2, [11C]2 was synthesized with 5 ± 1% radiochemical yield (non-decay-corrected), 77 ± 43 GBq/μmol molar activity, and ≥ 99% radiochemical purity (n =3). The average total synthesis time was 36 min from the end of bombardment. In vitro autoradiography for rat brain showed that the highest level was in the substantia nigra, followed by the striatum, hippocampus and cortex (Figure 1). PET imaging showed [11C]2 had a moderate initial brain uptake (SUV 0.8). Conclusions: We developed [11C]2 as a novel PET tracer for LRRK2. [11C]2 showed high in vitro specific binding to LRRK2 in the rat brain. Based on the present results, [11C]2 could serve as a lead compound for further development of PET tracer targeting LRRK2. Acknowledgements: This work was supported by JSPS KAKENHI grant number 24K10799.References: [1] J. P. L. Daher, et al., J Biol Chem. 2015, 290(32), 19433–19444. [2] W. Mori, et al., RSC Med. Chem. 2020, 11, 676-684. [3] Z. Chen, et al., Chem. Med Chem. 2019, 14(17), 1580-1585. [4] Z. Chen, et al., J Med Chem. 2022. [5] A. A. Estrada, et al., J Med Chem. 2012, 55, 9416–9433. |
