Radiolabeled inhibitors as probes for imaging mutant IDH1 expression in gliomas: Synthesis and preliminary evaluation of labeled butyl-phenyl sulfonamide analogs.
Radiolabeled inhibitors as probes for imaging mutant IDH1 expression in gliomas: Synthesis and preliminary evaluation of labeled butyl-phenyl sulfonamide analogs.
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DOI：
10.1016/j.ejmech.2016.04.066
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发表时间：
2016-08-25
影响因子：
6.7
通讯作者：
Zalutsky MR
中科院分区：
文献类型：
--
作者：
Chitneni SK;Reitman ZJ;Gooden DM;Yan H;Zalutsky MR
恶性神经胶质瘤经常在异柠檬酸脱氢酶1（IDH 1）基因中发生突变。研究表明，IDH突变通过由突变IDH 1酶的新形态代谢产物2-羟基戊二酸（2-HG）介导的机制参与肿瘤发病。这项工作的目的是合成和评价放射性标记的化合物，结合突变IDH 1酶的目标，使非侵入性成像的突变IDH 1表达在胶质瘤中的正电子发射断层扫描（PET）。基于已报道的IDH 1突变体的丁基-苯基磺酰胺抑制剂的化学结构，设计并合成了一个非放射性类似物的小型库。使用纯化的突变体IDH 1酶IDH 1-R132 H进行酶抑制测定，以测定合成化合物的IC 50和最大抑制效率。所选化合物1和4分别使用溴和苯酚前体用放射性碘（125 I）和/或18F标记。通过在正常小鼠中用[125 I]1进行组织分布研究来研究标记的抑制剂的体内行为。使用携带天然IDH 1-R132 H突变的等基因星形细胞瘤细胞系进行细胞摄取研究，以评估标记的抑制剂在IDH 1突变的肿瘤细胞中的潜在摄取。酶抑制试验显示，化合物1和4中苯环邻位具有碘或氟乙氧基取代基的化合物具有良好的抑制效力，IC 50值分别为1.7 μM和2.3 μM。化合物1和4抑制突变IDH 1活性并减少IDH 1突变星形细胞瘤细胞系中2-HG的产生。实现了1和4的放射性标记，[125 I]1（n=4）的平均放射化学产率为56.6 ± 20.1%，[18 F]4（n=3）的平均放射化学产率为67.5 ± 6.6%。[125 I]1在正常小鼠中表现出良好的生物分布特征，在注射后4 h从血液中快速清除并通过肝胆系统消除。与同基因WT-IDH 1对照相比，IDH 1-R132 H阳性肿瘤细胞中[125 I]1的摄取显著更高，注射后3 h的最大摄取比为1.67。标记的抑制剂与相应的非放射性类似物共孵育，并降低孵育培养基中FBS的正常浓度（10%），显着增加了IDH 1突变体和WT-IDH 1肿瘤细胞系中标记的抑制剂的吸收，这表明合成的标记丁基苯基磺酰胺抑制剂的显着非特异性结合。这些数据证明了开发基于酶抑制剂的突变IDH 1酶的放射性标记探针的可行性。通过修饰化学结构以降低亲脂性并增加效力来进一步优化标记的抑制剂，可以产生具有改善的特性的化合物，作为用于成像肿瘤中突变IDH 1表达的探针。
Malignant gliomas frequently harbor mutations in the isocitrate dehydrogenase 1 (IDH1) gene. Studies suggest that IDH mutation contributes to tumor pathogenesis through mechanisms that are mediated by the neomorphic metabolite of the mutant IDH1 enzyme, 2-hydroxyglutarate (2-HG). The aim of this work was to synthesize and evaluate radiolabeled compounds that bind to the mutant IDH1 enzyme with the goal of enabling noninvasive imaging of mutant IDH1 expression in gliomas by positron emission tomography (PET). A small library of nonradioactive analogs were designed and synthesized based on the chemical structure of reported butyl-phenyl sulfonamide inhibitors of mutant IDH1. Enzyme inhibition assays were conducted using purified mutant IDH1 enzyme, IDH1-R132H, to determine the IC50 and the maximal inhibitory efficiency of the synthesized compounds. Selected compounds, 1 and 4, were labeled with radioiodine (125I) and/or 18F using bromo- and phenol precursors, respectively. In vivo behavior of the labeled inhibitors was studied by conducting tissue distribution studies with [125I]1 in normal mice. Cell uptake studies were conducted using an isogenic astrocytoma cell line that carried a native IDH1-R132H mutation to evaluate the potential uptake of the labeled inhibitors in IDH1-mutated tumor cells. Enzyme inhibition assays showed good inhibitory potency for compounds that have iodine or a fluoroethoxy substituent at the ortho position of the phenyl ring in compounds 1 and 4 with IC50 values of 1.7 µM and 2.3 µM, respectively. Compounds 1 and 4 inhibited mutant IDH1 activity and decreased the production of 2-HG in an IDH1-mutated astrocytoma cell line. Radiolabeling of 1 and 4 was achieved with an average radiochemical yield of 56.6 ± 20.1% for [125I]1 (n=4) and 67.5 ± 6.6% for [18F]4 (n=3). [125I]1 exhibited favorable biodistribution characteristics in normal mice, with rapid clearance from the blood and elimination via the hepatobiliary system by 4 h after injection. The uptake of [125I]1 in tumor cells positive for IDH1-R132H was significantly higher compared to isogenic WT-IDH1 controls, with a maximal uptake ratio of 1.67 at 3 h post injection. Co-incubation of the labeled inhibitors with the corresponding nonradioactive analogs, and decreasing the normal concentrations of FBS (10%) in the incubation media substantially increased the uptake of the labeled inhibitors in both the IDH1-mutant and WT-IDH1 tumor cell lines, suggesting significant non-specific binding of the synthesized labeled butyl-phenyl sulfonamide inhibitors. These data demonstrate the feasibility of developing radiolabeled probes for the mutant IDH1 enzyme based on enzyme inhibitors. Further optimization of the labeled inhibitors by modifying the chemical structure to decrease the lipophilicity and to increase potency may yield compounds with improved characteristics as probes for imaging mutant IDH1 expression in tumors.