Henrottin Jean, Lemaire Christian, Egrise Dominique, Zervosen Astrid, Van den Eynde Benoit, Plenevaux Alain, Franci Xavier, Goldman Serge, Luxen André
Cyclotron Research Center, B30, Université de Liège, Sart-Tilman, B-4000, Liège, Belgium; Department of Chemistry, B6, Université de Liège, Sart-Tilman, B-4000, Liège, Belgium.
Cyclotron Research Center, B30, Université de Liège, Sart-Tilman, B-4000, Liège, Belgium.
Nucl Med Biol. 2016 Jun;43(6):379-89. doi: 10.1016/j.nucmedbio.2016.03.001. Epub 2016 Mar 11.
Indoleamine 2,3-dioxygenase (IDO) catalyzes the initial step in the catabolism of l-tryptophan along the kynurenine pathway and exerts immunosuppressive properties in inflammatory and tumor tissues by blocking locally T-lymphocyte proliferation. Recently, 1-(2-[(19)F]fluoroethyl)-dl-tryptophan (1-[(19)F]FE-dl-Trp) was reported as a good and specific substrate of this enzyme. Herein, the radiosynthesis of its radioactive isotopomer (1-[(18)F]FE-dl-Trp, dl-[(18)F]5) is presented along with in vitro enzymatic and cellular uptake studies.
The one-pot n.c.a. radiosynthesis of this novel potential PET imaging tracer, including HPLC purification and formulation, has been fully automated on a FASTlab™ synthesizer. Chiral separation of both isomers and their formulation were implemented on a second cassette. In vitro enzymatic and cellular uptake studies were then conducted with the d-, l- and dl-radiotracers.
The radiolabeling of the tosylate precursor was performed in DMF (in 5min; RCY: 57% (d.c.), n=3). After hydrolysis, HPLC purification and formulation, dl-[(18)F]5 was obtained with a global radiochemical yield of 18±3% (not decay corrected, n=7, in 80min) and a specific activity of 600±180GBq/μmol (n=5). The subsequent separation of l- and d-enantiomers was performed by chiral HPLC and both were obtained after formulation with an RCY (d.c.) of 6.1% and 5.8%, respectively. In vitro enzymatic assays reveal that l-[(18)F]5 is a better substrate than d-[(18)F]5 for human IDO. In vitro cellular assays show an IDO-specific uptake of the racemate varying from 30% to 50% of that of l-[(18)F]5, and a negligible uptake of d-[(18)F]5.
In vitro studies show that l-[(18)F]5 is a good and specific substrate of hIDO, while presenting a very low efflux. These results confirm that l-[(18)F]5 could be a very useful PET radiotracer for IDO expressing cells in cancer imaging.
吲哚胺2,3-双加氧酶（IDO）催化色氨酸沿犬尿氨酸途径分解代谢的第一步，并通过阻断局部T淋巴细胞增殖在炎症和肿瘤组织中发挥免疫抑制特性。最近，1-(2-[(19)F]氟乙基)-dl-色氨酸（1-[(19)F]FE-dl-Trp）被报道为该酶的一种良好且特异性的底物。在此，介绍了其放射性同位素异构体（1-[(18)F]FE-dl-Trp，dl-[(18)F]5）的放射性合成以及体外酶学和细胞摄取研究。
这种新型潜在PET成像示踪剂的一锅法n.c.a.放射性合成，包括HPLC纯化和制剂制备，已在FASTlab™合成仪上完全自动化。两种异构体的手性分离及其制剂制备在第二个模块上进行。然后用d-、l-和dl-放射性示踪剂进行体外酶学和细胞摄取研究。
对甲苯磺酸盐前体的放射性标记在DMF中进行（5分钟内；放射性化学产率：57%（衰变校正前），n = 3）。水解、HPLC纯化和制剂制备后，获得dl-[(18)F]5，总放射性化学产率为18±3%（未衰变校正，n = 7，80分钟内），比活度为600±180GBq/μmol（n = 5）。随后通过手性HPLC分离l-和d-对映体，制剂制备后二者的放射性化学产率（衰变校正后）分别为6.1%和5.8%。体外酶学分析表明，对于人IDO，l-[(18)F]5是比d-[(18)F]5更好的底物。体外细胞分析显示，外消旋体的IDO特异性摄取为l-[(18)F]5的30%至50%，而d-[(18)F]5的摄取可忽略不计。
体外研究表明，l-[(18)F]5是hIDO的良好且特异性底物，同时具有非常低的外排。这些结果证实，l-[(18)F]5可能是用于癌症成像中IDO表达细胞的非常有用的PET放射性示踪剂。
