Synthesis and initial in vitro evaluation of new P2X7R radioligands [11C]GSK1482160 analogs

• Published in: The Journal of nuclear medicine (1978) Vol. 60
• Main Authors: Gao, Mingzhang, Wang, Min, Meyer, Jill, Peters, Jonathan, Territo, Paul, Green, Mark, Hutchins, Gary, Zarrinmayeh, Hamideh, Zheng, Qi-Huang
• Format: Journal Article
• Language: English
• Published: New York Society of Nuclear Medicine 01.05.2019
• Subjects: Affinity; Analogs; Binding; Bombardment; Carbon dioxide; Chlorides; Dosimeters; Dosimetry; Evaluation; High-performance liquid chromatography; Inflammation; Liquid chromatography; Medical imaging; Methylation; Neurodegenerative diseases; Neurological diseases; Organic chemistry; Positron emission; Positron emission tomography; Purity; Pyroglutamic acid; Radiation; Radiation dosimetry; Radiochemistry; Radioisotopes; Radiology; Sodium carbonate; Sodium hydroxide; Solid phases; Synthesis; Target recognition; Tomography; Tracers
• ISSN: 0161-5505; 1535-5667

Objectives: The overexpression of purinergic receptor subtype 7 (P2X7R) is associated with neuroinflammation and plays an important role in various neurodegenerative diseases, and thus P2X7R has become a novel molecular imaging target for neuroinflammation via positron emission tomography (PET). We have previously developed and characterized [11C]GSK1482160 as a promising P2X7R radioligand for imaging neuroinflammation, clinical evaluation of [11C]GSK1482160 in healthy controls and patients is currently underway, and the estimation of radiation dosimetry for [11C]GSK1482160 in normal human subjects has been reported. Here we present the synthesis and initial in vitro evaluation of new P2X7R radioligands [11C]GSK1482160 analogs. Methods: The reference standards halo-GSK1482160 (F-, Br-, and I-) were synthesized from L-pyroglutamic acid or methyl L-pyroglutamate with 2-halo-3-(trifluoromethyl)benzylamine (F-, Br-, and I-) in three steps. Their corresponding precursors desmethyl-halo-GSK1482160 (F-, Br-, and I-) were synthesized from L-pyroglutamic acid with 2-halo-3-(trifluoromethyl)benzylamine (F-, Br-, and I-) in one step. The target tracers [11C]halo-GSK1482160 (F-, Br-, and I-) were prepared from desmethyl-halo-GSK1482160 (F-, Br-, and I-) with [11C]CH3OTf under basic conditions (NaOH-Na2CO3, solid, w/w 1:2) through N-[11C]methylation and isolated by HPLC combined with solid-phase extraction (SPE) method. The potency of halo-GSK1482160 (F-, Br-, and I-) in comparison with GSK1482160 (Cl-) was determined by a radioligand competitive binding assay using [11C]GSK1482160. Results: The chemical yields for halo-GSK1482160 (F-, Br-, and I-) and desmethyl-halo-GSK1482160 (F-, Br-, and I-) were moderate to high. The radiochemical yields for [11C]halo-GSK1482160 (F-, Br-, and I-) were 40-50% based on [11C]CO2 and decay-corrected to end of bombardment (EOB). The radiochemical purity was >99%, and molar activity at EOB was 370-1110 GBq/µmol. The binding affinity Ki value for halo-GSK1482160 (F-, Br-, and I-) and GSK1482160 (Cl-) is 54.2, 2.5, 1.9 and 3.1 nM, respectively. Conclusions: New P2X7R radioligands [11C]halo-GSK1482160 (F-, Br-, and I-) have been successfully radiosynthesized with high radiochemical yield and purity, and molar activity. [11C]F-GSK1482160 has ~17-fold less potency compared to [11C]GSK1482160, which prevents further in vivo evaluation of [11C]F-GSK1482160 in animals and human. [11C]Br-GSK1482160 and [11C]I-GSK1482160 display very similar even superior P2X7R affinity to the parent radioligand [11C]GSK1482160. The in vivo biological evaluation of [11C]Br-GSK1482160 and [11C]I-GSK1482160 is currently underway. Research Support : Showalter Young Investigator Award and Indiana University Department of Radiology and Imaging Sciences.