Pharmacologic characterizations of a P2X7 receptor-specific radioligand, [11C]GSK1482160 for neuroinflammatory response.
OBJECTIVE
The P2X7 receptor (P2X7R) is a key regulatory element in the neuroinflammatory cascade that provides a promising target for imaging neuroinflammation. GSK1482160, a P2X7R modulator with nanomolar binding affinity and high selectivity, has been successfully radiolabeled and utilized for imaging P2X7 levels in a mouse model of lipopolysaccharide-induced systemic inflammation. In the current study, we further characterized its binding profile and determined whether [C]GSK1482160 can detect changes in P2X7R expression in a rodent model of multiple sclerosis.


METHODS
[C]GSK1482160 was synthesized with high specific activity and high radiochemical purity. Radioligand saturation and competition binding assays were performed for [C]GSK1482160 using HEK293-hP2X7R living cells. Micro-PET studies were carried out in nonhuman primates. In vitro autoradiography and immunohistochemistry studies were then carried out to evaluate tracer uptake and P2X7 expression in experimental autoimmune encephalomyelitis (EAE) rat lumbar spinal cord at EAE-peak and EAE-remitting stages compared with sham rats.


RESULTS
[C]GSK1482160 binds to HEK293-hP2X7R living cells with high binding affinity (Kd=5.09±0.98 nmol/l, Ki=2.63±0.6 nmol/l). Micro-PET studies showed high tracer retention and a homogeneous distribution in the brain of nonhuman primates. In the EAE rat model, tracer uptake of [C]GSK1482160 in rat lumbar spinal cord was the highest at the EAE-peak stage (277.74±79.74 PSL/mm), followed by the EAE-remitting stage(149.00±54.14 PSL/mm) and sham (66.37±1.48 PSL/mm). The tracer uptake correlated strongly with P2X7-positive cell counts, activated microglia numbers, and disease severity.


CONCLUSIONS
We conclude that [C]GSK1482160 has the potential for application in monitoring neuroinflammation.
Departments of aRadiology bNeurology, Neuroscience, Physical Therapy and Occupational Therapy, Washington University School of Medicine cDepartment of Pharmacological and Physiological Science, Saint Louis University School of Medicine, St. Louis, Missouri, USA.
Junbin
J
Han
Hui
H
Liu
Chunling
C
Liu
Hongjun
H
Jin
Joel S
JS
Perlmutter
Terrance M
TM
Egan
Zhude
Z
Tu
D000818:Animals; D001692:Biological Transport; D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism; D002250:Carbon Radioisotopes; D018450:Disease Progression; D004681:Encephalomyelitis, Autoimmune, Experimental / Q000000981:diagnostic imaging / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006801:Humans; D008024:Ligands; D008252:Macaca fascicularis; D008297:Male; D051379:Mice; D049268:Positron-Emission Tomography; D011761:Pyrrolidonecarboxylic Acid / Q000737:chemistry / Q000378:metabolism*; D011854:Radiochemistry; D051381:Rats; D058486:Receptors, Purinergic P2X7 / Q000378:metabolism*; D013116:Spinal Cord / Q000000981:diagnostic imaging / Q000378:metabolism; D013379:Substrate Specificity
D002250:Carbon Radioisotopes; D008024:Ligands; C000604998:N-(2-chloro-3-(trifluoromethyl)benzyl)-N-methyl-5-oxopyrrolidine-2-carboxamide; D058486:Receptors, Purinergic P2X7; D011761:Pyrrolidonecarboxylic Acid