Jonathan Peters

Characterization of 11C-GSK1482160 for Targeting the P2X7 Receptor as a Biomarker for Neuroinflammation

The purinergic receptor subtype 7 (P2X7R) represents a novel molecular target for imaging neuroinflammation via PET. GSK1482160, a potent P2X7R antagonist, has high receptor affinity, high blood–brain barrier penetration, and the ability to be radiolabeled with 11C. We report the initial physical and biologic characterization of this novel ligand. Methods: 11C-GSK1482160 was synthesized according to published methods. Cell density studies were performed on human embryonic kidney cell lines expressing human P2X7R (HEK293-hP2X7R) and underwent Western blotting, an immunofluorescence assay, and radioimmunohistochemistry analysis using P2X7R polyclonal antibodies. Receptor density and binding potential were determined by saturation and association–disassociation kinetics, respectively. Peak immune response to lipopolysaccharide treatment in mice was determined in time course studies and analyzed via Iba1 and P2X7R Western blotting and Iba1 immunohistochemistry. Whole-animal biodistribution studies were performed on saline- or lipopolysaccharide-treated mice at 15, 30, and 60 min after radiotracer administration. Dynamic in vivo PET/CT was performed on the mice at 72 h after administration of saline, lipopolysaccharide, or lipopolysaccharide + blocking, and 2-compartment, 5-parameter tracer kinetic modeling of brain regions was performed. Results: P2X7R changed linearly with concentrations or cell numbers. For high-specific-activity 11C-GSK1482160, receptor density and Kd were 1.15 ± 0.12 nM and 3.03 ± 0.10 pmol/mg, respectively, in HEK293-hP2X7R membranes. Association constant kon, dissociation constant koff, and binding potential (kon/koff) in HEK293-hP2X7R cells were 0.2312 ± 0.01542 min−1⋅nM−1, 0.2547 ± 0.0155 min−1, and 1.0277 ± 0.207, respectively. Whole-brain Iba1 expression in lipopolysaccharide-treated mice peaked by 72 h on immunohistochemistry, and Western blot analysis of P2X7R for saline- and lipopolysaccharide-treated brain sections showed a respective 1.8- and 1.7-fold increase in signal enhancement at 72 h. Biodistribution of 11C-GSK1482160 in saline- and lipopolysaccharide-treated mice at 72 h was statistically significant across all tissues studied. In vivo dynamic 11C-GSK1482160 PET/CT of mice at 72 h after administration of saline, lipopolysaccharide, or lipopolysaccharide + blocking showed a 3.2-fold increase and 97% blocking by 30 min. The total distribution volumes for multiple cortical regions and the hippocampus showed statistically significant increases and were blocked by an excess of authentic standard GSK1482160. Conclusion: The current study provides compelling data that support the suitability of 11C-GSK1482160 as a radioligand targeting P2X7R, a biomarker of neuroinflammation.

Synthesis and preliminary biological evaluation of [11C]methyl (2-amino-5-(benzylthio)thiazolo[4,5-d]pyrimidin-7-yl)-D-leucinate for the fractalkine receptor (CX3CR1)

The reference standard methyl (2-amino-5-(benzylthio)thiazolo[4,5-d]pyrimidin-7-yl)-d-leucinate (5) and its precursor 2-amino-5-(benzylthio)thiazolo[4,5-d]pyrimidin-7-yl)-d-leucine (6) were synthesized from 6-amino-2-mercaptopyrimidin-4-ol and BnBr with overall chemical yield 7% in five steps and 4% in six steps, respectively. The target tracer [11C]methyl (2-amino-5-(benzylthio)thiazolo[4,5-d]pyrimidin-7-yl)-d-leucinate ([11C]5) was prepared from the acid precursor with [11C]CH3OTf through O-[11C]methylation and isolated by HPLC combined with SPE in 40-50% radiochemical yield, based on [11C]CO2 and decay corrected to end of bombardment (EOB). The radiochemical purity was >99%, and the specific activity (SA) at EOB was 370-1110GBq/μmol with a total synthesis time of ∼40-min from EOB. The radioligand depletion experiment of [11C]5 did not display specific binding to CX3CR1, and the competitive binding assay of ligand 5 found much lower CX3CR1 binding affinity.

THE MODEL-AD CONSORTIUM PRECLINICAL TESTING PIPELINE: PHARMACOKINETICS AND PHARMACODYNAMICS OF PROPHYLACTIC TREATMENT WITH LEVETIRACETAM IN THE 5XFAD MOUSE MODEL OF ALZHEIMER’S DISEASE

restrictive barrier properties controlled by tight junctions and polarized expression of selective transporters, the endothelial cells that form the BBB effectively regulates movement of metabolites and nutrients between blood and brain parenchyma. Any changes in the BBB may impair the clearance of neurotoxic molecules allowing their accumulation and deposition in brain parenchyma and vasculature, leading to neuronal dysfunction and degeneration, and contribute to the onset and progression of Alzheimer’s disease (AD). In AD and CAA, accumulation of amyloid-b (Ab) on microvessels results in a rupture of vessels wall and cerebral hemorrhage, which contribute to, and aggravate, dementia. Accumulation of Ab depends on the imbalance between the production and clearance of Ab. Several pathways for Ab clearance from the brain have been reported including transport across the BBB and enzymatic degradation. Despite our understanding of the pathways responsible for BBB dysfunction and clearance of Ab, the availability of drugs to treat CAA or AD remains lacking. Identifying strategies to rectify BBB integrity and function, and maximize clearance of Ab from the brain is of high clinical importance for the development of interventions, which prevent or delay onset of CAA and AD.Methods:In my lab, we developed a novel BBB model consisting of cerebrovascular endothelial cells and high-throughput screening (HTS) methodologies to screen for hit compounds that ameliorate Ab induced increases in endothelial cell permeability and enhance Ab clearance. Identified hits were then tested in vivo in AD mouse model for BBB tightness, Ab brain levels and Ab related pathology. Results:Multiple hit compounds were identified from the screening that were ranked for their potencies. Most potent compounds were in vivo evaluated in ADmouse model for their therapeutic effect against AD pathology. Our in vitro to in vivo studies have successfully identified candidate therapeutic molecules to test in future clinical studies. Conclusions:Our findings demonstrated the BBB as a therapeutic target to prevent and/or slow the progression of the amyloid pathogenesis disorders CAA and AD.