John Joseph Masters

Synthesis and Evaluation of 11C-LY2795050 as a κ-Opioid Receptor Antagonist Radiotracer for PET Imaging

Kappa-opioid receptors (KOR) are believed to be involved in the pathophysiology of depression, anxiety disorders, drug abuse, and alcoholism. To date, only 1 tracer, the KOR agonist 11C-GR103545, has been reported to be able to image KOR in primates. The goal of the present study was to synthesize the selective KOR antagonist 11C-LY2795050 and evaluate its potential as a PET tracer to image KOR in vivo. Methods: The in vitro binding affinity of LY2795050 was measured in radioligand competition binding assays. Ex vivo experiments were conducted using microdosing of the unlabeled ligand in Sprague–Dawley rats and in wild-type and KOR knockout mice, to assess the ligand’s potential as a tracer candidate. Imaging experiments with 11C-LY2795050 in monkeys were performed on the Focus-220 scanner with arterial blood input function measurement. Binding parameters were determined with kinetic modeling analysis. Results: LY2795050 displays full antagonist activity and high binding affinity and selectivity for KOR. Microdosing studies in rodents and ex vivo analysis of tissue concentrations with liquid chromatography–tandem mass spectrometry identified LY2795050 as an appropriate tracer candidate able to provide specific binding signals in vivo. 11C-LY2795050 was prepared in an average yield of 12% and greater than 99% radiochemical purity. In rhesus monkeys, 11C-LY2795050 displayed a moderate rate of peripheral metabolism, with approximately 40% of parent compound remaining at 30 min after injection. In the brain, 11C-LY2795050 displayed fast uptake kinetics (regional activity peak times of <20 min) and an uptake pattern consistent with the distribution of KOR in primates. Pretreatment with naloxone (1 mg/kg, intravenously) resulted in a uniform distribution of radioactivity. Further, specific binding of 11C-LY2795050 was reduced by the selective KOR antagonist LY2456302 in a dose-dependent manner. Conclusion: 11C-LY2795050 displayed favorable pharmacokinetic properties and binding profiles in vivo and therefore is a suitable ligand for imaging the KOR in primates. This newly developed KOR antagonist tracer has since been advanced to PET imaging of KOR in humans and constitutes the first successful KOR antagonist radiotracer.

A four component coupling strategy for the synthesis of d-phenylglycinamide-derived non-covalent factor Xa inhibitors

A novel isonitrile derivative was synthesized and used in an Ugi four component coupling reaction to explore aryl group substitution effects on inhibition of the coagulation cascade serine protease factor Xa.

Synthesis and evaluation of [C-11]LY2795050, an antagonist PET imaging tracer for the kappa opioid receptors

Introduction: The kappa opioid receptors (KOR) are believed to be involved in the pathophysiology of depression, anxiety disorders, drug abuse and alcoholism. To date only one tracer, the kappa opioid receptor agonist [C-11]GR103545, has been reported to be able to image KOR in nonhuman primates. The goal of the present study was to synthesize the selective KOR antagonist [C-11]LY2795050 and evaluate its potential as a PET tracer to image KOR in non-human primates.