Discovery of [11C]MK-6884: a positron emission tomography (PET) imaging agent for the study of M4 muscarinic receptor positive allosteric modulators (PAMs) in neurodegenerative diseases

The measurement of receptor occupancy (RO) using positron emission tomography (PET) has been instrumental in guiding discovery and development of CNS directed therapeutics. We and others have investigated muscarinic acetylcholine receptor 4 (M4) positive allosteric modulators (PAMs) for the treatment of symptoms associated with neuropsychiatric disorders. In this article, we describe the synthesis, in vitro, and in vivo characterization of a series of central pyridine-related M4 PAMs that can be conveniently radiolabeled with carbon-11 as PET tracers for the in vivo imaging of an allosteric binding site of the M4 receptor. We first demonstrated its feasibility by mapping the receptor distribution in mouse brain and confirming that a lead molecule 1 binds selectively to the receptor only in the presence of the orthosteric agonist carbachol. Through a competitive binding affinity assay and a number of physiochemical properties filters, several related compounds were identified as candidates for in vivo evaluation. These candidates were then radiolabeled with 11C and studied in vivo in rhesus monkeys. This research eventually led to the discovery of the clinical radiotracer candidate [11C]MK-6884

3‑Oxoisoindoline-1-carboxamides: Potent, State-Dependent Blockers of Voltage-Gated Sodium Channel Na_V1.7 with Efficacy in Rat Pain Models

The voltage-gated sodium channel Na_V1.7 is believed to be a critical mediator of pain sensation based on clinical genetic studies and pharmacological results. Clinical utility of nonselective sodium channel blockers is limited due to serious adverse drug effects. Here, we present the optimization, structure–activity relationships, and in vitro and in vivo characterization of a novel series of Na_V1.7 inhibitors based on the oxoisoindoline core. Extensive studies with focus on optimization of Na_V1.7 potency, selectivity over Na_V1.5, and metabolic stability properties produced several interesting oxoisoindoline carboxamides (<b>16A</b>, <b>26B</b>, <b>28</b>, <b>51</b>, <b>60</b>, and <b>62</b>) that were further characterized. The oxoisoindoline carboxamides interacted with the local anesthetics binding site. In spite of this, several compounds showed functional selectivity versus Na_V1.5 of more than 100-fold. This appeared to be a combination of subtype and state-dependent selectivity. Compound <b>28</b> showed concentration-dependent inhibition of nerve injury-induced ectopic in an ex vivo DRG preparation from SNL rats. Compounds <b>16A</b> and <b>26B</b> demonstrated concentration-dependent efficacy in preclinical behavioral pain models. The oxoisoindoline carboxamides series described here may be valuable for further investigations for pain therapeutics