Small Molecule Neuropeptide S and Melanocortin 4 Receptor Ligands as Potential Treatments for Substance Use Disorders

Allosteric Regulation of G-Protein-Coupled Receptors: From Diversity of Molecular Mechanisms to Multiple Allosteric Sites and Their Ligands

Allosteric regulation is critical for the functioning of G protein-coupled receptors (GPCRs) and their signaling pathways. Endogenous allosteric regulators of GPCRs are simple ions, various biomolecules, and protein components of GPCR signaling (G proteins and β-arrestins). The stability and functional activity of GPCR complexes is also due to multicenter allosteric interactions between protomers. The complexity of allosteric effects caused by numerous regulators differing in structure, availability, and mechanisms of action predetermines the multiplicity and different topology of allosteric sites in GPCRs. These sites can be localized in extracellular loops; inside the transmembrane tunnel and in its upper and lower vestibules; in cytoplasmic loops; and on the outer, membrane-contacting surface of the transmembrane domain. They are involved in the regulation of basal and orthosteric agonist-stimulated receptor activity, biased agonism, GPCR-complex formation, and endocytosis. They are targets for a large number of synthetic allosteric regulators and modulators, including those constructed using molecular docking. The review is devoted to the principles and mechanisms of GPCRs allosteric regulation, the multiplicity of allosteric sites and their topology, and the endogenous and synthetic allosteric regulators, including autoantibodies and pepducins. The allosteric regulation of chemokine receptors, proteinase-activated receptors, thyroid-stimulating and luteinizing hormone receptors, and beta-adrenergic receptors are described in more detail.

Structure-Activity Relationship Studies on Oxazolo[3,4-a]pyrazine Derivatives Leading to the Discovery of a Novel Neuropeptide S Receptor Antagonist with Potent In Vivo Activity

Neuropeptide S modulates important neurobiological functions including locomotion, anxiety, and drug abuse through interaction with its G protein-coupled receptor known as neuropeptide S receptor (NPSR). NPSR antagonists are potentially useful for the treatment of substance abuse disorders against which there is an urgent need for new effective therapeutic approaches. Potent NPSR antagonists in vitro have been discovered which, however, require further optimization of their in vivo pharmacological profile. This work describes a new series of NPSR antagonists of the oxazolo[3,4-a]pyrazine class. The guanidine derivative 16 exhibited nanomolar activity in vitro and 5-fold improved potency in vivo compared to SHA-68, a reference pharmacological tool in this field. Compound 16 can be considered a new tool for research studies on the translational potential of the NPSergic system. An in-depth molecular modeling investigation was also performed to gain new insights into the observed structure-activity relationships and provide an updated model of ligand/NPSR interactions.