Oleamide Analogues as Positive Allosteric Modulators of the Serotonin (5‐HT) 5‑HT 2C and 5‑HT 2A Receptors

Abstract

The G protein-coupled receptors (GPCRs) control crucial functions in the central nervous system (CNS) and are acknowledged as important medication targets. The serotonin (5-HT) 5-HT2R family (5-HT2AR, 5-HT2BR, 5-HT2CR) mediates a myriad of CNS functions. Of note, 5-HT2CR signaling is implicated in metabolic disorders (e.g., obesity) and a variety of neuropsychiatric disorders (e.g., anxiety, schizophrenia and substance use disorders). Activation of the brain 5-HT2AR mediates psychedelic states and mood and cognitive alterations evoked by hallucinogens, which is attractive for the application of psychedelic compounds in psychiatry. We sought to discover novel modulators to selectively potentiate 5-HT2CR and 5-HT2AR signaling while avoiding the undesired activation of 5-HT2BR, widely known as associated with valvulopathy and pulmonary hypertension adverse effects. The application of positive allosteric modulators (PAMs) is an appealing strategy to modulate 5-HT2CR and 5-HT2AR functional response by binding to a less conserved allosteric site. Our PAM discovery efforts have included a focus on the well-known natural product oleamide, which has been implicated in signaling modulation of 5-HT2AR and 5-HT2CR as well as 5-HT1AR and 5-HT7R, with an overall promiscuous pharmacological profile. Three series of oleamide-derived 5-HT2CR and 5-HT2AR PAMs are designed and synthesized via a fragment-based drug discovery approach. Pharmacological evaluation of novel small molecules was conducted in a cell-based, 5-HT-induced, intracellular calcium (Ca2+) release assay with physiologically relevant 5-HT2CR or 5-HT2AR expression levels. Multiple 5‑HT2CR and 5‑HT2ARPAMs were obtained with a functional increase of 5-HT-induced Ca2+ release by 20% or greater in the in vitro assay. In vitro distribution, metabolism, and pharmacokinetic analyses, off-target radioligand binding displacement studies and physicochemical properties indicate that our 5‑HT2CR and 5‑HT2AR PAMs display promising lead- and drug-like attributes. In silico molecular docking with the 5-HT2CR X-ray crystal structure has identified a potential PAM binding site for the oleamide-derived 5-HT2CR PAMs that is shared with our previously reported PAMs that do not share an oleamide scaffold. In conclusion, we have designed, synthesized, and optimized a novel series of 5‑HT2CR and 5‑HT2AR PAMs with promising in vitropharmacological andphysicochemical profiles as potential neurotherapeutics for impaired serotonergic controlled substance use disorders and other CNS disorders.