Discovery Campaigns for Pharmacologically Unique Agonists at the Mu-Opioid and 5-Hydroxytryptamine 2A Receptors

The more than 800 members of the superfamily of seven transmembrane proteins known as the G protein-coupled receptors (GPCRs) are involved in the regulation of all physiological processes and represent the most highly targeted receptor class by United States Food and Drug Administration-approved drugs (Wacker, 2017a). Improving available and discovering new drugs targeting these receptors is dependent upon a better understanding of their role in physiological and pathophysiological states. Thus choosing the correct GPCRs to target and the correct manner in which to target them is essential. An important part of this process – drug discovery – is to accurately quantify the actions of drugs at their receptor targets (i.e., their pharmacology), so that predictions can be made and inferences drawn as they move through and are refined in the discovery pipeline. This dissertation describes the development of an assay system, TRUPATH, for quantifying G protein-coupled receptor signaling through heterotrimeric G proteins based upon bioluminescence resonance energy transfer (BRET). Using this system, along with other pharmacological assays and behavioral, computation, and structural approaches, new agonists for two clinically-relevant GPCRs, the mu-opioid receptor (MOR) and the 5-hydroxytryptamine 2A receptor (5-HT2AR), were discovered. MOR is the primary target for opioids, such as morphine, which can induce fatal respiratory depression. Novel MOR compounds described here show reduced adverse effects compared to conventional MOR agonists while retaining antinociceptive properties. 5-HT2AR is the primary target for psychedelic drugs, such as LSD, which cause hallucinations but show promise in treating numerous psychiatric disorders. Novel 5-HT2AR compounds described here are selective for this receptor and exhibit a spectrum of signaling profiles that will be useful for interrogating this receptor’s function and may serve as useful clinical leads for diseases such as anxiety and depression.