Date of Award

January 2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Medicinal Chemistry and Molecular Pharmacology

First Advisor

Val J Watts

Committee Member 1

Jean-Christophe Rochet

Committee Member 2

Gregory H Hockerman

Committee Member 3

Donald F Ready

Abstract

G protein-coupled receptors (GPCRs) are drug targets that often activate multiple signaling pathways. The multiple GPCR responses provide opportunities for biased or functionally selective ligands to preferentially modulate one signaling pathway over another. Studies with several GPCRs have suggested that selective activation of signaling pathways downstream of a GPCR may lead to safer and more effective drug therapies. The dopamine D2 receptor is the main target in therapies for Parkinson’s disease and schizophrenia. First and second generation antipsychotic drugs antagonize dopamine D2 receptor. Notably, both these classes of drugs may cause side effects associated with D2 receptor antagonism (e.g. hyperprolactemia and extrapyramidal symptoms). The novel, “third generation” antipsychotic drug, aripiprazole is also used to treat schizophrenia, with the remarkable advantage that its tendency to cause extrapyramidal symptoms is minimal. In this work we studied the molecular pharmacology of aripiprazole and showed that the compound displays ligand bias for modulation of G proteins, being a partial agonist for Gαi/o and a robust antagonist for Gβγ signaling. We have also examined the activation of immediate effectors of the dopamine D2 receptor (i.e. Gαi/o, Gβγ, β-arrestin recruitment) and more complex signaling pathways (i.e., extracellular signal-regulated kinase phosphorylation, heterologous sensitization, and dynamic mass redistribution) in response to a series of D2 receptor ligands. The most commonly used methods to measure ligand bias were employed and compared. Functional selectivity analyses were also employed as tools to explore the relative contribution of immediate dopamine D2 receptor effectors for the activation of more complex signaling pathways. We have further identified novel classes of AC1 inhibitors through both chemical library screening and structure-activity relationship studies. The effects of our best inhibitor (W001) on acute and chronic signaling through the μ-opioid receptor were also examined, revealing an alternative method to induce functional selectivity (i.e. by targeting signaling components that are downstream of GPCRs). Lastly, we showed that W001, which is the most potent selective small molecule AC1 inhibitor described to date, has analgesic properties in a mouse model of inflammatory pain.

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