PROJECT SUMMARY Over 20 million Americans are addicted to drugs and psychostimulant use disorders (e.g. addiction to cocaine or methamphetamine) represents a major public health problem in the United States without any effective and safe pharmacotherapeutic options. Elevated dopamine (DA) neurotransmission and activation of mesolimbic dopamine receptors is a key pathophysiological underpinning of stimulant use disorders resulting in abnormal brain reward processing and drug taking. In the binge/intoxication stage of cocaine abuse, both signal transduction mechanisms and changes in gene transcription have been identified. For example, chronic exposure to a wide variety of abused drugs including the psychostimulants upregulates cyclic adenosine monophosphate (cAMP) production, cAMP-dependent protein kinase A (PKA) activity, and PKA-dependent protein phosphorylation in nucleus accumbens (NAc). Thus, drug targets impacting the cAMP/PKA molecular pathway in the NAc may be particularly useful for identifying therapeutic mechanisms for treating cocaine use disorder (CUD). We recently mined human brain RNA sequencing databases from the Genotype-Tissue Expression (GTEx) project with the goal to define druggable proteins expressed exclusively in the striatum that might regulate stimulant-induced dopamine responsive circuits. This led to our identification of GPR52, a novel orphan G protein-coupled receptor (GPCR) that is selectively and highly expressed medium spiny neurons (MSNs) in the NAc. We have determined that GPR52 is a Gαs/olf-coupled receptor that activates adenylyl cyclase to stimulate cAMP production. The present grant is built upon our recent progress in the design, synthesis and pharmacological evaluation of GPR52 agonists. We have synthesized new small molecules and identified promising lead molecules that exhibit GPR52 agonist profiles in Iive cell signaling assays. Our objective is to validate selective GPR52 agonist probes with a favorable pharmacokinetics (PK) profile, and analyze selected agonists in proof-of-concept behavioral models to validate therapeutic potential for CUD. Specific Aim 1 will synthesize and determine pharmacodynamic profiles of GPR52 agonists in vitro. Specific Aim 2 will pursue initial PK analyses and lead GPR52 agonists will be evaluated in rat in vivo proof-of-concept studies to establish potency and efficacy in behavioral models of CUD. There is a gap in our ability to maximize therapeutic strategies to reduce the psychological and medical impact of stimulant use disorders in patients. This project addresses this gap in treatment efficacy by presenting the novel concept that GPR52 activation may prove useful in reducing drug taking.