Project Summary Epigenetic pharmacotherapy for substance use disorder (SUD) is a rapidly expanding area of research. With the ability to bind to acetylated histones and regulate drug-induced transcriptional adaptations, members of the bromodomain and extra-terminal domain (BET) family of proteins (BRD2, BRD3, BRD4 and BRDT) have emerged as promising therapeutic targets. To date, however, only pan-BET bromodomain inhibitors, small molecules that bind to both bromodomains (BD1 and BD2) within all BET proteins, have been tested in SUD- related experiments. The use of these non-selective pharmacological inhibitors in SUD models limits our mechanistic understanding of individual BET proteins, bromodomain-selective functions (BD1 vs. BD2), and non- bromodomain BET interactions that regulate drug-induced neurobehavioral adaptations. New evidence from our laboratory indicates that selectively targeting individual BET domains and proteins is a novel and effective strategy to reduce cocaine-induced behavioral and transcriptional responses without causing sides effects observed with pan-BET inhibitors. To build on these exciting data and to advance the field of epigenetic pharmacotherapy for SUD, we propose to use highly selective, clinically relevant treatments, viral-mediated approaches, and multiomic analysis to investigate domain- and protein-specific mechanisms of BET proteins during cocaine-seeking behaviors. To achieve these goals, we will first investigate the behavioral and cell type- specific transcriptomic responses of domain-selective BET inhibitors in cocaine economic demand and reinstatement procedures. Next, using co-immunoprecipitation and mass-spectrometry, we will characterize BRD4 interactome changes following short- and intermittent-access cocaine self-administration, and in functional studies, we will use newly developed tools to identify a role for non-bromodomain mechanisms of BRD4 in cocaine self-administration. Finally, we will interrogate novel transcriptional and behavioral roles for BRD2 in cocaine-seeking behaviors. Together, these experiments will provide significant contributions to the field of addiction epigenetics as well as novel therapeutic targets to reduce cocaine use and relapse.